WO2016047434A1 - Water-based ink composition for writing instruments - Google Patents

Abstract

Provided is a water-based ink composition for writing instruments, said water-based ink for writing instruments containing oxidized cellulose and having suppressed non-uniformity of the viscosity distribution (viscosity differential) over time, excellent viscosity distribution stability over time, and excellent line quality. The water-based ink composition for writing instruments is characterized by at least containing 0.05-1.5% by mass of oxidized cellulose and 0.005-1% by mass of succinoglycan.

Description

Water-based ink composition for writing instruments

The present invention relates to a water-based ink composition for a writing instrument containing oxidized cellulose.

Conventionally, as a thickening agent exhibiting shear thinning used in ink compositions for writing instruments, natural systems, semi-synthetic systems obtained by chemically modifying natural products, and synthetic systems chemically synthesized from petrochemical raw materials are known. ing.

Among these, natural thickeners derived from cellulose are known as those obtained by physically finely processing cellulose itself, and powdered cellulose, fermented cellulose (bacterial cellulose), oxidized cellulose and the like are known. .
Examples of water-based ink compositions using these celluloses include: 1) an aqueous ink composition containing an alkali metal salt or ammonium salt of carboxymethyl cellulose (CMC) having a degree of etherification of 1.5 or more ( For example, see Patent Document 1) 2) Water-based ballpoint pen ink composition characterized by comprising at least water, a colorant, and fermented cellulose (for example, see Patent Document 2), 3) Oxidized cellulose (cellulose) having specific physical properties A water-based ink composition (for example, see Patent Document 3) containing at least one of a fiber), a colorant and a masking agent, and water is known.

However, the alkali metal salt or ammonium salt of CMC of Patent Document 1 has a high viscosity and does not improve the dispersion stability over time of pigments and the like. In addition, the fermented cellulose in the aqueous ballpoint pen ink composition of Patent Document 2 is composed of delicate fibrous particles, and has a dry-up performance by forming a soft resin film (cellulose fiber film) on the tip of the chip. In order to improve the ink viscosity, a conventional shear thinning agent (such as xanthan gum) is used in combination, and the dispersion stability of pigments and the like over time is not improved.
The water-based ink composition containing oxidized cellulose of Patent Document 3 is superior to conventional thickening / gelling agents, and is not affected by the temperature, colorant, hiding agent characteristics, etc. It has excellent dispersibility of the masking agent and prevents sedimentation separation during storage, but it has the property that non-uniform viscosity distribution (viscosity difference) tends to occur over time. At present, there is a problem in that sufficient viscosity distribution stability over time, and consequently dispersion stability over time, cannot be achieved.

On the other hand, the aqueous ink composition for writing instruments using succinoglycan as a thickener includes, for example, a coloring agent, succinoglycan, water and a water-soluble organic solvent as essential components, and water is 50% by weight or more. A water-based ink composition for a writing instrument containing an aqueous medium occupying the above (for example, see Patent Document 4) is known.
However, although the water-based ink composition using succinoglycan disclosed in Patent Document 4 exhibits excellent properties in terms of dispersion stability of particles, the combined use with oxidized cellulose and the viscosity distribution over time due to the combined use. There is no description or suggestion about the point where uniformity (difference in viscosity) does not occur.

JP-A-62-124170 (Claims, Examples, etc.) JP 2013-91730 A (Claims, Examples, etc.) JP 2013-181167 A (Claims, Examples, etc.) JP-A-6-88050 (Claims, Examples, etc.)

The present invention is to solve this problem in view of the above-mentioned problems of the prior art and the current situation, and is a non-uniformity in viscosity distribution over time, which is a problem of aqueous ink compositions for writing instruments when oxidized cellulose is used ( It is an object of the present invention to provide a water-based ink composition for a writing instrument that suppresses the difference in the upper and lower viscosity), is excellent in stability of viscosity distribution over time, and is excellent in drawing quality.

As a result of intensive studies in view of the above-described conventional problems and the like, the present inventors can obtain a water-based ink composition for a writing instrument for the above purpose by containing specific amounts of specific polysaccharides together with oxidized cellulose. As a result, the present invention has been completed.

That is, the present invention resides in the following (1) to (3).
(1) A water-based ink composition for a writing instrument comprising 0.05 to 1.5% by mass of oxidized cellulose and 0.005 to 1% by mass of succinoglycan.
(2) The aqueous ink composition for a writing instrument as described in (1) above, wherein the mass ratio of the oxidized cellulose and the succinoglycan is 30: 1 to 1: 2.
(3) A writing instrument comprising the water-based ink composition for a writing instrument described in (1) or (2) above.

