Negative thermal expansion material, method for manufacturing the same, and composite material

Abstract

The object of the present invention is to provide a negative thermal expansion material that consistently exhibits excellent negative thermal expansion characteristics over a wide temperature range of -30 to 150°C, and shows a more gradual volume decrease with increasing temperature compared to Zn2P2O7 between 100 and 150°C. The negative thermal expansion material of the present invention is characterized by containing 5 to 90 parts by mass of zinc pyrophosphate per 100 parts by mass of copper pyrophosphate, wherein the BET specific surface area of ​​the copper pyrophosphate is 0.2 to 8.0 m². 2 The BET specific surface area of ​​the zinc pyrophosphate is 0.2 to 8.0 m² / g. 2 It is preferable that it be / g.

Description

[Technical Field]

[0001] This invention relates to a negative thermal expansion material that contracts in response to temperature rise, a method for producing the same, and a composite material containing the negative thermal expansion material. [Background technology]

[0002] Many materials increase in length or volume due to thermal expansion when their temperature rises. In contrast, there are also materials that exhibit negative thermal expansion, where their volume decreases when heated (hereinafter sometimes referred to as "negative thermal expansion materials").

[0003] It is known that materials exhibiting negative thermal expansion can be used in conjunction with other materials to suppress changes in the thermal expansion of the material due to temperature changes.

[0004] Examples of materials exhibiting negative thermal expansion include β-eucryptite, zirconium tungstate (ZrW2O8), zirconium tungstate phosphate (Zr2WO4(PO4)2), and Zn. x CD 1-x (CN)2, manganese nitride, bismuth nickel iron oxide, etc. are known examples.

[0005] The linear expansion coefficient (hereinafter sometimes referred to as the "thermal expansion coefficient") of zirconium tungstate phosphate is -3.4 to -3.0 ppm / °C in the temperature range of 0 to 400°C, and it is known to have high negative thermal expansion. By using zirconium tungstate phosphate in combination with a material that exhibits positive thermal expansion (hereinafter sometimes referred to as a "positive thermal expansion material"), it is possible to manufacture a material with low thermal expansion (see Patent Documents 1-2, etc.). Furthermore, it has also been proposed to use a negative thermal expansion material in combination with a polymer compound such as a resin, which is a positive thermal expansion material (see Patent Document 3, etc.).

[0006] Furthermore, Patent Document 4 discloses that copper pyrophosphate of Cu2P2O7 has excellent negative thermal expansion properties in a temperature range of -150°C to 100°C.

[0007] In addition, Patent Document 5 discloses that zinc pyrophosphate of Zn2P2O7 has excellent negative thermal expansion properties in the temperature range of 100 to 150°C.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Summary of the Invention

Problems to be Solved by the Invention

[0009] Phosphates of Cu2P2O7 and Zn2P2O7 have advantages such as a smaller linear expansion coefficient compared to zirconium tungstate phosphate, can be manufactured from a more inexpensive raw material system, can be industrially advantageously manufactured, and have excellent water resistance.

[0010] However, copper pyrophosphate of Cu2P2O7 loses its negative thermal expansion characteristics in the high temperature range of 100 to 150°C. [[ID=D4]] [[ID=D5]]

[0011] ] In addition, in zinc pyrophosphate of Zn2P2O7, a rapid volume reduction occurs with an increase in temperature in the temperature range of 100 to 150°C. Therefore, in a composite material containing a negative thermal expansion material and a positive thermal expansion material, the positive thermal expansion material cannot follow the rapid volume reduction of the negative thermal expansion material, and as a result, it becomes difficult to achieve a zero thermal expansion rate or a low thermal expansion rate of the composite material containing the negative thermal expansion material. ]

[0012] ] ]Incidentally, there is a wide variety of positive thermal expansion materials and their usage environments, and there is a demand for the development of negative thermal expansion materials that consistently exhibit excellent negative thermal expansion characteristics over a wide temperature range from - to over 100°C.

