Carbon material dispersion liquid

Abstract

Provided is a carbon material dispersion liquid in which the carbon material is less likely to aggregate even when heated. 【Solution means】The carbon material dispersion liquid disclosed herein includes a crystalline carbon material, a dispersant having a basic functional group and a weight average molecular weight of 1000 or more, and a non-aqueous solvent. The carbon material in the carbon material dispersion liquid has a peak intensity ratio (I G / I D ) based on laser Raman spectroscopy of 45 or less. The carbon material dispersion liquid has the following formula: X = |D2 - D1| / D1 (where D1 is the median diameter (μm) of the carbon material in the carbon material dispersion liquid at 20°C, satisfying D1 ≦ 30. D2 is the median diameter (μm) of the carbon material in the carbon material dispersion liquid at 80°C.); The temperature change rate X of the dispersibility represented by is 1.0 or less.

Description

Technical Field

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

Background Art

[0002] Conventionally, carbon material dispersions containing a carbon material, a dispersant, and a solvent (aqueous solvent or non-aqueous solvent) have 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, when 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 studies of 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 liquid reaches a 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]

Means for Solving the Problems

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

[0007] The carbon material dispersion liquid disclosed herein suppresses aggregation of the carbon material even when the temperature is raised to about 80°C, for example, by coexisting the carbon material with the dispersant in a non-aqueous solvent. Thereby, the temperature change of dispersibility can be reduced.

Advantages 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 a high temperature (for example, about 80°C).

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0010] Hereinafter, preferred embodiments of the present invention will be described. It should be noted that the embodiments described herein are not intended to limit the present invention in particular. Also, members and parts having the same function are denoted by the same reference numerals, and redundant descriptions may be omitted or simplified as appropriate. In addition, in this specification, the notation "X to Y" (where X and Y are arbitrary numerical values) indicating a range includes the meaning of "greater than X" and "less than Y" as well as the meaning of "X or more and Y or less".

[0011] <Carbon material dispersion> The carbon material dispersion of this embodiment (hereinafter, also simply referred to as "dispersion") contains (A) a crystalline carbon material (hereinafter, also referred to as "crystalline carbon material"), (B) a dispersant having a basic functional group 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, for example, (D) additives, etc., if necessary. Although details will be described later, in this embodiment, when a predetermined crystalline carbon material coexists with a basic polymer dispersant in a non-aqueous solvent, for example, the basic functional group of the basic polymer dispersant is considered to act on the surface of the crystalline carbon material and bind to the crystalline carbon material. Thereby, for example, even when the temperature of the dispersion is raised to a high temperature of about 80°C, aggregation of the crystalline carbon material can be suppressed.

[0012] <(A) Crystalline carbon material> The crystalline carbon material is a carbon material in which carbon atoms are regularly arranged and the position of each carbon atom can be specified. In this regard, it is distinguished from an amorphous carbon material. As also described in the test examples (reference examples) to be described later, according to the studies of the present inventors, for an amorphous carbon material, unlike a crystalline carbon material, there is almost no temperature change in dispersibility, so the problems of the present invention do not occur in the first place.

[0013] In this embodiment, the peak intensity ratio (I 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 surface functional groups (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, through the defective portions on the surface, the (B) basic polymer dispersant can be more easily bonded. Therefore, even when exposed to a high temperature (for example, about 80 °C), the state of being bonded to the (B) basic polymer dispersant is likely to be maintained. As a result, the 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, 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 high conductivity can be easily obtained. Furthermore, the defective portions on the surface of the crystalline carbon material can be moderately suppressed, and the stability of the dispersion can be improved.

[0016] In addition, in this specification, the peak intensity ratio (I G / I D ) of the crystalline carbon material is a value measured by collecting the crystalline carbon material in the dispersion liquid, and the value may be different from the physical properties of the crystalline carbon material as a raw material (the material itself). The peak intensity ratio (I G / I D ) is, in the Raman spectrum measured by laser Raman spectroscopy, in the vicinity of 1350 cm -1 (typically in the range of 1310 cm -1 to 1390 cm -1 ), the maximum peak intensity I D of the D band, relative to the maximum peak intensity I -1 in the vicinity of 1580 cm -1 (typically in the range of 1560 cm -1 to 1600 cm G ) of the G band, and can be calculated as the ratio. The detailed measurement method will be described in the examples below.

[0017] Although not particularly limited, the crystalline carbon material preferably has a specific surface area based on the nitrogen adsorption method of 20 m 2 / g or more, more preferably 30 m 2 / g or more, and even more preferably 50 m 2 / g or more. In some embodiments, the specific surface area is preferably 100 m 2 / g or more, more preferably 150 m 2 / g or more, and even more preferably 200 m 2 / g or more. By setting the specific surface area to a predetermined value or more, the basic polymer dispersant (B) is more likely to bind to the surface of the crystalline carbon material. Therefore, the effects of the technology disclosed herein are more likely to be stably exhibited at a high level.

[0018] The specific surface area of the crystalline carbon material is preferably generally 1000 m 2 / g or less, more preferably 800 m 2 / g or less, and even more preferably 700 m 2It is more preferably below / g. In some embodiments, the specific surface area is preferably 400 m 2 / g or less, more preferably 350 m 2 / g or less, and even more preferably 300 m 2 / g or less. By setting the specific surface area to a predetermined value or less, it becomes easier to obtain high conductivity with a small amount. Therefore, it is possible to achieve both a high level of reduction in temperature change of dispersibility and high conductivity. Also, generally, the smaller the specific surface area, the smaller the amount of the (B) basic polymer dispersant required. Therefore, the amount of the (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 the nitrogen adsorption method using a conventionally known gas adsorption apparatus by the BJH method. The detailed measurement conditions are described in the examples below.

