Patent Publication Number: US-10325702-B2

Title: Structurally resilient positive temperature coefficient material and method for making same

Description:
BACKGROUND 
     Field 
     The present invention relates generally to positive temperature coefficient (PTC) materials and relates more particularly to a structurally resilient PTC material. 
     Description of Related Art 
     Positive temperature coefficient (PTC) devices are typically utilized in circuits to provide protection against over current conditions. PTC material in the PTC device is selected to have a relatively low resistance within a normal operating temperature range of the PTC device, and a high resistance above the normal operating temperature of the PTC device. 
     For example, a PTC device may be placed in series with a battery terminal so that all the current flowing through the battery flows through the PTC device. The temperature of the PTC device gradually increases as current flowing through the PTC device increases. When the temperature of the PTC device reaches an “activation temperature,” the resistance of the PTC device increases sharply. This in turn significantly reduces the current flow through the PTC device to thereby protect the battery from an overcurrent condition. In another example, a PTC device may be structured as a surface mount resettable fuse. The PTC resettable fuse may have two conductors or leads that couple to a printed circuit board (PCB) or the like. The PTC resettable fuse is designed to protect against damage causable by harmful overcurrent surges and overtemperature faults. 
     Existing PTC devices normally include a core material having PTC characteristics (i.e., the PTC material). Such PTC devices may be surrounded by a package that comprises a barrier/insulation material. Conductive pads, layers or leads may be electrically coupled to opposite surfaces of the PTC material so that current flows through a cross-section of the PTC material. 
     At normal temperature, conductive properties of the PTC material of existing PTC devices form low-resistance networks. However, if the temperature rises, either from high current through the PTC device or from an increase in the ambient temperature, the PTC material may melt or soften and become amorphous. This softening or melting of the PTC material disrupts the conductive properties of the PTC material, but also reduces the rigidity of existing PTC devices. A reduction in the rigidity of existing PTC devices, either from high current or from an increase in ambient temperature, may negatively affect the functionality of existing PTC devices implemented in an arrangement that applies compression forces on the existing PTC devices. 
     Other problems with existing PTC devices will become apparent in view of the disclosure below. 
     SUMMARY 
     Structurally resilient positive temperature coefficient (PTC) materials are disclosed herein. Furthermore, methods to provide structurally resilient PTC materials are disclosed herein. 
     In one implementation, a PTC material may include an internal support structure, where the PTC material at least partially covers the support structure. In a particular implementation, the internal support structure is a mesh that is at least partially covered by a PTC material. 
     In another implementation, a method provides a PTC material that includes an internal support structure. The method includes at least partially covering a support structure with a PTC material. In a particular implementation, the support structure is a mesh, and the method includes at least partially covering the mesh with a PTC material. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates an implementation of a structurally supported positive temperature coefficient (PTC). 
         FIG. 2  illustrates a cross-section view of a structurally supported PTC material, as viewed from the perspective of line I-I shown in  FIG. 1 . 
         FIG. 3  illustrates an exemplary support structure that may be used to provide structural stability in a PTC material. 
         FIG. 4  illustrates another cross-section view of the structurally supported PTC material, as viewed from the perspective of line I-I shown in  FIG. 1 . 
         FIG. 5  illustrates yet another cross-section view of the structurally supported PTC material, as viewed from the perspective of line I-I shown in  FIG. 1 . 
         FIG. 6  illustrates an exemplary set of operations for manufacturing a structurally supported PTC material. 
         FIG. 7  is a chart that illustrates the operational performance of conventional PTC material without internal structural enhancements. 
         FIG. 8  is a chart that illustrates the operational performance of structurally supported PTC material in accordance with one or more embodiments described herein. 
     
    
    
     DETAILED DESCRIPTION 
     Structurally supported positive temperature coefficient (PTC) materials are disclosed herein. Furthermore, methods to provide structurally supported PTC materials are disclosed herein. In one implementation, a structurally supported PTC material includes a support structure that is at least partially covered by a PTC material. In one example, the support structure is a mesh or lattice material. In another example, the support structure is at least one spacer material that includes a plurality of through holes, apertures, or through ways. In another example, the support structure is a plurality of single hole spacers. The holes or through ways of the aforementioned support structure materials may be square shaped, circular shaped, rectangle shaped, tetrahedral shaped, pyramidal shaped, triangular shaped, hexagon shaped, or the like. 
