Co-extrusion process for preparing roofing membranes

Abstract

A process for preparing a multi-layer roofing or structural membrane is provided including a top sheet including co-extruding a cap and inner layer and bonding the top sheet to a bottom sheet. The use of the co-extrusion process allows for multi-layer sheets that reduce the need for expensive fillers in all but a cap layer of the membrane. A scrim reinforcement layer is optionally embedded in the membrane. When installed on a roof substrate, the membrane can be sealed by heat welding the seams of the membrane sheets or by other means.

Description

[0001]The present application claims priority to and the benefit of the filing date of U.S. Provisional Patent Application No. 60 / 775,128, filed Feb. 21, 2006.BACKGROUND[0002]The present embodiments relate to a co-extrusion process for preparing roofing or other structural membranes comprising at least two polymeric sheets. More particularly, the present embodiments relate to a co-extrusion process for preparing multilayer membranes having a cap layer adhered to a one or more support layers.[0003]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.[0004]Because of its outstanding weathering resistance and flexibility, cured EPDM based roof sheeting has rapidly gained acceptance. This material is often prepared by vulcanizing the composition in the presence of sulfur or sulfur containing compounds such as mercaptans or using radiation cur...

AI Technical Summary

Benefits of technology

[0020]In a third aspect, there is provided a process for preparing a co-extruded sheet suitable for use in structural membranes comprising two or more layers, the process including the step of co-e

Problems solved by technology

Notwithstanding the usefulness of radiation curing and sulfur curing, a potential drawback of utilizing these elastomers is the lack of adhesion of EPDM, especially cured EPDM, to itself.

Under certain conditions, such stresses may manifest themselves in shear forces that can result in seam peel back under severe stress conditions.

Adhesives that meet these requirements are difficult to produce and can be time consuming to apply to the seams of EPDM sheets, thereby increasing the overall cost of installing the waterproof membrane.

Without such scrim, the TPO often becomes too “soupy” to laminate together and may not possess sufficient mechanical properties.

This scrim adds an additional cost to the TPO membrane.

Second, such membranes exhibit relatively weak bond strength with the roofing substrate.

In addition, present day TPO membranes are often too stiff and lacking in compliability (as indicated by the high secant modulus properties of TPO resins) due to the relatively high crystallinity of many TPOs to be easily bent to conform to the contours of a roof, and therefore are quite cumbersome to install due to this non-pliable property.

Finally, TPO layers, especially top layers, which must be loaded with various additives such as fire retardants, UV stabilizers, anti-oxidants, funcides can be expensive to produce due to the high cost of such additives.

Such a membrane suffers from the fact that the processing temperature of TPO and TPE and the curing temperature of EPDM are too close, thus making it difficult to seal the seam.

In addition, physically bonded thermoplastic and crosslinked rubber may reject each other in the long term, resulting in delamination and compromising the effectiveness of the membrane.

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