Printable NTC ink composition and method for manufacturing the same

Abstract

The present disclosure relates to a negative temperature coefficient (NTC) article and method of making the same, comprising a conductive percolated network of a material having a negative temperature coefficient (NTC) that can be printed as particles in a crosslinked dielectric polymer matrix. The particles comprise a spinel phase and contain at least a first metal M, preferably manganese (Mn). I and the second metal M, which is nickel (Ni). II The particles also include a C-spinel phase having the general formula M3O4, including: ##STR1## The particles also include a nickel oxide phase. The printable NTC material can be dispersed in a printable NTC ink including a dispersant, and can form an NTC product, such as a thermistor, after drying of the dispersant. During processing, the ink is maintained at a temperature of 300°C or less. Optionally, the spinel phase can be further dispersed with an additional metal, M III The weight fraction of nickel oxide (NiO) relative to the total mass of the printable NTC material is preferably in the range of 1 to 20 wt %.

Description

[Technical Field]

[0001] This disclosure relates to materials having a negative temperature coefficient (NTC), particularly powders, and methods for producing the same. This disclosure further relates to printable ink compositions containing NTC materials and methods for producing the same. [Background technology]

[0002] Materials with a negative temperature coefficient (NTC), such as ceramics, are used as sensing materials for temperature sensors in a variety of applications. These applications include washing machines, battery chargers, and air conditioning units. NTC ceramics are based on ceramics primarily composed of oxides of transition elements such as Mn, Fe, Co, Ni, and Cu. Dense, homogeneous ceramics, such as single-phase ceramics, are generally obtained by sintering. The production of dense ceramics typically involves heating a mixture of precursor materials to a temperature of approximately 1200 degrees Celsius or higher in the presence of air. At this temperature, the precursor materials are observed to crystallize into a single spinel crystal structure, resulting in the desired NTC properties.

[0003] For obtaining ceramic NTC products, for example temperature sensors of a given shape or dimension, two main routes are known. The first involves sintering a mixture of precursor materials, for example in a mold, into a predetermined form. Usually, the mixture is shaped by uniaxial pressure or hydrostatic pressure. After sintering, the ceramic scan is further machined, for example by sawing and / or mechanical milling, to the final form. Thus, a dense NTC product having a predetermined shape, for example the active component of a temperature sensor, can be obtained. Forming a sensor by sintering the starting material into the desired shape requires the design and manufacture of a mold, which slows down the process, is costly, lacks flexibility for design changes, and / or is unsuitable for small-scale batch production processes. Alternatively, NTC products having a special shape can be obtained by deposition of a composition containing preformed ceramic NTC particles, for example by sputtering or printing of thin films. Such particles can be obtained by milling or grinding a pre-fired NTC product or a sintered NTC product.

[0004] European Patent No. 2546840 discloses a method for manufacturing a ceramic thermistor having surface-mountable negative characteristics and containing at least one of Mn and Ni and Co. The manufacturing includes firing a dried and shaped green ceramic sheet containing a powdered ceramic material. To prevent erosion, Ti is incorporated into the ceramic material within a predetermined range for the combination of Mn, Ni and Co.

[0005] U.S. Patent No. 5,976,421 discloses a thermistor (also called an NTC resistor) of a ceramic material of indium-containing oxide of spinel. The manufacturing includes forming a mixture of a pre-calcined mixture of a starting formulation of appropriate metal oxides and a binder composition into a shaped body. The shaped body is sintered by a sintering process at 1250 °C to form a spinel NTC phase. The mixture of pre-calcined metal oxides is made by weighing appropriate metal precursor compounds in a ratio according to the desired spinel composition.

[0006] International Publication No. 2018 / 164570 discloses a printed temperature sensor including a sensor material containing semiconductor fine particles including a ceramic NTC material having a negative temperature coefficient. The sensor material is formed by mixing fine particles having strong NTC behavior with a solvent in a dielectric matrix composition (e.g., including a polymer) to form the sensor material as an ink or a paste. The ink or paste is hardened or cured by crosslinking the dielectric matrix and / or evaporating the solvent without melting or sintering the fine particles. SUMMARY OF THE INVENTION PROBLEMS TO BE SOLVED BY THE INVENTION

[0007] An object of the present invention is to improve the above by providing a printable NTC ink composition that gains benefits from improved applicability and / or provides improved stability over time against elevated temperature and / or high humidity. MEANS FOR SOLVING THE PROBLEMS

[0008] Aspects of this disclosure relate to methods for producing NTC ink compositions. The method comprises producing a printable NTC material comprising particles. The particles comprise a spinel phase containing manganese (Mn) and nickel (Ni) and a nickel oxide phase (NiO). The method further comprises dispersing the printable NTC material in a suitable printable carrier. Producing the printable NTC material involves mixing particles of at least a first ceramic precursor material containing Mn oxide and particles of a second ceramic precursor material containing Ni oxide. The particles of the first and second ceramic precursor materials have diameters ranging from 100 nanometers to 100 micrometers. The second ceramic precursor material is added to the first ceramic precursor to form a spinel phase and a nickel oxide phase as the second phase. Producing the printable NTC material further comprises heating the mixture of ceramic precursor materials at a temperature of 800°C to 1000°C in the presence of oxygen to form a printable NTC material comprising particles containing the spinel phase and the nickel oxide phase. Spinel is represented by the general formula M I M II Characterized by O4, spinel contains Mn and Ni. The weight fraction of the nickel oxide phase relative to the total mass of the printable NTC material ranges from 1 to 30% by weight.

