JP2017105907A - Aqueous ink composition for writing instrument - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an aqueous ink composition for writing instrument high in viscosity recoverability, having no ink dripping and no oozing of drawn lines and suitable for writing instrument such as aqueous ball point pen, marking pen.SOLUTION: There is provided an aqueous ink composition for writing instrument containing at least vegetable cellulose nanofiber without conducting an oxidation treatment on the same and having number average fiber short diameter of the cellulose nanofiber of 10 to 200 nm.SELECTED DRAWING: None

Description

  The present invention relates to an aqueous ink composition for a writing instrument containing vegetable cellulose nanofibers that have not been oxidized.

Conventionally, natural thickeners derived from cellulose have been used in ink compositions for writing instruments such as ballpoint pens and marking pens.
Examples of the aqueous ink composition using cellulose 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, 2) Water-based ballpoint pen ink composition comprising at least water, a colorant, and fermented cellulose (see, for example, Patent Document 2, 3) Oxidized cellulose (cellulose fiber) having specific physical properties A water-based ink composition containing at least one of a colorant and a masking agent and water (for example, see Patent Document 3), 4) containing 0.05 to 1.5% by mass of oxidized cellulose A water-based ink composition for a writing instrument (e.g., having an intrinsic viscosity value of 10 mPa · s or less derived from the Casson equation) Patent Document 4) it is known by the present applicant.

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 Documents 3 and 4 is superior to conventional thickening and gelling agents, and is not affected by temperature, colorant, hiding agent characteristics, etc. Specific rheological properties such that the decrease in viscosity with respect to stress is large can be obtained. On the other hand, once the viscosity has dropped, it has the property that it takes time to recover even if the shear stress is removed, so a standing period is required until the target viscosity is reached during ink production. In addition, when the viscosity recovery is not sufficient, ink dripping and blurring of the drawn lines occur in many cases.

JP-A-62-124170 (Claims, Examples, etc.) JP 2013-91730 A (Claims, Examples, etc.) JP 2013-181167 A (Claims, Examples, etc.) JP-A-2015-67722 (Claims, Examples, etc.)

  The present invention has been made in view of the above-mentioned problems of the prior art and the current situation, and is intended to solve this problem. It improves viscosity recovery, which is a problem of a water-based ink composition for writing instruments when oxidized cellulose is used. It is an object of the present invention to provide a water-based ink composition for writing tools suitable for writing tools such as water-based ballpoint pens and marking pens that have no property and no blurring of drawn lines.

  As a result of intensive studies in view of the above-described conventional problems, the present inventor has found that a water-based ink composition for a writing instrument can be obtained by containing cellulose nanofibers having specific properties. The 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, characterized in that it contains at least vegetable cellulose nanofibers not subjected to oxidation treatment, and the cellulose nanofibers have a number average fiber short axis of 10 to 200 nm.
(2) The aqueous ink composition for a writing instrument as described in (1) above, further comprising at least one selected from carboxymethylcellulose or a salt thereof and a polysaccharide.
(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, a water-based ink composition for a writing instrument suitable for a writing instrument such as a water-based ballpoint pen and a marking pen, which has high viscosity recoverability, no ink dripping property, no bleeding of writing lines, and a writing instrument equipped with the same. Provided.

Hereinafter, embodiments of the present invention will be described in detail.
The water-based ink composition for a writing instrument according to the present invention contains at least vegetable cellulose nanofibers not subjected to an oxidation treatment, and the number average fiber short diameter of the cellulose nanofibers is 10 to 200 nm. It is.

<Plant cellulose nanofiber>
The vegetable cellulose nanofiber used in the present invention is a vegetable cellulose nanofiber not subjected to oxidation treatment, and the cellulose nanofiber uses a number average fiber short axis of 10 to 200 nm.
The vegetable cellulose nanofibers of the present invention are 1) not oxidized, 2) vegetable cellulose nanofibers, and 3) the number average fiber short axis of the cellulose nanofibers is 10 to 200 nm. It is necessary to be.

In the present invention, “not oxidized” means 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]. The functional group of a constituent component such as glucose is refined to a nano size by physical treatment or the like without performing oxidation treatment. In general, oxidized cellulose is obtained by surface oxidation of a cellulose solid raw material derived from a natural product having an I-type crystal structure. Specifically, a part of β-glucose hydroxyl group (—OH group) constituting cellulose is converted to an aldehyde group (—CHO group). ) And at least one functional group of a carboxyl group (—COOH group). In the present invention, nanofibers called microfibrils are bundled to take a higher order structure without performing an oxidation treatment. The plant cellulose is refined to nano size.

  In the present invention, “vegetable” is obtained by aeration-stirring culture of cellulose-producing bacteria such as subspecies of acetic acid bacteria in an appropriate medium, and separating and recovering the cellulose fibers produced outside the cells. It distinguishes it from fermented cellulose. Note that fermented cellulose has a bulky portion called terminal complex (TC), which causes clogging of writing utensils such as ballpoint pens and sign pens, and is opaque and is not suitable for highly transparent inks. It is.

  The plant cellulose nanofiber of the present invention is obtained from a cellulose substrate such as plant cellulose purified from wood, bamboo, etc., and cellulose derivatives such as crystalline cellulose and water-insoluble carboxymethyl cellulose, as will be described later. The obtained plant cellulose is obtained by a treatment such as high-pressure dispersion. In general, the plant-derived cellulose derived from the above natural product, which is the raw material, almost always has a high-order structure with many bundles of nanofibers called microfibrils. Cannot be dispersed. In the vegetable cellulose nanofiber of the present invention, a strong cohesive force between microfibrils is weakened by a treatment such as high-pressure dispersion, and the dispersion treatment is performed to refine the nanofiber. By this treatment, the fiber becomes smaller and a difference appears in the minor axis.

