Thermally stable, fire resistant thermoset polymer compositions for heat / fire spreading applications

Abstract

Thermally stable, fire resistant thermoset polymer compositions for thermal / or spreading applications are disclosed. A thermoset polymer composition includes a thermoset polymer and at least one ceramizable filler. The thermoset polymer composition may include additional additives. The thermosetting polymer composition can be readily processed, is thermally stable, and retains its mechanical and insulating properties.

Description

Technical Field

[0001] The present invention relates to thermosetting polymer compositions for heat / fire spreading applications. In particular, the present invention relates to thermosetting polymer compositions comprising a thermosetting polymer and at least one ceramifiable filler. The thermosetting polymer composition may contain additional additives as desired. The resulting polymer composition is thermally stable, fire resistant, and maintains its insulating ability after exposure to heat or flame. Background Art

[0002] There are many applications where the base material needs to withstand high heat and avoid the spread of fire. This is especially true for objects with electronic devices where thermal runaway may occur. Thermal runaway is a process that is accelerated by increased temperature, which in turn releases energy and further increases the temperature. Thermal runaway may be associated with exothermic reactions or increased power flow and power dissipation. This risk is particularly present when lithium batteries are used in components. Thermal runaway leads to gas emission, higher temperatures, flames and smoke.

[0003] Ceramic materials can be used to prevent thermal runaway. However, ceramic materials are not flexible, low-cost or easy to manufacture. Therefore, a thermally stable, refractory material that can be easily manufactured and avoid these problems is needed. Preferably, the material is a polymer material with at least one ceramizable filler.

[0004] U.S. Patent No. 5,707,734 describes a polymer composite material with enhanced flame retardant behavior. The composite material comprises a polymer and glass fibers coated with fumed silica. The polymer can be selected from a wide variety of polymers including polybutylene, polyethylene terephthalate, polycarbonate, polyethylene, polypropylene, nylon, and mixtures of these polymers.

[0005] In the article Flame Retardant Mechanism of Silica Gel / Silica (Fire and Materials, Vol. 24, No. 6, 277-289, November / December 2000), Kashiwagi et al. studied various types of silica, silica gel, pyrogenic silica and fused silica in polypropylene and polyethylene oxide to determine their flame retardant effectiveness and mechanism. The pyrogenic silica and silica gel used in this study accumulate near the polymer surface when subjected to flames, acting as a thermal insulation layer and a barrier to the transport of degradation products to the surface.

[0006] US Patent No. 6,774,159 B2 describes a composition having high resistance to the spread of fire. The composition comprises a base polymer and a fireproofing additive comprising a metal hydroxide. The composition avoids the problems associated with metal hydroxides, namely high viscosity and reduced mechanical properties.

[0007] US Patent Publication No. US2009 / 0326108A1 describes a halogen-free flame retardant thermoplastic polyurethane composition. The flame retardant thermoplastic polyurethane composite resin composition can improve the flame retardancy and flaming-drip of thermoplastic polyurethane resin by ideally forming char during combustion. The halogen-free flame retardant used is hypophosphite, diphosphite, dipentaerythritol, talc or melamine derivatives.

[0008] In the article “Influence of Fumed Silica on Flame-Retardant Properties of Ethylene VinylAcetate / Aluminum Hydroxide Composites,” published in the Journal of Applied Polymer Science in 2010 (https: / / dpo.org / 10.1002 / app.33126), the authors describe the flammability and synergistic flame retardant effects of fumed silica. According to the authors’ results, the addition of fumed silica improved the UL 94 rating of the composite. Additionally, cone calorimeter testing showed that the addition of fumed silica significantly reduced the heat release rate of the composite when exposed to flames.

