Surface heating element and manufacturing method

Abstract

Surface Heating Element and Manufacturing Method. This invention relates to a surface heating element that generates heat using electricity and a method for manufacturing the same. One embodiment of the invention provides a surface heating element comprising a NiCr alloy, having an adhesion strength of 3N or more relative to a substrate or insulating layer, and a resistivity of 10⁻⁶. ‑4 Ωcm to 10 ‑2 With a strength of Ωcm, this surface-type heating element can be used even at high operating temperatures above 400°C. It suppresses material release, has high fracture toughness, low coefficient of thermal expansion, and heat resistance, thereby improving product reliability and lifespan.

Description

[0001] This application is a divisional application of the original invention patent application No. 202010533321.3 (filed on June 12, 2020, invention title: surface heating element and manufacturing method). Technical Field

[0002] This disclosure relates to a surface heating element and a method for manufacturing the same, which uses electricity to generate heat in the field of heating devices such as electric furnaces. Background Technology

[0003] A stove, used as a household or commercial cooking appliance, is a cooking appliance that heats food contained in a container by heating a container placed on the upper surface of the stove.

[0004] Traditionally, stoves used gas stoves that produced flames by using gas, but gradually, electric stoves have come into use, which include surface heating elements that generate heat by applying an electric current.

[0005] As surface-type heating elements, those currently in use are metal heating elements made by etching thin metal plates containing iron, nickel, silver, or platinum, or ceramic sintered bodies made by sintering non-metallic heating elements containing silicon carbide, zirconium oxide, or carbon.

[0006] Recently, a method for manufacturing surface heating elements has been disclosed that does not require the high-temperature heat treatment required for manufacturing conventional surface heating elements, such as the photonic sintering method disclosed in Korean Patent No. 10-1637122 (registered on June 30, 2016, and hereinafter referred to as the "Prior Art").

[0007] The existing photonic sintering method is a method of sintering a paste containing ceramic powder by using white light to irradiate the paste.

[0008] Existing surface heating elements, including those containing ceramic powder, have the following fundamental problems.

[0009] First, because most ceramic materials are non-conductive, they have an inherently high resistivity compared to conductive metallic materials.

[0010] The high resistivity of ceramic materials reduces the output of surface heating elements, thereby limiting the operating temperature of the finished stove.

[0011] In addition, ceramic materials have poor mechanical properties due to their low ductility and low toughness.

[0012] In particular, because ceramic materials have low toughness, the separation and damage of surface heating elements are caused by thermal deformation or thermal stress caused by repeated heating and cooling of the surface heating elements, as well as impacts caused by cooking utensils.

[0013] Furthermore, the coefficient of thermal expansion of ceramic materials differs greatly from that of glass, which is commonly used as a substrate for stoves and the like.

[0014] As the difference in thermal expansion coefficients between the substrate and the surface heating element increases, the difference in their thermal deformation also increases, resulting in higher thermal stress or thermal shock being applied to the surface heating element.

[0015] At the same time, when a metal material is used as a surface heating element, the metal material is different from the ceramic material that will be used as the substrate, thus causing different problems from the ceramic material in the prior art.

[0016] First, the problem of joining dissimilar materials is one of the long-standing unsolved challenges in the field of materials science.

[0017] Traditional surface heating elements are manufactured by a thermal sintering method, in which a paste is made by adding a large amount of glass material with a bonding function to a metal material powder, and then heating the paste at a high temperature.

[0018] However, the hot sintering method has a fundamental problem of causing deformation of the glass substrate. Furthermore, when the amount of glass frit added to the paste is less than or equal to a certain weight percentage (hereinafter also referred to as "wt%" or "%)), the adhesion between the substrate and the surface-type heating element, which includes a metallic material as a main component, decreases, causing the surface-type heating element to peel off or separate from the substrate. On the other hand, when the amount of glass frit added to the paste is increased, the resistivity, an inherent advantage of metallic materials, cannot be satisfied.

[0019] Meanwhile, although the prior art mentions that it is feasible to use metal materials for photonic sintering, no surface heating element made of metal materials is disclosed in any of the embodiments.

[0020] In particular, the metallic materials described in the prior art inherently lack high melting points; furthermore, alloys of metallic materials with other components have low melting points. Therefore, when metallic materials are used in surface-type heating elements for extended periods, metallic components may diffuse or leach out, leading to a reduction in product lifespan and reliability.

[0021] In addition, existing technologies have proposed components such as lithium, sodium, potassium, cadmium, mercury, boron, potassium, silicon, and germanium as metallic materials, and all of the above components are difficult to use or prohibited from being used as surface heating elements, and have problems including non-metallic or semiconductor. Summary of the Invention

[0022] In order to solve the above problems, this disclosure aims to provide a surface heating element with metal material as the main component.

[0023] Specifically, this disclosure aims to provide a surface heating element comprising a metallic material as a main component and a method for manufacturing the same, wherein the metallic material enables stable output at the operating temperature of the stove without reducing the output of the surface heating element or increasing the thickness of the surface heating element.

[0024] More specifically, this disclosure aims to provide a surface heating element and a method of manufacturing the same, the surface heating element comprising a metallic material having a low temperature coefficient of resistance, the metallic material indicating a resistance value that varies with temperature, thereby ensuring user safety against overcurrent by reducing the initial surge current required when the surface heating element starts operating.

[0025] In addition, this disclosure aims to provide a surface heating element and a method for manufacturing the same, the surface heating element comprising a metallic material as the main component, the metallic material having high resistance to thermal stress or thermal shock and high resistance to external impact by ensuring high ductility and / or high toughness.