[0020] As the type of the crystalline carbon material, those satisfying the above peak intensity ratio (I G / I D ) (preferably, those further satisfying the above specific surface area) are not particularly limited, and for example, one or more conventionally known materials can be appropriately used according to the use of the dispersion liquid or the like. Specific examples of the crystalline carbon material include so-called nanocarbons such as carbon nanotubes (A1), graphene (A2), and fullerenes (spherical carbon), and graphite (natural graphite, artificial graphite). Among them, nanocarbons have a high surface energy due to their small particle size and are likely to aggregate in the (C) non-aqueous solvent. Therefore, it is particularly effective to apply the technology disclosed herein. In particular, since the effects of the technology disclosed herein are likely to be stably exhibited at a high level, it is preferable to include at least one of carbon nanotubes and graphene, and more preferably to include carbon nanotubes.

[0021] Although not particularly limited, the crystalline carbon material preferably contains nanocarbons (particularly carbon nanotubes and graphene) as the main component (a component accounting for 50% by mass or more; the same shall apply hereinafter), more preferably 80% by mass or more of nanocarbons (particularly carbon nanotubes and graphene), still more preferably 95% by mass or more of nanocarbons (particularly carbon nanotubes and graphene), and particularly preferably consists substantially of nanocarbons (particularly carbon nanotubes and graphene) (98% by mass or more of nanocarbons (particularly carbon nanotubes and graphene)).

[0022] (A1) A carbon nanotube (CNT) is a carbon material having a structure in which a planar graphite forming a carbon hexagon network is rolled into a cylindrical shape. The type of CNT is not particularly limited, and one or more conventionally known types can be appropriately used. The CNT may be a single-walled carbon nanotube (SWCNT) having a structure in which a single layer of graphite is rolled into a cylindrical shape, or a multi-walled carbon nanotube (MWCNT) having a structure in which two or more layers of graphite are rolled into a cylindrical shape. Among them, it is more preferable to contain multi-walled carbon nanotubes because of their excellent conductivity and the ease of stably exhibiting the effects of the technology disclosed herein at a high level. Note that the CNT may contain impurities (for example, a catalyst and an amorphous carbon material) depending on, for example, the manufacturing process.

[0023] Although not particularly limited, the average outer diameter (average diameter) of the CNT is preferably 1 nm or more. In some embodiments, the average outer diameter of the CNT is more preferably 3 nm or more, and even more preferably 5 nm or more. When the average outer diameter is equal to or greater than a predetermined value, it becomes easier for the (B) basic polymer dispersant to penetrate between the CNT bundles, and it becomes easier to improve the dispersibility. Therefore, the effects of the technology disclosed herein are likely to be exhibited at a high level. The average outer diameter of the CNT is preferably generally 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 equal to or less than a predetermined value, the number of CNTs per unit mass increases, and it becomes easier to efficiently form a conductive network, and the conductivity can be improved.

[0024] Note that the average outer diameter of the CNT can be calculated by observing a plurality of CNTs with an electron microscope, measuring the radial length of each CNT, and taking the number average value thereof. More specifically, for example, using a transmission electron microscope (TEM), observation is performed at a magnification of, for example, 400,000 times, and the radial length is measured for 50 CNTs arbitrarily extracted from the field of view, and it can be calculated by the number average value thereof.

[0025] Although not particularly limited, the average fiber length of the CNT is preferably 1 μm or more, and more preferably 5 μm or more. In some embodiments, the average fiber length of the CNT is even more preferably 50 μm or more, and particularly preferably 80 μm or more, 100 μm or more. When the average fiber length is equal to or greater than a predetermined value, it becomes easier for the (B) basic polymer dispersant to entangle on the surface. Therefore, even when exposed to a high temperature (for example, about 80 °C), it becomes easier to maintain the state of being bound to the (B) basic polymer dispersant, and the effects of the technology disclosed herein are likely to be stably exhibited at a high level. Also, when the average fiber length is long, the CNTs are likely to entangle and aggregate in the (C) non-aqueous solvent. Therefore, it is particularly effective to apply the technology disclosed herein. Furthermore, it becomes easier to effectively form a conductive network, and the conductivity can be improved.

[0026] Also, the average fiber length of the CNT is preferably generally 1000 μm or less, more preferably 500 μm or less, still more preferably, for example, 400 μm or less, 200 μm or less. In some embodiments, the average fiber length of the CNT is preferably 50 μm or less, more preferably 30 μm or less, still more preferably 10 μm or less. When the average fiber length is below a predetermined value, it becomes difficult for CNTs to be rounded or entangled with each other in the (C) non-aqueous solvent. Therefore, it is possible to achieve high levels of both reduction of temperature change in dispersibility and conductivity.

[0027] Incidentally, the average fiber length of the CNT can be calculated by observing a plurality of CNTs with an electron microscope, measuring the length in the axial direction of each CNT, and taking the number average value thereof. More specifically, for example, using a scanning electron microscope (SEM), observations are made at a magnification of, for example, 10,000 times, and the lengths in the axial direction are measured for 50 CNTs arbitrarily extracted from the field of view, and the number average value can be calculated therefrom.

[0028] The CNT is 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 CNT is preferably generally 10 or more, more preferably 100 or more. In some embodiments, the average aspect ratio is preferably generally 1000 or more, more preferably 2000 or more, still more preferably, for example, 5000 or more. When the average aspect ratio is above a predetermined value, it becomes easier to exhibit the effects of the technology disclosed herein at a high level, and it is possible to achieve high levels of both reduction of temperature change in dispersibility and conductivity. Also, although not particularly limited, the upper limit value of the average aspect ratio is preferably generally 100,000 or less, more preferably 50,000 or less, still 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 nets are arranged planar. The type of graphene is not particularly limited, and one or more conventionally known types can be appropriately used. Graphene may be single-layer graphene or multi-layer graphene in which a plurality of single-layer graphenes are stacked. Among them, it is more preferable to contain multi-layer graphene because it has excellent conductivity and the effects of the technology disclosed herein are likely to be stably exhibited at a high level.

