Carbon material dispersion

Abstract

The present invention provides a carbon material dispersion liquid that is less prone to agglomeration of carbon materials even when heated. [Solution] The carbon material dispersion disclosed herein comprises a crystalline carbon material, a dispersant having basic functional groups and a weight-average molecular weight of 1000 or more, and a non-aqueous solvent. The carbon material in the carbon material dispersion has a peak intensity ratio (I) based on laser Raman spectroscopy. G / I D The temperature change rate X of dispersibility, expressed by the following formula: X = |D2 - D1| / D1 (where D1 is the median diameter (μm) of the carbon material in the carbon material dispersion at 20°C, satisfying D1 ≤ 30, and D2 is the median diameter (μm) of the carbon material in the carbon material dispersion at 80°C), is 1.0 or less.

Description

Technical Field

[0001] The present invention relates to a carbon material dispersion.

Background Art

[0002] Conventionally, a carbon material dispersion containing a carbon material, a dispersant, and a solvent (aqueous solvent or non-aqueous solvent) has been used in various applications (for example, Patent Documents 1 and 2).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, in manufacturing a desired product, it is required that the carbon material be well dispersed in the solvent in the carbon material dispersion. However, according to the study by the present inventors, when a crystalline carbon material is dispersed in a non-aqueous solvent, the dispersibility of the carbon material may change depending on the temperature. Specifically, even if the carbon material is well dispersed in the non-aqueous solvent under a room temperature (for example, 25 ± 10°C) environment, when the dispersion becomes high temperature (for example, 80°C) during the manufacturing process of the desired product, the carbon material may aggregate and the dispersibility may decrease.

[0005] The present invention has been made in view of this point, and its main object is to provide a carbon material dispersion in which the carbon material is less likely to aggregate even when the temperature is raised.

Means for Solving the Problems

[0006] The present invention provides a carbon material dispersion comprising a crystalline carbon material, a dispersant having basic functional groups and a weight-average molecular weight of 1000 or more, and a non-aqueous solvent. The carbon material in the carbon material dispersion is measured by a peak intensity ratio (I) based on laser Raman spectroscopy. G / I D ) is 45 or less. And the above carbon material dispersion is given by the following formula: X = |D2 - D1| / D1 …(1) However, in equation (1), D1 is the median diameter (μm) of the carbon material in the carbon material dispersion at 20°C, satisfying D1 ≤ 30. D2 is the median diameter (μm) of the carbon material in the carbon material dispersion at 80°C; The rate of change of temperature X for dispersivity, expressed as , is 1.0 or less.

[0007] The carbon material dispersion disclosed herein suppresses aggregation of the carbon material even when the temperature is raised to, for example, about 80°C, by coexisting the carbon material with the dispersant in a non-aqueous solvent. This reduces the temperature dependence of the dispersibility. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a carbon material dispersion liquid in which the carbon material is less likely to aggregate even when exposed to high temperatures (for example, around 80°C). [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 is a schematic diagram illustrating the effects of the technology disclosed herein. [Figure 2] Figure 2 is a graph showing the temperature dependence of the median diameter of a carbon material. [Modes for carrying out the invention]

[0010] Preferred embodiments of the present invention will be described below. Naturally, the embodiments described herein are not intended to particularly limit the present invention. Furthermore, the same reference numerals are used for members and parts that perform the same function, and redundant explanations may be omitted or simplified as appropriate. In this specification, the notation "X~Y" (where X and Y are arbitrary numerical values) indicates a range, encompassing not only the meaning of "greater than X" and "less than Y," but also "greater than X" and "less than Y."

[0011] <Carbon material dispersion liquid> The carbon material dispersion of this embodiment (hereinafter also simply referred to as "dispersion") comprises (A) a crystalline carbon material (hereinafter also referred to as "crystalline carbon material"), (B) a dispersant having basic functional groups and a weight-average molecular weight of 1000 or more (hereinafter also referred to as "basic polymer dispersant"), and (C) a non-aqueous solvent. The dispersion of this embodiment may further contain other optional components, such as (D) additives, as needed. As will be described in detail later, in this embodiment, when a predetermined crystalline carbon material is placed in a non-aqueous solvent together with a basic polymer dispersant, it is thought that, for example, the basic functional groups of the basic polymer dispersant act on the surface of the crystalline carbon material and bind to it. As a result, aggregation of the crystalline carbon material can be suppressed even when the dispersion is heated to a high temperature of, for example, about 80°C.

[0012] <(A) Crystalline carbon materials> Crystalline carbon materials are carbon materials in which carbon atoms are arranged in a regular pattern, and the position of each carbon atom can be identified. In this respect, they are distinguished from amorphous carbon materials. Furthermore, as described in the test examples (reference examples) later, according to the inventors' studies, amorphous carbon materials, unlike crystalline carbon materials, have almost no temperature-dependent dispersibility, and therefore the problems of the present invention do not arise in the first place.

[0013] In this embodiment, the peak intensity ratio (I) of the crystalline carbon material in the dispersion is determined by laser Raman spectroscopy. G / I D) is 45 or less. The G band is a peak derived from the graphite structure, and the D band is a peak derived from structural defects. The peak intensity ratio (I G / I D ) indicates that the lower the value, the lower the graphitization degree of the crystalline carbon material and the more structural defects there are. Consequently, it may indicate that the amount of functional groups on the surface (typically the amount of acidic functional groups) is large. By setting the peak intensity ratio (I G / I D ) to a predetermined value or less, a predetermined amount of defective portions can exist on the surface of the crystalline carbon material. And, (B) the basic polymer dispersant can easily bind through the defective portions on the surface. Therefore, even when exposed to a high temperature (for example, about 80 °C), the state of binding with the (B) basic polymer dispersant is likely to be maintained. As a result, a state in which the crystalline carbon material is dispersed in the (C) non-aqueous solvent can be stably maintained, and the effects of the technology disclosed herein can be appropriately exerted.

[0014] From the viewpoint of stably exerting the effects of the technology disclosed herein at a high level, the peak intensity ratio (I G / I D ) is preferably 40 or less, more preferably 39 or less. In some embodiments, the peak intensity ratio (I G / I D ) is more preferably 20 or less, further preferably 10 or less, and particularly preferably 5 or less, 3 or less, 2 or less, 1 or less.

[0015] The lower limit of the peak intensity ratio (I G / I D ) is not particularly limited, but is preferably 0.5 or more, more preferably 0.6 or more, and further preferably 0.7 or more. In some embodiments, the peak intensity ratio (I G / I D ) is preferably 10 or more, more preferably 20 or more. By setting the peak intensity ratio (I G / I D ) to a predetermined value or more, the crystallinity of the crystalline carbon material increases, and it becomes easier to obtain high conductivity. Furthermore, the defective portions on the surface of the crystalline carbon material can be moderately suppressed, and the stability of the dispersion liquid can be improved.

[0016] In this specification, the peak intensity ratio (I) of crystalline carbon materials is defined as G / I D The peak intensity ratio (I) is a value measured by sampling crystalline carbon material from a dispersion, and may differ from the physical properties of the crystalline carbon material (the raw material itself). G / I D ) is measured in the Raman spectrum by laser Raman spectroscopy at 1350 cm⁻¹. -1 Nearby (typically 1310cm) -1 ~1390cm -1 The maximum peak intensity of the D band appearing in the range I D 1580cm -1 Nearby (typically 1560cm) -1 ~1600cm -1 The maximum peak intensity of the G band appearing in the range I G It can be calculated as the ratio of . A detailed measurement method will be described in the examples below.

[0017] While not particularly limited, crystalline carbon materials have a specific surface area of ​​20 m² based on nitrogen adsorption. 2 It is preferable that the amount be 30m or more. 2 It is more preferable that it be 50m or more per gram. 2 It is even more preferable that the specific surface area is 100 m² or more. In some embodiments, the specific surface area is 100 m². 2 It is preferable that it be 150m or more / g. 2 It is more preferable that it be 200m or more per gram. 2 It is even more preferable that the concentration be 1 / g or higher. By making the specific surface area greater than a predetermined value, the (B) basic polymer dispersant can more easily adhere to the surface of the crystalline carbon material. Therefore, the effects of the technology disclosed herein can be more easily and stably exhibited at a high level.

