JPH04270771A - Water-based black ink composition for writing utensil - Google Patents

Abstract

PURPOSE:To provide the subject composition containing a carbon black pigment, a dispersing agent, an aqueous medium and earthy graphite having a specific nature and giving a written line free from blotting and having remarkably improved blackness and excellent light-resistance, water-resistance, etc. CONSTITUTION:The objective composition is produced by compounding (A) a water-based ink composition for writing utensil consisting of a carbon black pigment (BC), a dispersing agent (preferably water-soluble acrylic resin in an amount of 1-200wt.% based on BC) and an aqueous medium (preferably water or a mixture consisting of a combination of water and a water-soluble organic solvent such as ethylene glycol) with (B) 0.5-10wt.% of earthy graphite having an average particle diameter of <=1.0mum and a purity (carbon content) of >=96wt.% and, as necessary, (C) a pH modifier, a preservative, etc.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a black water-based ink composition for writing instruments, and more specifically, a writing instrument that does not smudge written lines and has significantly increased blackness while maintaining fastness such as light resistance and water resistance. The present invention relates to a black aqueous ink composition for use.

0002

[Prior Art] Conventionally, black water-based ink used for writing instruments such as water-based felt-tip pens, plastic pens, ballpoint pens, and felt-tip pens has been produced by dissolving a water-soluble dye as a coloring agent in an aqueous medium such as water or a water-soluble organic solvent. There are also known pigments with water-dispersible pigments dispersed in them. However, when dyes are used, there are problems with blurring of written lines and fastness such as light fastness and water resistance.Ink with dispersed pigments solves the fastness and blurring of drawn lines to some extent, but The degree of blackness was extremely unsatisfactory. The reason for this is that when the black pigment content is increased to increase the blackness, the viscosity of the ink also increases, making it difficult for the ink to flow out from the nib of the writing instrument using capillary action.

Various methods have been proposed to increase blackness. For example, there are methods of using aniline black or iron black instead of carbon black pigment, but these methods do not provide a blackness superior to that of carbon black. Furthermore, as seen in JP-A-63-145381, it has been proposed to increase the hiding power and blackness by incorporating white resin particles, but since the resin particles are white, , does not have a large effect on increasing blackness. Furthermore, in Japanese Patent Publication No. 58-55996, there is an example of blending graphite as a solid anti-wear agent in water-based ink for ballpoint pens, but conventional graphite has a large particle size.
There were problems such as clogging at the pen tip and lack of dispersion stability.

0004

[Problem to be solved by the invention] Carbon black pigment (hereinafter abbreviated as CB) to increase the blackness of written lines
When the content of is increased, the blackness increases to some extent, but the ink viscosity also increases and the fluidity decreases, making it difficult for the ink to flow out from the pen tip. Therefore, it is necessary to set the CB content to give an ink viscosity that can ensure the amount of ink flowing out from the pen tip, but with such a content, when writing on paper, the CB spreads uniformly over the paper fibers. and cannot be completely adhered to. Also, CB
Since they are extremely fine particles, they intensively penetrate into the concave portions of the paper fibers together with the ink vehicle, resulting in a problem in that it is not possible to provide sufficient blackness to the entire drawn line.

The purpose of the present invention is to use CB, which is a black pigment, to prevent blurring of written lines, ensure light resistance and water resistance, and maintain an ink viscosity that can ensure the amount of ink flowing out from the pen tip. However, it is an object of the present invention to provide a black aqueous ink composition for a writing instrument that gives sufficient blackness to the entire drawn line.

[0006]

[Means for Solving the Problems] As a result of intensive research in order to increase the blackness of drawn lines, the present inventors added a specific finely ground high-purity earthy graphite to a water-based ink composition for writing instruments containing CB. It was discovered that by adding CB, a black water-based ink with sufficiently excellent blackness of written lines can be obtained even with a small amount of CB, and the present invention was completed.

That is, the present invention provides a carbon black pigment,
A water-based ink composition for writing instruments consisting of a dispersant and an aqueous medium further contains an average particle size of 1.0 μm or less and a purity (carbon content).
This is a black aqueous ink composition for writing instruments containing 96% by weight or more of earthy graphite.

The CB used in the present invention can be any commercially available color CB, and is not limited to channel black, furnace black, acidic, alkaline, etc. If the amount of CB used is too large, there will be a problem that the ink viscosity will increase, making it difficult to flow out from the pen tip, and if it is too small, the blackness of the drawn line will be unsatisfactory, so the preferred range is a water-based ink composition. Inside, 2-20
% by weight.