[0009] In a further embodiment, the present invention relates to an NTC ink composition. The NTC ink composition comprises an NTC material, for example, a printable NTC material obtainable by the method according to the present invention. The printable NTC ceramic ink composition comprises an acceptable printable carrier and a printable NTC material dispersed in the carrier. The printable NTC material comprises particles having a diameter in the range of 100 nanometers to 50 micrometers. At least a substantial portion of the particles comprises a spinel phase and a nickel oxide phase. The spinel phase is generalized by formula M I M II O4 [in the formula, M I represents Mn, and M IIIt can be characterized by [containing Mn and Ni]. The weight fraction of nickel oxide present as the second phase relative to the total mass of the printable NTC material is in the range of 1 to 30% by weight. Generally, the printable medium comprises a (curable) polymer and / or its precursor, a solvent or mixture of solvents, and optionally a dispersant.

[0010] NTC ink compositions can be used to manufacture NTC products, such as thermistors, by a method including solvent removal. Depending on the chemical properties of the polymer, the method may include polymer curing. Advantageously, as described herein, the inks enable the formation of NTC products with improved NTC properties, such as printing. NTC products can be provided in a wide variety of three-dimensional shapes without requiring complex molding and / or sintering processes.

[0011] In conjunction with the use of the ink composition, further or additional embodiments of the present disclosure relate to products having a negative temperature coefficient (NTC) and to methods for producing products having a negative temperature coefficient (NTC), which include curing the ink and evaporating the solvent contained in the ink.

[0012] The features, aspects and advantages of the apparatus, systems and methods of this disclosure, as well as other features, aspects and advantages, will be better understood from the following description, the appended claims and the appended drawings. [Brief explanation of the drawing]

[0013] [Figure 1] Figure 1 shows the phase diagram of a Mn-Ni oxide composition. [Figure 2] Figure 2 shows the phase diagram of the Mn-Ni oxide system obtained at a cooling rate of 300°C / hour (top) and the phase diagram of the Mn-Ni oxide system obtained by quenching (bottom). [Figure 3] Figure 3 schematically shows the method for producing the NTC ink composition according to the present invention. [Figure 4]Figure 4 shows the XRD diffraction pattern of the printable NTC material according to the present invention. [Figure 5] Figure 5 compares the time behavior of a reference thermistor and a thermistor manufactured using the ink according to the present invention. [Modes for carrying out the invention]

[0014] The terms used to describe specific embodiments are not intended to limit the invention. Where used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless otherwise explicitly indicated in the context. The term “and / or” includes any and all combinations of one or more of the listed items relating to the invention. The term “comprises and / or comprising” indicates that a described feature is present, but it should be understood that this does not preclude the presence or addition of one or more other features. Where a particular step in a method is referred to as following another step, it should be understood that, unless otherwise specified, the particular step may immediately follow the other step, or one or more intermediate steps may be performed before the particular step is executed. Similarly, where connections between structures or components are described, it should be understood that, unless otherwise specified, the connection may be established directly or via an intermediate structure or component.

[0015] The present invention will be described in more detail below with reference to the accompanying drawings illustrating embodiments of the invention. In the drawings, absolute and relative sizes of systems, components, layers, and areas may be exaggerated for clarity. Embodiments may be described with reference to schematic and / or cross-sectional views of possible idealized embodiments and intermediate structures of the invention. In the description and drawings, similar numbers refer to similar elements throughout. Relative terms and their derivatives should be interpreted as referring to the orientation described below or the orientation shown in the drawings being considered. These relative terms are for illustrative purposes only and do not require the system to be constructed or operated in a particular orientation unless otherwise stated.

[0016] As used herein, the terms “ceramic” or “dense ceramic” can be understood to refer to sintered macroscopic products, such as NTC active elements of sensors formed from sintered precursor materials, and not to NTC materials formed using the NTC particles of the present invention. It can be understood that the NTC particles are not sintered into a single macroscopic phase.

[0017] Spinel is a general formula AB2X4 or M I M II It can be understood as a class of minerals in O4. Spinel crystallizes in a cubic (isoaxial) crystal system, with anion X (generally a chalcogen like oxygen) arranged in a cubic close-packed lattice, and cations A and B occupying some or all of the octahedral and tetrahedral sites in the lattice. The mineral spinel MgAl2O4 has the usual spinel structure. Note that if the Ni content is low and the Mn content is high, tetragonal spinel is formed.

