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

Abstract

The purpose of the present invention is to provide a negative thermal expansion material having a consistently excellent negative thermal expansion property in a wide temperature range of -30 to 150°C, and exhibiting a gradual decrease in volume with increasing temperature compared with Zn2P2O7 in the temperature range of 100 to 150°C. The negative thermal expansion material according to the present invention is characterized by containing 5 to 90 parts by mass of zinc pyrophosphate relative to 100 parts by mass of copper pyrophosphate. It is preferable that the BET specific surface area of the copper pyrophosphate is 0.2 to 8.0 m2 / g and that the BET specific surface area of the zinc pyrophosphate is 0.2 to 8.0 m2 / g.

Description

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

[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.

[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.). 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 contains Cu ２ P ２ O ７ It has been disclosed that copper pyrophosphate exhibits excellent negative thermal expansion properties in a temperature range of -150°C to 100°C.

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

[0008] Japanese Unexamined Patent Application Publication No. 2005-35840, Japanese Unexamined Patent Application Publication No. 2015-10006, Japanese Unexamined Patent Application Publication No. 2018-2577, Chinese Patent Application Publication No. 110229001, International Publication No. WO 2022 / 114004 Pamphlet

[0009] Cu ２ P ２ O ７ Pyrophosphates such as Zn₂P₂O₇ have advantages including a smaller coefficient of linear expansion than zirconium tungsten phosphate, can be produced from cheaper raw material systems, can be produced industrially advantageously, and are excellent in water resistance.

[0010] However, Cu ２ P ２ O ７ copper pyrophosphate loses negative thermal expansion properties in a high temperature range of 100 to 150°C.

[0011] In addition, for zinc pyrophosphate of Zn₂P₂O₇, a rapid volume decrease occurs as the temperature rises within the temperature range of 100 to 150°C. For this reason, 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 decrease of the negative thermal expansion material, and as a result, it becomes difficult to achieve a zero coefficient of thermal expansion or a low coefficient of thermal expansion for the composite material containing the negative thermal expansion material.

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

[0013] Accordingly, the present invention provides a negative thermal expansion material that consistently has excellent negative thermal expansion properties over a wide temperature range from -30 to 150°C, and exhibits a gradual volume decrease as the temperature rises between 100 and 150°C compared to Zn ２ P ２ O ７ , and an object of the present invention is to provide said negative thermal expansion material.

[0014] The inventors, while investigating a negative thermal expansion material that consistently exhibits excellent negative thermal expansion characteristics over a wide temperature range from minus 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, Zn ２ P ２ O ７ In contrast, it becomes a negative thermal expansion material that exhibits a gradual volume decrease with increasing temperature. Furthermore, we have discovered that, at least between 90 and 130°C, the thermal expansion coefficient of this negative thermal expansion material is lower than the theoretical value calculated from the mixing ratio of copper pyrophosphate and zinc pyrophosphate due to the synergistic effect of copper pyrophosphate and zinc pyrophosphate, and have completed 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 having a density of / 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 negative thermal expansion materials (1) to (2) characterized by having a density of / g.

[0018] Furthermore, the present invention (4) relates to a material with a BET specific surface area of ​​0.2 to 8.0 m². ２ The present invention provides negative thermal expansion materials (1) to (3) characterized by having a density of / g.

[0019] Furthermore, in the present invention (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 present invention provides negative thermal expansion materials (1) to (4) characterized by being within / g.

[0020] Furthermore, the present invention (6) has a thermal expansion coefficient between -30 and 150°C of -9 × 10 ―６The present invention provides negative thermal expansion materials (1) to (5) characterized by having a temperature of / K or less.

[0021] Furthermore, the present invention (7) has a thermal expansion coefficient of -1.0 × 10 between -30 and 25°C. ―６ The present invention provides a negative thermal expansion material (6) characterized by having a temperature of / K or less.

