Membrane cover having a protective layer to prevent deterioration of UV stabilizers therein

Abstract

The membrane structure according to the present invention has a top layer containing three plies. The top ply has UV stabilizers embedded therein; the bottom ply has stretch-resistant elements embedded therein; and the middle ply contains a co-extruded polyvinylidene chloride barrier film for example, for protecting the top ply against bio-gas infiltrations therein. In another aspect, the top and bottom plies containing polyethylene for protecting the middle ply from the weather and from corrosive environments under the membrane cover. In yet another aspect, the membrane structure has two foam layers affixed to the bottom ply. Each foam layer is made of juxtaposed strips of semi-rigid, closed-cell, polyethylene foam; wherein each strip in one foam layer is laid astride the adjoining edges of a pair of strips in the other foam layer. The strips of foam are bonded together and to the undersurface of the bottom ply by strips of fused polyethylene.

Description

FIELD OF THE INVENTION [0001] This invention pertains to membrane covers for industrial, municipal and agricultural reservoirs and lagoons, and more particularly, it pertains to a floating membrane cover having a top layer, UV stabilizers in the top layer, a structural layer in contact with the liquid surface of a reservoir and a bio-gas-impermeable shield laid between the top layer and the structural layer. BACKGROUND OF THE INVENTION [0002] It has been noted that the useful life of a membrane cover covering a wastewater reservoir in a warm-weather region where the cover is exposed to much sunlight, is somewhat reduced as compared to covers installed in colder climates. After analysing several installations of different ages and in different environmental conditions, it was understood that the porosity of a membrane cover increases with temperature and that the bio-gases generated under a membrane cover slowly seep or migrate upward through the membrane layers and react with the me...

AI Technical Summary

Benefits of technology

[0005] In the present invention, however, there is provided a membrane structure having a top layer with UV stabilizers embedded therein, and a bio-gas shield laid beneath the top layer for preventing the migration of bio-gases into the top layer.

[0006] More particularly, the present invention consists of a membrane structure wherein the top layer is made of three plies. The top ply has UV stabilizers embedded therein; the bottom ply has stretch-resistant elements embedded therein; and the middle ply is a bio-gas shield for protecting the top ply against bio-gas infiltration in the top ply.

[0007] In this arrangement, the bottom ply has a first impermeability to bio-gases, wherein this first impermeability to bio-gases is comparable to the properties of membrane covers of the prior art. The middle ply has a second impermeability to bio-gases, and the second impermeability to bio-gases has a greater extent than the impermeability of the bottom ply. Preferably the impermeability to bio-gases of the middle ply is twice as much as the impermeability to bio-gases of the bottom ply. The UV stabilizers in the top ply are thereby protected against corrosion.

[0008] In yet another aspect of the present invention, the top and bottom plies contain polyethylene, for protecting the middle ply from weather conditions and from corrosive environments under the cover.

[0010] Each foam layer has a thickness of about one-half inch such that a stiffness provided by these two layers prevents wind-induced fluttering in a membrane cover made with this structure.

Problems solved by technology

As these metal oxides are modified or corroded, the UV protection is lost and the life of the membrane cover is proportionally reduced.

It is believed that the problem of deterioration of UV stabilizers in a membrane cover has not been addressed in the prior art.

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