[0009] In a 2012 article, "Thermal Stability of High Density Polyethylene Fumed Silica Nanocomposites" (published in the Journal of Thermal Analysis and Calorimetry, Vol. 109, No. 2, August 2012), Dorigato et al. described how to prepare high-density polyethylene-based nanocomposites by melt mixing using surface-functionalized fumed silica nanoparticles. These materials were studied to determine their ability to improve mechanical properties and resist thermal degradation. Thermogravimetric analysis showed that the selected nanoparticles effectively increased the decomposition temperature and reduced the mass loss rate. The formation of a char-rich layer was responsible for limiting the diffusion of oxygen through the sample. Cone calorimeter testing demonstrated the effectiveness of the functionalized nanoparticles in delaying ignition time and reducing heat release rate values. The data showed that functionalized fumed silica nanoparticles can provide an effective way to enhance the flammability of polyolefins.

[0010] US Patent Publication No. US2015 / 0152222A1 describes a flame retardant thermoplastic polyurethane composition comprising a non-halogen flame retardant. The thermoplastic polyurethane composition can be used in various applications requiring high flame performance and low smoke performance as well as high tensile strength, such as wire and cable applications, film applications, and molding applications.

[0011] US Patent Publication No. US 2015 / 0170789A1 describes a refractory composition. The refractory composition comprises at least one polymer and at least one ceramic material. The composition does not contain a material that produces significant ionic conductivity when melted below a threshold temperature, and substantially does not contain magnesium hydroxide Mg(OH)2.

[0012] In a 2019 article, “Synergistic Effects of Metal Hydroxides and Fumed Nanosilica as Fire Retardants for Polyethylene” (published in Flame Retardancy and Thermal Stability of Materials, 2:30-48), Fredi et al. described the effects of aluminum / magnesium hydroxide microfillers and organically modified fumed silica nanoparticles on linear low-density polyethylene. The authors found that increased viscosity contributed to the synergistic effect between metal hydroxides and nanosilica. The authors concluded that metal hydroxides and fumed nanosilica enhanced the mechanical properties and fire resistance of polyethylene.

[0013] U.S. Patent No. 10,854,356 B2 describes a fire-resistant cable with a ceramizable layer. The applicant describes a composition based on a mixture of a specific thermoplastic ethylene polymer, silicon dioxide as a filler and hydrated magnesium silicate as a stabilizer. The composition can be used to manufacture a cable that has suitable mechanical properties when in service and effectively maintains the cable in service in the presence of fire and mechanical stress.

[0014] In “Enhancing Thermo-Mechanical Properties of Epoxy Composites using FumedSilica with Different Surface Treatments” (Polymers, 13, 2691, 2021), Kim et al. discuss their research on improving the thermal and mechanical properties of epoxy / fumed silica composites. Based on their data, Kim et al. concluded that the thermal stability of the composites was improved by the addition of silicon nanoparticles and that the pyrolysis process was slowed down when subjected to pyrolysis.

[0015] Even with all of these advances, there remains a need for thermosetting polymer materials having improved fire spread resistance, thermal stability, and insulation properties, which can be easily processed while still retaining the essential mechanical properties of thermosetting polymers. Summary of the invention

[0016] One embodiment is directed to a thermally stable, fire-resistant thermosetting polymer composition comprising a thermosetting polymer and at least one ceramizable filler.

[0017] One embodiment is directed to a method of forming a thermally stable, fire-resistant thermoset polymer comprising a thermoset polymer and at least one ceramizable filler.

[0018] Another embodiment is directed to the use of a thermally stable, fire-resistant thermosetting polymer composition comprising a thermosetting polymer and at least one ceramizable filler in an object that may be subjected to excessive heat or exposure to fire.

[0019] Yet another embodiment is directed to a battery enclosure made from a thermally stable, fire-resistant thermosetting polymer comprising a polymer and at least one ceramizable filler.

[0020] Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiments, which illustrate by way of example the principles of the invention. DETAILED DESCRIPTION

[0021] In the description of the embodiments of the present invention disclosed herein, any reference to direction or orientation is intended only for the convenience of description, and is not intended to limit the scope of the present invention in any way.Relative terms such as "lower", "higher", "horizontal", "vertical", "higher", "lower", "up", "down", "top" and "bottom" and their derivatives (e.g., "horizontally", "downwardly", "upwardly", etc.) should be interpreted as referring to the orientation as described or discussed at the time. These relative terms are only for the convenience of description, and do not require the device to be constructed or operated with a specific orientation, unless explicitly stated. Unless otherwise clearly described, terms such as "attach", "fix", "connect", "couple", "interconnect", etc. refer to the relationship in which structures are directly or indirectly fastened or attached to each other through intermediate structures, as well as the two cases of removable or rigid attachment or association.