[0022] Furthermore, the present invention (8) has a thermal expansion coefficient between 90 and 130°C of -6 × 10 ―６ The present invention provides a negative thermal expansion material (6) characterized by having a temperature of / K or less.

[0023] Furthermore, the present invention (9) relates to a material with a BET specific surface area of ​​0.2 to 8.0 m². ２ For 100 parts by mass of copper pyrophosphate per gram, the BET specific surface area is 0.2 to 8.0 m². ２ The present invention provides a method for producing a negative thermal expansion material, characterized by including a step of mixing it with 5 to 90 parts by mass of zinc pyrophosphate at a concentration of 1g / g.

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

[0025] 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, which are among (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.

[0028] According to the present invention, it has consistently excellent negative thermal expansion characteristics over a wide temperature range of -30 to 150°C, and between 100 and 150°C, Zn ２ P ２ O ７In comparison, this method provides a negative thermal expansion material that exhibits a gradual volume decrease with increasing temperature.

[0029] Zn prepared in the example ２ P ２ O ７ X-ray diffraction pattern of the (ZNP1) sample. Cu prepared in the example. ２ P ２ O ７ X-ray diffraction pattern of the (CUP1) sample. Relationship between thermal shrinkage rate (%) and temperature (°C) of compacted molded bodies using negative thermal expansion material samples of Examples 1-2, Comparative Example 2, and Comparative Example 4. Relationship between thermal shrinkage rate (%) and temperature (°C) of compacted molded bodies using negative thermal expansion material samples of Example 3 and Comparative Examples 6-8.

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

[0031] The negative thermal expansion material of the present invention is copper pyrophosphate (Cu ２ P ２ O ７ ) and zinc pyrophosphate (Zn ２ P ２ O ７ It contains ).

[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 x 10 ―６ It has negative thermal expansion properties 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 7.0 m 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, 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.

[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 x 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 7.0 m ２ A concentration 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, 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.

[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 m ２ Within / g, preferably ±4.5m ２ A value of less than / g is preferable from the viewpoint of improving the fluidity of the negative thermal expansion material and 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 consistently exhibits particularly excellent negative thermal expansion characteristics over a wide temperature range of -30 to 150°C, and between 100 and 150°C, Zn ２ P ２ O ７ In contrast to the above, from the viewpoint of providing a negative thermal expansion material that exhibits a gradual volume decrease with increasing temperature, the ratio of zinc pyrophosphate to copper pyrophosphate is 10 to 80 parts by mass, more preferably 10 to 60 parts by mass.

[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 x 10 ―６ ~-9 x 10 ―６ Having 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 x 10 ―６ Having 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 x 10 ―６ ~-7 x 10 ―６ Having 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, TMA4000SE manufactured by NETZSCH JAPAN). The measurement conditions are nitrogen atmosphere, load of 10 g, and temperature range of -35°C to 170°C, and measurements are taken twice repeatedly. 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 gram, 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, the first raw material, copper pyrophosphate, is a commercially available hydrated copper pyrophosphate (Cu ２ P ２ O ７ 3H ２ From the viewpoint of industrially advantageous production, it is preferable that the copper pyrophosphate hydrate is obtained by calcining it using O).

[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 it facilitates obtaining a homogeneous mixture with the second component, zinc pyrophosphate, when converted to copper pyrophosphate 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.

[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, the second raw material, zinc pyrophosphate, is a commercially available hydrated zinc pyrophosphate (Zn ２ P ２ O ７ 3H ２ From the viewpoint of industrially advantageous production, it is preferable that the zinc pyrophosphate hydrate is obtained by calcining it using O).

[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, and the BET specific surface area is 0.2 to 8.0 m². 2 / g, particularly preferably 0.3 to 7.0 m 2 / g, more preferably 0.4 to 6.0 m 2 The value is / g. 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 makes handling easier 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). These methods may also 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, Zn ２ P ２ O ７ In contrast, it shows a more gradual decrease in volume with increasing temperature.