[0013] Therefore, the present invention aims to provide a negative thermal expansion material that consistently exhibits excellent negative thermal expansion characteristics over a wide temperature range of -30 to 150°C, and shows a more gradual volume decrease with increasing temperature compared to Zn2P2O7 between 100 and 150°C. [Means for solving the problem]

[0014] The inventors, while investigating a negative thermal expansion material that consistently exhibits excellent negative thermal expansion characteristics over a wide temperature range from - to over 100°C, found that a material containing a specific amount of zinc pyrophosphate relative to copper pyrophosphate exhibits consistently excellent negative thermal expansion characteristics over a wide temperature range between -30 and 150°C, and between 100 and 150°C, it exhibits a more gradual volume decrease with increasing temperature compared to Zn2P2O7. Furthermore, we discovered that the negative thermal expansion material exhibits a lower coefficient of thermal expansion than the theoretical value calculated from the mixing ratio of copper pyrophosphate and zinc pyrophosphate, at least between 90 and 130°C, due to the synergistic effect of copper pyrophosphate and zinc pyrophosphate. This led to the completion of the present invention.

[0015] In other words, the present invention (1) provides a negative thermal expansion material characterized by containing 5 to 90 parts by mass of zinc pyrophosphate per 100 parts by mass of copper pyrophosphate.

[0016] Furthermore, in the present invention (2), the BET specific surface area of ​​the copper pyrophosphate is 0.2 to 8.0 m². 2 The present invention provides a negative thermal expansion material (1) characterized by being / g.

[0017] Furthermore, in the present invention (3), the BET specific surface area of ​​the zinc pyrophosphate is 0.2 to 8.0 m². 2 The present invention provides a negative thermal expansion material characterized by being / g, as described in (1) and (2).

[0018] Further, the present invention (4) provides the negative thermal expansion material of (1) to (3), characterized in that the BET specific surface area is 0.2 to 8.0 m 2 / g.

[0019] Also, the present invention (5) provides the negative thermal expansion material of (1) to (4), characterized in that the difference in the BET specific surface area of zinc pyrophosphate relative to the BET specific surface area of copper pyrophosphate (zinc pyrophosphate - copper pyrophosphate) is within ±5.5 m 2 / g.

[0020] Further, the present invention (6) provides the negative thermal expansion material of (1) to (5), characterized in that the thermal expansion coefficient between -30 and 150 °C is -9 × 10 ―6 / K or less.

[0021] Also, the present invention (7) provides the negative thermal expansion material of (6), characterized in that the thermal expansion coefficient between -30 and 25 °C is -1.0 × 10 ―6 / K or less.

[0022] Also, the present invention (8) provides the negative thermal expansion material of (6), characterized in that the thermal expansion coefficient between 90 and 130 °C is -6 × 10 ―6 , / K or less. ,

[0023] ,Further, the present invention (9) provides a method for manufacturing a negative thermal expansion material, characterized in that it includes a step of mixing 5 to 90 parts by mass of zinc pyrophosphate having a BET specific surface area of 0.2 to 8.0 m 2 / g with 100 parts by mass of copper pyrophosphate having a BET specific surface area of 0.2 to 8.0 m 2 [[,END]] / g. [[,ID=38]]

[0024] [[END,]] Also, the present invention (10) provides a method for manufacturing a negative thermal expansion material of (9), characterized,in that the copper pyrophosphate is obtained by firing a hydrated copper pyrophosphate salt at 550 to 850 °C.

[0025] It should be noted that there are some punctuation and grammar issues in the original text that may affect the understanding and translation. The above translation tries to be as accurate as possible based on the original text.Furthermore, the present invention (11) provides a method for producing the negative thermal expansion material of (9), characterized in that the zinc pyrophosphate is obtained by calcining a hydrated zinc pyrophosphate salt at 550 to 850°C.

[0026] Furthermore, the present invention (12) provides a composite material characterized by containing a negative thermal expansion material and a positive thermal expansion material from any of (1) to (8).

