Core-shell type negative thermal expansion material and manufacturing method thereof

Abstract

To provide a negative thermal expansion material with electrically low resistance, excellent in thermal conductivity, while excellent in oxidation resistance when used in an environment at which an oxidation reaction will progress, such as an outdoor use.SOLUTION: A core-shell type negative thermal expansion material includes a core including an inorganic oxide having negative thermal expansion properties and a shell including a nickel alloy layer. A manufacturing method of a core-shell type negative thermal expansion material applies an electroless nickel plating treatment to an inorganic oxide to serve as a core having negative thermal expansion properties to form a nickel alloy layer at a shell.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a core-shell type negative thermal expansion material containing a negative thermal expansion material in the core and a nickel alloy in the shell, and a method for producing the same. [Background technology]

[0002] Generally, materials have the property of increasing in length and volume due to thermal expansion as the temperature rises. Such materials exhibit positive thermal expansion relative to temperature (hereinafter, they may be referred to as "positive thermal expansion materials"). Therefore, parts using such positive thermal expansion materials will experience changes in length and volume as the temperature of the environment changes, resulting in a decrease in dimensional stability. On the other hand, there are also known materials that have the property of shrinking in length or volume as the temperature rises. These materials exhibit negative thermal expansion with respect to temperature (hereinafter, they may be referred to as "negative thermal expansion materials").

[0003] Examples of negative thermal expansion materials include β-eucryptite, zirconium tungstate (ZrW2O8), zirconium tungstate phosphate (Zr2WO4(PO4)2), Zn x CD 1-x (CN)2, manganese nitride, bismuth-nickel-iron composite oxide, copper-vanadium composite oxide, etc. are known.

[0004] By using such negative thermal expansion materials in combination with positive thermal expansion materials, changes in length and volume due to temperature changes in the usage environment can be suppressed, making it possible to produce a low-thermal expansion material with excellent dimensional stability (see, for example, Patent Documents 1 to 3). Although negative thermal expansion materials have such useful properties, research is being conducted to further improve them and add additional properties. For example, Patent Document 4 discloses a technique for performing surface treatments such as coating with an inorganic compound to address the problem of elements constituting a negative thermal expansion material eluting when the material comes into contact with water. Furthermore, Non-Patent Documents 1 and 2 propose a technique for copper plating to impart properties such as low electrical resistance and excellent thermal conductivity to negative thermal expansion materials. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-35840 [Patent Document 2] Japanese Patent Application Laid-Open No. 2015-10006 [Patent Document 3] International Publication No. 2017 / 61403 [Patent Document 4] Japanese Patent Publication No. 2020-147486 [Non-patent literature]

[0006] [Non-Patent Document 1] Ceramics International Vol.38,p541-545(2012) [Non-patent document 2] Journal of MATERIALS RESEARCH,Vol.14,No.3,p780-789(1999) Summary of the Invention [Problem to be solved by the invention]

[0007] As described in the aforementioned non-patent document, one method for imparting low resistance and excellent thermal conductivity is to plate a negative thermal expansion material with a metal. However, for example, copper plating, which is used in conventional technology, has poor oxidation resistance. Therefore, when used outdoors or in an environment exposed to the atmosphere, oxidation progresses and electrical resistance tends to increase after use under atmospheric exposure. Therefore, further improvements are required for applications requiring electrical reliability. Therefore, an object of the present invention is to provide a negative thermal expansion material that has low electrical resistance, excellent thermal conductivity, and excellent oxidation resistance even when used in environments where oxidation reactions progress, such as outdoors. [Means for solving the problem]

[0008] As a result of extensive research in light of the above-mentioned problems, the inventors discovered that nickel plating a negative thermal expansion material can impart excellent oxidation resistance, leading to the completion of the present invention.

[0009] That is, the present invention provides a core-shell negative thermal expansion material in which the core contains an inorganic oxide having negative thermal expansion properties and the shell contains a nickel alloy layer.

[0010] The present invention also provides a method for producing a core-shell negative thermal expansion material, in which an inorganic oxide having negative thermal expansion as a core is subjected to electroless nickel plating to form a nickel alloy layer on the shell. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide a negative thermal expansion material that has low electrical resistance, excellent thermal conductivity, and excellent oxidation resistance, and a method for producing the same. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 2 is a graph showing the results of measuring the volume resistivity of the negative thermal expansion materials obtained in Example 1 and Reference Example 1. [Figure 2] 1 is a scanning electron microscope (SEM) photograph of the core-shell negative thermal expansion material obtained in Example 1. [Figure 3] 1 shows a secondary electron image and a Ni element mapping image obtained by analyzing the core-shell type negative thermal expansion material obtained in Example 1 using an energy dispersive X-ray analyzer (SEM-EDX). [Figure 4] FIG. 1 is a graph showing the results of measuring the volume resistance of the negative thermal expansion materials obtained in Example 2 and Reference Example 2. [Figure 5] FIG. 10 is a graph showing the results of measuring the volume resistivity of the negative thermal expansion materials obtained in Example 3 and Reference Example 3. DETAILED DESCRIPTION OF THE INVENTION

[0013] The core-shell negative thermal expansion material of the present invention (hereinafter also referred to as "the present negative thermal expansion material") has a core-shell structure in which the core contains an inorganic oxide having negative thermal expansion properties (hereinafter also referred to as "the present core material") and the shell contains a nickel alloy layer (hereinafter also referred to as "the present nickel alloy layer").

[0014] The core material is an inorganic oxide having negative thermal expansion, i.e., a negative coefficient of linear expansion, which indicates a negative thermal expansion with respect to temperature. The coefficient of linear expansion of the core material may be less than 0 in the range of 25°C to 500°C. For example, the core material may have an inorganic oxide having a coefficient of linear expansion of -20 ppm / °C to -0.05 ppm / °C in the range of room temperature to 500°C. The linear expansion coefficient of the core material is preferably −15 ppm or more and −0.05 ppm or less, and more preferably −10 ppm or more and −0.1 ppm or less, in the range of 25°C or more and 500°C or less, from the viewpoint that a material with low thermal expansion can be obtained by using it in combination with a positive thermal expansion material.

