Plate-like alumina-containing ink composition

Abstract

The object of the present invention is to provide an ink composition containing alumina particles that can achieve high hiding power. Specifically, the ink composition is characterized by containing plate-like alumina particles that have a volume-based median diameter D50 of 1 μm to 5 μm, an aspect ratio of 10 to 50, and a metal oxide layer on the surface.

Description

[Technical field]

[0001] The present invention relates to an ink composition containing platy alumina. [Background technology]

[0002] Conventionally, ink compositions containing, for example, a colorant and a solvent such as an organic solvent or water are known, and pigment inks containing a pigment as the colorant are widely used. Among them, inks containing titanium oxide as a white pigment, which has excellent hiding power and clarity, are widely used.

[0003] In ink compositions for writing instruments, alumina may be added together with a colorant such as titanium oxide (Patent Documents 1 and 2). For example, a ballpoint pen tip has a ball and a ball holder, and by adding alumina, it is possible to reduce wear of the ball seat (referring to the contact part between the ball and the ball holder) caused by friction generated by the rotation of the ball during writing. In addition, when writing long distances, the frictional force between the ball and the ball seat is smaller than the frictional force between the paper surface and the ball, so skipping of the line can be prevented. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2015-091944 A [Patent Document 2] JP 2020-203969 A [Non-patent literature]

[0005] [Non-Patent Document 1] Machida,S.et.al.CrystEngComm,2022,24,5405-5409 Summary of the Invention [Problem to be solved by the invention]

[0006] However, alumina has low hiding power, and when added as an additive, there is a risk of reducing the inherent hiding power of the ink composition.

[0007] Non-Patent Document 1 shows that plate-like NaNbO3 on the submicron order has high hiding power, but when alumina is similarly made on the submicron order, the improvement in hiding power is insufficient.

[0008] An object of the present invention is to provide an ink composition containing alumina particles that can achieve high hiding power. [Means for solving the problem]

[0009] As a result of intensive research, the present inventors have found that an ink coating film having excellent hiding power can be obtained by surface-treating alumina particles having a specific particle size and thickness, and have thus completed the present invention.

[0010] (1) An ink composition containing plate-like alumina particles having a volume-based median diameter D50 of 1 μm or more and 5 μm or less, an aspect ratio of 10 or more and 50 or less, and a metal oxide layer on the surface.

[0011] (2) The composition according to the above (1), wherein the plate-like alumina particles have a volume-based cumulative particle diameter D100 of 15 μm or less as measured by laser diffraction particle size distribution measurement.

[0012] (3) The ink composition according to (1) or (2) above, wherein the metal oxide is silicon dioxide.

[0013] (4) The ink composition according to any one of the above (1) to (3), further comprising titanium oxide particles.

[0014] (5) The ink composition according to any one of (1) to (4) above, further comprising the platelet alumina particles in an amount of 1% by mass or more and 15% by mass or less based on the total amount of the ink composition. Effect of the Invention

[0015] According to the present invention, by subjecting alumina particles having a specific particle size and thickness to a surface treatment, it is possible to provide an ink composition that achieves high hiding power. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Hereinafter, an embodiment of the present invention will be described in detail.

[0017] [Ink composition] The ink composition of the present invention is characterized in that it contains alumina particles having a specific particle size and aspect ratio, and the alumina particles have a metal oxide layer on the surface thereof.

[0018] (Alumina particles) The D50 of the alumina particles is 1 μm to 5 μm, and more preferably 1.1 μm to 4 μm. When the D50 is within the above range, the dry hide effect is easily exhibited when a metal oxide layer described later is provided, and the hiding power of the ink coating can be improved.

[0019] Although there is no particular limitation on the D100 of the alumina particles, it is preferable that the D100 is 15 μm or less. When the D100 is 15 μm or less, the ratio of coarse alumina particles is reduced, and a uniform and vivid color can be obtained when the ink is applied to the ink film.

[0020] In this specification, D50 and D100 refer to values ​​calculated from a volume-based cumulative particle size distribution measured by a laser diffraction particle size distribution measuring device.

[0021] The aspect ratio, which is the ratio of the average particle diameter (D50) to the thickness of the alumina particles, is from 10 to 50, preferably from 12 to 45, and more preferably from 15 to 40. When the aspect ratio of the alumina particles is within the above range, good hiding performance can be obtained when the alumina particles are formed into an ink coating film.