[0030] In addition, for crystalline carbon materials other than CNT (for example, graphene, fullerene, graphite), their properties such as size and shape are not particularly limited. Crystalline carbon materials other than CNT 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 less than 0.5 or exceeding 1.5. In some embodiments, it is preferable that the crystalline carbon material other than CNT is spherical. In this specification, "spherical" refers to a shape that can be generally regarded as a sphere (ball), including elliptical, polyhedral, disk-spherical, etc. Also, "non-spherical" includes shapes such as plate-like, scaly, flaky, irregular shapes.

[0031] The average particle size of the crystalline carbon material other than CNT 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 equal to or greater than a predetermined value, it becomes easier for the (B) basic polymer dispersant to bind to the surface. Also, dispersion becomes easier, and the effects of the technology disclosed herein are likely to be stably exhibited at a high level. Also, the average particle size of the crystalline carbon material other than CNT 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 equal to or less than a predetermined value, it becomes easier to efficiently form a conductive network and the conductivity can be improved. The average particle size of the crystalline carbon material other than CNT can be measured and calculated, for example, by a method conforming to the average outer diameter and average fiber length of the above-described CNT.

[0032] The crystalline carbon material (particularly nanocarbons) of this embodiment has a small particle size and is easily oxidized on the surface. The crystalline carbon material may have an acidic functional group (typically an oxygen-containing functional group) such as a hydroxyl group, a carboxyl group, or a sulfo group on the surface. The crystalline carbon material has an acidic functional group on the surface, which makes it easier to bind with the basic polymer dispersant (B) in the dispersion liquid. Therefore, the effect of the technology disclosed herein is easily exerted at a high level and in a stable manner. The presence of an acidic functional group on the surface of the crystalline carbon material, and the type and amount of the acidic functional group can be confirmed by a conventionally known titration method (e.g., the Boehm method) or surface analysis using X-ray photoelectron spectroscopy (XPS).

[0033] The crystalline carbon material of the present embodiment may be produced by any method. In some embodiments, the crystalline carbon material may be surface-modified by, for example, a conventionally known oxidation treatment, plasma treatment, ozone treatment, high-temperature treatment, heat treatment, or the like. This allows the crystalline carbon material to stably contain many acidic functional groups.

[0034] In some embodiments, the crystalline carbon material has the following formula: Y = A1 × C1 / [Peak intensity ratio (I G / I D )] …(2) In the above formula (2), A1 is the specific surface area (m 2 / g), and C1 is the concentration (mass %) of the crystalline carbon material in the dispersion; It is preferable that the index Y represented by the formula (1) is 10 or more and 1200 or less. The larger the value of the index Y, the wider the area to be covered by the basic polymer dispersant (B), and the index Y can be used as an index for determining the amount of the basic polymer dispersant (B) to be added. By setting the index Y within the above range, the effect of the technology disclosed herein is easily exerted stably at a high level. In addition, by reducing the amount of the basic polymer dispersant (B) to be added, it is possible to achieve both a high level of reduction in temperature change of dispersibility and electrical conductivity.

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

[0036] The concentration C1 of the crystalline carbon material may vary depending on, for example, the type of the crystalline carbon material used, etc., and is not particularly limited. However, when the total of the dispersion liquid is 100% by mass, it is preferably approximately 0.01 to 10% by mass. The concentration C1 of the crystalline carbon material is more preferably 0.1% by mass or more, and further preferably, for example, 0.2% by mass or more, 0.3% by mass or more, 0.4% by mass or more. When the concentration C1 is a predetermined value or more, a conductive network is likely to be formed, and the conductivity can be improved. Also, when the concentration C1 of the crystalline carbon material increases, it is likely to aggregate in the (C) non-aqueous solvent, so it is particularly effective to apply the technology disclosed herein. The concentration C1 of the crystalline carbon material is more preferably 5% by mass or less, and in some embodiments, further preferably, for example, 2% by mass or less, 1% by mass or less. When the concentration C1 is a predetermined value or less, it is less likely to aggregate in the (C) non-aqueous solvent even when exposed to a high temperature (for example, about 80°C), and the temperature change in dispersibility can be reduced better. Therefore, it becomes easier to exhibit the effects of the technology disclosed herein at a high level.

[0037] <(B) Basic polymer dispersant> The basic polymer dispersant is a component for dispersing the (A) crystalline carbon material in the (C) non-aqueous solvent. In the present embodiment, the weight average molecular weight (Mw) of the basic polymer dispersant is 1000 or more. Thereby, the dispersant is entangled with the (A) crystalline carbon material and is likely to strongly bind to the (A) crystalline carbon material. Therefore, even when exposed to a high temperature (for example, about 80°C), the state of binding to the (A) crystalline carbon material is likely to be maintained, and the state in which the crystalline carbon material is dispersed in the (C) non-aqueous solvent can be stably maintained. Thereby, the effects of the technology disclosed herein can be appropriately exhibited.

[0038] In the present specification, the "polymer (polymeric compound)" refers to all compounds (typically polymers) having a weight-average molecular weight (Mw) of 1000 or more. For example, it is a term that includes oligomers having a weight-average molecular weight of 1000 or more and less than 5000, and polymers having a weight-average molecular weight of 5000 or more. In some embodiments, the basic polymer dispersant preferably contains a polymer, and more preferably mainly consists of a polymer. Thereby, it becomes easier to exhibit the above-described effects at a higher level.

[0039] In some embodiments, the weight-average molecular weight of the basic polymer dispersant is preferably 5000 or more, more preferably 10,000 or more, still more preferably 15,000 or more, and particularly preferably 20,000 or more, 30,000 or more, for example. Also, the weight-average molecular weight of the basic polymer dispersant is preferably 100,000 or less, more preferably 50,000 or less, still 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. Also, it becomes easier to suppress the viscosity of the dispersion liquid and improve the handleability. Further, when (A) the crystalline carbon material is CNT, the dispersant is more likely to penetrate between the bundles of CNT, and it becomes easier to improve the dispersibility.