[0015] Examples of the core material include inorganic oxides such as β-eucryptite, zirconium tungstate (ZrW2O8), zirconium tungstate phosphate (Zr2WO4(PO4)2), bismuth-nickel-iron composite oxide, copper-vanadium composite oxide, etc. These inorganic oxides may be used alone or in combination of two or more. Among these inorganic oxides, zirconium tungstate and zirconium tungstate phosphate are preferred as the core material, with zirconium tungstate phosphate being particularly preferred, from the viewpoint of their large negative thermal expansion.

[0016] The inorganic oxide used in the core material may be a commercially available inorganic oxide, or may be prepared separately. An example of a method for producing an inorganic oxide is to use inorganic salts containing the metals contained in the target inorganic oxide as precursors, mix these precursors, and bake them to produce the inorganic oxide. Examples of the inorganic salt include fluorides, chlorides, bromides, hydroxides, carbonates, sulfates, and nitrates.

[0017] The precursors, which are inorganic salts containing the metals, may be mixed by either wet mixing or dry mixing. In wet mixing, these precursors are dispersed or dissolved in a dispersion medium or solvent such as water or alcohol, and the resulting dispersions or solutions are mixed to obtain a mixed solution. The dispersions or solutions may be mixed all at once or by adding them dropwise. The dispersion medium or solvent in the resulting mixed liquid is removed by drying or the like, and then the resulting mixture is fired to produce the desired inorganic oxide.

[0018] Dry mixing is carried out using a mixing device. Examples of the mixing device include a blade-equipped agitator such as a Henschel mixer, pressure kneader, Banbury mixer, or planetary mixer; a media-equipped grinder such as a ball mill, attritor, basket mill, sand mill, sand grinder, Dyno Mill, Dispermat, SC Mill, spike mill, or agitator mill; or a disperser equipped with other mechanisms such as a microfluidizer, nanomizer, ultimizer, ultrasonic homogenizer, dissolver, disper, high-speed impeller, or thin-film swirling high-speed mixer. Mixing in this manner may be carried out batchwise or continuously. The resulting mixture can be calcined to produce the desired inorganic oxide.

[0019] During the mixing, the ratio of the amounts of the precursors is adjusted according to the composition ratio of the desired inorganic oxide, and the mixture is mixed and fired to obtain the desired inorganic oxide.

[0020] The firing temperature is the temperature at which the mixture is oxidized to the desired inorganic oxide, and is usually 300° C. or higher and 2000° C. or lower. From the viewpoint of firing efficiency, the firing temperature is preferably 500° C. or higher and 1800° C. or lower.

[0021] The core of the negative thermal expansion material contains the core material. The core may contain other auxiliary components in addition to the core material. Examples of such auxiliary components include alkali metal elements such as Li, Na, and K; alkaline earth metal elements such as Mg, Ca, Sr, and Ba; transition metal elements such as Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Nb, Mo, Ag, Hf, and Ta; rare earth elements such as La, Ce, Nd, Sm, Eu, Tb, Dy, Ho, and Yb; metal elements other than transition metals such as Al, Zn, Ga, Cd, In, Sn, Pb, and Bi; semimetal elements such as B, Si, Ge, Sb, and Te; nonmetal elements such as S; and halogen elements such as F, Cl, Br, and I. The core may contain one or more of these elements. The content of the minor element in the core is preferably 0.1% by mass to 3% by mass, and more preferably 0.2% by mass to 2% by mass, based on 100% by mass of the total amount of the core. When two or more types of minor element are contained, the content of the minor element is calculated based on the total mass of the minor element. The content of the minor element can be measured by a powder pressing method, a molten glass bead method, or the like, using a measuring device such as a fluorescent X-ray analyzer.

[0022] The content of the core material in the core is preferably 60% by mass to 100% by mass, more preferably 80% by mass to 100% by mass, and even more preferably 95% by mass to 100% by mass, where the total mass of the core is 100% by mass. From the viewpoint of the thermal expansion coefficient of the obtained negative thermal expansion material, it is particularly preferable that the amount of the core material in the core is 100% by mass, i.e., the core contains only the core material.

[0023] The shape of the core material may be, for example, spherical, granular, plate-like, scale-like, whisker-like, rod-like, filament-like, irregular crushed stone-like shape having one or more ridges (hereinafter also referred to as "crushed shape"), or a combination thereof.

[0024] A preferred example of the core material is one in which the zirconium tungstate phosphate is preferably contained in an amount of from 60% by mass to 100% by mass, more preferably from 80% by mass to 100% by mass, and particularly preferably from 95% by mass to 100% by mass, where the total mass of the core is taken as 100% by mass.

[0025] The core material may be coated with another component, and for example, the zirconium tungstate phosphate is preferably coated with another component as the core material. The coating film that coats the zirconium tungstate phosphate is preferably a coating film containing a metal such as Zn, Si, Al, Ba, Ca, Mg, Ti, V, Sn, Co, Fe, or Zr.

[0026] The negative thermal expansion material has the nickel alloy layer. Note that the nickel alloy in the present invention contains nickel and one or more metallic or non-metallic elements that form an alloy with nickel. By including this nickel alloy layer in the negative thermal expansion material, it is possible to obtain a negative thermal expansion material with excellent oxidation resistance. Furthermore, by including this nickel alloy layer in the negative thermal expansion material, it is possible to obtain a negative thermal expansion material that not only has oxidation resistance but also low electrical resistance and excellent conductivity. Therefore, by using this negative thermal expansion material, it is possible to obtain a material that not only has low electrical resistance and excellent conductivity, but also does not experience a decrease in electrical resistance or conductivity even when used outdoors where oxidation reactions occur.

[0027] Examples of metal elements or non-metal elements other than nickel that form alloys with nickel include iron, gold, silver, copper, palladium, cobalt, chromium, molybdenum, phosphorus, boron, etc. Examples of nickel alloys include nickel-iron alloys, nickel-gold alloys, nickel-silver alloys, nickel-copper alloys, nickel-palladium alloys, nickel-cobalt alloys, nickel-chromium alloys, nickel-iron-chromium alloys, nickel-molybdenum alloys, nickel-phosphorus alloys, and nickel-boron alloys.

