Polymer blends for rooftop curable heat seamable roof sheeting and method for covering roofs

Abstract: A rooftop curable heat seamable sheet material for roofing prepared from an uncured polymeric composition of matter which comprises 100 parts by weight of a polymer blend comprising from about 10 to 95 parts by weight of an polymer selected from the group consisting of polyolefins having up to about 2 percent by weight crystallinity, which polyolefins are prepared from monomers having at least 2 carbon atoms, and mixtures thereof; from about 5 to 90 parts by weight of a crystallinity enhancing polymer and mixtures thereof; from about 20 to 300 parts by weight of a filler selected from the group consisting of reinforcing and non-reinforeing materials and mixtures thereof per 100 parts of the polymer blend; from about 1.5 to 10 parts by weight of a cure package a cure package capable of allowing the composition of matter to cure at temperatures of at least 50°C, per 100 parts of the polymer blend; and from about 20 to 150 parts by weight of a processing material and mixtures thereof, per 100 parts of the polymer blend. A method for covering a roof comprises the steps of applying layers of self-adhering sheet material prepared from an uncured heat seamable polymeric composition of matter comprising blends of polyolefins with crystallinity enhancing polymers, fillers, processing materials and a cure package capable of allowing the composition of matter to cure at temperatures of at least 50°C to the roof being covered; overlapping adjacent edges of the layers; heating the overlapped areas to about the softening point of the sheet material and seaming the overlapped areas under sufficient pressure to provide an acceptable seam strength. The composition of matter is curable at temperatures of at least about 50°C, at temperature readily encountered on the roof of a building. For practice of the method, the composition of matter is self-adhering, without the use of an adhesive.

Description: TECHNICAL FIELD The present invention relates generally to sheeting material used for covering roofs. More particularly the sheeting material comprises a blend of an ethylenepropylene-diene terpolymer, referred to herein as EPDM, or ethylene-propylene copolymer, referred to herein as EPR, or other similar olefin type polymers with a crystallinity enhancing polymer. The blend also includes thiuram and thiazole accelerators and is extended with high levels of fillers and processing oils. A method is also provided for covering roofs which includes the step of employing an uncured, self-adhering EPDM, EPR or similar polyolefin sheeting material of the present invention. BACKGROUND OF THE INVENTION Polymeric roof sheeting is used as single ply roofing membrane for covering industrial and commercial flat roofs. Such membranes are generally applied to the roof surface in vulcanized or cured state. Because of outstanding weathering resistance and flexibility, cured EPDM based roof sheeting has been rapidly gaining acceptance. This material normally is prepared by vulcanizing uncured compositions in the presence of sulfur or sulfur containing compounds such as mercaptans. Our earlier U.S. patent, No. 4,803,020 also teaches the use of radiation crosslinking promoters in an EPDM sheeting composition which can be cured by ionizing radiation. Notwithstanding the usefulness of radiation and sulfur curing, a disadvantage with utilizing these elastomers is the lack of adhesion of EPDM, especially cured EPDM, to itself. This is a serious problem because in applying EPDM sheets to a roof, it is usually necessary to splice the cured EPDM sheets together. This splice or seam area is subjected to both short term and long term stresses such as those caused by roof movement, heavy winds, freeze-thaw cycling and thermal cycling. Such stresses may manifest themselves in shear forces or peel forces, i.e. , the seam peels back under severe stress conditions or results in a partially open seam (often referred to as a fish-mouth condition) under less severe conditions. In view of the foregoing problem, it has been necessary to utilize an adhesive to bond the cured EPDM sheets together. As will be evident from the above discussion, an adhesive for bonding cured EPDM elastomer roofing sheets together must meet a number of requirements which are extremely difficult to satisfy. Thus, the adhesive must provide sufficient peel and adhesive strength to permit the splice formed by bonding the cured EPDM roofing sheets together to resist both short term and long term or stress conditions referred to hereinabove. Moreover, the adhesive must be resistant to oxidation, hydrolysis and chemical attach from ponded water. Additionally, the adhesive must provide the important property often referred to in the adhesive art as "Quick Stick". The term "Quick Stick" means the characteristics of two sheets of material which have been coated with an adhesive composition to develop virtually immediate adhesive strength when placed in contact with each other. Quick Stick is an extremely important property in an adhesive which is utilized to splice cured EPDM elastomer roofing sheets together. Thus, adhesive compositions presently known generally require anywhere from about two (2) to about seven (7) days at room temperature ( i.e. 22°C.) to attain maximum adhesive strength. At higher ambient temperature, this time period may be somewhat less, but at minimum it will generally be at least 24 hours. The conventional procedure for splicing the EPDM roofing sheets together is to make the splice within a relatively short period of time after the adhesive coating has been applied to each sheet, generally within 30 minutes but often less. Accordingly, the adhesive composition must provide sufficient immediate adhesive strength or Quick Stick to permit the splice to withstand stresses