Abstract:
An integral single piece extruded LED light strip and an associated process for producing such an LED light strip. The light strip includes first and second bus elements spaced apart from one another by a predetermined distance. The light strip also includes at least one light emitting diode (LED) connected between the bus elements that is illuminated when the first bus element conducts electricity provided from a power source. An extruded plastic material completely encapsulates the first and second bus elements and the LED, thereby providing a barrier to protect the elements from damage and to make the light strip impervious to moisture. A process for manufacturing an integrally formed single piece light strip includes the steps of continuously feeding bus elements to an extruder; continuously feeding circuitry having at least one LED operatively mounted thereon to the extruder; and extruding a thermoplastic material at a temperature below that which would damage the circuitry or the LED to thereby encapsulate the bus elements, the circuitry and the LED and to operatively connect the circuitry to the bus elements.

Description:
This is a division of U.S. patent application Ser. No. 08/520,237, filed Aug. 28, 1995, now U.S. Pat. No. 5,927,845. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates generally to light strips and, more particularly, to an integral single piece light strip containing light emitting diodes, and a process for forming such a light strip, in which the diodes and associated circuitry are protected from moisture ingress and from other potential causes of damage. 
     Light emitting diode (LED) light strips are commonly used to provide visual pathways or marked locations in otherwise dark, unlit areas. Such LED light strips are advantageous when compared to bulb or lamp-based markers in that the strips are relatively inexpensive to manufacture and are relatively easy to install. Further, the LEDs used in these light strips typically have a longer life than conventional lamps or bulbs. 
     Present LED light strips consist of circuitry including a plurality of LEDs mounted on a substrate and connected to electrical conductors. The circuitry is encased within a tube-like, partially transparent protective sheathing and connected to a power source for selective LED illumination. Two exemplary types of LED strips are described generally in U.S. Pat. No. 5,130,909 to Gross, issued Jul. 14, 1992 and entitled “Emergency Lighting Strip” and U.S. Pat. No. 4,597,033 to Meggs et al., issued Jun. 24, 1986 and entitled “Flexible Elongated Lighting System.” Such strips are utilized in a variety of indoor and outdoor configurations such as emergency pathway markers, exit door indicators and ornamental lighting arrangements. 
     Regardless of the application, it is imperative that the LED circuitry is housed within some type of protective sheathing. The protective sheathing must be of sufficient strength to prevent damage to the circuitry due to excessive loads, such as the weight of machinery, being directly applied to the strip. Further, because the LED circuitry is highly susceptible to damage and malfunction caused by exposure to moisture, the protective sheathing must be impervious to moisture. 
     While the aforementioned LED light strips protect the circuitry housed within, the strips have associated limitations. The tube-like sheathings typically used as housings for present LED light strips provide minimal protection against mechanical damage to the LED circuitry due to excessive loads placed on the sheathings. Further, the aforementioned light strips provide the LED circuitry with only limited protection from moisture. The sheathing seals or strip ends through which the LED circuitry is inserted are typically susceptible to moisture penetration. Further, protective sheathings such as those described in the above-mentioned patents are substantially hollow, thereby increasing the susceptibility of such sheathings to moisture condensation. As a result, such light strips often prove to be unreliable from a moisture protection standpoint, especially in outdoor lighting applications or other applications in which the strips are exposed to extreme weather conditions. Consequently, it would be desirable to encase the LED circuitry in a more permanent type of protective sheathing that did not have the above mentioned drawbacks associated with tube-like sheathings. 
     One such type of permanent protective sheathing is commonly used for encapsulating electroluminescent (EL) lamps and is formed by sealing a multi-layer EL lamp configuration by a conventional sheet, or hard, lamination process. In this conventional hard lamination process, a top layer of protective film is either adhesively bonded or thermally fused to a bottom layer of protective film through the use of high temperatures and high pressure rollers, thereby sandwiching the EL lamps between the layers. 
     While EL strips formed through the above hard lamination process provide a layer of protection, the multi-layer EL lamps housed within such strips are also susceptible to moisture damage. Moisture is often capable of penetrating into the interior of the two-piece strips through the fused or bonded seal joining the two-piece housing, especially when the strips are utilized in outdoor applications or after the bonded or fused seal connecting the two-piece housing weakens upon aging of the strip. In addition, such a hard lamination process would not be desirable for use with LED circuitry. EL lamps include multiple layers of substantially flat conductive and non-conductive material that are easily sandwiched between top and bottom laminate layers. Conversely, because LEDs in LED light strips typically have a height of 0.040 inch or more, the high pressure rollers typically used to bond or fuse the two-piece housing could crush protruding LEDs during formation of an LED strip. In addition, the high temperatures associated with the bonding or fusing steps in a hard lamination process would subject the LEDs and associated circuitry to heat damage, thus rendering an LED strip manufactured by such a process nonfunctional. 
