Luminescent welt cord

A welt having a strip of transparent plastic material which is folded over a cord or rope saturated with a phosphorescent paint so as to encase the cordage and protect both it and the paint. The welt, after being exposed briefly to an ordinary bright light, remains luminous for time intervals on the order of hours, allowing portions of the welt to be seen in the dark.

BACKGROUND OF THE INVENTION 
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. 
SUMMARY OF THE INVENTION 
The primary object of this invention is to provide an inexpensive, 
long-lived device for decorating and for strengthening a piece of 
upholstery along its seams and edges, with the contours of the piece when 
it is situated in a darkened room or other enclosure or out-of-doors after 
dark being outlined in a low level of luminous flux for several hours 
after the piece has been exposed either to light from an ordinary electric 
lamp or to sunlight. 
A further object is to provide a wear-resistant device for demarcating the 
edges of a carpet along a hallway or within a stairwell which has been 
abruptly plunged into darkness due to an electric power outage. 
A still further object is to provide a device which can be permanently 
attached to a piece of furniture or to its slipcover to enable persons to 
perceive its overall location during a blackout or for several hours after 
lights are out at night. 
According to the present invention, means for decorating a piece of 
upholstery and demarcating its whereabouts in an otherwise darkened 
setting for at least a few hours after lights have been extinguished 
includes a welt in which a cord saturated with a phosphorescent paint is 
encased in a strip of flexible, transparent plastic material so that the 
strip forms a thick-walled, tight-fitting enclosure about the cord to 
reduce not only the likelihood of its being eroded by flaking or by 
abrasion but also to diminish the rate of interchange between the 
atmosphere and any gases evaporating from the paint. At the same time, the 
strip, which is not bonded to the cord, can be stretched independently of 
it, helping to insure that the thick walls of the strip continue to 
provide an air-sealed, crack-free enclosure for maintaining an environment 
surrounding the paint which tends to preserve its flexibility and which 
contains a lower concentration of oxidizing agents and of water capable of 
attacking the phosphor than if the paint, upon drying, were left exposed 
to the atmosphere. 
Other objects and advantages will appear from the following description of 
an example of the invention, when considered in connection with the 
accompanying drawings, and the novel features will be particularly pointed 
out in the appended claims.