[0040] The weight-average molecular weight of the basic polymer dispersant can be calculated by comparing the measured value by gel permeation chromatography (GPC) with the calibration curve using a standard sample (polystyrene). As the weight-average molecular weight, it is more preferable to adopt the average value when measured a plurality of times (for example, 2 times). The detailed measurement conditions are described in the examples described later.

[0041] The molecular weight distribution (Mw / Mn), which is the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of the basic polymer dispersant, is preferably approximately 1 to 20, more preferably 1 to 10, and even more preferably, for example, 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, the "number average molecular weight" can be calculated from the value measured under the same measurement conditions as the weight average molecular weight described above.

[0042] Also, although not particularly limited, since it is easy to exhibit the above-described effects at a higher level, the number average molecular weight (Mn) of the basic polymer dispersant is preferably approximately 1000 or more. 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 approximately 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 can be, for example, a functional group with an acid dissociation constant pKa of generally 8 or more, preferably 9 or more in water at 25°C. The basic functional group is preferably a nitrogen-containing group having a nitrogen atom (N). Examples of the basic functional group 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. The amino group includes a heterocyclic amino group such as a pyridinyl group (-C5H4N), and the group having an amidine skeleton includes a heterocyclic group such as an imidazoline ring. Among them, the amino group is preferable in that it can also interact with parts other than the defective parts of the crystalline carbon material. In particular, a primary or secondary amino group that is likely to strongly bind to the defective parts of the (A) crystalline carbon material is preferable. The type of the basic functional group in the basic polymer dispersant may be one type or two or more types. The fact that the dispersant has a basic functional group, and the type and amount of the basic functional group can be confirmed by conventionally known titration methods and spectroscopic measurements such as infrared absorption spectroscopy, nuclear magnetic resonance spectroscopy, and X-ray photoelectron spectroscopy (XPS).

[0044] In this specification, the "basic functional group" does not include substantially neutral functional groups such as amide groups and imide groups. That is, in the amide group and imide group, the lone pair of electrons on nitrogen resonates and delocalizes with the electron orbit of the adjacent carbonyl group, so the basicity is much weaker than that of, for example, an amino group, and it becomes a substantially neutral functional group. Therefore, a compound having only such a neutral functional group, for example, a vinylpyrrolidone-based polymer such as polyvinylpyrrolidone (PVP) commonly used in this type of dispersion liquid, does not exhibit the effects of the technology disclosed herein, as described in the comparative examples below.

[0045] The basic polymer dispersant preferably has an amine value. That is, the amine value (total amine value) is preferably not less than the detection lower limit value (although it depends on the measurement accuracy, generally not less than 0.1 mgKOH / g). In some embodiments, the basic polymer dispersant preferably has an amine value of not less than 1 mgKOH / g, more preferably not less than 3 mgKOH / g, still more preferably not less than 5 mgKOH / g, and may be, for example, not less than 10 mgKOH / g or not less than 20 mgKOH / g. By setting the amine value to a predetermined value or more, the basic polymer dispersant forms a hydrogen bond with the surface of the crystalline carbon material, particularly at the site of acidic functional groups, and is likely to strongly bind to the (A) crystalline carbon material. Therefore, the effects of the technology disclosed herein are likely to be stably exhibited at a high level. From the viewpoint of suppressing the viscosity of the dispersion liquid and improving the handleability, the amine value of the basic polymer dispersant is preferably generally not more than 100 mgKOH / g, more preferably not more than 75 mgKOH / g, and still more preferably not more than 50 mgKOH / g.

[0046] Note that the amine value of the basic polymer dispersant is the number of milligrams of potassium hydroxide equivalent to the acid required to neutralize 1 g of the dispersant. The amine value of the basic polymer dispersant can be measured in accordance with conventionally known methods, for example, the methods 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 be an amphoteric compound. The acidic functional group can be, for example, a functional group having an acid dissociation constant pKa of generally not more than 6, preferably not more than 5 in water at 25°C. Examples of the acidic functional group include a hydroxy group (hydroxyl group), a carboxyl group, a sulfo group, etc. The type of the acidic functional group in the dispersant may be one type or two or more types. The fact that the dispersant has an acidic functional group, and the type and amount of the acidic functional group can be confirmed by conventionally known titration methods, 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 generally be 1 to 20 mgKOH / g, for example, 2 to 10 mgKOH / g. In some embodiments, it is preferable that the acid value of the basic polymer dispersant is less than the amine value. Thereby, (A) the basic polymer dispersant is likely to strongly bind to the surface of the crystalline carbon material, and the effects of the technology disclosed herein are likely to be stably exhibited at a high level. The acid value of the basic polymer dispersant can be measured in accordance with a conventionally known method, for example, the method specified in JIS K 0070:1992.

[0049] The basic polymer dispersant is not particularly limited as long as it has a basic functional group and satisfies the above weight average molecular weight (preferably, it further satisfies the above molecular weight distribution or the above number average molecular weight). For example, depending on the use of the dispersion liquid and the type of (C) non-aqueous solvent, etc., one or more conventionally known ones can be appropriately used. The basic polymer dispersant can exist in both a state where the functional group exhibiting basicity is not ionized (non-ionic) or a state where it is ionized (ionic) by salt formation or the like.

[0050] The structure of the basic polymer compound is not particularly limited. The molecular structure of the basic polymer compound may be, for example, (1) linear straight-chain, (2) branched type in which one or more side chains (carbon chains branched from the main chain. The same applies hereinafter. For example, graft chains.) are bonded to a linear main chain (the carbon chain having the largest number of carbon atoms. The same applies hereinafter.), or (3) comb type in which a plurality of side chains are regularly arranged on the same side along the main chain, etc. The basic functional group as described above may be contained in the main chain or in one or more side chains. Further, the main chain may be substituted at the terminal or both terminals with an ionic group (for example, the basic functional group as described above).

[0051] In the first embodiment, the basic polymer dispersant preferably contains one or more basic functional groups in the main chain. Specific examples of such basic polymer dispersants include compounds having an amine structure in the main chain, such as polyamines, polyimines, compounds represented by the following chemical formula (I), modified products thereof, and 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 amine) having no ring structure.