[0027] Furthermore, the present invention (13) provides a composite material of (12) characterized in that the positive thermal expansion material is at least one selected from metal, alloy, glass, ceramics, rubber, and resin. [Effects of the Invention]

[0028] According to the present invention, it is possible to provide a negative thermal expansion material that consistently exhibits excellent negative thermal expansion characteristics over a wide temperature range of -30 to 150°C, and shows a more gradual volume decrease with increasing temperature compared to Zn2P2O7 between 100 and 150°C. [Brief explanation of the drawing]

[0029] [Figure 1] X-ray diffraction pattern of the Zn2P2O7(ZNP1) sample prepared in the example. [Figure 2] X-ray diffraction pattern of the Cu2P2O7(CUP1) sample prepared in the example. [Figure 3] This diagram shows the relationship between the thermal shrinkage rate (%) and temperature (°C) of compacted molded articles using negative thermal expansion material samples from Examples 1-2, Comparative Example 2, and Comparative Example 4. [Figure 4] A diagram showing the relationship between the thermal shrinkage rate (%) and temperature (°C) of compacted molded articles using negative thermal expansion material samples from Example 3 and Comparative Examples 6-8. [Modes for carrying out the invention]

[0030] The present invention will be described below based on its preferred embodiments.

[0031] The negative thermal expansion material of the present invention contains copper pyrophosphate (Cu2P2O7) and zinc pyrophosphate (Zn2P2O7).

[0032] The first component of the negative thermal expansion material according to the present invention, copper pyrophosphate, has a thermal expansion coefficient of -25 × 10⁻¹⁰ between -30 and 100°C when used alone. ―6 ~-10×10 ―6 It has a negative thermal expansion property of / K.

[0033] The preferred physical properties of copper pyrophosphate to be contained in the negative thermal expansion material according to the present invention are a BET specific surface area of ​​0.2 to 8.0 m². 2 / g, preferably 0.3 to 7.0m 2 A particle size of 0.2 to 10 μm, preferably 0.3 to 8.0 μm, is preferable from the viewpoint that a homogeneous mixture with the second component, zinc pyrophosphate, is easily obtained, and when used as a filler, the fluidity of the negative thermal expansion material is good and the dispersibility into the positive thermal expansion material is good.

[0034] The second component of the negative thermal expansion material according to the present invention, zinc pyrophosphate, has a thermal expansion coefficient of -130 × 10⁻¹⁰ between 100 and 150°C when used alone. ―6 ~-100×10 ―6 Although it is a material with negative thermal expansion of / K, its negative thermal expansion changes depending on the particle size. That is, the larger the BET specific surface area, the smaller the coefficient of thermal expansion.

[0035] The preferred physical properties of zinc pyrophosphate to be contained in the negative thermal expansion material according to the present invention are a BET specific surface area of ​​0.2 to 8.0 m². 2 / g, preferably 0.3 to 7.0m 2A particle size of 0.2 to 10 μm, preferably 0.3 to 8 μm, is preferable from the viewpoint that a homogeneous mixture with the first component, copper pyrophosphate, can be easily obtained, and when used as a filler, the fluidity of the negative thermal expansion material will be good and the dispersibility into the positive thermal expansion material will be good.

[0036] Furthermore, the difference in the BET specific surface area of ​​zinc pyrophosphate compared to the BET specific surface area of ​​copper pyrophosphate contained in the negative thermal expansion material according to the present invention (zinc pyrophosphate - copper pyrophosphate) is ±5.5 m². 2 Within / g, preferably ±4.5m 2 It is preferable that the value be within / g, as this improves the fluidity of the negative thermal expansion material and enhances its dispersibility into the positive thermal expansion material when used as a filler.

[0037] The negative thermal expansion material according to the present invention contains 5 to 90 parts by mass of zinc pyrophosphate per 100 parts by mass of copper pyrophosphate.

[0038] The reason for this is that if the amount of zinc pyrophosphate is less than 5 parts by mass per 100 parts by mass of copper pyrophosphate, the negative thermal expansion between 90°C and 130°C is insufficient. On the other hand, if the amount of zinc pyrophosphate exceeds 90 parts by mass per 100 parts by mass of copper pyrophosphate, the negative thermal expansion between -30°C and 25°C is insufficient.

[0039] Furthermore, the negative thermal expansion material according to the present invention has consistently excellent negative thermal expansion characteristics over a wide temperature range of -30 to 150°C, and in the range of 100 to 150°C, it exhibits a more gradual volume decrease with increasing temperature compared to Zn2P2O7. From this viewpoint, the ratio of zinc pyrophosphate to copper pyrophosphate is 10 to 80 parts by mass, more preferably 10 to 60 parts by mass, per 100 parts by mass of copper pyrophosphate.

