Permeable water resistive roof underlayment

Abstract

The present invention relates to a water resistant, UV resistant, vapor permeable, air barrier roofing underlayment assembly for use on flat or low sloped roofs comprising a substrate of permeable polyester, a permeable copolymer acrylate coating bonded to the permeable polyester substrate and a pressure sensitive permeable copolymer adhesive secured to the acrylate coating. The permeable coating is a copolymer including a primary polymer of n-butyl acrylate and contains carbon black.

Claims

1. An underlayment for a roof having a slope angle of 5° or less, that is an air barrier and self-adhering, vapor-permeable, water-resistive, and UV-resistant, the underlayment comprising: a substrate of polyester having a surface; a foamed, permeable copolymer coating attached to the polyester substrate's surface, wherein the foamed, permeable copolymer coating includes an n-butyl acrylate copolymer that; includes n-butyl acrylate in an amount ranging from 30% to 98% by weight, and has a foam density that ranges from 50% to 65% of the copolymer's density before foaming; and a permeable pressure-sensitive adhesive bonded to said foamed, permeable copolymer coating; the underlayment having a permeability of 25 perms or more.

2. The underlayment as claimed in claim 1, wherein the underlayment has a permeability of about 35 perms or more.

3. The underlayment as claimed in claim 1, wherein the permeable-pressure-sensitive adhesive does not include a solvent.

4. The underlayment as claimed in claim 1, wherein the foamed, permeable copolymer coating includes n-butyl acrylate copolymer with solids ranging from about 30% to about 55% of the foamed, permeable copolymer coating.

5. The underlayment as claimed in claim 1, wherein the foamed permeable copolymer coating has a permeability that ranges from about 30 perms to about 60 perms.

6. The underlayment as claimed in claim 1, wherein the polyester substrate ranges in thickness from about 180 mils to about 220 mils, and has a permeability that ranges from about 65 perms to about 80 perms.

7. The underlayment as claimed in claim 1, wherein the foamed permeable copolymer coating includes carbon black.

8. A membrane for a flat or low sloped roof, that is an air barrier, and water-resistant, vapor-permeable, and self-adhering, the membrane comprising: a substrate of polyester having a surface, and that is permeable and consists of a single ply; a foamed, permeable n-butyl acrylate copolymer coating attached to the polyester substrate's surface, comprising n-butyl acrylate copolymer, wherein the n-butyl acrylate copolymer has a foam density that ranges from 50% to 65% of the n-butyl acrylate copolymer's density before foaming; a pressure-sensitive, permeable, co-polymer acrylate adhesive bonded with the foamed, permeable n-butyl acrylate copolymer coating; and wherein, the combination of the substrate, the foamed, permeable n-butyl acrylate copolymer coating, and the pressure-sensitive, permeable copolymer acrylate adhesive has a permeability that ranges from about 25 perms to about 45 perms.

9. The membrane of claim 8 wherein said low sloped roof has a sloped angle of 5° or less.

10. The membrane of claim 8 wherein the pressure-sensitive, permeable, copolymer acrylate adhesive includes a silicon release film.

11. The membrane as claimed in claim 8 wherein the foamed, permeable n-butyl acrylate copolymer coating includes carbon black.

12. The membrane of claim 8 wherein the foamed, permeable n-butyl acrylate copolymer includes solids ranging from about 20% to about 50%.

13. The membrane of claim 8 wherein the pressure-sensitive, permeable, copolymer acrylate adhesive includes a removable silicon release film mounted thereto to form an exterior surface of said roofing membrane.

14. A membrane laminate for a flat roof, that is an air barrier and water-resistant, UV-resistant, vapor-permeable, and self-adhering, the laminate comprising: a substrate of polyester having a surface and that is vapor permeable; a foamed, vapor-permeable, solvent-free, n-butyl acrylate copolymer coating attached to the polyester substrate's surface, wherein the foamed, vapor-permeable, solvent-free, n-butyl acrylate copolymer coating includes carbon black; a permeable, pressure-sensitive, copolymer adhesive attached to the foamed, vapor-permeable, solvent-free, n-butyl acrylate copolymer coating, wherein the permeable, pressure-sensitive, copolymer adhesive is vapor permeable; and wherein the combination of the substrate, the foamed, vapor-permeable, solvent-free, n-butyl acrylate copolymer coating, and the permeable, pressure-sensitive, copolymer adhesive has a permeability greater than 25 perms.

15. The membrane laminate as claimed in claim 14 wherein the foamed, vapor-permeable, solvent-free, n-butyl acrylate copolymer coating has a thickness ranging from about 80 mils to about 100 mils.