[0052]

Chemical formula

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

[0054] In the second embodiment, the basic polymer dispersant preferably has a branched or comb-like structure containing at least a basic functional group in the side chain. Among these, it is more preferable that each of a plurality of side chains contains a basic functional group. The side chain is a site with a higher degree of freedom in the dispersion liquid compared to the main chain. Therefore, by including a basic functional group in the side chain, the basic polymer dispersant is more likely to bind firmly (for example, at many sites) to the surface of the (A) crystalline carbon material, particularly to the site of the acidic functional group. Thus, even when exposed to a high temperature (for example, about 80°C), the state of being bound to the (A) crystalline carbon material is likely to be maintained, and the effects of the technology disclosed herein are likely to be stably exhibited at a high level. In some embodiments, it is preferable that the basic polymer dispersant further contains a basic functional group in the main chain. In some other embodiments, when the basic polymer dispersant has an acidic functional group, it is preferable to contain an acidic functional group (for example, a carboxyl group) in the main chain, for example.

[0055] Note that a basic polymer dispersant having a basic functional group in the side chain can be prepared, for example, by reacting a first compound constituting the main chain with a second compound serving as a basic functional group source (for example, an acid-base reaction). The second compound is preferably an organic amine, and as an example, aliphatic amines having a hydroxyl group such as aminoethanol and 2-amino-2-methylpropanol can be mentioned.

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

[0057] The maleic copolymer is a copolymer and its derivative containing maleic acid units as main repeating units and having basic functional groups in the side chains. Specific examples of the maleic copolymer include, for example, styrene maleic copolymer, ethylene maleic copolymer, isobutylene maleic copolymer, and their salts and modified products, etc.

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

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

[0060] Moreover, 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 a predetermined value or less, the conductive network of the (A) crystalline carbon material can be efficiently formed, and high conductivity can be easily achieved. Therefore, it is possible to achieve both a high level of reduction in temperature change of dispersibility and conductivity.

[0061] From the viewpoint of electrical conductivity, the mass of the basic polymer dispersant contained in the dispersion is preferably equal to or less than the mass of the (A) crystalline carbon material. The mass ratio of the basic polymer dispersant to the (A) crystalline carbon material (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 difficult for the electrical conductivity to be inhibited, and makes it easier to achieve high electrical conductivity. In addition, 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, since this makes it easier to stably exert 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 solvent> The non-aqueous solvent is (A) a dispersion medium for dispersing the crystalline carbon material. The non-aqueous solvent substantially does not contain water. 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 the Karl Fischer titration method (JIS K0068:2001).

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

[0064] The non-aqueous solvent preferably contains an aprotic polar solvent (for example, NMP) as the main component (a component accounting for 50% by mass or more), more preferably 80% by mass or more is an aprotic polar solvent (for example, NMP), still more preferably 95% by mass or more is an aprotic polar solvent (for example, NMP), and particularly preferably consists substantially of an aprotic polar solvent (for example, NMP) (98% by mass or more is an aprotic polar solvent (for example, NMP)). Thereby, the effects of the technology disclosed herein can be stably exhibited at a high level and easily.

[0065] <(D) Additive> The additive is an optional component. As the additive, one or more additives known to be conventionally usable for this kind of application can be appropriately used for the purpose of improving various properties of the dispersion liquid or the like. Specific examples of the additive include, for example, a carbon material that does not satisfy the conditions of the above (A) crystalline carbon material (for example, an amorphous carbon material such as carbon black, activated carbon, hard carbon, soft carbon, etc., and a carbon material with a peak intensity ratio (I G / I D ) exceeding 45), and inorganic additives such as metal oxides; dispersants that do not satisfy the conditions of the above (B) basic polymer dispersant (for example, dispersants having no basic functional group or dispersants having a weight average molecular weight of less than 1000), and organic additives such as organic binders, antioxidants, defoamers, preservatives, plasticizers, colorants (pigments, dyes, etc.); pH adjusters such as inorganic bases and organic bases; and the like.

[0066] When the dispersion liquid contains an optional component, the mass of the optional component (for example, (D) additive) contained in the dispersion liquid is typically preferably less than the content of the (A) crystalline carbon material and / or the mass of the (B) basic polymer dispersant. As an example, when the total amount of the dispersion liquid is 100% by mass, the concentration of the additive is preferably 5% by mass or less, more preferably 3% by mass or less, and particularly preferably 2% by mass or less, 1% by mass or less, 0.5% by mass or less, 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 liquid disclosed herein can be prepared by mixing the (A) crystalline carbon material, the above (B) basic polymer dispersant, and other optional components in the (C) non-aqueous solvent, and dispersing or dissolving the (A) crystalline carbon material, the (B) basic polymer dispersant, and other optional components in the (C) non-aqueous solvent. The (A) crystalline carbon material and / or the (B) basic polymer dispersant may be added in the total amount at once or divided and added two or more times.

[0068] For mixing, for example, conventionally known mixing devices such as a disper, a planetary mixer, a kneader, a propeller stirrer, an ultrasonic homogenizer, a magnetic stirrer, a jet mill, a ball mill, a bead mill, and a sand mill can be appropriately used. Among them, from the viewpoint of reducing contamination of the medium, a device that does not use a medium (mediumless) is preferable. Also, from the viewpoint that dispersion easily proceeds homogeneously, a circulation-type dispersion device is preferable. Further, since the processing time can be shortened, a device that utilizes the shearing force of high-speed stirring is preferable. As an example of such a mixing device, a high-pressure homogenizer can be mentioned.

[0069] The carbon material dispersion liquid disclosed herein is such that even when exposed to a high temperature (for example, about 80 °C), (A) the crystalline carbon material is less likely to aggregate and the temperature change in dispersibility is reduced. Specifically, the following formula: X = |D2 - D1| / D1 …(1) However, in the above formula (1), D1 is the median diameter (μm) of the (A) crystalline carbon material in the dispersion liquid at 20 °C, and satisfies D1 ≤ 30. D2 is the median diameter (μm) of the (A) crystalline carbon material in the dispersion liquid at 80 °C; The temperature change rate X represented by is 1.0 or less. The median diameters D1 and D2 are volume-based particle diameters (D50 diameters) based on the laser diffraction / scattering method. The detailed measurement method is described in the examples below.