[0028] Among these metals, nickel-phosphorus alloys or nickel-boron alloys, which are alloys with phosphorus or boron, are preferred from the viewpoint of the oxidation resistance, chemical resistance, wear resistance, etc. of the resulting negative thermal expansion material. The nickel alloy layer may contain one or more alloys.

[0029] The negative thermal expansion material has a shell containing the nickel alloy layer, and the nickel alloy layer contained in the shell may be one type or two or more types. The shell may contain other auxiliary components in addition to the nickel alloy layer. Examples of such auxiliary components include alkali metal elements such as Li, Na, and K; alkaline earth metal elements such as Mg, Ca, Sr, and Ba; transition metal elements such as Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Nb, Mo, Ag, Hf, and Ta; rare earth elements such as La, Ce, Nd, Sm, Eu, Tb, Dy, Ho, and Yb; metal elements other than transition metals such as Al, Zn, Ga, Cd, In, Sn, Pb, and Bi; semimetal elements such as B, Si, Ge, Sb, and Te; nonmetal elements such as S; and halogen elements such as F, Cl, Br, and I. The shell may contain one or more of these elements.

[0030] Methods for forming the nickel alloy layer include dry methods using vapor deposition, sputtering, mechanochemical methods, hybridization methods, etc., and wet methods using electrolytic plating, electroless plating, etc. The nickel alloy layer may also be formed on the surface of the negative thermal expansion material by combining these methods.

[0031] The nickel alloy layer is preferably formed on the surface of the negative thermal expansion material by the electroless plating method described below, since this makes it easier to obtain the negative thermal expansion material.

[0032] This negative thermal expansion material has a core-shell structure in which the core contains the core material and the shell contains the nickel alloy layer. A core-shell structure is a structure in which there is a core near the center and a shell around it. In the core-shell structure of this negative thermal expansion material, the shell may directly cover the surface of the core, or there may be another layer between the core and the shell, but the outermost surface of this negative thermal expansion material is the shell containing the nickel alloy layer. When there is another layer between the core and the shell, an example of the other layer is the coating film that covers the core.

[0033] The shell on the outermost surface of the negative thermal expansion material may cover the entire surface of the negative thermal expansion material, or may cover the surface of the negative thermal expansion material intermittently. The coverage of the negative thermal expansion material by the shell is set appropriately depending on the desired properties of the negative thermal expansion material, but for example, the coverage is 50% or more, preferably 70% or more, more preferably 80% or more, even more preferably 90% or more, and particularly preferably 100%, of the entire surface of the negative thermal expansion material taken as 100%.

[0034] The linear expansion coefficient of this negative thermal expansion material is preferably -1 ppm / K or less in the range of 25°C to 200°C, from the viewpoint that when used in combination with a positive thermal expansion material, it is easy to keep the thermal expansion of the resulting material low. The linear expansion coefficient of this negative thermal expansion material is more preferably -2 ppm / K or less in the range of 25°C to 200°C, and even more preferably -5 ppm / K. The linear expansion coefficient of this negative thermal expansion material is usually -20 ppm / K or more in the range of 25°C to 200°C, and is preferably -10 ppm / K or more from the viewpoint that when used in combination with a positive thermal expansion material, it is easy to control the thermal expansion of the resulting material.

[0035] It is preferable to appropriately select the linear expansion coefficient of the inorganic oxide used in the core material and the linear expansion coefficient of the nickel alloy used in the nickel alloy layer so that the linear expansion coefficient of the negative thermal expansion material falls within the above range, and to obtain the negative thermal expansion material. In addition, the linear expansion coefficient of the negative thermal expansion material can be set within the above range by adjusting the thickness of the nickel alloy layer. For example, the core material may be an inorganic oxide having a linear expansion coefficient of -2 ppm / K or less, preferably -3 ppm or less, at 25° C. to 500° C., and the nickel alloy layer may be a nickel alloy having a linear expansion coefficient of 16 ppm / K or less. When two or more inorganic oxides are used, it is preferable to use inorganic oxides whose linear expansion coefficients are within the above ranges. Examples of inorganic oxides that satisfy the above linear expansion coefficient include zirconium tungstate phosphate and zirconium tungstate, and examples of nickel alloys include nickel-phosphorus alloys and nickel-boron alloys. Furthermore, since the nickel alloy layer is usually a positive thermal expansion material, reducing the thickness of the nickel alloy layer can reduce the linear expansion coefficient of the negative thermal expansion material. From the viewpoint of the linear expansion coefficient of the negative thermal expansion material, the thickness of the nickel alloy layer is preferably 0.01 μm or more and 5 μm or less, and more preferably 0.01 μm or more and 4.5 μm or less.

[0036] When this negative thermal expansion material is used as a conductive material, the volume resistance of this material is 1×10 -1 It is preferable that the resistance is Ω·cm or less, and 0.8×10 -1 It is preferable that the resistivity is Ω·cm or less. The volume resistance of this negative thermal expansion material is governed by the volume resistance of the shell of this negative thermal expansion material. -1 Ω·cm or less is preferable, and 0.8×10 -1 The resistance is preferably Ω·cm or less. Examples of such nickel alloys include nickel-phosphorus alloys and nickel-boron alloys.

[0037] When used in combination with a thermal expansion material, the average particle size of the negative thermal expansion material is preferably 1 μm or more and 50 μm or less, and more preferably 1 μm or more and 30 μm or less, from the viewpoint of the dispersibility of the negative thermal expansion material in the resulting material. The average particle size is the D50 value obtained by the laser diffraction scattering method. D50 can be measured by dynamic light scattering using a laser particle size analyzer, which is used in the laser diffraction scattering method. D50 is the volume average particle size of particles, and is the particle size at which the cumulative volume distribution curve reaches 50% when plotted from the smallest diameter side in the particle size distribution.

[0038] When the average particle size of the negative thermal expansion material is within the above range, for example, an inorganic oxide having an average particle size of 0.02 μm to 50 μm, preferably 0.02 μm to 30 μm, may be used as the core material. The average particle size of the inorganic oxide is the D50 value measured by the dynamic light scattering method using a laser particle size analyzer or the like, as described above.