[0022] Furthermore, the features and benefits of the present invention are described with reference to preferred embodiments. Therefore, the present invention should be expressly not limited to such embodiments describing some possible non-limiting combinations of features that may exist alone or in other feature combinations, the scope of the present invention being defined by the appended claims.

[0023] The thermally stable, fire-resistant composition comprises a thermosetting polymer and at least one ceramizable filler, and optionally other additives.

[0024] Examples of thermosetting polymers that can be used in the thermally stable, fire-resistant thermosetting polymer composition include, but are not limited to, silicones, epoxies, acrylates, vinyl esters, phenolic resins, cyanoacrylates, melamines, urea-formaldehyde resins, and reactive polyurethanes, and mixtures thereof. The thermosetting polymer can be formed from desired solvents, binders, and viscosity modifiers as needed to obtain a thermosetting polymer having desired properties.

[0025] The thermally stable, flame-resistant thermosetting polymer composition comprises at least one ceramizable filler and optionally other desired additives. Examples of other suitable additives include conductive fillers, reinforcing fillers, phosphorus-based flame retardants, synergists, and other conventional additives used in polymer processing.

[0026] Thermally stable, fire-resistant thermosetting polymer compositions include at least one ceramizable filler. Ceramizable fillers can include any type of filler that can react with other fillers to form inorganic residues and ceramic layers when exposed to fire or high temperatures (greater than or equal to 500°C). Examples of ceramizable fillers include, but are not limited to, magnesium carbonate, sodium bicarbonate, and potassium bicarbonate. In one embodiment, the ceramizable filler can be a flame retardant. The flame retardant is preferably halogen-free, environmentally safe, and nontoxic. These ceramizable fillers significantly reduce the amount of smoke released by the base polymer, and reduce the damage to such polymers when exposed to fire. Ceramizable fillers can include at least one silica-based flame retardant. An example of a silica-based flame retardant is pyrogenic silica. Aerosil pyrogenic silica from Evonik is an example of commercially available pyrogenic silica. Other flame retardants that can be used as ceramizable fillers include metal oxides and metal hydroxides, such as magnesium hydroxide, aluminum hydroxide, calcium hydroxide, and magnesium oxide. In one embodiment, preferably, the ceramic filler is a combination of fumed silica, magnesium hydroxide, aluminum hydroxide and calcium hydroxide. In one embodiment, based on the gross weight of the ceramic filler, magnesium hydroxide can be in the range of about 20 to 98 weight %, aluminum hydroxide is in the range of about 0 to about 40 weight %, calcium hydroxide is in the range of about 0 to about 40 weight %, and fumed silica is in the range of about 2 to about 30 weight %. In another embodiment, the ceramic filler can include aluminum polyphosphate and fumed silica.

[0027] Reinforcing fillers can be used for heat-stable, fire-resistant thermosetting polymer compositions. Examples of reinforcing fillers include: carbon fibers, glass fibers, ceramic fibers, whiskers, polymer fibers, nanofibers or nano hollow fibers, and blends thereof. These reinforcing fillers help improve the intensity and dimensional stability of heat-stable, fire-resistant thermosetting polymer compositions when they are subjected to flames.

[0028] Carbon fibers that can be used in the present invention include, but are not limited to, carbon nanotubes and carbon fibers. Typically, these carbon fibers improve the heat resistance of the polymer composition and can be burned after the composition is subjected to fire. Any known carbon fiber can be used in the present invention. Typically, the carbon fiber has a nominal diameter of about 1 to about 50 microns, preferably about 5 to about 20 microns. The amount of carbon fiber that can be used in the thermally stable, fire-resistant thermosetting polymer composition is in the range of about 0 to about 50 volume % of the total thermosetting polymer composition.