[0018] The specific surface area of ​​crystalline carbon materials is approximately 1000 m². 2 It is preferable that it be less than / g, and 800m 2 It is more preferable that it be less than or equal to / g, and 700m 2It is even more preferable that the specific surface area is less than or equal to / g. In some embodiments, the specific surface area is 400m². 2 It is preferable that it be less than or equal to / g, and 350m 2 It is more preferable that it be less than / g, and 300m 2 It is even more preferable that the amount is less than or equal to / g. By keeping the specific surface area below a predetermined value, it becomes easier to obtain high conductivity with a small amount. Therefore, it is possible to combine reduced temperature dependence of dispersibility and conductivity at a high level. In addition, generally, the smaller the specific surface area, the less (B) basic polymer dispersant is required. Therefore, the amount of (B) basic polymer dispersant can be reduced.

[0019] In this specification, the specific surface area can be calculated by analyzing the amount of nitrogen measured by nitrogen adsorption using a conventionally known gas adsorption apparatus with the BJH method. Detailed measurement conditions are described in the examples below.

[0020] As for the type of crystalline carbon material, the above peak intensity ratio (I G / I D The material is not particularly limited as long as it satisfies the above-mentioned specific surface area (preferably also satisfies the above-mentioned specific surface area), and one or more conventionally known materials can be used as appropriate, for example, depending on the application of the dispersion. Specific examples of crystalline carbon materials include so-called nanocarbons such as carbon nanotubes (A1), graphene (A2), and fullerene (spherical carbon), as well as graphite (natural graphite, artificial graphite). Among these, nanocarbons have high surface energy due to their small particle size and tend to aggregate in (C) non-aqueous solvents, so the application of the technology disclosed herein is particularly effective. In particular, it is preferable to include at least one of carbon nanotubes and graphene, and more preferable to include carbon nanotubes, as this makes it easier to stably and at a high level to exhibit the effects of the technology disclosed herein.

[0021] While not particularly limited, the crystalline carbon material is preferably mainly composed of nanocarbons (especially carbon nanotubes and graphene) (a component accounting for 50% or more by mass; the same applies hereinafter), more preferably 80% or more by mass of nanocarbons (especially carbon nanotubes and graphene), even more preferably 95% or more by mass of nanocarbons (especially carbon nanotubes and graphene), and particularly preferably substantially composed of nanocarbons (especially carbon nanotubes and graphene) (98% or more by mass of nanocarbons (especially carbon nanotubes and graphene)).

[0022] (A1) Carbon nanotubes (CNTs) are carbon materials having a structure in which planar graphite forming a carbon hexagonal network is rolled into a tubular shape. The type of CNT is not particularly limited, and one or more conventionally known types can be used as appropriate. CNTs may be single-walled carbon nanotubes (SWCNTs) having a structure in which one layer of graphite is rolled into a tubular shape, or multi-walled carbon nanotubes (MWCNTs) having a structure in which two or more layers of graphite are rolled into a tubular shape. Among these, it is more preferable to include multi-walled carbon nanotubes because they have excellent conductivity and the effects of the technology disclosed herein are more likely to be exhibited at a stable and high level. Note that CNTs may contain impurities (e.g., catalysts or amorphous carbon materials) derived from the manufacturing process, for example.

[0023] While not particularly limited, the average outer diameter (average diameter) of the CNTs is preferably 1 nm or more. In some embodiments, the average outer diameter of the CNTs is more preferably 3 nm or more, and even more preferably 5 nm or more. When the average outer diameter is above a predetermined value, (B) the basic polymer dispersant can easily penetrate between the CNT bundles, improving dispersibility. Therefore, the effects of the technology disclosed herein are more likely to be exhibited at a high level. The average outer diameter of the CNTs is preferably about 100 nm or less, more preferably 50 nm or less, even more preferably 20 nm or less, and particularly preferably 15 nm or less. When the average outer diameter is below a predetermined value, the number of CNTs per unit mass increases, making it easier to efficiently form a conductive network and improve conductivity.

[0024] The average outer diameter of carbon nanotubes (CNTs) can be calculated by observing multiple CNTs with an electron microscope, measuring the radial length of each CNT, and averaging the results. More specifically, for example, using a transmission electron microscope (TEM), observation can be performed at a magnification of, say, 400,000x, and the radial length of 50 CNTs arbitrarily selected from the field of view can be measured and the average result calculated.

[0025] While not particularly limited, the average fiber length of the CNTs is preferably 1 μm or more, and more preferably 5 μm or more. In some embodiments, the average fiber length of the CNTs is even more preferably 50 μm or more, and particularly preferably 80 μm or more, or 100 μm or more. When the average fiber length is above a predetermined value, the (B) basic polymer dispersant becomes more easily entangled on the surface. Therefore, even when exposed to high temperatures (e.g., around 80°C), the state of being bound with the (B) basic polymer dispersant is more easily maintained, and the effects of the disclosed technology are more easily and stably exhibited at a high level. In addition, when the average fiber length is long, the CNTs tend to entangle and aggregate with each other in the (C) non-aqueous solvent. Therefore, applying the disclosed technology is particularly effective. Furthermore, it becomes easier to effectively form a conductive network, and conductivity can be improved.

[0026] Furthermore, the average fiber length of the CNTs is preferably 1000 μm or less, more preferably 500 μm or less, and even more preferably 400 μm or less, or 200 μm or less. In some embodiments, the average fiber length of the CNTs is preferably 50 μm or less, more preferably 30 μm or less, and even more preferably 10 μm or less. When the average fiber length is below a predetermined value, the CNTs are less likely to curl or entangle with each other in a non-aqueous solvent. Therefore, it is possible to achieve a high level of both reduced temperature dependence of dispersibility and conductivity.

[0027] The average fiber length of carbon nanotubes (CNTs) can be calculated by observing multiple CNTs with an electron microscope, measuring the length of each CNT in the axial direction, and averaging these lengths. More specifically, for example, using a scanning electron microscope (SEM) at a magnification of 10,000x, the length of 50 CNTs arbitrarily extracted from the field of view can be measured in the axial direction, and the average length of these lengths can be calculated.

[0028] The CNTs are preferably fibrous, with an average fiber length longer than the average outer diameter. The average aspect ratio (average fiber length / average outer diameter) of the CNTs is preferably 10 or more, and more preferably 100 or more. In some embodiments, the average aspect ratio is preferably 1000 or more, more preferably 2000 or more, and even more preferably 5000 or more. When the average aspect ratio is above a predetermined value, the effects of the technology disclosed herein are more easily realized at a high level, and a high level of reduced temperature dependence of dispersibility and conductivity can be achieved. Although not particularly limited, the upper limit of the average aspect ratio is preferably 100,000 or less, more preferably 50,000 or less, and even more preferably 30,000 or less. In some embodiments, the average aspect ratio may be 10,000 or less.

[0029] (A2) Graphene is a sheet-like carbon material having a structure in which carbon hexagonal networks are arranged in a planar manner. The type of graphene is not particularly limited, and one or more conventionally known types can be used as appropriate. The graphene may be single-layer graphene or multilayer graphene, which is formed by stacking multiple single-layer graphenes. Among these, it is more preferable to include multilayer graphene because it has excellent conductivity and the effects of the technology disclosed herein are more likely to be exhibited at a stable and high level.

[0030] Furthermore, the properties, such as size and shape, of crystalline carbon materials other than CNTs (e.g., graphene, fullerene, graphite) are not particularly limited. Crystalline carbon materials other than CNTs may be spherical with an average aspect ratio (major axis / minor axis) of approximately 0.5 to 1.5, or non-spherical with an average aspect ratio of less than 0.5 to greater than 1.5. In some embodiments, it is preferable that the crystalline carbon material other than CNTs be spherical. In this specification, "spherical" refers to a shape that can be generally considered to be a sphere (ball), and includes elliptical, polygonal, disc-spherical, etc. Also, "non-spherical" includes plate-like, flaky, flake-like, irregularly shaped, etc.