According to the present invention, the non-uniformity of viscosity distribution over time (viscosity difference), which is a problem of the oxidized cellulose-containing aqueous ink composition, is suppressed, and the viscosity distribution stability over time is excellent, and the drawn line quality is improved. A water-based ink composition for a writing instrument that is superior to the above is provided.

Hereinafter, embodiments of the present invention will be described in detail.
The aqueous ink composition for a writing instrument of the present invention is characterized by containing 0.05 to 1.5% by mass of oxidized cellulose and at least 0.005 to 1% by mass of succinoglycan.

<Oxidized cellulose>
The oxidized cellulose used in the present invention has cellulose I type crystal structure and constitutes cellulose [(C ₆ H ₁₀ O ₅ ) n: a natural polymer in which a number of β-glucose molecules are linearly polymerized by glycosidic bonds]. There is no particular limitation as long as a part of the hydroxyl group (—OH group) of β-glucose is modified with at least one functional group of an aldehyde group (—CHO) and a carboxyl group (—COOH group). Examples thereof include those obtained by oxidizing at least the hydroxyl group (—OH group) at the C ₆ position of glucose to an aldehyde group (—CHO) and a carboxyl group (—COOH group).

The oxidized cellulose used in the present invention is a fiber obtained by surface-oxidizing a cellulose solid raw material derived from a natural product having an I-type crystal structure to a nano size. In general, cellulose derived from natural products, which is a raw material, has almost no exception, so that nanofibers called microfibrils are multi-bundled to form a higher order structure. It is something that cannot be done. In the oxidized cellulose of the present invention, a part of the hydroxyl groups of the cellulose fiber is oxidized to introduce aldehyde groups and carboxyl groups, and the hydrogen bonds between the surfaces, which are the driving force of the strong cohesive force between the microfibrils, are weakened and dispersed. However, it is refined to nano size.

In the present invention, the effect of the present invention can be exerted by using the above-mentioned oxidized cellulose having the above physical properties and the specific carboxymethyl cellulose or a salt thereof described later. Preferably, the number average fiber diameter of the oxidized cellulose is 2 to 150 nm. Is desirable.
From the viewpoint of dispersion stability, it is more preferable that the number average fiber diameter is 3 to 80 nm. By making the number average fiber diameter of this oxidized cellulose 2 nm or more, the function as a dispersion medium is exhibited, and conversely, by making the number average fiber diameter 150 nm or less, the dispersion stability of the cellulose fiber itself is further improved. be able to.
In the present invention, the number average fiber diameter can be measured, for example, as follows. That is, a sample diluted with water added to cellulose fibers is dispersed, cast onto a carbon film-coated grid that has been subjected to a hydrophilic treatment, and this is observed with a transmission electron microscope (TEM). From the obtained image, The number average fiber diameter can be measured and calculated.
The cellulose constituting the specific cellulose fiber has a natural product-derived type I crystal structure, for example, in the diffraction profile obtained by wide-angle X-ray diffraction image measurement, in the vicinity of 2 theta = 14 to 17 °. It can be identified by having typical peaks at two positions near 2 theta = 22 to 23 °.

The production of oxidized cellulose used in the present invention is, for example, an oxidation process in which natural cellulose is used as a raw material, an N-oxyl compound is used as an oxidation catalyst in water, and the natural cellulose is oxidized by acting a co-oxidant to obtain a reactant fiber. It can be obtained by at least three steps: a reaction step, a purification step for obtaining a reactant fiber impregnated with water by removing impurities, and a dispersion step for dispersing the reactant fiber impregnated with water in a solvent.

In the oxidation reaction step, a dispersion liquid in which natural cellulose is dispersed in water is prepared. Here, natural cellulose means purified cellulose isolated from cellulose biosynthetic systems such as plants, animals, and bacteria-producing gels. More specifically, softwood pulp, hardwood pulp, cotton pulp such as cotton linter and cotton lint, non-wood pulp such as straw pulp and bagasse pulp, BC, cellulose isolated from sea squirt, and seaweed The cellulose can be exemplified, but is not limited thereto. Natural cellulose is preferably subjected to a treatment for increasing the surface area such as beating, whereby the reaction efficiency can be increased and the productivity can be increased. Furthermore, when natural cellulose that has been isolated and purified and stored in Never Dry is used, the microfibril bundles are likely to swell. The average fiber diameter can be reduced, which is preferable.
The dispersion medium of natural cellulose in the reaction is water, and the concentration of natural cellulose in the reaction aqueous solution is arbitrary as long as the reagent can sufficiently diffuse, but usually about 5% with respect to the weight of the reaction aqueous solution. It is as follows.

