BACKGROUND OF THE INVENTION

Roofing sheets are generally supplied in rolled up form for use in the formation of roofing membranes wherein overlapping sections of the material are used to form one or more plies of the finished roofing membranes. In addition they may be used on sidewalls of buildings. Such roofing membranes and systems are used primarily on commercial buildings or buildings of low slope by reason of their durability and comparatively low cost. One type of roofing sheet which is in demand for economical installations is a modified asphalt sheet. However, since modified asphalt is not fire resistant, it has been the practice to manufacture the sheet with a glass mat reinforcement and to cover it with a separate flame retardant composition such as a glass cap sheet or coating. Obviously, this procedure requires several time consuming steps to complete the roofing installation.

Accordingly, it is an object of this invention to simplify the operation necessary for providing a fire retardant roofing membrane.

Another object is to eliminate the necessity for a glass mat reinforcement either alone or in addition to the polyester reinforcment in the sheet and to provide a fire retardant roof covering with a material which incorporates fire retardancy, thus eliminating the need for membranes of different composition and top coating operations.

These and other objects will become apparent from those skilled in the art from the following description and disclosure.

THE INVENTION

In accordance with this invention there is provided a modified asphalt sheet which is impregnated, i.e. saturated or coated on its upper and/or lower surfaces with a composition comprising (a) between about 35 and about 85 wt. % petroleum asphalt or an asphaltic blend having a Brookfield viscosity at 210°F. of between about 500 and about 4,000 cps, a penetration at 77°F. (100 g. , 5 seconds, mm/10) of from about 20 to about 350 dmm and a softening point of from about 80° to about 200°F.; (b) between about 2 and about 50 wt. % of a modifier and <■-• ^' between about 10 and about 50 wt. % of colemanite, combined to provide 100% composition.

In the above composition, the asphaltic component is more desireably used in a concentration of from about 45 to about 80 wt. % and is preferably one having a viscosity of from about 1500 to about 3000 cps; a penetration of fr'om about 80 to about 200 dmm and a softening point of from about 100° to about 150°F. Such asphalts include roofing flux, straight reduced, thermal and air blown asphalts, mopping asphalt, liquid cut-back asphalts, etc. It will be apparent that asphalts of relatively lower penetration and higher viscosity can be employed when diluted with a cutting oil, such as for example, gas oil, to provide the asphaltic component having properties within the above ranges. °

Suitable modifier components are those conventionally employed for saturation of polyester roofing mat, and include from about 5%-95% to about 40%-60% by weight blends of isotactic polypropylene having a melt flow of from about 2 to 200 and atactic polypropylene homopolymer or copolymer containing up to 40% ethylene comonomer. An alternate modifier component which can be employed in the present composition is a synthetic polymer such as polyisobutylene, polybutylene or blends thereof.

These modifiers generally comprise between about 2 and about 50 wt. % of the flame retardant composition. Still another alternate is a styrene-butadiene, styrene-ethylene-butadiene-styrene, styrene-butadiene-styrene block copolymers or styrene-butadiene-rubber containing from about 10 to about 50 wt. % styrene, preferably from about 25 to about 35 wt. % styrene. When the styrene containing modifier is selected, the copolymer generally comprises between about 2 and about 20 wt. %, preferably between about 8 and about 15 wt. % of the composition.

Colemanite is a natural blend of hydrated oxides as represented by a particular type of calcium borate generally containing between about 30 and about 55% B ₂ 0 ₃ and between about 20 and about 35% CaO. This mineral may also contain up to about 12% other oxides such as silicon dioxide, aluminum oxide and magnesium oxide. The colemanite is preferably used in the present composition in a concentration of from about 10 to about 50% and is generally employed as granular material having a mesh size of from about 75% to about 80% minus 200 mesh screen.

A particular advantage of colemanite is its high cost effectiveness and availability over other borate compounds and compositions containing colemanite within the above ranges can be easily applied to polyester mats to achieve a Class A rating in the ASTM E-108 and UL 790 fire tests. Consequently, it is not necessary to apply a separate fire retardant top coating to the modified asphalt membrane. Also, the need for glass mat reinforcement is completely eliminated. Thus, the cost of the completed roof is greatly reduced and greater fire protection is afforded by coverage with the present inherently fire resistant roofing ply or plies. It is to be understood,

however, that the present composition is also suitable for coating or impregnation of other reinforcing mats such as glass mats, glass/polyester composites, etc.

