Incorporation of sorbents, e.g., desiccants, into resin matrices has been revealed in several contexts. Formation of these resins into structural or functional shapes by various processes has been described in certain applications. Similarly, fillers have been added to structural molding resins. Low cost mineral or other fillers have been added to resin-containing compositions to extend the resin and reduce costs, while maintaining strength sufficient for the intended end-use application of the molded article. It is also a frequent practice to add reinforcing materials, such as glass fibers or beads to enhance mechanical properties of molding resins, e.g., hardness, tensile displacement, and so on. With reinforcing additives, just as with fillers, it has been found there are ranges within which the desired effects of extending the resin or reinforcing the molded article are accomplished while maintaining satisfactory injection molding and mechanical properties.
Nevertheless, molding compositions comprising reinforcing additives have not been entirely satisfactory for a number of end-use applications. For example, a molding composition having relatively high loading levels of reinforcing additives, such as glass fibers and glass beads have the affect of limiting the loading factor of sorbent additives which may be introduced into such molding compositions for optimal adsorption performance. However, with a corresponding reduction in the loading of reinforcing additives and an increase in the loading of sorbent additives, there was also a potential for a reduction in desirable mechanical properties, such as hardness, tensile strength, and other mechanical properties.
Thus, existing resin/sorbent matrices suffer from several drawbacks. The materials are often brittle and insufficient to survive standard drop testing. Additionally, particulate material may be released from the matrices thereby degrading part performance and/or device functionality. Due to the structure of these matrices, water may be adsorbed or absorbed at a faster rate, which in fact may be too fast for common manufacturing procedures. In other words, the ability for a part to adsorb water may be exhausted prior to its assembly in a device because environmental conditions are not controlled in the manufacturing area. Existing resin/sorbent matrices are often quite expensive to manufacture and use due to the use of exotic resin, additional processing steps and the use of multi-resin materials having phase boundaries. Additionally, existing resin/sorbent matrices may pose compatibility issues due to materials typically used as binders.
It is well known that lamp assemblies, in particular, lamp assemblies used in the automotive and marine industries, are exposed to aggressive environments under a variety of conditions. For example, tractor trailers typically include a plurality of lamps about the base of the trailer as well as about the tractor portion. As tractor trailers carry goods in a variety of environments, e.g., from the cold winters of high latitude regions to the humid summer heat of equatorial regions, lamp assemblies experience a wide range of temperature as well as ambient relative humidity. While in marine applications, e.g., runner and indicator lamps, lamp assemblies may be exposed to fluids such as salt water.
In addition to the environmental factors, lamp assemblies are exposed to harsh cleaning solutions. For example, tractors are cleaned with a variety of solutions, while trailers may be cleaned with even more aggressive solutions as the trailers may be used to carry items which are difficult to remove. Similarly, it is common to use acidic solutions such as a 50/50 blend of muratic acid and water to clean boat hulls, thereby exposing the lamp assemblies to extremely aggressive solutions.
In view of the foregoing, it should be appreciated that internal electronic components of lamp assemblies are exposed to a variety of environmental conditions which degrade their performance and useful life. For example, lamp assemblies commonly include light emitting diodes (LEDs) as light sources, and these LEDs require driving circuitry and electrical connections in order to function properly. The above described environmental conditions, in particular elevated relative humidity levels, have detrimental effects on the electronics of the lamp assemblies due to moisture ingress through the housing, the lens covers, and wiring harnesses and connector entry points. Compounding the problem is that the thermoplastic or thermoset polymers most commonly used for these types of applications are extremely poor moisture barriers and are primarily selected for these types of applications because of their dimensional stability or ability to be bonded together to form the assemblies. Heretofore, the ingress of contaminates have been slowed through the use of epoxy fillers, potting materials, and designed in gaskets or seals. Thus, preventing the exposure of the electronics to humidity is important, although heretofore has required expensive and labor intensive solutions.
For example, U.S. Pat. No. 5,632,551 entitled “LED Vehicle Lamp Assembly” teaches hermetically sealing a lamp assembly by introducing an epoxy resin over the entire circuit board thereby protecting the LEDs and circuit board from vibration, fatigue, moisture and the like. Arrangements of this type are expensive to manufacture, time consuming, labor intensive and use materials that are not environmentally friendly, and in some instance may require the use of special protective equipment, e.g., ventilator systems.
Furthermore, some devices require EMI shielding and/or static dissipation. For example, a device comprising an electrically noisy power supply may need shielding around the power supply so that the device will satisfy regulatory test standards, e.g., UL, CSA, CE, etc. EMI shielding is typically accomplished by a number of secondary technologies which involve the addition of an EMI material inside a structure such as a housing. These materials are typically sprayed onto the surface of a material to provide an EMI shield. They tend to be costly, and difficult to apply and control.
As can be derived from the variety of devices and methods directed at providing a multifunctional molding composition having moisture barrier properties, and EMI shielding and/or electrically conductive properties, many means have been contemplated to accomplish the desired end, i.e., prevention of the ingress of moisture within an enclosure while simultaneously adsorbing moisture already present therein and providing EMI shielding and/or electrical conductivity. Heretofore, tradeoffs between performance and cost were required. Thus, there is a long-felt need for a multifunctional molding composition which prevents the ingress of moisture within an enclosure formed from the molding composition while simultaneously adsorbing moisture already present therein and providing EMI shielding and/or electrical conductivity, which is cost effective and easy to produce.