In addition, many N-oxyl compounds that can be used as an oxidation catalyst for cellulose have been reported (“Cellulose” Vol. 10, 2003, pages 335 to 341, using “TEMPO derivatives by I. Shibata and A. Isogai). The article entitled “Catalyzed Oxidation of Cellulose: HPSEC and NMR Analysis of the Oxidation Products”), in particular, TEMPO (2,2,6,6-tetramethyl-1-piperidine-N-oxyl), 4-acetamido-TEMPO, 4-Carboxy-TEMPO and 4-phosphonooxy-TEMPO are preferable in the reaction rate at room temperature in water. A catalytic amount is sufficient for the addition of these N-oxyl compounds, preferably 0.1 to 4 mmol / l, more preferably 0.2 to 2 mmol / l.

As the co-oxidant, hypohalous acid or a salt thereof, hypohalous acid or a salt thereof, perhalogen acid or a salt thereof, hydrogen peroxide, a perorganic acid, and the like can be used in the present invention. Hypohalites such as sodium hypochlorite and sodium hypobromite. When sodium hypochlorite is used, it is preferable in terms of the reaction rate to advance the reaction in the presence of an alkali metal bromide such as sodium bromide. The addition amount of the alkali metal bromide is about 1 to 40 times mol, preferably about 10 to 20 times mol for the N-oxyl compound. In general, the amount of co-oxidant added is preferably in the range of about 0.5 to 8 mmol with respect to 1 g of natural cellulose, and the reaction is completed within about 5 to 120 minutes and at most 240 minutes.
The pH of the aqueous reaction solution is preferably maintained in the range of about 8-11. The temperature of the aqueous solution is arbitrary at about 4 to 40 ° C., but the reaction can be performed at room temperature, and the temperature is not particularly required to be controlled.

In the refining process, reactant fibers and compounds other than water contained in the reaction slurry such as unreacted hypochlorous acid and various by-products are removed from the system. Since it is not dispersed evenly to the nanofiber unit, a normal purification method, that is, washing with water and filtration are repeated to obtain a dispersion of high-purity (99% by mass or more) reactant fiber and water. As the purification method in the purification step, any apparatus can be used as long as it can achieve the above-described object, such as a method using centrifugal dehydration (for example, a continuous decanter).
The aqueous dispersion of the reactant fibers thus obtained has a solid content (cellulose) concentration in the range of approximately 10% to 50% by mass in the squeezed state. In the subsequent step, when dispersing in nanofibers, a solid content concentration higher than 50% by mass is not preferable because extremely high energy is required for dispersion.

Furthermore, in the present invention, a dispersion of oxidized cellulose can be obtained by dispersing the reaction fiber (water dispersion) impregnated with water obtained in the above-described purification step in a solvent and performing a dispersion treatment, It can be set as the oxidized cellulose used by drying this dispersion.
Here, the solvent as the dispersion medium is usually preferably water, but in addition to water, alcohols that are soluble in water depending on the purpose (methanol, ethanol, isopropanol, isobutanol, sec-butanol, tert-butanol, methyl) Cellosolve, ethyl cellosolve, ethylene glycol, glycerin, etc.), ethers (ethylene glycol dimethyl ether, 1,4-dioxane, tetrahydrofuran, etc.), ketones (acetone, methyl ethyl ketone), N, N-dimethylformamide, N, N-dimethylacetamide Dimethyl sulfoxide or the like may be used. Moreover, these mixtures can also be used conveniently. Furthermore, when diluting and dispersing the dispersion of the above-described reactant fibers with a solvent, the dispersion is gradually added by adding a solvent little by little. You may be able to get Due to operational problems, the dispersion conditions can be selected so that the state after the dispersion step is a viscous dispersion or gel. The oxidized cellulose used may be a dispersion of the above oxidized cellulose.
The oxidized cellulose that can be used in the present invention is not limited to the above-described production method and the like, and some of the hydroxyl groups (—OH groups) of the cellulose are aldehyde groups (—CHO) and carboxyl groups (—COOH). The production method is not particularly limited as long as it is modified with at least one functional group.