[0009] As the dispersant used in the present invention, conventionally known pigment dispersants can be used, particularly preferably water-soluble resin dispersants, which may be natural products, semi-synthetic products, or synthetic products.
Synthetic products are preferred from the viewpoint of mold and rot problems and viscosity characteristics suitable for water-based inks for writing instruments. Examples of such synthetic water-soluble resins include water-soluble acrylic resins, water-soluble styrene-acrylic resins, and water-soluble styrene-maleic resins. The amount of these water-soluble resins is CB
The content is selected within the range of 1 to 200% by weight. If the amount is less than 1% by weight, the dispersion stability of the pigment and the stability of the ink over time will be poor, and if it exceeds 200% by weight, the viscosity of the ink will increase, making it difficult for the ink to flow out from the pen tip.

The aqueous medium used in the composition of the present invention is water or a mixture of water and a water-soluble organic solvent, and examples of the water-soluble organic solvent include polyhydric alcohols such as ethylene glycol, diethylene glycol, and glycerin. Examples include glycol ethers such as ethylene glycol monomethyl ether and diethylene glycol monomethyl ether, and glycol ether esters such as ethylene glycol monoethyl ether acetate. These water-soluble organic solvents may be used alone or in combination of two or more, and an aqueous solution in which they are dissolved at a ratio of 5 to 200 parts by weight per 100 parts by weight of water is preferred.

[0011] The earthy graphite used in the present invention differs from conventionally commercially available general scale graphite, earthy graphite, and synthetic graphite in that it has an average particle diameter of 1.0 μm or less and has a high purity (carbon content). 96% by weight or more of natural earthy graphite. The earthy graphite has an average particle size of 1.0 μm or less,
In order to make the purity 96% by weight, it is ground in an aqueous solution with a viscosity of 2 to 70 poise, and this suspension is further
It is a powder obtained by diluting it to 40 centipoise and classifying it using power to remove coarse particles, and it has a much superior blackness compared to the silver-gray color tone of scale graphite and synthetic graphite. Furthermore, if the average particle diameter is 1.0 μm or more, there is a risk of clogging in the nib of the writing instrument, and at the same time, concentration variations due to sedimentation of the pigment in the ink storage body within the writing instrument become noticeable. Further, if the purity is 96% by weight or less, problems arise in the dispersion stability of the ink composition due to the influence of impurities such as silicon dioxide, iron oxide, aluminum oxide, etc.

If the content of the earthy graphite in the aqueous ink composition of the present invention is too small, the blackness of the drawn line cannot be obtained, and if it is too large, it will lead to an increase in ink viscosity;
Even though it has a high blackness among the graphites, it is several steps inferior to carbon black, so the silver-gray tone of graphite is emphasized, and the blackness decreases, so it is preferable to use it in water-based inks. , in the range of 0.5 to 10% by weight. In the present invention, the above water-soluble resin dispersant can be used as is as the dispersant for earthy graphite in the water-based ink, but it does not necessarily have to be the same as the dispersant used for dispersing CB, and can be selected as appropriate. However, it is used in an amount that does not excessively increase the viscosity of the water-based ink.

The composition of the present invention may optionally contain additives used in conventionally known water-based ink compositions, such as preservatives, fungicides, rust preventives, pH regulators, humectants, and lubricants. can be blended. The aqueous ink composition for writing instruments of the present invention consists of the above-mentioned components and formulations, and a conventional pigment dispersion method can be employed. For example, the above-mentioned components may be blended, mixed and ground using a ball mill, roll mill, bead mill, homomixer, ultrasonic dispersion machine, etc., and then subjected to a dispersion treatment. A typical method is to prepare dispersions separately and mix them in an appropriate ratio.

[0014]

[Operation] Although the water-based ink composition for writing instruments of the present invention contains CB and the above-mentioned earthy graphite, it has excellent long-term dispersion stability and maintains the same ink flow performance as conventional water-based ink compositions. In addition, it is possible to provide extremely excellent blackness of written lines. Furthermore, since a pigment is used as the dye, it has sufficient light resistance and water resistance, and there is no problem with blurring of written lines.

[0015] Although the theoretical basis for the effect of significantly increasing blackness cannot be clearly explained,
When writing on paper using a writing instrument that uses water-based ink containing pigment as a coloring agent, it will be considered that the paper will be colored under the following circumstances. The ink that flows out from the pen tip adheres to the paper fibers together with the pigment and vehicle (aqueous medium other than the pigment, resin solution, etc.), and at the same time penetrates in the plane direction of the fibers and in the depths of the fibers. The aggregate state of paper fibers is never uniform, and if you look at the details, it has a very uneven structure, and like water flowing to a low place, it concentrates and penetrates into the concavities between the fibers. . When using CB alone, a large amount of CB is aggregated and deposited in the recesses, and since CB is an extremely fine particle, a large amount of CB permeates into the fibers in the recesses, resulting in a very small amount of CB attached to the convex parts of the fibers. Therefore, the coloring power of the CB flowing out from the pen tip cannot be fully exhibited in the entire written line, and the degree of blackness is low.