[0026] In addition, this disclosure aims to provide a surface heating element and a method for manufacturing the same, the surface heating element comprising a metal material for high temperature as the main component, the metal material having a small difference in the coefficient of thermal expansion between the substrate and / or insulating layer and the surface heating element, so as to reduce the thermal stress or thermal shock applied to the surface heating element.

[0027] In particular, this disclosure aims to provide a surface heating element and a method for manufacturing the same, wherein the surface heating element comprises a high-melting-point metal material for high temperatures as the main component, and is able to suppress the diffusion and detachment of the metal component even when used for a long time at high temperatures.

[0028] Furthermore, this disclosure aims to provide a surface heating element and a method for manufacturing the same, the surface heating element comprising a metal material as the main component, the metal material having excellent adhesion not only to substrates made of the same material, but also to substrates made of dissimilar materials.

[0029] The purpose of this disclosure is not limited to the objectives described above, and other objectives and advantages not mentioned herein may be understood from the following description and may be more clearly understood from exemplary embodiments of this disclosure. Furthermore, it will be apparent that the objectives and advantages of this disclosure may be achieved through schemes and combinations thereof indicated by the following aspects.

[0030] The main technical feature of a surface heating element according to one embodiment of the present disclosure for achieving the above objectives is that the surface heating element is made of a metallic material including a NiCr alloy.

[0031] Specifically, in a surface-type heating element according to one embodiment of the present disclosure, the Ni content of the NiCr alloy can be in the range of 60 wt% to 95 wt% (hereinafter also referred to as "%").

[0032] More specifically, the resistivity of a surface-type heating element according to one embodiment of this disclosure can be 10. -4 Ωcm to 10 -2 Within the range of Ωcm.

[0033] In particular, the adhesion strength of the surface heating element to the substrate or insulating layer beneath it for arranging the surface heating element can be 5N or more.

[0034] In this case, the substrate can be formed from any of glass, glass ceramic, Al2O3, AlN, polyimide, polyether ether ketone (PEEK), and ceramic.

[0035] Preferably, the substrate may be formed of glass or glass-ceramic.

[0036] More preferably, the substrate may be formed of glass ceramic.

[0037] The insulating layer may include any one of boron nitride, aluminum nitride, and silicon nitride.

[0038] The insulating layer may also include glass frit as an adhesive.

[0039] In this case, the adhesive or glass frit may include borosilicate components and / or bentonite components.

[0040] A method for manufacturing a surface heating element according to another embodiment of the present disclosure for achieving the above objectives has the main technical feature that the method includes: coating the substrate with a surface heating element layer by applying a surface heating element paste comprising a NiCr alloy component onto the substrate.

[0041] Specifically, the Ni content of the NiCr alloy powder can be in the range of 60wt% to 95wt% (hereinafter also referred to as "%"), and the particle size of the NiCr alloy powder can be from 10nm to 10μm.

[0042] In this case, the substrate can be formed from any of glass, glass ceramic, Al2O3, AlN, polyimide, polyether ether ketone (PEEK), and ceramic.

[0043] Furthermore, another key technical feature of the method for manufacturing a surface-type heating element according to another embodiment of the present disclosure is that the method includes: photonic sintering of the surface-type heating element paste comprising the NiCr alloy powder applied to the substrate.

[0044] Specifically, the total light irradiation intensity during the photonic sintering can be between 40 and 70 J / cm². 2 Within the range.

[0045] More specifically, a method for manufacturing a surface-type heating element of the present disclosure includes: coating the substrate with a surface-type heating element layer by applying a surface-type heating element paste comprising a NiCr alloy component onto the substrate; drying the applied surface-type heating element layer; and photonic sintering the dried surface-type heating element layer.

[0046] In addition, the method may also include forming an insulating layer on the substrate before coating with a surface-type heating element layer.

[0047] In this case, the insulating layer may include any one of boron nitride, aluminum nitride, and silicon nitride.

[0048] The insulating layer may include glass frit as a binder, and the binder includes borosilicate components and / or bentonite components.

[0049] In addition to the NiCr alloy powder, the surface heating element paste may also include glass frit, organic binder and solvent.

[0050] In addition, the surface heating element paste may also include additives.

[0051] As a specific and non-limiting embodiment, the surface heating element paste may include 30% to 80% NiCr alloy powder; less than 3% but not including 0% glass frit; 10% to 30% organic binder; 5% to 30% solvent; and 1 wt% to 10 wt% additives.

[0052] In this case, the organic binder may be ethyl cellulose, and the solvent may be butyl carbitol acetate. Attached Figure Description

[0053] The above and other objects, features, and advantages of this disclosure will become more apparent to those skilled in the art from the detailed description of exemplary embodiments thereof with reference to the accompanying drawings, in which:

[0054] Figure 1 This is a plan view of a surface heating device according to an embodiment of the present disclosure as viewed from above the substrate (10);

[0055] Figure 2 It shows along Figure 1 An enlarged cross-sectional view of an embodiment of a surface heating device with an AA′ section cut out;

[0056] Figure 3 It shows along Figure 1 An enlarged cross-sectional view of another embodiment of the AA′ section of the surface heating device;

[0057] Figure 4 This illustrates an embodiment in which a short circuit occurs in the heating element of the surface-type heating element layer during high-power operation due to a decrease in the resistivity of the substrate, causing damage to the heater module.