[0039] Furthermore, when the average particle size of the negative thermal expansion material is within the above range, the thickness of the shell alloy layer may be controlled so that the average thickness of the shell is, for example, 0.01 μm or more and 10 μm or less, more preferably 0.01 μm or more and 5 μm or less. For example, in order to set the average particle size of the negative thermal expansion material within the above range, the average particle size of the core material is preferably 0.05 μm or more and 30 μm or less, and the thickness of the nickel alloy layer is preferably 0.01 μm or more and 5 μm or less, and more preferably 0.01 μm or more and 4.5 μm or less.

[0040] The BET specific surface area of ​​this negative thermal expansion material is 6m 2 / g or less is preferable, and 0.05m 2 / g or more 5m 2 / g or less is more preferable. The BET specific surface area is determined by the BET method. The BET method is a method for calculating the specific surface area by measuring the amount of gas physically adsorbed on the particle surface when the particle is kept at a low temperature under certain conditions. Helium gas is usually used as the gas for physical adsorption. The BET specific surface area of ​​the present thermally expandable material can be measured by the BET single-point method using, for example, a BET specific surface area measuring device (AUTOSORB-1, manufactured by Quantachrome Instruments Co., Ltd.).

[0041] For example, the particle size of the core material may be adjusted so that the BET specific surface area of ​​the negative thermal expansion material falls within the above range. By increasing the particle size of the core material, the BET specific surface area of ​​the negative thermal expansion material can be reduced.

[0042] One method for producing this negative thermal expansion material is to apply electroless nickel plating to an inorganic oxide having negative thermal expansion as a core to form a nickel alloy layer on the shell (hereinafter, sometimes referred to as "this production method"). This production method makes it possible to easily produce a core-shell negative thermal expansion material.

[0043] The inorganic oxide having negative thermal expansion is as described above, and may be a commercially available inorganic oxide having negative thermal expansion, or may be prepared separately by the method described above and used. For example, when zirconium tungstate phosphate is used as the core material, zirconium tungstate phosphate can be obtained by reacting a zirconium source, a tungsten source, and a phosphorus source. Examples of methods include wet-mixing a zirconium source such as zirconium chloride, a tungsten source such as ammonium tungstate, and a phosphorus source such as ammonium phosphate and firing the resulting mixture, mixing zirconium phosphate, tungsten oxide, and a reaction accelerator such as MgO in a wet ball mill and firing the resulting mixture, firing a mixture containing zirconium oxide, tungsten oxide, and ammonium dihydrogen phosphate, and firing a reaction precursor made of a mixture of a tungsten compound and an amorphous compound containing phosphorus and zirconium.

[0044] When the zirconium tungstate phosphate coated with a coating film containing an inorganic compound, preferably a metal such as Zn, Si, Al, Ba, Ca, Mg, Ti, V, Sn, Co, Fe, or Zr, is used as the core material, the surface of which is coated with the inorganic compound. The coating treatment can be carried out by a wet method or a dry method. In the dry method, zirconium tungstate phosphate and a solid inorganic compound are mixed using a mixing device such as a Henschel mixer, an airflow pulverizer, etc. In the wet method, zirconium tungstate phosphate and a diluted solution obtained by diluting the inorganic compound with a solvent are mixed, and then the mixture is heated and dried as necessary.

[0045] When the coating treatment is performed by a dry method, an organic compound or inorganic salt containing an element that serves as a precursor of an inorganic compound may be used, and the organic compound or inorganic salt may be converted into an oxide by heat treatment at a temperature equal to or higher than the decomposition temperature of the organic compound or inorganic salt. The organic compound may be any compound that can be converted into an oxide by heat treatment, and examples thereof include carboxylates of elements that serve as precursors of inorganic compounds and alkoxides of elements that serve as precursors of inorganic compounds. The carboxylic acid of the carboxylate may be either a monocarboxylic acid or a polycarboxylic acid, and examples thereof include acetic acid, citric acid, gluconic acid, formic acid, and lactic acid. Examples of inorganic salts include nitrates and carbonates of elements that serve as precursors of inorganic compounds.

[0046] When the coating treatment is carried out by a wet method, a method in which a water-soluble inorganic salt containing an element that serves as a precursor of the inorganic compound and an alkaline agent are added to a slurry in which zirconium tungstate phosphate is dispersed in water to adjust the pH to 6 or more and 10 or less, and a hydroxide containing an element that serves as a precursor of the inorganic compound is precipitated on the surface of the zirconium tungstate phosphate to coat it may be used. A more specific method for the coating treatment is described in Patent Document 4. When the core material has a plurality of coating films, the coating treatment may be carried out a plurality of times, and if necessary, the type of inorganic compound may be changed and the coating treatment may be carried out a plurality of times.

[0047] In this manufacturing method, after forming the core material and, if necessary, other layers such as an inorganic compound coating, by the above-mentioned method, the nickel alloy layer is formed so as to become the outermost surface of the negative thermal expansion material. The nickel alloy layer is formed by electroless nickel plating on the core material, or on the core material with other layers on its surface (hereinafter, both may be collectively referred to as "the core"). As a result, the nickel alloy layer becomes the outermost surface of the negative thermal expansion material, and the negative thermal expansion material has a core-shell structure.

[0048] Electroless nickel plating is a process in which the core to be plated is immersed in a plating bath containing ionized nickel and a reducing agent. This electroless nickel plating process causes an oxidation-reduction reaction on the surface of the object to be plated, resulting in the deposition of a plating film on the surface of the object to be plated.

[0049] In the electroless nickel plating process, for example, an electroless nickel plating bath containing a plating solution containing water as a solvent, a dispersant, a nickel salt, a reducing agent, a complexing agent, etc. is prepared, and the core is mixed with the plating solution. The mixing may be performed by directly immersing the core in the electroless nickel plating bath, or by dispersing the core in a dispersion medium such as water or alcohol to form a slurry, and then mixing the slurry with the plating solution. When a slurry is used, the dispersion medium is preferably one that is highly miscible with the solvent used in the plating bath, and more preferably, the two are the same.