[0031] The average particle size of crystalline carbon materials other than CNTs is preferably 1 nm or more, more preferably 5 nm or more, and even more preferably 10 nm or more. When the average particle size is above a predetermined value, the (B) basic polymer dispersant adheres more easily to the surface. Dispersion becomes easier, and the effects of the technology disclosed herein are more likely to be exhibited stably at a high level. Furthermore, the average particle size of crystalline carbon materials other than CNTs is preferably 150 nm or less, more preferably 100 nm or less, and even more preferably 70 nm or less. When the average particle size is below a predetermined value, a conductive network is more easily formed, and conductivity can be improved. The average particle size of crystalline carbon materials other than CNTs can be measured and calculated, for example, by a method similar to that used for the average outer diameter and average fiber length of CNTs described above.

[0032] The crystalline carbon materials (especially nanocarbons) of this embodiment have small particle sizes and their surfaces are easily oxidized. The crystalline carbon materials may have acidic functional groups (typically oxygen-containing functional groups) such as hydroxyl groups, carboxyl groups, and sulfo groups on their surfaces. The presence of acidic functional groups on the surface of the crystalline carbon materials makes them more likely to bond with (B) basic polymer dispersants in the dispersion. Therefore, the effects of the technology disclosed herein are more likely to be exhibited stably at a high level. The presence of acidic functional groups on the surface of the crystalline carbon material, as well as the type and amount of acidic functional groups, can be confirmed by conventionally known titration methods (e.g., Boehm method) or surface analysis by X-ray photoelectron spectroscopy (XPS).

[0033] The crystalline carbon material of this embodiment may be manufactured by any method. In some embodiments, the crystalline carbon material may be surface-modified by, for example, conventionally known oxidation treatments, plasma treatments, ozone treatments, high-temperature treatments, heat treatments, etc. This allows it to stably contain many acidic functional groups.

[0034] In some embodiments, the crystalline carbon material is given by the following formula: Y = A1 × C1 / [Peak intensity ratio (I G / I D )] …(2) However, in the above formula (2), A1 is the specific surface area (m²) of the crystalline carbon material. 2 C1 is the concentration (mass%) of the crystalline carbon material in the dispersion ( / g). The index Y, represented by the formula, is preferably between 10 and 1200. The larger the value of index Y, the wider the area that should be covered by (B) basic polymer dispersant, and it can serve as an indicator for determining the amount of (B) basic polymer dispersant to add. By setting index Y within the above range, the effects of the technology disclosed herein are more likely to be exhibited stably at a high level. Furthermore, by reducing the amount of (B) basic polymer dispersant added, it is possible to achieve a high level of both reduced temperature dependence of dispersibility and conductivity.

[0035] In some embodiments, the index Y may be, for example, 50 or more, or even 100 or more. Also, from the viewpoint of more stably exhibiting the effects of the technology disclosed herein, the index Y may be, for example, 1000 or less, or even 500 or less, or in one example, 200 or less.

[0036] The concentration C1 of the crystalline carbon material is not particularly limited, as it can vary depending on, for example, the type of crystalline carbon material used. However, when the entire dispersion is considered as 100% by mass, a concentration of approximately 0.01 to 10% by mass is preferred. A concentration of crystalline carbon material C1 of 0.1% by mass or more is more preferred, for example, 0.2% by mass or more, 0.3% by mass or more, or 0.4% by mass or more is even more preferred. When the concentration C1 is above a predetermined value, a conductive network is more easily formed, and conductivity can be improved. Furthermore, as the concentration C1 of the crystalline carbon material increases, aggregation in the (C) non-aqueous solvent becomes more likely, so applying the techniques disclosed herein is particularly effective. A concentration C1 of crystalline carbon material is more preferably 5% by mass or less, and in some embodiments, for example, 2% by mass or less, or 1% by mass or less is even more preferred. When the concentration C1 is below a predetermined value, aggregation in the (C) non-aqueous solvent becomes less likely even when exposed to high temperatures (for example, around 80°C), and the temperature change in dispersibility can be better reduced. Therefore, it becomes easier to achieve a high level of effectiveness with the technologies disclosed herein.

[0037] <(B) Basic polymer dispersant> The basic polymer dispersant is a component for dispersing (A) a crystalline carbon material in (C) a non-aqueous solvent. In this embodiment, the weight-average molecular weight (Mw) of the basic polymer dispersant is 1000 or more. This allows the dispersant to entangle with (A) the crystalline carbon material and bond strongly with it. Therefore, even when exposed to high temperatures (e.g., around 80°C), the bonded state with (A) the crystalline carbon material is more easily maintained, and the crystalline carbon material can be stably dispersed in (C) a non-aqueous solvent. This allows the effects of the technology disclosed herein to be appropriately demonstrated.

[0038] In this specification, "polymer (polymer compound)" refers to all compounds with a weight-average molecular weight (Mw) of 1000 or more (typically polymers), and is a term that includes, for example, oligomers with a weight-average molecular weight of 1000 or more and less than 5000, and polymers with a weight-average molecular weight of 5000 or more. In some embodiments, the basic polymer dispersant preferably contains a polymer, and more preferably is mainly composed of a polymer. This makes it easier to exhibit the above-mentioned effects at a higher level.

[0039] In some embodiments, the weight-average molecular weight of the basic polymer dispersant is preferably 5,000 or more, more preferably 10,000 or more, even more preferably 15,000 or more, and particularly preferably 20,000 or more, or 30,000 or more. Furthermore, the weight-average molecular weight of the basic polymer dispersant is preferably 100,000 or less, more preferably 50,000 or less, and even more preferably 40,000 or less. When the weight-average molecular weight is below a predetermined value, (A) the conductivity of the crystalline carbon material is less likely to be inhibited, and it becomes easier to exhibit high conductivity. In addition, the viscosity of the dispersion is suppressed, making it easier to improve handling. Furthermore, when (A) the crystalline carbon material is CNT, the dispersant can easily penetrate between the CNT bundles, making it easier to improve dispersibility.

[0040] The weight-average molecular weight of the basic polymer dispersant can be calculated by comparing the measurement value obtained by gel permeation chromatography (GPC) with a calibration curve using a standard sample (polystyrene). It is more preferable to use the average value obtained from multiple measurements (e.g., two measurements) as the weight-average molecular weight. Detailed measurement conditions are described in the examples below.

[0041] The basic polymer dispersant has a molecular weight distribution (Mw / Mn), which is the ratio of the weight-average molecular weight (Mw) to the number-average molecular weight (Mn), preferably about 1 to 20, more preferably 1 to 10, and even more preferably 1 to 9. In some embodiments, the molecular weight distribution of the basic polymer dispersant is more preferably 5 or less, and even more preferably 4 or less. In this specification, "number-average molecular weight" can be calculated from a value measured under the same measurement conditions as the weight-average molecular weight described above.

[0042] Furthermore, although not particularly limited, the number-average molecular weight (Mn) of the basic polymer dispersant is preferably 1000 or more, as this makes it easier to exhibit the above-mentioned effects at a higher level. In some embodiments, the number-average molecular weight (Mn) is more preferably 3000 or more, even more preferably 4000 or more, and may be, for example, 5000 or more. The number-average molecular weight (Mn) is preferably 20,000 or less, more preferably 10,000 or less, and may be, for example, 5000 or less.

[0043] The basic polymer dispersant of this embodiment has a basic functional group. The basic functional group may be, for example, a functional group whose acid dissociation constant pKa in water at 25°C is approximately 8 or higher, preferably 9 or higher. The basic functional group is preferably a nitrogen-containing group having a nitrogen atom (N). Examples of basic functional groups include primary, secondary, and tertiary amino groups, imino groups, groups having an amidine skeleton, and nitrogen-containing heterocyclic groups such as pyridine, pyrimidine, and pyrazine. Amino groups include heterocyclic amino groups such as pyridinyl groups (-C5H4N), and groups having an amidine skeleton also include heterocyclic groups such as imidazoline rings. Among these, amino groups are preferred because they can interact with parts other than the defects in the crystalline carbon material (A). In particular, primary or secondary amino groups that readily bond with the defects in the crystalline carbon material (A) are preferred. The basic functional groups in a basic polymer dispersant may be one type or two or more types. The presence of basic functional groups in the dispersant, as well as the type and amount of basic functional groups, can be confirmed by conventional titration methods or by spectroscopic measurements such as infrared absorption spectroscopy, nuclear magnetic resonance spectroscopy, and X-ray photoelectron spectroscopy (XPS).