[0058] Figure 5 This indicates that at 40 J / cm 2 An image of the microstructure of the surface heating element layer 30 formed by the total light irradiation intensity;

[0059] Figure 6 This indicates that at 60 J / cm 2 Images of the microstructure of the surface heating element layer 30 formed by the total light irradiation intensity; and

[0060] Figure 7 This shows 70 J / cm 2 An image of the microstructure of the surface heating element layer 30 formed by the total light irradiation intensity. Detailed Implementation

[0061] The above-described objects, features, and advantages of this disclosure will be described in detail with reference to the accompanying drawings, thus enabling those skilled in the art to readily implement the technical concept of this disclosure. In the following description of this disclosure, detailed descriptions of the prior art will be omitted where it is determined that such detailed descriptions would unnecessarily obscure the subject matter of this disclosure. Exemplary embodiments of this disclosure will be described in detail below with reference to the accompanying drawings. In the drawings, the same reference numerals are used to indicate the same or similar components.

[0062] In the following text, the arrangement of any component on the “upper (or lower)” of a component or on (or below) a component may mean not only that any component is arranged to contact the upper (or lower) surface of the component, but also that other components are inserted between the component and any component arranged on (or below) the component.

[0063] In addition, it should be understood that when a component is described as “connected” or “coupled” to another component, the component can be directly connected or coupled to the other component, other components can be “inserted” between these components, or each component can be “connected” or “coupled” by means of other components.

[0064] The following describes some embodiments of surface heating elements and methods for manufacturing the same according to the present disclosure.

[0065] refer to Figures 1 to 3 An electric furnace 1 according to one embodiment of the present disclosure includes: a substrate 10, the surface of which is made of an electrically insulating material; an insulating layer 20 disposed on the substrate 10; a surface heating element layer 30 formed by sintering a predetermined powder containing oxide powder and disposed on the insulating layer 20 disposed on the substrate 10; and a power supply unit 50 configured to supply power to the surface heating element layer 30.

[0066] In this case, the substrate 10 can be manufactured in various sizes and shapes according to the needs of the apparatus using the electric furnace 1. As a non-limiting embodiment, the substrate 10 of this disclosure can be a plate-like member. In addition, the substrate 10 can have different thicknesses for each location in the substrate if necessary. Furthermore, the substrate 10 can be bent if necessary.

[0067] In this disclosure, the material forming the substrate 10 is sufficient as long as it is an insulating material, and there are no particular limitations. As a non-limiting embodiment, the substrate in this disclosure can be not only a ceramic substrate containing glass, glass-ceramic, alumina (Al2O3), aluminum nitride (AlN), etc., but also formed from polymeric materials such as polyimide (PI) or polyetheretherketone (PEEK). However, the substrate preferably includes any one of glass, glass-ceramic, and ceramic. This is because these materials essentially ensure insulating properties and are advantageous compared to other materials in terms of stain resistance, fingerprint resistance, and visual performance. In particular, glass-ceramic is most preferred because, compared to other ceramic materials, glass-ceramic, in addition to having the advantages of ordinary amorphous glass (such as transparency and aesthetics), also ensures impact resistance and low expansion.

[0068] As a non-limiting embodiment, the insulating layer 20 may be disposed on either of the two surfaces of the substrate 10 (i.e., the surface on which the surface heating element layer 30 is formed). When the electric furnace of the embodiments of this disclosure includes the insulating layer 20, the insulating layer 20 shall be formed on all or a portion of the substrate 10. In this case, the portion of the substrate refers at least to the part of the substrate 10 that can be touched by a user during furnace operation and / or the part where the surface heating element layer is in contact with the substrate.

[0069] The thickness of the insulating layer formed on the substrate after firing is preferably 5 to 100 μm. When the thickness of the insulating layer is less than 5 μm, it is difficult to ensure the electrical stability of the insulating layer. On the other hand, when the thickness of the insulating layer is greater than 100 μm, due to the material differences or differences in the coefficients of thermal expansion between the insulating layer, the substrate, and the surface heating element layer, problems such as the possibility of cracking may occur, resulting in the consumption of a large amount of material and an increase in processing time.

[0070] The insulating layer 20 preferably comprises any one of boron nitride, aluminum nitride, and silicon nitride as a main component, which can stably ensure resistivity even at high temperatures. All components share a common characteristic: they are ceramic-based insulators.

[0071] When an insulating layer 20 is formed between the substrate 10 and the surface heating element layer 30, the insulating layer can protect the user from electric shock caused by leakage current that may result from the decrease in resistivity of the substrate at high temperatures. Furthermore, the insulating layer 20, due to its relatively high resistivity at high temperatures, prevents short-circuit current in the surface heating element layer 30 during high-power operation (see [link to documentation]). Figure 4 As a result, damage to the surface heating element layer 30 can be prevented.

[0072] The insulating layer 20 of the embodiments of this disclosure should ensure adhesion to the substrate 10 and / or the surface heating element layer 30, and at the same time have a higher high-temperature resistivity than the substrate and compatibility with printing and subsequent processing.

[0073] Therefore, in embodiments of this disclosure, more preferably, the insulating layer 20 further includes an inorganic binder. More particularly, more preferably, the insulating layer 20 of embodiments of this disclosure includes a glass frit as an inorganic binder to reduce the firing temperature. More specifically, the insulating layer 20 of embodiments of this disclosure includes borosilicate and / or bentonite as a glass frit. Specifically, because borosilicate has approximately 50 × 10⁻⁶... -7 The coefficient of thermal expansion in m / ℃ is approximately the average of the coefficients of thermal expansion of the substrate 10 and the surface heating element layer 30, which will be described below. Therefore, it can help suppress cracks or peeling of the surface heating element layer 30 due to the difference in the coefficient of thermal expansion with respect to the substrate 10.