[0029] Glass fiber can also be added as reinforcing filler in heat-stable, fire-resistant thermosetting polymer composition.The example of such glass fiber includes but is not limited to chopped glass fiber, continuous glass fiber, ground glass, glass ball and glass beads.Any known glass fiber can be used in the present invention.Typically, the nominal diameter of glass fiber is about 1 to about 50 microns, preferably about 5 to about 20 microns.The amount of glass fiber used in heat-stable, fire-resistant polymer composition is in the range of about 0 to about 50 volume % of total thermosetting polymer composition.

[0030] Similarly, ceramic fibers can also be added to the thermally stable, fire-resistant thermosetting polymer composition. The ceramic fibers can be oxide-based ceramic fibers or non-oxide-based ceramic fibers or blends thereof. Examples of oxide-based ceramic fibers include, but are not limited to, Al2O3, SiO2, Al2O3-SiO2, or ZrO2. Examples of non-oxide-based ceramic fibers include, but are not limited to, SiC, BN, or Si3N4. The amount of ceramic fibers that can be used in the thermally stable, fire-resistant thermosetting polymer composition is in the range of about 0 to about 50 volume percent.

[0031] In addition, the heat-stable, fire-resistant thermosetting polymer composition can include polymer fibers as reinforcing fillers. Examples of suitable polymer fibers include aramid fibers and continuous polyethylene fibers. Any known polymer fibers can be used in the present invention. Typically, the nominal diameter of the polymer fiber is from about 1 to about 50 microns, preferably from about 5 to about 20 microns. The polymer fibers used in the heat-stable, fire-resistant polymer composition are in the range of from about 0 to about 50 volume %.

[0032] The thermally stable, fire-resistant thermosetting polymer composition may also contain nanofibers or nano hollow fibers as reinforcing fillers. Examples of such fibers include, but are not limited to, carbon nanotubes, graphene, graphene nanosheets, and Dragonite™ Halloysite (aluminosilicate clay) (available from Applied Minerals, Inc.). The diameter of the nanotubes ranges from about 0.1 to about 100 nanometers, preferably from about 0.4 to about 40 nanometers.

[0033] Additionally, bromine or phosphorus-based flame retardant packages may be added to the heat stable, flame retardant polymer composition as synergists. The addition of synergists helps promote char formation and maintain the integrity of the heat stable, flame resistant polymer composition when subjected to flames or high temperatures.

[0034] Other conventional additives can be added to the heat-stable, fire-resistant thermosetting polymer composition. The example of conventional additives includes: pigment, dye, pore-forming agent (voiding agent), antistatic agent, foaming agent, plasticizer, free radical scavenger, antiblocking agent, dust-proof agent, antifouling agent, surfactant, slip aid, optical brightener, plasticizer, viscosity modifier, gloss modifier, dispersion stabilizer, UV stabilizer, UV absorber, antioxidant, lubricant, heat stabilizer, hydrolysis stabilizer, crosslinking activator, coupling agent, layered silicate, radiation sunscreen (such as barium sulfate), tungsten metal, non-oxide bismuth salt, filler, colorant, reinforcing agent, adhesion promoter (such as but not limited to 2-hydroxyethyl-methacrylate-phosphate), impact strength modifier and their combination in any. Such additives of conventional amount can be included.

[0035] In addition, the thermosetting polymer used in the heat-stable, fire-resistant thermosetting polymer composition can be cross-linked or cured. One way to cross-link the thermosetting polymer composition is to use heat or moisture. Another way to cross-link the thermosetting polymer composition is to cross-link at room temperature. In addition, radiation may be used to cross-link the thermosetting polymer composition. Radiation cross-linking occurs when the thermosetting polymer composition is exposed to agents such as ultraviolet light, electron beams or gamma radiation. If radiation is used as a cross-linking agent, the product is exposed to radiation in the range of 50 KGy to 1100 KGY. Alternatively, the thermosetting polymer composition can be double cross-linked. Examples of double cross-linking include, but are not limited to, ultraviolet radiation and thermal cross-linking, and ultraviolet and moisture cross-linking. The type of cross-linking used and the cross-linking conditions depend on the thermosetting polymer used in the composition.