       FIG. 1  illustrates an implementation of a structurally supported PTC material  100 . The structurally supported PTC material  100  includes PTC material  102  that at least partially covers a support structure  104 . At least partially covering the support structure  104  with the PTC material  102  provides at least a partially integrated structure. That is, the PTC material  102  may at least partially cover top and bottom surfaces of the support structure  104 . In the example shown in  FIG. 1 , the support structure  104  is a mesh or lattice material. The support structure  104  may include strands  106  that define the mesh or lattice material of the support structure  104 . More particularly, the strands  106  of the support structure  104  define a plurality of holes or apertures  108  of the support structure  104 . The support structure  104  may alternatively be at least one spacer material (see  FIG. 3 ) that includes a plurality of through holes, apertures or through ways, or the support structure  104  may be structured from a plurality of single hole spacers. The holes or through ways of the aforementioned support structure materials may be square shaped, circular shaped, rectangle shaped, tetrahedral shaped, pyramidal shaped, triangular shaped, hexagon shaped, or the like. The support structure  104  may alternatively have a different size and/or shape than illustrated and described herein. The structurally supported PTC material  100  illustrated in  FIG. 1  is shown as a sheet or film. However, the structurally supported PTC material  100  may be provided in other shapes and sizes than that illustrated in  FIG. 1 . 
     The PTC material  102  may include one or more conductive and polymer fillers. The conductive filler may include conductive particles of tungsten carbide, nickel, carbon, titanium carbide, or a different conductive filler or different materials having similar conductive characteristics. The polymer filler may include particles of polyvinylidene difluoride, polyethylene, ethylene tetrafluoroethylene, ethylene-vinyl acetate, ethylene butyl acrylate or different materials having similar characteristics. Furthermore, the PTC material  100  to may comprise a plurality of layers that include unique conductive and polymer fillers. 
     The support structure  104  may be an electrically nonconductive material. For example, the support structure  104  may be glass, Kevlar, polymer, ceramic, carbon fiber, insulated metal, fabric, or the like. In another implementation, the support structure  104  may include electrically conductive material. For example, the support structure  104  may be glass, Kevlar, polymer, ceramic, carbon fiber, fabric, or the like, that includes one or more electrically conductive material disposed therein. The one or more electrically conductive material may include one or more of tungsten carbide, nickel, carbon, titanium carbide, or a different conductive material. Alternatively, the support structure  104  may be an electrically conductive material, such as silver, copper, gold, aluminum, stainless steel, or the like. In one example, one or more of the strands  106  of the support structure  104  may comprise electrically conductive material and others of the one or more strands  106  may comprise electrically nonconductive material and/or only electrically nonconductive material. Similarly, as discussed in the foregoing, the support structure  104  may comprise at least one spacer material (see  FIG. 3 ) that includes a plurality of through holes, apertures or through ways, or the support structure  104  may be structured from a plurality of single hole spacers. The spacers defining the support structure  104  may comprise electrically conductive material and/or electrically nonconductive material. 
     The strands  106  of the support structure  104  may have a diameter of approximately 50 μm. However, the diameter of the strands  106  may be less than or greater than 50 μm. The apertures  108  of the support structure  104  may have a width and/or length of at least 115 μm. In one example, at least one of the apertures  108  is defined by an opening of 115×145 μm. The size of the apertures  108  may be less than or greater than 115 μm. In one particular implementation, the support structure  104  has a material free open area of approximately 55% and a thermal stability of approximately 250° C. Therefore, in one implementation, the support structure  104  resists melting, softening, and the like up to approximately 250° C. In one implementation, the support structure  104  is inert to organic solvents. Furthermore, the support structure  104  may have a compression strength capable of tolerating a force of approximately 150 kg/cm 2 . In particular, the support structure  104  may be structurally stable up to at least a force of approximately 150 kg/cm 2 . Therefore, the support structure  104  resists cracking, breaking, deformation, or the like up to at least a force of approximately 150 kg/cm 2 . The support structure  104  may have a compression strength capable of tolerating a force of less than or greater than 150 kg/cm 2 . 
