Carbon-based coloring composition

Abstract

The purpose of the present invention is to provide a coloring composition which is capable of obtaining beautiful paintings and glossy paintings with little unevenness in depth, has excellent writing feel and long-term stability, and contributes to environmental protection. A coloring composition containing a carbon-based powder as a pigment component, in which 70% by mass or more of the carbon-based powder is particles having a particle diameter of 50-600 nm, for example, in the range of 100-400 nm, as measured by a dynamic light scattering method. It is preferable that 5% by mass or more of the carbon-based powder are particles having a particle diameter in the range of 400-600 nm. It is also preferable that the carbon-based powder have a fixed carbon content of 40-98 mass%. In addition, at least 70% by mass of the carbon-based powder is preferably biomass carbon.

Description

Technical Field

[0001] This invention relates to carbon-based coloring compositions, and more particularly, to coloring compositions containing specific carbon-based powders as pigment components, especially black inks. Background Technology

[0002] Carbon-based materials have long been used as black pigments. For example, soot has been used as a black pigment for writing since ancient times. In recent years, carbon black produced by the thermal decomposition of petroleum-based gases and oils has been widely used. Among them, carbon black obtained by furnace process has become the main type of carbon used in pigments because it is easy to control the particle size and has a high yield (see, for example, Patent Documents 1 and 2).

[0003] Carbon black generally tends to have higher blackness and tinting strength with smaller average particle size. Therefore, most commercially available pigment carbon blacks have an average particle size of approximately 10 nm to 60 nm, particularly 15 nm to 40 nm. On the other hand, from the viewpoint of obtaining aesthetically pleasing paintings and printed materials, the use of carbon black with larger particle sizes is also being studied. For example, Patent Document 3 discloses an ink composition containing carbon black and clay minerals with a particle size distribution of approximately 0.1 μm to 0.5 μm. In addition, Patent Document 4 discloses the use of lampblack with a median primary particle size of 50 nm to 200 nm as a pigment, from the viewpoint of uniformly forming an electroplated coating film on the surface of a metal substrate.

[0004] Furthermore, from the perspective of protecting the Earth's environment and eliminating petroleum, research has begun on replacing carbon black pigments with bio-based carbon, such as charcoal, also known as biomass carbon. For example, Patent Document 1 discloses a non-petroleum-based black ink containing pigments made from an aqueous carrier and carbonized hemp. Patent Document 2 discloses a method for manufacturing carbon black that also uses biomass powders such as wood powder as raw materials.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Publication No. 2022-529318

[0008] Patent Document 2: International Publication No. 2011 / 013161

[0009] Patent Document 3: Japanese Patent Application Publication No. 6-234946

[0010] Patent Document 4: Japanese Patent Publication No. 2023-507510 Summary of the Invention

[0011] The technical problem that the invention aims to solve

[0012] While general-purpose charcoal black pigments (carbon black for coloring) possess excellent blackness and tinting strength, their range of expression tends to be limited for aesthetic applications, especially in art-related situations. For example, as described in Patent Document 3, compared to conventional inks, it is more difficult to achieve beautiful paintings with "determined baselines" and "beautiful bleed." This is believed to be because charcoal black exhibits a wide particle size distribution of approximately 0.05 μm to 5 μm, while the particle size of charcoal black in ink ranges from approximately 0.05 μm to 0.5 μm, and general-purpose charcoal black pigments show a narrow distribution within the range of approximately 10 nm to 60 nm. Because coloring with charcoal black can easily result in monotonous tones, high-grade inks often use traditional carbon materials. Furthermore, it is difficult to achieve a glossy finish, such as with pencil writing, with general-purpose charcoal black.

[0013] However, even if the average particle size and particle size distribution of the carbon black used for coloring are simply increased by means of ink, a beautiful painting may not necessarily be obtained. As shown in the examples described later, for coloring compositions containing carbon-based pigments mainly composed of powder with a particle size exceeding 600 nm, unevenness in color depth is easily produced during painting, and the writing feel is also easily deteriorated.

[0014] Furthermore, especially for liquid coloring compositions such as inks and coatings, the rapid settling of large particles presents a challenge in ensuring long-term stability. The use of clay minerals in the technology described in Patent Document 3 is also intended to prevent particle settling. Patent Document 3 specifically uses commercially available carbon black with an average particle size of 20 nm to 30 nm. The coating composition described in Patent Document 4 also actually uses lampblack with an average particle size of approximately 100 nm. It is believed that for coloring compositions containing carbon-based pigments with an average particle size significantly exceeding 100 nm, it is necessary to control certain factors other than the average particle size, while still exhibiting good physical properties.

[0015] The technology of using biomass charcoal as carbon-based pigments also faces challenges that need to be addressed. For example, biomass charcoal, a representative example, hardens significantly due to the temperature during carbonization. Therefore, it is difficult to obtain carbon-based powders with fine particles, such as those smaller than 1 μm. In Patent Document 1, charcoal pulverized to 2 μm to 5 μm is used as pigment, but this makes it difficult to achieve a good writing feel and ensure long-term stability. In the technology described in Patent Document 2, biomass is micronized to a size of 1 μm to 100 μm at the raw material stage, and then subjected to thermal decomposition for carbonization at a relatively low temperature of 400°C to 600°C, resulting in carbon black with a size of 10 nm to 30 nm. However, carbon produced using this low-temperature thermal decomposition is unlikely to produce a glossy finish, such as that found in pencil writing.

[0016] In order to solve the above problems, the present invention aims to provide a coloring composition that can produce beautiful paintings with less unevenness in shade, glossy paintings, excellent writing feel and long-term stability, and thus contribute to environmental protection.

[0017] Solution for solving the problem

[0018] In order to solve the above-mentioned problems, the inventors of the present invention conducted in-depth research and found that by controlling the particle size distribution of the carbon-based powder used as a pigment component, a coloring composition can be obtained that can easily produce beautiful and glossy paintings, with excellent writing feel and long-term stability. In addition, such carbon-based powder can effectively utilize biomass.

[0019] That is, the present invention provides the following (1) to (10).

[0020] (1) A coloring composition containing carbon-based powder as a pigment component, wherein more than 70% by mass of the carbon-based powder consists of particles with a particle size in the range of 50 nm to 600 nm as determined by dynamic light scattering.

[0021] (2) The coloring composition of (1) above, wherein 5% by mass or more of the carbon-based powder are particles with a particle size in the range of 400 nm to 600 nm as determined by dynamic light scattering method.

[0022] (3) The coloring composition of (1) or (2) above, wherein the fixed carbon content of the carbon-based powder is 40% to 98% by mass.

[0023] (4) The coloring composition of any one of (1) to (3) above, wherein the ash content of the carbon-based powder is 2% to 40% by mass.

[0024] (5) The coloring composition of any one of (1) to (4) above, wherein 70% by mass or more of the carbon-based powder is biomass carbon.

[0025] (6) The coloring composition of (5) above, wherein the biomass carbon is a byproduct in the preparation of fuel gas for biomass power generation by gasification.

[0026] (7) Ink, paint, powder paint, pigment, crayon, colored chalk, Conté pen or solid ink formed from any of the coloring compositions in (1) to (6) above.

[0027] (8) A water-based ink, which is a coloring composition of any one of (1) to (6) above, comprising a composition containing the carbon-based powder, a water-soluble polymer and water.

[0028] (9) An oil-based ink, which is a coloring composition of any one of (1) to (6) above, comprising an oil-based composition containing the carbon-based powder, an organic solvent and a binder, wherein the binder is selected from one or more of the group consisting of thermoplastic polymers, thermosetting polymer precursors and vegetable oils.

[0029] (10) A polymer composition or polymer molded body containing the coloring composition of any one of (1) to (6) above.

[0030] Invention Effects

[0031] The coloring composition of the present invention can easily produce beautiful paintings with minimal unevenness and a glossy finish. The coloring composition of the present invention also exhibits excellent writing feel and long-term stability, and in particular, by using biomass charcoal as a pigment, it also contributes to environmental protection. Attached Figure Description

[0032] Figure 1 This is a schematic diagram illustrating an example of the particle size distribution of carbon-based powders that can be used in the coloring compositions of the present invention.

[0033] Figure 2 This is a histogram showing the results of determining the particle size distribution of the carbon-based powder used in Example 1 by dynamic light scattering.

[0034] Figure 3 This is a histogram showing the results of determining the particle size distribution of the carbon-based powder used in Comparative Example 1 by dynamic light scattering. Detailed Implementation

[0035] The following describes representative embodiments of the present invention in detail, but the present invention is not limited thereto.

[0036] <<Coloring Compositions>>

[0037] This embodiment relates to a coloring composition containing carbon-based powder as a pigment component, wherein 70% by mass or more of the carbon-based powder consists of particles with a particle size in the range of 50 nm to 600 nm as determined by dynamic light scattering. The main components of the coloring composition, primarily composed of carbon-based powder, will be described below.

[0038] <Carbon-based powder>

[0039] In this embodiment, carbon-based powder refers to powder with carbon as its main component, including, for example, all powders with a fixed carbon content of 40% by mass or more. Examples include carbon black, such as furnace black, thermal black, lampblack, acetylene black, channel black, contact black, and Ketjen black; biomass carbon, primarily carbon, such as wood charcoal, bamboo charcoal, animal charcoal, and lignite; various activated carbons; and carbides such as tar; as well as natural graphite and artificial graphite, but not limited to these. In the coloring composition of this embodiment, any type of carbon-based powder can be used, and carbon-based powders with desired properties can be used depending on the purpose. It should be noted that the chemical properties of suitable carbon-based powders will be described in detail later.

[0040] The most significant feature of the coloring composition of this embodiment is that the carbon-based powder of the pigment component has a particle size distribution in the range of 50 nm to 600 nm, with at least 70% by mass of all particles. As a result of this particle size distribution, the coloring composition of this embodiment can easily produce beautiful paintings with a clear baseline, beautiful bleeding, and minimal unevenness in color depth. Furthermore, although the average particle size of the pigment component is relatively large, it does not easily settle when formulated, for example, into inks, exhibiting excellent long-term stability. Moreover, by appropriately selecting the type of carbon-based powder to be formulated according to the purpose, coloring compositions suitable for glossy drawings such as pencil writing, drawings with high blackness, etc., can be produced. Next, the particle size distribution of the carbon-based powder will be explained.

[0041] [Particle size distribution of carbon-based powders]

[0042] In the coloring composition of this embodiment, 70% by mass or more of the carbon-based powder of the pigment component consists of particles with a particle size in the range of 50 nm to 600 nm, for example, 100 nm to 400 nm, as determined by dynamic light scattering. Here, the particle size distribution of the carbon-based powder can be any distribution as long as "70% by mass or more consists of particles with a particle size in the range of 50 nm to 600 nm". For example, it can be... Figure 1 The particle size distribution shown in (a) is close to the normal distribution, and it can also be as follows: Figure 1 (b) Figure 1 (c) shows a distribution biased towards either the smaller or larger particle size side. Alternatively, it could be a distribution with two peaks in the 50nm–600nm range, or as shown in [the diagram]. Figure 1 (d) shows a distribution with small peaks outside the range of 50 nm to 600 nm.

[0043] For the coloring composition of this embodiment, carbon-based powders with a desired particle size distribution can be used according to their purpose and application. For example, carbon-based powders with a desired particle size distribution can be used. Figure 1(d) shows that when carbon-based powders with a particle size distribution having small peaks in the region of more than 600 nm, especially in the range of about 1 μm to 5 μm, are incorporated into coloring compositions such as inks and coatings, long-term stability is not significantly compromised, and beautiful paintings with "clear baselines" and "beautiful bleed" can be easily obtained, similar to those painted with ink.

[0044] The blackness of the coloring composition can also be adjusted by adjusting the particle size distribution of the carbon-based powder. For example, in the case of carbon black, there is a general tendency for a smaller average particle size to result in a higher blackness. Furthermore, for carbon black with the same average particle size, there is a tendency for a wider particle size distribution to result in a lower blackness. Therefore, for example, as a carbon-based powder, it is possible to use carbon-based powder with particles in the range of 50 nm to 600 nm, particularly 100 nm to 400 nm, comprising 70% or more, 75% to 99% by mass, particularly 80% to 95% by mass of the total carbon-based powder, to improve the blackness of the coloring composition. Additionally, beautiful paintings can be easily obtained using carbon-based powders in which 5% or more, for example 7% to 30% by mass, 8% to 20% by mass, particularly 10% to 15% by mass of the total carbon-based powder, have a particle size in the range of 400 nm to 600 nm, for example 400 nm to 500 nm, as determined by dynamic light scattering.

[0045] It should be noted that even among carbon blacks with similar average particle size and particle size distribution, there is a tendency for carbon blacks with larger specific surface areas (i.e., higher roughness) to have higher blackness. Furthermore, for biomass carbons such as charcoal, in addition to particle size, the blackness also varies depending on ash content and firing temperature. By selecting desired carbon-based powders from these various particle size distributions and materials, or by combining multiple types, it is possible to create coloring compositions suitable for the target painting characteristics.

[0046] When preparing carbon-based powders with a desired particle size distribution, carbon-based powders with a known particle size distribution can be used alone, or multiple powders can be used in combination. However, as described later, carbon-based powders with an average particle size exceeding 600 nm can also be pulverized. It should be noted that in this invention, the particle size of the carbon-based powder is defined based on values ​​obtained by dynamic light scattering. However, in selecting or preparing carbon-based powders, values ​​obtained by other methods such as electron microscopy, specific surface area, and catalog values ​​can also be referenced. The composition, material properties, and other chemical characteristics of the carbon-based powders will be described below.

[0047] [Composition of carbon-based powders]

[0048] Carbon-based powders typically contain moisture and ash in addition to carbon. The composition remaining after removing moisture, ash, and volatile components from carbon-based powders is called "fixed carbon," and its percentage varies depending on the type of carbon-based powder and manufacturing conditions. For example, commercially available rubber black typically has a fixed carbon content of over 99% by mass, while colored carbon black has a fixed carbon content as high as 90% to 95% by mass. Biomass charcoal, on the other hand, has a lower fixed carbon content of around 35% to 90% by mass, and the variation is significant depending on the type of charcoal. As a representative example of biomass charcoal, the fixed carbon content of charcoal produced at low carbonization temperatures (usually around 400℃ to 700℃) is typically 60% to 85% by mass, mostly around 65% to 80% by mass. For white charcoal produced at high carbonization temperatures (usually above 800℃), the fixed carbon content is typically 70% to 95% by mass, mostly around 75% to 85% by mass.

[0049] In the coloring composition of this embodiment, if the fixed carbon content of the carbon-based powder is 40% to 98% by mass, a wider range of painting expressions with greater variation can be achieved. For example, by combining carbon-based powder with a fixed carbon content of 40% to 80% by mass, particularly about 50% to 70% by mass, it is easy to obtain paintings with a grayish feel and a glossy finish, similar to pencil drawings. Furthermore, by combining carbon-based powder with a fixed carbon content of 70% to 98% by mass, particularly about 80% to 95% by mass, it is easy to obtain paintings with high blackness and clear distinction between shades.

[0050] There are no particular restrictions on the ash content of the carbon-based powder. In general carbon black, the ash content is typically around 1% by mass or less. Even in biomass charcoal, it is usually around 1% to 10% by mass, and in most cases around 2% to 5% by mass. However, depending on the raw materials and manufacturing method, there are cases where the ash content can reach around 40% by mass. It is also possible to obtain a glossy drawing, such as pencil writing, by adjusting the ash content. Therefore, in the coloring composition of this embodiment, carbon-based powders with any ash content can be used depending on the purpose. For example, carbon-based powders with an ash content of 2% to 40% by mass can be used, but this is not a limitation.

[0051] Carbon-based powders can sometimes exhibit varying affinity with solvents and binders in coloring compositions due to their ash content and volatile organic compound (VOC) content. Therefore, a high ash content is not necessarily undesirable. Furthermore, carbon-based powders with higher VOC content, such as 5% to 30% by mass, and especially 10% to 25% by mass, often possess a large number of carbonyl and hydroxyl functional groups on their surface. This results in excellent affinity with co-applied binders and superior dispersibility in coloring compositions, sometimes leading to good long-term stability. When considering the target painting characteristics and the affinity and dispersibility with components other than pigments, selecting a suitable type of carbon-based powder is sufficient.

[0052] From the viewpoint of obtaining a coloring composition that easily produces beautiful black paintings and exhibits excellent pigment dispersibility and long-term stability, carbon-based powders can be used with the following fixed carbon content: 60% to 95% by mass, more preferably 70% to 90% by mass, particularly 75% to 85% by mass; ash content: 2% to 20% by mass, particularly 3% to 10% by mass; and volatile components such as water and organic matter: 1% to 25% by mass, more preferably 1% to 10% by mass, particularly about 2% to 5% by mass. However, these component amounts are merely standards, and depending on the type of carbon-based powder, even outside these numerical ranges, a coloring composition with excellent long-term stability and capable of producing beautiful paintings can be formed. Hereinafter, several representative carbon-based powders suitable for the coloring composition of this embodiment will be described.

[0053] [Carbon black]

[0054] In the coloring composition of this embodiment, the carbon-based powder used as the pigment component can be ordinary carbon black. Various commercially available carbon black varieties are available for coloring applications, rubber reinforcement applications, etc., making it easy to select a suitable variety based on the desired painting characteristics and dispersibility.

[0055] As mentioned above, various types of carbon black, such as furnace black and lampblack, can be used. However, thermal black is preferred as the main component to meet the requirement that more than 70% by mass of the particles fall within the particle size range of 50 nm to 600 nm. Commercially available thermal blacks have an average particle size of about 150 nm to 500 nm. Therefore, by using them alone or in combination, carbon-based powders with a particle size range of 50 nm to 600 nm, for example, 100 nm to 400 nm, can be produced.

[0056] Pyrolytic carbon black can also be used together with furnace black, coloring carbon black, and other carbon-based powders. Pyrolytic carbon black typically has a small specific surface area, around 5 m². 2 / g~15m2 It has a blackness of around / g and tends to have low blackness. Therefore, it is compared with a specific surface area of ​​20m². 2 / g~150m 2 Various furnace blacks within the range of / g, with a specific surface area of ​​20m² 2 / g~600m 2 / g, especially 50m 2 / g~300m 2 By using coloring carbon black in the range of approximately / g, the desired blackness can be adjusted. Alternatively, these carbon blacks can also be used in combination with the biomass carbon described below.

[0057] Biomass carbon

[0058] Biomass carbon refers to carbon compounds made from biological resources, such as charcoal and bamboo charcoal. Specifically, it is sometimes defined as "a solid substance produced by heating biomass at a temperature exceeding 350°C under controlled oxygen concentrations at non-combustible levels." Besides charcoal and bamboo charcoal, there are various other materials, including carbon derived from rice husks and straw, animal charcoal derived from animal bones and livestock manure, and carbon derived from papermaking sludge and sewage sludge. Any of these materials can be used in the coloring composition of this embodiment.

[0059] The use of biomass carbon also contributes to environmental protection. In the coloring composition of this embodiment, it is desirable that the carbon-based powder comprises at least 70% by mass, more preferably at least 80% by mass, further preferably at least 90% by mass, and particularly preferably almost 100% by mass of biomass carbon. For example, by using a byproduct from the preparation of fuel gas for biomass power generation by gasification as a pigment component, it makes a significant contribution to environmental protection through depetroleum treatment.

[0060] (Byproducts of biomass power generation)

[0061] Biomass power generation, broadly speaking, refers to all power generation systems that use biomass as fuel. Specifically, gasification-based biomass power generation refers to a method where biomass, such as wood, is heated and decomposed in a gasifier to generate combustible gas, which is then used as fuel to drive an engine for power generation. Compared to direct combustion (i.e., using the heat from burning biomass to generate high-pressure steam, which then powers a turbine to generate electricity), it has the following advantages: even with a small-scale system, the impact of heat dissipation is less, and efficient and stable power generation is possible. Here, during biomass gasification, while generating fuel gas, a side reaction produces biomass carbides. This byproduct is useful as a pigment component in the coloring composition of this embodiment.

[0062] During biomass gasification, tar components from the biomass are sometimes produced. This tar can be carbonized to produce the pigment component in the coloring composition of this embodiment. Such tar carbides and the carbonized byproducts of the gasification process are types of charcoal. When these are adjusted into carbon-based powders with a desired particle size distribution, common pulverization methods for charcoal and the like can be applied. Hereinafter, using charcoal and bamboo charcoal, which can be considered representative examples of biomass carbon, as examples, the carbon-based powders used in this embodiment will be further explained.

[0063] (Charcoal / Bamboo Charcoal)

[0064] Charcoal and bamboo charcoal are carbon-based materials obtained by heating wood and bamboo (hereinafter sometimes collectively referred to as "wood materials") in a low-oxygen atmosphere, respectively. Generally, when wood materials are heated, they undergo thermal decomposition at 150℃–400℃, carbonization at 250℃–800℃, carbonization at around 600℃–1800℃, and graphitization above around 1600℃. If such heating is carried out in a low-oxygen atmosphere like a charcoal kiln, thermal decomposition and carbonization begin rapidly at 250℃–300℃. Generally, charcoal obtained by heating to around 400℃–700℃ is called black charcoal, while charcoal obtained by heating to high temperatures above 800℃ is called white charcoal. Black charcoal is usually made from woods such as oak and has the advantage of being easy to ignite. White charcoal is usually made from hardwoods such as oak and has the advantage of a stable and long-lasting flame. Binchotan is a type of white charcoal.

[0065] The properties of charcoal are influenced not only by the raw materials but also by the manufacturing methods and conditions. For example, typical black charcoal has a fixed carbon content of 60% to 85% by mass, an ash content of 1% to 5% by mass, a moisture content of 5% to 10% by mass, and volatile matter of approximately 10% to 25% by mass. In contrast, typical white charcoal has a fixed carbon content of 70% to 90% by mass, particularly 75% to 85% by mass, an ash content of 1% to 5% by mass, particularly 2% to 3% by mass, a moisture content of 5% to 10% by mass, and volatile matter of approximately 5% to 10% by mass. It should be noted that bamboo charcoal can also be prepared using the same methods as wood charcoal, resulting in a carbon-based powder with similar properties. However, when manufactured under the same conditions as wood charcoal, although the specific type of bamboo used as raw material also matters, bamboo charcoal is harder than wood charcoal, and its ash content tends to be higher, for example, 10% to 40% by mass, typically around 15% to 30% by mass.

[0066] Charcoal and bamboo charcoal tend to exhibit higher carbonization temperatures, higher ash content, lower blackness, and a greater tendency to develop a glossy finish. They also tend to have higher specific gravity and harderness with higher carbonization temperatures. For example, the specific gravity of charcoal is approximately 1.5 to 1.7 at carbonization temperatures of 350℃ to 450℃, and approximately 1.8 to 1.9 at carbonization temperatures of 1000℃ to 1500℃. Furthermore, the hardness of charcoal, measured as 1 (based on lead sheet) and 20 (based on saw steel sheet), varies considerably depending on the type of wood used as raw material. However, it generally has a hardness of around 1 to 3 at carbonization temperatures below 500℃, around 5 to 15 (approximately 7 to 10) at carbonization temperatures of 600℃ to 700℃, and around 16 to 20 at carbonization temperatures above 800℃. This tendency can be used as a reference when selecting carbon-based powders that correspond to the target drawing characteristics, or when adjusting the carbon-based powder to the desired particle size distribution.

[0067] (Activated carbon)

[0068] Activated carbon is a carbon-based powder made by reactivating carbides, typically wood charcoal or bamboo charcoal, to create a material with a larger surface area. Activation is usually performed by heating the carbides in a steam atmosphere at a temperature of approximately 800℃ to 1200℃. Most wood charcoal has a very small specific surface area, around 200 m². 2 / g~400m 2 Approximately / g, depending on the variety, it is 10m 2 / g~100m 2 It is around / g, but through activation, the specific surface area can be increased to 800m². 2 / g~1200m 2 Approximately / g. Typically, the specific surface area is less than 800m². 2 The amount of charcoal is 800 m² / g, and its specific surface area is 800 m² / g 2 Carbon with a density of 6g or more is called activated carbon, and there is no essential difference between the two. Therefore, when using activated carbon as the carbon-based powder in this embodiment, the type of activated carbon can be selected according to the same criteria as wood charcoal and bamboo charcoal.

[0069] (graphite)

[0070] Graphite can also be used as the carbon-based powder in this invention. Graphite is a layered substance with hexagonal plate-like crystals, also known as "graphite". Because of its unique metallic luster, it is a useful pigment component for coloring compositions intended for drawing characteristics such as pencil writing. Various natural graphite and synthetic graphite can be used as graphite, but used pencils, mechanical pencil leads, etc., can also be recycled, and the pulverized carbon-based powder can be used in the coloring composition of this embodiment.

[0071] [Particle size adjustment]

[0072] As described above, various carbon-based powders can be used as pigment components in the coloring composition of this embodiment, but amorphous carbon such as carbon black and biomass carbon is preferred, and biomass carbon such as charcoal and bamboo charcoal is particularly preferred. In particular, biomass carbon such as charcoal and bamboo charcoal has lower hardness than graphite and is easier to pulverize, so it can be easily adjusted to the desired particle size distribution.

[0073] There are no particular limitations on the method for adjusting the particle size; various conventional methods such as ball milling, spray milling, roller milling, bead milling, sand milling, salt milling, and colloid milling can be used. When using carbon-based powders such as biomass carbon (e.g., charcoal, bamboo charcoal), the particle size distribution can be adjusted to the specified distribution in this embodiment by pulverizing the powder under shear force during the preparation of the coloring composition. For example, by mixing large-particle-size carbon-based powder with a polymer material serving as a binder in the coloring composition under high shear force, the carbon-based powder is uniformly dispersed in the binder, and the particles can be pulverized under shear force to adjust to an appropriate particle size distribution. Hereinafter, the preparation method of the coloring composition of this embodiment will be described for components other than the carbon-based powder, such as the binder.

[0074] <Formation of the coloring composition>

[0075] The carbon-based powders described above can be used to form coloring compositions. For example, when the carbon-based powders are mixed with binders and solvents such as polymers, inks and coatings can be formed. When thermosetting resins or oils are used as binders, the mixtures with carbon-based powders can also be used as powder coatings. The mixtures of carbon-based powders and binders can also be mixed with drying oils or water to form oil-based or water-based pigments. Carbon-based powders can also be mixed with beeswax or wax to make crayons, mixed with slurries such as carbohydrates to make colored chalk, mixed with clay, cellulose, etc. to make Conté pencils, and mixed with glue to make solid inks. The present invention also includes inks, coatings, powder coatings, pigments, crayons, colored chalk, Conté pencils, and solid inks composed of the coloring compositions of this embodiment. Hereinafter, components other than carbon-based powders that can be used in the coloring compositions of this embodiment will be described.

[0076] <Adhesive>

[0077] The binder used in the coloring composition of this embodiment is not particularly limited, and conventional polymers, drying oils, etc., can be used. Examples of polymers include acrylic polymers such as (meth)acrylic acid, (meth)acrylate, (meth)acrylamide, and (meth)acrylonitrile; alkyd resins; polyamides; polyurethanes; vinyl resins such as polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), and polyvinyl butyral (PVB); polyepoxides such as polyethylene oxide (PEO) and polypropylene oxide; carbohydrates such as carboxymethyl cellulose (CMC), alginate, and gum arabic; and silicone resins, but are not limited to these. Thermosetting polymers such as epoxy resins, phenolic resins, urea resins, and unsaturated polyester resins can also be used. Elastomers such as natural rubber (NR), epoxidized NR, SBR, carboxylated SBR, NBR, carboxylated NBR, and acrylic rubber can also be used as binders.

[0078] Adhesives can also be liquid. For example, mixing carbon-based powders with adjusted particle size distribution with polymer emulsions, latexes, or solutions can form water-based or oil-based inks and coatings. Furthermore, drying oils such as linseed oil, castor oil, poppy oil, and sunflower oil are liquid before drying (oxidative polymerization), so carbon-based powders can be mixed into them to produce inks and coatings.

[0079] In a more preferred embodiment, a polymer that is solid at room temperature is used as a binder. The carbon-based powder is mixed with the solid binder and then pulverized. The resulting mixture is dissolved in water or an organic solvent to form inks, coatings, etc., with carbon-based powder of adjusted particle size distribution as the pigment component. For example, PVA, PVP, etc., with a degree of polymerization of 500 to 3000, particularly around 1000 to 2000, can be used.

[0080] Here, if water-soluble resins such as acrylic polymers, PVA, PVP, PEO, and CMC are used as binders, water can be further added to form water-based inks and water-based coatings. Alternatively, if thermoplastic polymers such as alkyd resins and PVB, thermosetting polymer precursors such as epoxy compounds, or vegetable oils such as linseed oil are used as binders, oil-based inks and oil-based coatings can be formed. Furthermore, this invention includes water-based inks composed of a composition containing the aforementioned carbon-based powder, water-soluble polymers, and water. This invention also includes oil-based inks composed of an oil-based composition containing the aforementioned carbon-based powder, an organic solvent, and a binder, wherein the binder is selected from one or more of the group consisting of thermoplastic polymers, thermosetting polymer precursors, and vegetable oils.

[0081] Solvent

[0082] When the coloring composition of this embodiment is a water-based ink or paint, the main solvent is naturally water. In addition, it may contain alcohols such as ethanol, 1-propanol, and 2-propanol, as well as alcohol ethers such as ethyl cellosolve (ethylene glycol monoethyl ether) and butyl cellosolve (ethylene glycol monobutyl ether). However, from the viewpoint of human safety and environmental protection, it is preferable that 90% or more, particularly 95% or more, of the solvent is water, and even more preferably, that the entire amount of the solvent is water. When the coloring composition of this embodiment is an oil-based ink or paint, a solvent that meets the solubility of the adhesive and the characteristics of the target coloring composition can be selected from various known organic solvents.

[0083] <Other Additives>

[0084] In the coloring compositions of this embodiment, particularly liquid compositions such as inks and coatings, components other than carbon-based powders and binders may be incorporated as additives. Examples of additives include polishing agents, matting agents, viscosity modifiers, surfactants, emulsifiers, defoamers, pH adjusters, dispersants, stabilizers, rust inhibitors, antistatic agents, chelating agents (complexing agents), flow modifiers, preservatives, antioxidants, deterioration inhibitors, bactericides, antimicrobial agents, ultraviolet absorbers, extreme pressure agents, and various chemical reagents, fragrances, sweeteners, inorganic fillers, lubricants, plasticizers, etc., but are not limited to these.

[0085] In the coloring composition of this embodiment, since the particle size distribution of the carbon-based powder is adjusted, it is dispersed in the composition with high uniformity. The sedimentation of large-particle-size powder is suppressed, exhibiting long-term stability. This stability can be further improved by adding surfactants, viscosity modifiers, etc. Additionally, black pigments other than carbon-based powders, such as aniline black, iron oxide pigments, and other pigments and dyes of various hues, can be added to allow for arbitrary variations in the hue of the coloring composition. When such additives are used, their amounts are preferably 0.1% to 5% by mass, particularly 0.5% to 2% by mass, totaling approximately 0.1% to 15% by mass, particularly 0.5% to 5% by mass.

[0086] <<Preparation of Coloring Compositions>>

[0087] By mixing the above-mentioned components, primarily carbon-based powder, the coloring composition of this embodiment can be prepared. Hereinafter, a preferred method for preparing the coloring composition will be described using an embodiment for preparing water-based ink as an example; however, the present invention is not limited to this embodiment.

[0088] <Ink Preparation>

[0089] As described above, the ink of the present invention is prepared by mixing carbon-based powder, binder, solvent, and any additives in a mass ratio of, for example, 4–40:1–30:30–95:0–15, particularly 8–30:7–25:50–85:0–5. The mixing order of these components is not particularly limited; however, especially when the binder is a solid polymer, it is preferable to first mix the carbon-based powder in the binder, and then dissolve or disperse the mixture in the solvent. Any additives, if solid, are preferably mixed with the carbon-based powder in the binder; if liquid, they are preferably added when the mixture is dissolved.

[0090] In the compounding of solid polymers, carbon-based powders are typically subjected to strong shear forces. Due to these shear forces, carbon-based powders of uniform hardness will gradually be pulverized from large particles, such as those with a particle size of 1 μm or more. On the other hand, small particles, such as those with a particle size of 100 nm or less, are less susceptible to shearing, and their particle size remains almost unchanged during compounding. As a result, even when using carbon-based powders with an average particle size of 1 to 2 μm or more and an average particle size of over 600 nm as raw materials, more than 70% by mass of the particles can be finely refined into carbon-based powders with a particle size in the range of 50 nm to 600 nm, for example, 100 nm to 400 nm, after compounding. Therefore, according to this embodiment, carbon-based powders conforming to the present invention can be well dispersed in polymer binders.

[0091] This micronization, achieved through shear force during mixing, is particularly evident in carbon-based powders containing biomass carbon such as charcoal and bamboo charcoal, especially black charcoal and black bamboo charcoal, with a charcoal hardness of approximately 1 to 15. From this perspective, biomass carbon with a charcoal hardness of 1 to 15, further to 2 to 10, and especially 3 to 8, is preferred. On the other hand, when a high-shear mixing machine can be used and a glossy painting effect is desired, biomass carbon with a charcoal hardness of 8 to 18, further to 10 to 16, and especially 12 to 15, can also be used. Furthermore, like general-purpose carbon black, biomass carbon typically possesses functional groups such as carbonyl and hydroxyl groups on its surface. Therefore, during mixing, these functional groups interact with the polymers of the binder, facilitating uniform micro-dispersion within the binder. Consequently, for inks and coatings obtained by dissolving and dispersing such mixtures, even with a relatively large particle size of 100 nm or more, the risk of sedimentation is low.

[0092] [Mixing Method]

[0093] There are no particular limitations on the mixing method of carbon-based powders in adhesives, and various conventional methods can be used. Preferred methods include applying high shear forces during mixing, such as using extruders (e.g., twin-screw extruders), twin-roll mixing rollers (e.g., rubber mixing rollers), Banbury mixers, kneaders, etc., but are not limited to these. There are also no particular limitations on the mixing conditions. From the viewpoint of increasing shear force, it is preferable to mix at a temperature approximately 1 to 10°C or higher above the softening temperature of the polymer used as the adhesive, and at a temperature around the melting point of the polymer.

[0094] It is also possible to perform mixing in two stages. For example, by mixing 70% to 90% of all carbon-based powders in the first stage, and then mixing 30% to 10% of harder or larger-particle-size carbon-based powders in the second stage, it is easy to prepare a mixture containing... Figure 1 (d) shows a coloring composition of pigment components with a particle size distribution. Alternatively, the mixture obtained in a closed mixing mill such as a Banbury mixer or kneader may be subjected to repeated shearing forces through cooling and rolling via two-roll or three-roll mills.

[0095] Next, the mixture obtained above is dissolved or dispersed in water, organic solvents, etc., thereby forming water-based or oil-based inks. There are no particular restrictions on the method of dissolution and dispersion; general-purpose mixers, such as dispersers, ball mills, SG mills, roller mills, planetary mixers, etc., can be used.

[0096] <<Uses of Coloring Compositions>>

[0097] The coloring composition of the present invention exhibits excellent writing feel and long-term stability, which is beneficial for producing beautiful paintings with minimal unevenness and a glossy finish. Therefore, it is suitable not only for printing, coating, and marking applications, but also for art-related uses. When using biomass carbon such as charcoal or bamboo charcoal, especially activated carbon, as a carbon-based powder, it can also impart adsorption properties to the coating film. Furthermore, when the coloring composition of the present invention is incorporated into polymer compositions or molded articles, it can also form a characteristic appearance such as a glossy black finish, or impart adsorption properties. In addition, the present invention also includes polymer compositions and polymer molded articles containing the above-described coloring composition.