16. The membrane laminate as claimed in claim 14 wherein the membrane laminate is capable of supporting a water column at least 24 inches high for at least 48 hours.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present invention will be described with reference to the appended Figures, in which:

(2) FIG. 1 is a schematic enlarged cross sectional view of the inventive underlayment used on a typical flat roof construction; and

(3) FIG. 2 is a schematic cross section view of a typical flat roof system with the inventive underlayment;

(4) These and other objects, advantages, and novel features of the present invention will become apparent when considered with the teachings contained in the detailed disclosure along with the accompanying drawings.

DESCRIPTION OF THE INVENTION

(5) The present invention is directed toward a self-adhering water-resistant vapor permeable roofing underlayment membrane as shown in FIG. 1 which can be successfully used to cover flat and low sloped roofs ranging from about 0° to about 2° in slope as is shown in FIG. 2. Roofs from about 0° to about 5° can also be covered. The self-adhering roofing system is a UV stabilized, vapor permeable, water resistant, air barrier and is also rot proof and tear resistant. With vapor permeance ranging from about 25 perms to about 45 perms, most preferably about 35 perms, the underlayment membrane 10 allows the roof assembly to breathe or “dry out” as necessary during the seasonal changes. This helps to reduce or eliminate conditions that are conducive to mold, mildew, lumber distortion, insulation deterioration and metal corrosion. The drying aspect is of utmost importance in energy efficiency with single ply constructs in humid localities.

(6) The present roof underlayment 10 as seen in FIG. 1 is constructed of permeable polyester sheet or membrane 12 of material ranging from about 180 mils to about 220 mils in thickness with a permeability ranging from about 65 perms to about 80 perms with a preferred permeability of about 75 perms. The polyester sheet 12 is premade and packaged in rolls which are unrolled at the manufacturing facility and coated at different stages. In some selected usages, permeable polypropylene can be used. The sheet of polyester which forms the substrate 12 of the underlayment 10 is coated with a permeable n-butyl acrylate copolymer coating 14 by a knife over roller in the first process stage.

(7) The coating 14 is mixed prior to application on the polyester base layer and run through a foamer (high speed dispersion mixer) so that it formed with encapsulated air bubbles. These air bubbles are interconnected in the copolymer to form a permeable coating ranging from about 80 mils to about 100 mils in thickness with a permeability ranging from about 30 perms to about 60 perms when it is cured. The coating 14 is coated on the substrate 12 with a knife and roller in a wet application. The coating 14 is a wet foamed copolymer with the primary monopolymer being n-butyl acrylate mixed with another acrylate monopolymer.

(8) Acrylates are the salts, esters and conjugate bases of acrylic acid and its derivatives. Acrylates contain vinyl groups; that is two carbon atoms double bonded to each other, directly attached to the carbonyl carbon.

(9) Other polymers which can be mixed with the n-butyl acrylate are methyl acrylate, methyl methacrylate and methyl acrylic acid. Carbon black at approximately 1% by weight of the copolymer solution is added to the copolymer. A suitable copolymer base coating is manufactured by BASF SE Corporation and sold under the trademark ACRONAL® 4250. This coating has a viscosity of 300 and a density (lb/gal of 8.6) with pH of about 7.7 with a temperature low point of −28° C.

(10) The n-butyl acrylate polymer in the coating 14 ranges from 20 to 55% solids, with a pH ranging 7.7 to 8.0, and a preferred viscosity at 73° F. (cps) of 300 using a Brookfield RV viscometer Spindle #4 @ 100 rpm. The viscosity can effectively range from 100 to 500 depending on the percentage of solids. As previously noted, carbon black is also added to the copolymer to reduce tackiness, add strength and increase the UV effectiveness of the underlayment. The copolymer is foamed with a high speed dispersion mixer at 700 rpm with a 32% air injection with entrained air bubbles so that it has a foam density ranging from about 50% to about 65% preferably from about 55% to about 60%. The coating 14 is applied to the polyester substrate 12.

(11) The coating 14 is then heat cured after leaving the coating blade setting the foamed air bubbles in place in the copolymer providing the coating with permeability. The coating 14 copolymer ranges from about 30% to about 98% n-butyl acrylate.

(12) A copolymer pressure sensitive adhesive 16 is run through a second foamer so that it is formed with encapsulated air bubbles and is then applied to the cured acrylate coating 14 by a second blade coater, at a thickness ranging from about 4 mils to about 10 mils and cured as previously noted for the coating 14 to lock the air bubbles in place. Suitable pressure is applied to laminate the underlayment and the pressure sensitive adhesive has a preferred thickness of about 5 mils. The completed underlayment 10 has a permeability ranging from about 25 perms to about 45 perms and a preferred range from about 30 perms to about 40 perms.

(13) The copolymer portion of the pressure sensitive adhesive (PSA) 16 has a backbone consisting of n-butyl acrylate, 2-ethylhexyl acrylate, and vinyl acetate. The structure of the backbone is shown in Table I below as follows:

(14) TABLE-US-00001 TABLE I (Structure of PSA Polymer Backbone)

(15) The adhesive fully bonds to the coating 14 for air tightness and ease of installation and requires no primer for use on any substrate.