from winds, movement, handling by installers, etc. until the adhesive achieves its maximum strength which as indicated will generally take from two (2) to seven (7) days. Commercial contact adhesives which are conventionally employed for bonding cured EPDM elastomer roofing sheets together generally consist of solutions of neoprene or neoprene-type or butyl or butyl-type polymers in aromatic or aromatic-aliphatic solvents containing 2-butanone often along with tackifying resins. However, such adhesives have not proven to be very satisfactory due to their lower than desirable peel adhesion strengths. Thus, the neoprene or butyl-type adhesives often provide peel adhesion values at 22°C of only 17.9 to 35.8 kg/m (1 to 2 pounds per linear inch). Pressure sensitive and contact adhesive compositions containing neutralized, partially neutralized or unneutralized sulfonate elastomers, tackifying resins and organic solvents or organic solvent mixtures are known in the prior art as shown by U.S. Pat. No. 3,801,531 and 3,867,247. U.S. Pat. No. 3,801,531 relates to pressure sensitive adhesive compositions which contain thiouronium derivatives of unsaturated elastomers or neutralized, partially neutralized or unneutralized sulfonated elastomers including sulfonated EPDM, tackifying resins including phenol formaldehyde or alkylphenol formaldehyde resins and organic solvents or organic solvent mixtures including a preferred 90:10 mixture of toluene and isopropyl alcohol. However, the patent does not disclose or suggest the use of alkylphenols or ethoxylated alkylphenols in such compositions. U.S. Pat. No: 3,867,247 relates to adhesive contact cements which contain neutralized, partially neutralized or unneutralized sulfonated butyl elastomers, tackifying resins including phenol formaldehyde or alkylphenol formaldehyde resins and organic solvents or organic solvent mixtures including a preferred 90:10 mixture of toluene and isopropyl alcohol. However, the patent does not disclose or suggest the use of alkylphenols or ethoxylated alkylphenols in such compositions. The adhesive compositions described in the aforementioned patents suffer from a significant disadvantage which materially limits their usefulness as a contact adhesive for bonding cured EPDM elastomer roofing sheets together and that is their deficiency in Quick Stick properties. One such adhesive system for EPDM elastomers that provides good Quick Stick is described in U.S. Pat. No. 4,480,012, owned by the Assignee of record herein. Such adhesives comprise a neutralized sulfonated EPDM elastomeric terpolymer; an organic hydrocarbon solvent; a para-alkylated phenol formaldehyde tackifying resin and an alkylphenol or ethoxylated alkylphenol. While the use of such adhesive compositions is an effective means of joining and sealing the edges of elastomeric roofing material, if the use of adhesives could be eliminated, the additional labor material costs and related hardware necessary to apply the adhesive would effect a significant cost savings. Moreover, elimination of the need to cure the material prior to its application to a roof would also be advantageous. Of course, the use of EPDM rubber is not limited to roofing materials, In order to increase use of EPDM and enhance its useful properties it is known to form blends with other polymers. U.S. Pat. No. 4,687,810, for instance, is directed toward a rubber blend comprising EPDM rubber, high-diene hydrocarbon rubber and a vulcanizing agent for the former but not the latter. Such blends can be employed in tire sidewalls. U.S. Pat. No. 4,833,194, discloses blends of crystalline and amorphous polymers, such as EPR type rubbers, which provide uncured thermoplastic elastomers having good physical properties and weatherability. Typical of such blends are those comprising from about 5 to about 45 percent by weight of an amorphous ethylene-propylene elastomer having less than 65 percent by weight of ethylene; from about 55 to about 95 percent by weight of an crystalline ethylene-propylene elastomer having at least 60 percent by weight of ethylene; and, from about 2 to about 35 parts by weight of a crystalline polymer made from an olefin monomer. U.S. Pat. No. 4,855,362, provides polymer alloys, or blends, which comprise a highly unsaturated rubbery polymer, a modified EPDM and at least one thermoplastic polyolefin. The blends are formed in order to take advantage of the properties of the unsaturated rubbery polymer and the EPDM, which polymers are difficult to blend. By modifying the EPDM with N-chlorothio-sulfonamides, they become co-curable with the unsaturated rubbery polymer. This patent also notes in the Background section that blends of thermoplastic materials, such as polypropylene, with EPDM have been found to possess superior strength, high temperature mechanical properties and good compression set. U.S. Pat. No. 4,130,535 discloses thermoplastic elastomers which comprise 25-75 weight percent of thermoplastic polyolefin resin, such as polypropylene, and 75-25 weight percent of monoolefin copolymer rubber, such as EPDM. EP-A-0 484 872 relates to a process for curing a heat-weldable roofing membrane by applying elemental sulfur on the exterior surface of the roofing membrane, said membrane being a blend of (a) 50 to 80% by weight of an ethylene/propylene/nonconjugated diene elastomer and (b) 20 to 50% by weight of an ethylene-containing polymer selected from the group consisting of polyethylene, an ethylene alpha-monoolefin copolymer wherein the monoolefin contains from 3 to 12 carbon atoms and is present in amounts of 2 to 8% by weight, and an ethylene/vinyl acetate copolymer having a vinyl acetate content up to about 10% by weight, said membrane containing a cure accelerator. The roofing membrane is exposed to ambient outdoor temperatures resulting in migration of sulfur to the interior of the membrane