Polymer-backed roll roofing sheet

Abstract

A roofing product used in commercial built-up roofs includes a roll roofing sheet having a backing film adhered to one side thereof, the backing film being miscible with an adherent substance when the roofing sheet is unrolled and applied to a roof using the adherent substance. Prior to the unrolling of the roofing sheet, the backing film inhibits the transfer of material to an opposite side of the roofing sheet.

Description

FIELD OF THE INVENTION

The present invention relates to roofing materials, and, more specifically, to a roll roofing sheet especially adapted for installation on flat and low-pitch roofing structures.

BACKGROUND OF THE INVENTION

Over the years, various types of roofing materials and roofing systems have been developed and used to meet the demands of commercial and residential buildings with varying roof pitches ranging from flat to steeply pitched. Each type of material (e.g., stone, ceramic, wood, metal, rubber and asphalt/bitumen) has benefits and limitations in performing its intended function.

Asphalt roofing has wide popularity and can be made in many forms and compositions to provide it with different desirable properties, depending upon the application. For example, it may be reinforced using different fabric mat materials, such as fiberglass, polyester or other natural and synthetic materials. The asphalt may be modified by incorporating other compositions, such as styrene-butadiene-styrene (SBS) or atactic polypropylene (APP). Asphalt roofing material may be made in a variety of forms including shingles of various shapes and sizes, as well as continuous sheets of roofing material commonly referred to as “roll roofing sheets.”

Modified bitumen membranes (i.e., asphalt mixed with chemical modifiers) were developed in Europe during the late 1960's for roofing applications and found a market in the United States in the 1980's. These products are an important part of the roofing industry, in that they are necessary components of built-up roofing (“BUR”), which is the preferred roofing type for commercial buildings. The membranes are provided in rolls as roll roofing sheets with a size and weight permitting manual handling, whereby they can be rolled out over an area of the roof that is to be covered.

During installation, a waterproof base roll roofing sheet is spread over a roof deck. The base roll roofing sheet may be covered by one or more intermediate waterproof roll roofing sheets secured to each other by, for instance, melted hot-mopped asphalt. The uppermost roll roofing sheet is typically called the cap sheet.

In some parts of the country (e.g., in California and other southwestern states), state or local regulations require that the exposed portions of all cap sheets meet certain minimum standards for reflectivity, typically those standards which fall under the Energy Star® criteria. The standards may be met by providing the cap sheet with a white reflective coating that is applied to the cap sheet at the factory, as is described in co-pending, co-owned U.S. Patent Publication Nos. 2005/0257875, 2005/0261407, and 2005/0261409, which are incorporated herein by reference. When the cap sheet comes off the production line, the side which has been coated white (i.e., the “front” or “top”) meets, or exceeds, the Energy Star® reflectivity criteria. Typically, however, the opposite side of the cap sheet (i.e., the “back” or “bottom” side) is still somewhat tacky, and partially transfers to the front side, diminishing the reflectivity of the front side when the cap sheet is rolled for shipment and/or storage. It is common to coat the non-reflective side of the cap sheet with sand or talc to prevent the cap sheet from sticking to the machinery used in the manufacturing process, as well as for preventing transfer of material between the front and back sides when rolled. Sand or talc from the back side of the membrane degrades the reflective surface, with the degree of degradation increasing in direct proportion to the amount of time that the membrane is stored in its rolled configuration.

The reflective coating may be further degraded during installation of the cap sheet. Most commonly, the cap sheet will be installed by a two-person team using hot asphalt (i.e., “the hot mop” process). The asphalt is heated in kettles at the work site to temperatures of about 350° C. to about 450° C. One person spreads the molten asphalt onto the membrane to be covered and the other person rolls the cap sheet over the asphalt. The hot asphalt fuses adjacent layers. When the cap sheet membrane is unrolled, sand or talc remains loosely adhered to the reflective surface, where it presents a slipping hazard to the workers. The act of brushing the sand or talc off the top of the cap sheet for collection and removal further degrades the reflective surface. If the sand or talc were to be left on the cap sheet, it would interfere with the reflectivity of the cap sheet and promote weathering of the reflective surface. In the foregoing circumstances, it remains an objective to maximally preserve the reflectivity of the cap sheet without burdensome changes in the methods used to produce or install the membrane.

SUMMARY OF THE INVENTION

The present invention overcomes the disadvantages and shortcomings of the prior art discussed above by providing a roofing product which includes a roll roofing sheet having a backing film adhered to one side thereof. When the roofing sheet is in the form of a roll, the backing film inhibits the transfer of material to an opposite side of the roll roofing sheet. When the roofing sheet is unrolled and applied to a roof using an adherent substance, the backing film is miscible with the adherent substance. By way of example, the backing film can be made from a combination of a low density polypropylene (LDPP) and ethylene-vinyl acetate (EVA). The proportion of LDPP to EVA can range from 20%-80% LDPP to 20%-80% EVA with a preferred ratio of about 60% EVA to 40% LDPP.