[0074] The electric furnace of the present disclosure includes an insulating layer 20 or a surface heating element layer 30 on a substrate 10. In this case, when viewed from above, the heating elements of the surface heating element layer 30 are arranged in a predetermined shape on the substrate 10 or the insulating layer 20.

[0075] For reference Figure 1In one embodiment, the heating element can be formed on the surface of the insulating layer 20 by extending circumferentially in a zigzag pattern while changing direction based on a semi-circle. In this case, the heating element can be formed continuously from the first terminal unit 31 to the second terminal unit 32 in a predetermined shape.

[0076] The surface-type heating element layer 30 of the embodiments of this disclosure comprises a NiCr alloy. In the NiCr alloy of this disclosure, the substrate is nickel (Ni), and chromium (Cr) is provided as a solute. In this case, the weight percentage of Cr content in the NiCr alloy (hereinafter also referred to as "wt%" or "%)) is preferably in the range of 5 to 40. When the Cr content in the Ni-Cr alloy is less than 5 wt%, the corrosion resistance decreases, and therefore the surface-type heating element layer may be susceptible to the effects of high temperatures or chemicals. On the other hand, when the Cr content is greater than 40 wt%, the processability of the Ni substrate, characterized by a face-centered cubic lattice, decreases, and the heat resistance of the NiCr alloy decreases. As a result, when the electric furnace is used at high temperatures for extended periods, the lifespan and reliability of the electric furnace may be reduced.

[0077] Table 1 below summarizes the mechanical and electrical properties of the NiCr alloy used to form the surface heating element layer 30 of the embodiments of this disclosure, as well as the mechanical and electrical properties of materials currently in use or known for surface heating elements.

[0078] Mechanical / Electrical Properties of Materials Used in Surface Heating Elements

[0079] <![CDATA[Fracture toughness (MPam 1 / 2 )]]> Coefficient of thermal expansion (m / ℃) Resistivity (Ωcm) Ag 40～105 <![CDATA[180×10 -7 ]]> <![CDATA[1.6×10 -6 ]]> Lanthanum cobalt oxide 0.9～1.2 <![CDATA[230×10 -7 ]]> <![CDATA[9.0×10 -3 ]]> Glass 0.6～0.9 <![CDATA[1×10 -7 ]]> - <![CDATA[MoSi2]]> 6.0 <![CDATA[65~90×10 -7 ]]> <![CDATA[2.7×10 -5 ]]> SiC 4.6 <![CDATA[40×10 -7 ]]> <![CDATA[1.0×10 -2 ]]> NiCr 110 <![CDATA[120×10 -7 ]]> <![CDATA[1.4×10 -4 ]]>

[0080] First, as can be seen from Table 1, compared with other ceramic materials, Ag and NiCr exhibit very high fracture toughness due to the inherent ductility and stiffness of metals, which is one of their mechanical properties. When the material used for surface heating elements has high fracture toughness, the material itself has high resistance to the thermal shock generated when using surface heating elements, thus significantly improving the life and reliability of the electric furnace.

[0081] Furthermore, as can be seen from Table 1, the NiCr of the embodiments of this disclosure has a lower coefficient of thermal expansion than the existing Ag. The coefficient of thermal expansion is one of the important factors in determining thermal stress or thermal shock, which is derived from the temperature change that occurs when using a surface-type heating element. When NiCr alloy and Ag are exposed to the same temperature change, NiCr alloy has a lower coefficient of thermal expansion than Ag, and therefore experiences less thermal shock or thermal stress compared to Ag. In summary, the reduced thermal stress or thermal shock of surface-type heating elements made of NiCr alloy is beneficial for improving the lifespan and reliability of the electric furnace.

[0082] In addition to mechanical properties, resistivity is also shown in Figure 1. Most materials suitable for use as surface-type heating elements have a resistivity of approximately 10⁻⁶ at room temperature. -5 Ωcm to 10 -2 Ωcm, except for Ag. When the resistivity of a surface heating element is greater than 10 Ωcm. -2 At a resistivity of Ωcm, it may be impossible to design the heating element pattern due to the excessively high resistivity. Additionally, when the resistivity is greater than 10 Ωcm... -2 When the resistivity of the surface heating element is less than Ωcm, the output is too low, resulting in a low heating temperature, making it unsuitable for use as a cooking utensil. On the other hand, when the resistivity of the surface heating element is less than 10 Ωcm... -5 At Ωcm, the output is very high due to the extremely low resistivity, which results in excessively high temperatures from the heat generated by the applied current. This is unsuitable in terms of lifespan and reliability.

[0083] Based on the above criteria, it can be seen that Ag alone is not suitable for use as a surface heating element, while the NiCr alloy of the embodiments of this disclosure can be used alone as a surface heating element, and can also be used in combination with other components as a surface heating element.

[0084] Meanwhile, although not shown in Table 1, the materials used for surface heating elements need to have small resistivity changes depending on temperature.

[0085] The resistivity of a material typically changes with temperature. However, depending on the type of material, the nature of how resistivity changes with temperature varies considerably.

[0086] For example, in the cases of lanthanum cobalt oxide (LC) or ceramic materials (such as MoSi2 and SiC) shown in Table 1, electricity is typically transferred via lattice vibrations. As temperature increases, the lattice constituting the ceramic material vibrates more extensively and rapidly. Therefore, the resistivity of the ceramic material tends to decrease with increasing temperature.