[0018] As a known manufacturing method of ceramics, for example, in International Publication No. 2018 / 164570 or U.S. Patent No. 5,976,421, materials (precursors) are generally provided in a relative ratio such that a single spinel phase is formed after calcination. As described in the publication by Groen et al. (W.A. Groen, C. Metzmacher, P. Huppertz and S. Schuurman, “Aging of NTC Ceramics in the system Mn-Ni-Fe-O” Journal of Electroceramics 7, 77 (2001)), in order to obtain a long-term stable ceramic, a composition close to the composition in which the formation of NiO is observed is required. This means that for ceramics sintered at a temperature of 1200 °C, it must have a composition of approximately Mn(Mn 1.35 Ni 0.65 )O4. When the Ni content is higher, ceramics in which NiO is formed adjacent to the spinel phase are formed.

[0019] Figure 1 shows a phase diagram experimentally derived in the formation of Mn-Ni-oxide-based ceramics according to the present invention. Figure 2 details the phase diagram of the Mn-Ni-oxide system in the temperature range of 1000 to 1300 °C. In Figures 1 and 2, the observed phases are marked at the corresponding locations in the phase diagram. Some of the tested compositions are marked with dots. The tested compositions are marked with dots. The upper figure in Figure 2 is for the case of the system obtained at a cooling rate of 300 °C / hour, and the lower figure in Figure 2 is for the case of the system quenched after heating.

[0020] As disclosed herein, and as seen in Figures 1 and 2, a single spinel phase having a high nickel content (e.g., Mn[[ID= (13]] 3-x Ni xCeramics essentially formed in the formula (where x > approximately 0.6) can be manufactured as long as heating does not result in exceeding the phase boundary 10, for example, as long as the temperature does not exceed approximately 1050°C. The formation of ceramics with macrophase-separated second phases can be avoided by not sintering the printable NTC material and / or not exposing the mixture of ceramic precursors to temperatures above approximately 1050°C. The formation of multiphase ceramics makes it difficult to produce high-quality thermistors in terms of homogeneity and / or long-term stability. In general, it is considered difficult to produce ceramic products with good homogeneity from multiphase systems.

[0021] In the field of NTC ceramics, ceramics or mixtures for their manufacture having the compositions specified herein, i.e., relatively high nickel or nickel oxide content, are generally considered unsuitable as starting materials for manufacturing ceramic thermistors. This is because sintering of such mixtures, which is considered an essential step, is known to cause unfavorable phase separation. Furthermore, the phase separation process leads to the formation of heterogeneous ceramics. For example, in sintered products containing a continuous macrophase-separated NiO phase under thermal load, cracking of the sintered product can occur due to the essential difference in thermal expansion between the spinel phase and the NiO phase.

[0022] As described herein, the inventors have surprisingly found that sensor materials, such as thermistors, formed from printable NTC materials advantageously exhibit improved long-term stability and / or reduced electrical resistance drift over time. By not subjecting the printable NTC material to the sintering step typically performed to produce dense ceramics, it is possible to avoid macroscale phase separation, such as demixing or formation of multiphase ceramics, including ceramics having a separated nickel oxide phase in addition to the Mn-Ni spinel phase.

[0023] The inventors believe that the observed stability may be due to the relatively high nickel oxide content incorporated into the printable NTC material particles (at the mesoscale level, rather than the macroscale level, i.e., within the dimensions of the formed particles (100 nm to 100 μm)), which may mitigate problems related to mechanical stability, such as mechanical stability against thermal loads, but do not wish to be constrained by any theory.

[0024] Figure 3 schematically shows a method 100 for producing a printable NTC ink composition according to the present invention.

[0025] A method for producing an NTC ink composition includes a step 1 of mixing at least a first ceramic powder precursor material and a second ceramic powder precursor material, a second step 2 of heating the mixture, and a third step of dispersing the formed printable NTC material in a suitable carrier.

[0026] Generally, the first ceramic precursor material contains a type A metal, i.e., a metal incorporated into the A position of the spinel phase, such as manganese. Generally, the second ceramic precursor material contains a type B metal, such as nickel, incorporated into at least a portion of the B position of the spinel phase. The precursor, also called the starting compound, is supplied, e.g., weighed, according to the desired composition. The mixture comprises at least a Mn oxide-based ceramic precursor and a second ceramic precursor material containing nickel oxide. It will be understood that the second ceramic precursor material is added to the first ceramic precursor material in an amount that contains at least the amount necessary to form the spinel phase. Furthermore, the mixture contains an excess of precursor material to form the nickel oxide phase. The exact amount of ceramic precursor material can be calculated depending on the amount of the desired NiO phase relative to the total printable NTC material and the overall composition of the desired spinel phase. For example, if the goal is to produce a printable NTC material having a spinel phase with 10 grams of general composition Mn2NiO4 and 2 grams of NiO (20 wt%), a suitable precursor mixture may contain approximately 6.8 grams of Mn2O3 and 3.2 + 2.0 = 5.2 grams of NiO.