The adherent substance can be either hot asphalt or an adhesive/solvent mixture. When the adherent substance is hot asphalt, the backing film melts and merges with the hot asphalt. When the adherent substance is an adhesive/solvent mixture, the backing film dissolves into the adhesive/solvent mixture.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, reference is made to the accompanying drawings, in which:

FIG. 1 is a schematic view of a built-up roof constructed using a cap sheet in accordance with the present invention;

FIG. 2 is a vertical cross-section of the cap sheet shown schematically in FIG. 1;

FIG. 3 is a procedure flow diagram of a process for manufacturing a roll roofing cap sheet in accordance with the present invention; and

FIG. 4 is a schematic diagram of an apparatus for applying and adhering a backing film to the cap sheet shown schematically in FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

As shown in FIG. 1, in a typical BUR installation 10, a structural deck 12 is covered by a waterproof base roll roofing sheet 14. The base roll roofing sheet 14 may be covered by one or more intermediate waterproof roll roofing sheets 16. The uppermost roll roofing sheet in a BUR is cap sheet 18. The roll roofing sheets 14, 16, 18 may be secured to each other by melted hot-mopped asphalt 20, or by using a torch to fuse the membranes.

With reference to FIG. 2, the cap sheet 18 is in the form of a layered modified bitumen membrane. More particularly, the cap sheet 18 includes a fiberglass or polyester reinforcing mat 22, which is sandwiched between and bonded to a top layer 24 and a bottom layer 26. Numerous granules 28 are embedded in the top layer 24. The granules 28 are produced, for example, from crushed stone, ceramic or other hard, finely divided materials and each one is coated with a reflective coating 30. A backing film 32 is adhered to the bottom layer 26.

The top layer 24 and the bottom layer 26 are formed from modified bitumen, such as SBS or APP. At present, about 60% of modified bitumen roll roofing sheets used in the roofing industry are based on atactic polypropylene modified bitumen (“APP membranes”). Styrene-butadiene-styrene modified bitumen membranes (“SBS membranes”) account for substantially all of the remainder of commercial roofing applications. The SBS membranes are generally more rubbery and easier to handle than the APP membranes, and have lower melting points. It is strongly preferred that SBS membranes be used for the top layer 24 and the bottom layer 26, rather than APP membranes. However, the fabrication process and layered roll roofing sheets discussed herein with respect to SBS membranes can be applied, with a few obvious modifications, to APP membranes, or other membranes based on modified bitumen.

The backing film 32 is made from a combination of a low density polypropylene (LDPP) and ethylene-vinyl acetate (EVA). The proportion of LDPP to EVA can range from 20%-80% LDPP to 20%-80% EVA with a preferred ratio of about 60% EVA to 40% LDPP. The backing film 32 could be made from other polymeric materials, such as linear low density films like PET (polyethyleneterephthalate) films, vinyl films, or a combination of low density and high density films, including, but not limited to PET, HDPE, HDPP, LDPP, LDPE, and EVA, as is known in the art. The objective in selecting a material or a combination of materials is to give the backing film 32 an overall melting point of approximately that of the hot-mopped BUR asphalt 20 (see FIG. 1), which is preferably about 105° C. This allows the backing film 32 to melt and mix with the melted BUR asphalt 20 upon contact, solidifying in union with the BUR asphalt 20 as both cool below their respective melting points to thereby form a solid bond merged interface joining the two layers. The backing film 32 comes in a sheet that is preferably about 40.25 inches wide with a tolerance range of about 39.75 inches to about 42 inches. The backing film 32 has a thickness of preferably about 0.45 mils with a tolerance range of about 0.3 mil to about 1.0 mil. The backing film 32 can be obtained pre-made from a manufacturer such as Pliant Corporation of Schaumberg, Ill., USA which can be found at the web site www.pliantcorp.com.

The cap sheet 18 of FIG. 2 can be conventionally fabricated in a sequence of steps on a roofing machine, such as the one shown diagrammatically in FIG. 3. With continuing reference to FIG. 3, fiberglass or polyester mat material 34 is provided to mat unwinder stand and splicer apparatus 36, which produces a continuous woven mat or felt 38, thereby forming a fibrous reinforcement for the roofing material to be produced. Simultaneously, asphalt 40, modifying polymers 42, and optional mineral stabilizers 44 are added to a mixing tank 46 from which liquefied modified asphalt 48 issues and which is directed to impregnation vat 50. The impregnation vat 50 receives the continuous mat 38, which is dipped into the liquefied modified asphalt 48 in the vat 50, thereby producing an asphalt impregnated mat 54. At the granule application station 56, granules 58 are distributed onto the asphalt impregnated mat 54 producing a granule-faced roofing material 60. The granules 58 will embed into the surface of the asphalt impregnated mat 54 due to the temperature of the asphalt and its softened state at high temperatures. The granule-faced roofing material 60 is then fed through water cooling trays 62 to lower the temperature of the asphalt for further processing and to lock the applied granules 58 onto the surface of the mat 54. After leaving the water cooling tray 62, the roofing material 64 has a backing film 66 applied at a backing applicator station 68 to be discussed hereinbelow with reference to FIG. 4. The roofing material 64 is then further cooled and dried by air knives and/or cooling fans 70. After its accumulation on a finish looper (accumulator) 72, the roofing material 64 is fed to a roll winder/cutter 74 to produce the finished roofing material 76 in the form of roll roofing which is then placed in storage 78.