[0087] On the other hand, in the metals shown in Table 1 (e.g., Ag and NiCr), electricity is transferred via free electrons. As temperature increases, the crystal lattice constituting the metal vibrates more extensively and rapidly. However, in the case of metals, electrical transfer is generally carried out by free electrons, and the movement of these free electrons is restricted by lattice vibrations. Therefore, the metal lattice vibrates more extensively and rapidly with increasing temperature, thus interfering with the movement of free electrons. As a result, the resistivity of the metal tends to increase with increasing temperature.

[0088] The resistivity of the NiCr alloy of this disclosure varies very little from room temperature to the maximum operating temperature at which the electric furnace can be used, within the range of 5%. When the NiCr alloy is used as a surface heating element for an electric furnace, the initial surge current required at the start of furnace operation is reduced, thereby eliminating the danger to the user caused by overcurrent, and enabling stable operation of the electric furnace without the need for additional units such as AC triodes (TRIACs).

[0089] On the other hand, when Ag is used as a surface heating element in an electric furnace, Ag’s low resistivity and high temperature coefficient of resistance lead to a risk of a significant increase in the initial surge current at the start of the furnace’s operation, and result in the disadvantage of needing a separate unit such as TRIAC.

[0090] In embodiments of this disclosure, the surface heating element layer 30 is thickly applied to the substrate 10 or the insulating layer 20 in the form of a paste.

[0091] The paste disclosed herein refers to a mixture of media containing essential components such as solvents and organic binders, as well as optional components such as various types of organic additives and particles (powders) of inorganic substances responsible for the main functions on the substrate after firing (or sintering).

[0092] More specifically, the surface-type heating element layer 30 of the embodiments of this disclosure comprises NiCr alloy powder. The NiCr alloy powder of the embodiments of this disclosure preferably has an average particle size (D50) of 10 nm to 10 μm. When the average particle size (D50) of the NiCr alloy powder is less than 10 nm, the surface area of ​​the powder increases excessively, and the activity of the powder increases. As a result, the NiCr alloy powder in paste form cannot be uniformly dispersed. On the other hand, when the average particle size (D50) of the NiCr alloy powder is greater than 10 μm, due to the excessively large particle size of the NiCr alloy powder, the necking between powder particles is small, or in other words, the powder cannot be uniformly dispersed. As a result, the resistivity increases excessively, and the adhesion between the surface-type heating element layer 30 and the substrate 10 or the insulating layer 20 below it decreases.

[0093] Meanwhile, the NiCr alloy powder of this disclosure can be prepared by various methods. As a non-limiting embodiment, the NiCr alloy powder can be prepared by the explosion of wires, thermal plasma treatment, etc., and can also be prepared by various methods other than the exemplary methods described above.

[0094] The NiCr alloy powder disclosed herein can be included in a paste along with other inorganic substances and a medium. More specifically, the paste of embodiments of this disclosure may include 30 to 80 wt% NiCr alloy powder, less than 3 wt% but not exceeding 0 wt% glass frit, 10 wt% to 30 wt% organic binder, 5 wt% to 30 wt% solvent, and 1 wt% to 10 wt% of various types of additives.

[0095] The NiCr alloy powder applied to the paste used to form the surface-type heating element layer 30 of this disclosure determines the electrical and mechanical properties of the surface-type heating element layer 30. Specifically, the NiCr alloy powder determines the resistivity of the final surface-type heating element layer 30 to determine the performance of the electric furnace including the surface-type heating element. Furthermore, the NiCr alloy powder determines the fracture toughness and adhesion of the surface-type heating element layer 30, thereby significantly affecting the lifespan and reliability of the electric furnace.

[0096] When the NiCr alloy powder content is less than 30 wt%, the resistivity of the final surface-type heating element layer 30 increases excessively. Furthermore, the thickness of the final surface-type heating element layer 30 after sintering may decrease excessively. On the other hand, when the NiCr alloy powder content is greater than 80 wt%, the adhesion between the final surface-type heating element layer 30 and the underlying insulating layer 20 decreases.

[0097] In the paste component, the glass frit serves as an inorganic binder that allows the surface heating element layer 30 to bond with the underlying insulating layer 20, and also plays a role in regulating the resistance of the surface heating element layer 30. Furthermore, the glass frit imparts electrode protection and insulation properties to the surface heating element layer 30.

[0098] When the glass frit content is 0 wt% (i.e., excluding the glass frit), the adhesion between the final surface-type heating element layer 30 and the underlying insulating layer 20 weakens. On the other hand, when the glass frit content is greater than 3 wt%, the resistivity of the final surface-type heating element layer 30 increases excessively, thus reducing its output.

[0099] In the paste components, when the paste is applied using methods such as screen printing, the organic binder plays a role in mixing the NiCr powder and glass frit to disperse the mixture, and also affects the flowability of the paste and the stability of the coating.

[0100] The organic adhesives disclosed herein may include thermoplastic resins and / or thermosetting resins. As thermoplastic adhesives, acrylic-based, ethyl cellulose-based, polyester-based, polysulfone-based, phenoxy-based, and polyamide-based adhesives may be used. As thermosetting adhesives, amino, epoxy, and phenolic adhesives may be used; in this case, the organic adhesives may be used alone or in combination of two or more.

[0101] When the content of the organic binder is less than 10 wt%, the mechanical stability of the coating decreases when coated with the surface heating element paste, making it difficult to maintain the coating stably. On the other hand, when the content of the organic binder is greater than 30 wt%, the mechanical stability of the coating decreases due to its high fluidity, and the thickness of the surface heating element layer 30 is ultimately excessively reduced.