<Water-based ink composition for writing instruments>
The aqueous ink composition for a writing instrument according to the present invention is characterized by containing at least 0.05 to 1.5% by mass of oxidized cellulose and 0.005 to 1% by mass of succinoglycan. Used as an ink composition for a writing instrument such as a ballpoint pen.
In the present invention, the content (solid content) of the oxidized cellulose is 0.05 to 1.5% by mass (hereinafter simply referred to as “%”), preferably in the aqueous ink composition for writing instruments (total amount). Is preferably 0.1 to 1.0%.
If the content of oxidized cellulose is less than 0.05%, sufficient thickening action cannot be obtained, and precipitation of solids such as pigments may occur over time. On the other hand, if the content exceeds 1.5% Since the viscosity is increased, the phenomenon of broken lines in writing lines and ink ejection failure may occur.

Succinoglycan used as a thickener of the present invention is a kind of polysaccharide derived from microorganisms. In addition to saccharide units derived from galactose and glucose, succinic acid and pyruvic acid and acetic acid as an optional component or these It contains units derived from acid salts.
Examples of succinoglycans that can be used include commercially available Leozan SH (manufactured by RHODIA). In the present invention, “succinoglycan” includes purified products and modified products.

The content of these succinoglycans is 0.005 to 1%, preferably 0.01 to 1%, based on the total amount of the aqueous ink composition.
When the content is less than 0.005%, the effect of the present invention is not sufficiently exhibited. On the other hand, when the content exceeds 1%, the rheological properties are inhibited, which is not preferable.
In the present invention, from the viewpoint of further improving the effects of the present invention, it is preferable that the mass ratio of the oxidized cellulose and the succinoglycan is 30: 1 to 1: 2, more preferably 25: 1. It is desirable to set it to ˜1: 2.

The aqueous ink composition for a writing instrument of the present invention contains at least a colorant and a water-soluble solvent in addition to the oxidized cellulose and succinoglycan.
Colorants that can be used include pigments and / or water-soluble dyes. There is no restriction | limiting in particular about the kind of pigment, Arbitrary things can be used from the inorganic type and organic type pigment conventionally used for writing instruments, such as a water-based ballpoint pen.

Examples of inorganic pigments include carbon black and metal powder.
Examples of organic pigments include azo lakes, insoluble azo pigments, chelate azo pigments, phthalocyanine pigments, perylene and perinone pigments, anthraquinone pigments, quinacridone pigments, dye lakes, nitro pigments, and nitroso pigments. Specifically, phthalocyanine blue (C.I. 74160), phthalocyanine green (C.I. 74260), Hansa Yellow 3G (C.I. 11670), disazo yellow GR (C.I. 21100), permanent red 4R (C.I. 12335), brilliant carmine 6B (C.I. 15850), quinacridone red (C.I. 46500), etc. can be used.
Also, a plastic pigment composed of particles of styrene or acrylic resin can be used. Further, the hollow resin particles having voids inside the particles can be used as white pigments, or resin particles (pseudo pigments) dyed with a basic dye described later having excellent color development and dispersibility.

As the water-soluble dye, any of direct dyes, acid dyes, food dyes, and basic dyes can be used.
Examples of the direct dye include C.I. I. Direct Black 17, 19, 19, 22, 32, 38, 51, 71, C.I. I. Direct yellow 4, 26, 44, 50, C.I. I. Direct Red 1, 4, 23, 31, 37, 39, 75, 80, 81, 83, 225, 226, 227, C.I. I. Direct Blue 1, 15, 71, 86, 106, 119 and the like.
Examples of the acid dye include C.I. I. Acid Black 1, 2, 24, 26, 31, 31, 52, 107, 109, 110, 119, 154, C.I. I. Acid Yellow 7, 17, 19, 23, 25, 29, 38, 42, 49, 61, 72, 78, 110, 127, 135, 141, the same 142, C.I. I. Acid Red 8, 9, 9, 14, 26, 27, 35, 37, 51, 52, 57, 82, 87, 92, 94, 115, 129, 131, 186, 249, 254, 265, 276, C.I. I. Acid Violet 18, 17 and C.I. I. Acid Blue 1, 7, 9, 22, 23, 25, 40, 41, 43, 62, 78, 83, 90, 93, 103, 112, the same 113, 158, C.I. I. Acid Green 3, 9, 16, 25, 27 and the like.
Most of the food dyes are directly contained in the acid dyes or acid dyes. I. Food yellow 3 is mentioned.
Examples of basic dyes include C.I. I. Basic Yellow 1, 2 and 21, C.I. I. Basic Orange 2, 14, 32, C.I. I. Basic Red 1, 2, 9, 9, 14 C.I. I. Basic Brown 12, Basic Black 2, 8 and the like.
Examples of the resin particles dyed with a basic dye include fluorescent pigments obtained by dyeing acrylonitrile copolymer resin particles with a basic fluorescent dye. Specific product names include Sinloi Color SF Series (Sinloihi Co., Ltd.), NKW and NKP Series (Nippon Fluorochemicals Co., Ltd.).