[0022] The alumina particles are aluminum oxide and may be transition alumina of various crystal forms such as γ, δ, θ, κ, etc., or may contain alumina hydrate in transition alumina. However, it is basically preferable that the alumina particles be in the α crystal form (α type) because of its superior stability.

[0023] The alumina particles may further contain molybdenum, and may also contain impurities derived from the raw materials or the shape control agent, so long as the effects of the present invention are not impaired.

[0024] The alumina particles used in the present invention may be produced by any method as long as the performance of D50 and aspect ratio is satisfied, and may be produced by a known and commonly used production method such as a hydrothermal method, a flux method, etc. A production method for more simply obtaining desired alumina particles includes the method described in JP 2016-222501 A in which an aluminum compound is calcined in the presence of a molybdenum compound and a shape control agent.

[0025] (Metal oxide layer) The metal oxide layer contained in the alumina particles is preferably one or more of zinc oxide, silicon dioxide, zirconium dioxide, and titanium oxide. Silicon dioxide is particularly preferable because it forms a porous structure and contains air on the surface of the alumina, thereby increasing the difference in refractive index between the binder and the metal oxide layer.

[0026] The metal oxide layer is preferably a single layer. A single layer is more excellent in improving hiding power due to the difference in refractive index. Note that a single layer means that it is made of one type of component, and indicates that there are not two types of layers, for example, a zinc oxide layer and a silicon dioxide layer.

[0027] The metal oxide layer may be formed on at least a part of the surface of the alumina particle, but more preferably, it is formed on the entire surface of the alumina particle. Note that the "surface of the alumina particle" means the outside of the surface of the alumina particle. Therefore, it is clearly distinguished from the surface layer containing mullite or germanium that is formed on the inside of the surface of the alumina particle.

[0028] The thickness of the metal oxide layer is not particularly limited, but from the viewpoints of hiding power and cost, it is 0.1 nm or more, but is thin enough not to be measured in an SEM image.

[0029] The amount of metal oxide in the metal oxide layer relative to the amount of alumina in the alumina particles is not particularly limited, but is preferably 5% by mass or less, more preferably 3% by mass or less, and more preferably more than 0% by mass. Being within the above range is preferable because it provides excellent hiding power when made into an ink composition.

[0030] [Method of forming metal oxide layer] The method for forming the metal oxide layer is not particularly limited and can be a known method. For example, in the case of silicon dioxide, a porous silicon dioxide layer can be formed by adding a solution of sodium silicate, adjusting the pH with a strong acid, and then drying.

[0031] The content of the alumina particles having a metal oxide may be appropriately set depending on the application, but is preferably 1 to 15 mass % and more preferably 3 to 12 mass % based on the total mass of the ink composition. By being within the above range, it is preferable to have both excellent hiding power and color development.

[0032] (Titanium oxide particles) The ink composition of the present invention may further contain titanium oxide particles. The titanium oxide particles are not particularly limited, and either rutile type or anatase type may be used, but the average particle size is preferably 0.01 μm or more. For example, known titanium oxides such as Bayertitan R-FD-1, R-KB-3, and R-CK-20 (all manufactured by Bayer), TIPAQUE R-630, R-615, and R-830, and LPT series (all manufactured by Ishihara Sangyo Kaisha, Ltd.), Unitane OR-342 (manufactured by ACC), Ti-pure R-900 and R-901 (manufactured by Chemours), and Luxelene Silk series (manufactured by Sumitomo Chemical Co., Ltd.) may be used.

[0033] The amount of the additive is preferably 0.001% by mass or more and 10% by mass or less, more preferably 0.005% by mass or more and 5% by mass or less, and particularly preferably 0.02% by mass or more and 4% by mass or less, based on the total mass of the ink composition. When the amount is within the above range, the resulting coating film has excellent hiding power and L value, and is also excellent in ink discharge performance, which is preferable.

[0034] (Organic solvent) The ink composition of the present invention may contain an organic solvent, for example, aromatic hydrocarbon solvents such as toluene, xylene, ethylbenzene, etc., aliphatic hydrocarbon solvents such as n-hexane, n-heptane, isoheptane, n-octane, isooctane, etc., cycloparaffin solvents such as methylcyclohexane, ethylcyclohexane, etc., ketone solvents such as methyl isobutyl ketone, methyl ethyl ketone, etc., glycol solvents such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, polyethylene glycol, glycerin, etc., glycol ether solvents such as ethylene glycol monomethyl ether, diethylene glycol monomethyl ether, etc., which may be used alone or in combination of two or more. Glycol ether solvents are preferred from the viewpoints of water solubility and excellent writing properties and safety.

[0035] The content of the organic solvent is not particularly limited, but from the viewpoint of the drying speed of the ink coating, it is preferably 10 to 90 mass % relative to the total mass of the ink composition, and more preferably 20 to 80 mass %.

[0036] (resin) The ink composition of the present invention may contain a resin, such as a polyvinyl butyral resin, a ketone resin, a polyacetal resin, a polyvinyl alcohol resin, a cellulose resin, a terpene resin, an alkyd resin, a phenoxy resin, a polyvinyl acetate resin, a polyvinylpyrrolidone resin, an ethylene oxide polymer, an acrylic resin, a styrene-acrylic resin, a styrene-maleic acid resin, or the like, and these may be used alone or in combination of two or more kinds.

[0037] From the viewpoints of ink viscosity and ink leakage, the content of the resin is preferably from 0.05 to 30% by mass, and particularly preferably from 0.1 to 25% by mass, based on the total mass of the ink composition.

[0038] (Dispersant) The ink composition of the present invention may contain a dispersant, and examples thereof include nonionic surfactants such as glycerin fatty acid esters, polyoxyethylene methyl ether, polyoxyethylene lanolin alcohol, polyoxyethylene alkylamines, and polyoxyethylene fatty acid amides; anionic surfactants such as alkyl sulfates, N-acylamino acid salts, polyoxyethylene alkyl ether acetates, and alkyl phosphates; cationic surfactants such as alkylamine salts and quaternary ammonium salts; amphoteric surfactants such as alkyl betaines, alkyl amine oxides, and phosphatidylcholines; and polymeric surfactants such as acrylics.

[0039] The content of the dispersant is appropriately determined depending on other components such as the solvent used, but from the viewpoints of dispersion stability and ink viscosity, it is preferably 0.1 to 30 mass %, and particularly preferably 0.5 to 20 mass %, relative to the total mass of the ink composition.

[0040] (Other additives) If necessary, additives such as colorants such as organic pigments, inorganic pigments, acid dyes, basic dyes, and direct dyes; rust inhibitors such as benzotriazole, tolyltriazole, dicyclohexylammonium nitrite, diisopropylammonium nitrite, saponin, metal salt compounds, and phosphate compounds; preservatives such as carbolic acid, sodium salt of 1,2-benzthiazolin-3-one, sodium benzoate, sodium dehydroacetate, potassium sorbate, propyl paraoxybenzoate, and 2,3,5,6-tetrachloro-4-(methylsulfonyl)pyridine; antifoaming agents such as silicones, mineral oils, polyethers, and fluorines; antioxidants; stabilizers; inorganic salts such as sodium carbonate, sodium phosphate, and sodium acetate; and pH adjusters such as organic basic compounds such as water-soluble amine compounds.

[0041] [Method of producing ink composition] The ink composition of the present invention can be produced by a known method without any particular limitation. The ink composition can be produced by mixing the above-mentioned components in appropriate amounts and using various stirrers such as a propeller stirrer, homodisper, or homomixer, or various dispersers such as a bead mill. When a pigment is added as a colorant, it is preferable to use a disperser such as a bead mill or a paint conditioner.

[0042] (viscosity) The viscosity of the ink composition is not particularly limited, but is preferably 20°C at a shear rate of 5 sec -1 The ink viscosity (at rest) is preferably 30,000 mPa·s or less, and more preferably 25,000 mPa·s or less. When it is equal to or less than the upper limit, it is preferable because it provides excellent ink dischargeability and writing comfort. From the viewpoint of suppressing ink leakage, it is preferably 500 mPa·s or more, and more preferably 1,000 mPa·s or more.

[0043] [Application] The structure of the writing implement to which the ink composition of the present invention is applied is not particularly limited. The ink composition of the present invention is not only highly opaque, but is also expected to exhibit low abrasion effects due to the use of alumina, and is therefore suitable for use as an ink for a ballpoint pen having a ball and a ball seat. By using the writing implement of the present invention, it is possible to stably draw lines while maintaining opaqueness.

[0044] The present invention will now be described in more detail with reference to examples, but the present invention is not limited to the following examples.

[0045] (Synthesis of Alumina) [Production Example 1] A mixture was obtained by mixing 142.3 g of aluminum hydroxide (manufactured by Nippon Light Metal Co., Ltd., average particle size 1 μm), 3.7 g of silicon dioxide (manufactured by Kanto Chemical Co., Ltd., special grade), and 4.7 g of molybdenum trioxide (manufactured by Taiyo Koko Co., Ltd.) in a mortar. The mixture was placed in a crucible and heated to 1200°C at 5°C / min in a ceramic electric furnace, and then fired by holding at 1200°C for 10 hours. The temperature was then lowered to room temperature at 5°C / min, and the crucible was removed to obtain 95 g of a light blue powder.

[0046] Next, 50 g of the obtained light blue powder was dispersed in 150 mL of 0.5% ammonia water, and the dispersion solution was stirred at room temperature (25 to 30 ° C) for 0.5 hours, after which the ammonia water was removed by filtration, and the molybdenum remaining on the particle surface was removed by washing with water and drying, obtaining 47 g of light blue powder. The obtained powder was confirmed to have a plate-like shape by SEM observation. Furthermore, when X-ray diffraction (XRD) measurement was performed, a sharp peak scattering due to α-alumina appeared, and no alumina crystal peaks other than the α crystal structure were observed, confirming that the particles were plate-like alumina particles with a dense crystal structure. In addition, the α-conversion rate was 99% or more (almost 100%).

[0047] [Production Example 2] A mixture was obtained by mixing 142.3 g of aluminum hydroxide (manufactured by Nippon Light Metal Co., Ltd., average particle size 2 μm), 2.8 g of silicon dioxide (manufactured by Kanto Chemical Co., Ltd., special grade), and 4.7 g of molybdenum trioxide (manufactured by Taiyo Koko Co., Ltd.) in a mortar. The resulting mixture was placed in a crucible and heated to 1200°C at 5°C / min in a ceramic electric furnace, and then fired by holding at 1200°C for 10 hours. The temperature was then lowered to room temperature at 5°C / min, and the crucible was removed to obtain 95 g of a light blue powder.

[0048] Next, 50 g of the obtained light blue powder was dispersed in 150 mL of 0.5% ammonia water, and the dispersion solution was stirred at room temperature (25 to 30 ° C) for 0.5 hours, after which the ammonia water was removed by filtration, and the molybdenum remaining on the particle surface was removed by washing with water and drying, obtaining 47 g of light blue powder. The obtained powder was confirmed to have a polygonal plate shape by SEM observation. Furthermore, when X-ray diffraction (XRD) measurement was performed, a sharp peak scattering due to α-alumina appeared, and no alumina crystal system peaks other than the α crystal structure were observed, confirming that the alumina particles were plate-shaped with a dense crystal structure. In addition, the α-conversion rate was 99% or more (almost 100%).

[0049] [Production Example 3] 50 g of aluminum hydroxide (manufactured by Nippon Light Metal Co., Ltd., average particle size 12 μm), 0.65 g of silicon dioxide (manufactured by Kanto Chemical Co., Ltd., special grade), and molybdenum trioxide (manufactured by Taiyo Koko Co., Ltd.) were mixed. The mixture was mixed in a mortar with 1.72 g of 1,200°C (manufactured by Sigma-Aldrich Co., Ltd.) to obtain a mixture. The mixture was placed in a crucible and heated to 1200°C at 5°C / min in a ceramic electric furnace, and then fired at 1200°C for 10 hours. The temperature was then lowered to room temperature at 5°C / min, and the crucible was removed to obtain 34.2 g of a light blue powder. The powder was crushed in a mortar until it passed through a 106 μm sieve.

[0050] Next, the obtained light blue powder was dispersed in 150 mL of 0.5% ammonia water, and the dispersion solution was stirred at room temperature (25 to 30 ° C) for 0.5 hours, after which the ammonia water was removed by filtration, and the molybdenum remaining on the particle surface was removed by washing with water and drying, obtaining 33.5 g of light blue powder. The obtained powder was confirmed to have a plate-like shape and extremely few aggregates by SEM observation. Furthermore, when XRD measurement was performed, a sharp peak scattering due to α-alumina appeared, and no alumina crystal peaks other than the α crystal structure were observed, confirming that the particles were plate-like alumina particles with a dense crystal structure. In addition, the α-conversion rate was 99% or more (almost 100%).

[0051] For comparison, titanium oxide particles (Tipaque R-830, manufactured by Ishihara Sangyo Kaisha, Ltd.) were prepared (T-1).

[0052] (Measurement of particle size distribution) 0.05 g of plate-like alumina particles were mixed with 50 g of 0.2% hexametaphosphoric acid aqueous solution and dispersed for 5 minutes using an ultrasonic homogenizer. The particle size distribution was measured using a laser light scattering diffraction particle size analyzer (Microtrackbell, MT3300EXII) to determine the 50% and 100% volume average diameters D50 and D100 (μm).

[0053] (Measurement of average thickness D) For the plate-like alumina particles, the thickness of 50 particles was measured using a scanning electron microscope (SEM), and the average value was adopted as the average thickness D (μm). The aspect ratio D50 / D was calculated using the following formula.

[0054] (Aspect ratio D50 / D) Aspect ratio = Particle diameter of plate-shaped alumina particles D50 / Average thickness of plate-shaped alumina particles D

[0055] (Analysis of Alpha Conversion Rate of Plate-shaped Alumina Particles) The plate-like alumina particles were placed on a measurement sample holder with a depth of 0.5 mm, and packed flat with a constant load. The resultant was then placed in a wide-angle X-ray diffractometer (Rigaku Corporation, Rint-Ultma) and measurements were performed under the following conditions: Cu / Kα radiation, 40 kV / 30 mA, scan speed of 2 degrees / min, and a scan range of 10 to 70 degrees. The α conversion rate was calculated from the ratio of the strongest peak heights of α-alumina and transition alumina.

[0056] [Production Examples 4 to 6] (Formation of metal oxide layer) The plate-like alumina particles obtained in the above Production Example were dispersed in ion-exchanged water, and No. 3 sodium silicate (Fuji Chemical Co., Ltd.) was added dropwise with stirring to give 3 parts by mass of silicon oxide per 100 parts by mass of alumina. After the dropwise addition, the mixture was stirred for 10 minutes, and 1M sulfuric acid was added dropwise to adjust the pH to 6.0.The mixture was then filtered, washed with ion-exchanged water, and dried at 150°C for 5 hours to obtain a light blue powder.

[0057] The fillers used in the examples and comparative examples are as shown in Table 1.

[0058] [Table 1]

[0059] (Production of ink composition) 5.5 parts by mass of Typaque R-830 ​​(Ishihara Sangyo Kaisha, Ltd.), 1.0 part by mass of Primal ASE-60 (Dow Chemical Company, Ltd.), 6.5 parts by mass of purified glycerin (New Japan Chemical Co., Ltd.), 11.7 parts by mass of Joncryl 70J (BASF Corporation), and 12.9 parts by mass of ion-exchanged water were mixed. 4 parts by mass of a filler shown in Table 1 was added to the resulting mixture and further mixed to obtain a white ink composition.

[0060] [Evaluation of Concealment] The obtained white ink composition was applied to a colored drawing paper (Koikura, manufactured by PLUS Co., Ltd.) to form a coating film using a bar coater RDS20. The coating film was dried at room temperature for one day and night, and the hiding power of the coating surface was evaluated by the L value. The L value was measured using a spectro-guide 45 / 0 gloss (manufactured by BYK-Gardner GmbH). An L value of 89 or more was evaluated as a good coating film that sufficiently hid the coating surface, and an L value below that was evaluated as an X for insufficient hiding power.

[0061] The evaluation results are shown in Table 2.

[0062] [Table 2]

[0063] It was confirmed from Examples 1 and 2 and Comparative Example 1 that the hiding power is improved when a metal oxide layer is formed on alumina particles having a specific particle size.

[0064] From Examples 1 and 2 and Comparative Example 2, it was confirmed that the formation of a metal oxide layer improves the hiding power.

[0065] It was confirmed from Examples 1 and 2 and Comparative Example 3 that the alumina particles having a metal oxide layer formed thereon have better hiding power than the titanium oxide particles alone.

Claims

1. A white ink composition containing plate-like alumina particles having a volume-based median diameter D50 of 1 μm or more and 5 μm or less, an aspect ratio of 10 or more and 50 or less, and having a metal oxide layer made of silicon dioxide on the surface.

2. 2. The white ink composition according to claim 1, wherein the plate-like alumina particles have a volume-based cumulative particle diameter D100 of 15 μm or less, as measured by laser diffraction particle size distribution measurement.

3. The white ink composition according to claim 1 or 2, further comprising titanium oxide particles.

4. 3. The white ink composition according to claim 1, wherein the content of the platelet alumina particles in the ink composition is from 1% by mass to 15% by mass based on the total amount of the ink composition.