[0070] The fact that the temperature change rate X is 1.0 or less means that the median diameter D2 at 80 °C is suppressed to 2.0 times or less the median diameter D1 at 20 °C. From the viewpoint of exerting the effects of the technology disclosed herein at a higher level, the temperature change rate X is more preferably 0.8 or less, further preferably 0.5 or less, particularly preferably 0.2 or less, and among them, 0.1 or less and 0.05 or less are preferable.

[0071] Also, although not particularly limited, the median diameter D1 at 20°C is preferably generally 0.1 μm or more, more preferably 0.5 μm or more, and even more preferably 1.0 μm or more, since the effects of the technology disclosed herein are likely to be stably exhibited. The median diameter D2 at 80°C may 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 the crystalline carbon material (A) of 0.4% by mass or more, and an adjusted pH of 6.5 or more when diluted with pure water so that the concentration of the crystalline carbon material (A) becomes 0.2% by mass. The value of this adjusted pH is typically determined by the combination of the crystalline carbon material (A) and the basic polymer dispersant (B). The adjusted pH being at a predetermined value or more means that the dispersion is somewhat neutral or basic. By setting the adjusted pH to a predetermined value or more, a sufficient amount of basic functional groups of the basic polymer dispersant (B) is obtained, and the median diameter D2 is likely to be kept small even when the dispersion is exposed to a high temperature (for example, about 80°C). Therefore, the temperature change rate X can be stably kept small, and the effects of the technology disclosed herein are likely to be exhibited at a high level.

[0073] The upper limit of the value of the adjusted pH is not particularly limited, but considering the influence in the subsequent process of manufacturing the desired product, it is preferably generally 11 or less, for example, 10 or less. In some embodiments, the value of the adjusted pH 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 and then measuring the pH is that pH is basically a method for evaluating the proton concentration, and there is basically no concept of pH in non-aqueous solvents (C), especially aprotic solvents such as NMP. Therefore, it is necessary to dilute with pure water and adjust the pH under conditions where protons are sufficiently present before measuring the pH.

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

[0076] Thus, by coexisting the (A) crystalline carbon material with the (B) basic polymer dispersant in the (C) non-aqueous solvent, for example, compared with the case of coexisting with a dispersant that does not satisfy the above (specifically, a dispersant having no basic functional group or a dispersant having a weight average molecular weight of less than 1000), the temperature change of dispersibility can be relatively reduced. Therefore, even when the temperature of the dispersion is raised to a high temperature (for example, about 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 construed as particularly limited, the inventors are considering the effects caused by the combination of (A) to (C) as follows. FIG. 1 is a schematic diagram for explaining the effects of the technology disclosed herein, and shows the (A) crystalline carbon material 10 and the (B) basic polymer dispersant 20 in the (C) non-aqueous solvent. Here, as an example of the crystalline carbon material 10, fibrous CNTs are shown.

[0078] As shown in FIG. 1, the crystalline carbon material 10, particularly nanocarbons, has a small particle size and is easily oxidized on the surface. Therefore, the crystalline carbon material 10 often has an acidic functional group (typically an oxygen-containing functional group) such as a hydroxyl group or a carboxyl group on its surface. On the other hand, the basic polymer dispersant 20 has a basic functional group. Therefore, in the dispersion liquid, the acidic functional group on the surface of the crystalline carbon material 10 and the basic functional group of the basic polymer dispersant 20 are bonded (for example, hydrogen bonded in an acid-base reaction), and the crystalline carbon material 10 and the basic polymer dispersant 20 are easily strongly bonded to each other. In addition, the basic polymer dispersant 20 is likely to have a larger volume (three-dimensional size) in the dispersion liquid as the weight-average molecular weight increases. Therefore, steric repulsion between the crystalline carbon materials 10 is likely to occur. Due to the above effects, according to the technology disclosed herein, the basic polymer dispersant 20 is less likely to dissociate from the crystalline carbon material 10 even at high temperatures. In other words, it is believed that the state in which the crystalline carbon material 10 and the basic polymer dispersant 20 are bound together can be stably maintained, and 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 m based on a nitrogen adsorption method. 2 / g or more 700m 2 / g or less is preferable. By making the specific surface area a predetermined value or more, the (B) basic polymer dispersant is easily bound to the surface of the crystalline carbon material. Therefore, the effects of the technology disclosed herein are easily achieved at a high level and in a stable manner. Furthermore, by making the specific surface area a predetermined value or less, high conductivity is easily obtained with a small amount. Therefore, it is possible to achieve both a high level of conductivity and a reduction in temperature change in dispersibility.

[0080] In the dispersion of the present embodiment, it is preferable that the carbon material contains at least one of carbon nanotubes and graphene. Thereby, the effects of the technology disclosed herein are likely to be stably exhibited at a high level. In addition, since nanocarbons have a high surface energy due to their small particle size and tend to aggregate in a (C) non-aqueous solvent, it is particularly effective to apply the technology disclosed herein.

[0081] In the dispersion of the present embodiment, it is preferable that the carbon material contains carbon nanotubes. Carbon nanotubes are fibrous and a (B) basic polymer dispersant is likely to entangle on the surface. Therefore, even when exposed to a high temperature (for example, about 80 ° C), the state of being combined with the (B) basic polymer dispersant is likely to be maintained, and the effects of the technology disclosed herein are likely to be stably exhibited at a high level. In addition, being fibrous makes it easier for carbon nanotubes to entangle and aggregate with each other in a (C) non-aqueous solvent. Therefore, it is particularly effective to apply the technology disclosed herein.

