Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2003-03-04
2004-06-01
Nutter, Nathan M. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S216000, C525S232000, C525S240000
Reexamination Certificate
active
06743864
ABSTRACT:
FIELD OF THE INVENTION
The present invention concerns polyolefin compositions having improved tenacity, while retaining softness and good mechanical properties, which can be advantageously used in flat sheet material, such as single ply roofing membranes for covering industrial and commercial flat roofs, and in other roofing applications. These compositions may be obtained by a sequential polymerization process.
BACKGROUND OF THE INVENTION
Traditionally, the building industry has utilized conventional built-up asphalt or fiber glass roofing as a preferred material in roofing construction. More recently, however, membrane roofing materials have displaced the conventional materials as a preferred material due to their cold cracking resistance, ease of installation, and overall improved and increased leak protection over time. Further, the membrane systems are easier and safer to install and are therefore more desirable to the contractor as well as the consumer.
Two membrane types are utilized in this field: thermoplastic and elastomeric.
Thermoplastic membranes, such as those formed from polyvinyl chloride (PVC), chlorinated polyethylene (CPE), chlorosulfonated polyethylene and the like, can be heat sealed or solvent welded to provide dependable seals of higher strength; however, these membranes also have serious disadvantages. For example, the thermoplastic material must be plasticized to provide the flexibility necessary for a roofing membrane, and plasticizers are quite expensive and leach out of the membrane over time thus resulting in the loss of flexibility, embrittlement and decreased cold crack resistance of the membrane. Further, the capacity of the thermoplastic materials to accept fillers is limited.
Moreover, there is a need for a PVC sheeting alternative, in view of the trend toward a chlorine-free environment.
Elastomeric membranes, such as vulcanized ethylene/propylene/diene terpolymers EPDM rubbers, has been rapidly gaining acceptance, because of outstanding weathering resistance and flexibility. This material normally is prepared by vulcanizing the composition in the presence of sulfur or sulfur containing compounds.
However, these membranes are difficult to seal, due to the lack of adhesion of EPDM, especially cured EPDM, to itself, and require an adhesive for seaming the membrane in order to provide a leak-free, continuous roofing cover. These adhesives add a significant material cost and are difficult and time-consuming to apply. Further, the adhesives often weaken over time, causing delamination of the membranes and subsequent leaks in the roofing cover. Elastomeric membranes also require an additional costly curing step.
In order to avoid the curing procedure, in the state of the art it was proposed to use sheeting materials for roofing applications comprising an EPDM in combination with highly crystalline thermoplasticity promoters, such as high density polyethylene (HDPE), low density polyethylene (LDPE) and other similar olefin type polymers. For instance, U.S. Pat. No. 5,256,228 discloses a heat seamable sheet material for roofing, prepared from an uncured polymeric composition which comprises 100 parts by weight of a polymer blend comprising from 50 to 90 parts by weight of polyolefins having up to 2 percent by weight crystallinity, and from 10 to 50 parts by weight of a highly crystalline thermoplasticity promoter such as HDPE or LDPE; 50-250 parts by weight of a filler; and 20-150 parts by weight of a processing material.
Nevertheless, the presence of crystalline polyethylene resins have many disadvantages. For instance, higher crystallinity levels result in less thermal dimensional stability, expansion or contraction over large temperature ranging observed in the field; this may result in bucking or stress on the sheet. Moreover, the lower melting characteristics of polyethylene result in limitations for applications at elevated temperatures, such as in dark colored sheet. Finally, polyethylene has a narrow melting point range, which results in a narrow heat welding process window.
Polyolefin compositions having good mechanical properties have been used in many application fields, due to the characteristics which are typical of polyolefins (such as chemical inertia, mechanical properties and nontoxicity); moreover, these compositions show outstanding cost/performance ratios. In the state of the art, these compositions have been obtained by way of sequential copolymerization of propylene, optionally containing minor quantities of olefin comonomers, and then ethylene/propylene or ethylene/alpha-olefin mixtures. Catalysts based on halogenated titanium compounds supported on magnesium chloride are commonly used for this purpose.
For instance, U.S. Pat. No. 5,286,564, in the name of the same Applicants, describes flexible polyolefin compositions comprising, in parts by weight:
A) 10-50 parts of an isotactic propylene homopolymer or copolymer;
B) 5-20 parts of an ethylene copolymer, insoluble in xylene at room temperature; and
C) 40-80 parts of an ethylene/propylene copolymer containing less than 40% by weight of ethylene and being soluble in xylene at room temperature; the intrinsic viscosity of said copolymer is preferably from 1.7 to 3 dl/g.
Said compositions have flexural modulus values of less than 150 MPa and Shore D hardness between 20 and 35. Although these mechanical properties are advantageous for certain applications, the compositions prepared in Examples 1-5 show values of Tensile Strength at Break ranging from 13.8 to 17.3 MPa; for many applications, such as in roofing sheets, these polymers do not show a satisfactory tenacity, which is a property strictly related to tensile strength at break and to elongation at break properties. Tenacity is fundamental in roofing applications, wherein there is the tendency of roofing to break under the action of the wind.
As it is well known in the art, the strength and flexibility of thermoplastic polyolefin compositions may be enhanced decreasing the rubber content; nevertheless, to the increase in strength is usually associated an increase in stiffness that causes various drawbacks. For instance, the increase in stiffness of a flexible membrane limits the installation of the membrane around corner, chimneys, vents etc., where the membrane must be flexible to bend around the obstruction.
The European Patent Application No. 1202876.7, in the name of the same Applicants, describes a polyolefin composition comprising:
(A) from 8 to 25% by weight of a crystalline propylene homopolymer or copolymer; and
(B) from 75 to 92% by weight of an elastomeric fraction comprising a first elastomeric copolymer of propylene with 15-32% wt ethylene, the intrinsic viscosity of the xylene soluble fraction ranging from 3.0 to 5.0 dl/g; and a second elastomeric copolymer of propylene with more than 32% up to 45% wt. of ethylene, the intrinsic viscosity of the xylene soluble fraction ranging from 4.0 to 6.5 dl/g.
These polyolefin compositions have flexural modulus values lower than 60 MPa and very good hardness values (Shore A hardness lower than 90); nevertheless, they exhibit low tenacity values. In fact, the polyolefin compositions prepared in Examples 1-3 of the above-mentioned application show values of Tensile Strength at Break equal to 5.5, 11.7 and 11.2 MPa respectively. As reported above, such values are not fully satisfactory for roof sheeting, since the increase in flexibility is associated to an enhanced stiffniess.
A strong need therefore exists for softer materials which are easier to install, and at the same time possess a satisfactory tenacity, strength, and tear and puncture resistance. In other words, it is felt the need for polyolefin compositions which exhibit a good balance of flexibility over a variable temperature range, and tenacity, as well as good mechanical properties; moreover, these compositions must be heat-sealable and oil-resistant and must not undergo degradation when exposed to the elements.
SUMMARY OF THE INVENTION
The present invention concerns a polyolefin composition comprising:
(A) from ab
Butala Robert G.
Ennis Gerald John
Glogovsky Todd
Goberti Paolo
Han Choong Y.
Basell Poliolefine Italia S.p.A.
Nutter Nathan M.
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