[0102] The solvent is preferably highly volatile, sufficient to evaporate even under relatively low levels of heat at atmospheric pressure, while ensuring complete dissolution of the organic matter (especially polymers) in the paste. Furthermore, the solvent should boil sufficiently at a temperature below the decomposition temperature or boiling point of any other additives contained in the organic medium. That is, solvents with a boiling point less than 150°C measured at atmospheric pressure are most commonly used.

[0103] The solvents disclosed herein are selected according to the type of organic adhesive. Commonly used solvents include aromatic hydrocarbons, ethers, ketones, lactones, ether alcohols, esters, diesters, etc. As non-limiting examples, such solvents include butylcarbitol, butylcarbitol acetate, acetone, xylene, methanol, ethanol, isopropanol, methyl ethyl ketone, ethyl acetate, 1,1,1-trichloroethane, tetrachloroethylene, amyl acetate, 2,2,4-triethylpentanediol-1,3-monoisobutyrate, toluene, dichloromethane, and fluorocarbons. In this case, the solvent can be used alone or in combination of two or more. In particular, solvents that are mixed with other solvents are preferred for complete dissolution of the polymer adhesive.

[0104] When the solvent content is less than 5 wt%, the paste does not have sufficient fluidity, making it difficult to form the surface heating element layer 30 by coating methods such as screen printing. On the other hand, when the solvent content is greater than 30 wt%, the paste has high fluidity, thus reducing the mechanical stability of the coating.

[0105] The paste disclosed herein may include additives such as plasticizers, release agents, dispersants, removers, defoamers, stabilizers, and wetting agents. As a non-limiting embodiment, phosphate-based dispersants may be added to uniformly disperse the NiCr powder.

[0106] After preparation, a paste for forming the surface-type heating element layer 30 of this disclosure is applied to the surface of a substrate or insulating layer. The paste can be prepared by mixing NiCr alloy powder, glass frit powder, organic solvent, organic binder, and additives at 10°C to 30°C for 2 to 6 hours using a mixer and a three-roll mill. As a non-limiting embodiment of the coating method, a screen printing machine can be used to apply the paste. As another embodiment, the surface-type heating element layer can be formed by casting the paste onto another flexible substrate, removing volatile solvents while heating the cast layer to form a green tape, and then using rollers to laminate the tape onto the substrate.

[0107] Following the coating step, the applied paste for the surface-type heating element layer 30 is dried at a predetermined temperature. The drying step is typically carried out at a relatively low temperature of 200°C or lower. During the drying step, the solvent is primarily evaporated.

[0108] After the drying step, the surface heating element layer 30 can be formed by a firing process such as sintering.

[0109] In conventional processes for manufacturing surface-mount heating elements, prolonged high-temperature heat treatment is performed to sinter components with high melting points, such as metal alloys and ceramics. This prolonged high-temperature heat treatment requires an isolated system (e.g., internal insulation). Furthermore, surface-mount heating elements can become contaminated by pollutants in the prolonged high-temperature atmosphere, thus damaging the heating element. Additionally, because the underlying insulating layer 20 and / or substrate 10 are also exposed to the prolonged high-temperature atmosphere, the materials that can be used as the insulating layer 20 and substrate 10 are severely limited, and the insulating layer 20 and substrate 10 are highly susceptible to contamination.

[0110] On the other hand, in the manufacturing method of the surface heating element disclosed herein, a heat treatment method that does not require long-term high-temperature heat treatment is used to sinter the surface heating element layer 30. Therefore, in the manufacturing method of the surface heating element disclosed herein, a photonic sintering process using intense pulsed white light is employed.

[0111] As a non-limiting embodiment, intense pulsed white light emitted from a xenon lamp can be used. When a dried paste for a surface-type heating element is irradiated with intense pulsed white light, the paste is sintered by the radiation energy of the intense pulsed white light, thereby forming a surface-type heating element.

[0112] More specifically, when a dried paste is irradiated with intense pulsed white light, the organic matter (especially the binder) present in the paste is first burned off. In the preceding drying step, the solvent in the organic media component constituting the paste is largely evaporated. Therefore, after the drying step, the binder in the remaining organic media component serves to bind the solid powder components in the dried paste, thus maintaining the mechanical strength of the dried paste. Subsequently, in the initial stage of photon sintering, the binder is eliminated by the radiant energy of the intense pulsed white light; this phenomenon or step is called binder burn-off.

[0113] After the binder is burned off, most of the organic mediator components are no longer present in the paste. Therefore, the remaining powder components are sintered by irradiation with intense pulsed white light to form the final surface-type heating element layer 30. In this case, the NiCr alloy powder, as a powder component, is sintered by intense pulsed white light to form necks between the individual powder particles, thereby reducing the macroscopic resistivity of the surface-type heating element layer 30.

[0114] The total light irradiation intensity in the photonic sintering process disclosed herein is preferably 40 J / cm². 2 Up to 70J / cm 2 Within the range. When the total light intensity is less than 40 J / cm². 2 At this time, it is difficult to form necking and coupling between NiCr powder particles, resulting in excessively high resistivity of the surface-type heating element layer 30. On the other hand, when the total light irradiation intensity is greater than 70 J / cm 2 At that time, NiCr particles were oxidized due to excessive light irradiation intensity, and the oxide film formed on the surface of NiCr particles caused an excessive increase in the resistivity of the surface heating element layer 30.