These colorants may be used alone or in combination of two or more. The content in the total amount of the aqueous ink composition for writing instruments is usually 0.5 to 30%, preferably 1 It is in the range of ~ 15%.
If the content of this colorant is less than 0.5%, coloring may be weak or the hue of the handwriting may not be known. On the other hand, if it exceeds 30%, writing defects may occur. This is not preferable.

Examples of water-soluble solvents that can be used include glycols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, polyethylene glycol, 3-butylene glycol, thiodiethylene glycol, glycerin, ethylene glycol monomethyl ether, diethylene glycol monomethyl ether, and the like. These can be used alone or in combination. The content of the water-soluble solvent is preferably 5 to 40% in the total amount of the water-based ink composition for writing instruments.

The water-based ink composition for a writing instrument of the present invention includes the above-mentioned oxidized cellulose, succinoglycan, colorant, water-soluble solvent, and water as a balance (tap water, purified water, distilled water, ion-exchanged water, pure water) In addition to water and the like, a dispersant, a lubricant, a pH adjuster, a rust inhibitor, a preservative, a fungicide, and the like can be appropriately contained as long as the effects of the present invention are not impaired.

When a pigment is used as the colorant, it is preferable to use a dispersant. This dispersant acts on the pigment surface to improve the affinity with water and to stably disperse the pigment in water. Nonionic, anionic surfactants and water-soluble resins are used. A water-soluble polymer is preferably used.
Lubricants include nonionics such as fatty acid esters of polyhydric alcohols, higher fatty acid esters of sugars, polyoxyalkylene higher fatty acid esters, and alkyl phosphates, which are also used in pigment surface treatment agents, and alkyl sulfonic acids of higher fatty acid amides. Examples thereof include salts, anionic compounds such as alkyl allyl sulfonates, polyalkylene glycol derivatives, fluorosurfactants, and polyether-modified silicones.

Examples of pH adjusters include ammonia, urea, monoethanolamine, diethanolamine, triethanolamine, sodium tripolyphosphate, sodium carbonate, and alkali metal salts of phosphoric acid and alkali metal hydrates such as sodium hydroxide. Etc. In addition, as rust preventives, benzotriazole, tolyltriazole, dicyclohexylammonium nitrite, saponins, etc., as antiseptics or fungicides, phenol, sodium omadin, sodium benzoate, benzimidazole compounds, etc. Can be mentioned.

The water-based ink composition for writing instruments of the present invention is a combination of the above oxidized cellulose, succinoglycan, colorant, water-soluble solvent, and other components as appropriate according to the application of the ink for writing instruments (for ballpoint pens and marking pens). The aqueous ink composition for writing instruments is prepared by stirring and mixing with a stirrer such as a homomixer, homogenizer or disper, and if necessary, by removing coarse particles in the ink composition by filtration or centrifugation. be able to.
For an aqueous ballpoint pen, the aqueous ink composition for a writing instrument can be prepared by filling an aqueous ballpoint pen provided with balls having a diameter of 0.18 to 2.0 mm.
The aqueous ballpoint pen to be used is not particularly limited as long as it has a ball having a diameter in the above-mentioned range. In particular, the water-based ink composition is filled in an ink storage tube of a polypropylene tube, and a tip stainless tip (ball is A refilled water-based ballpoint pen with a super steel alloy) is desirable.