[0040] The negative thermal expansion material according to the present invention has a thermal expansion coefficient of -9 × 10 between -30 and 150°C. ―6 / K or less, preferably -25 × 10―6 ~-9×10 ―6 A value of / K is preferable from the viewpoint of increasing the counteracting effect of the negative thermal expansion material on the positive thermal expansion material.

[0041] Furthermore, the negative thermal expansion material according to the present invention has a thermal expansion coefficient of -1.0 × 10 between -30 and 25°C. ―6 / K or less, preferably -15 × 10 ―6 ~-2.0 × 10 ―6 A value of / K is particularly preferable from the viewpoint of increasing the counteracting effect of the negative thermal expansion material on the positive thermal expansion material.

[0042] Furthermore, the negative thermal expansion material according to the present invention has a thermal expansion coefficient of -6 × 10 between 90 and 130°C. ―6 / K or less, preferably -25 × 10 ―6 ~-7×10 ―6 A value of / K is particularly preferable from the viewpoint of increasing the counteracting effect of the negative thermal expansion material on the positive thermal expansion material.

[0043] In this invention, the coefficient of thermal expansion is determined by the following procedure. First, 1.00 g of the sample is ground and mixed in a mortar for 3 minutes, then 0.15 g is weighed out and the entire amount is filled into a φ6 mm mold. Next, a compacted powder molded body is produced by molding it with a pressure of 10 MPa using a hand press. Then, the coefficient of thermal expansion of the produced compacted powder molded body is measured using a thermomechanical measuring device (for example, NETZSCH JAPAN TMA4000SE). The measurement conditions are nitrogen atmosphere, load of 10 g, and temperature range of -35°C to 170°C, and the measurement is repeated twice. The coefficients of thermal expansion between -30 to 150°C, -30 to 25°C, and 90 to 130°C in the second measurement are taken as the coefficient of thermal expansion of the negative thermal expansion material.

[0044] The negative thermal expansion material of the present invention has, for example, a BET specific surface area of ​​0.2 to 8.0 m². 2 For 100 parts by mass of copper pyrophosphate per g, the BET specific surface area is 0.2 to 8.0 m². 2 The product can be manufactured industrially advantageously by including a step of mixing 5 to 90 parts by mass, preferably 10 to 80 parts by mass, and more preferably 10 to 60 parts by weight of zinc pyrophosphate per gram.

[0045] In the method for producing a negative thermal expansion material of the present invention, it is preferable from the viewpoint of industrially advantageous production that the first raw material, copper pyrophosphate, is obtained by calcining a commercially available hydrated copper pyrophosphate (Cu2P2O7·3H2O).

[0046] Preferred physical properties of the hydrated copper pyrophosphate include an average particle size of 3 μm or less, preferably 0.1 to 2.0 μm, as determined by SEM observation. This is preferable because when copper pyrophosphate is produced by calcination, a homogeneous mixture with the second component, zinc pyrophosphate, is easily obtained, and when used as a filler, it improves the fluidity of the negative thermal expansion material and the dispersibility into the positive thermal expansion material.

[0047] By calcining the hydrated copper pyrophosphate at a temperature of 550 to 850°C, preferably 600 to 800°C, for 1 hour or more, preferably 1.5 to 8 hours, copper pyrophosphate with a BET specific surface area within that range can be obtained.

[0048] Furthermore, in the method for producing the negative thermal expansion material of the present invention, it is preferable from the viewpoint of industrially advantageous production that the second raw material, zinc pyrophosphate, is obtained by calcining a commercially available hydrated zinc pyrophosphate (Zn2P2O7·3H2O).

[0049] Preferred physical properties of hydrated zinc pyrophosphate include an average particle size of 3 μm or less, preferably 0.1 to 2.0 μm, as determined by SEM observation. This is preferable because it facilitates obtaining a homogeneous mixture with the first component, copper pyrophosphate, when zinc pyrophosphate is produced by calcination, and when used as a filler, it improves the fluidity of the negative thermal expansion material and the dispersibility into the positive thermal expansion material.

[0050] By calcining the hydrated zinc pyrophosphate at a temperature of 550 to 850°C, preferably 600 to 800°C, for 1 hour or more, preferably 1.5 to 8 hours, zinc pyrophosphate with a BET specific surface area within that range can be obtained.