[0050] The concentration of the core in the slurry is preferably 0.1 g / L or more and 500 g / L or less, more preferably 1 g / L or more and 300 g / L or less. The core is thoroughly dispersed in the dispersion medium within this range to prepare a slurry. The dispersion operation can be carried out by normal stirring, high-speed stirring, or using a shear dispersion device such as a colloid mill or homogenizer. Ultrasound may also be used in combination with the dispersion operation. If necessary, a dispersant such as a surfactant may be added during the dispersion operation. Examples of dispersants include the same dispersants used in plating baths. The slurry prepared as described above is added to the electroless nickel plating bath.

[0051] Examples of water in the plating bath include pure water, ion-exchanged water, industrial water, tap water, distilled water, etc. Among these, pure water and ion-exchanged water are preferred from the viewpoint of preventing the inclusion of impurities.

[0052] Examples of dispersants in the plating bath include surfactants such as nonionic surfactants and zwitterionic surfactants, and water-soluble polymers. The surfactants and water-soluble polymers may be used in combination. Examples of nonionic surfactants include polyoxyalkylene ether surfactants such as polyethylene glycol, polyoxyethylene alkyl ether, and polyoxyethylene alkylphenyl ether.

[0053] Examples of the zwitterionic surfactant include betaine surfactants such as alkyldimethyl acetate betaine, alkyldimethylcarboxymethyl acetate betaine, and alkyldimethylamino acetate betaine. Examples of the water-soluble polymer include polyvinyl alcohol, polyvinylpyrrolidinone, and hydroxyethyl cellulose. These dispersants can be used alone or in combination of two or more. The amount of dispersant used varies depending on the type, but is generally 0.5 g / L or more and 30 g / L or less relative to the volume of the plating solution. In particular, it is preferable that the amount of dispersant used is 1 g / L or more and 10 g / L or less relative to the volume of the plating solution, from the viewpoint of further improving the adhesion of the nickel alloy layer.

[0054] As the nickel salt, for example, nickel chloride, nickel sulfate, or nickel acetate is used. The concentration of the nickel salt in the plating solution is preferably 0.01 g / L or more and 50 g / L or less. The nickel salt is ionized in the plating bath to generate ionized nickel.

[0055] Examples of the reducing agent include phosphorus-containing compounds, boron-containing compounds, hydrazine compounds, organic acids, and hydrogen peroxide. From the viewpoint of uniformity of the thickness of the nickel alloy layer to be formed, the reducing agent is preferably a phosphorus-containing compound or a boron-containing compound. Examples of the phosphorus-containing compound include sodium hypophosphite, potassium hypophosphite, ammonium hypophosphite, etc. Among these compounds, sodium hypophosphite is more preferred. Examples of the boron-containing compound include dimethylamine borane, tetrahydroboric acid, sodium borohydride, potassium borohydride, etc. Among these compounds, dimethylamine borane is more preferred.

[0056] When a phosphorus-containing compound such as sodium hypophosphite is used as the reducing agent, the concentration of the reducing agent in the plating solution is preferably 0.1 g / L or more and 50 g / L or less.When a boron-containing compound such as dimethylamine borane is used as the reducing agent, the concentration of the reducing agent in the plating solution is preferably 0.1 g / L or more and 50 g / L or less.

[0057] Examples of the complexing agent include compounds that have a complexing effect on nickel ions, such as carboxylic acids or salts thereof, such as citric acid, hydroxyacetic acid, tartaric acid, malic acid, lactic acid, gluconic acid, or alkali metal salts or ammonium salts thereof; amino acids such as glycine; amino acids such as ethylenediamine and alkylamines; other ammonium salts; ethylenediaminetetraacetic acid; and pyrophosphoric acid or salts thereof. These can be used alone or in combination of two or more.

[0058] The concentration of the complexing agent in the plating solution is preferably 1 g / L or more and 100 g / L or less, and more preferably 5 g / L or more and 50 g / L or less. By adjusting the concentration of the complexing agent within the above range, the pH of the plating solution can be adjusted to a range of 3 to 14. By adjusting the pH within this range, the electroless nickel plating process proceeds quickly.

[0059] The electroless nickel plating process begins immediately upon mixing the core with the plating bath, and is accompanied by the generation of hydrogen gas. The electroless nickel plating process is completed when the generation of hydrogen gas has completely ceased. Electroless nickel plating is usually carried out at a temperature of 20°C or higher and 90°C or lower.

[0060] The thickness of the nickel alloy layer can be adjusted to a desired thickness by adjusting the concentrations of the nickel salt, reducing agent, and complexing agent in the plating solution. In order to obtain a desired thickness for the nickel alloy layer, the electroless nickel plating treatment may be carried out multiple times. When the electroless nickel plating treatment is performed multiple times, the electroless nickel plating treatment is followed by (i) a first aqueous solution containing one of a nickel salt, a reducing agent, and an alkali, and a second aqueous solution containing the remaining two; or (ii) a first aqueous solution containing a nickel salt, a second aqueous solution containing a reducing agent, and a third aqueous solution containing an alkali; It is preferable to add any one of the following to the solution after the electroless nickel plating treatment is completed. By adding these aqueous solutions, the electroless nickel plating treatment can be continued.

[0061] The aqueous solution (i) or (ii) may be added all at once, in several batches, or continuously. When the aqueous solution (i) or (ii) is added, the electroless nickel plating process starts again, and by adjusting the amount added, the thickness of the nickel alloy layer formed can be controlled to the desired thickness.

[0062] After the addition of the plating solution is completed and the generation of hydrogen gas has completely ceased, it is preferable to continue stirring while maintaining the liquid temperature for a while to complete the reaction.

[0063] In the case of (i) above, it is preferable to use a first aqueous solution containing a nickel salt and a second aqueous solution containing a reducing agent and an alkali, but this combination is not limiting. In this case, the first aqueous solution does not contain a reducing agent or an alkali, and the second aqueous solution does not contain a nickel salt. The nickel salt and reducing agent may be those described above. As the alkali, for example, hydroxides of alkali metals such as sodium hydroxide and potassium hydroxide can be used.

[0064] In the case of (ii) above, the first to third aqueous solutions each contain a nickel salt, a reducing agent, and an alkali, and each aqueous solution does not contain the other two components other than the components in question.