[0027] In principle, any suitable type of ceramic precursor material (starting compound) or combination thereof can be used. Suitable starting compounds include, but are not limited to, oxides, hydroxides, carbonates, acetates, and oxalates. In preferred embodiments, ceramic precursor materials are used that are essentially binary metal oxides of each metal present in the mixture, such as NiO and Mn2O3. In another or further embodiment, at least a portion of the first precursor material and / or the second precursor material is replaced with pre-sintered NTC ceramic particles.

[0028] Preferably, the ceramic precursors contained in the mixture are thoroughly mixed. Thorough mixing allows for the formation of a homogeneous powder mixture. Preferably, one or more, preferably all, of the ceramic precursor materials in the mixture are in powder form, such as fine particles. Generally, the fine particles have a mass-average diameter of 100 nm to 50 micrometers, preferably 0.5 to 5 micrometers. Preferably, the particles have an average dimension (D) of 100 micrometers or less. 90 ) has. Preferably, all particles are smaller than 100 micrometers. Larger particles may reduce printability and / or lead to the formation of printed NTC products with inconsistent properties.

[0029] In some embodiments, one or more ceramic precursors are mechanically pulverized, for example, by ball milling or grinding, to obtain smaller fragments. Optionally, the particles are sieved through multiple sieves to provide a narrower particle size distribution. For example, sieving to obtain particle size distributions of less than 10 μm, 10–20 μm, and greater than 20 μm. In some embodiments, the mixture of ceramic precursors is subjected to a mechanical pulverization step, such as grinding or milling. This can reduce the number of processing steps and / or improve the homogeneity of the mixture. We have found that smaller particles and / or better intermixing result in printable NTC materials with more reproducible electrical properties.

[0030] In step 2, the mixture is heated (calcined) in the presence of oxygen, generally air. The required calcination time can be experimentally determined, for example, by X-ray diffraction. It has been found that a calcination time of about 2 hours is usually sufficient. Calcination preferably involves exposing the mixture to a temperature of at least 750°C, for example, 850°C or higher. The temperature does not exceed the sintering conditions, for example, the temperature does not exceed 1200°C. Preferably, the temperature does not exceed 1100°C. Exposure to temperatures above 1100°C or 1200°C may result in sintering separation and / or macrophase separation, i.e., the formation of a macrophase-separated second phase in addition to the spinel phase. Therefore, the temperature during calcination is preferably in the range of about 800°C to about 1050°C, for example, in the range of 850°C to 1000°C. The inventors have found that calcination within the above temperature range promotes solid-phase reactions between the ceramic precursor materials, resulting in the formation of particles containing the spinel phase and the nickel oxide phase.

[0031] The oxidizing agent may be present in the mixture of ceramic precursors and / or added to the mixture of ceramic precursors. Generally, the mixture is calcined in the presence of air. Calcination in the presence of air favorably provides an excess of oxidizing agent, enabling spinel formation and, at the same time, allowing for the removal of potential contaminants, e.g., by burning.

[0032] As described, by calcining a mixture of ceramic precursor materials at a temperature within the above range for a suitable time in the presence of a suitable amount of oxygen, a spinel phase having a desired composition can be formed. The reaction product, e.g., printable NTC material, is not completely sintered. It may be advantageous for the particles in the formed powder (contained in the NTC material) to have dimensions similar to those of the precursor, for example, in the range of 100 nanometers to 100 micrometers, preferably in the range of 500 nanometers to 5 micrometers. At least a portion, preferably the majority, of the particles, most preferably 90% by weight or more of the particles, constitute the spinel phase. In addition to the spinel phase, the particles contain a NiO phase.

[0033] The amount of NiO in printable NTC materials is variable over a wide range. It will be understood that the weight fraction of nickel oxide relative to the total mass of NiO and spinel phase in printable NTC materials is at least greater than 0 wt%, for example, 1 wt% or more. From a theoretical standpoint, the majority of printable NTC material, for example more than 50 wt%, may be nickel oxide. In applications where the mixture is used to manufacture NTC products, such as thermistors, we have found that the upper limit is 50 wt%. We have found that higher fractions of electrical insulating material hinder the formation of the overall conductive percolation network in the formed, for example, printed NTC product. Generally, the amount of nickel oxide is in the range of 1 to 30 wt%. Preferably, the amount of NiO is in the range of 3 to 20 wt%, for example, 5 or 10 wt%. For example, the amount of NiO may be in the range of 5 to 30 wt% or 5 to 20 wt%.

