Heat weld indicator for thermoplastic roofing membrane

DETAILED DESCRIPTION A roofing membrane heat seal indicator provides a positive, visually perceptible indication that a joint or seam has been raised to a sufficiently high temperature to achieve a proper seal.
The heat seal indicator is applied to one surface of a roofing membrane adjacent an edge.
The surface having the indicator is arranged on a roof to form the upper (exposed) surface of an overlapping membrane seam.
The heat seal indicator is preferably applied parallel to a longitudinal edge of the membrane as a line, bead, dot or ridge.
The heat seal indicator is also preferably disposed on the membrane a short distance from a longitudinal edge such that it is generally laterally centered over the seam region.
As the adjacent surfaces of the overlapped membranes are heated, heat passes through the upper membrane to the heat seal indicator, causing a change in color, appearance or both.
The heat seal indicator may be a temperature sensitive ink or compound, such as cobalt salts that change color upon being subjected to a temperature indicating that the lower membrane surface has been subjected to a sufficiently high temperature to achieve an appropriate seal.
Alternatively, the indicator may be an adhered layer of a ground or flaked polymer, such as a polyethylene, which is initially opaque but melts to become translucent, thereby indicating obtainment of a proper sealing temperature.
If desired, both indicators may be combined wherein temperature sensitive particles are suspended in polyethylene or any polymeric resin melting at the proper temperature.
The material is flaked and then adhered to or made into an ink and applied to the membrane surface.
Alternatively, the polymer indicator may be disposed over a white or colored line on the membrane.
Another alternative comprehends a raised ridge on the upper membrane surface which is covered by a distinctly colored material which melts when heated.
Thus is it an object of the present invention to provide a linear seal indicator for an overlapping roofing membrane seam for indicating that such membranes have been subjected to a sufficiently high temperature to achieve a seal