Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2001-09-24
2003-06-17
Szekely, Peter (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S071000, C428S147000
Reexamination Certificate
active
06579921
ABSTRACT:
FIELD OF INVENTION
The present invention relates to waterproofing products, particularly elastomer-modified roof membranes using thermoplastic rubber (TR) modified bituminous compositions with an improved cost/performance balance.
BACKGROUND TO THE INVENTION
Bitumen is an excellent waterproofing material that has long been used in roofing applications. It is easy to apply and cheap. Roofing-grade bitumens (usually known as oxidized or ‘blown’ bitumen) have been used successfully for more many decades.
However, air-blown bitumens cannot cope with the demands of modern roofs: roofing felts need to last longer than ever and to be stable under the very varied conditions that exist worldwide. Modem roofs tend to be lighter than their predecessors, and better insulated, which widens even further the temperature range to which the surface is subject.
Such demands triggered the introduction of bituminous roofing membranes modified with various polymers about 20 to 30 years ago. Although use of polymer-modified bitumen membranes has become very widespread and, in some regions even more common than air-blown bitumen, only two polymer types have yet achieved significant commercial success in bituminous roofing applications, namely thermoplastic polyolefin (‘plastomer’) and thermoplastic rubbers (TRs). Amorphous (or atactic) polypropylene (APP) is the most prominent plastomer. TRs are represented almost exclusively by the styrene-butadiene-styrene (SBS) triblock copolymers.
Field studies and well documented application histories have helped the roofing industry to appreciate the improved properties and long-term performance of SBS-modified bitumen membranes.
The roofing industry, however, is looking more than ever to optimize the cost-performance balance of their modified bitumen roofing products. In practice, this means that the manufacturers of SBS modified roofing membranes aim to use the lowest amount of SBS copolymer possible without jeopardizing membrane properties and characteristics.
Conventional practice involves using SBS as a modifier at loading levels generally from about 10 to about 15 wt % of the bitumen, typically about 12% to 14 wt %. It has been found, when the bitumen is modified with this level of SBS, the bitumen goes through a phase inversion (the change of a compound into an isometric form) in which its characteristics change to those of the rubber additives. This results in a bituminous membrane with an excellent balance of flexibility at cold temperatures (i.e. below −20° C.) and high flow resistance at high temperatures (i.e. above 110° C.). Below this range of SBS loading, the modified membranes tend to fail the above performance targets and other criteria that may be specified by the relevant roofing authorities.
An objective of this invention is to develop and manufacture SBS-modified roofing sheets using a lower amount of SBS co-polymer without jeopardizing performance criteria of the products or to achieve a better performance at the same loading level with respect to conventional SBS-modified roofing sheets.
It has been recognized that bitumens are complex mixtures of hydrocarbon molecules, ranging from low molecular weight oil (maltene fraction) to heavy, polymeric-type molecules (asphaltenes). Bitumen-polymer blending has undergone years of research and practical development. More than ten types of SBS copolymers have found use in modified bitumens, and all differ in composition and molecular structure. In roofing sheet design, the bitumen type is one of most significant variables and proper selection is considered highly important.
For roofing membrane applications, in addition to SBS polymers and asphalt, other ingredients including fillers, such as, limestone-CaCO3, must be incorporated into the blend. The fillers make up as much as 15% to 30% by wt of the compound.
Therefore, SBS and filler together blended into the bitumen binder determine the rheological behavior of the modified bitumen. The modified bitumen is then coated on a polyester fiber mat or glass fiber mat. These membranes may, if desired, be coated with granules to provide enhanced properties, such as resistance to UV degradation.
The present invention is directed towards developing SBS/filler modified roofing membranes at a lower loading levels of SBS without jeopardizing performance criteria of the products or achieving better performance at the same loading level with respect to conventional materials and methods.
SUMMARY OF INVENTION
According to the present invention, in-situ vulcanization of SBS copolymer into .filler-filled bitumen matrix using conventional cross-linking reagents is employed to more effectively use the elastomer without jeopardizing the characteristics of the modified roofing membrane.
As far as I am aware, there is no prior art teaching that the technique of in-situ cross-linking of the elastomer can be applied to the above-described bituminous roofing membrane system to achieve both higher temperature performance and even better low temperature flexibility of the product in comparison to a non-cross linked system containing the same amount and type of SBS copolymer.
It has been recognized, however, that the prior art that the technique of the in-situ cross-linking of the elastomer has been applied for the paving grade modified bitumen products where SBS is used in relatively lower amounts, generally in a range from 2 to 5%, in which the bitumen behavior predominates.
However, once SBS is loaded up to the higher levels required for modified roofing membrane systems, in-situ cross-linking has been considered to (i) increase the risk of not only forming an un-processable, highly viscous, gel-like binder and (ii) degrade the low temperature flexibility of the finished product.
Accordingly, in one aspect of the present invention, there is provided a roofing membrane having cold flexibility below about −20° C., preferably below about −25° C., and high flow resistance (stiffness) above about 110° C., preferably above about 120° C. This membrane comprises a matrix-filled fibrous substrate and a filled elastomer-modified bituminous composition comprising about 10 to about 30 wt % of a mineral filler and a bituminous composition comprising bitumen and about 8 to 15 wt % of said bitumen of an elastomer having a conjugated diene structure cross-linked to an extent to permit a reduction of about 10 to 20 wt % in the amount of elastomer in the bituminous composition for the same low and high temperature properties or a concomitant improvement in low and high temperature properties at the same amount of elastomer.
In the present invention, the elastomer modifier may be a diene rubber or butadiene based polymer or co-polymer, preferably a styrenic elastomer, such as a styrene-butadiene random copolymer (SBR), a di-block copolymer (SB) or a tri-block copolymer (SBS) or a combination thereof. As mentioned previously, elastomers having a conjugated diene structure, namely SBS, have conventionally been used in an amount of about 10 to about 15 wt %, typically about 12 to about 14 wt %. By effecting cross-linking according to the invention, the amount of such elastomer employed may be reduced by about 10 to 20% without any loss of low temperature flexibility as compared to the non-cross-linked composition. Similarly, at the same loading level as the non-cross-linked composition, improvements in both low temperature and high temperature performance are achieved in comparison to the non-cross-linked composition.
The cross-linking reagents used in this invention may be different types of reagents among those conventional chemical additives used in bituminous systems, such as elemental sulfur, a sulfur based vulcanization system and/or a phenol-aldehyde resin based cross-linking system.
As may be seen from the experimental results herein, differing amounts of cross-linking reagent are required when a different type of cross-linking reagent is used according to the process procedures of the invention. In general, when sulfur is used for cross-linking, the amount employed
Liang Zhi Zhong
Zhang Yan-Ping
Polyphalt Inc.
Sim & McBurney
Szekely Peter
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