With reference to FIGS. 3 and 4, the backing film 66 is applied to the mat 54 at the backing applicator station 68 using a two-roll mill apparatus 80, which includes a film roller 82 and a tension roller 84 acting in conjunction with conveyor rollers 86 of the roofing machine shown diagrammatically in FIG. 3. The backing film 66 is un-rolled from the film roller 82 onto the mat 54 in the opposite direction of movement (see arrow) of the mat 54 as the mat 54 is rolled over the conveyer rollers 86. The tension roller 84 pushes the backing film 66 onto the surface of the mat 54. The backing film 66 sticks naturally to the mat 54 since the material of the mat is still hot at this point in the manufacturing process. The tension roller 84 thus guides the backing film 66 over and onto the entire surface area of the mat 54.

The present invention is adapted for other techniques for constructing built-up roofs. For instance, bitumen layers and a cap sheet can be adhered together with adhesives mixed with solvents (combined aromatic and aliphatic), instead of with melted asphalt. The composition of the backing film remains the same as when melted hot-mopped asphalt is used. However, instead of melting and merging with the hot asphalt, the backing film dissolves into the adhesive/solvent mixture, thereby forming a mechanical bond between the uppermost bitumen layer and the cap sheet. The solvent present in the adhesive/solvent mixture can be either aromatic or aliphatic. In one preferred embodiment, the solvent constitutes about 15%-25% by weight of the adhesive/solvent mixture. The adhesive can be any traditional asphaltic adhesive as is known in the art, provided it can be applied to the backing film at a temperature which starts at 45° C. and rises.

This invention has been described with reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention as defined in the appended claims. For instance, the present invention can be used in other types of roofing, such as APP, SBS, and SEBS modified roofing membranes. These and other variations and modifications are included in the present invention as defined in the appended claims.

Claims

1. A roofing product, comprising a roll roofing sheet having a backing film adhered to one side thereof, said backing film being miscible with an adherent substance used to apply said roofing sheet to a roof when said roofing sheet is unrolled, and said backing film inhibiting the transfer of material to an opposite side of said roofing sheet when said roofing sheet is in the form of a roll.

2. The roofing product of claim 1, wherein said backing film is made from at least one polymeric material.

3. The roofing product of claim 2, wherein said backing film is made from a combination of a low density polypropylene (LDPP) and ethylene-vinyl acetate (EVA).

4. The roofing product of claim 3, wherein the proportion of LDPP to EVA ranges from 20%-80% LDPP to 20%-80% EVA by weight.

5. The roofing product of claim 3, wherein the proportion of LDPP to EVA is about 60% EVA to 40% LDPP by weight.

6. The roofing product of claim 2, wherein said backing film is made from a material selected from the group consisting of linear low density films, vinyl films, and a combination of low density and high density films.

7. The roofing product of claim 6, wherein said low density film is polyethyleneterephthalate (PET).

8. The roofing product of claim 6, wherein said combination of low density and high density films is selected from the group consisting of PET, HDPE, HDPP, LDPP, LDPE, and EVA.

9. The roofing product of claim 1, wherein said roll roofing sheet includes at least one layer of modified bitumen.

10. The roofing product of claim 9, wherein said at least one layer of modified bitumen is an SBS membrane.

11. The roofing product of claim 9, wherein said at least one layer of modified bitumen is selected from the group consisting of an APP membrane, an SBS membrane, and an SEBS membrane.

12. The roofing product of claim 1, wherein said roll roofing sheet further comprises:

a first modified bitumen layer having a top surface and a bottom surface, said bottom surface of said first modified bitumen layer being attached to said backing film;

a reinforcing mat having a top surface and a bottom surface, said bottom surface of said reinforcing mat being attached to said top surface of said first modified bitumen layer;

a second modified bitumen layer having a top surface and a bottom surface, said bottom surface of said second modified bitumen layer being attached to said top surface of said reinforcing mat; and

a plurality of granules embedded in said top surface of said second modified bitumen layer.

13. The roofing product of claim 12, wherein said plurality of granules and said second modified bitumen layer are coated with a reflective coating.

14. The roofing product of claim 13, wherein said reflective coating has a white color.

15. The roofing product of claim 1, wherein said backing film is miscible with molten asphalt.

16. The roofing product of claim 15, wherein said backing film is solid at room temperature.

17. The roofing product of claim 1, wherein said backing film dissolves when it comes in contact with an adhesive/solvent mixture.