       FIG. 2  illustrates a cross-section view of the structurally supported PTC material  100 , as viewed from the perspective of line I-I shown in  FIG. 1 . As is illustrated, the PTC material  102  at least partially covers one or more of the strands  106  associated with the support structure  104 . Specifically, the PTC material  102  may not completely cover each of the strands  106 . For example, an upper portion of one or more of the strands  106  may not be completely covered by the PTC material  102 . Moreover, lower and/or side portions of the PTC material  102  may not be completely covered by the PTC material  102 . In one example, the PTC material  102  completely covers all of the strands  106  or a majority of the strands  106 . The strands  106  illustrated in  FIG. 2  have a cross-section that is circular. However, other cross-sectional shapes, such as square or rectangle, may be associated with the strands  106 . 
       FIG. 3  illustrates an exemplary support structure  302  that may be used to provide structural stability in the PTC material  102 . The support structure  302  is an example of a spacer material that includes a plurality of through holes, apertures or through ways  304 . The support structure  302  is shown as having three apertures  304 . However, the illustrated number of apertures  304  is purely exemplary. The support structure  302  may be provided as a sheet or film that includes many of the apertures  304 . Such a sheet or film may be integrated with the PTC material  102  to provide structural stability for the PTC material  102 . Alternatively, multiple separate support structures  302  may be combined together and integrated with the PTC material  102  to provide structural stability. 
       FIG. 4  illustrates another cross-section view of the structurally supported PTC material  100 , as viewed from the perspective of line I-I shown in  FIG. 1 . As is illustrated, the PTC material  102  at least partially covers one or more of the strands  106  associated with the support structure  104 . In this embodiment, at least one electrically conductive layer  402  is applied over a first surface  404  of the PTC material  100 . In the figure, the electrically conductive layer  402  is shown as being in contact with the PTC material  102 . However, one or more layers may be disposed between the PTC material  102  and the electrically conductive layer  402 . In another embodiment, another electrically conductive layer  406  is applied over a second surface  408  of the PTC material  100 . In  FIG. 4 , the electrically conductive layer  406  is shown as being in contact with the PTC material  102 . However, one or more layers may be disposed between the PTC material  102  and the electrically conductive layer  406 . 
       FIG. 5  illustrates yet another cross-section view of the structurally supported PTC material  100 , as viewed from the perspective of line I-I shown in  FIG. 1 . As is illustrated, the PTC material  102  at least partially covers one or more of the strands  106  associated with the support structure  104 . In this embodiment, at least one electrically conductive layer  502  is applied over a first surface  504  of the PTC material  100 . In the figure, the electrically conductive layer  402  is shown as being in contact with the PTC material  102 . However, one or more layers may be disposed between the PTC material  102  and the electrically conductive layer  502 . In another embodiment, another electrically conductive layer  506  is applied over a second surface  508  of the PTC material  100 . In  FIG. 5 , the electrically conductive layer  506  is shown as being in contact with the PTC material  102 . However, one or more layers may be disposed between the PTC material  102  and the electrically conductive layer  506 . 
       FIG. 6  illustrates an exemplary set of operations for manufacturing a structurally supported PTC material. At block  602 , a PTC material may be provided in a powdered form. Alternatively, the PTC material may be provided in a liquid form, also known as PTC ink. The PTC material may include one or more conductive and polymer fillers. The conductive filler may include conductive particles of tungsten carbide, nickel, carbon, titanium carbide, or a different conductive filler or different materials having similar conductive characteristics. The polymer filler may include particles of polyvinylidene difluoride, polyethylene, ethylene tetrafluoroethylene, ethylene-vinyl acetate, ethylene butyl acrylate or different materials having similar characteristics. 