[0034] The spinel phase has the general formula AB2O4, where A represents the metal at position A of the spinel crystal lattice, and B represents a different and / or the same metal at position B. The spinel phase has the general formula M I M2 II It can be represented by O4(AB2O4). The spinel phase is thought to impart NTC electrical properties to the printable NTC material. The NiO phase is an electrical insulating phase. In one embodiment, the spinel phase is given by the general formula M 1 M2 II It can also be represented as O4. Compared to Mn3O4, some of the Mn atoms are replaced by Ni, and Mn 3-x Ni x This can be understood as giving the overall composition of O4. In some embodiments, a high nickel content in the spinel phase may be desirable. Therefore, in some embodiments, x can be understood to be in the range of 1 to 2.0 or 1 to 1.6. In some embodiments, x is in the range of 0.7 to 1.5. The amount of Ni incorporated is thought to affect the conductivity of the formed spinel.

[0035] In some preferred embodiments, the mixture of ceramic precursor materials further comprises a third ceramic precursor material. The third ceramic precursor material comprises iron (Fe), cobalt (Co), or copper (Cu), for example, copper oxide or cobalt oxide. Iron, cobalt, or copper can be incorporated into the spinel phase together with, for example, nickel and manganese. The molar ratio (Fe, Co, and Cu) / Ni in the precursor mixture is in the range of 0 to 0.25, for example, in the range of 0.001 to 0.25, for example, in the range of 0.01 to 0.25. It has been found that the addition of Fe, Cu, and / or Co reduces the resistivity of the formed spinel phase, enabling the manufacture of sensor products with reduced overall electrical resistance, such as thermistors. By adding the third precursor material, the formed spinel phase ceramic is given the general formula M I M II It contains O4, in the formula, M I It can be understood that represents Mn, and M II is Mn 2-x-y Ni x-y M III yIt can be understood that this represents (Mn as the overall composition) 3-x-y Ni x-y M III y (It becomes), M III x is Fe, Co, or Cu, x is in the range of 0.70 to 1.5, and y is in the range of 0 to 0.25, for example, 0.001 to 0.25. In embodiments containing Fe, Co, or Ni, such additions can be understood to form a spinel phase ceramic in which some of the nickel is replaced with copper or cobalt.

[0036] The method preferably does not include a sintering step in order to produce dense ceramics. The sintering step can be understood to include heating at a temperature of 1100°C or higher, for example, in the range of 1100°C to 1400°C, or for example, in the range of 1200°C to 1300°C. When a mixture of ceramic precursor materials or a formed printable NTC material is subjected to the sintering step, sintering with macrophase separation occurs, and it has been found that an unstable ceramic product containing NiO in addition to a macrophase-separated second phase, such as a spinel phase. The formation of the second phase can be avoided by not exposing the mixture or the formed printable NTC material (including particles having a spinel phase and a NiO phase) to a temperature exceeding the phase segregation temperature in the above composition.

[0037] The first ceramic precursor, the second ceramic precursor, and any other ceramic precursors included in the mixture preferably contain binary oxides of each metal, such as NiO and Mn2O3. More preferably, the first ceramic precursor, the second ceramic precursor, and any other ceramic precursors included in the mixture, such as copper-based or cobalt-based precursors, consist of binary oxides. Using ceramic precursors containing, preferably consisting of, binary metal oxides, binary metal oxides can reduce the level of impurities in the resulting printable NTC material (for example, by reducing impurities from residual ligands or their decomposition products formed during calcination).

[0038] In some embodiments, after calcination, the mixture is cooled at a controlled rate. Surprisingly, it has been found that the cooling rate affects the thermoelectric behavior of sensor materials, such as thermistors, which include the formed printable NTC material. In some embodiments, the cooling rate is controlled to a rate of about 400°C or less per hour or about 300°C or less per hour, for example, 100°C, 200°C or 300°C per hour. In other embodiments, the mixture is quenched. Quenching can be understood as relating to a nearly instantaneous cooling from an initial temperature (e.g., 1000°C) to a final temperature (e.g., 50°C). Nearly instantaneous can be understood as completing at least 90% of the cooling trajectory in a few minutes, for example, 15 minutes or 10 minutes, preferably faster, for example, within 5 minutes or within 1 minute, for example, 30 seconds. For example, a sample heated to 1000°C can be quenched to 50°C at a cooling rate exceeding 4000°C per hour, e.g., over approximately 8000°C / h. As described herein, we have found that faster cooling reduces the overall resistance in NTC sensors formed from printable NTC materials. We have further found that quenching results in improved stability compared to a sample of the same composition cooled slowly.