[0044] In this specification, the term "basic functional group" does not include nearly neutral functional groups such as amide groups and imide groups. That is, because the lone pair of electrons on the nitrogen of an amide orimide group resonates and delocalizes with the electron orbital of the adjacent carbonyl group, its basicity is much weaker than, for example, that of an amino group, making it a nearly neutral functional group. Therefore, compounds having only such neutral functional groups, such as vinylpyrrolidone polymers like polyvinylpyrrolidone (PVP), which are commonly used in conventional dispersions of this type, do not exhibit the effects of the technology disclosed herein, as will be described in the comparative examples below.

[0045] The basic polymer dispersant preferably has an amine value. That is, it is preferable that the amine value (total amine value) is above the detection limit (generally 0.1 mg KOH / g or higher, depending on the measurement accuracy). In some embodiments, the basic polymer dispersant preferably has an amine value of 1 mg KOH / g or higher, more preferably 3 mg KOH / g or higher, even more preferably 5 mg KOH / g or higher, and may be, for example, 10 mg KOH / g or higher, or 20 mg KOH / g or higher. By setting the amine value above a predetermined value, the basic polymer dispersant can hydrogen bond with the surface of the (A) crystalline carbon material, particularly the acidic functional group sites, and bond more strongly with the (A) crystalline carbon material. Therefore, the effects of the technology disclosed herein are more likely to be exhibited stably at a high level. From the viewpoint of suppressing the viscosity of the dispersion and improving handling, the amine value of the basic polymer dispersant is preferably about 100 mg KOH / g or less, more preferably 75 mg KOH / g or less, and even more preferably 50 mg KOH / g or less.

[0046] The amine value of a basic polymer dispersant is the amount of potassium hydroxide in milligrams equivalent to the acid required to neutralize 1 g of the dispersant. The amine value of a basic polymer dispersant can be measured according to conventionally known methods, such as those specified in JIS K 7237:1995 or AOCS Official Method Tf-64.

[0047] In some embodiments, the basic polymer dispersant may further have acidic functional groups in addition to basic functional groups. The basic polymer dispersant may also be an amphoteric compound. The acidic functional group may be, for example, a functional group whose acid dissociation constant pKa in water at 25°C is approximately 6 or less, preferably 5 or less. Examples of acidic functional groups include hydroxyl groups, carboxyl groups, and sulfo groups. The dispersant may contain one type of acidic functional group or two or more types. The presence of acidic functional groups in the dispersant, as well as the type and amount of acidic functional groups, can be confirmed by conventionally known titration methods or by spectroscopic measurements such as infrared absorption spectroscopy, nuclear magnetic resonance spectroscopy, and X-ray photoelectron spectroscopy (XPS).

[0048] When the basic polymer dispersant has an acidic functional group, the acid value (total acid value) of the basic polymer dispersant may be approximately 1 to 20 mg KOH / g, for example, 2 to 10 mg KOH / g. In some embodiments, it is preferable that the acid value of the basic polymer dispersant is less than the amine value. This makes it easier for the basic polymer dispersant to strongly bond to the surface of the (A) crystalline carbon material, and the effects of the technology disclosed herein are more easily and stably exhibited at a high level. The acid value of the basic polymer dispersant can be measured according to conventionally known methods, for example, the method specified in JIS K 0070:1992.

[0049] The basic polymer dispersant is not particularly limited as long as it has basic functional groups and satisfies the above weight-average molecular weight (preferably also satisfies the above molecular weight distribution or number-average molecular weight), and depending on the application of the dispersion and the type of non-aqueous solvent, one or more conventionally known dispersants can be used as appropriate. The basic polymer dispersant can exist in both a state in which the basic functional groups are not ionized (nonionic) or in a state in which they are ionized by salt formation or the like (ionic).

[0050] The structure of basic polymer compounds is not particularly limited. The molecular structure of a basic polymer compound may be, for example, (1) linear, straight chain, (2) branched, with one or more side chains (carbon chains branching off from the main chain; the same applies hereinafter) attached to a linear main chain (carbon chain with the maximum number of carbon atoms; the same applies hereinafter), or (3) comb-shaped, with multiple side chains regularly arranged on the same side along the main chain. The basic functional groups described above may be included in the main chain or in one or more side chains. Furthermore, the main chain may have its terminal or both terminals substituted with ionic groups (for example, basic functional groups as described above).

[0051] In the first embodiment, the basic polymer dispersant preferably contains one or more basic functional groups in its main chain. Specific examples of such basic polymer dispersants include compounds having an amine structure in their main chain, such as polyamines, polyimines, compounds shown in the following chemical formula (I), and modified versions thereof, as well as salts containing these compounds. In the first embodiment, the basic polymer dispersant preferably has a linear structure. In the first embodiment, the basic polymer dispersant is more preferably an aliphatic amine (chain-like amine) that does not have a cyclic structure.

[0052] [ka] In the above chemical formula (I), R 1 ,R 4 R is an aliphatic hydrocarbon group. 1 The number of carbon atoms is preferably approximately 10 to 30. 2 ,R 3 Each of these is independently an alkyl group or a hydroxyalkyl group. 2 ,R 3 The number of carbon atoms is preferably about 1 to 10. 2 ,R 3 At least one of them is more preferably a hydroxyalkyl group. 4 It is more preferable that it be an alkylene group. 4 The number of carbon atoms is preferably about 1 to 10.

[0053] In the first embodiment, the basic polymer dispersant is preferably mainly composed of the compound of formula (I) or a salt thereof, more preferably 80% by mass or more is the compound of formula (I) or a salt thereof, even more preferably 95% by mass or more is the compound of formula (I) or a salt thereof, and particularly preferably substantially composed of the compound of formula (I) or a salt thereof (98% by mass or more is the compound of formula (I) or a salt thereof).

[0054] In a second embodiment, the basic polymer dispersant preferably has a branched or comb-like structure, with at least one basic functional group in its side chains. More preferably, each of the multiple side chains contains a basic functional group. The side chains are regions with a higher degree of freedom in the dispersion compared to the main chain. Therefore, by including basic functional groups in the side chains, the basic polymer dispersant is more likely to bond more strongly (for example, to many regions) to the surface of the (A) crystalline carbon material, particularly to the sites of acidic functional groups. Thus, even when exposed to high temperatures (for example, around 80°C), the bond with the (A) crystalline carbon material is more easily maintained, and the effects of the technology disclosed herein are more likely to be exhibited stably at a high level. In some embodiments, the basic polymer dispersant is further preferably also having a basic functional group in its main chain. In some other embodiments, if the basic polymer dispersant has an acidic functional group, it is preferable, for example, for the main chain to contain an acidic functional group (for example, a carboxyl group).

[0055] Basic polymer dispersants having basic functional groups in their side chains can be prepared, for example, by reacting a first compound constituting the main chain with a second compound that serves as a source of basic functional groups (e.g., an acid-base reaction). The second compound is preferably an organic amine, and examples include aliphatic amines having hydroxyl groups, such as aminoethanol and 2-amino-2-methylpropanol.