where, together with the cure accelerator, it effects cure of the membrane. SUMMARY OF THE INVENTION It is thus an object of the present invention to provide polymer blends for heat seamable roof sheeting materials that need not be cured prior to or during application but which will cure subsequently on the rooftop when exposed to sunlight. It is another object of the present invention to provide polymer blends for heat seamable roof sheeting materials which eliminate the need for a solvent-based splicing adhesive and the related labor and hardware necessary for mixing and application thereof. It is yet another object of the present invention to provide polymer blends comprising EPDM, EPR, or other similar olefinic type polymers and a crystallinity enhancing polymer which improves the green strength and splice adhesion of heat seamable roof sheeting materials. It is still another object of the present invention to provide a method for covering roofs which employs polymer blend heat seamable roof sheeting materials which do not require curing and which can be joined and seamed together at their edges without the use of adhesives. In general the present invention relates to a rooftop curable heat seamable sheet material for roofing prepared from an uncured polymeric composition of matter comprising 100 parts by weight of a polymer blend comprising from at least 10 to 95 parts by weight of a polymer selected from the group consisting of polyolefins having up to 2 percent by weight crystallinity and an average molecular weight Mn of at least 30,000 and Mw of at least 100,000, prepared from monomers having at least 2 carbon atoms and mixtures thereof; and from 5 to 90 parts by weight of a crystallinity enhancing polymer selected from the group consisting of polyethylene and polypropylene homopolymers; poly(ethylene-co-propylene) random copolymers and poly(ethylene-b-octene) and poly(ethylene-b-octene) and poly(ethylene-b-butene) block copolymers; from 20 to 300 parts by weight of a filler selected from the group consisting of reinforcing and non-reinforcing fillers and mixtures thereof per 100 parts of said polymer blend; from 1.5 to 10 parts by weight of a cure package capable of allowing the composition of matter to cure at temperatures of at least 50°C per 100 parts of the polymer blend comprising 0.25 to 2.0 parts by weight per 100 parts by weight of the polymer blend of sulfur as crosslinking agent and one or more sulfur vulcanizing accelerators; and from 20 to 150 parts by weight of a processing material selected from the group consisting of paraffinic oils, naphthenic oils and waxes and mixtures thereof, per 100 parts of said polymer blend. A method for covering a roof is also provided and comprises the steps of applying layers of rooftop curable sheet material as defined above to the roof being covered; overlapping adjacent edges of the layers; heating the overlapped areas to about the softening point of the sheet material and seaming the overlapped areas under sufficient pressure to provide an acceptable seam strength the composition of matter having sufficient self-adhesion, without the use of an adhesive. At least one or more of the foregoing objects which shall become apparent to those skilled in the art are described in greater detail with reference to the specification which follows. PREFERRED EMBODIMENT OF THE INVENTION As noted hereinabove, the roof sheeting materials of the present invention comprise a blend of EPDM, EPR or similar olefin type polymers with crystallinity enhancing polymers. The term EPDM is used in the sense of its definition as found in ASTM D-1418-85 and is intended to mean a terpolymer of ethylene, propylene and a diene monomer. Illustrative methods for preparing such terpolymers are found in U.S. Pat. No. 3,280,082. The preferred terpolymers contain from 60 to 95 weight percent ethylene and from zero to 12 weight percent of the diene with the balance of the terpolymer being propylene or some other similar olefin type polymer. The diene monomer utilized in forming the EPDM terpolymer is preferably a non-conjugated diene. Illustrative examples of non-conjugated dienes which may be employed are dicyclopentadiene, alkyldicyclopentadiene, 1,4-pentadiene, 1,4-hexadiene, 1,5-hexadiene, 1,4-heptadiene, 2-methyl-1,5-hexadiene, cyclooctadiene, 1,4-octadiene, 1,7-octadiene, 5-ethylidene-2-norbornene, 5-n-propylidene-2-norbornene, 5-(2-methyl-2-butenyl)-2-norbornene and the like. A typical EPDM is Vistalon® MD-744 (Exxon Chemical Co.) a terpolymer having a Mooney Viscosity (ML/4 at 125°C) of about 52; an ethylene/propylene (E/P) ratio of 61/39 weight percent and 2.7 weight percent of unsaturation. The term EPR is used in the sense of its definition as found in ASTM D-1418 and is intended to mean a copolymer of ethylene and propylene. The preferred copolymers contain from 60 to 95 weight percent ethylene with the balance to total 100 weight percent being propylene. A typical EPR is Vistalon® 719 (Exxon Chemical Co.) having an ethylene/propylene ratio of 75/25 weight percent. To be useful as a roofing material in the present invention the EPDM can have up to 2 weight percent crystallinity, from the ethylene component; an M n as measured by GPC of at least 30,000 and an M w, as measured by GPC of at least 100,000. Similarly, the EPR can have up to 2 weight percent crystallinity (ethylene); an M n, as measured by GPC of at least 30,000 and an M w, as measured by GPC of at least 100,000. We have found that the selection of an amorphous EPDM or EPR having low crystallinity (up to 2 percent by weight) and weight average molecular weight ( M w = 100,000) is necessary to provide a roofing material which does not require curing prior to application, if ever, and which does not require any type of adhesive, solvent-based or the like, to join and seam the spliced edges. Also useful as a roofing