[0039] In step 3, the formed particles are dispersed in a suitable printable carrier. The relative amount of the printable NTC material is preferably in the range of 30 to 65 volume percent (about 70 to 90 wt%). Therefore, the relative amount of the printable carrier is preferably in the range of 35 to 70 volume percent (about 10 to 30 wt%). As a result, a printable NTC ink composition is provided, comprising a suitable printable carrier and particles having a spinel phase and a NiO phase dispersed in the carrier. Here, the spinel phase is general formula M I M II O4 [in the formula, M I represents Mn, and M II is Mn 2-x Ni x It can be characterized according to the representation of Mn.3-x Ni x It has an overall composition of O4 [wherein x is in the range of 0.7 to 1.5], or the general formula M I M II O4 [in the formula, M II is Mn 2-x-y Ni x-y M III y This represents (the overall composition is Mn 3-x-y Ni x-y M III y O4), M III [where x is Fe, Co, or Cu, x is in the range of 0.7 to 1.5, and y is in the range of 0 to 0.25, for example, 0.001 to 0.25].

[0040] Optionally or further, the printable NTC material described herein may be mechanically ground into smaller particles. Mechanical grinding may include sieving, for example, sieving through a number of sieves, to provide a narrower particle size distribution or to remove particles of a certain size or larger. For example, to obtain a portion of particles having a size distribution of less than 10 μm, a portion having a size of 10 to 20 micrometers, and a portion of particles larger than that. Using smaller particles can reduce the settling velocity, i.e., improve the stability of the suspension of such particles in a carrier, for example, an ink or paste.

[0041] A suitable printable carrier itself may be known. The printable carrier generally contains at least a solvent that can be evaporated at a temperature of 300°C or less, preferably 200°C or less, in order to reduce the thermal load on the printed NTC product.

[0042] The processing temperature is preferably such that it prevents matrix decomposition and particle decomposition (e.g., macroscale phase segregation in the particles and / or particle sintering). For example, temperatures below 300°C have been found to be suitable for preventing particle decomposition. Higher temperatures, such as up to 400°C, are also conceivable, insofar as the particles essentially retain their properties (e.g., no sintering and no macroscale phase segregation). The upper limit of ink processing can be defined by the stability limits of the polymer matrix, for example, below 250°C or below 350°C, as the matrix itself is.

[0043] As is generally known and as described in International Publication No. 2018164570, an NTC thermistor includes an electrical circuit. The electrical circuit generally includes a pair of electrodes. A sensor material, such as a product having a negative temperature coefficient (NTC) as disclosed herein, or a cured, printable NTC ink composition, is provided, for example, printed, between the electrodes.

[0044] The term “printable” should not be interpreted as being limited to low-viscosity formulations such as inks suitable for inkjet or spray impregnation processes, but clearly also encompasses relatively high-viscosity compositions such as pastes that are particularly suitable for manufacturing processes including screen printing. For details on possible compositions as printable carriers, the levels of spinel phase particles dispersed therein, and further additives that may be included, refer to International Publication No. 2018164570 (incorporated herein by reference). In particular, it should be understood that a suitable printable carrier preferably comprises a non-conductive dielectric matrix. The dielectric matrix can function as a binder, e.g., a curable binder, to improve the printing behavior of the ink and / or impart mechanical stability to the printed product after curing. We have found that the thermoelectric properties of the NTC material can be preserved without merging the particles by melting or sintering by mixing particles (printable NTC material) at concentrations such that they come into contact with each other after coating (e.g., after printing) and form an interconnected network within the sensor material. Thus, printable temperature sensors are given reliable electrical properties applicable to conventional substrates, for example, under low-temperature conditions. By making the volume ratio of particles to dielectric matrix sufficiently high above the percolation threshold, it can be ensured that the microparticles form connected components across the dielectric matrix on the order of the electrode gap size. This can generally be achieved by making the microparticles relatively high packing density, for example, greater than 0.5 (50 percent), preferably greater than 0.7. The minimum required ratio can also be experimentally measured from the conductivity or resistance behavior of the sensor material. For example, the ratio of microparticles to dielectric matrix is ​​preferably large enough to bring the conductivity of the sensor material close to that of pure NTC material, for example, within 50 percent, at which ratio it has substantially the same conductivity as pure NTC material. For common materials, this may correspond to a mass ratio of microparticles to dielectric matrix greater than 3:1.

[0045] The sensor material comprises NTC particles having a specific composition including a NiO phase, as disclosed herein. The interconnection network of particles functions as a conductive path with a negative temperature coefficient between electrodes.

[0046] As disclosed herein, sintering or fusion of NTC particles and the formation of a macroscale phase-segregated NiO phase can be avoided, for example, by limiting the thermal load on the NTC particles.

[0047] In other words, the ink processing, including coating, polymer curing, and solvent evaporation, is preferably carried out in a temperature range of 300°C or less, and preferably 200°C or less.

[0048] By limiting the thermal load, particles in a product with a negative temperature coefficient (NTC) can, advantageously, remain as individual particles in contact with each other without forming a sintered interconnected network. Furthermore, low-temperature processing avoids macroscale phase segregation of the NiO phase.