[0056] Furthermore, the first compound constituting the main chain is not particularly limited and may be, for example, a homopolymer, or a copolymer such as a block copolymer, alternating copolymer, random copolymer, or graft copolymer. Examples of the first compound include poly(meth)acrylic acid, polyvinyl alcohol, polyvinyl acetate, polyamide, polyimide, polyacrylonitrile, polyester, polyurethane, (meth)acrylic copolymer, maleic acid copolymer, urethane copolymer, amine copolymer (ethyleneimine, allylamine, etc.), etc. In some embodiments, the first compound is preferably a compound having a carboxyl group (for example, poly(meth)acrylic acid or maleic acid copolymer). That is, the basic polymer dispersant is preferably a carboxyl group-containing compound (for example, a poly(meth)acrylic acid dispersant or a maleic acid dispersant). In this specification, "(meth)acrylic acid" is a term that includes acrylic acid and methacrylic acid.

[0057] Maleic acid copolymers are copolymers and derivatives that contain maleic acid units as the main repeating units and have basic functional groups in their side chains. Specific examples of maleic acid copolymers include styrene-maleic acid copolymers, ethylene-maleic acid copolymers, isobutylene-maleic acid copolymers, and their salts and modified products.

[0058] In the second embodiment, the basic polymer dispersant is preferably mainly composed of a carboxyl group-containing compound (e.g., a poly(meth)acrylic acid-based dispersant or a maleic acid-based dispersant), more preferably 80% by mass or more is a carboxyl group-containing compound (e.g., a poly(meth)acrylic acid-based dispersant or a maleic acid-based dispersant), even more preferably 95% by mass or more is a carboxyl group-containing compound (e.g., a poly(meth)acrylic acid-based dispersant or a maleic acid-based dispersant), and particularly preferably consists substantially of a carboxyl group-containing compound (e.g., a poly(meth)acrylic acid-based dispersant or a maleic acid-based dispersant) (98% by mass or more is a carboxyl group-containing compound (e.g., a poly(meth)acrylic acid-based dispersant or a maleic acid-based dispersant)).

[0059] The concentration C2 of the basic polymer dispersant can vary depending on, for example, the properties and content of the (A) crystalline carbon material used, the type of (C) non-aqueous solvent used, and the properties of the basic polymer dispersant. Therefore, although not particularly limited, in some embodiments, the concentration C2 of the basic polymer dispersant is preferably about 0.01 to 10% by mass when the entire dispersion is considered as 100% by mass. A concentration C2 of 0.1% by mass or higher is more preferable. In some embodiments, a concentration C2 of, for example, 0.2% by mass or higher, or 0.3% by mass or higher, is even more preferable. When the concentration C2 is above a predetermined value, the temperature change in dispersibility can be better reduced, and the effects of the technology disclosed herein can be more easily demonstrated at a high level.

[0060] Furthermore, the concentration C2 of the basic polymer dispersant is more preferably 5% by mass or less, more preferably 2% by mass or less, even more preferably 1% by mass or less, and particularly preferably 0.5% by mass or less. When the concentration C2 is below the predetermined value, (A) the conductive network of the crystalline carbon material can be efficiently formed, making it easier to achieve high conductivity. Therefore, it is possible to combine reduced temperature dependence of dispersibility with high conductivity at a high level.

[0061] From the viewpoint of conductivity, the mass of the basic polymer dispersant contained in the dispersion is preferably equal to or less than the mass of the crystalline carbon material (A). The ratio of the mass of the basic polymer dispersant to the crystalline carbon material (A) (B / A, the same as the concentration ratio C2 / C1) is preferably 2 or less, more preferably 1.5 or less, and even more preferably 1 or less. This makes it less likely for conductivity to be inhibited and makes it easier to achieve high conductivity. Furthermore, the above ratio (B / A) is preferably 0.01 or more, more preferably 0.02 or more, and even more preferably 0.03 or more, as this makes it easier to stably exhibit the effects of the technology disclosed herein at a high level. In some embodiments, the above ratio (B / A) is preferably 0.1 or more, and more preferably 0.5 or more.

[0062] <(C) Non-aqueous solvents> The non-aqueous solvent is a dispersion medium for dispersing (A) crystalline carbon material. The non-aqueous solvent is substantially water-free. The water content in the non-aqueous solvent is preferably 1000 ppm or less, more preferably 500 ppm or less, and particularly preferably 100 ppm or less. The water content in the non-aqueous solvent can be measured, for example, by Karl Fischer titration (JIS K0068:2001).

[0063] The type of non-aqueous solvent is not particularly limited; for example, one type of organic solvent or a combination of two or more organic solvents can be used as appropriate, depending on the application of the dispersion. Examples of organic solvents include aprotic polar solvents such as N-methyl-2-pyrrolidone (NMP), N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide; alcohol-based solvents such as methanol, ethanol, n-propanol, isopropanol, and cyclohexanol; ester-based solvents such as methyl acetate, ethyl acetate, butyl acetate, methyl butyrate, ethyl butyrate, butyl butyrate, methoxybutyl acetate, methyl cellosolve acetate, ethyl cellosolve acetate, propylene glycol monomethyl ether acetate, and γ-butyrolactone; carbonate-based solvents such as dimethyl carbonate, diethyl carbonate, ethylene carbonate, and propylene carbonate; ketone-based solvents such as acetone, methyl ethyl ketone, and cyclohexanone; and hydrocarbon-based solvents such as toluene, xylene, cyclohexane, and heptane. Among these, aprotic polar solvents are preferred, and NMP is particularly preferred.

[0064] The non-aqueous solvent is preferably mainly composed of an aprotic polar solvent (e.g., NMP) (making up 50% by mass or more), more preferably 80% by mass or more is an aprotic polar solvent (e.g., NMP), even more preferably 95% by mass or more is an aprotic polar solvent (e.g., NMP), and particularly preferably consists substantially of an aprotic polar solvent (e.g., NMP) (with 98% by mass or more being an aprotic polar solvent (e.g., NMP)). This makes it easier to stably exhibit the effects of the technology disclosed herein at a high level.

[0065] <(D) Additives> Additives are optional components. As additives, one or more types known to be usable for this type of application can be used as appropriate, for the purpose of improving the properties of the dispersion. Specific examples of additives include, for example, carbon materials that do not satisfy the above-mentioned (A) crystalline carbon material conditions (e.g., amorphous carbon materials such as carbon black, activated carbon, hard carbon, soft carbon, etc., or peak intensity ratio (I G / I D Examples include: carbon materials with a ratio of 45 or more; inorganic additives such as metal oxides; dispersants that do not satisfy the conditions of (B) basic polymer dispersants (for example, dispersants that do not have basic functional groups or dispersants with a weight-average molecular weight of less than 1000); organic additives such as organic binders, antioxidants, defoamers, preservatives, plasticizers, and colorants (pigments, dyes, etc.); pH adjusters such as inorganic bases and organic bases; and so on.

[0066] If the dispersion contains optional components, the mass of the optional components (e.g., (D) additives) in the dispersion is preferably less than the mass of (A) crystalline carbon material and / or (B) basic polymer dispersant. For example, when the total dispersion is considered to be 100% by mass, the concentration of the additive is preferably 5% by mass or less, more preferably 3% by mass or less, and even more preferably 2% by mass or less, 1% by mass or less, 0.5% by mass or less, or 0.1% by mass or less, from the viewpoint of stably exhibiting the effects of the technology disclosed herein at a high level.

[0067] The carbon material dispersion disclosed herein can be prepared by mixing (A) a crystalline carbon material, (B) a basic polymer dispersant, and other optional components in (C) a non-aqueous solvent, thereby dispersing or dissolving (A) the crystalline carbon material, (B) the basic polymer dispersant, and other optional components in (C) the non-aqueous solvent. (A) the crystalline carbon material and / or (B) the basic polymer dispersant may be added all at once or in two or more portions.

[0068] For mixing, conventionally known mixing devices such as dispersers, planetary mixers, kneaders, propeller stirrers, ultrasonic homogenizers, magnetic stirrers, jet mills, ball mills, bead mills, and sand mills can be used as appropriate. Among these, devices that do not use a medium (medium-less) are preferred from the viewpoint of reducing contamination of the medium. Furthermore, circulating dispersion devices are preferred because dispersion proceeds more uniformly. In addition, devices that utilize the shear force of high-speed stirring are preferred because they can shorten the processing time. An example of such a mixing device is a high-pressure homogenizer.