material in the present invention are copolymers of ethylene and butene. Other similar olefinic type polymers can be used to practice this invention. Generally speaking any amorphous polymer having up to 2 percent by weight crystallinity and selected from the group consisting of polyolefins prepared from monomers containing at least 2 carbon atoms can be employed. For purposes of discussion herein, references to EPDM, EPR or similar olefinic polymers is intended to include any of the amorphous polymers of the present invention. The composition or compound employed to form the roof sheeting material comprises a blend of 100 total parts by weight of EPDM, EPR or other similar type olefin type polymers, including mixtures of two or more types, and a crystallinity enhancing polymer to which is added basically fillers, processing oil and accelerators as well as optionally other components including curatives, all of which are discussed hereinbelow. The crystallinity enhancing polymers of the present invention are selected from the group consisting of polyolefin homopolymers, random copolymers and block copolymers. Homopolymers include polyethylene and polypropylene. Random copolymers include poly(ethylene-co-propylene) copolymers. Block copolymers include poly(ethylene-b-octene) and poly(ethylene-b-butene) copolymers. Mixtures of the foregoing polymers can be employed or a single polymer can be employed to comprise the polymeric blend, with the EPDM or EPR polymer comprising from 10 to 95 parts by weight for a total of 100 parts of polymer. Typical examples of commercially available crystallinity enhancing polymer additives that can be blended with EPDM, EPR or other similar polyolefins, materials have been set forth in Table I along with melting temperatures and percent of crystallinity. With respect to the filler, suitable fillers are selected from the group consisting of reinforcing and non-reinforcing materials, and mixtures thereof, as are customarily added to rubber. Examples include both inorganic and organic materials such as carbon black, ground coal and cryogenically ground rubber, as well as non-black fillers and the like. Generally, preferred fillers include carbon black, ground coal and cryogenically ground rubber. Carbon black is used in an amount of 20 parts to 300 parts per 100 parts of the polymer blend (phr), preferably in an amount of 60 to 150 phr. The preferred range of carbon black herein (60 to 150 phr) is about equal to the amount of carbon black normally used in preparing sulfur cured EPDM sheeting. The carbon black useful herein is any carbon black. Preferred are furnace blacks such as GPF (general purpose furnace), FEF (fast extrusion furnace) and SRF (semi-reinforcing furnace). The ground coal employed as a filler in the compositions of the invention is a dry, finely divided black powder derived from a low volatile bituminous coal. The ground coal has a particle size ranging from a minimum of 0.26 microns to a maximum of 2.55 microns with the average particle size of 0.69 ± 0.46 as determined on 50 particles using Transmission Electron Microscopy. The ground coal produces an aqueous slurry having a pH of 7.0 when tested in accordance with ASTM D-1512. A preferred ground coal of this type is designated Austin Black which has a specific gravity of 1.22 ± 0.03, an ash content of 4.58% and a sulfur content of 0.65%. Austin Black is commercially available from Coal Fillers, Inc., P.O. Box 1063, Bluefield, Virginia. Amounts range from 5 to 65 phr with 15 to 35 being preferred. Finally, essentially any cryogenically ground rubber may be employed as a filler in the composition of the invention. The preferred cryogenically ground rubbers are cryogenically ground EPDM, butyl, neoprene and the like. A preferred cryogenically ground rubber is a cryogenically ground EPDM rubber. The preferred cryogenically ground EPDM rubber is a fine black rubbery powder having a specific gravity of 1.129 ± 0.015 and a particle size ranging from 30 to 300 microns with an average particle size ranging from 50 to 80 microns. Amounts range from 5 to 40 phr with 10 to 25 being preferred. Mixtures of Austin black and cryogenically ground rubber useful herein may be utilized as a partial replacement for carbon black. Where mixtures of these two fillers are employed the relative amounts thereof can be widely varied; the overall total not exceeding 60 phr. The ratio of Austin black to cryogenically ground rubber may range from a desired ratio of 2:1 to perhaps even a ratio of 3:1. Amounts thereof fall within the range of amounts normally employed in preparing sulfur cured conventional roof sheeting. With respect next to the non-black mineral fillers, suitable fillers are selected from the group comprising of hard clays, soft clays, chemically modified clays, calcined clays, mica, talc, alumina trihydrates, calcium carbonate, titanium dioxide, amorphous precipitated hydrated silica, silicates, silicon dioxide and mixtures thereof. These fillers may partially replace "black" fillers, i.e. carbon black and other related petroleum-derived materials. Some four basic types of clays are normally used as reinforcing fillers for rubber elastomers. The different types of clay fillers include; airfloated, water washed, calcined and surface treated or chemically modified. The airfloated clays are the least expensive and most widely used. They are divided into two general groups, hard and soft, and offer a wide range of reinforcement and loading possibilities. Hard Clays are used in the amount of 20 parts to 200 parts per 100 parts of polymer (phr), preferably in an amount from 65 to 175 phr. Any commercially available hard clay may be used. The preferred airfloated hard clays used are: Suprex®, Barden R®; LGB® all commercially available from J.M. Huber Corporation. The airfloated soft clays are used in the amount of 20 parts