[0049] Figure 4 shows the XRD diffraction pattern of a printable NTC material composition manufactured according to the present invention. The NTC material consists of a NiO phase and Mn 1.74 Cu 0.16 Ni 1.1 It contains a spinel phase having the composition of O4. The amount of the NiO phase is 5 wt%. The printable NTC material was formed from a mixture of corresponding binary metal oxide powders weighed in corresponding amounts. This mixture was calcined at a temperature of 950°C for 2 hours in the presence of air. Part of the calcined mixture was quenched to room temperature (indicated as "quenched"), and part of the calcined mixture was cooled at 300°C / hour (indicated as "300°C / h"). XRD diffraction patterns show the presence of a spinel phase with NiO at both cooling rates.

[0050] Printed sensors (thermistors) were fabricated from these powders. The performance of these thermistors was compared to thermistors (indicated as "Reference") fabricated under similar conditions, except that a known composition with a comparable spinel phase composition but without the NiO phase was used. The electrical properties (resistivity) of these thermistors were tracked as a function of time under approximately 85°C and approximately 85% relative humidity (RH). As is evident from the graph (Figure 5), the thermal stability of the thermistors formed according to the present invention leveled off after approximately 8 hours of exposure, while the normalized resistance of the Reference thermistor continued to drift. Furthermore, it can be seen that the absolute value of the normalized resistance of sensors fabricated from the quenched printable NTC material according to the present invention is lower than the resistance of samples obtained using a cooling rate of 300°C / h.

[0051] For the sake of clarity and conciseness, each feature is described herein as part of the same or distinct embodiment; however, it will be understood that the scope of the invention may also encompass embodiments having all or some combinations of the described features.

[0052] When interpreting the attached claims, please understand that the word “including” does not exclude the existence of any element or act other than those listed in a particular claim. The words “a” or “an” preceding an element do not exclude the existence of multiple such elements. No reference numerals in the claims limit their scope. Some “means” may refer to the same or different element(s) (item(s)). ) or can be represented by an implemented structure or function. Any disclosed device or part thereof may be used together or separated into further parts unless otherwise specified. Where one claim references another, it may indicate a synergistic effect achieved by the combination of each of their features. However, the mere fact that particular means are described in different claims does not mean that combinations of these means cannot be used advantageously. Thus, this embodiment may encompass all practical combinations of claims unless explicitly excluded by the context, and each claim may essentially reference any prior claim. The aspects relating to this disclosure also include the following aspects. <1> A method for producing an NTC product comprising a conductive percolation network of a material having a negative temperature coefficient (NTC) that can be printed as particles in a crosslinked dielectric polymer matrix, To manufacture a printable NTC material containing particles comprising a spinel phase containing Mn and Ni and a nickel oxide phase; Forming a printable NTC ink composition by dispersing the printable NTC material in a suitable printable carrier comprising a curable polymer and / or its precursor and a solvent for forming a dielectric matrix; and The ink composition is applied and processed to form an NTC product. Includes, Manufacturing the aforementioned printable NTC material is Mixing particles of at least a first ceramic precursor material containing Mn and particles of a second ceramic precursor material containing Ni, wherein the particles of the first ceramic precursor material and the particles of the second ceramic precursor material have a diameter in the range of 100 nanometers to 100 micrometers; and The mixture of ceramic precursor materials is heated in the presence of oxygen at a temperature of 800°C to 1000°C to form a printable NTC material containing particles comprising a spinel phase containing Mn and Ni and a nickel oxide phase, wherein the weight fraction of the nickel oxide phase relative to the total mass of the printable NTC material is in the range of 1 to 30% by weight. Includes, The second ceramic precursor material is added in excess of at least the first ceramic precursor to form the nickel oxide phase. The application and processing of the ink includes curing the polymer and evaporating the solvent, and is carried out in a temperature range of 300 degrees Celsius or less. How to manufacture NTC products. <2> The weight fraction of the nickel oxide phase is in the range of 3 to 30% by weight. <1> Methods used. <3> The spinel phase is Mn 3-x Ni x O 4 The overall composition is as follows: [wherein x is in the range of 0.7 to 1.5] <1> or <2> Methods used. <4> The mixture of ceramic precursor materials comprises a third ceramic precursor material containing ions of a transition metal selected from Fe, Co, and Cu, wherein the molar ratio (Fe, Co, and Cu) / Ni in the mixture is in the range of 0.001 to 0.25 and Mn 3-x-y Ni x-y M III y [In the ceremony, M IIIThe spinel has an overall composition of [where is Fe, Co, or Cu, x is in the range of 0.7 to 1.5, and y is in the range of 0.001 to 0.25]. <1> or <2> Methods used. <5> The process includes grinding or milling the formed printable NTC material. <1> ~ <4> The method described in any one of the following ways. <6> The first ceramic precursor material, the second ceramic precursor material, and any further ceramic precursor material, are essentially formed from a binary metal oxide. <1> ~ <5> The method described in any one of the following ways. <7> After heating, the mixture is cooled at a rate of 400°C or less per hour. <1> ~ <6> The method described in any one of the following ways. <8> After heating, the mixture is quenched. <1> ~ <5> The method described in any one of the following ways. <9> Dielectric polymer matrix and NTC material containing particles, Products having a negative temperature coefficient (NTC) including, The particles are dispersed in the matrix to form a conductive percolation network, the particles have a diameter in the range of 500 nanometers to 50 micrometers, the particles comprise a spinel phase and a nickel oxide phase, the spinel phase comprises Mn and Ni, and the weight fraction of the nickel oxide phase relative to the total mass of the NTC material is in the range of 1 to 30% by weight. NTC products. <10> The aforementioned spinel is Mn 3-x Ni x The overall composition is as follows: [wherein x is in the range of 0.7 to 1.5] <9> NTC products as listed. <11> The spinel phase is Mn 3-x-y Ni x-y M III y [In the ceremony, M III The overall composition is as follows: is Fe, Co, or Cu, x is in the range of 0.75 to 1.5, and y is in the range of 0.001 to 0.25. <9> NTC products as listed. <12> The weight fraction of the nickel oxide phase relative to the total mass of the NTC material is in the range of 3 to 30% by weight. <9> ~ <11> An NTC product listed in any one of the following. <13> A permissible printable carrier comprising a curable polymer and / or its precursor and a solvent for forming a crosslinked dielectric polymer matrix, Printable NTC material dispersed in the carrier, A printable NTC ink composition comprising, The printable NTC material comprises particles having a diameter in the range of 500 nanometers to 50 micrometers, the particles comprising a spinel phase and a nickel oxide phase, the spinel phase comprising Mn and Ni, and the weight fraction of nickel oxide relative to the total mass of the printable NTC material being in the range of 1 to 30% by weight. Printable NTC ink composition. <14> The aforementioned spinel is Mn 3-x Ni x The overall composition is as follows: [wherein x is in the range of 0.7 to 1.5] <13> The printable NTC ink composition described above. <15> The spinel phase is Mn 3-x-y Ni x-y M III y [In the ceremony, M III The overall composition is as follows: is Fe, Co, or Cu, x is in the range of 0.75 to 1.5, and y is in the range of 0.001 to 0.25. <13> The printable NTC ink composition described above.