[0056] 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 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 / K or higher. In the negative thermal expansion material of the present invention, particularly preferably -25×10 -6 to -9×10 -6 / K.

[0057] Further, the coefficient of thermal expansion between -30°C and 25°C of the negative thermal expansion material obtained by the method for producing a negative thermal expansion material of the present invention is -1.0×10 -6 / K or less, preferably -1.5×10 -6 / K or less. There is no particular restriction on the lower limit, but it is -20×10 -6 / K or higher, preferably -15×10 -6 / K or higher. In the negative thermal expansion material of the present invention, particularly preferably -15×10 -6 to -2.0×10 -6 / K.

[0058] Further, the coefficient of thermal expansion between 90°C and 130°C of the negative thermal expansion material obtained by the method for producing a negative thermal expansion material of the present invention is -6×10 -6 / K or less, preferably -7×10 -6 / K or less. There is no particular restriction on the lower limit, but it is -40×10 -6 / K or higher, preferably -35×10 -6 / K or higher. In the negative thermal expansion material of the present invention, particularly preferably -25×10 -6 to -7×10 -6 / K.

[0059] The negative thermal expansion material of the present invention is used as powder or paste. When the negative thermal expansion material of the present invention is used as a paste, the negative thermal expansion material of the present invention is mixed and dispersed in a solvent and / or a low-viscosity liquid resin, and used in the form of a paste. 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, further contain a binder, a flux material, a dispersant and the like, and be used in the form of a paste.

[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] Organic compounds used as positive thermal expansion materials are not particularly limited, but include rubber, polyolefins, polycycloolefins, polystyrene, ABS, polyacrylate, polyphenylene sulfide, phenolic resins, polyamide resins, polyimide resins, epoxy resins, silicone resins, polycarbonate resins, polyethylene resins, polypropylene resins, polyethylene terephthalate resins (PET resins), and polyvinyl chloride resins. Inorganic compounds used as positive thermal expansion materials include silicon dioxide, silicates, graphite, sapphire, various glass materials, concrete materials, and various ceramic materials.

[0062] Because the composite material of the present invention contains the negative thermal expansion material of the present invention, which has excellent negative thermal expansion properties, it is possible to achieve a negative thermal expansion coefficient, zero thermal expansion coefficient, or low thermal expansion coefficient by adjusting the blending ratio with other compounds.

[0063] The present invention will be described below with reference to examples, but the present invention is not limited to these examples. (X-ray diffractometer) In the examples, an X-ray diffractometer (Ultima IV manufactured by Rigaku Corporation) is used to perform measurements under the following measurement conditions.

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

[0065] <Preparation of Zn2P2O7 Sample> The average particle sizes of zinc pyrophosphate trihydrate and copper pyrophosphate trihydrate were determined by the average value of 50 particles arbitrarily extracted at a magnification of 1000x using a scanning electron microscope.

[0066] (ZNP1 sample) Zinc pyrophosphate trihydrate (Zn2P2O7·3H2O, average particle size 1.2 μm) was calcined at 660°C for 1.5 hours. X-ray diffraction analysis of the calcined powder revealed that it was single-phase Zn2P2O7 (see Figure 1). ２ P ２ O ７ It was used as a sample.

[0067] (ZNP2 sample) Zinc pyrophosphate trihydrate (Zn2P2O7·3H2O, average particle size 1.2 μm) was calcined at 700°C for 1.5 hours. X-ray diffraction analysis of the calcined powder revealed that it was single-phase Zn2P2O7. ２ P ２ O ７ It was used as a sample.

[0068] (ZNP3 sample) Zinc pyrophosphate trihydrate (Zn2P2O7·3H2O, average particle size 1.2 μm) was calcined at 600°C for 1.5 hours. X-ray diffraction analysis of the calcined powder revealed that it was single-phase Zn2P2O7. ２ P ２ O ７ It was used as a sample.