to 200 parts per 100 parts of polymer(phr), preferably in an amount from 75 to 175 phr. The preferred airfloated soft clays used are Paragon®; Hi-White R®, and K-78® commercially available from J.M. Huber Corporation. Water washed clays are normally considered as semi-reinforcing fillers. This particular class of clays are more closely controlled for particle size by the water-fractionation process. This process permits the production of clays within controlled particle size ranges. The preferred ranges of water washed clays are very similar to the preferred amounts of airfloated soft clays mentioned hereinabove. Some of the preferred water washed clays include Polyfil® DL, Polyfil®F, Polyfil®FB, Polyfil®HG-90, Polyfil®K and Polyfil® XB, all are commercially available from J.M. Huber Corporation. The third type of clay includes the calcined clays. Clays normally contain approximately 14 percent water of hydration, and most of this can be removed by calcination. The amount of bound water removed determines the degree of calcination. The preferred ranges of calcined clays are very similar to the preferred amounts of airfloated hard clays mentioned hereinabove. Some of the preferred calcined clays include Polyfil® 40, Polyfil®70, and Polyfil® 80, all commercially available from J.M Huber Corporation. The final type of clay includes the chemically modified reinforcing clays. Cross-linking ability is imparted to the clay by modifying the surface of the individual particles with a polyfunctional silane coupling agent. Chemically modified clays are used in the amount of 20 parts to 200 parts per 100 parts of polymer(phr), preferably in an amount from 60 to 175 phr. Normally the specific gravity of most clays is 2.60 at 25° C. The preferred chemically modified clays are commercially available from J.M. Huber Corporation and include: Nucap® 100, Nucap® 200, Nucap® 190, Nucap®290, Nulok® 321, Nulok® 390 and Polyfi1® 368. Other useful non-black fillers include amorphous silica (silicon dioxide). Silicas are generally classed as wet-process, hydrated silicas because they are produced by a chemical reaction in water, from which they are precipitated as ultrafine, spherical particles. Silica can be employed in the amount of 20 parts to 50 parts·per 100 parts of polymer(phr), preferably in an amount from 20 to 50 phr. The useful upper range is limited by the high viscosity imparted by fillers of this type. Some of the commercially available silicas which may be used include: Hi-Sil® 215, Hi-Sil® 233, Hi-Sil® EP and Silene® D all produced by PPG Industries. Also, a number of useful commercial grades of different silicas are available from J.M. Huber Corporation. Finely ground calcium carbonate is employed in the amount of about 20 parts to 200 parts per 100 parts of polymer(phr), preferably in an amount from 35 to 90 phr. Calcium carbonate generally has a specific gravity of 2.71 and is commercially available from a number of suppliers including Harwick Chemical, J.M. Huber Corporation, Georgia Marble, Genstar Stone Products and Omya, Inc. Titanium dioxide is employed in the amount of 5 parts to 80 parts per 100 parts of polymer(phr), preferably in an amount from 10 to 50 phr. Both the rutile and anatase form of titanium dioxide may be used, however, the rutile form is preferred and includes such products as TiPure® R-960, which is a fine, white powder having a specific gravity of 3.90 and commercially available from DuPont Co. Other commercially available non-black mineral fillers that may be employed to practice this invention include; talc (magnesium silicate), mica (mixtures of sodium and potassium aluminum silicate) and alumina trihydrate. With respect to the processing material, it is included to improve the processing behavior of the composition ( i.e. reduce mixing time and increase rate of sheet forming) and includes processing oils, waxes and the like). The process oil is included in an amount ranging from 20 parts to 150 parts process oil phr, preferably in an amount ranging from 60 parts to 135 phr. A preferred processing oil is a paraffinic oil, e.g. Sunpar 2280 which is available from the Sun Oil Company. Other petroleum derived oils including naphthenic oils are also useful. Regarding the cure package, sulfur and sulfur vulcanizing accelerators and mixtures thereof employed in the rooftop curable membrane composition may range from 1.5 phr to as high as 10 phr by weight with the preferred amounts ranging from 1.5 to 6 phr. Sulfur is employed in amounts of 0.25 to 2 phr. The roof sheeting compound is not cured prior to application and needed not be cured subsequent thereto. The presence of sulfur enhances bonding of the seams. In addition, the cure package provides one or more vulcanizing accelerators including thioureas such as ethylene thiourea; N,N-dibutylthiourea; and N,N-diethylthiourea; thiuram monosulfides and disulfides such as tetramethylthiuram monosulfide (TMTMS); tetrabutylthiuram disulfide (TBTMS); tetramethyl-thiuram disulfide (TMTDS); and tetraethylthiuram monosulfide (TETDS); benzothiazole sulfenamides such as N-oxydiethylene-2-benzothiazole sulfenamide; N-cyclohexyl-2-benzothiazole sulfenamide; N,N-diisopropyl-2-benzothiazolesulfenamide; and N-tert-butyl-2-benzothiazole sulfenamide; 2-mercaptoimidazoline; N,N-diphenyl-guanadine; N,N-di-(2-methylphenyl)guanadine; 2-mercaptobenzothiazole; 2-(morpholinodithio)-benzothiazole disulfide; and zinc 2-mercaptobenzothiazole; dithiocarbamates such as tellurium diethyldithiocarbamate; copper dimethyldithiocarbamate; bismuth dimethyldithiocarbamate; cadmium diethyldithiocarbamate; lead dimethyldithiocarbamate; zinc diethyldithiocarbamate and zinc dimethyldithiocarbamate. It should be appreciated that the foregoing list is not exclusive, and that other vulcanizing agents known in the art to be effective in the curing of EPDM terpolymers may also be