1. Field of the Invention
The present invention relates generally to strips of material which are folded over a cord and placed at the edge or seam of a piece of upholstery such as a slip cover, carpet or the like to reinforce and to decorate it.
2. Description of the Prior Art
As is well-known, phosporescent paints once they have been excited remain luminous with a soft, slowly decaying radiation. Such paints can generate a useful level of luminous flux for several hours when placed in the dark after having absorbed sunlight or artificial light of a suitable wavelength. Although they do not require continuous irradiation to maintain such levels, the initial, most intense luminescence can only be restored by once again exposing the paints to either a natural or an artificial light.
In the event of a blackout or other emergency in which the normal electric power supply is cut off, objects coated with phosphorescent paint will glow for extended periods of time, helping to demarcate walkways, exit doors and the like if they are so coated. Phosphorescent paints have also been employed for ornamentation; such applications include the once popular artifice of decorating wallpapers and lampshades with phosphorescent designs which, after the light is switched off, remain luminous for hours.
In phosphorescent paints, the luminescent material or phosphor, which is almost exclusively a zinc sulfide or alkaline earth sulfide, is formed of relatively large particles. Contrary to standard paint practice, which is to get the pigment ground as finely as possible, the phosphors in these paints are ordinarily reduced to grains of not less than about 0.1 mm diameter, corresponding to 200 mesh, since grinding the phosphor further decreases its luminous efficiency. Because of the coarseness of the grains, phosphorescent coatings on an exposed surface tend to flake off, requiring frequent replacement. Although in some cases this problem can be obviated by applying a transparent overcoat as soon as the surface is dry, the protective layer itself is easily eroded and must be repeatedly renewed. Moreover, protecting the paint with an overcoat is not always feasible and is especially difficult to achieve in the case of phosphorescent designs on carpets, upholstery and other flexible surfaces. When an overcoat is bonded to such surfaces, it tends to crack after they have been repeatedly flexed.
Not only must a phosphorescent coating be protected from erosion but also the phosphor in the paint must be shielded from the oxidizing action of the atmosphere and from moisture. An overcoat, if feasible, can do both, extending the lifetime of a coating by reducing the rate of oxidation of its phosphor and by keeping out water as well as by minimizing flaking. On the other hand, if no overcoat is provided, chemical attack by the atmosphere on the phosphor can result in a coating losing its capacity to phosphoresce in six to twelve months.