[0051] The mixing process of copper pyrophosphate and zinc pyrophosphate can be carried out by either a dry or wet method, but the dry method is preferred because it is easier to manufacture. In the case of dry mixing, there are no particular restrictions as long as the mixing process can be carried out uniformly, and mixing devices such as high-speed mixers, super mixers, turbosphere mixers, Eilich mixers, Henschel mixers, Nauter mixers, ribbon blenders, V-type mixers, conical blenders, jet mills, cosmo-mizers, paint shakers, bead mills, and ball mills can be used. At the laboratory level, mixing with a household mixer or mortar and pestle is sufficient.

[0052] The average particle size of the negative thermal expansion material obtained by the method for producing the negative thermal expansion material of the present invention, as determined by SEM observation, is preferably 0.2 to 10.0 μm, particularly preferably 0.3 to 9.0 μm, and even more preferably 0.4 to 8.0 μm. The BET specific surface area is 0.2 to 8.0 m². 2 / g, particularly preferably 0.3 to 7.0m 2 / g, more preferably 0.4~6.0m 2 The average particle size and / or BET specific surface area of ​​the negative thermal expansion material being within the above range is preferable because it facilitates handling when using the negative thermal expansion material as a filler in resins, glass, etc.

[0053] Furthermore, the negative thermal expansion material according to the present invention may have its particle surface treated as necessary in order to improve resin dispersibility and moisture resistance of the negative thermal expansion material.

[0054] Examples of surface treatments include coating the particle surface with a silane coupling agent, a titanate coupling agent, a fatty acid or its derivative, or an inorganic compound containing one or more elements selected from Zn, Si, Al, Ba, Ca, Mg, Ti, V, Sn, Co, Fe, and Zr (see, for example, WO2020 / 095837, WO2020 / 261976, WO2019 / 087722, and Japanese Patent Publication No. 2020-147486). Alternatively, these methods may be combined as appropriate for surface treatment.

[0055] The negative thermal expansion material obtained by the method for producing the negative thermal expansion material of the present invention consistently exhibits excellent negative thermal expansion characteristics over a wide temperature range of -30 to 150°C, and between 100 and 150°C, it shows a more gradual volume decrease with increasing temperature compared to Zn2P2O7.

[0056] The thermal expansion coefficient of the negative thermal expansion material obtained by the method for producing the negative thermal expansion material of the present invention between -30 and 150°C is -9 × 10 -6 / K or less, preferably -10 × 10 -6 It is less than or equal to / K, and there are no particular restrictions on the lower limit, but -40 × 10 -6 / K or higher, preferably -35×10 -6 It is 10 / K or higher. In the negative thermal expansion material of the present invention, when combined with a positive thermal expansion material, the coefficient of thermal expansion is more likely to cancel out the positive expansion, and is therefore particularly preferably -25 × 10 -6 ~-9×10 -6 It is / K.

[0057] Furthermore, the thermal expansion coefficient of the negative thermal expansion material obtained by the method for manufacturing the negative thermal expansion material of the present invention between -30 and 25°C is -1.0 × 10⁻⁶ -6 / K or less, preferably -1.5 × 10 -6 It is less than or equal to / K, and there are no particular restrictions on the lower limit, but -20 × 10 -6 / K or higher, preferably -15 × 10 -6 It is 15 × 10⁻¹⁰ or higher. In the negative thermal expansion material of the present invention, when combined with a positive thermal expansion material, the coefficient of thermal expansion is more likely to cancel out the positive expansion, and is therefore particularly preferably -15 × 10⁻¹⁰.-6 ~-2.0 × 10 -6 It is / K.

[0058] Furthermore, the thermal expansion coefficient of the negative thermal expansion material obtained by the method for manufacturing the negative thermal expansion material of the present invention between 90 and 130°C is -6 × 10⁻⁶ -6 / K or less, preferably -7 × 10 -6 It is less than or equal to / K, and there are no particular restrictions on the lower limit, but -40 × 10 -6 / K or higher, preferably -35×10 -6 It is 10 / K or higher. In the negative thermal expansion material of the present invention, when combined with a positive thermal expansion material, the coefficient of thermal expansion is more likely to cancel out the positive expansion, and is therefore particularly preferably -25 × 10 -6 ~-7×10 -6 It is / K.