utilized. For a list of additional vulcanizing agents, see The Vanderbilt Rubber Handbook , referenced hereinabove. Amounts of the various components that can be employed in the cure package are set forth in Table II hereinbelow which provides both broad and preferred ranges for each type of component, when present. Again, the total amount of the cure package employed ranges between 1.5 and 10 phr, depending upon the amount of sulfur, the vulcanizing accelerators selected and the ultimate destination or use of the EPDM composition. That is, when employed as a rooftop curable sheet membrane in a warm climate, different accelerators and/or amounts thereof will be selected than where the sheet membrane is to be installed in a cooler climate. The amounts of sulfur and vulcanizing accelerators employed in the composition are based on parts per hundred rubber by weight. Cure Package Components Ingredients Broad Range, phr Preferred Range, phr Sulfur 0.25- 2.0 0.5- 1.5 Thiuram accelerators TMTMS 0.5 - 4 1 - 2 TMTDS 0.5 - 3.5 1 - 2 TETDS 0.75 - 3.5 1 - 2.5 Thiazole accelerators Captax - MBT 0.25 - 3 0.35 - 2 Altax - MBTS 0.25 - 3 0.35 - 2.5 Sulfenamide accelerators N-cyclohexyl-2-benzothiazole sulfenamide 0.5 - 3.5 1 - 2.5 N-tert-butyl-2-benzothiazole sulfenamide 0.5 - 3.5 1 - 2.5 Dithiocarbamate accelerators Copper dimethyldithiocarbamate 0.5 - 3.0 1 - 2.5 Dimethylcyclohexyl-ammonium dibutyl dithiocarbamate 0.5 - 2.75 1 - 2.5 Tellurium diethyldithiocarbamate 0.5 - 2.5 1 - 2 It is to be understood that the cure package comprises sulfur and at least one or more of the foregoing accelerators and thus, the amounts presented in Table II are those wherein one or more of the above accelerators are present. As noted hereinabove, the roof sheeting compound is not cured prior to application and needed not be cured subsequent thereto. The presence of the cure package allows the sheet material to cure at temperatures of at least 50° C, readily obtainable when exposed to sunlight in most climates. Optional ingredients include, for example, other elastomers ( e.g., butyl elastomer, neutralized sulfonated EPDM, neutralized sulfonated butyl) in place of minor amounts of the EPDM, secondary inorganic fillers ( e.g., talc, mica, clay, silicates, whiting) with total secondary filler content usually ranging from 10 to 150 phr, and conventional amounts of other conventional agents, such as zinc oxide, stearic acid, antioxidants, antiozonants, flame retardants, and the like. The compounding ingredients can be admixed, utilizing an internal mixer (such as a Banbury mixer), an extruder, and/or a two-roll mill, or other mixers suitable for forming a viscous relatively uniform admixtures. When utilizing a type B Banbury internal mixer, in a preferred mode, the dry or powdery materials such as carbon black are added first followed by the liquid process oil and finally EPDM or other polyolefin and crystallinity enhancing polymer (this type of mixing can be referred to as an upside-down mixing technique). The resulting admixture is sheeted to a thickness ranging from 0.125 to 5 mm (5 to 200 mils), preferably from 0.875 to 1.5 mm (35 to 60 mils), by conventional sheeting methods, for example, milling, calendering or extrusion: Preferably, the admixture is sheeted to at least 0.10 cm (0.040 inches) which is the minimum thickness specified in standards set by the Roofing Council of the Rubber Manufacturers Association for non-reinforced black EPDM rubber sheets for use in roofing applications. In many cases, the admixture is sheeted to 0.10-0.13 cm (40-45 gauge) thickness since this is the thickness for a large percentage of "single-ply" roofing membranes used commercially. The sheeting can be cut to desired length and width dimensions at this time. The method of the present invention is practiced by utilizing an EPDM or EPR based elastomeric composite sheet material as described herein. As the sheet is unrolled over the roof substructure in an otherwise conventional fashion, the seams of adjacent sheet layers are overlapped. Overlapping (seam width) can vary according to meet the environment as well as the requirements specified by the architect, building contractor or roofing contractor and thus, does not constitute a limitation of the present invention. Assuming an overlap of several inches, the next step is to apply heat and pressure to the edge area to form the seam. Temperature is conveniently applied from 80° to 550°C. Generally, the seam area, comprising overlapping edges of adjacent sheets, should be heated to about the softening point of the sheet material. Numerous techniques which utilize heat and pressure can be used to produce an effective seam as are known to those skilled in the art. Pressure can vary widely from a minimum of 20.1 kPa to 413.8 kPa (3 psi) up to (60 psi), typically so long as it is adequate to provide an acceptable seam strength. In order to demonstrate practice of the present invention, several compounds were prepared and subjected to both peel and shear adhesion tests, as will now be set forth in detail. The EPDM polymer selected included Vistalon® MD-744. Characterization of the polymer is presented in Table III hereinbelow. POLYMER CHARACTERIZATION STUDY Vistalon® MD-744 ML/4 at 125°C 53 Ethylene Content, wt % 60 Crystallinity, wt % <1 Tg, °C (by DSC) -56.4 Tm, °C (by DSC) 41.6 Unsaturation, % 2.7 Type of unsaturation ENB M n 73,200 M w 360,400 M n/ M w ratio 4.92 The following examples are submitted for the purpose of further illustrating the nature of the present invention and are not to be considered as a limitation on the scope thereof. Parts and percentages are by weight, unless otherwise indicated. In the examples illustrated in Table IV, Example No. 1 provided a sulfur cured black EPDM membrane. The remaining examples Nos. 2-6 comprised sulfur cured black EPDM membranes with increasing amounts of a