[0082] In the dispersion of the present embodiment, the carbon material has the following formula: Y = A1 × C1 / [peak intensity ratio (I G / I D )] …(2) However, in formula (2), A1 is the specific surface area (m 2 / g) of the carbon material, and C1 is the concentration (mass%) of the carbon material; It is preferable that the index Y represented by is 10 or more and 1200 or less. By setting the index Y within the above range, the effects of the technology disclosed herein are likely to be stably exhibited at a high level. In addition, the addition amount of the (B) basic polymer dispersant can be reduced to achieve high levels of both reduction in temperature change of dispersibility and conductivity.

[0083] In the dispersion of the present embodiment, it is preferable that the concentration C1 of the carbon material is 0.1% by mass or more and 5% by mass or less. When the concentration C1 is equal to or higher than a predetermined value, a conductive network is likely to be formed, and the conductivity can be improved. Further, when the concentration C1 is equal to or lower than a predetermined value, even when exposed to a high temperature (for example, about 80°C), it is less likely to aggregate in the (C) non-aqueous solvent, and the temperature change in dispersibility can be reduced better. Therefore, it is possible to achieve both a reduction in the temperature change in dispersibility and high-level conductivity.

[0084] In the dispersion of the present embodiment, it is preferable that the weight average molecular weight of the dispersant is 40,000 or less. When the weight average molecular weight is equal to or lower than a predetermined value, it is less likely to inhibit the conductivity of the (A) crystalline carbon material, and it is easier to exhibit high conductivity. Also, it is easier to improve the handleability by suppressing the viscosity of the dispersion. Further, when the (A) crystalline carbon material is CNT, the dispersant is likely to penetrate between the bundles of CNT, and it is easier to improve the dispersibility. Therefore, the effects of the technology disclosed herein are likely to be stably exhibited at a high level.

[0085] In the dispersion of the present embodiment, it is preferable that the amine value of the dispersant is 5 mgKOH / g or more. By setting the amine value to be equal to or higher than a predetermined value, the basic polymer dispersant hydrogen-bonds to the surface of the (A) crystalline carbon material, particularly at the sites of acidic functional groups, and is likely to strongly bind to the (A) crystalline carbon material. Therefore, the effects of the technology disclosed herein are likely to be stably exhibited at a high level.

[0086] In the dispersion of the present embodiment, it is preferable that the dispersant has a branched or comb-shaped structure containing at least the basic functional group in the side chain. The side chain is a site with a higher degree of freedom in the dispersion than the main chain. Therefore, by including a basic functional group in the side chain, the basic polymer dispersant is more likely to bind more firmly (at many sites) to the surface of the (A) crystalline carbon material, particularly at the sites of acidic functional groups. Therefore, even when exposed to a high temperature (for example, about 80°C), the state of binding to the (A) crystalline carbon material is likely to be maintained, and the effects of the technology disclosed herein are likely to be stably exhibited at a high level.

[0087] In the dispersion liquid of this embodiment, the temperature change rate X is preferably 0.2 or less, which allows the effects of the technology disclosed herein to be exerted at a higher level.

[0088] In the dispersion of the present embodiment, the median diameter D1 is preferably 1.0 μm or more, which makes it easier for the effects of the technology disclosed herein to be stably exhibited.

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

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

[0091] <Applications of carbon material dispersion liquid> The carbon material dispersion liquid disclosed herein can be used for various applications. For example, in an application for producing an electrode, a conductive film can be formed on a substrate by applying (typically coating) the carbon material dispersion liquid onto the substrate and drying it. In this case, the dispersion liquid 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. As the active material or the resin binder, various materials that are conventionally known to be usable in this type of application can be appropriately used.

[0092] In particular, in the application of manufacturing electrodes (positive electrodes 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 particularly preferable to apply the technology disclosed herein. As another aspect of the technology disclosed herein, there is provided a method for manufacturing a conductive film including a step of preparing a conductive slurry, a step of applying the prepared conductive slurry onto a substrate, and a step of removing a non-aqueous solvent by drying the conductive slurry applied to the substrate.

[0093] Hereinafter, examples of the present invention will be described, but the present invention is not intended to be limited to those shown in such examples.

[0094] Here, first, six types of carbon materials shown in Table 1, the following four types of dispersants, and NMP as a non-aqueous solvent were prepared. The specific surface area was measured as follows. <Specific surface area> The carbon material was pretreated at 300 °C for 720 minutes under reduced pressure, and after sufficient degassing, a fully automatic gas adsorption amount measuring device (autosorb-iQ manufactured by Anton Paar Co., Ltd.) was used to adsorb nitrogen gas on the surface at liquid nitrogen temperature, and the amount of nitrogen adsorbed in a monolayer was measured. Then, the measurement results were analyzed by the BJH method to calculate the specific surface area of the carbon material.

Table 1

[0095] <Dispersant> · Dispersant A: BYK ET3002 (manufactured by BYK 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: Nopcosperse 092 (manufactured by San Nopco); cationic surfactant · Dispersant D: Pitchkol K30 (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.); PVP

[0096] For the dispersant prepared above, the molecular weight was measured according to the following procedure. The results are shown in Table 2. <Measurement of Molecular Weight> Using gel permeation chromatography (GPC), the molecular weights of Dispersants A to C were measured under the following conditions. Then, by comparing the measured values with the calibration curve using a standard sample (polystyrene, manufactured by Tosoh Corporation), the weight average molecular weight and number average molecular weight in terms of polystyrene were calculated. Pretreatment: The sample was collected, the eluent was added, and it was left standing overnight at room temperature to dissolve, and then filtered through a polytetrafluoroethylene cartridge filter with a pore size of 0.5 μm. Apparatus: HLC-8320GPC (manufactured by Tosoh Corporation) Column: TSKgel guardcolumn SuperAW-H (4.6 mm I.D. × 3.5 cm) + TSKgel SuperAWM-H (6.0 mm I.D. × 15 cm) × 2 columns Column temperature: 40 °C Eluent: NMP + 10 mM LiBr Flow rate: 0.3 mL / min Sample concentration: 0.1% (based on solute) Detector: RI (refractive index) detector (polarity (+))

[0097]

Table 2

[0098] <Preparation of Dispersion> Next, in an environment of 25°C, the carbon material, dispersant, and non-aqueous solvent (NMP) shown in Table 3 were added to a polypropylene container in the amounts shown in Table 3, and using a propeller stirrer, they were stirred 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 having a basic functional group, molecular weight 89.14) that is commonly used as a pH adjuster was further added as an additive.

