|1.||A laminated tape structure adapted to surround and protect metallic cable stays of outdoor structures comprising: a first opaque film of PVF having a thickness of between about 1 and about 3 mils.; a second film of substantially transparent PVF of a thickness of between about 1 and about 2 mils. ; a laminating adhesive having a thickness of between about 0.25 and about 1 mil. interposed between said films and adhering the facing surfaces thereof together; and a pressuresensitive adhesive on the exposed surface of said opaque film adapted to engage and contact a tubular housing surrounding said cable.|
|2.||A laminated tape structure as claimed in claim 1 wherein: said opaque film is white in color.|
|3.||A laminated tape structure as claimed in claim 2, wherein: the temperature at the outer surface of said tubular housing exposed to a 250 watt heat lamp spaced four inches therefrom for a period of three hours is about 35 percent lower than the the temperature at the outer surface of said tube without said laminated tape structure applied thereto.|
|4.||A laminated tape structure as claimed in claim 3, wherein: the temperature at the inner surface of said tubular housing exposed to a 250 watt heat lamp spaced four inches therefrom for a period of three hours is about 30 percent lower than the the temperature at the inner surface of said tube without said laminated tape structure applied thereto.|
|5.||A method of protecting metal cables permanently exposed to the elements and encased in a polyethylene tubular housing comprising the steps of: laminating a first opaque film of PVF having a thickness of between about 1 and about 3 mils. to a second film of substantially transparent PVF of having a thickness of between about 1 and about 2 mils.; and applying a pressuresensitive adhesive to the exposed surface of said opaque film; and wrapping said laminated tape structure around said cable enclosing tubular housing to completely encase said housing within said laminated tape structure.|
The present invention relates to film and tape structures made therefrom and the use thereof to protect structures exposed to the elements for extended time periods, and more particularly to laminated PVF tape structures. Background Of The Invention
There exists certain situations and structures which require protection against the elements. For example, in construction of a variety of outdoor structures, such as those utilizing cable stays, it has been found necessary in order to extend the life of the metallic cables to utilize some protective covering. One suitable way to protect such cable stays has been the use of black polyethylene tubing which forms an enclosure or housing for the stays. Such polyethylene tubular housings constitute an excellent weather protective material.
Used alone, however, such black tubing is subject to wide temperature swings, which can result in undesirable cable thermal expansion and wear. One approach for minimizing or reducing the thermal heating of the enclosed cable is to coat the tubing a lighter color for temperature control. This also has the benefit of providing a decorative effect. Such procedures are expensive, labor-intensive, and messy. Furthermore, the life expectancy of such coatings, particularly when used in conjunction with permanent outdoor installations, is sufficiently limited to require repeated applications with the concomitant increase in costs of maintenance.
A simpler alternative has been to utilize a tape in an attempt to provide a decorative wrapping
of the cable stay housing. The tape has an apparent advantage in that it is not messy, and colored tapes can be utilized to provide the desired decorative effects. However, polyvinylchloride (PVC) tapes, which have been used, appear to have a limited life span, e.g., no more than three to seven years in the lab and in field tests. PVC tapes deteriorate upon exposure to the elements, e.g., temperature cycling and to ultraviolet radiation, which, of course, would occur when such tape is utilized for protection of structural stays and their housings. The necessity to rewrap stay housings every five to ten years is not a satisfactory solution of the problem, since there continues to exist relatively high maintenance costs, even though the appearance for a portion of this limited life span may be satisf ctory.
Attempts to improve the performance of PVC films by over laminating them with clear pol vinylfloride (PVF) film do not appear to successfully solve the problem. The PVC film still appears to react to the ultraviolet radiation, as is well-known, with resultant deterioration as a result thereof. One of the intended advantages of such a laminate was to utilize the clear covering film as a protector for the underlying colored PVC material, but as indicated above, the use of such a construction apparently does not satisfactorily solve the problem.