[0059] The negative thermal expansion material of the present invention is used as a powder or a paste. When the negative thermal expansion material of the present invention is used as a paste, it is mixed and dispersed in a solvent and / or a low-viscosity liquid resin and used in paste form. Alternatively, the negative thermal expansion material of the present invention may be dispersed in a solvent and / or a low-viscosity liquid resin, and if necessary, a binder, flux, dispersant, etc., may be added and used in paste form.

[0060] The negative thermal expansion material of the present invention is used as a positive thermal expansion material in combination with various organic or inorganic compounds to form a composite material. The composite material of the present invention includes the negative thermal expansion material and the positive thermal expansion material of the present invention.

[0061] The organic compounds used as positive thermal expansion materials are not particularly limited, and examples include rubber, polyolefin, polycycloolefin, polystyrene, ABS, polyacrylate, polyphenylene sulfide, phenol resin, polyamide resin, polyimide resin, epoxy resin, silicone resin, polycarbonate resin, polyethylene resin, polypropylene resin, polyethylene terephthalate resin (PET resin), and polyvinyl chloride resin. In addition, examples of the inorganic compounds used as positive thermal expansion materials include silicon dioxide, silicate, graphite, sapphire, various glass materials, concrete materials, and various ceramic materials.

[0062] Since the composite material of the present invention contains the negative thermal expansion material of the present invention having excellent negative thermal expansion characteristics, it is possible to achieve a negative thermal expansion rate, a zero thermal expansion rate, or a low thermal expansion rate depending on the blending ratio with other compounds.

Example

[0063] Hereinafter, the present invention will be described by way of examples, but the present invention is not limited thereto. (X-ray diffractometer) In the examples, measurements are performed under the following measurement conditions using an X-ray diffractometer (UltimaIV manufactured by Rigaku Corporation).

[0064] X-ray source: Cu-Kα Tube voltage: 40 kV Tube current: 40 mA Scanning speed: 1° / sec Smoothing: Weighted averaging method Kα2 removal: Intensity ratio 0.5

[0065] <Preparation of Zn2P2O7 sample> Note that the average particle diameters of the following zinc pyrophosphate trihydrate and copper pyrophosphate trihydrate were determined based on the average values of 50 particles arbitrarily extracted at a magnification of 1000 times in scanning electron microscope observations.

[0066] (ZNP1 sample) Zinc pyrophosphate trihydrate (Zn2P2O7·3H2O, average particle size 1.2 μm) was calcined at 660 °C for 1.5 hours. When the calcined powder was analyzed by X-ray diffraction, it was found to be single-phase Zn2P2O7 (see Fig. 1). This was used as the Zn2P2O7 sample.

[0067] (ZNP2 sample) Zinc pyrophosphate trihydrate (Zn2P2O7·3H2O, average particle size 1.2 μm) was calcined at 700 °C for 1.5 hours. When the calcined powder was analyzed by X-ray diffraction, it was found to be single-phase Zn2P2O7. This was used as the Zn2P2O7 sample.

[0068] (ZNP3 sample) Zinc pyrophosphate trihydrate (Zn2P2O7·3H2O, average particle size 1.2 μm) was calcined at 600 °C for 1.5 hours. When the calcined powder was analyzed by X-ray diffraction, it was found to be single-phase Zn2P2O7. This was used as the Zn2P2O7 sample.

[0069] <Preparation of Cu2P2O7 sample> (CUP1 sample) Copper pyrophosphate trihydrate (Cu2P2O7·3H2O, average particle size 1.0 μm) was calcined at 600 °C for 1.5 hours. When the calcined powder was analyzed by X-ray diffraction, it was found to be single-phase Cu2P2O7 (see Fig. 2). This was used as the Cu2P2O7 sample.

[0070] (CUP2 sample) I Copper pyrophosphate trihydrate (Cu2P2O7·3H2O, average particle size 1.0 μm) was calcined at 700 °C for 1.5 hours. When the calcined powder was analyzed by X-ray diffraction, it was found to be single-phase Cu2P2O7. This was used as the Cu2P2O7 sample.

[0071] <Physical property evaluation> The average particle size and BET specific surface area of the Zn2P2O7 sample and Cu2P2O7 sample obtained above were measured. The results are shown in Table 1. The average particle size of the Zn2P2O7 sample and Cu2P2O7 sample was determined by the average value of 50 particles arbitrarily extracted at a magnification of 1000 times in scanning electron microscope observation.

