Stock material or miscellaneous articles – Structurally defined web or sheet – Discontinuous or differential coating – impregnation or bond
Reexamination Certificate
2000-05-02
2003-07-01
Thomas, Alexander S. (Department: 1772)
Stock material or miscellaneous articles
Structurally defined web or sheet
Discontinuous or differential coating, impregnation or bond
C428S188000, C428S215000, C428S314400, C428S317100, C428S317500, C428S319300
Reexamination Certificate
active
06586080
ABSTRACT:
FIELD AND BACKGROUND OF THE INVENTION
The present invention relates to a sealing sheet assembly and to methods of making and using same. More particularly, the present invention relates to a sheet assembly useful in water and/or gas proofing a surface of a construction which may find uses in various construction and civil engineering applications including, but not limited to, water-proofing constructional surfaces, e.g., roofs, cabins, walls and underground foundation waterproofing, fluid-proofing fluid reservoirs, waterproofing underwater containers, e.g., submarines, and fluid-proofing containers under internal or external pressure, e.g., aircrafts and spacecrafts.
Most particularly, the present invention relates to a multi-layer flexible polymeric sealing sheet bondable to a construction surface, which is less damageable by strains and movements inflicted upon it by the construction surface as compared with the prior art, such that desired sealing capabilities are maintained even under conditions such as massive cracks formation, fissures and/or structural spaces formation within the surface.
The term “construction surface” as used herein refers to any surface which is expected to be water or fluid impermeable.
Flexible sheet-like membranes and laminates (referred to herein as “sheets”) are frequently used for waterproofing by applying one or more layers of same onto a protected surface. Such sheets are made of a variety of materials, such as, but not limited to, coal tar, bitumen and synthetic polymers, which are formed as sheet-like substances of desired sealing properties. Material and substance properties should meet the requirements of any particular structure, building, authority, climate, chemical and physical environment, required durability, cost effectiveness and the like.
The trend towards irregular roof surfaces, such as, but not limited to, folded plates, hyperbolic paraboloids, domes and barrel shells, has increased the use of plastics or synthetic rubber thermoplastic polymer elastomers as roof coatings. Their advantages include light weight, shape adaptability, good heat reflectivity and high elasticity at moderate temperatures.
Prior art sheets are typically made of thick, flexible and strong materials to prevent their rupture during use. They are either bonded or laid non-bonded over the protected surface.
Bonding is advantageous because lateral massive spread (flood) of water in case of a tear in the sheet is prevented, however, bonding is disadvantageous because, as further detailed below, rapture of the bonded sheet due to cracks formation in the protected surface is readily occurring.
As a result, in many cases a preferred solution for roofing is to lay a loose water-proof sheet, which is not bonded to the surface. This solution is designed to free the membrane from all sorts of stresses caused by sheer and tensile forces resulting from the substrate as a result of thermal and constructive stresses. These forces express themselves often by demonstrating cracks, spaces and fissures which are in widening and shrinking motion (usually cyclic) through the cross-section of the roof or through the walls of the construction.
This motion exhibits a change in the cracks width that tends to increase as a function of many physical factors: e.g., thermal changes or age of the building/construction. In new constructions or after a short period of physical and chemical activities to which the construction is exposed, cracks might appear as a result of climate changes; day and night cycles; extreme changes in temperature; erosion and corrosion of constructive materials; changes in humidity; mistakes in engineering; earth movements; different values of thermal modules of expansion; shrinkage and inflating as a result of vapour pressure, etc.
Often these movements of the construction substrate do not appear in cycles, but expressed as continuous widening of the cracks and spaces or of the expansion joint that are designed to reduce such stresses.
The disadvantages of this concept are that the sheet is subject to elevation and flapping caused by storm wind. Unsolved disadvantage is flooding extensive areas of the protected surface under the sheet, even in the event of a single tiny tear in the sheet. Thus, loose laying is advantageous because the sheet is mostly not affected by cracks formation, however, it is disadvantageous since if a tear should occur massive lateral spread of water is experienced.
Examples of prior art sheets include (i) ethylene propylene diene monomer (EPDM) sheets, which accept about 250%-450% elongation and are typically used at thicknesses ranging between 0.8-1.5 millimeters, mostly in a non-bonded free floating sheet, protected from wind effects by a layer of gravel or concrete placed thereon; (ii) reinforced bitumen sheets, 4-5 millimeters thick, bonded to the surface, which accept 30%-120% elongation and have tensile strength of about 30-80 Kg/5 centimeters; and (iii) plasticized, textile reinforced poly vinyl chloride (PVC) sheets, which accept about 15-25% elongation, 1-2 millimeters thick, having a tensile strength of about 100-160 Kg/5 centimeters, applied mostly as non-bonded free floating sheets, protected from wind elevation by screws or alternatively as bonded sheets being fully bonded to the construction surface.
To illustrate the cracks formation effect upon a protective sheet, consider a crack in a covered surface which grows from 0.05 millimeters in width at the time of application to 3 millimeters thereafter. This represents a 6,000% increase in width. A prior-art, flexible roofing sheet, firmly bonded to the working surface will usually tear under such conditions, causing failure of its sealing properties.
Therefore, wherever massive cracking or strong movement is expected, thicker and/or free-floating (non-bonded) sheets are preferably employed.
In large constructions, thermal and constructive stresses cause tremendous movements, e.g., between constructive roofing elements. In extreme, but quite frequent cases, massive and quick forming cracks, which demonstrate expansion in ranges of thousands percents per hour, cycling on a daily basis, combine shearing action with abrasion upon the sealing sheet. No bonded prior art sheet can withstand these forces without tearing.
When a lower zone of the sheet cross section reaches its maximal elongation ability, rupturing tends to climb along the cross-section, even as a result of smaller changes in stress. Often, a rupture tends to enlarge itself through the whole thickness of the sheet, even without any additional tensile or shear stresses, causing a failure of the sheet.
The use of a strong sealing material will commonly be of no help due to the forceful structural tension.
The cost of a thick monolayer (2.5-4 mm thick) with high and lasting elongation ability (e.g., above 300% after 10-15 years of aging) characterized by chemical and mechanical resistance properties is rather excessive. Such a sheet may provide very good values of bridging ability above small and medium cracks. But, even a 4 mm thick elastic sheet, bonded to the substrate, will not withstand massive movements associated with crack or space formation and/or joints-expansion. When the lower zone of the membrane cross section comes to its maximal elongation ability it ruptures. The rupture tends to progress along the cross-section to the upper surface of the sheet. Most often, the rupture tends to enlarge itself through the whole width of the sheet, even without any additional tensile or shear stresses applied thereto, causing a failure of the coating in the most critic location in the construction, where there is a crack.
Lateral tear resistance of polymeric sheets is not in direct proportion to their thickness. Once an initiation of a long and deep tear is experienced, soon thereafter a total local breaking of the sheet occurs.
Elastic polymers characterized in high elongationability cannot be efficiently reinforced. In such conditions, elastomers and thermoplastic polymers forming a sheet show high values of creepi
G. E. Ehrlich Ltd.
Thomas Alexander S.
LandOfFree
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