[0069] <Cnet ２ P ２ O ７ Sample Preparation > (CUP1 Sample) Copper pyrophosphate trihydrate (Cu2P2O7·3H2O, average particle size 1.0 μm) was calcined at 600°C for 1.5 hours. X-ray diffraction analysis of the calcined powder revealed that it was single-phase Cu2P2O7 (see Figure 2). This Cu ２ P ２ O ７ It was used as a sample.

[0070] (CUP2 sample) Copper pyrophosphate trihydrate (Cu2P2O7·3H2O, average particle size 1.0 μm) was calcined at 700°C for 1.5 hours. X-ray diffraction analysis of the calcined powder revealed that it was single-phase Cu2P2O7. ２ P ２ O ７ It was used as a sample.

[0071] <Physical property evaluation> The Zn2P2O7 sample and Cu obtained above ２ P ２ O ７The average particle size and BET specific surface area were measured for the samples. The results are shown in Table 1. Note that the Zn2P2O7 sample and Cu ２ P ２ O ７ The average particle size of the sample was determined by the average value of 50 particles arbitrarily extracted at a magnification of 1000x using a scanning electron microscope.

[0072]

[0073] (Examples 1-5) Cu prepared as described above ２ P ２ O ７ Sample and Zn ２ P ２ O ７ The sample was 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) Cu prepared above ２ P ２ O ７ Sample and Zn ２ P ２ O ７ The sample was thoroughly mixed in a mortar in the proportions shown in Table 2, and this was used as the negative thermal expansion material sample.

[0080] (Physical Property Evaluation) 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 samples was determined by the average value of 50 particles arbitrarily extracted at a magnification of 1000x using a scanning electron microscope.

[0081]

[0082] (Evaluation of Negative Thermal Expansion) The linear 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. In addition, the theoretical value of the linear 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 expansion coefficient of copper pyrophosphate sample between -30 and 150°C, or between 90 and 130°C (ppm / K) E2: Linear expansion coefficient of zinc pyrophosphate sample between -30 and 150°C, or between 90 and 130°C (ppm / K) A1: Mixing ratio of copper pyrophosphate sample to negative thermal expansion material sample (mass%) A2: Mixing ratio of zinc pyrophosphate sample to negative thermal expansion material sample (mass%)

[0084] (Measurement of Linear Expansion Coefficient (Thermal Expansion Coefficient)) Linear expansion was measured for the obtained sample at -30 to 150°C as described below. (Preparation of Compacted Molded Body) 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 molded body was prepared by molding it with a pressure of 10 MPa using a hand press. The thermal expansion coefficient of the prepared compacted molded 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 at -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 (%) of the compacted molded body and the temperature (°C) 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]

[0086] From the results in Table 3, the negative thermal expansion material of the embodiment of the present invention exhibits a coefficient of thermal expansion that is equivalent to or smaller than the theoretically calculated coefficient of thermal expansion between -30 and 150°C. On the other hand, between 90 and 130°C, the coefficient of thermal expansion is smaller than the theoretically calculated coefficient of thermal expansion due to the synergistic effect of copper pyrophosphate and zinc pyrophosphate, indicating even better negative thermal expansion properties. Furthermore, from Figures 3 and 4, it can be seen that the embodiment of the present invention (Embodiment 1, Example 2, Example 3) consistently exhibits negative thermal expansion properties between -30 and 150°C. In addition, the negative thermal expansion material of the embodiment of the present invention (Embodiment 1, Example 2, Example 3) is Zn ２ P ２ O ７ Compared to the negative thermal expansion material alone (Comparative Example 4), it can be seen that the volume decreases gradually with increasing temperature between 100 and 150°C. Furthermore, comparing the negative thermal expansion material of Example 3 with that 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 that 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 negative thermal expansion material of the other example 4 as well, between -30 and 150°C, and Zn ２ P ２ O ７ It was also confirmed that, compared to a single negative thermal expansion material, it exhibits 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 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 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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