[0069] The carbon material dispersion disclosed herein exhibits reduced temperature dependence of dispersibility, as the crystalline carbon material (A) is less prone to aggregation even when exposed to high temperatures (e.g., around 80°C). For details, see the following equation: X = |D2 - D1| / D1 …(1) However, in the above equation (1), D1 is the median diameter (μm) of the crystalline carbon material (A) in the dispersion at 20°C, satisfying D1 ≤ 30. D2 is the median diameter (μm) of the crystalline carbon material (A) in the dispersion at 80°C; The temperature change rate X of dispersibility, expressed as , is 1.0 or less. Note that the median diameters D1 and D2 are volume-based particle diameters (D50 diameter) based on laser diffraction and light scattering methods. Detailed measurement methods are described in the examples below.

[0070] The above temperature change rate X being 1.0 or less means that the median diameter D2 at 80°C is kept to 2.0 times or less than the median diameter D1 at 20°C. From the viewpoint of exhibiting the effects of the technology disclosed herein at a higher level, the temperature change rate X is more preferably 0.8 or less, even more preferably 0.5 or less, particularly preferably 0.2 or less, and among these, 0.1 or less and 0.05 or less are preferred.

[0071] Furthermore, although not particularly limited, the median diameter D1 at 20°C is preferably 0.1 μm or more, more preferably 0.5 μm or more, and even more preferably 1.0 μm or more, as this allows the effects of the disclosed technology to be more stably exhibited. The median diameter D2 at 80°C may also vary depending on the median diameter D1 at 20°C, but is preferably 30 μm or less, more preferably 20 μm or less, and even more preferably 10 μm or less.

[0072] In some embodiments, the dispersion preferably has a concentration C1 of (A) crystalline carbon material of 0.4% by mass or more, and an adjusted pH of 6.5 or more when diluted with pure water to a concentration of 0.2% by mass of (A) crystalline carbon material. This adjusted pH value is typically determined by the combination of (A) crystalline carbon material and (B) basic polymer dispersant. An adjusted pH of or above a predetermined value means that the dispersion is somewhat neutral or basic. By setting the adjusted pH to or above a predetermined value, the basic functional groups of (B) basic polymer dispersant are present in sufficient quantity, making it easier to keep the median diameter D2 small even when the dispersion is exposed to high temperatures (e.g., around 80°C). Therefore, the temperature change rate X can be stably kept small, making it easier to achieve the effects of the technology disclosed herein at a high level.

[0073] The upper limit of the adjusted pH value is not particularly limited, but considering the influence on subsequent processes in manufacturing the desired product, it is generally preferred to be 11 or less, for example, 10 or less. In some embodiments, the adjusted pH value is more preferably 8 or less, and even more preferably 7.5 or less.

[0074] The reason for deliberately diluting the dispersion with pure water before measuring the pH is that pH is fundamentally an evaluation method for measuring proton concentration, and (C) non-aqueous solvents, especially aprotic solvents like NMP, basically do not have the concept of pH. Therefore, it is necessary to dilute with pure water and adjust the conditions to one where protons are sufficiently present before measuring the pH.

[0075] As described above, the carbon material dispersion disclosed herein comprises (A) a crystalline carbon material, (B) a dispersant having basic functional groups and a weight-average molecular weight of 1000 or more, and (C) a non-aqueous solvent. The crystalline carbon material (A) in the dispersion has a peak intensity ratio (I) based on laser Raman spectroscopy. G / I D The coefficient of the carbon material dispersion is 45 or less, and the temperature change rate X of dispersibility represented by formula (1) above is 1.0 or less.

[0076] Thus, by coexisting the above-mentioned (A) crystalline carbon material with the above-mentioned (B) basic polymer dispersant in (C) a non-aqueous solvent, the temperature dependence of the dispersibility can be relatively reduced compared to the case where it is coexisted with a dispersant that does not satisfy the above conditions (specifically, a dispersant that does not have basic functional groups, or a dispersant with a weight-average molecular weight of less than 1000). Therefore, even if the dispersion is heated to a high temperature (for example, around 80°C), aggregation of the (A) crystalline carbon material can be suppressed, and the dispersed state of the (A) crystalline carbon material can be stably maintained.

[0077] Although not intended to be interpreted restrictively, the inventors have considered the effects resulting from the combination of (A) to (C) above as follows. Figure 1 is a schematic diagram illustrating the effects of the technology disclosed herein, and shows (A) crystalline carbon material 10 and (B) basic polymer dispersant 20 in (C) a non-aqueous solvent. As an example of the crystalline carbon material 10, fibrous CNTs are shown here.

[0078] As shown in Figure 1, crystalline carbon materials 10, particularly nanocarbons, have small particle sizes and their surfaces are easily oxidized. Therefore, crystalline carbon materials 10 often have acidic functional groups (typically oxygen-containing functional groups) such as hydroxyl groups and carboxyl groups on their surfaces. On the other hand, basic polymer dispersants 20 have basic functional groups. Thus, in the dispersion, the acidic functional groups on the surface of the crystalline carbon material 10 and the basic functional groups of the basic polymer dispersant 20 bond together (for example, through acid-base reactions and hydrogen bonding), making it easier for the crystalline carbon material 10 and the basic polymer dispersant 20 to bond strongly. Furthermore, the larger the weight-average molecular weight of the basic polymer dispersant 20, the larger its volume (steric size) tends to be in the dispersion. Therefore, steric repulsion between the crystalline carbon materials 10 is more likely to occur. Due to the combined effects of these factors, the technology disclosed herein makes it difficult for the basic polymer dispersant 20 to dissociate from the crystalline carbon material 10 even at high temperatures. In other words, it is possible to stably maintain the bonded state between the crystalline carbon material 10 and the basic polymer dispersant 20, and it is thought that aggregation of the crystalline carbon material 10 can be suppressed even at high temperatures.

[0079] In the dispersion of this embodiment, the carbon material has a specific surface area of ​​150 m² based on the nitrogen adsorption method. 2 / g or more 700m 2 It is preferable that the specific surface area is less than or equal to / g. By making the specific surface area greater than or equal to a predetermined value, the (B) basic polymer dispersant can more easily adhere to the surface of the crystalline carbon material. Therefore, the effects of the technology disclosed herein can be more easily and stably exhibited at a high level. Furthermore, by making the specific surface area less than or equal to a predetermined value, it becomes easier to obtain high conductivity with a small amount. Therefore, it is possible to combine reduced temperature dependence of dispersibility and conductivity at a high level.

[0080] In the dispersion of this embodiment, it is preferable that the carbon material includes at least one of carbon nanotubes and graphene. This makes it easier for the effects of the technology disclosed herein to be exhibited at a stable and high level. Furthermore, since nanocarbons have a high surface energy due to their small particle size and tend to aggregate in non-aqueous solvents, the technology disclosed herein is particularly effective in this case.

[0081] In the dispersion of this embodiment, the carbon material preferably contains carbon nanotubes. Carbon nanotubes are fibrous, and (B) basic polymer dispersants easily become entangled on their surface. Therefore, even when exposed to high temperatures (for example, around 80°C), the state in which they are bound to (B) basic polymer dispersants is easily maintained, and the effects of the technology disclosed herein are easily and stably exhibited at a high level. Furthermore, because they are fibrous, carbon nanotubes tend to entangle and aggregate with each other in (C) non-aqueous solvents. Therefore, applying the technology disclosed herein is particularly effective.

[0082] In the dispersion of this embodiment, the carbon material is given by the following formula: Y = A1 × C1 / [Peak intensity ratio (I G / I D )] …(2) However, in equation (2), A1 is the specific surface area (m²) of the carbon material. 2 C1 is the concentration (mass%) of the carbon material ( / g), where C1 is the concentration (mass%) of the carbon material mentioned above. It is preferable that the index Y represented by is between 10 and 1200. By setting index Y within the above range, the effects of the technology disclosed herein are more likely to be exhibited stably at a high level. Furthermore, by reducing the amount of (B) basic polymer dispersant added, it is possible to achieve a high level of both reduced temperature dependence of dispersibility and conductivity.