[0016] The present invention contains the earthy graphite,
Its shape is plate-like (scale-like), and its average particle diameter is 1.
Although it is less than 0 μm, it is considerably larger than CB, and compared to spherical CB, it does not penetrate into paper fibers, and has a very high probability of adhering to a flat surface, so CB can be concentrated in concave areas and deep into the fibers. Since it has a high effect of preventing the penetration of graphite and has a high blackness compared to graphite, it is presumed that it is possible to obtain a remarkable increase in the blackness of the written lines.

[0017]

EXAMPLES The present invention will be explained in more detail with reference to Examples below, but the present invention is not limited to these Examples in any way. (Example 1) <CB dispersion> Carbon black (MA100 Mitsubishi Kasei)
10.0% by weight water-soluble styrene acrylic resin (ammonia neutralized)
3.0 〃 Ethylene glycol

20.0 Preservatives

0.5
〃 purified water

Residual <Earth-like graphite dispersion> Earth-like graphite (average particle size 0.5 μm, Nippon Graphite Industries) 10.0% by weight Water-soluble acrylic resin (ammonia neutralized)
5.0 Ethylene glycol
15.0 Glycerin
5.0 〃
Preservative

0.5 Purified water

remainder

[0018]C
Dispersion B is made by dissolving a water-soluble resin in a mixture of aqueous ammonia, water, and ethylene glycol, adding carbon black to this, mixing and dispersing it in a bead mill, and then removing coarse particles in a centrifuge. A preservative and purified water were added and mixed to obtain the above composition. As an earthy graphite dispersion, a water-soluble resin was dissolved in an aqueous medium, earthy graphite with an average particle size of 0.5 μm and a purity of 99.5% by weight was added, and the mixture was charged into a ball mill, subjected to a dispersion treatment for 24 hours, and then After standing for a day and night, the supernatant was collected. 80% by weight of CB dispersion
A black aqueous ink composition for writing instruments was prepared by mixing the earthy graphite dispersion liquid at a ratio of 20% by weight, and the composition was filled into a plastic pen.

(Example 2) Carbon black (MCF88 Mitsubishi Kasei)
8.0% by weight earthy graphite (average particle size 0.5μm Nippon Graphite Industries)
2.0 Water-soluble styrene acrylic resin (ammonia neutralized) 3.
5 〃 Ethylene glycol

15.0 Glycerin

5.0 Preservatives

0.5
〃 purified water

The remaining water-soluble resin was dissolved in aqueous ammonia, ethylene glycol, and glycerin, and carbon black and earthy graphite were added thereto and mixed and dispersed in a bead mill. A preservative and purified water were added to this to obtain the above composition, and after standing for a day and night, the supernatant liquid was packed into the same plastic pen as in Example 1.

(Comparative Example 1) Carbon black (MA100 Mitsubishi Kasei)
16.0% by weight Water-soluble styrene acrylic resin (ammonia neutralized)
4.0 Ethylene glycol

15.0 Glycerin

5.0 〃
Preservative

0.5 Purified water

The rest of the dispersion was treated with a bead mill in the same manner as the CB dispersion of Example 1, coarse particles were removed with a centrifuge, and the composition was adjusted to the above composition, which was then filled into a plastic pen. The CB content in the ink composition was twice the 8% by weight of Examples 1 and 2. (Comparative Example 2) CB prepared in Example 1 as Comparative Example 2
The dispersion was simply packed into a plastic pen.

The plastic pens obtained in the above Examples and Comparative Examples were used to draw lines on high-quality paper using a plotter under certain conditions, and the drawn lines were analyzed using a color difference meter. The degree of blackness was calculated from the reflectance and expressed as the optical density D (the larger the value of the optical density D, the greater the degree of blackness, and if ΔD=0.02 or more, the difference in the degree of blackness could be visually determined). ). Table 1 below shows the results of measurements taken at the initial stage and after 3 months at room temperature. As mentioned above, the present invention can significantly increase the degree of blackness of written lines on paper, as is clear from the test results of the examples.

[0022]

Effects of the Invention Since the coloring agents of the ink composition of the present invention are CB and earthy graphite, both of which are black pigments, blurring of written lines is prevented, and there is no problem in light resistance and water resistance. We added CB to the limit that maintains the ink viscosity to ensure the amount of ink flowing out from the pen tip, and we also added high-purity graphite with a particle size of 1.0 μm or less, which has a high degree of blackness, so that the CB goes deep into the paper fibers. Coupled with the effect of preventing the penetration of the pen, it was possible to obtain a remarkable increase in the blackness of the written lines.

Claims (1)

[Claims] Claim 1: A water-based ink composition for writing instruments comprising a carbon black pigment, a dispersant, and an aqueous medium, further containing earthy graphite having an average particle diameter of 1.0 μm or less and a purity (carbon content) of 96% by weight or more. A black aqueous ink composition for writing instruments.