While a colored opaque PVF film does exist and might provide suitable ultraviolet resistance and color fastness, such film still would be subject to scratching and discoloration. Furthermore, the longer lived PVF films are difficult to apply, often wrinkle during application, and produce air bubbles during the wrapping operation. This results in
difficult, imperfect wrapping, excess overlap for assured protection, with resulting increases in cost. This is particularly true in view of the fact that the PVF material is substantially more expensive than other alternative materials.
However, if color fastness and the maintenance of an attractive appearance and maintenance-free life span could be ensured, the increased costs of the material would be more than offset by the reduced costs, particularly in labor and maintenance efforts. Summary Of The Invention
In accordance with the present invention, there is provided a laminated tape structure adapted and suitable for winding around cable stay housings, which, because it has satisfactory winding characteristics, is strong, cost effective, and exceptionally long-lived. The material is available in a variety of colors. In accordance with the present invention, there is provided a laminar structure composed of an underlayer comprised of an opaque PVF film of desired color, laminated to a clear, transparent PVF overlayer by suitable laminating adhesive. The bottom surface of the PVF underlayer is coated with a suitable all-weather, pressure-sensitive adhesive, typically having a suitable release liner.
A laminated tape, in accordance with the present invention, has good confor ability, is capable of smooth application without stretching or wrinkling, and can be used on suitable semi-automatic wrapping equipment. Use of a laminated tape incorporating the present invention permits a wide choice of colors without sacrificing color stability, in spite of long-term ultraviolet exposure.
Tensile strength of the laminated structure incorporating the present invention is greater than existing single or dual constructions, and allows for less overlap during the wrapping to produce greater yield and a lower cost per square foot of cable surface. The laminated tape structure incorporating the present invention provides better thermal protection, which results in less thermal expansion and deterioration and aging of the cable stays and longer cable life.
Numerous other advantages and features of the present invention will become readily apparent from the following detailed description of the invention and the embodiments thereof, from the claims, and from the accompanying drawings in which the details of the invention are fully and completely disclosed as a part of this specification. Brief Description Of The Drawings
The one figure of the drawing illustrates a laminated tape structure incorporating the present invention applied to a tubular structure such as a cable stay housing. Description Of Preferred Embodiments
While this invention is susceptible of embodiment in many different forms, there is shown in the drawing, and will be described herein in detail, a specific embodiment thereof with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the invention to the specific embodiment illustrated.
Laminated film, in accordance with the present invention, formed into tape, is particularly adaptable to be applied to structural cable stay housings which are permanently and continuously
exposed to the elements and to ultraviolet rays from the sun, and in which a long life span is particularly desirable and necessary in order to minimize costs. A laminated tape structure 10 incorporating the present invention comprises a laminate of a clear, transparent PVF film 12, typically having a thickness of about 1 - 1-1/2 mil., laminated to an opaque, colored PVF film 14, typically having a thickness of about 1 - 2 mil., utilizing a laminate adhesive 16, typically having a thickness of between about 1/4 and 1 mil. to produce a composite laminated structure having an overall thickness of from 3 to 4-1/2 mil. A pressure-sensitive adhesive 18, typically having a thickness of about 1 to 1-1/2 mil. can be applied to the exposed surface of the colored film to adhere the resultant laminated tape to the surface of a tubular cable -stay housing 20.
Such a laminated tape structure provides desired long-life and resistance to deterioration upon exposure to the elements and ultraviolet radiation, and exhibits other characteristics desirable for use in such applications. Limited strength tests provide the following results:
TABLE I. FILM STRENGTH PROPERTIES
(Propogating) lbs MD .175 .13 ASTM D-1922
CD .21 .17 Elmendorf
Where MD is the Machine (longitudinal) direction and CD is the Cross (transverse) Direction.