[0099] Subsequently, the preliminary mixture was put into the raw material tank of a high-pressure homogenizer (manufactured by Sugino Machine, Starburst HJP-25001V2), and a circulating dispersion treatment was performed on the preliminary mixture. The dispersion treatment was carried out using a single nozzle chamber at a nozzle diameter of 0.15 mm and a pressure of 150 MPa. The progress of the dispersion was monitored using a laser diffraction / light scattering particle size distribution measuring device (LA-960V2 manufactured by Horiba, Ltd.), and the circulation treatment was carried out until the particle size (median diameter) at a cumulative frequency of 50% became 30 μm or less. Thereby, a carbon material dispersion was prepared. In Table 3, the specific surface area A1 (m 2 / g) of the carbon material, the concentration C1 (mass%) of the carbon material, and the peak intensity ratio (I G / I D ) in the dispersion liquid described later, and the index Y calculated therefrom are also shown.

[0100] <Measurement of the adjusted pH of the dispersion liquid> The carbon material dispersion prepared above was separated, diluted with pure water so that the concentration of the carbon material became 0.2 mass%, and a preparation liquid for measurement was prepared. Then, under the condition that protons were sufficiently present, the pH of the preparation liquid was measured with a pH meter. The results are shown in Table 3.

[0101]

Table 3

[0102] <Evaluation of the temperature change of dispersibility> First, in an environment of 20°C, the carbon material dispersion prepared above was diluted with NMP so that the transmittance at a wavelength of 650 nm was 85 - 95% to prepare a measurement solution. Next, using a laser diffraction / light scattering particle size distribution measuring device (LA-960V2 manufactured by Horiba, Ltd.), the particle size distribution of the carbon material dispersion at 20°C was measured. In addition, the measurement was carried out three times with an integration count after filling the measurement solution into a batch cell. Then, the particle diameter (median diameter) at a cumulative frequency of 50% was determined. The results are shown in Table 4.

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

[0104] Next, from the median diameters of the carbon material at 20°C and 80°C, according to the following formula: X = |D2 - D1| / D1 …(1) However, in formula (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 the dispersibility was calculated. Then, the temperature change of the dispersibility was 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 (I of the carbon material in the dispersion G / I D) Measurement> First, the dispersion liquid was applied to a slide glass and dried at 100° C. for 30 minutes to prepare a sample for evaluation. Next, the sample for evaluation was measured under the following conditions using a laser Raman measurement device (manufactured by Renishaw, inVia). From the obtained spectrum, -1 The maximum peak intensity of the D band that appears near I D 1580cm -1 The maximum G-band peak intensity I appears near G The ratio (I G / I D The measurement was performed five times for the same sample at different measurement points, and the arithmetic average value was calculated as the peak intensity ratio (I G / I D The results are also shown in Table 4. Light source: Semiconductor laser (532 nm) Objective lens: 50x Beam diameter: 1μm Laser power: 5% Exposure time: 60 seconds Number of times: 1

[0106] [Table 4]

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

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

[0109] The preferred embodiments of the present invention have been described above. However, the above-described embodiments are merely examples, and the present invention can be implemented in various other forms.

Explanation of Reference Numerals

[0110] 10 CNT (crystalline carbon material) 20 Basic polymer dispersant (dispersant)

Claims

1. A crystalline carbon material; a dispersant having a basic functional group and a weight average molecular weight of 1000 or more; a non-aqueous solvent including an aprotic polar solvent; A carbon material dispersion comprising: The carbon material in the carbon material dispersion liquid has a peak intensity ratio (I Ｇ / I Ｄ ) is 45 or less, and The carbon material dispersion liquid has a structure represented by the following formula: X=|D2−D1| / D1 (1) In the formula (1), D1 is a median diameter (μm) of the carbon material in the carbon material dispersion at 20° C., and D1≦30 is satisfied. D2 is a median diameter (μm) of the carbon material in the carbon material dispersion at 80° C.; The temperature change rate X of dispersibility represented by is 1.0 or less. Carbon material dispersion.

2. The carbon material has a specific surface area of ​​150 m based on a nitrogen adsorption method. ２ / g or more 700m ２ / g or less, The carbon material dispersion liquid according to claim 1 .

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

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

5. The carbon material is represented by the following formula: Y = A1 x C1 / [peak intensity ratio (I Ｇ / I Ｄ ) ] … (2) In the formula (2), A1 is the specific surface area (m ２ / g), and C1 is the concentration of the carbon material (mass %); The index Y represented by is 10 or more and 1200 or less. The carbon material dispersion liquid 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 liquid according to claim 5 .

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

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

9. The dispersant has a branched or comb-shaped structure containing the basic functional group at least in a side chain. The carbon material dispersion liquid according to any one of claims 1 to 6.

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

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

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

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

14. A crystalline carbon material; an ionic dispersant having a basic functional group and a weight average molecular weight of 1000 or more; A non-aqueous solvent; A carbon material dispersion comprising: The carbon material in the carbon material dispersion liquid has a peak intensity ratio (I Ｇ / I Ｄ ) is 45 or less, and The carbon material dispersion liquid has a structure represented by the following formula: X=|D2−D1| / D1 (1) In the formula (1), D1 is a median diameter (μm) of the carbon material in the carbon material dispersion at 20° C., and D1≦30 is satisfied. D2 is a median diameter (μm) of the carbon material in the carbon material dispersion at 80° C.; The temperature change rate X of dispersibility represented by is 1.0 or less. Carbon material dispersion.

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