The roofing membrane can be a mono or multi ply structure depending on the desired thickness of the roof covering. Generally, a thickness of from about 0.07 to about one inch is sufficient to provide good weathering preferably between about 0.12 and about 0.2 inch.

The method of coating a reinforcing mat is conventional and includes dipping, spraying, soaking or mechanical coating with a doctor blade or similar device. When coating a surface of the mat, the present composition is generally applied in a thickness of from about 0.05 to about 0.5 inch. Saturation of the mat provides inherent fire retardant throughout the felt.

The present composition is easily prepared by mixing the components in any order at a temperature of from about 100 to about 500°F. for a period of from about 1 to 24 hours, preferably at about 325-400°F. for 2 to 6 hours. The composition is then applied to the mat at about the same temperature to provide a product suitable for installation. The roofing sheet obtained shows no deterioration in flexibility so that it can be easily unrolled for overlaying a roof deck and can be easily handled in roofing construction.

Many methods of roofing can be employed for the purposes of this invention. For example, the present roofing sheet can be utilized as the sole roof covering over the entire deck or a base and top covering with instant roofing sheet can be combined with intermediate roofing layers of a different composition, e.g. an impregnated or non-impregnated glass mat. Also, alternate layers of roof covering can be employed. The specific roofing procedure for installation is conventional and need not be further discussed.

Having generally described the invention, reference is now had to the following examples which are provided to illustrate preferred embodiments but which are not to be construed as limiting to the scope of the invention as more broadly discussed above and as defined in the appended claims.

EXAMPLE 1

The following ingredients for the flame retardant composition were introduced into a metal container and mixed for 4 hours at 380 °F.

Ingredients wt. %

(1) AC-5 Asphalt 57.5

Isotactic polypropylene 3.5 (melt flow 60-90)

Atactic polypropylene/polyethylene blend 20.0

Polyethylene (melt flow 75-35) 6.0

Colemanite 13.0 (1) Per ASTM D3381 Table 2

The above melt was applied to a 12x20 inch sheet of polyester roofing mat (0.038" thick) by coating on a 2 roll mill to build a thickness of 0.157". The resulting product was then subjected to a flame test which comprised subjecting a 4x8 inch sample of the above, mounted on a l"/ft slope to the frame of a propane burner for 90 seconds. The results of this test are as reported in Table I.

A full sized roll of roofing sheet having the above composition was prepared and sent to Underwriters Laboratories (Northbrook, Illinois) for fire retardancy testing and quality classification The above formulation was assigned a Class A rating, indicating minimal flame and char damage, substantially no sheet flow coupled with high flame extinguishing properties.

When 7 wt. % polyisobutylene is substituted for isotactic polypropylene in the above composition, the resulting product has substantially the same beneficial properties.

EXAMPLE 2

The following ingredients for the flame retardant composition were introduced into a metal container and mixed for 4 hours at 380 °F.

Ingredients wt. %

(2) Asphalt (Penetration 130 dmm) 65.63

(3) Kraton 1101 6.00

(4) Kraton 1102 3.38 Colemanite 25.00

(2) softening point 120°F. (3) 31/69 styrene-butadiene copolymer, 0.94 specific gravity, Brookfield viscosity (toluene solution) at 77°F, 4,000 cps (25 wt.% polymer) (4) 28/72 styrene-butadiene copolymer, 0.94, Brookfield viscosity (toluene solution) at 77°F, 1,200 cps (25 wt. % polymer) .

The above melt was applied to a 12x20 inch sheet of polyester roofing mat (0.038 " thick) by coating on a 2 roll mill to build a thickness of 0.157 inch. The resulting product was then subjected to a flame test which comprised sujecting a 4x8 inch sample of the above, mounted on a l"/ft slope to the flame of a propane burner for a 90 seconds. The results of this test are as reported in Table I.

A full sized roll of roofing sheet having the above composition was prepared and the was then tested for fire retardancy by Underwriters Laboratory as described above. This sheet was given a Class A rating.

TABLE I 90 Second Burn Test

Product Tested Char Formation Flow

Example 1 excellent none

Example 2 very good very slight

Commercial Sample excellent none Manville Dynakap FR SBS

Commercial Sample very good none Siplast Paradiene FR SBS