The thermal protection provided by such a laminated structure for the cable enclosed within the black polyethylene tubing is also improved dramatically. The thermal shield effect was evaluated by measuring the inner and outer surface temperature of a 4 inch diameter tubular polyethylene housing with and without tape. When tape was used, it had a 50% overlap. This structure was exposed for 3 hours to a 250 watt heat lamp positioned 4 inches away from the outer surface. A thermocouple was used to take the temperature readings of the outside and the inside surfaces of the tubular housing. The results are shown in Table III:
TABLE III. TEMPERATURE OF PVF WRAPPED PE PIPE
As shown, the PVF tape laminate reduced the external temperature by 35% and the inside surface temperature by 30%, compared to an unprotected pipe. Such a structure provided a 23% reduction in external temperature and a 28% reduction in internal temperature when compared with a pipe wrapped with a non-laminated white PVF tape.
Thus, the use of the laminated structure incorporating the present invention provides increased thermal protection and reduces the
agnitude of temperature cycles of the cable within the polyethylene tubular housing, thus increasing the life span not only of the tube itself, but of the shielded cable contained therein. Use of the laminated structure also permits the use of a higher tape caliper and a resulting stiffer tape. A 2 mil. white PVF tape is not stiff enough to be wrapped smoothly around the tubular housing, and exhibits a tendency to wrinkle and bubble. This requires additional overlap to ensure proper coverage. The laminated structure incorporating the present invention can increase the tape caliper, as indicated above, to about 3 - 4 mils., thereby increasing stiffness by a factor of 2 to 3, producing a tape capable of being wrapped in a much smoother fashion, with semi-automatic machine wrapping, such as on a modified Midwestern Tapester Model 212. This allows for a lower percentage overlap, increased tape utilization, lower costs, and higher efficiencies.
The adhesion of the TΞDLAR brand films to the polyethylene pipe is sufficiently good to permit the reduction in tape overlap and improved efficiencies. The use of a laminated structure having a clear tape laminated to an opaque, colored tape in which the clear tape material has good resistance to abrasive environmental pollutants maintains color integrity and extends satisfactory appearance of the wrapped stays. In accordance with the present invention, laminated structures have been constructed utilizing Du Pont' s TEDLAR brand PVF film, laminated by use of a synthetic acrylic or polyester catalyzed laminating adhesive. A suitable synthetic pressure-sensitive adhesive can be applied to the exposed surface of the colored PVF film.
Thus, there has been disclosed a laminated structure comprised of two layers of PVF film, one a transparent, clear film, and the other an opaque, colored film, laminated together to exhibit improved tensile, tear, stiffness properties compared to existing structures in which the stiffer laminated structure produces smoother wrapping tape without significant additional cost, and which results in extended life span of the protective tape when applied to the polyethylene cable stay housings constantly exposed to the atmosphere, to pollutants, and to ultraviolet radiation, which provides improved thermal protection for the black polyethylene tube and the cable stay protected thereby, and which is projected as having exceptional long life requiring reduced maintenance with resulting lower costs.
An example of one such laminated structure comprises a 1 mil. UV clear PVF film, sold by Du Pont under the registered trademark TEDLAR, a 1/4 - 1/2 mil. synthetic clear laminating adhesive, 1-1/2 - 2 mil., Du Pont colored TEDLAR brand PVF film, 1 - 1-1/2 mil. synthetic PS adhesive, and Kraft silicone release liner. The overall tape caliper was about 3-3/4 mil. The tape was cut into widths of about 4 inches. The DuPont TEDLAR brand PVF film is described in Technical Bulletins of the Du Pont Company, Finishes & Fabricated Products Department, Nos. TD-1A (Rev. 6/86), TD-2 (Rev. 8/84) , TD-3 (Rev. 6/86), TD-4 (Rev. 1/85), TD-5 (Rev. 1/15), and TD-6 (Rev. 8/83) .
From the foregoing, it will be observed that numerous variations and modifications may be effected without departing from the true spirit and scope of the novel concept of the invention. It is to be understood that no limitation with respect to the
specific apparatus illustrated herein is intended or should be inferred. It is, of course, intended to cover by the appended claims all such modifications as fall within the scope of the claims.
Next Patent: A BAG AND A METHOD OF MAKING IT