[0072] [Table 1]

[0073] (Examples 1-5) The Cu2P2O7 sample and Zn2P2O7 sample prepared above were thoroughly mixed in a mortar in the proportions shown in Table 2, and this was used as the negative thermal expansion material sample.

[0074] (Comparative Example 1) The copper pyrophosphate (CUP1) sample prepared above was thoroughly mixed in a mortar and pestle to obtain the negative thermal expansion material sample.

[0075] (Comparative Example 2) The copper pyrophosphate (CUP2) sample prepared above was thoroughly mixed in a mortar and pestle to obtain the negative thermal expansion material sample.

[0076] (Comparative Example 3) The zinc pyrophosphate (ZNP1) sample prepared above was thoroughly mixed in a mortar and pestle to obtain the negative thermal expansion material sample.

[0077] (Comparative Example 4) The zinc pyrophosphate (ZNP2) sample prepared above was thoroughly mixed in a mortar and pestle to obtain the negative thermal expansion material sample.

[0078] (Comparative Example 5) The zinc pyrophosphate (ZNP3) ​​sample prepared above was thoroughly mixed in a mortar and pestle to obtain the negative thermal expansion material sample.

[0079] (Comparative Examples 6-9) The Cu2P2O7 sample and Zn2P2O7 sample prepared above were thoroughly mixed in a mortar in the proportions shown in Table 2, and this was used as the negative thermal expansion material sample.

[0080] (Evaluation of physical properties) The average particle size and BET specific surface area were measured for the negative thermal expansion material samples obtained in the examples and comparative examples. The average particle size was measured as follows. (Average particle size) The average particle size of the negative thermal expansion material sample was determined by the average value of 50 particles arbitrarily extracted at a magnification of 1000x using a scanning electron microscope.

[0081] [Table 2]

[0082] (Evaluation of negative thermal expansion) The linear thermal expansion coefficient (thermal expansion coefficient) was measured for the negative thermal expansion material samples obtained in the examples and comparative examples as described below, and the results are shown in Table 3. Furthermore, the theoretical linear thermal expansion coefficient (C) calculated from the mixing ratio of copper pyrophosphate and zinc pyrophosphate using the following formula (1) is also shown in Table 3.

[0083] C(ppm / K)={E1×A1 / 100}+{E2×A2 / 100} (1) E1: Linear thermal expansion coefficient (ppm / K) of copper pyrophosphate samples between -30 and 150°C, or between 90 and 130°C. E2: Linear thermal expansion coefficient (ppm / K) of zinc pyrophosphate samples between -30 and 150°C, or between 90 and 130°C. A1: Mixing ratio (mass%) of copper pyrophosphate sample to negative thermal expansion material sample A2: Mixing ratio (mass%) of zinc pyrophosphate sample to negative thermal expansion material sample

[0084] (Measurement of linear expansion coefficient (thermal expansion coefficient)) The obtained samples were subjected to linear expansion measurements at -30 to 150°C as described below. (Preparation of compacted powder bodies) 1.00 g of the sample was ground and mixed in a mortar for 3 minutes, then 0.15 g was weighed and the entire amount was filled into a φ6 mm mold. Next, a compacted powder body was produced by molding with a pressure of 10 MPa using a hand press. The thermal expansion coefficient of the produced compacted powder body was measured using a thermomechanical measuring device (NETZSCH JAPAN TMA4000SE). The measurement conditions were nitrogen atmosphere, load of 10 g, and temperature range of -35°C to 170°C, and measurements were taken twice. The thermal expansion coefficients for the second measurement in the ranges of -30°C to 150°C, -30°C to 25°C, and 90°C to 130°C were calculated. Furthermore, the relationship between the thermal shrinkage rate (%) and temperature (°C) of the compacted powder body is shown in Figure 3 (Example 1, Example 2, Comparative Example 2, Comparative Example 4) and Figure 4 (Example 3, Comparative Example 6, Comparative Example 7, Comparative Example 8).