     Therefore, a need exists for an improved single piece integral LED light strip that is impervious to moisture and that provides a high degree of protection against other forms of potential damaging elements. There also exists a need for a soft lamination process for producing such an elongated single piece integral LED light strip in which a protective housing encapsulates the LED circuitry so that an integral single piece LED light strip is produced in a cost effective manner without subjecting the circuitry to damaging high pressures or high temperatures. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention relates to an integral single piece extruded LED light strip having first and second bus elements spaced apart from one another by a predetermined distance and being operatively connected to a power source to conduct electricity. Further, at least one light emitting diode (LED) is connected between the bus elements and is illuminated when the bus elements conduct electricity provided from the power source. An extruded soft laminate plastic material completely encapsulates the first and second bus elements and the LED, and urges the first and second bus elements and the LED into operative contact. Further, the extruded plastic material provides a barrier that protects the elements from damage and makes the light strip impervious to moisture. 
     The present invention also relates to a soft lamination process for manufacturing an integrally formed single piece light strip. The process includes the steps of continuously feeding bus elements to an extruder; continuously feeding circuitry having at least one LED operatively mounted thereon to the extruder; and extruding a thermoplastic at a temperature below that which would damage the circuitry to thereby encapsulate the bus elements and the circuitry and to operatively connect the circuitry to the bus elements. 
    
    
     These and other various advantages and features of the present invention will become apparent from the following description and claims, in conjunction with the appended drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view illustrating a light strip according to a preferred embodiment of the present invention; 
     FIG. 2 is a perspective view, partially in cross-section and broken away, illustrating the LED circuitry encapsulated within the plastic material; 
     FIG. 3 is a cross-sectional view of the strip shown in FIG. 1 mounted into a protective track; 
     FIG. 4 is a schematic view illustrating a process for manufacturing the LED light strip according to the present invention; 
     FIG. 5 illustrates a second embodiment of the present invention; 
     FIG. 6 illustrates a third embodiment of the present invention; 
     FIG. 7 illustrates a fourth embodiment of the present invention; 
     FIG. 8 is a plan view illustrating the implementation of multiple discrete segments of an LED light strip of the type shown in FIG. 1 to illuminate a section of an airport taxiway; and 
     FIGS. 9A-9B are plan views illustrating alternative configurations of LEDs implemented in the LED light strip of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to the drawings, an LED light strip according to the preferred embodiment of the present invention is shown generally at  10  in FIG.  1 . The light strip includes LED circuitry, shown generally at  12  and described in detail below, encapsulated within an integral single piece thermoplastic housing  14  having no internal voids. Thus, the light strip  10  is not only durable and capable of withstanding considerable loads, but also is impervious to moisture, and thereby protects the LED circuitry  12  from damage due to moisture ingress. The thermoplastic housing  14  is preferably composed of a low vapor transmission rate polymeric material such as Surlyn®, an ionomer resin, a high density polyethylene, or polychlorotrifluoroethylene. 
     FIG. 2 shows the light strip of FIG. 1 with the housing partially cut away along sectional line  2 - 2  to reveal the encapsulated LED circuitry. As shown in FIG. 2, the LED circuitry  12  is mounted on a substrate  16  containing a printed circuit. Preferably, the substrate is a polyester film having a thickness of approximately 0.005 inches. However, any substrate, such as a fiberglass or a polyimide substrate, exhibiting parameters necessary for the manufacturing process described below may be used. The printed circuit includes conductive bus contacts  20   a ,  20   b  that extend longitudinally through the length of the strip and that are operatively connected to the printed circuit tracks  22 . A resistor  24  (FIG. 1) and light emitting diodes (LEDs)  26  of the type well known in the art are operatively contacted to the PCB tracks  22  between the conductive bus contacts  20   a ,  20   b . The printed circuit bus contacts  20   a ,  20   b  electrically contact bus elements  30   a ,  30   b , respectively, which also extend longitudinally through the length of the strip. As will be described in more detail below, bus elements  30   a ,  30   b  are connected to a remote power source. Therefore, electricity is selectively supplied over the bus elements  30   a ,  30   b  from a remote power source to illuminate the LEDs  26  in response to certain predetermined conditions dependent upon the particular light strip application. While FIG. 1 shows three LEDs  26  mounted on the substrate  16 , it should be appreciated at this point that any number of LEDs may be implemented in a similar manner. 
