Pptc materials using one-step thermal application process

Abstract

The invention discloses a PPTC (Polymeric Positive Temperature Coefficient) material using a one-step thermal application process. A method for preparing a polymeric positive temperature coefficient (PPTC) compound and conformally applying such compound to a substrate may include preparing and mixing raw materials to form a PPTC mixture; processing the PPTC mixture by a polymer blending apparatus, wherein the PPTC mixture is heated and extruded into a PPTC compound; performing a bunching process on the polymer compound to establish crosslinking between polymer chains in the PPTC compound; and applying a PPTC compound to the substrate using a thermal application process, wherein the PPTC compound is heated and conformally applied to the surface of the substrate.

Description

Technical Field

[0001] The embodiments relate to the field of circuit protection devices, including fuse devices. Background Technology

[0002] In various applications, polymeric positive temperature coefficient (PPTC) devices can be used as overcurrent or overtemperature protection devices, as well as current or temperature sensors. In overcurrent or overtemperature protection applications, PPTC devices can be considered as resettable fuses, designed to exhibit low resistance when operating under predetermined conditions, such as low current. The resistance of the PPTC device can be changed by direct heating due to increased ambient temperature, or by resistance heating generated by the current flowing through it. For example, a PPTC device may comprise a composite PPTC material formed from a polymer material and a conductive filler, wherein the PPTC material transitions from a low-resistance state to a high-resistance state due to thermally induced changes in the polymer material, such as melt transition or glass transition. At the transition temperature (sometimes called the "trip temperature"), which can range from room temperature to well above, the polymer material may expand and disrupt the conductive network of the conductive filler particles in the PPTC material, thereby significantly reducing the conductivity of the PPTC material. This change in resistance gives the PPTC material fuse-like properties, which can be reversible when the PPTC material cools back to room temperature.

[0003] PPTC materials are typically formed by compounding a polymer material with a conductive filler and then extruding or molding the mixture into sheets or plates of the desired shape. This type of process produces PPTC materials that are typically rigid and cannot be modified to be conformally applied to flexible substrates as desired for certain applications (e.g., flexible heaters or temperature sensors). PPTC materials suitable for flexible applications can be produced by a process involving dissolving a polymer material in a solvent and mixing the resulting solution with a conductive filler to form "PPTC ink." The PPTC ink can then be printed or otherwise conformally applied to the desired surface, after which the ink dries (i.e., the solvent evaporates). This type of process is associated with various disadvantages. For example, the steps of dissolving the polymer material during the preparation of the PPTC ink and removing the solvent after application can be time-consuming. Furthermore, the solvents required to dissolve the polymer material are environmentally unfriendly.

[0004] This disclosure is made in light of these and other considerations. Summary of the Invention

[0005] This overview is provided to present, in a simplified form, the selection of concepts further described below in the detailed description. This overview is not intended to identify key or substantial features of the claimed subject matter, nor is it intended to help determine the scope of the claimed subject matter.

[0006] A method for preparing a polymer positive temperature coefficient (PPTC) compound and conformally applying such a compound to a substrate according to embodiments of the present disclosure may include: preparing and mixing raw materials to form a PPTC mixture; processing the PPTC mixture using a polymer blending apparatus, wherein the PPTC mixture is heated and extruded into a PPTC compound; performing a beaming process on the polymer compound to establish crosslinking between polymer chains in the PPTC compound; and applying the PPTC compound to the substrate using a thermal application process, wherein the PPTC compound is heated and conformally applied to the surface of the substrate. Attached Figure Description

[0007] Various embodiments of the disclosed technology will now be described by way of example with reference to the accompanying drawings, in which:

[0008] Figure 1 This is a flowchart illustrating a method for preparing a polymeric positive temperature coefficient compound according to embodiments of the present disclosure and conformally applying such a compound to a substrate. Detailed Implementation

[0009] This embodiment will now be described more fully below with reference to the accompanying drawings, in which some exemplary embodiments are illustrated. The subject matter of this disclosure may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. These embodiments are provided so that this disclosure will be exhaustive and complete, and will fully convey the scope of the subject matter to those skilled in the art. In the drawings, the same reference numerals consistently refer to the same elements.

[0010] As used herein, elements or operations listed in the singular and beginning with the word "a" or "an" are understood to potentially include elements or operations in the plural form, unless otherwise indicated. Furthermore, various embodiments herein have been described in the context of one or more elements or components. Elements or components may include any structure arranged to perform a particular operation. Although by way of example, an embodiment may be described as having a limited number of elements in a particular topology, it may include more or fewer elements in alternative topologies as desired for a given implementation. Note that any reference to "an embodiment" or "an embodiment" means that a specific feature, structure, or characteristic described in connection with that embodiment is included in at least one embodiment. The phrases "in one embodiment," "in some embodiments," and "in various embodiments" appearing in various places in the specification do not necessarily all refer to the same embodiment.