[0098] Example

[0099] The present invention will now be described in more detail with reference to embodiments. It should be noted that these embodiments are provided to facilitate a better understanding of the concepts and scope of the invention as disclosed in this specification or in the appended claims, and are described only for the purpose of illustrating specific methods and implementations. The present invention is not limited by these embodiments in any way.

[0100] [Example 1]

[0101] A water-based black ink was prepared using bamboo charcoal as the pigment component and PVA (polyvinyl alcohol manufactured by Fujifilm and Kojun Pharmaceutical Co., Ltd., with an average degree of polymerization of 1500–1800) as the binder. As the bamboo charcoal raw material, a commercially available product with an average particle size (measured by dynamic light scattering) of approximately 10 μm, an ash content of approximately 20% by mass, a fixed carbon content of 75% by mass, and a charcoal hardness of 15, obtained at a carbonization temperature of 800°C, was used.

[0102] Using a two-roll mill, 50g of the above-mentioned bamboo charcoal was mixed in 50g of PVA at a temperature of 40℃~80℃. 100g of the resulting mixture was dispersed in 400g of water (total amount 500g) and ground with a bead mill to prepare ink sample-1 (10% by mass of bamboo charcoal and 10% by mass of binder relative to the total amount of ink).

[0103] (Particle size distribution of bamboo charcoal particles in ink)

[0104] A portion of the ink sample-1 obtained above was collected, and the particle size distribution of bamboo charcoal in the sample was determined using a particle size analyzer based on dynamic light scattering (Microtrack UPA-EX150 manufactured by Nikkiso Co., Ltd.). The measurement results are shown in Table 1 and below. Figure 2 As shown in the histogram, 98% by volume (98% by mass) of the bamboo charcoal particles have a particle size in the range of 50 nm to 600 nm, 85% by volume (85% by mass) of the particles have a particle size in the range of 100 nm to 400 nm, and 13% by volume (13% by mass) of the particles have a particle size in the range of 400 nm to 600 nm.

[0105] (Drawing Experiment)

[0106] Ink sample-1 was applied to high-quality paper using a No. 10 nylon flat brush to evaluate its drawing properties. According to the ink sample, it can be applied smoothly without producing a sense of disharmony, resulting in a uniform, even, and glossy drawing. It should be noted that no bamboo charcoal particles settled in ink sample-1 even several days after preparation.

[0107] [Comparative Example 1]

[0108] Except for omitting the two-roll mixing process, the same procedures as in Example 1 were performed to prepare ink sample-2. The particle size distribution of the bamboo charcoal particles in this sample is shown in Table 1 and... Figure 3As shown. For the bamboo charcoal in ink sample-2, the average particle size was 2062 nm, with particles ranging from 50 nm to 600 nm accounting for approximately 1% by volume, and no particles ranging from 100 nm to 400 nm were present. Using ink sample-2, the same painting test as in Example 1 was conducted, resulting in an inconsistent feel due to the brush tip getting stuck during application, and uneven color distribution was observed in the resulting paintings. Furthermore, for ink sample-2, sedimentation of bamboo charcoal particles was observed several days after preparation.

[0109] [Table 1]

[0110] [Table 1. Results of particle size distribution determination of bamboo charcoal in ink sample-1 and ink sample-2]

[0111]

[0112] * The percentage of particles with a diameter in the range of, for example, 50 nm to 600 nm, in mass %.

[0113] The experimental results above demonstrate that using the black ink according to the present invention produces beautiful paintings with minimal unevenness in color depth and offers a good writing feel. Furthermore, the black ink according to the present invention does not exhibit pigment sedimentation, indicating excellent long-term stability. The bamboo charcoal used as a raw material is a non-petroleum biomass product, contributing to environmental protection, and the effects of the present invention are significant.

Claims

1. A coloring composition comprising carbon-based powder as a pigment component, More than 70% by mass of the carbon-based powder consists of particles with a particle size in the range of 50 nm to 600 nm, as determined by dynamic light scattering.

2. The coloring composition according to claim 1, wherein, More than 5% by mass of the carbon-based powder consists of particles with a particle size in the range of 400 nm to 600 nm, as determined by dynamic light scattering.

3. The coloring composition according to claim 1, wherein, The fixed carbon content of the carbon-based powder is 40% to 98% by mass.

4. The coloring composition according to claim 1, wherein, The ash content of the carbon-based powder is 2% to 40% by mass.

5. The coloring composition according to claim 1, wherein, The carbon-based powder contains more than 70% by mass of biomass carbon.

6. The coloring composition according to claim 5, wherein, The biomass carbon is a byproduct of fuel gas preparation in biomass power generation via gasification.

7. An ink, coating, powder coating, pigment, crayon, colored chalk, Conté pen, or solid ink formed from the coloring composition according to any one of claims 1 to 6.

8. A water-based ink, which is the coloring composition according to any one of claims 1 to 6, comprising a composition containing the carbon-based powder, a water-soluble polymer and water.

9. An oil-based ink, comprising the coloring composition according to any one of claims 1 to 6, comprising an oil-based composition containing the carbon-based powder, an organic solvent and a binder, wherein the binder is selected from one or more of the group consisting of thermoplastic polymers, thermosetting polymer precursors and vegetable oils.

10. A polymer composition or polymer molded article comprising the coloring composition according to any one of claims 1 to 6.

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