[0115] Furthermore, throughout the entire photonic sintering process, the photonic sintering process disclosed herein can be operated with 1 to 30 pulses. The pulse duration (or pulse on-time) is preferably in the range of 1 to 40 ms, and the pulse interval (or pulse off-time) is preferably in the range of 1 to 500 ms.

[0116] The surface heating element layer 30, ultimately sintered using the photonic sintering process disclosed herein, preferably has a thickness of 1 to 100 μm. When the thickness of the surface heating element layer 30 is less than 1 μm, it is difficult to ensure dimensional stability of the surface heating element layer, and the thermal and mechanical stability of the surface heating element layer 30 decreases due to localized heating. On the other hand, when the thickness of the surface heating element layer 30 is greater than 100 μm, due to differences in the materials or coefficients of thermal expansion of the insulating layer, the substrate, and the surface heating element layer 30, problems such as a high probability of cracking and increased processing time arise.

[0117] Meanwhile, the surface-type heating element layer 30 using the NiCr alloy powder of this disclosure preferably has 10 -4 Up to 10 -2 The resistivity in Ωcm. When the resistivity of a surface heating element is greater than 10 Ωcm. -2 At a resistivity of Ωcm, the output of surface-mount heating elements decreases due to excessively high resistivity. Therefore, the thickness of the surface-mount heating element should be increased to reduce its resistivity. However, increasing the thickness also affects the coefficient of thermal expansion, thus significantly reducing the stability of the surface-mount heating element. On the other hand, when the resistivity of the surface-mount heating element is less than 10 Ωcm... -4 At a resistivity of Ωcm, due to the excessively low resistivity, a current exceeding the allowable current flows, resulting in an excessive increase in the output of the surface heating element. Therefore, to increase the resistivity of the surface heating element, the terminal resistance should be increased by reducing the thickness. However, excessively thin surface heating elements also lead to a decrease in their heat resistance.

[0118] Furthermore, the adhesion strength of the surface heating element layer 30 of the present invention relative to the underlying substrate 10 or insulating layer 20 is preferably 5.0 N or more. There is no upper limit to the adhesion strength of the surface heating element layer 30 disclosed herein. However, when the adhesion strength is less than 5.0 N, the surface heating element layer 30 may separate or break due to the excessively low adhesion strength, thereby reducing the lifespan and reliability of the electric furnace.

[0119] Example

[0120] In embodiments of this disclosure, a paste for a surface heating element comprising NiCr alloy powder, ethyl cellulose with an average molecular weight of about 100, butyl carbitol acetate solvent, and a phosphate-based dispersant is applied by screen printing for coating a surface heating element layer, then dried and photonic sintered to manufacture a surface heating element layer 30.

[0121] The adhesion strength of the surface-type heating element layer 30 disclosed herein was measured using an RST3 scratch tester, commercially available from Anton Paar GmbH. This tester measures the adhesion strength while increasing the load from 0 to 30 N, and in this case, the adhesion strength is measured under conditions where the scratch length at the tip is 5 mm.

[0122] Table 2 below shows the results of measuring the resistivity, oxygen content, adhesion strength, and sintering shrinkage of the surface-type heating element layer 30 under total light irradiation intensity conditions in the photonic sintering process of this disclosure.

[0123] Table 2 Evaluation based on the characteristics of total light intensity

[0124]

[0125] First, under the processing conditions of the embodiment (i.e., the total light irradiation intensity is 40 to 70 J / cm²), 2 Within a certain range, resistivity and adhesion strength are measured to meet the requirements of the surface-type heating element of this disclosure.

[0126] On the other hand, when the total light intensity is less than 40 J / cm 2 During this process, the NiCr alloy powder was not properly sintered. In other words, the surface-type heating element layer 30 had essentially the same state before and after photonic sintering. As a result, necking between the NiCr alloy powder particles was not properly formed, thus the surface-type heating element layer 30 had a high resistivity. Furthermore, the surface-type heating element layer 30 did not have sufficient adhesion strength to the substrate, and therefore separated from the substrate.

[0127] Simultaneously, with the increase of total light irradiation intensity, the NiCr alloy powder was sintered more fully and thus further densified. As a result, with the increase of light irradiation intensity, the sintering shrinkage rate increased, thus appropriately forming necking between NiCr alloy powder particles. Therefore, both resistivity and adhesion strength that meet specifications were measured.

[0128] On the other hand, when the total light intensity is greater than 70 J / cm 2 When the substrate shrinks due to excessive light intensity, it may crack or break in severe cases.

[0129] Figures 5 to 7 The embodiments of the present disclosure are shown at 40 J / cm. 2 60J / cm 2 and 70J / cm 2 The microstructure of the surface heating element layer 30 formed by the total light irradiation intensity.

[0130] like Figures 5 to 7 As shown, the surface-type heating element layer 30 exhibits a microstructure in which the necking between NiCr alloy powder particles develops better with increasing total light irradiation intensity. Furthermore, the trend of the microstructure according to the total light irradiation intensity level is highly consistent with the measurement results in Table 1. In other words, as the light irradiation intensity increases within the range of total light irradiation intensity according to the embodiments of this disclosure, the necking between NiCr alloy powder particles develops better, resulting in a decrease in resistivity and an increase in adhesion strength.

[0131] On the other hand, when the total light intensity is greater than 70 J / cm 2At that time, the NiCr alloy was excessively oxidized due to its high strength. As a result, the study found that even when the necking between NiCr alloy powder particles was fully formed, the resistivity of the surface heating element layer 30 increased excessively due to excessive oxidation, thus failing to meet specifications. In addition, the substrate shrank due to excessive light irradiation intensity, which in severe cases led to cracks or breakage.