(16) The pressure sensitive adhesive (PSA) is an acrylic solution. The polymeric portion of the PSA makes up at least 95% of the adhesive formulation and has a copolymer backbone of n-butyl acrylate (about 60% by weight), 2-ethylhexyl acrylate (about 32% by weight) and vinyl acetate (about 7% by weight) forming a copolymer blend capable of bonding and crosslinking with the coating 14. Proper foaming of the adhesive is critical to good micropore formation. The aeration process includes high sheer mixing to entrain air in the mixed adhesive liquid solution. This is the same aeration process used for the coating. The self-adhering adhesive 16 is evenly applied on the n-butyl acrylate coating, cured and the micropores are formed and fixed throughout the PSA. The coating method used with the present invention for both the coating 14 and the PVA 16 was accomplished with a blade coater. This is a non-contact coating method and it does not crush or destroy the foam in the copolymer during coating. After application, the adhesive must be heated to lock-in the micropore formation. The adhesive in the present invention was reformulated by adding surfactants and water to the copolymer to control bubble size, bubble density, viscosity, and stability of the copolymer. The peel value of the adhesive is reduced by the introduction of voids (air bubbles) and the addition of carbon black and a surfactant such as long chain alcohols create a stable inverse emulsion.

(17) The acrylate polymer coating 14 does not require a slip sheet when applied. It is dry enough to be rolled onto itself. The pressure sensitive adhesive 16 is applied to a siliconized release film 17 and then laminated to the polyester and coating composite.

(18) Microscopy of the modified adhesive surface was performed revealing a porous structure of the adhesive having a bubble density (number of pores) ranging from about 4000 pores in 1.0 in.sup.2 to about 4600 pores in 1.0 in.sup.2, preferably about 4400 pores in 1.0 in.sup.2 with a majority of the pores, preferably about 80% to about 90% of the bubbles/pores having a size ranging from about 200 microns to about 300 microns. The pores formed are generally round and oval in shape and form a vapor pathway through the adhesive layer. The majority of the pores 100 formed by the bubbles appear to be distributed evenly across the surface penetrating through the adhesive layer when the polymer mixture is heat treated to set the pores in the adhesive. Preferably, the density of the foamed adhesive should fall between about 0.65 and about 0.75 after aeration.

(19) The adhesive copolymer which was manufactured and as shown in Table I ranges from about 45% by weight to about 50% by weight, preferably about 48% to about 49% by weight. The copolymer was mixed with a first solvent-free, surfactant-based wetting agent, preferably ranging from about 4% by weight to about 6% by weight, and most preferably about 5% by weight to provide emulsification and bubble size; and a second surfactant such as a foaming agent ranging from about 1.5% by weight to about 2.0% by weight, and preferably about 1.7% by weight to provide foam formation. A polymeric based thickener was added to the mixture in a range from about 0.2% by weight to about 0.4% by weight, preferably about 0.30% by weight. The adhesive copolymer composition was added to water ranging from about 40% by weight to about 50% by weight, preferably about 43% by weight to about 45% by weight and mixed in a high speed dispersion mixer at 500 rpm to form uniform bubbles in the mixture and fed into a coater feeder as previously described. The foamed adhesive was coated onto the cured porous n-butyl acrylate coating and heat cured to form the pores in place in the copolymer. The pressure sensitive adhesive and underlayment is laminated to reduce tackiness of the pressure sensitive adhesive and the need for a slip sheet.

(20) For industry testing standards, the present underlayment 10 will support a water column of twenty four (24) inches of water for forty eight (48) hours.

(21) Construction of a typical roof composite for a commercial flat roof 20 using the underlayment is shown in FIG. 2. In FIG. 2, a typical construction of a flat composite deck roof deck 21 using the inventive underlayment 10 which allows for drying of the roof composite from the inside out is shown. In this embodiment, a ½ inch mechanically attached thermal barrier board 24 fastened to the metal roof deck 22 by mechanical fasteners such as screws or nails 23. The permeable membrane underlayment 10 of the present invention is mounted on the barrier board 24 and secured thereto by the pressure sensitive adhesive 16. Two layers of polyiso 26, 3 inches and 2.2 inches, (5.2 inches total), thickness as needed for insulation value, are set in low rise foam adhesive 27. A ½ inch cover board 28 is set in low rise foam adhesive 27 which has been layered on the top polyiso layer 26 and the roof is covered with a PVC, or other single ply roof membrane 29 which is also set in low rise foam adhesive 27.

(22) The principles, preferred embodiments and modes of operation of the present invention have been described in the foregoing specification. However, the invention should not be construed as limited to the particular embodiments which have been described above. Instead, the embodiments described here should be regarded as illustrative rather than restrictive. Variations and changes may be made by others without departing from the scope of the present invention as defined by the following claims: