Carbon nanotube dispersion and method for producing same

Abstract

The present invention relates to a carbon nanotube dispersion liquid containing carbon nanotubes, a first dispersant which is a carboxyalkyl cellulose having a weight-average molecular weight of 9,000 g / mol or less, a second dispersant which is polyvinyl butyral (PVB), and a solvent, and a method for producing the same. The carbon nanotube dispersion liquid of the present invention has a low initial viscosity and a low rate of change in viscosity, and is excellent in storage stability and processability.

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2023-0044854, filed April 5, 2023, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to a carbon nanotube dispersion liquid which has a low initial viscosity, little change in viscosity over time, excellent storage stability, and excellent processability during the coating process, and a method for producing the same. [Background technology]

[0003] Carbon nanotubes are giant molecules in which a hexagonal honeycomb-shaped graphite surface, in which one carbon atom is bonded to three other carbon atoms, is rolled up with a nanometer-sized diameter. Carbon nanotubes are lightweight because they are hollow, and have electrical conductivity as good as copper, thermal conductivity as good as diamond, and tensile strength comparable to that of steel. Depending on the rolled shape, they can be divided into single-walled carbon nanotubes (SWCNT), multi-walled carbon nanotubes (MWCNT), and rope carbon nanotubes.

[0004] Carbon nanotubes have recently been widely used as conductive materials in secondary batteries due to their excellent electrical conductivity. However, carbon-based conductive materials, including carbon nanotubes, have a problem of not dispersing uniformly in electrode slurry compositions and tending to agglomerate. If the conductive material agglomerates in the electrode slurry composition, the conductive material cannot be distributed uniformly in the active material layer during the electrode formation process, which leads to reduced performance of the secondary battery. Therefore, various technologies for achieving uniform dispersion of the conductive material in the electrode slurry composition are being researched.

[0005] The most common approach is to improve dispersibility by introducing a dispersant together with the conductive material. Specifically, a method is known in which a polymer component, such as a cellulose-based dispersant or hydrogenated nitrile butadiene rubber (HNBR), is introduced as a dispersant to improve dispersibility in the dispersion state. Specifically, when a cellulose-based dispersant, which has been known as a dispersant for carbon nanotube dispersions, is used alone, it has the effect of reducing the rate of change in viscosity over time, but the initial viscosity of the dispersion itself is high. Furthermore, when the cellulose-based dispersant is used together with a conventional polymer dispersant, such as hydrogenated nitrile butadiene rubber (HNBR), not only the initial viscosity but also the rate of change in viscosity over time increases.

[0006] Therefore, there is a need for the development of a novel carbon nanotube dispersion that has low initial viscosity, minimizes viscosity change over time, and maintains excellent viscosity and viscosity stability. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] KR10-2022-0003984 A Summary of the Invention [Problem to be solved by the invention]

[0008] The present invention aims to provide a carbon nanotube dispersion liquid, which has excellent processability during the coating process due to the low initial viscosity of the dispersion liquid itself, and which has excellent storage stability due to little change in viscosity over time, and a method for producing the same. [Means for solving the problem]

[0009] In order to solve the above problems, the present invention provides a carbon nanotube dispersion and a method for producing the same.

[0010] Specifically, (1) the present invention provides a carbon nanotube dispersion liquid comprising carbon nanotubes, a first dispersant, a second dispersant, and a solvent, wherein the first dispersant is a carboxyalkyl cellulose having a weight-average molecular weight of 9,000 g / mol or less, the second dispersant is polyvinyl butyral (PVB), and the weight ratio of the first dispersant to the second dispersant is 1:2.5 to 1:10.

[0011] (2) The present invention provides a carbon nanotube dispersion liquid according to (1) above, wherein the total content of the first dispersant and the second dispersant is 50 parts by weight or more and 700 parts by weight or less per 100 parts by weight of carbon nanotubes.

[0012] (3) The present invention provides a carbon nanotube dispersion according to either (1) or (2) above, wherein the content of the first dispersant is 0.1 to 5 wt % based on the total weight of the dispersion.

[0013] (4) The present invention provides a carbon nanotube dispersion according to any one of (1) to (3) above, wherein the content of the second dispersant is 0.1 to 5 wt % based on the total weight of the dispersion.

[0014] (5) The present invention provides a carbon nanotube dispersion according to any one of (1) to (4) above, wherein the carbon nanotube content is 5% by weight or less based on the total weight of the dispersion.

[0015] (6) The present invention provides the carbon nanotube dispersion liquid according to any one of (1) to (5) above, wherein the first dispersant is carboxymethyl cellulose (CMC) or carboxyethyl cellulose (CEC).

[0016] (7) The present invention provides the carbon nanotube dispersion liquid according to any one of (1) to (6) above, wherein the first dispersant has an average molecular weight of 2,000 g / mol to 8,000 g / mol.

[0017] (8) The present invention provides the carbon nanotube dispersion liquid according to any one of (1) to (7) above, wherein the second dispersant is polyvinyl butyral with a vinyl alcohol unit content of 10 to 22 wt %.

[0018] (9) The present invention provides the carbon nanotube dispersion liquid according to any one of (1) to (8) above, wherein the second dispersant has an average molecular weight of 20,000 g / mol or less.

[0019] (10) The present invention provides a method for producing a carbon nanotube dispersion liquid according to any one of (1) to (9), comprising a step (S10) of mixing carbon nanotubes, a first dispersant, a second dispersant and a solvent, and a step (S20) of dispersing the mixture.

[0020] (11) The present invention provides the method for producing a carbon nanotube dispersion according to (10), wherein the step S20 includes a step (S21) of stirring at a speed of 5,000 to 10,000 rpm for 30 minutes or longer. [Effects of the Invention]

[0021] The carbon nanotube dispersion of the present invention has excellent processability during the coating process due to the low initial viscosity of the dispersion itself, and also has excellent storage stability due to little change in viscosity over time. DETAILED DESCRIPTION OF THE INVENTION

[0022] The present invention will now be described in more detail.

[0023] The terms and words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted as having meanings and concepts that are consistent with the technical idea of ​​the present invention, based on the principle that inventors can appropriately define the concepts of terms in order to best explain their inventions.

[0024] The terms used in this specification are merely used to describe exemplary embodiments and are not intended to limit the present invention. The singular expressions include the plural expressions unless the context clearly indicates otherwise.

[0025] In this specification, the terms "comprises," "includes," "has," and the like are intended to specify the presence of embodied features, numbers, steps, components, or combinations thereof, but are not intended to preclude the possible presence or addition of one or more different features, numbers, steps, components, or combinations thereof.

[0026] In this specification, the "specific surface area" is measured by the BET method, and specifically, can be calculated from the amount of nitrogen gas adsorbed at liquid nitrogen temperature (77 K) using a BELSORP-mino II manufactured by BEL Japan.

[0027] In this specification, the "length of a carbon nanotube" can be measured using an atomic force microscope or a scanning electron microscope.

[0028] Carbon nanotube dispersion The present invention provides a carbon nanotube dispersion liquid comprising carbon nanotubes, a first dispersant, a second dispersant, and a solvent, wherein the first dispersant is a carboxyalkyl cellulose having a weight-average molecular weight of 9,000 g / mol or less, the second dispersant is polyvinyl butyral (PVB), and the weight ratio of the first dispersant to the second dispersant is 1:2.5 to 1:10.

[0029] As mentioned above, when a cellulose-based dispersant, which is known as a dispersant for conventional carbon nanotube dispersions, is used alone, it has the effect of reducing the rate of viscosity change over time, but suffers from the problem of high initial viscosity of the dispersion itself. To address this drawback, conventional polymer-based dispersants, such as hydrogenated nitrile butadiene rubber (HNBR), have been used in addition to the cellulose-based dispersant. However, this approach results in an increase in both the initial viscosity and the rate of viscosity change over time. Therefore, the inventors of the present invention conducted extensive research into a dispersant that can maintain the technical advantages of conventional cellulose-based dispersants while improving their disadvantage of high initial viscosity. As a result, they discovered that when polyvinyl butyral (PVB) is used together with a carboxyalkyl cellulose having a specific weight-average molecular weight of 9,000 g / mol or less, it is possible to reduce both the initial viscosity and the rate of viscosity change over time, thereby completing the present invention.

[0030] In particular, in the present invention, it has been confirmed that the initial viscosity and the rate of change in viscosity over time can be further reduced by controlling the weight ratio of the first dispersant, which is carboxyalkyl cellulose having a weight-average molecular weight of 9,000 g / mol or less, to the second dispersant, which is polyvinyl butyral (PVB), to 1:2.5 to 1:10.

[0031] (1) Carbon nanotubes The carbon nanotubes function as the conductive material in the dispersions of the present invention and can be single-walled or multi-walled carbon nanotubes.

[0032] The carbon nanotubes used in the present invention are not particularly limited, but preferably have a specific surface area of ​​800 to 2,000 m 2 / g, and the length is preferably 0.1 to 10 μm. When the carbon nanotubes satisfy the above conditions, they can have particularly excellent electrical conductivity. The specific surface area is measured by the BET method, and specifically, can be calculated from the amount of nitrogen gas adsorbed at liquid nitrogen temperature (77 K) using a specific surface area measuring device (BELSORP-mino II manufactured by BEL Japan). The length can be measured using an atomic force microscope or a scanning electron microscope.

[0033] In the carbon nanotube dispersion of the present invention, the carbon nanotube content can be 5.0 wt% or less, specifically 0.1 wt% or more, 0.2 wt% or more, 0.3 wt% or more, 0.4 wt% or more, 0.5 wt% or more, or 5.0 wt% or less, 4.5 wt% or less, 4.0 wt% or less, 3.5 wt% or less, 3.0 wt% or less, 2.5 wt% or less. On the other hand, if the carbon nanotube content is too low, sufficient conductivity cannot be achieved when used for applications such as conductive materials, and if the carbon nanotube content is too high, the viscosity of the dispersion may become too high, reducing processability.

[0034] (2) Dispersant In order to improve the dispersibility of the carbon nanotubes, the carbon nanotube dispersion liquid according to the present invention uses carboxyalkyl cellulose having a weight-average molecular weight of 9,000 g / mol or less as the first dispersant and polyvinyl butyral (PVB) as the second dispersant.

[0035] (2-1) First dispersant The first dispersant used in the present invention is characterized by being a carboxyalkyl cellulose having a weight average molecular weight of 9,000 g / mol or less.

[0036] Specifically, the first dispersant can be carboxymethyl cellulose (CMC) or carboxyethyl cellulose (CEC). The cellulose-based component significantly contributes to suppressing the increase in viscosity of the dispersion over time, thereby improving the dispersibility of the carbon nanotube dispersion.

[0037] In the carbon nanotube dispersion of the present invention, the content of the first dispersant can be 0.1 to 5 wt % relative to the total weight of the dispersion, specifically 0.1 wt % or more, 0.2 wt % or more, 0.3 wt % or more, 0.4 wt % or more, 0.5 wt % or more, 0.6 wt % or more, 0.7 wt % or more, 0.8 wt % or more, 0.9 wt % or more, 1 wt % or more, and can be 5 wt % or less, 4.8 wt % or less, 4.6 wt % or less, 4.4 wt % or less, 4.2 wt % or less, 4.0 wt % or less, 3.8 wt % or less, 3.6 wt % or less, 3.4 wt % or less, 3.2 wt % or less, or 3.0 wt % or less.

[0038] If the content of the first dispersant component is less than the above range, the effect of the carboxyalkyl cellulose may be insufficient, resulting in a decrease in the dispersibility of the dispersion or a significant change in the viscosity of the dispersion over time. Also, if the content of the first dispersant component is more than the above range, when the carbon nanotube dispersion is applied to an electrode, an excessive amount of dispersant may inhibit the conductivity of the electrode, and the dispersant may act as an impurity in the electrode.

[0039] Meanwhile, the weight average molecular weight (Mw) of the first dispersant used in the present invention may be 9,000 g / mol or less, preferably 2,000 g / mol to 8,000 g / mol, and more specifically, 2,000 g / mol or more, 2,500 g / mol or more, 3,000 g / mol or more, 3,500 g / mol or more, 4,000 g / mol or more, 4,500 g / mol or more, or 5,000 g / mol or more, and may be 8,000 g / mol or less, or 7,500 g / mol or less.

[0040] (2-2) Second dispersant The second dispersant used in the present invention is characterized as being polyvinyl butyral (PVB).

[0041] When the polyvinyl butyral dispersant of the present invention is applied to a carbon nanotube dispersion, it can prevent aggregation of the carbon nanotubes due to the interaction between the butyral group and the carbon nanotubes, and as a result, it can play a role in reducing the initial viscosity of the dispersion.

[0042] In the carbon nanotube dispersion of the present invention, the second dispersant may have a vinyl alcohol unit content in the polyvinyl butyral of 10 to 22 wt%, specifically, the vinyl alcohol unit content may be 10 wt% or more, 11 wt% or more, 12 wt% or more, 13 wt% or more, 14 wt% or more, 15 wt% or more, 16 wt% or more, 17 wt% or more, or 22 wt% or less, 21 wt% or less, 20 wt% or less, 19 wt% or less, or 18 wt% or less. If the vinyl alcohol unit content exceeds 22 wt%, the effect of the interaction between the butyral group and the carbon nanotubes may be reduced, and the viscosity of the dispersion may increase.

[0043] In the carbon nanotube dispersion of the present invention, the content of the second dispersant can be 0.1 to 5 wt % relative to the total weight of the dispersion, specifically 0.1 wt % or more, 0.2 wt % or more, 0.3 wt % or more, 0.4 wt % or more, 0.5 wt % or more, 0.6 wt % or more, 0.7 wt % or more, 0.8 wt % or more, 0.9 wt % or more, 1 wt % or more, and can be 5 wt % or less, 4.8 wt % or less, 4.6 wt % or less, 4.4 wt % or less, 4.2 wt % or less, 4.0 wt % or less, 3.8 wt % or less, 3.6 wt % or less, 3.4 wt % or less, 3.2 wt % or less, or 3.0 wt % or less.

[0044] If the content of the second dispersant component is less than the above range, the effect achieved by the polyvinyl butyral component will be insufficient, and the initial viscosity of the dispersion itself may become excessively high. If the content of the second dispersant component is more than the above range, the content of the cellulose-based component will decrease relatively, and the viscosity of the dispersion may change significantly over time.

[0045] Meanwhile, the second dispersant used in the present invention may have a weight average molecular weight (Mw) of 20,000 g / mol or less.

[0046] The weight ratio of the first dispersant to the second dispersant may be 1:2.5 to 1:10, specifically, the amount of the second dispersant may be 250 parts by weight or more, or 300 parts by weight or more, and 1000 parts by weight or less, 900 parts by weight or less, 800 parts by weight or less, 700 parts by weight or less, 600 parts by weight or less, or 500 parts by weight or less, relative to 100 parts by weight of the first dispersant. Within this range, the synergistic effect between the first dispersant and the second dispersant is maximized, carbon nanotubes are uniformly dispersed in the carbon nanotube dispersion, and the viscosity can be maintained at a predetermined level over time along with a low viscosity.

[0047] On the other hand, the total content of the first dispersant and the second dispersant may be 50 parts by weight or more and 700 parts by weight or less per 100 parts by weight of carbon nanotubes. Specifically, the total content of the first dispersant and the second dispersant may be 50 parts by weight or more, 100 parts by weight or more, 150 parts by weight or more, or 200 parts by weight or more per 100 parts by weight of carbon nanotubes, and may be 700 parts by weight or less, 650 parts by weight or less, 600 parts by weight or less, or 550 parts by weight or less.

[0048] If the total content of the first dispersant and the second dispersant is greater than the above range, the excess dispersant may inhibit the conductivity of the electrode when the carbon nanotube dispersion is applied to the electrode, and the dispersant may act as an impurity in the electrode. On the other hand, if the total content is less than the above range, the effects of improving dispersibility, reducing viscosity, and suppressing changes in viscosity over time may be insufficient, and in particular, gel shrinkage may occur and the viscosity stability may be significantly reduced.

[0049] By controlling the weight ratio of the first dispersant and the second dispersant, the carbon nanotube dispersion of the present invention can reduce both the initial viscosity and the change in viscosity over time, as described above, thereby achieving excellent coating processability and storage stability.

[0050] (3) Solvent The solvent used in the present invention is a solvent for dispersing the carbon nanotubes and the dispersant, and can be used to prevent aggregation when powdered carbon nanotubes are directly applied to the preparation of an electrode slurry composition.

[0051] The solvent may be one that can dissolve or disperse the carbon nanotubes and dispersant to a predetermined level or more, and may be included in an amount that allows the electrode slurry composition to have an appropriate viscosity, taking into consideration the processability of the electrode slurry composition to be prepared using the carbon nanotube dispersion liquid.

[0052] The solvent is not particularly limited as long as it is one that is commonly used in the art for dispersing the carbon nanotubes and dispersants, and can be, for example, one or more selected from the group consisting of amide-based polar organic solvents, alcohol-based solvents, glycol-based solvents, glycol ether-based solvents, ketone-based solvents, ester-based solvents, and aqueous solvents.

[0053] The amide-based polar organic solvent may be one or more selected from the group consisting of N-methylpyrrolidone (NMP), dimethylformamide (DMF), diethylformamide, and dimethylacetamide (DMAc).

[0054] The alcohol solvent may be one or more selected from the group consisting of methanol, ethanol, 1-propanol, 2-propanol (or isopropyl alcohol), 1-butanol, 2-methyl-1-propanol, 2-butanol, 1-methyl-2-propanol, pentanol, hexanol, heptanol, octanol, glycerin, trimethylolpropane, pentaerythritol, and sorbitol.

[0055] The glycol-based solvent may be one or more selected from the group consisting of ethylene glycol, diethyl glycol, triethylene glycol, propylene glycol, 1,3-propanediol, 1,3-butanediol, 1,5-pentanediol, and hexylene glycol.

[0056] The glycol ether solvent may be one or more selected from the group consisting of ethylene glycol monomethyl ether, diethylene glycol monomethyl ether, triethylene glycol monomethyl ether, tetraethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monoethyl ether, triethylene glycol monoethyl ether, tetraethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, and tetraethylene glycol monobutyl ether.

[0057] The ketone solvent may be one or more selected from the group consisting of acetone, methyl ethyl ketone, methyl propyl ketone, and cyclopentanone.

[0058] The ester solvent can be one or more selected from the group consisting of ethyl acetate, gamma-butyrolactone, and epsilon-propiolactone.

[0059] The aqueous solvent may be water.

[0060] The carbon nanotube dispersion of the present invention can have an initial viscosity of 10,500 cP or less, preferably 10,000 cP or less, when measured at 25°C with a No. 1 rotor at 1 rpm using a viscometer (Viscometer TV-25, manufactured by TOKI SANGYO Co., Ltd.). Furthermore, the viscosity of the dispersion that satisfies the initial viscosity requirement can change by 25% or less, preferably 20% or less, over one week.

[0061] The one-week viscosity change rate is calculated by determining how much the viscosity increases over one week when the dispersion is stored at 25°C for one week, and can be calculated using the following formula 1.

[0062] [Formula 1] Viscosity change rate (%) = (viscosity after 1 week - initial viscosity) / (initial viscosity) * 100%

[0063] On the other hand, the viscosity can be measured using a viscometer (viscometer TV-25, manufactured by TOKI SANGYO Co., Ltd.) by starting measurement at 1 rpm with a No. 1 rotor and recording the value after 10 minutes.

[0064] Method for producing carbon nanotube dispersion The present invention provides a method for producing the above-mentioned carbon nanotube dispersion liquid, specifically, a method for producing a carbon nanotube dispersion liquid including a step (S10) of mixing carbon nanotubes, a first dispersant, a second dispersant and a solvent, and a step (S20) of dispersing the mixture.

[0065] In the method for producing a carbon nanotube dispersion of the present invention, the carbon nanotubes, the first dispersant, the second dispersant, and the solvent are as described above.

[0066] Meanwhile, step S10, in which all of the above components are mixed, can be carried out using a method generally applied to mixing processes. For example, an impeller and a container can be attached to a dissolution tank (Dispermat-CA, manufactured by VMA-Getzmann) and mixed at 400 rpm for 10 minutes, and then carbon nanotubes can be added and treated at 8,000 rpm for 60 minutes.

[0067] In addition, the step S20 can disperse the mixture to prepare a final dispersion, and the physical properties of the carbon nanotubes in the dispersion can be made uniform in this dispersion step.

[0068] Furthermore, step S20 may include a step (S21) of stirring at a speed of 5,000 to 10,000 rpm for 30 minutes or more, and preferably a step of stirring at a speed of 8,000 rpm for 60 minutes. By controlling the stirring speed and time in this manner, more uniform dispersion is possible, and the viscosity of the resulting carbon nanotube dispersion can be maintained at a lower level.

[0069] The carbon nanotube dispersion produced by the carbon nanotube dispersion production method of the present invention may have an initial viscosity of 12,000 cP or less, preferably 10,000 cP or less. Furthermore, while satisfying the initial viscosity requirement, the viscosity change rate of the dispersion over one week may be 30% or less, preferably 20% or less.

[0070] Hereinafter, the present invention will be described in detail with reference to examples and experimental examples in order to specifically explain the present invention. However, the present invention is not limited to these examples and experimental examples. The examples according to the present invention can be modified into various other forms, and the scope of the present invention should not be interpreted as being limited to the examples detailed below. The examples of the present invention are provided to more completely explain the present invention to those skilled in the art.

[0071] material Specific surface area is 1,160m 2 Carbon nanotubes (TUBALL, manufactured by OCSiAl) with a molecular weight of 1 / g and a length of 5 μm or more were prepared. N-methyl-2-pyrrolidone (NMP) was prepared as a solvent.

[0072] In the examples, the first dispersant used was carboxymethyl cellulose (weight average molecular weight: 5,200 g / mol) or carboxyethyl cellulose (weight average molecular weight: 7,000 g / mol), and the second dispersant used was polyvinyl butyral (product name: Mowital B14S, manufactured by Kuraray Corporation; weight average molecular weight: 10,000 g / mol, polyvinyl alcohol content: 14 to 18 wt%).

[0073] In the comparative examples, the first dispersant used was methylcellulose (weight average molecular weight: 9,000 g / mol), carboxymethylcellulose (weight average molecular weight: 250,000 g / mol), carboxymethylcellulose (weight average molecular weight: 5,200 g / mol), or Poly(9-vinylcarbazole) (product name: Poly(9-vinylcarbazole), manufactured by Sigma-Aldrich).The second dispersant used was phenol novolac (product name: KPH-F2002, manufactured by Kolon Industries), hydrogenated nitrile butadiene rubber (HNBR) (product name: Therban AT 3404, manufactured by Arlanxeo), or polyvinyl butyral (product name: Mowital B14S, manufactured by Kuraray; weight average molecular weight: 10,000 g / mol, polyvinyl alcohol content: 14 to 18 wt%).

[0074] Examples and Comparative Examples A mixture was prepared by mixing the first dispersant, second dispersant, and NMP as a solvent, as described above. After fitting an impeller and container into a dissolution tank (Dispermat-CA, VMA-Getzmann), the mixture was stirred at 400 rpm for 10 minutes to mix the dispersant and solvent. Carbon nanotubes (TUBALL, OCSiAl) were added so that their content in the dispersion was 0.6 wt %, and the mixture was processed at 8,000 rpm for 60 minutes.

[0075] The resultant was treated 10 times at a pressure of 20,000 psi using a high-pressure disperser (PICOMAX, manufactured by Micronox) to prepare a carbon nanotube dispersion.

[0076] The concentration of carbon nanotubes used in each example and comparative example, the type and content (based on the total weight of the dispersion) of the first dispersant and the second dispersant used, and the weight ratio between the dispersants are summarized in Table 1 below.

[0077] [Table 1]

[0078] Experimental example: Confirming the initial viscosity and viscosity change rate of the dispersion liquid The viscosity of the carbon nanotube dispersions of Examples 1 to 4 and Comparative Examples 1 to 9 was measured, and the viscosity was measured again after leaving them at 25° C. for one week. The results are shown in Table 2 below.

[0079] The viscosity was measured using a viscometer (viscometer TV-25, manufactured by TOKI SANGYO) at 25°C and 1 rpm using a No. 1 rotor.

[0080] [Table 2]

[0081] As can be seen from Table 2, when Examples 1 to 4, which use the same carbon nanotubes and solvent at the same content, are compared with Comparative Examples 1 to 9, Examples 1 to 4, which use the first dispersant and second dispersant of the present invention in a specific weight ratio range, not only have a low initial viscosity, but also a low rate of change in viscosity after one week. On the other hand, Comparative Example 1, which uses the first dispersant of the present invention alone, has a low rate of change in viscosity, but a high initial viscosity of 13,000 cP. Comparative Example 2, which uses polyvinyl butyral (PVB) alone, has a low initial viscosity, but a high rate of change in viscosity, at 34%.

[0082] In particular, in the case of Comparative Examples 3 and 4, in which hydrogenated nitrile butadiene rubber (HNBR) or phenol novolac was used as the second dispersant, the initial viscosity and viscosity change rate were excessively high, or the initial viscosity was so high that it was impossible to measure, and it was confirmed that the storage stability and processability were significantly poor.

[0083] Similarly, Comparative Example 7, in which the first dispersant was not the first dispersant of the present invention but a different component, Poly(9-vinylcarbazole), was used as the first dispersant; Comparative Example 8, in which methylcellulose was used instead of a cellulose-based or carboxyalkyl cellulose; and Comparative Example 9, in which carboxymethylcellulose was used but with a weight-average molecular weight much higher than that required in the present invention, all had problems, similar to Comparative Examples 3 and 4, such as excessively high initial viscosity and viscosity change rate, or difficulty in viscosity measurement itself.

[0084] Finally, in Comparative Examples 5 and 6, in which the first dispersant and the second dispersant were used in the same manner but in an inappropriate ratio, the viscosity change rate was excessively high at 30% or more, or the initial viscosity was excessively high at 12,500 cP or more.

[0085] Therefore, it was confirmed that the dispersion of the present invention has excellent processability due to its low initial viscosity and low rate of change in viscosity, and thus has improved storage stability.

Claims

1. carbon nanotubes, a first dispersant, a second dispersant, and a solvent; the first dispersant is a carboxyalkyl cellulose having a weight average molecular weight of 9,000 g / mol or less; the second dispersant is polyvinyl butyral (PVB); The carbon nanotube dispersion liquid, wherein the weight ratio of the first dispersant to the second dispersant is 1:2.5 to 1:

10.

2. 2. The carbon nanotube dispersion liquid according to claim 1, wherein the total content of the first dispersant and the second dispersant is 50 parts by weight or more and 700 parts by weight or less with respect to 100 parts by weight of the carbon nanotubes.

3. 2 . The carbon nanotube dispersion liquid according to claim 1 , wherein the content of the first dispersant is 0.1% by weight or more and 5% by weight or less with respect to the total weight of the dispersion liquid.

4. 2. The carbon nanotube dispersion liquid according to claim 1, wherein the content of the second dispersant is 0.1 wt % or more and 5 wt % or less with respect to the total weight of the dispersion liquid.

5. 2. The carbon nanotube dispersion according to claim 1, wherein the carbon nanotube content is 5% by weight or less based on the total weight of the dispersion.

6. The carbon nanotube dispersion liquid according to claim 1 , wherein the first dispersant is carboxymethyl cellulose (CMC) or carboxyethyl cellulose (CEC).

7. The carbon nanotube dispersion liquid according to claim 1 , wherein the first dispersant has an average molecular weight of 2,000 g / mol or more and 8,000 g / mol or less.

8. The carbon nanotube dispersion liquid according to claim 1 , wherein the second dispersant is polyvinyl butyral, and the content of vinyl alcohol units in the polyvinyl butyral is 10% by weight or more and 22% by weight or less.

9. A method for producing a carbon nanotube dispersion liquid according to any one of claims 1 to 8, The carbon nanotube dispersion liquid according to claim 1 , wherein the second dispersant has an average molecular weight of 20,000 g / mol or less.

10. A step (S10) of mixing carbon nanotubes, a first dispersant, a second dispersant, and a solvent; and dispersing the mixture (S20).

11. The method for producing a carbon nanotube dispersion liquid according to claim 10, wherein step S20 includes a step (S21) of stirring at a speed of 5,000 rpm or more and 10,000 rpm or less for 30 minutes or more.

Images