[0036] In another aspect, the present invention relates to the preparation of heat-stable, fire-resistant thermosetting polymer compositions.Method comprises providing thermosetting polymer and ceramizable filler, and providing any required other additive.Use any conventional process that material is mixed together thermosetting polymer, ceramizable filler and any other other additive are mixed together.Mixing device can be any suitable device used in the field of mixed concentrated solids.For example, the mixing device for thermosetting polymer can be used to mix thermosetting polymer and additive, such as dual asymmetric centrifugal mixers, for example, FlackTek SpeedMixer bladeless mixer, Ross mixer, kneading mixer, two-roll mixer, three-roll mill or any other device that additive can be compounded into the thermosetting polymer.

[0037] Once the thermosetting polymer is mixed with the desired additives, it can be further processed. For example, a thermally stable, fire-resistant thermosetting polymer composition can be injection molded using processes such as reaction injection molding (RIM) or resin transfer molding (RTM). Alternatively, the thermosetting polymer can be compression molded.

[0038] Thermally stable, fire-resistant thermosetting polymers can be used in multilayer systems. In addition, the thermally stable, fire-resistant polymer composition can include additional support layers. Examples of possible support layers include, but are not limited to, metal support layers, such as aluminum foil, plates, and non-metallic support layers, such as polymer films and plates.

[0039] The thermally stable, fire-resistant thermosetting polymers of the present invention can be used for 3D printing. Any 3D printing method can be used, including but not limited to laser sintering, selective laser sintering, fused deposition modeling, fused filament fabrication, and digital light processing.

[0040] The heat-stable, fire-resistant thermosetting polymer compositions of the present invention have a variety of uses. For example, the thermosetting polymer compositions can be made into connectors, wires, cables, printed circuit boards or EMI shielding and other computer components. The thermosetting polymer compositions can be used to make electronic components that meet the UL 94V standard, such as smart phones, motors, electric powertrains (e-powertrains), batteries and battery housings, chargers for electric vehicles, and other components of electric vehicles. The thermosetting polymer compositions can be used in the construction industry for any object that may cause a fire hazard due to overheating or short circuiting of electronic devices used in the object. In addition, the heat-stable, fire-resistant thermosetting polymer compositions of the present invention can be used to form any type of outer cover or housing that requires fire resistance.

[0041] It is believed that when the heat-stable, fire-resistant thermosetting polymer composition with ceramic filler and optional additive is subjected to fire or high temperature (greater than or equal to 500°C), energy is released due to thermal decomposition. When the polymer composition is degraded due to flame or high temperature, it forms inorganic residues, and char, which plays a role in providing good cohesion between the polymer composition and the inorganic residue. On the surface of the inorganic residue, a ceramic layer is also formed for the residue to provide reinforcement. It is believed that the structure obtained after the thermosetting polymer composition is degraded due to flame or high temperature is fireproof by blocking heat transfer, and isolates the contact between the thermosetting polymer and oxygen, thus working in flame retardant and fireproof. This structure helps the basic thermosetting polymer composition to maintain good thermal stability, and keeps its insulation. Insulation can be electrical insulation (i.e., higher than 10 6 Volume resistivity of ohm.cm, preferably higher than 10 9 The ceramic portion of the structure enhances the shape of an object made from the thermosetting polymer composition. In addition, it is believed that the structure absorbs soot particles, resulting in lower smoke content.

[0042] Example

[0043] In the following embodiment of hereinafter stating, unless otherwise specified, otherwise use the ceramizable filler bag that comprises the following: 65 % by weight of magnesium hydroxide, 13 % by weight of calcium hydroxide, 9 % by weight of aluminium hydroxide, and 13 % by weight of pyrogenic silica, all weights are based on total ceramizable filler bag weight.This ceramizable filler is used for various polymer compositions, and carries out fire resistance test.About fire resistance test, heat-stabilized, fire-resistant polymer composition is prepared into 1 mm thick sample.Sample is sandwiched between two metal plates, clamps, and its bottom face is encountered open flame, and temperature is about 1050 ℃ to about 1100 ℃.