[0065] In either case (i) or (ii), the concentration of the nickel salt in the aqueous solution is preferably 10 g / L or more and 1000 g / L or less, more preferably 50 g / L or more and 500 g / L or less. When a phosphorus-containing compound is used as the reducing agent, the concentration of the phosphorus-containing compound in the aqueous solution is preferably 100 g / L or more and 1000 g / L or less, and more preferably 100 g / L or more and 800 g / L or less. When a boron-containing compound is used as the reducing agent, the concentration of the boron-containing compound in the aqueous solution is preferably 5 g / L or more and 200 g / L or less, and more preferably 10 g / L or more and 100 g / L or less. When hydrazine or a derivative thereof is used as the reducing agent, the concentration of hydrazine or a derivative thereof in the aqueous solution is preferably 5 g / L or more and 200 g / L or less, and more preferably 10 g / L or more and 100 g / L or less. The concentration of alkali in the aqueous solution is preferably 5 g / L or more and 500 g / L or less, and more preferably 10 g / L or more and 200 g / L or less.

[0066] From the viewpoint of production efficiency of the negative thermal expansion material, the electroless nickel plating treatment is preferably carried out once or more and five times or less in total, more preferably once or more and three times or less. When the electroless nickel plating treatment is performed two or more times, the next electroless nickel plating treatment may be performed continuously after the completion of each electroless nickel plating treatment, or the next electroless nickel plating treatment may be performed intermittently after the completion of each electroless nickel plating treatment. In this case, after the completion of the electroless nickel plating treatment, it is preferable to separate the core from the plating solution by a method such as filtration, and then disperse the core in water to prepare a new aqueous slurry and add it.

[0067] In addition to the electroless nickel plating process, the manufacturing method may also include pre-treating the core, if necessary. The pretreatment may be, for example, a sensitization treatment in which tin ions are adsorbed onto the surface of the core. To adsorb tin ions onto the surface of the core particles, for example, the core may be placed in an aqueous solution of stannous chloride and stirred for a predetermined period of time.

[0068] The present manufacturing method may include post-treatment such as isolating, washing, and drying the negative thermal expansion material obtained by the electroless nickel plating treatment. The isolation method may be, for example, filtration or drying. The washing method may include washing the obtained negative thermal expansion material with an appropriate solvent, or dissolving it in a solvent and then recrystallizing it. The drying method may be, for example, drying under normal pressure or drying under reduced pressure.

[0069] As mentioned above, this negative thermal expansion material is a substance that has the property of decreasing in length and volume as the temperature rises. Therefore, by using it in combination with a positive thermal expansion material, it is possible to provide a low thermal expansion material in which changes in length and volume due to temperature changes in the usage environment are suppressed. Furthermore, since this negative thermal expansion material has low electrical resistance, excellent thermal conductivity, and excellent oxidation resistance, it is possible to provide a low thermal expansion material that does not reduce the required performance in terms of electrical resistance or thermal conductivity even when used in the environment in which it is used, particularly when the material containing this negative thermal expansion material is exposed to the atmosphere, etc.

[0070] For example, by mixing this negative thermal expansion material with a polymer compound, a polymer composition with low thermal expansion can be obtained. Such a polymer composition becomes a material with a suppressed thermal expansion coefficient due to the high negative thermal expansion property of this negative thermal expansion material. Furthermore, since this negative thermal expansion material has low electrical resistance and excellent thermal conductivity, and the resulting polymer composition has excellent oxidation resistance, the resulting polymer composition becomes a material with little deterioration in electrical properties and thermal conductivity even when used outdoors for long periods of time.

[0071] Examples of polymer compounds include rubber, polyolefin resin, polycycloolefin resin, polystyrene resin, ABS resin, polyacrylate resin, polyphenylene sulfide resin, phenol resin, polyamide resin, polyimide resin, epoxy resin, silicone resin, polycarbonate resin, polyethylene resin, polypropylene resin, polyethylene terephthalate resin, and polyvinyl chloride resin. These may be used alone or in combination of two or more kinds.

[0072] The content of the negative thermal expansion material in the polymer composition is appropriately set depending on the type of polymer compound used and the application and purpose of the resulting polymer composition. The content of the negative thermal expansion material in the polymer composition is usually 1% by volume or more and 90% by volume or less, assuming the polymer composition to be 100% by volume.

[0073] The polymer composition may contain additives, such as antioxidants, heat stabilizers, ultraviolet absorbers, lubricants, release agents, colorants including dyes and pigments, flame retardants, crosslinking agents, softeners, dispersants, curing agents, polymerization initiators, and inorganic fillers. The content of each of these additives is usually 10% by volume or more and 90% by volume or less, with the polymer composition being 100% by volume.

[0074] Although the negative thermal expansion material and the manufacturing method have been described above, the present invention is not limited to the configuration of the above embodiment. For example, the negative thermal expansion material may be configured in the above embodiment with any other configuration added, or may be replaced with any configuration that exhibits a similar function. Furthermore, the manufacturing method may include any other process, device, or function added, or may be replaced with any process that produces a similar effect. [Example]

[0075] The present invention will be further described below with reference to examples, but the scope of the present invention is not limited to these examples. The properties in the examples were measured by the following methods.

[0076] (1) Evaluation of volume resistivity 1.0 g of the negative thermal expansion material obtained in the examples and comparative examples was placed in a vertically placed resin cylinder with an inner diameter of 10 mm, and the electrical resistance between the upper and lower electrodes was measured at room temperature (20°C, 50% RH) with a load applied to determine the volume resistance. The lower the volume resistance, the lower the connection resistance of the negative thermal expansion material.

[0077] (2) Evaluation of oxidation resistance The negative thermal expansion materials obtained in the examples and comparative examples were exposed to the atmosphere at 25°C for 24 hours, and the metallic luster of the surface was observed.

[0078] (3) Average particle size The particle size distribution of the core-shell particles was measured by a laser diffraction scattering method using water as a measurement solvent. The particle size at 50% volume (D50) of the obtained particle size distribution was taken as the average particle size of the primary particles of the core-shell negative thermal expansion material.

[0079] (4) BET specific surface area It was determined by the BET method.

[0080] (5) Shell layer thickness measurement The cross section of the obtained negative thermal expansion material was observed with a scanning electron microscope (SU3800, manufactured by Hitachi High-Technologies Corporation) and an energy dispersive X-ray analyzer (Quantax, manufactured by BRUKER).