     FIG. 3 illustrates a cross-sectional view of the light strip shown in FIG.  1 . According to the preferred embodiment of the present invention, the light strip is approximately 0.4 inches in height and 1.3 inches in width. Also, as shown in FIG. 3, if a particular application so dictates, the LED light strip may be mounted in a protective track  34  formed from aluminum or a high density plastic. The strip is pulled into the aluminum track from one end and then is permanently attached to the track through the use of a bonding agent of the type well known in the art. Subsequent to the formation of a shallow channel in a concrete, asphalt or other similar surface through use of a cutting tool well known in the art, the track  34 , and the light strip housed within, may be inserted into the channel and thus flush mounted with the finished surface with negligible effect on surface integrity. Thus, the track  34  provides additional protection to the light strip from large loads placed upon the light strip and further facilitates the flush mounting of the light strip in areas such as an airport taxiway or an automobile highway. Such a light strip/track system could include light strips using different color lamps that could alternately be activated or flashed as required by a central control such as an airport control tower. It is also contemplated that such a system could be designed to conform to the pertinent sections of FAA Circular AC150/5345-46A. 
     FIG. 4 illustrates a dual extrusion assembly line for manufacturing an LED light strip according to a preferred embodiment of the present invention. As shown, a continuous length of an LED light strip substrate  40  including resistors and LEDs operatively mounted to a printed circuit on the substrate is fed from are LED light strip roll  42 . Although a continuous length of LED light strip substrate is shown being fed from the roll  42 , it should be appreciated that discrete sections of light strip substrate could also be individually fed from the roll  42  or other similar feed mechanism. A first continuous length of a first bus element  44  is fed from a first bus element roll  46 . Similarly, a second continuous length of a second bus element  50  is fed from a second bus element roll  52 . As with the light strip substrate, the bus elements  44 ,  50  could also be fed in discrete sections rather than in a continuous length manner. The bus elements may be fed in a manner so that the elements are positioned above or below the conductive bus contacts of the substrate as desired. The continuous lengths of the substrate-mounted LED circuitry  40  and bus elements  44  and  50  are brought together through feeder rolls  54   a  and  54   b , and are then fed into a molten thermoplastic stream supplied from extruders  60   a  and  60   b  in the form of both a top layer and a bottom layer. The thermoplastic material is extruded at a temperature less than 350° F., the temperature at which thermal distortion of the LEDs and wrinkling of the polyester substrate occurs. However, the extrusion temperature may vary according to the particular type of thermoplastic material used and the particular process parameters. 
     Once the extruders  60   a  and  60   b  have encapsulated the circuitry and the bus elements within the single piece housing, top and bottom layers of extruded thermoplastic material are each individually profiled by forming rolls  62   a ,  62   b  upon exit of the die  56  at a temperature of approximately 340° F. It should be noted that the distance traveled from the die to the forming rolls  62   a ,  62   b  may be varied to allow for various degrees of cooling of the newly formed strip in relation to the particular mass of the extruded strip. 
     It should be further appreciated that, through this profiling, both the top layer and the bottom layer of extruded material may breathe, allowing for control of extruded material displacement upon introduction of the substrate mounted LED circuitry into the extrusion, and therefore allowing excess extruded material to be vented to the side and trimmed by a strip trimmer (not shown). 
     Upon exiting the die and passing through the forming rolls  62   a ,  62   b , the newly formed LED light strip  63  is fed into a cooling tank  64 . Preferably, the cooling tank contains cooled water into which the newly formed strip  63  is immersed for a predetermined amount of time. After this predetermined amount of time, the LED light strip  63  is fed from the cooling tank  64  through feed rollers  70   a ,  70   b  to a cutting machine  72  of the type well known in the art and is cut into discrete segments of a predetermined length. The light strip may be cut into discrete segments corresponding to the discrete printed circuits printed on the polyester substrate to which the LEDs are electrically contacted. The extruded thermoplastic material thus encapsulates the substrate mounted LED circuitry and the bus elements in a single piece housing. Because each of the individual LEDs in the strip array are sealed in the thermoplastic material formed in the housing, the LEDs are isolated from one another. Thus, as the LED light strip is cut to a desired length between any discrete printed circuit formed on the polyester substrate, the LED configurations will not be exposed. 
     FIG. 5 shows an alternate embodiment of the present invention generally at  110 . With the light strip  110 , a substrate  112  includes conductive bus contacts  114 ,  116 ,  120  which electrically contact bus elements  124 ,  126 ,  128 . The bus elements  124  and  126  and the corresponding conductive bus contact strips  114  and  116  are positioned adjacent to one another, with contact strip  120  and the corresponding bus element  128  being located on the far right side of the strip  110 . The printed circuit track  130  is thus connected between the bus contact  114  and the bus contact  120 , while the printed circuit track  140  is connected between the bus contact  116  and the bus contact  120 . A resistor  132  and LEDs  134   a - 134   c  are electrically contacted to the printed circuit track  130 , while a resistor  142  and LEDs  144   a - 144   c  are electrically contacted to the printed circuit  140 . To prevent the printed circuit track  130  from electrically contacting the bus contact  116 , a nonconductive pad  150  is located between the bus element  126  and the printed circuit track  130  to insulate the track  130  from electrical contact with the bus element. 