[0011] According to this disclosure, an improved method is proposed for preparing polymer positive temperature coefficient (PPTC) compounds and conformally applying such compounds to a substrate (e.g., a substrate within a PPTC device). Figure 1 The diagram shows an example flowchart illustrating such a method.

[0012] refer to Figure 1 Box 100 of the example method shown can collect and prepare (measure or weigh) raw materials that will form a PPTC compound. The raw materials may include a polymer, a conductive filler, and optionally, one or more additives. The polymer included in the PPTC compound may be selected from semi-crystalline polymers, such as polyethylene copolymers (ethylene-vinyl acetate, ethylene-acrylic acid copolymers, ethylene-butyl acrylate copolymers, polyolefin elastomers, polyethylene oxide, etc.), fluoropolymers (polyvinyl fluoride, polyvinyl fluoride, polytetrafluoroethylene, ethylene-tetrafluoroethylene copolymers, etc.), polyesters (polycaprolactone, etc.), polyethers (polyethylene glycol, polytetrahydrofuran, etc.), polyurethanes, polyamides or copolymers thereof, and diene elastomers or copolymers thereof. This disclosure is not limited thereto. The amount of polymer in the PPTC compound can range from 60% to 95% by volume.

[0013] The conductive filler included in the PPTC compound can be selected from carbon black, carbon fiber, carbon nanotubes, graphite, graphene, metal or metal carbide particles (such as copper, nickel, tungsten carbide, titanium carbide), etc. This disclosure is not limited thereto. The amount of conductive filler in the PPTC compound can range from 1 vol% to 40 vol%.

[0014] Optional additives included in PPTC compounds may include, but are not limited to, inorganic fillers, flame retardants, antioxidants, coupling agents, arc inhibitors, crosslinking agents, pigments (e.g., providing visual indications of PPTC properties, such as trip temperature), etc.

[0015] The aforementioned raw materials (including polymers, conductive fillers, and optional additives) can be weighed, and appropriate amounts of each raw material can be mixed together to form a “PPTC mixture”.

[0016] refer to Figure 1 Box 110 of the example method shown illustrates that the PPTC mixture can be processed using conventional polymer blending equipment, wherein the PPTC mixture can be heated and extruded. During such a process, the PPTC mixture can be heated to a temperature ranging from 100 degrees Celsius to 350 degrees Celsius, depending on the type of polymer used, and the heated PPTC mixture can be extruded into the form of wires, sheets, or pellets, depending on the type of polymer blending equipment used. This disclosure is not limited thereto. The extruded product is hereinafter referred to as a "PPTC compound".

[0017] refer to Figure 1 Box 120 of the example method shown illustrates that the PPTC compound may undergo a beaming process to establish crosslinks between polymer chains within the PPTC compound. This process creates a network of polymer chains within the PPTC compound, which significantly contributes to the "resettable" properties of the PPTC compound (i.e., the ability of the PPTC compound to reduce resistance when cooled to a temperature below its trip temperature). In this context, the beaming process may be referred to as a "pre-beaming" process because the beaming is performed prior to the application of the PPTC compound in the device. The pre-beaming process can be performed using any conventional beaming techniques and associated equipment, including but not limited to electron beaming and gamma irradiation. If electron beaming is used, the beaming dose can range from 1 megarad to 100 megarads. If gamma irradiation is used, the beaming dose can range from 1 kilogray to 100 kilogras. This disclosure is not limited thereto. In various embodiments, the pre-beaming process may be omitted, and the beaming process may alternatively be performed after the application of the PPTC compound in the device.

[0018] refer to Figure 1Block 130 of the example method shown describes the application of a PPTC compound to a substrate using a heated application process (hereinafter referred to as a "thermal process"), wherein the PPTC compound can be melted or softened and can be applied to the substrate in a manner that conforms to and adheres to the surface of the substrate. The thermal process can include hot pressing, thermal spraying, molding, etc. In various embodiments, the substrate can be a flexible polymer insulating film, such as that formed from polyimide, polyester, polyamide, fluoropolymer, polyolefin, silicone, epoxy, etc. This disclosure is not limited thereto. The substrate can form the basis of a flexible PPTC device (i.e., a PPTC device that can be conformally applied to another structure / surface) and can include a pair of metal electrodes adhered thereto for connecting PPTC devices within a circuit. When the PPTC compound is applied to the substrate via the thermal process, it can bridge and connect the metal electrodes, thereby providing a conductive path between them.