[0085] [Table 3]

[0086] As shown in Table 3, the negative thermal expansion material of the embodiment of the present invention exhibits a linear expansion coefficient that is equivalent to or smaller than the theoretically calculated coefficient in the range of -30 to 150°C. On the other hand, in the range of 90 to 130°C, the linear expansion coefficient is smaller than the theoretically calculated coefficient due to the synergistic effect of copper pyrophosphate and zinc pyrophosphate, indicating even better negative thermal expansion properties. Furthermore, Figures 3 and 4 show that the embodiments of the present invention (Examples 1, 2, and 3) consistently exhibit negative thermal expansion properties between -30 and 150°C. Additionally, the negative thermal expansion materials of the embodiments of the present invention (Examples 1, 2, and 3) show a more gradual volume decrease with increasing temperature between 100 and 150°C compared to the negative thermal expansion material of Zn2P2O7 alone (Comparative Example 4). Furthermore, comparing the negative thermal expansion material of Example 3 with the negative thermal expansion material of Comparative Example 8, Figure 4 and Table 3 show that the negative thermal expansion material of Comparative Example 8 has insufficient negative thermal expansion between -30 and 25°C compared to the negative thermal expansion material of Example 3, and that a rapid volume decrease occurs with increasing temperature between 100 and 150°C. Also, comparing the negative thermal expansion material of Example 3 with the negative thermal expansion material of Comparative Example 6, Figure 4 shows that the negative thermal expansion material of Example 3 consistently decreases in volume even between 100 and 150°C, whereas the negative thermal expansion material of Comparative Example 6 shows almost no volume decrease between 100 and 150°C.

[0087] Furthermore, a consistent volume decrease was observed in the other negative thermal expansion materials of Example 4 as well, between -30 and 150°C. It was also confirmed that, compared to the negative thermal expansion material of Zn2P2O7 alone, it showed a gradual volume decrease with increasing temperature between 100 and 150°C.

Claims

1. A negative thermal expansion material characterized by containing 5 to 90 parts by mass of zinc pyrophosphate per 100 parts by mass of copper pyrophosphate.

2. The BET specific surface area of ​​the aforementioned copper pyrophosphate is 0.2 to 8.0 m². ２ The negative thermal expansion material according to claim 1, characterized in that it is / g.

3. The BET specific surface area of ​​the aforementioned zinc pyrophosphate is 0.2 to 8.0 m². ２ The negative thermal expansion material according to claim 1, characterized in that it is / g.

4. The BET specific surface area is 0.2 to 8 m². ２ The negative thermal expansion material according to claim 1, characterized in that it is / g.

5. The difference in the BET specific surface area of ​​zinc pyrophosphate compared to the BET specific surface area of ​​copper pyrophosphate (zinc pyrophosphate - copper pyrophosphate) is ±5.5 m ２ The negative thermal expansion material according to claim 1, characterized in that it is within / g.

6. The coefficient of thermal expansion between -30 and 150°C is -9 × 10⁻⁶ ―６ The negative thermal expansion material according to claim 1, characterized in that it is ppm / K or less.

7. The negative thermal expansion material according to claim 6, characterized in that its thermal expansion coefficient between -30 and 25°C is -1.0 ppm / K or less.

8. The coefficient of thermal expansion between 90°C and 130°C is -6 × 10⁻⁶ ―６ The negative thermal expansion material according to claim 6, characterized in that it is ppm / K or less.

9. BET specific surface area is 0.2 to 8.0 m² ２ For 100 parts by mass of copper pyrophosphate at a concentration of 1g, the BET specific surface area is 0.2 to 8.0 m². ２ A method for producing a negative thermal expansion material, characterized by including a step of mixing it with 5 to 150 parts by mass of zinc pyrophosphate at a concentration of 1g / g.

10. The method for producing a negative thermal expansion material according to claim 9, characterized in that the copper pyrophosphate is obtained by calcining a hydrated copper pyrophosphate salt at 550 to 850°C.

11. The method for producing a negative thermal expansion material according to claim 9, characterized in that the zinc pyrophosphate is obtained by calcining a hydrated zinc pyrophosphate salt at 550 to 850°C.

12. A composite material characterized by comprising the negative thermal expansion material and the positive thermal expansion material described in claim 1.

13. The composite material according to claim 12, characterized in that the positive thermal expansion material is at least one selected from metal, alloy, glass, ceramics, rubber, and resin.

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