[0044] The above-mentioned ceramizable filler bag is joined in rigid epoxy resin and flexible epoxy resin.Flexible epoxy resin is the epoxy resin with Shore A hardness less than 60 and elongation higher than 8%.Ceramic filler bag accounts for 50 weight % of polymer composition.Rigid epoxy resin is the EpoxiCure 2 resin system from Buehler (a department of Illinois Tool Works, Inc.).Flexible epoxy resin can be a flexible epoxy resin such as Duralco 4538 resin from Cotronics Corp.Composition can be made into 1 millimeter plate and carry out fire resistance test at 1100 ℃.Rigid epoxy resin fails and breaks, and flexible epoxy resin is self-supporting and does not break.

[0045] In another embodiment, a ceramizable filler package is added to the epoxy resin. A 1 mm plate is made from the sample and placed in a furnace at 800°C for 5 minutes. The sample forms a dense ceramic layer, is self-supporting, and maintains its shape.

[0046] Those skilled in the art will appreciate that, without departing from the principles of the invention, the invention may be used in a variety of modified forms of structure, arrangement, proportion, size, material and components, and the invention may adopt other forms used in the practice of the invention, which are particularly suitable for specific environments and operating requirements. Therefore, the presently disclosed embodiments are considered in all aspects to be illustrative and not restrictive, and the scope of the invention is defined by the appended claims and is not limited to the foregoing description or embodiments.

Claims

1. A thermally stable, insulating, fire-resistant thermosetting polymer composition comprising a thermosetting polymer and at least one additive, wherein the at least one additive comprises a ceramizable filler, wherein the thermosetting polymer composition is ceramized and maintains its insulating properties after exposure to high temperature or flame.

2. The composition of claim 1, wherein the thermosetting polymer is a flexible epoxy resin.

3. The composition of claim 1, wherein the ceramizable filler comprises fumed silica and a metal hydroxide, preferably wherein the ceramizable filler comprises fumed silica, magnesium hydroxide, calcium hydroxide and aluminum hydroxide.

4. The composition of claim 1, wherein the thermally stable, flame resistant polymer composition comprises a reinforcing filler, preferably wherein the reinforcing filler is selected from glass fibers, ceramic fibers, whiskers, polymer fibers, nanofibers or nano hollow fibers and blends thereof.

5. The composition of claim 1, wherein the composition retains its mechanical properties after exposure to high temperature or flame.

6. A method for forming a thermally stable, fire-resistant thermosetting polymer composition, the method comprising: mixing a thermosetting polymer with at least one additive, the at least one additive comprising a ceramizable filler; and exposing such thermosetting polymer composition to high temperature or flame to form a ceramizable layer.

7. The method according to claim 6, wherein the ceramizable filler comprises fumed silica and a metal hydroxide, preferably wherein the ceramizable filler comprises fumed silica, magnesium hydroxide, calcium hydroxide and aluminum hydroxide.

8. The method of claim 6, wherein the thermosetting polymer is a flexible epoxy resin.

9. An object made of a thermally stable, fire-resistant thermosetting polymer comprising the thermosetting polymer and a ceramizable filler, wherein the object can withstand high temperatures or flames.

10. The object of claim 9, wherein the thermosetting polymer is a flexible epoxy, preferably wherein the flexible epoxy has a Shore A hardness of less than 60 and an elongation greater than 8%.

11. The object according to claim 9, wherein the ceramizable filler comprises fumed silica and a metal hydroxide, preferably wherein the ceramizable filler comprises fumed silica, magnesium hydroxide, calcium hydroxide and aluminum hydroxide.

12. A battery casing made from a thermally stable, fire-resistant thermosetting polymer composition comprising a thermosetting polymer and a ceramizable filler.

13. The battery housing of claim 12, wherein the thermosetting polymer is a flexible epoxy resin.

14. The battery housing of claim 12, wherein the ceramizable filler comprises fumed silica and a metal hydroxide.

15. The battery housing of claim 12, wherein the ceramizable filler comprises fumed silica, magnesium hydroxide, calcium hydroxide, and aluminum hydroxide.