[0083] In the dispersion of this embodiment, the concentration C1 of the carbon material is preferably 0.1% by mass or more and 5% by mass or less. When the concentration C1 is above a predetermined value, a conductive network is more easily formed, and conductivity can be improved. Furthermore, when the concentration C1 is below a predetermined value, aggregation in the (C) non-aqueous solvent becomes less likely even when exposed to high temperatures (for example, around 80°C), and the temperature change in dispersibility can be reduced more effectively. Therefore, a high level of both reduced temperature change in dispersibility and conductivity can be achieved.

[0084] In the dispersion of this embodiment, the dispersant preferably has a weight-average molecular weight of 40,000 or less. When the weight-average molecular weight is below a predetermined value, the conductivity of the crystalline carbon material (A) is less likely to be inhibited, and it becomes easier for it to exhibit high conductivity. In addition, the viscosity of the dispersion is reduced, making it easier to improve handling. Furthermore, if the crystalline carbon material (A) is CNT, the dispersant can easily penetrate between the CNT bundles, making it easier to improve dispersibility. Therefore, the effects of the technology disclosed herein are more likely to be exhibited stably at a high level.

[0085] In the dispersion of this embodiment, the dispersant preferably has an amine value of 5 mg KOH / g or higher. By setting the amine value to a predetermined value or higher, the basic polymer dispersant can hydrogen bond with the surface of the crystalline carbon material (A), particularly with the acidic functional group sites, and bond more strongly with the crystalline carbon material (A). Therefore, the effects of the technology disclosed herein can be exhibited stably at a high level.

[0086] In the dispersion of this embodiment, it is preferable that the dispersant has a branched or comb-like structure in which at least the basic functional group is included in the side chain. The side chain is a region with a higher degree of freedom in the dispersion compared to the main chain. Therefore, by including the basic functional group in the side chain, the basic polymer dispersant is more likely to bond more strongly (to many regions) to the surface of the (A) crystalline carbon material, particularly to the sites of the acidic functional group. Thus, even when exposed to high temperatures (for example, around 80°C), the bond with the (A) crystalline carbon material is more easily maintained, and the effects of the technology disclosed herein are more likely to be exhibited stably at a high level.

[0087] In the dispersion of this embodiment, it is preferable that the temperature change rate X is 0.2 or less. This allows the effects of the technology disclosed herein to be realized at a higher level.

[0088] In the dispersion of this embodiment, it is preferable that the median diameter D1 is 1.0 μm or greater. This makes it easier for the effects of the technology disclosed herein to be consistently exhibited.

[0089] In the dispersion of this embodiment, it is preferable that the concentration C1 of the carbon material is 0.4% by mass or more, and that the adjusted pH when diluted with pure water to a concentration of 0.2% by mass of the carbon material is 6.5 or more. This makes it possible to stably keep the temperature change rate X small, and makes it easier to exert the effects of the technology disclosed herein at a high level.

[0090] In the dispersion of this embodiment, the ratio of the concentration C2 of the dispersant to the concentration C1 of the carbon material (C2 / C1) is preferably 0.1 or more and 2 or less. When the above concentration ratio is above a predetermined value, the temperature change in dispersibility can be reduced more effectively, and the effects of the technology disclosed herein can be demonstrated at a high level. Furthermore, when the above concentration ratio is below a predetermined value, the conductive network of the crystalline carbon material (A) can be efficiently formed, and high conductivity can be easily achieved. Therefore, it is possible to achieve both a reduction in temperature change in dispersibility and high conductivity at a high level.

[0091] <Applications of carbon material dispersions> The carbon material dispersion disclosed herein can be used for various applications. For example, in applications for creating electrodes, a conductive film can be formed on a substrate by applying (typically coating) the carbon material dispersion onto the substrate and drying it. In this case, the dispersion can also be understood as a conductive slurry. The conductive slurry may further contain an active material (positive electrode active material or negative electrode active material) and a resin binder. Various materials conventionally known to be usable in this type of application can be used as the active material or resin binder.

[0092] In particular, in applications for manufacturing electrodes (positive and / or negative electrodes) of secondary batteries, aggregation due to heat generation is likely to occur during the process of preparing (kneading) the conductive slurry. Therefore, it is especially preferable to apply the technology disclosed herein. As another aspect of the technology disclosed herein, a method for manufacturing a conductive film is provided, comprising the steps of: preparing a conductive slurry; applying the prepared conductive slurry onto a substrate; and removing a non-aqueous solvent by drying the conductive slurry applied to the substrate.

[0093] The following describes examples relating to the present invention, but it is not intended to limit the present invention to those shown in these examples.

[0094] Here, we first prepared the six types of carbon materials shown in Table 1, the four types of dispersants described below, and NMP as a non-aqueous solvent. The specific surface area was measured as follows. <Specific surface area> Carbon materials were pre-treated under reduced pressure at 300°C for 720 minutes and thoroughly degassed. Then, nitrogen gas was adsorbed onto the surface at liquid nitrogen temperature using a fully automated gas adsorption measurement device (autosorb-iQ manufactured by Anton Paar Co., Ltd.), and the amount of nitrogen adsorbed as a monolayer was measured. The measurement results were then analyzed using the BJH method to calculate the specific surface area of ​​the carbon material. [Table 1]

[0095] <Dispersant> • Dispersant A: BYK ET3002 (manufactured by Bic Chemie Japan); modified styrene-maleic acid copolymer, amine value 5.1 mg KOH / g, acid value 4.3 mg KOH / g • Dispersant B: Electrosperse 4000 (manufactured by Cargill); modified polyamide • Dispersant C: Nopcospers 092 (manufactured by Sunopco); cationic surfactant Dispersant D: Pitzcol K30 (manufactured by Daiichi Kogyo Seiyaku); PVP

[0096] The molecular weight of the dispersant prepared above was measured using the following procedure. The results are shown in Table 2. <Measuring molecular weight> The molecular weights of dispersants A to C were measured using gel permeation chromatography (GPC) under the following conditions. The measured values ​​were then compared with a calibration curve using a standard sample (polystyrene, manufactured by Tosoh Corporation) to calculate the weight-average molecular weight and number-average molecular weight in polystyrene equivalents. Pretreatment: The sample was collected, dissolved in eluent, and allowed to stand overnight at room temperature. The sample was then filtered through a 0.5 μm pore size polytetrafluoroethylene cartridge filter. Equipment: HLC-8320GPC (manufactured by Tosoh) Columns: TSKgel guardcolumn SuperAW-H (4.6mm I.D. × 3.5cm) + TSKgel SuperAWM-H (6.0mm I.D. × 15cm) × 2 Column temperature: 40℃ Eluent: NMP+10mM LiBr Flow rate: 0.3mL / min Sample concentration: 0.1% (solute base) Detector: RI (Refractive Index) detector (polarity (+))

[0097] [Table 2] Table 2 shows the arithmetic mean values ​​for two measurements (N=2) in the upper section, and the results for each measurement in the lower section. The weight-average molecular weight of dispersant D, according to the catalog, is 45,000.

[0098] <Preparation of dispersion> Next, under conditions of 25°C, the carbon materials, dispersants, and non-aqueous solvents (NMP) shown in Table 3 were added to a polypropylene container in the amounts shown in Table 3. The mixture was then stirred using a propeller stirrer at a rotation speed of 340 rpm for 30 minutes to prepare a preliminary mixture. For Comparative Examples 1-2, an organic base (2-amino-2-methyl-1-propanol, molecular weight 89.14, having a basic functional group) commonly used as a pH adjuster was further added as an additive.

[0099] Next, the premix was introduced into the raw material tank of a high-pressure homogenizer (Sugino Machine, Starburst HJP-25001V2), and a circulating dispersion treatment was performed on the premix. The dispersion treatment was carried out using a single nozzle chamber with a nozzle diameter of 0.15 mm and a pressure of 150 MPa. The progress of dispersion was monitored using a laser diffraction / light scattering particle size distribution analyzer (Horiba, Ltd., LA-960V2), and the circulation treatment was continued until the particle size (median diameter) at a cumulative frequency of 50% was 30 μm or less. This prepared a carbon material dispersion. Table 3 shows the specific surface area A1 (m²) of the carbon material. 2 The concentration of the carbon material C1 (mass%) and the peak intensity ratio (I) in the dispersion, which will be described later. G / I D ) and the index Y calculated from it are shown together.