crystallinity enhancing copolymer. Complete formulations for each example appear in Table IV, hereinabove with all parts given on the basis of parts per hundred parts of rubber (phr) by weight, unless otherwise specified. Detailed Peel and Shear Adhesion Test Procedure Each of the above rubber compounds was subjected to adhesion testing which necessitated the building of test pads comprising 15.2 × 15.2 cm (6 x 6 inch) sheets reinforced by a fiber reinforcement scrim, according to the following procedure: 1. A 25.4 × 50.8 cm (10 x 20-inch) two roll mill was utilized to prepare a number of 15.2 × 15.2 cm (6 x 6-inch) sheets of rubber approximately 1.0 cm (40 mils) in thickness for building adhesion test pads. 2. In order to reinforce the uncured sheets of rubber, a 15.2 × 15.2 cm (6 x 6-inch) sheet of PVC treated polyester scrim (10 x 10 epi cord construction) was inserted between two 15.2 × 15.2 cm (6 x 6-inch) sheets of rubber. 3. The rubber-scrim assembly was covered with a layer of a Mylar film and placed in the cavity of a metal curing mold 15.2 × 15.2 × 0.2 cm (6 x 6 x 0.075-inch). 4. The rubber-scrim assembly was then pressed in a Mylar film for about five minutes at 149°C. 5. Two of the 15.2 × 15.2 cm (6 x 6-inch) scrim reinforced rubber pads were seamed together using a hand-held heating gun (Leister). Approximately 66 to 79 N (15 to 18 pounds force) was supplied by means of a roller such as a standard 5.0 cm (two-inch) wide metal roller. Satisfactory seams (either peel or shear) could be formed using only 13 to 18 N (3 to 4 pounds force) and the standard 5.0 cm (two-inch) wide rubber roller. The seams were allowed to equilibrate for 24 hours before testing. 6. A clicker machine with a 2.5 cm (one-inch) wide die was utilized to prepare a number of test specimens for seam peel (Type B, 90° peel) and shear (Type A, 180° peel) adhesion testing. 7. Testing machine: Model 1130 Instron Universal Tester - a testing machine of the constant rate-of-jaw separation type. The machine was equipped with suitable grips capable of clamping the specimens firmly and without slippage throughout the tests. 8. The 2.5 cm (one-inch) wide specimens were tested at the rate (both crosshead and chart speed) of 5.0 cm (two inches) per minute using the adhesion test set forth in ASTM D-413 (machine method). Both peel and shear adhesion strength were determined at room temperature (i.e., 23°C) as well as occasionally at 70° and 100°C. Specimens were allowed 15 minutes to preheat prior to testing at elevated temperatures. 9. Adhesion strength is defined as: peel adhesion strength (lbs/inch) = pounds force x sample width; shear adhesion strength (lbs/square inch) = pounds force x sample width. Physical properties of each of the rubber compounds were measured and have been reported in Table V hereinbelow. The unaged, thermoplastic black and oil filled membranes featuring blends of EPDM and crystallinity enhancing polymers exemplified in Table V were characterized as harder, higher modulus polymeric compositions having improved unaged die C tear resistance as compared to the sulfur cured 100% EPDM membrane control, Example No. 1. Physical properties after increasing periods of heat aging are presented in Table VI hereinbelow. Peel and shear adhesion at increasing temperatures for Example Nos. 1-6 are reported in Tables VII and VIII hereinbelow. Crosshead and chart speeds for all adhesion tests were conducted at the rate of 5.0 cm (two inches) per minute (ipm). Based on the test results in Tables VI, VII, and VIII, physical properties as well as peel adhesion and seam shear strength adhesion values for Example Nos. 2-6 were generally significantly better than for the sulfur cured EPDM membrane Example No. 1 (control) thereby demonstrating that the use of EPDM, EPR or other similar olefin type polymers including ethylene-octene or ethylene-butene copolymers or blends thereof and crystallinity enhancing polymers ( e.g. , homopolymers of ethylene and propylene, random and block copolymers of ethylene and propylene, etc.) in black and oil filled compounds with accelerators, using sufficient pressure and heat (usually in the form of hot air) allow the formation of a self-adhering seam without the use of adhesives. It is to be understood that the invention is not limited to the specific type of EPDM exemplified herein or by the disclosure or other typical EPDM, EPR or other similar olefin type polymers provided herein, the Examples Nos. 2-6 having been provided merely to demonstrate practice of the subject invention. Those skilled in the art may readily select other EPDM or EPR as well as other similar polyolefins and crystallinity enhancing polymers. Similarly, the invention is not necessarily limited to the particular fillers and processing oil exemplified or the amounts thereof. In conclusion, it should be clear from the foregoing examples and specification disclosure that the use of EPDM, EPR or other similar polyolefins with crystallinity enhancing polymers to prepare sheet material for roofing allows such sheet material to be seamed using pressure and heat. The seams are self adhering without the use of adhesives. Moreover, the sheet materials do not require curing prior to or during installation. It is to be understood that the invention is not limited to the specific types of EPDM and crystallinity enhancing polymers exemplified herein or by the disclosure of other typical polyolefins and crystallinity enhancing polymers provided herein, the examples having been provided merely to demonstrate practice of the subject invention. Those skilled in the art may readily select other polymers than EPDM, EPR and crystallinity enhancing polymers according to the disclosure made hereinabove. Similarly, the invention is not necessarily limited to the particular fillers, processing oil or accelerators exemplified or the amounts thereof.