     At block  604 , a support structure is provided. In one example, the support structure is a mesh or lattice material. In another example, the support structure is at least one spacer material that includes a plurality of through holes, apertures, or through ways. In another example, the support structure is a plurality of single hole spacers. The holes or through ways of the aforementioned support structure materials may be square shaped, circular shaped, rectangle shaped, tetrahedral shaped, pyramidal shaped, triangular shaped, hexagon shaped, or the like. The support structure may be an electrically nonconductive material. For example, the support structure may be glass, Kevlar, polymer, ceramic, carbon fiber, insulated metal, fabric, or the like. In another implementation, the support structure may include electrically conductive material. For example, the support structure may be glass, Kevlar, polymer, ceramic, carbon fiber, fabric, or the like, that includes one or more electrically conductive material disposed therein. The one or more electrically conductive material may include one or more of tungsten carbide, nickel, carbon, titanium carbide, or a different conductive material. Alternatively, the support structure may be an electrically conductive material, such as silver, copper, gold, aluminum, stainless steel, or the like. In one example, one or more of the strands (e.g., strands  106 ) of the support structure may comprise electrically conductive material and others of the one or more strands may comprise electrically nonconductive material and/or only electrically nonconductive material. Similarly, as discussed in the foregoing, the support structure may comprise at least one spacer material (see  FIG. 3 ) that includes a plurality of through holes, apertures or through ways, or the support structure may be structured from a plurality of single hole spacers. The spacers defining the support structure may comprise electrically conductive material and/or electrically nonconductive material. 
     The strands of the support structure may have a diameter of approximately 50 μm. However, the diameter of the strands may be less than or greater than 50 μm. The apertures of the support structure may have a width and/or length of at least 115 μm. In one example, at least one of the apertures is defined by an opening of 115×145 μm. The size of the apertures may be less than or greater than 115 μm. In one particular implementation, the support structure has a material free open area of approximately 55% and a thermal stability of approximately 250° C. In one implementation, the support structure is inert to organic solvents. Furthermore, support the structure may have a compression strength capable of tolerating a force of approximately 150 kg/cm 2 . The support structure may have a compression strength capable of tolerating a force of less than or greater than 150 kg/cm 2 . 
     At block  606 , the PTC material and the support structure are combined. In one example, combining the PTC material and the support structure provides at least a partially integrated structure that includes the PTC material and the support structure in the PTC material. In one embodiment, the support structure is placed on a rigid surface, such as a conductive substrate or a plate, and the PTC material is applied over the support structure. PTC material in powdered form may be sprayed over the support structure. PTC material in ink form may also be sprayed over the support structure. Alternatively, PTC material in ink form may be applied over the support structure using an application blade. PTC material in powdered form may be combined with the support structure by way of compression using a press or roll press to achieve a desired thickness of the structurally supported PTC material. PTC material in ink form may be combined with the support structure using an application blade (e.g., Doctor Blade) to achieve a desired thickness of the structurally supported PTC material. In one or more embodiments, the process of combining the PTC material and the support structure may include providing one or more electrically conductive surface over a surface or surfaces of the structurally supported PTC material. 
     At block  608 , the combined PTC material and support structure, which provide the structurally supported PTC material, is allowed to harden by drying. In one implementation, the combined PTC material and support structure are hardened in an oven. 
       FIG. 7  is a chart that illustrates conventional polymeric positive coefficient (PPTC) film material performance without structural enhancements. The PPTC film material without pressure exertion thereon exhibits a rapid increase in resistance at and beyond the polymer melting range. This is a proper operating characteristic of the PPTC film material. However, when pressure is applied to the PPTC film material, the PPTC film material may not be able to achieve a proper resistance value at and beyond the polymer melting range of the polymer used in the PTC material. 
       FIG. 8  is a chart that illustrates the operational performance of structurally supported PTC material in accordance with one or more embodiments described herein. In particular, PTC material structurally supported or enhanced according to one or more embodiments described herein is shown to exhibit a rapid increase in resistance at and beyond the polymer melting range, with or without pressure or force applied to the PTC material. Therefore, structurally supported PTC material in accordance with one or more embodiments described herein may be advantageously used in arrangements and/or environments that may be subject to direct or indirect forces. 
     While structurally enhanced/supported PTC material and a method for manufacturing structurally enhanced/supported PTC material have been described with reference to certain embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the spirit and scope of the claims of the application. Other modifications may be made to adapt a particular situation or material to the teachings disclosed above without departing from the scope of the claims. Therefore, the claims should not be construed as being limited to any one of the particular embodiments disclosed, but to any embodiments that fall within the scope of the claims.