Like reference characters indicate corresponding parts throughout the 
several views of the drawings. 
DESCRIPTION OF THE PREFERRED EMBODIMENT 
As illustrated in the drawings, a welt, designated generally by the numeral 
10, embodying the present invention comprises an elongated, rectangular 
strip 11 of flexible, transparent plastic material such as vinyl, 
polyethylene or the like. One of the longer edges of the strip 11 is first 
folded over a cord 12 and then stitched against it with nylon thread to 
form a close-fitting enclosure about the cord but one in which the cord 
slides independently of the walls of the strip as it is being stretched. 
Alternately, the strip 11 is formed of a shrinkable, transparent plastic 
material; and the sides of the strip are joined together by heat treatment 
so that when the strip cools, a close fit is achieved between the strip 
and the cord. In the preferred embodiment, the band 14 extends 
transversely from the longitudinal centerline of the strip 11 for the 
length thereof, forming an overlay to facilitate the attachment of the 
welt 10 within a seam or along the edge of a piece of upholstery such as a 
carpet (FIG. 3). By way of example, the width of the overlay measures from 
1 to 2 inches. 
The cord 12 is preferably 2-ply cotton thread but can range in thickness 
from 3/16 inch to 21/2 inches. It is important that the cord 12 be made of 
cotton or of another natural fiber capable of absorbing a paint vehicle 
such as an acrylic resin or water for luminous acrylic and latex paints, 
respectively. The cord 12 is initially soaked in a phosphorescent paint to 
the point of saturation and then allowed to dry. If the cord 12 is 
saturated with a luminous acrylic paint, the cord takes only about 3 to 5 
minutes to dry. Saturating the cord 12 with paint insures that some of it 
will remain embedded in the cord to make it luminescent even though a 
portion of the paint dried on the surface of the cord may flake off as the 
welt is being assembled. 
Immediately after the initial drying of the phosphorescent paint, the cord 
12 is then encased within the strip 11 to form the welt 10. Provided a 
tight-fitting enclosure is promptly formed about the cord 12, the paint 
will retain its flexibility and its capacity to phosphoresce for 
substantially greater periods of time than if the paint, once dried, were 
left exposed to the atmosphere. I have found that phosphorescent paint on 
a cord 12 without any protective enclosure flakes and no longer exhibits 
significant luminescence within six to twelve months whereas the same 
paint on a cord 12 protected by a close-fitting strip 11 remains flexible 
and continues to generate useful levels of luminous flux for over one and 
a half years. The lifetime of the phosphors within the paint is further 
extended by heat sealing the ends 18 of the welt 10 once it has been cut 
to length for a particular application (FIG. 3). Moreover, the relatively 
thick walls of the strip 11 provide ample protection for children or pets 
that might chew on a welt 10 attached to a piece of upholstery as well as 
shield the cord 12 from abrasion due to normal wear even when the welt is 
installed along the edge of a carpet 16. 
Several compositions of luminous paints are widely known which are suitable 
for use in the welt 10. Preferred paints includes mixtures of a zinc 
sulfide phosphor, i.e., zinc sulfide in which an activator such as copper 
or silver is incorporated at extremely low concentrations, with acrylic 
resin as a vehicle, denaturated alcohol as a solvent, and aluminum 
stearate as a suspending agent. Alternately, mixtures of a zinc sulfide 
phosphor with latex as a vehicle and water as a solvent can be used. The 
paint preferably has a slight greenish-yellow pigmentation because such 
paints are among those with the brightest phospborescence. No radioactive 
materials are utilized in making these paints; and their ingredients in 
general have a low toxicity, according to Strobolite Co., Inc., 
manufacturer of Strobolite Luminous Acrylic and Latex Paints. A paint 
mixture with an acrylic vehicle but having an alkaline earth phosphor 
other than zinc sulfide which could be modified by replacing its alkaline 
earth phosphor with a zinc sulfide one to obtain a preferred 
phosphorescent paint is described in U.S. Pat. No. 2,436,182. 
I have found that one gallon of luminous acrylic paint costing 
approximately $150.000 is sufficient to saturate up to 8 spools or 2000 
yards of 2-ply cotton thread at an average cost for the paint alone of 
about 2.5 cents per linear foot. A sharp reduction in the costs normally 
associated with decorating with phosphorescent paints is brought about in 
the case of the welt 10 because of its thick-walled but long-lived strip 
11 protecting the chemical composition and flexibility of the paint 
saturating the cord 12. 
Although the welt 10 will phosphoresce for a few hours after being exposed 
to the light from an ordinary match for a few seconds, the welt 
phosphoresces most intensely after receiving a higher dosage of light 
radiation. Because the brightness of the phosphorescent paints are very 
low in any situation, the welt 10 is best viewed in total darkness. The 
exponential decay in its brightness after any light falling on it has been 
extinguished is compensated in part by the capacity of the human eye to 
adapt to darkness. Because this dark adaptation reaches its full value 
only an hour after the eye has been exposed to bright light, a person 
coming from a brightly illuminated room into the dark perceives the ever 
decaying intensity of the light from the welt 10 to grow brighter during 
the first minutes and afterwards for quite a time to decay less strongly 
than is the actual situation. 
In the preferred embodiment of the invention, phosphorescent paints which 
glow after an exciting light source has been removed are mentioned. 
However, fluorescent materials which glow while being excited by light of 
a suitable wavelength may also be used. 
By the term "luminescent" which is used in the foregoing specification and 
in the appended claims is meant that property of a material which causes 
visible light to be emitted after an exciting light source has been 
removed as well as that property of a material to glow under a source of 
light of low visibility and suitable wavelength such as an ultraviolet 
light source.