[0081] (6) Evaluation of negative thermal expansion performance A polymer composition was produced using the negative thermal expansion materials obtained in Example 1 and Reference Example 1 as a negative thermal expansion filler. Specifically, 5.8 g of the negative thermal expansion filler and 4.2 g of an epoxy resin (JER828, manufactured by Mitsubishi Chemical Corporation, epoxy equivalent weight 160-175) as a polymer compound were mixed using a vacuum mixer (Thinky Awatori Rentaro ARV-310) at a rotation speed of 2000 rpm to produce a 14% by volume paste. Next, 100 μL of a curing agent (Curesol, manufactured by Shikoku Kasei) was added to the paste, and the mixture was mixed using the vacuum mixer at a rotation speed of 1500 rpm and cured at 150°C for 1 hour to obtain the target polymer composition. This polymer composition was cut into a cylindrical shape with a diameter of 5 mm and a length of 10 mm to serve as a measurement sample. The linear expansion coefficient of this measurement sample was measured from 30° C. to 200° C. at a temperature rise rate of 1° C. / min using a thermomechanical analyzer (TMA; 4000SE, manufactured by NETZSCH).

[0082] Example 1 (i) Pretreatment Average particle diameter 22.4μm, specific surface area 0.3m 2 Zirconium tungstate phosphate (manufactured by Nippon Chemical Industry Co., Ltd.) with a linear expansion coefficient of −3 ppm / °C was used as the core material. 69 g of the zirconium tungstate phosphate was added to 10 mL of an aqueous conditioner solution (KRH-161, manufactured by Rohm and Haas Electronic Materials Co., Ltd.) with stirring, followed by stirring for 5 minutes while applying ultrasonic waves at a liquid temperature of 60°C to perform surface modification and dispersion treatment of the zirconium tungstate phosphate. This aqueous solution was filtered, and the core material, which had been repulped and washed once, was dispersed in 200 mL of pure water to obtain a dispersion. This dispersion was stirred for 2 minutes and then filtered. Subsequently, the core material was repulped and washed once, and then added to 200 mL of pure water to form a slurry. 0.1 g of stannous chloride was added to the slurry. The mixture was stirred at room temperature for 5 minutes to sensitize the core material, allowing tin ions to be adsorbed onto the surface. The aqueous solution was then filtered, and the core material, which had been repulped and washed once, was made into 200 mL of slurry and maintained at 60°C. To this slurry, 1.5 mL of a 12 g / L aqueous palladium chloride solution was added. The mixture was stirred at 60°C for 5 minutes, and an activation treatment was performed to capture palladium ions on the surface of the core material. The aqueous solution was then filtered, and the core material was repulped and washed with hot water once to make 100 mL of slurry. 10 mL of a 0.5 g / L aqueous dimethylamine borane solution was added, and the mixture was stirred for 2 minutes while applying ultrasound to obtain a pretreated slurry.

[0083] (ii) Preparation of plating bath Three liters of an electroless nickel-phosphorus plating bath was prepared from an aqueous solution containing 5 g / L sodium tartrate, 0.1 g / L nickel sulfate hexahydrate, 10 g / L trisodium citrate, 0.25 g / L tetramethylethylenediamine, 0.15 g / L sodium pyrophosphate, 0.1 g / L sodium hypophosphite, and 2 g / L polyethylene glycol, and the temperature was raised to 70°C.

[0084] (iii) Electroless nickel plating The slurry of the pretreated core material was added to this electroless nickel plating bath and stirred for 5 minutes, after which it was confirmed that the bubbling of hydrogen had ceased. To this slurry, 420 mL of a 224 g / L nickel sulfate aqueous solution and 420 mL of a mixed aqueous solution containing 210 g / L sodium hypophosphite and 80 g / L sodium hydroxide were continuously added in portions at an addition rate of 2.5 mL / min using a metering pump, and electroless plating was initiated. After the entire amount of the nickel sulfate aqueous solution and the mixed aqueous solution of sodium hypophosphite and sodium hydroxide were added, stirring was continued for 5 minutes while maintaining the temperature at 70° C. The liquid was then filtered, and the filtrate was washed three times and then dried in a vacuum dryer at 110° C. to obtain a core-shell negative thermal expansion material in which a nickel alloy layer was formed as a shell layer on the surface of the core material. The average particle size of the obtained core-shell negative thermal expansion material was 22.77 μm, and the thickness of the nickel alloy layer was 185 nm.

[0085] The results of measuring the volume resistivity of the obtained core-shell type negative thermal expansion material are shown in Figure 1, the results of evaluating the oxidation resistance are shown in Table 1, and the results of evaluating the negative thermal expansion performance are shown in Table 2. In addition, a scanning electron microscope (SEM) photograph of the obtained core-shell type negative thermal expansion material is shown in Figure 2, and the results of observation with an energy dispersive X-ray analyzer (SEM-EDX) are shown in Figure 3.

[0086] Example 2 (i) Pretreatment Average particle size 1.3μm, specific surface area 2.5m 2 Pretreatment was carried out in the same manner as in Example 1, except that zirconium tungstate phosphate (manufactured by Nippon Chemical Industry Co., Ltd.) having a tensile strength of 10 ...

[0087] (ii) Preparation of plating bath A plating bath was prepared in the same manner as in Example 1.

[0088] (iii) Electroless nickel plating The plating process was carried out in the same manner as in the electroless nickel plating process of Example 1, to obtain a core-shell negative thermal expansion material. The average particle size of the obtained core-shell negative thermal expansion material was 1.7 μm, and the thickness of the nickel alloy layer was 170 nm.

[0089] The volume resistivity of the obtained core-shell negative thermal expansion material was measured, and the results are shown in FIG. 4 and Table 1, respectively, showing the results of evaluation of the oxidation resistance.

[0090] Example 3 (i) Pretreatment Average particle diameter 45μm, specific surface area 0.4m 2 Pretreatment was carried out in the same manner as in Example 1, except that zirconium tungstate having a linear expansion coefficient of -9 ppm / °C was used as the core material, to obtain a slurry of pretreated zirconium tungstate. (ii) Preparation of plating bath A plating bath was prepared in the same manner as in Example 1. (iii) Electroless nickel plating The plating process was carried out in the same manner as in the electroless nickel plating process of Example 1, to obtain a core-shell negative thermal expansion material. The average particle size of the obtained core-shell negative thermal expansion material was 46 μm, and the thickness of the nickel alloy layer was 190 nm.