[0132] According to this disclosure, a surface heating element designed using a metal component with a high melting point is provided, which can further increase the operating temperature of the electric furnace using the surface heating element, and improve the lifespan and reliability of the stove product by preventing the metal component from escaping at high temperatures.

[0133] Furthermore, the surface-type heating element according to this disclosure is designed to possess the inherent high ductility and fracture toughness of metal. Therefore, it is possible to ensure resistance to thermal stress and thermal shock caused by differences in temperature and coefficient of thermal expansion between the surface-type heating element and the underlying substrate or insulating layer.

[0134] Furthermore, the surface heating element of this disclosure is designed to have a lower coefficient of thermal expansion than other metals. As a result, the difference in the coefficient of thermal expansion between the surface heating element and the underlying substrate or insulating layer is reduced, thus reducing the thermal stress and thermal shock applied to the surface heating element.

[0135] Reduced thermal stress and thermal shock, along with ensured resistance to thermal stress and thermal shock, can significantly improve the lifespan and reliability of stoves, such as electric furnaces, as end products.

[0136] Furthermore, because the surface heating element of this disclosure comprises a metal with a low temperature coefficient of resistance (temperature coefficient of resistance refers to the change in resistance value with temperature), the initial surge current required when starting stove operation is reduced, thus ensuring user safety against overcurrent. In addition, the surface heating element of this disclosure eliminates the need for additional control units such as AC transistors (TRIACs).

[0137] Furthermore, the metallic material of the surface heating element disclosed herein can be used alone as a surface heating element without mixing with other metals or ceramic powders because the resistivity of the material itself is higher than that of other metals. Therefore, the surface heating element of this disclosure can exhibit improved reactivity with other materials, as well as the stability and storability of the paste, and also achieves cost reduction in terms of material costs.

[0138] Furthermore, the manufacturing method of the surface-type heating element according to this disclosure employs a photonic sintering method, thus eliminating the need for prolonged high-temperature heat treatment processes compared to conventional thermal sintering methods. Therefore, the manufacturing method of this disclosure ensures design freedom in selecting the materials for the substrate and / or insulating layer by eliminating prolonged high-temperature processes.

[0139] Furthermore, the method for manufacturing the surface heating element disclosed herein can provide a surface heating element of higher quality by fundamentally eliminating material contamination that may be caused by the insulation system during long-term high-temperature heat treatment.

[0140] Meanwhile, the manufacturing method of the surface-type heating element disclosed herein essentially eliminates the need for an insulation system required for high-temperature heat treatment. Furthermore, it eliminates the need for additional facilities to generate a reducing process atmosphere, thus simplifying the process setup. In addition, the photonic sintering method in this disclosure shortens the cycle time of the entire process by reducing the unit process time, thereby improving productivity.

[0141] Although this disclosure has been described above with reference to the accompanying drawings, it is obvious that this disclosure is not limited to the embodiments and drawings disclosed herein, and various modifications can be made by those skilled in the art within the spirit and scope of this disclosure. Furthermore, even if the effects of the construction of this disclosure are not explicitly described in the above description of the embodiments, it is obvious that the predictable effects should be understood through the corresponding construction.

Claims

1. A surface heating element comprising a surface heating element layer, wherein: The surface-type heating element layer comprises a NiCr alloy; The adhesion strength of the surface heating element layer to the substrate or insulating layer is 5N or more; and The surface type heating element has a resistivity in the range of 10 -4 Ωcm to 10 -2 Ωcm. The substrate is formed from any one of glass, glass ceramic, Al2O3, AlN, polyimide, polyetheretherketone (PEEK), and ceramic.

2. The surface-type heating element according to claim 1, wherein, The insulating layer includes any one of boron nitride, aluminum nitride, and silicon nitride.

3. The surface-type heating element according to claim 2, wherein, The insulating layer includes glass frit as an adhesive.

4. The surface-type heating element according to claim 3, wherein, The glass material includes at least one of borosilicate and bentonite components.

5. A method for manufacturing a surface heating element to generate heat using electricity, the method comprising: A substrate is provided, wherein the substrate is formed of any one of glass, glass ceramic, Al2O3, AlN, polyimide, polyetheretherketone (PEEK), and ceramic; The substrate is coated with a surface heating element layer by applying a surface heating element paste comprising a NiCr alloy component onto the substrate. The applied surface heating element layer is dried, wherein the surface heating element paste comprises: 30 wt% to 80 wt% NiCr alloy powder; less than 3 wt% but not exceeding 0 wt% glass frit; 10 wt% to 30 wt% organic binder; 5 wt% to 30 wt% solvent; and 1 wt% to 10 wt% additives; and Photonic sintering is performed on the dried surface heating element layer.

6. The method according to claim 5, further comprising: An insulating layer is formed on the substrate before the surface heating element layer is coated.

7. The method according to claim 6, wherein, The insulating layer includes any one of boron nitride, aluminum nitride, and silicon nitride.

8. The method according to claim 7, wherein, The insulating layer includes glass frit as an adhesive.

9. The method according to claim 8, wherein, The glass material includes at least one of borosilicate and bentonite components.

10. The method according to claim 5, wherein, The Ni content of the NiCr alloy powder is in the range of 60wt% to 95wt%, and The average particle size of the NiCr alloy powder is 10 nm to 10 μm.

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