[0019] In various embodiments, the thermal process of block 130 of the example method can be a hot pressing process. This can include cutting a PPTC compound into desired sizes and shapes to form “PPTC elements” suitable for application to a substrate (e.g., metal electrodes suitable for bridging a PPTC device). The PPTC elements can then be placed on the substrate, and the substrate can be placed in a hot press. The hot press can laminate the PPTC elements to the substrate under heat and pressure. In various examples, hot pressing can be performed at temperatures ranging from 80 degrees Celsius to 350 degrees Celsius (depending on the melt temperature of the polymer), at pressures ranging from 20 pounds per square inch (psi) to 10,000 pounds per square inch (psi) (depending on the type of polymer and the hot pressing temperature), and for times ranging from 1 second to 6,000 seconds. This disclosure is not limited thereto.

[0020] refer to Figure 1 Box 140 of the example method shown illustrates that the PPTC device can undergo various processes after the PPTC element has been applied to the substrate. Such processes can be referred to as "post-application" processes. Post-application processes can include, but are not limited to, bundling (as a supplement to or alternative to the pre-bundling process described above), insulating coating, heat treatment, encapsulation, etc. This disclosure is not limited thereto.

[0021] Those skilled in the art will appreciate the many benefits offered by the methods of this disclosure. For example, the methods of this disclosure facilitate the conformal application of PPTC elements to flexible substrates, requiring only a single thermal process step. Furthermore, the methods of this disclosure do not require the use of any of the environmentally hazardous solvent types conventionally used when applying PPTC compounds to flexible substrates.

[0022] While this embodiment has been disclosed with reference to certain embodiments, many modifications, alterations, and changes to the described embodiments are possible without departing from the scope and domain of this disclosure, as defined in the appended claims. Therefore, this embodiment should not be limited to the described embodiments and may have the full scope defined by the language of the following claims and their equivalents.

Claims

1. A method for preparing a polymer positive temperature coefficient (PPTC) compound and conformally applying such a compound to a substrate, the method comprising: Prepare and mix the raw materials to form a PPTC mixture; The PPTC mixture is processed using a polymer blending device, wherein the PPTC mixture is heated and extruded into a PPTC compound; A bundle-bonding process is performed on the polymer compound to establish crosslinks between polymer chains in the PPTC compound; as well as The PPTC compound is applied to a substrate using a thermal application process, wherein the PPTC compound is heated and conformally applied to the surface of the substrate.

2. The method according to claim 1, wherein, The PPTC mixture includes a polymer and a conductive filler.

3. The method according to claim 2, wherein, The polymer includes at least one of the following: ethylene-vinyl acetate, ethylene-acrylic acid copolymer, ethylene-butyl acrylate copolymer, polyolefin elastomer, polyethylene oxide, polyvinyl fluoride, polyvinyl fluoride, polytetrafluoroethylene, ethylene-tetrafluoroethylene copolymer, polycaprolactone, polyethylene glycol, and polytetrahydrofuran.

4. The method according to claim 2, wherein, The conductive filler includes at least one of the following: carbon black, carbon fiber, carbon nanotubes, graphite, graphene, copper, nickel, tungsten carbide, and titanium carbide.

5. The method according to claim 2, wherein, The PPTC mixture also includes additives.

6. The method according to claim 5, wherein, The additives include at least one of the following: inorganic fillers, flame retardants, antioxidants, coupling agents, arc inhibitors, crosslinking agents, and pigments.

7. The method according to claim 1, wherein, The PPTC mixture is heated to a temperature ranging from 100 degrees Celsius to 350 degrees Celsius before extrusion.

8. The method according to claim 1, wherein, The focusing process is an electron focusing process.

9. The method according to claim 1, wherein, The focusing process is a gamma irradiation process.

10. The method according to claim 1, wherein, The bunching process is a pre-bubbling process performed before the PPTC compound is applied to the substrate.

11. The method according to claim 1, wherein, The bunching process is a first bunching process performed before the PPTC compound is applied to the substrate, and the method further includes a second bunching process performed after the PPTC compound is applied to the substrate.

12. The method according to claim 1, wherein, The heat application process includes one of the following: hot pressing, hot spraying, and molding.

13. The method according to claim 1, wherein, The heat application is a hot pressing process, wherein the PPTC compound is cut into the desired size and shape to form PPTC elements, and the PPTC elements are laminated to the substrate in a hot press.

14. The method according to claim 13, wherein, The hot pressing process is performed at temperatures ranging from 80 degrees Celsius to 350 degrees Celsius and at pressures ranging from 20 pounds per square inch to 10,000 pounds per square inch.

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