The method for producing a water-based ink composition for a writing instrument of the present invention can be produced without any particular change compared to other methods for producing a water-based ink composition.
That is, the water-based ink composition for a writing instrument of the present invention includes a component such as a mixer, and a bead mill, a homomixer, a homogenizer, and a high-pressure homogenizer that can apply strong shearing to the components including the above-described oxidized cellulose and succinoglycan. A thixotropic ink (for example, a gel ink water-based ballpoint pen ink) can be produced by mixing and stirring by setting the stirring condition to a suitable condition using an ultrasonic homogenizer, a high-pressure wet medialess atomizer, or the like. it can.
Further, the pH (25 ° C.) of the aqueous ink composition for a writing instrument of the present invention is adjusted to 5 to 10 by a pH adjuster or the like from the viewpoints of usability, safety, stability of the ink itself, and matching with the ink container. It is preferably adjusted, and more preferably 6 to 9.5.

The water-based ink composition for a writing instrument of the present invention is mounted on a ballpoint pen, a marking pen or the like having a pen tip such as a ballpoint pen tip, a fiber tip, a felt tip, or a plastic tip.
As the ballpoint pen in the present invention, the water-based ink composition for writing instruments having the above composition is accommodated in a ballpoint pen ink container (refill), and is not compatible with the water-based ink composition housed in the ink container. Examples of the ink follower include substances having a small specific gravity with respect to the water-based ink composition, such as polybutene, silicone oil, mineral oil, and the like.
The structure of the ballpoint pen and the marking pen is not particularly limited. For example, a collector structure (ink holding mechanism) in which the shaft tube itself is used as an ink container and the water-based ink composition for a writing instrument having the above configuration is filled in the shaft tube. It may be a direct liquid ballpoint pen or a marking pen provided.

In the water-based ink composition for a writing instrument of the present invention configured as described above, even if the oxidized cellulose used has a low viscosity of 0.05 to 1.5% in the water-based ink composition for a writing instrument, the viscosity is high. As a thickening and gelling agent for water-based ink compositions for writing instruments, it exhibits a rheology control effect in a smaller amount than conventional fine cellulose and xanthan gum, and also exhibits this oxidation property. When cellulose is used, the viscosity distribution over time is suppressed by adding 0.005 to 1% of succinoglycan in the ink composition. A water-based ink composition for a writing instrument having excellent stability and line drawing quality can be obtained.

Next, the present invention will be described in more detail with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[Examples 1 to 6 and Comparative Examples 1 to 4]
Using oxidized cellulose having the following physical properties, a predetermined amount of each water-based ink composition for a writing instrument is mixed with a composition shown in Table 1 below, specifically, a composition such as succinoglycan and a colorant. It was prepared by changing the stirring conditions (shearing force, pressure, stirring time) appropriately using a chemical conversion apparatus (Yoshida Kikai Kogyo Co., Ltd., Nanovaita), mixing and stirring by a wet method, and filtering with a 10 μm bag filter. The pH at room temperature (25 ° C.) of each water-based ink composition for writing instruments was measured with a pH meter (manufactured by HORIBA), and was within the range of 7.9 to 8.2.

Viscosity values of the aqueous ink compositions for writing instruments obtained in Examples 1 to 6 and Comparative Examples 1 to 4 were measured by the following method.
When measuring the viscosity value, it is stored for 1 month at room temperature in a glass bottle 2.5 × 2.5 × 5 cm [ink filling height (height of the top surface filled with ink from the bottom in the glass bottle): 4 cm]. After that, use a syringe to remove the ink near the top of the glass bottle (about 0.5 cm from the top of the ink filling height), and in the same way as above, the ink near the bottom of the glass bottle (about 0.5 cm from the bottom of the ink filling height) The viscosity value at a shear rate of 38.3 s ⁻¹ at 25 ° C. was measured with an EMD viscometer (manufactured by Tokyo Keiki Co., Ltd.). In the present invention, the favorable viscosity distribution is preferably such that, under the above conditions, the upper / lower ratio (up / down) of the viscosity is in the range of 0.95 to 1.6, preferably 0.95 to 1.3. Those in the range are particularly preferred. The evaluation was made according to the following judgment (evaluation) criteria.
Judgment (evaluation) criteria:
○: Viscosity ratio is 0.95 to 1.3 or less △: Viscosity ratio is more than 1.3 and less than 1.6 ×: Viscosity ratio is less than 0.95 or more than 1.6 With respect to the aqueous ink compositions for writing instruments obtained in Examples 1 to 6 and Comparative Examples 1 to 4, an aqueous ballpoint pen was prepared by the following method, and the drawing quality (threading property) was evaluated by the following evaluation method. It was.
These results are shown in Table 1 below.

[Oxidized cellulose used]
After dispersing dry sulphite bleached softwood pulp equivalent to 2 g dry weight (mainly consisting of fibers with a fiber diameter greater than 1000 nm), 0.025 g TEMPO and 0.25 g sodium bromide in 150 ml water, A 13% by mass sodium hypochlorite aqueous solution was added with sodium hypochlorite so that the amount of sodium hypochlorite was 2.5 mmol with respect to 1 g of pulp to initiate the reaction. During the reaction, a 0.5 M aqueous sodium hydroxide solution was added dropwise to keep the pH at 10.5. When the pH no longer changes, the reaction is considered to be complete, the reaction product is filtered through a glass filter, washed with a sufficient amount of water and filtered five times to impregnate 25% by weight of water with a solid content of 25% by mass. Reactant fibers were obtained.
Next, water was added to the reactant fiber to make a 2% by mass slurry, which was then treated with a rotary blade mixer for about 5 minutes. Since the viscosity of the slurry significantly increased with the treatment, water was gradually added and the dispersion treatment with the mixer was continued until the solid content concentration became 0.15% by mass. The dispersion of oxidized cellulose having a cellulose concentration of 0.15% by mass thus obtained was subjected to removal of suspended solids by centrifugation, and then the concentration was adjusted with water to give a cellulose concentration of 0.1% by mass. A transparent and slightly viscous dispersion of oxidized cellulose was obtained. Oxidized cellulose obtained by drying this dispersion was used. In addition, the oxidized cellulose shown to each Example etc. of Table 1 displays what was manufactured above by solid content concentration of each Example etc.

The number average fiber diameter of the oxidized cellulose obtained above was confirmed and measured by the following method.
<Number average fiber diameter>
The number average fiber diameter of the oxidized cellulose was measured as follows.
That is, a sample diluted with water added to oxidized cellulose was dispersed at 12000 rpm for 15 minutes using a homomixer, then cast on a carbon film-coated grid that had been subjected to a hydrophilic treatment, and this was measured with a transmission electron microscope (TEM). The number average fiber diameter was measured and calculated from the observed and obtained images. As a result, the number average fiber diameter was about 140 nm.

<Confirmation of cellulose I type crystal structure>
It was confirmed as follows that the oxidized cellulose used had an I-type crystal structure.
That is, in the diffraction profile obtained by wide-angle X-ray diffraction image measurement, since there are typical peaks at two positions near 2 theta = 14 to 17 ° and 2 theta = 22 to 23 °, the type I crystal It was confirmed to have a structure.

(Production of water-based ballpoint pen)
A water-based ballpoint pen was produced using each ink composition obtained above. Specifically, using a shaft of a ballpoint pen [Mitsubishi Pencil Co., Ltd., trade name: Signo UM-100], an inner diameter of 4.0 mm, a length of 113 mm, an ink containing tube made of polypropylene, and a stainless tip (a cemented carbide ball, A water ballpoint pen is manufactured by filling each water-based ink with a refill consisting of a joint connecting the receiving tube and the tip with a ball diameter of 0.7 mm, and an ink follower mainly composed of mineral oil at the rear end of the ink. did.

[Evaluation method of drawing quality (spinning)]
Using this water-based ballpoint pen, “GDP” was written on the manuscript paper, and evaluation was performed based on the following evaluation criteria.
Evaluation criteria:
A: There is no problem of thread-like dirt on the drawn line, and it is recognized as an excellent drawn line.
○: Slight thread-like stains are observed on the drawn lines.
Δ: A small amount of thread-like dirt is observed on the drawn line.
X: A large amount of thread-like dirt is recognized in the drawn line.

As is apparent from the results in Table 1 above, the aqueous ink compositions for writing instruments of Examples 1 to 6 according to the present invention maintain satisfactory uniformity of viscosity distribution over time and are excellent in line drawing quality. It has been found.

An aqueous ink composition for writing instruments suitable for writing instruments such as water-based ballpoint pens and marking pens can be obtained.

Claims (3)

1. A water-based ink composition for a writing instrument comprising 0.05 to 1.5% by mass of oxidized cellulose and 0.005 to 1% by mass of succinoglycan.
2. The water-based ink composition for a writing instrument according to claim 1, wherein the mass ratio of the oxidized cellulose to the succinoglycan is 30: 1 to 1: 2.
3. A writing instrument comprising the water-based ink composition for a writing instrument according to claim 1 or 2 mounted thereon.