     FIG. 6 shows the electrical interconnection of two LED light strips  210  and  212 . As shown, a first end of the light strip  210  includes an electrical connector  214   a , while a second end includes an electrical connector  214   b . Similarly, the light strip  212  includes a first end having an electrical connector  216   a  that mates with the connector  214   b  of the light strip  210 . A second end of the light strip  212  includes an electrical connector  216   b  for connection with another light strip or with a terminating element (not shown). The connector  214   a  shown is capable of mating with an electrical socket  220  of a remote power source  222  for providing electrical power to the light strip. As shown, the electrical connectors  214   a ,  214   b  and  216   a ,  216   b  are metal connector pins heat staked into the thermoplastic to contact the strip bus elements for interconnection of the light strips or for connection of light strips to the power source  22 . Corresponding pins in the strips may be interconnected by wires  224 ,  226  and then encased within a protective covering  230 . The electrical connectors may also be of the type such as the connector disclosed in U.S. Pat. No. 5,391,088, assigned to AMP, Inc. and entitled “Surface Mount Coupling Connector”, hereinafter incorporated by reference. Alternatively, the housing encapsulating the bus elements could be stripped away from the bus elements and the bus elements could be interconnected or connected to a remote power source through conventional wiring techniques. 
     FIG. 7 illustrates another preferred embodiment of the present invention, which is shown generally at  300 . The light strip includes a substrate  316  including printed circuit bus contacts  320   a ,  320   b  electrically contacting bus elements  330   a ,  330   b  and PCB tracks  322  connected between the bus contacts  320   a ,  320   b . A resistor  342  and LEDs  344   a ,  344   b  are mounted to the PCB tracks  322  and are selectively illuminated when the bus elements  330   a ,  330   b  conduct electricity supplied from a remote power source. 
     However, the LED light strip  310  also includes a microcontroller  352  of the type well known in the art. The microcontroller  352  makes the strip  300  addressable so that the LED circuitry contained within the LED light strip may be pulsed or selectively illuminated in a particular pattern in order to more clearly mark a particular pathway. 
     FIG. 8 illustrates one contemplated environment in which the multiple light strips  10  of the present invention may be implemented. In this particular environment, discrete sections of light strips are inserted into protective flush mounted tracks such as the track  34  and electrically interconnected by aforementioned means to form an airport holding box for a jet airplane  50 . It is contemplated that implementation of these light strips for airplane holding boxes or for actual runway lighting would more clearly mark such pathways than presently used and more expensively implemented lighting systems. In addition, the LED light strip of the present invention represents a significant improvement over conventional airport lighting systems, such as halogen MR-16 light systems, in that LED light strips can be surface mounted to the runways with only minor disturbance to the actual integrity of the runway surface, as the light strip of the present invention eliminates the necessity of burying cables associated with typical runway light systems. Further, because the LED light strips are surface mounted, additional complications, such as problems often encountered with ground water tables, are avoided. 
     It is also contemplated that the LED light strips of the present invention may be manufactured and implemented with any number of desired rows or configurations of encapsulated LEDs. FIGS. 9A and 9B show two such alternative configurations. The LED light strip shown at  400  in FIG. 9A includes a plurality of LEDs, indicated generally at  442 , configured on a PCB track  422  to form an X. The LED light strip shown at  500  in FIG. 9B includes a plurality of LEDs, indicated generally at  542 , configured on a PCB track  522  to form an arrow or chevron. Strips such as those shown at  400  and  500  could be correspondingly utilized in conjunction with a microcontroller, such as the microcontroller  352  shown in FIG. 7, to selectively indicate either a STOP or a GO condition in response to a particular runway or other type of traffic environment condition. 
     It should be appreciated that any number of bus wires may be run and any number of rows or configuration of substrate mounted LED circuits may be electrically connected to the bus elements in the process described above. 
     Further, it should be appreciated that the LED light strip of the present invention is completely impervious to moisture ingress and may therefore be used in certain underwater applications such as for aquarium or pool lighting. Use of such LED light strips could result in savings over current lighting systems. 
     It should also be appreciated that the LED light strips may be formed in a variety of cross-sectional shapes, such as rectangular, bowed, elliptical or any other desired shape through the above-described process through manipulation of the thermoplastic extruder on the shaping rollers in a manner well known in the art. 
     While the above description constitutes the preferred embodiment of the present invention, it should be appreciated that the invention may be modified without departing from the proper scope or fair meaning of the accompanying claims. Various other advantages of the present invention will become apparent to those skilled in the art after having the benefit of studying the foregoing text and drawings taken in conjunction with the following claims.