Claims

1. A method for producing an NTC product comprising a conductive percolation network of a material having a negative temperature coefficient (NTC) that can be printed as particles in a crosslinked dielectric polymer matrix, To manufacture a printable NTC material containing particles comprising a spinel phase containing Mn and Ni and a nickel oxide phase; Forming a printable NTC ink composition by dispersing the printable NTC material in a suitable printable carrier comprising a curable polymer and / or its precursor and a solvent for forming a dielectric matrix; and The NTC ink composition is applied and processed to form an NTC product. Includes, Manufacturing the aforementioned printable NTC material is A mixture of ceramic precursor materials is formed by mixing particles of a first ceramic precursor material containing at least Mn and particles of a second ceramic precursor material containing Ni, wherein the particles of the first ceramic precursor material and the particles of the second ceramic precursor material have a diameter in the range of 100 nanometers to 100 micrometers; The mixture of ceramic precursor materials is heated in the presence of oxygen at a temperature of 800°C to 1000°C to form a printable NTC material containing particles comprising a spinel phase containing Mn and Ni and a nickel oxide phase, where the total mass of the printable NTC material is The weight fraction of the nickel oxide phase is in the range of 1 to 30% by weight; and After heating, the mixture is quenched. Includes, The second ceramic precursor material is added in excess to the first ceramic precursor in order to form the nickel oxide phase. The application and treatment of the NTC ink composition includes curing the curable polymer and evaporating the solvent, and is carried out in a temperature range of 300 degrees Celsius or less. A method for manufacturing NTC products.

2. The method according to claim 1, wherein the weight fraction of the nickel oxide phase is in the range of 3 to 30% by weight.

3. The spinel phase is Mn ３－ｘ Ni ｘ O ４ The method according to claim 1 or claim 2, having an overall composition of [wherein x is in the range of 0.7 to 1.5].

4. The mixture of ceramic precursor materials comprises a third ceramic precursor material containing ions of a transition metal selected from Fe, Co, and Cu, wherein the molar ratio (Fe, Co, and Cu) / Ni in the mixture is in the range of 0.001 to 0.25 and Mn ３－ｘ－ｙ Ni ｘ－ｙ M ＩＩＩ ｙ [In the formula, M ＩＩＩ The method according to claim 1 or 2, which forms a spinel phase having an overall composition of [where is Fe, Co or Cu, x is in the range of 0.7 to 1.5, and y is in the range of 0.001 to 0.25].

5. The method according to any one of claims 1 to 4, comprising grinding or milling the formed printable NTC material.

6. The method according to any one of claims 1 to 5, wherein the first ceramic precursor material, the second ceramic precursor material, and any further ceramic precursor material are formed essentially from a binary metal oxide.

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