Claims: A rooftop curable heat seamable sheet material for roofing prepared from an uncured polymeric composition of matter comprising: 100 parts by weight of a polymer blend comprising from at least 10 to 95 parts by weight of a polymer selected from the group consisting of polyolefins having up to 2 percent by weight crystallinity and an average molecular weight Mn of at least 30,000 and Mw of at least 100,000, prepared from monomers having at least 2 carbon atoms and mixtures thereof; and from 5 to 90 parts by weight of a crystallinity enhancing polymer selected from the group consisting of polyethylene and polypropylene homopolymers; poly(ethylene-co-propylene) random copolymers and poly(ethylene-b-octene) and poly(ethylene-b-octene) and poly(ethylene-b-butene) block copolymers; from 20 to 300 parts by weight of a filler selected from the group consisting of reinforcing and non-reinforcing fillers and mixtures thereof per 100 parts of said polymer blend; from 1.5 to 10 parts by weight of a cure package capable of allowing the composition of matter to cure at temperatures of at least 50°C per 100 parts of the polymer blend comprising 0.25 to 2.0 parts by weight per 100 parts by weight of the polymer blend of sulfur as cross-linking agent and one or more sulfur vulcanizing accelerators; and from 20 to 150 parts by weight of a processing material selected from the group consisting of paraffinic oils, naphthenic oils and waxes and mixtures thereof, per 100 parts of said polymer blend. A rooftop curable heat seamable sheet material, as set forth in claim 1, wherein said crystallinity enhancing polymers are selected from the group consisting of polyethylene and polypropylene homopolymers; poly(ethylene-co-propylene) random copolymers and poly(ethylene-b-octene) and poly(ethylene-b-butene) block copolymers. A rooftop curable heat seamable sheet material, as set forth in claim 1, wherein said polymer comprises EPDM having an ethylene content of 60 percent by weight, a weight average molecular weight of 360,000 and 1-2 percent by weight crystallinity. A rooftop curable heat seamable sheet material, as set forth in claim 1, wherein said filler comprises 110 parts by weight of carbon black and said composition of matter includes 70 parts by weight of said processing material. A rooftop curable heat seamable sheet material, as set forth in claim 1, wherein said vulcanizing accelerator is selected from the group consisting of thioureas; thiuram monosulfides and disulfides; benzothiazole sulfenamides; dithiocarbamates; 2-mercaptoimidazoline; N,N-diphenyl-guanadine; N,N-di-(2-methylphenyl) guanadine; 2-mercaptobenzothiazole; 2-(morpholinodithio)-benzothiazole disulfide; and zinc 2-mercaptobenzothiazole. A rooftop curable heat seamable sheet material, as set forth in claim 5, wherein said cure package comprises from 0.25 to 2 parts by weight of sulfur; from 1 to 4 parts by weight of at least one thiuram accelerator; from 0.25 to 2 parts by weight of a thiazole accelerator and from 1 to 1.25 parts by weight of a sulfenamide accelerator per 100 parts by weight of said polymer. A rooftop curable heat seamable sheet material, as set forth in claim 5, wherein said cure package comprises 1.25 parts by weight sulfur; 1.5 parts by weight of a thiuram accelerator; 0.5 to 0.75 parts by weight of a thiazole accelerator and 1 to 1.5 parts by weight of a sulfenamide accelerator per 100 parts by weight of said polymer. A rooftop curable heat seamable sheet material, as set forth in claim 1, exhibiting a peel adhesion value of at least 35.7 kg/m (2 pounds/inch) wherein the outer edges of the two sheets are seamed together in the absence of an adhesive. A rooftop curable heat seamable sheet material, as set forth in claim 1, exhibiting a shear adhesion value of at least 103.4 kPa (15 pounds/square inch) wherein the outer edges of the two sheets are seamed together in the absence of an adhesive. A method for covering a roof comprising the steps of: applying layers of a rooftop curable sheet material as defined in claims 1 to 9; overlapping adjacent edges of said layers; heating the overlapped areas to about the softening point of the sheet material; and seaming the overlapped areas under sufficient pressure to provide an acceptable seam strength said composition of matter having sufficient self-adhesion without the use of an adhesive. A method, as set forth in claim 10, wherein said step of heating is conducted at a temperature of at least 82°C.

Inventors: VALAITIS JOSEPH K, VALAITIS, JOSEPH K.
Applicants: BRIDGESTONE CORP, BRIDGESTONE CORPORATION
Application year: 1993
Main classification: C08L23
IPC codes: E04D5, C08L91, C08L23, C08K3, C08J5, C08L53, C08L89