[0100] <Measurement of pH adjustment of dispersion> The carbon material dispersion prepared above was divided and diluted with pure water to a carbon material concentration of 0.2% by mass to prepare a measurement solution. Then, under conditions where sufficient protons were present, the pH of the measurement solution was measured using a pH meter. The results are shown in Table 3.

[0101] [Table 3]

[0102] <Evaluation of temperature-dependent dispersion> First, under conditions of 20°C, the carbon material dispersion prepared above was diluted with NMP to achieve a transmittance of 85-95% at a wavelength of 650 nm to prepare a measurement solution. Next, the particle size distribution of the carbon material dispersion at 20°C was measured using a laser diffraction / light scattering particle size distribution analyzer (LA-960V2, manufactured by Horiba, Ltd.). The measurement was performed by filling a batch-type cell with the measurement solution and accumulating the results three times. The particle size (median diameter) at a cumulative frequency of 50% was then determined. The results are shown in Table 4.

[0103] Next, 1 mL of the dispersion was taken into a glass bottle and heated for 10 minutes in a water bath heated to 80°C. Then, as in the case of 20°C, the particle size distribution of the dispersion after heating (at 80°C) was measured using a laser diffraction / light scattering particle size distribution analyzer. The particle size (median diameter) at a cumulative frequency of 50% was then determined. The results are shown in Table 4. Figure 2 shows, as an example, the change in median diameter of the carbon material in Example 1-1 and Comparative Example 1-1.

[0104] Next, from the median diameter of the carbon material at 20°C and 80°C, the following formula is used: X = |D2 - D1| / D1 …(1) However, in equation (1), D1 is the volume-based median diameter (μm) of the carbon material in the carbon material dispersion before heating (at 20°C), and D2 is the volume-based median diameter (μm) of the carbon material in the carbon material dispersion after heating (at 80°C). The temperature change rate X of dispersibility was calculated according to the following criteria. The temperature change of dispersibility was then evaluated according to the following criteria. The results are shown in Table 4. ·AAA:X ≤ 0.05 • AA : 0.05 < X ≤ 0.2 • A: 0.2 < X ≤ 0.5 • B: 0.5 < X ≤ 1.0 · C :1.0 < X

[0105] <Peak intensity ratio of carbon material in dispersion (I G / I D ) measurement> First, the dispersion was applied to a glass slide and dried at 100°C for 30 minutes to prepare the evaluation sample. Next, the evaluation sample was measured using a laser Raman analyzer (Renishaw Corporation, inVia) under the following conditions. From the obtained spectrum, the 1350 cm⁻¹ spectrum was selected. -1 Maximum peak intensity of the D band appearing nearby I D 1580cm -1 Maximum peak intensity of the G band appearing nearby I G The ratio (I G / I D The peak intensity ratio (I) of the carbon material in the dispersion was calculated. Measurements were performed five times for the same sample, changing the measurement point each time, and the arithmetic mean was used. G / I D ) was used. The results are shown in Table 4. Light source: Semiconductor laser (532nm) Objective lens: 50x Beam diameter: 1 μm Laser power: 5% Exposure time: 60 seconds Count: 1

[0106] [Table 4]

[0107] As shown in Table 4, in Comparative Examples 1-1, 2-1, 3-1, and 5-1, where "Dispersant D (PVP)" was used as the dispersant, the median diameter D2 increased after heating, the temperature change rate X of dispersibility exceeded 1, and the temperature change of the median diameter was large. Furthermore, in Comparative Example 1-2, where 2-amino-2-methyl-1-propanol (molecular weight 89.14), a small molecule with a basic functional group, was used in combination as an additive, the temperature change rate X of dispersibility actually worsened compared to Comparative Example 1-1. In addition, as a carbon material, the peak intensity ratio (I G / I DIn Comparative Example 4-1, which used "CNT D" with a large ) value, dispersion to a median diameter D1 of 30 μm or less at 20°C was not possible in the first place. Table 4 also shows an example of a reference case using amorphous "AB (acetylene black)" as the carbon material. However, when amorphous "AB" is used, there is almost no temperature dependence of the dispersibility of the carbon material, and therefore there was no need to apply the technology disclosed herein.

[0108] In contrast to these comparative examples, in the examples comprising (A) a crystalline carbon material, (B) a basic polymer dispersant having basic functional groups and a weight-average molecular weight of 1000 or more, and (C) a non-aqueous solvent, the increase in median diameter D2 was suppressed even after heating, and the temperature change rate X of dispersibility was relatively suppressed. In particular, in Examples 1-1 to 1-3, which used "CNT A" as the carbon material, the temperature change rate X of dispersibility was significantly suppressed in all cases. These results demonstrate the significance of the technology disclosed herein.

[0109] Preferred embodiments of the present invention have been described above. However, the embodiments described above are merely illustrative, and the present invention can be implemented in various other forms. [Explanation of symbols]

[0110] 10 CNTs (crystalline carbon materials) 20 Basic polymer dispersants (dispersants)

Claims

1. Crystalline carbon material, A dispersant having a basic functional group and a weight-average molecular weight of 1000 or more, Non-aqueous solvents and A carbon material dispersion containing, The carbon material in the carbon material dispersion has a peak intensity ratio (I) based on laser Raman spectroscopy. Ｇ / I Ｄ ) is 45 or less, and The carbon material dispersion is given by the following equation: X = |D2 - D1| / D1 ... (1) However, in equation (1), D1 is the median diameter (μm) of the carbon material in the carbon material dispersion at 20°C, satisfying D1 ≤ 30. D2 is the median diameter (μm) of the carbon material in the carbon material dispersion at 80°C; The rate of change of temperature X of the dispersiveness, expressed as X, is 1.0 or less. Carbon material dispersion.

2. The carbon material has a specific surface area of ​​150 m² based on nitrogen adsorption. ２ / g or more 700m ２ It is less than or equal to / g. A carbon material dispersion according to claim 1.

3. The carbon material comprises at least one of carbon nanotubes and graphene. A carbon material dispersion according to claim 1.

4. The carbon material includes carbon nanotubes, A carbon material dispersion according to claim 1.

5. The carbon material is given by the following formula: Y = A1 × C1 / [peak intensity ratio (I Ｇ / I Ｄ ) ] ... (2) However, in formula (2), A1 is the specific surface area (m²) of the carbon material. ２ The value is ( / g), and C1 is the concentration (mass%) of the carbon material; The index Y, represented by [formula], is between 10 and 1200. A carbon material dispersion according to claim 1.

6. The concentration C1 of the carbon material is 0.1% by mass or more and 5% by mass or less. The carbon material dispersion according to claim 5.

7. The dispersant has a weight-average molecular weight of 40,000 or less. A carbon material dispersion according to any one of claims 1 to 6.

8. The dispersant has an amine value of 5 mg KOH / g or more. A carbon material dispersion according to any one of claims 1 to 6.

9. The dispersant has a branched or comb-like structure, with at least the basic functional group in its side chain. A carbon material dispersion according to any one of claims 1 to 6.

10. The aforementioned temperature change rate X is 0.2 or less. A carbon material dispersion according to any one of claims 1 to 6.

11. The median diameter D1 is 1.0 μm or more. A carbon material dispersion according to any one of claims 1 to 6.

12. The carbon material dispersion has a carbon material concentration C1 of 0.4% by mass or more, and The adjusted pH when the carbon material is diluted with pure water to a concentration of 0.2% by mass is 6.5 or higher. A carbon material dispersion according to any one of claims 1 to 6.

13. The ratio of the concentration C2 of the dispersant to the concentration C1 of the carbon material (C2 / C1) is 0.1 or more and 2 or less. A carbon material dispersion according to claim 5 or 6.

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