[0091] The volume resistivity of the obtained core-shell negative thermal expansion material was measured, and the results are shown in FIG. 5 and Table 1, respectively, showing the results of evaluation of the oxidation resistance.

[0092] Comparative Example 1 (i) Pretreatment Pretreatment was carried out in the same manner as in Example 1, to obtain a slurry of pretreated zirconium tungstate phosphate.

[0093] (ii) Adjustment of plating solution Three liters of a plating bath was prepared, which consisted of an aqueous solution containing 7.2 g / L of copper sulfate, 80 g / L of sodium potassium tartrate, 150 g / L of sodium hydroxide, and 0.1 g / L of nickel sulfate.

[0094] (iii) Electroless plating The pretreated zirconium tungstate phosphate slurry was added to this electroless plating bath and electroless plating was carried out for 20 minutes. The solution was then filtered, and the filtrate was washed three times and then dried in a vacuum dryer at 110°C to obtain a core-shell negative thermal expansion material in which a copper layer was formed as a shell layer on the surface of the core material. The average particle size of the obtained core-shell negative thermal expansion material was 22.5 μm, and the thickness of the copper layer was 180 nm. The oxidation resistance of the obtained core-shell negative thermal expansion material was evaluated, and the results are shown in Table 1.

[0095] [Table 1]

[0096] As a result of the evaluation of oxidation resistance, no change in the surface color tone was observed for the core-shell type negative thermal expansion materials of Examples 1 to 3, but the copper-plated material of Comparative Example 1 lost its metallic luster, and it was confirmed that oxidation was clearly progressing. As is clear from Table 1, the electrical resistance of the negative thermal expansion material of this example, which has a nickel alloy layer as a shell layer, hardly decreases before and after exposure to the atmosphere. On the other hand, the volume resistivity of the negative thermal expansion material of Comparative Example 1, which has a copper layer as a shell layer, after exposure to the atmosphere decreases significantly compared to the volume resistivity before exposure to the atmosphere. Therefore, the negative thermal expansion material has superior oxidation resistance compared to conventional negative thermal expansion materials having a copper layer.

[0097] [Reference example 1] In Example 1, the volume resistivity of zirconium tungstate phosphate (manufactured by Nippon Chemical Industry Co., Ltd.) was measured without electroless plating treatment. The results are shown in Figure 1. In addition, negative thermal expansion performance was evaluated. The results are shown in Table 2.

[0098] [Table 2]

[0099] From the results in FIG. 1, the volume resistance value of the core-shell type negative thermal expansion material obtained in Example 1 was lower than that of the negative thermal expansion material of Reference Example 1. Furthermore, from the results in Table 2, the nickel-plated core-shell type negative thermal expansion material of Example 1 exhibited the same level of linear expansion coefficient as the normal negative thermal expansion material of Reference Example 1. This shows that the core-shell type negative thermal expansion material of Example 1 has low electrical resistance while still possessing conventional negative thermal expansion properties.

[0100] [Reference example 2] In Example 2, the volume resistivity of zirconium tungstate phosphate (manufactured by Nippon Chemical Industry Co., Ltd.) was measured without electroless plating treatment, and the results are shown in FIG.

[0101] [Reference example 3] In Example 3, the volume resistivity of the zirconium tungstate was measured without electroless plating treatment, and the results are shown in FIG.

[0102] 4, the volume resistance value of the core-shell type negative thermal expansion material obtained in Example 2 was lower than that of the negative thermal expansion material of Reference Example 2. Similarly, the result of FIG. 5 shows that the volume resistance value of the core-shell type negative thermal expansion material obtained in Example 3 was lower than that of the negative thermal expansion material of Reference Example 3. This shows that the core-shell type negative thermal expansion materials of Examples 2 and 3 have low electrical resistance.

Claims

1. A core-shell negative thermal expansion material, wherein the core contains an inorganic oxide having negative thermal expansion properties and the shell contains a nickel alloy layer.

2. The core-shell negative thermal expansion material according to claim 1, wherein the inorganic oxide having negative thermal expansion has a linear expansion coefficient of -20 ppm / K or more and -0.05 ppm / K or less at 25°C or more and 500°C or less.

3. 3. The core-shell negative thermal expansion material according to claim 1, wherein the inorganic oxide having negative thermal expansion is zirconium tungstate phosphate.

4. 3. The core-shell negative thermal expansion material according to claim 1, wherein the nickel alloy layer is a nickel-phosphorus alloy layer or a nickel-boron alloy layer.

5. The core-shell negative thermal expansion material according to claim 1 or 2, wherein the linear expansion coefficient at 25°C or higher and 200°C or lower is -1 ppm / K or less.

6. Volume resistance is 1 x 10 －１ 3. The core-shell negative thermal expansion material according to claim 1, wherein the resistance is Ω·cm or less.

7. 3. The core-shell negative thermal expansion material according to claim 1, wherein the average particle size is 1 μm or more and 50 μm or less.

8. BET specific surface area is 6m ２ 3. The core-shell negative thermal expansion material according to claim 1, wherein the coefficient of thermal expansion is 0.1 / g or less.

9. A method for manufacturing a core-shell negative thermal expansion material, in which an inorganic oxide having negative thermal expansion as a core is subjected to electroless nickel plating to form a nickel alloy layer as a shell.

10. 10. The method for producing a core-shell type negative thermal expansion material according to claim 9, wherein the inorganic oxide having negative thermal expansion is zirconium tungstate phosphate.

11. The method for producing a core-shell negative thermal expansion material according to claim 9 or 10, wherein the electroless nickel plating treatment is performed using either a phosphorus-containing compound or a boron-containing compound as a reducing agent.

12. The method for producing a core-shell negative thermal expansion material according to claim 11, wherein the phosphorus-containing compound is sodium hypophosphite.

13. The method for producing a core-shell negative thermal expansion material according to claim 11, wherein the boron-containing compound is dimethylamine borane.

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