In the present invention, it is necessary that the plant-derived cellulose nanofibers have a number average fiber short diameter of 10 to 200 nm. By using a short diameter in this range, the effects of the present invention can be exhibited.
In the present invention, the “number average fiber short diameter” means a value (n: 10 × 5 = 50) obtained by measuring the fiber widths at any five locations for 10 fibers and averaging them. is there. This number average fiber short diameter can be measured, for example, as follows. That is, a sample obtained by adding water to cellulose nanofiber (cellulose fiber) and dispersing it is dispersed and cast on a carbon film-coated grid that has been hydrophilized, and this is observed with a transmission electron microscope (TEM). From the obtained image, the number-average fiber short diameter can be measured and calculated.
By making the number average fiber short axis of the vegetable cellulose nanofibers 10 nm or more, the function as a dispersion medium is exhibited, and conversely, by making the number average fiber short diameter 200 nm or less, the cellulose fibers themselves are dispersed. Stability can be further improved.

Examples of the production of plant cellulose nanofibers used in the present invention include plant cellulose purified from wood, bamboo, or pulp thereof, and crystalline cellulose or water obtained from plant cellulose. Plant cellulose (dispersion) obtained from a cellulose substrate such as insoluble carboxymethylcellulose (CMC) or its cellulose derivative (sodium salt) is refined by high-pressure dispersion treatment using a high-pressure homogenizer or the like ( The method of manufacturing the cellulose nanofiber by defibration is mentioned.
Examples of plant cellulose refined from wood, bamboo, or these pulps include, for example, softwood pulp, hardwood pulp, cotton pulp such as cotton linter and cotton lint, straw pulp and bagasse pulp, etc. Examples include cellulose isolated from wood pulp and the like, but are not limited thereto. These celluloses can preferably be further refined by increasing the surface area such as beating, and the productivity can be increased. Furthermore, when plant cellulose is used that has been stored in a dry dry state after isolation and purification, the microfibril bundles are likely to swell. The number average fiber minor axis after the treatment can be reduced, which is preferable.
The crystalline cellulose, carboxymethyl cellulose (CMC), or cellulose derivative thereof is not particularly limited as long as the raw material is processed using plant cellulose, and the target cellulose nanofiber is further obtained using a commercially available product. It can be.

Examples of the apparatus used for the high-pressure dispersion treatment include, for example, a high-pressure wet medialess atomizer (Nanovaita, manufactured by Yoshida Machine Industry), a wet atomizer (Starburst, manufactured by Sugino Machine), and a high-pressure emulsifier / disperser (BERYU). Can be used.
Further, before the above high-pressure dispersion treatment or high-pressure injection treatment, those that have been pulverized by a disk mill or the like by a wet method or the like may be used. Cellulose suspension concentration (for example, solid content concentration of 0.2 to 10% by mass), as well as the processing conditions of each device, specifically, the number of times and time (for example, 1 to 15 times), By adjusting the temperature (for example, 20 ° C. to 200 ° C.), the pressure (for example, 100 to 250 MPa), the speed of injection, etc. (for example, 100 to 1000 m / s), etc. Cellulose nanofibers having an average fiber short diameter (10 to 200 nm) will be obtained.

  Moreover, the method of manufacturing a vegetable cellulose nanofiber by the underwater counter collision method (ACC) using the collision of the opposing high-pressure water flow is mentioned. This method is a technology in which plant-derived natural cellulose fibers suspended in water are simultaneously separated into two opposing chambers, and are jetted from both nozzles toward one point at high speed to cause collision. By changing the collision speed, the number of collisions, etc., cellulose nanofibers having a suitable number average fiber short diameter (10 to 200 nm) can be obtained.

  The vegetable cellulose nanofiber that can be used in the present invention is not limited to the above-described production method and the like, is not subjected to the oxidation treatment described above, is a vegetable cellulose nanofiber, and the cellulose nanofiber. If the number average fiber short axis of the fiber is 10 to 200 nm, the production method is not particularly limited. Preferably, cellulose nanofibers obtained by high-pressure dispersion treatment are desirable from the viewpoint of cost, workability, versatility, and the like. Further, the cellulose nanofibers obtained by the above high-pressure dispersion treatment and the like are aqueous dispersions, and this dispersion can be dried to obtain vegetable cellulose nanofibers intended for use in the present invention. Otherwise, the cellulose nanofiber dispersion may be used as it is.

<Water-based ink composition for writing instruments>
The aqueous ink composition for a writing instrument according to the present invention is characterized in that it contains at least plant cellulose nanofibers having a number average fiber short diameter within the above range that is not subjected to the oxidation treatment. Used as an ink composition for a writing instrument such as a ballpoint pen.
In the present invention, the content (solid content) of vegetable cellulose nanofibers having the above characteristics is preferably 0.05 to 3% by mass (hereinafter simply referred to as “total amount”) in the aqueous ink composition for writing instruments. "%"), More preferably 0.1 to 2%.
If the content of the plant cellulose nanofiber is less than 0.05%, the rheological properties unique to the plant cellulose nanofiber having the above characteristics are not expressed. On the other hand, if the content exceeds 1.5%, the viscosity increases. For this reason, the fluidity of the ink may decrease, which is not preferable.

The water-based ink composition for a writing instrument of the present invention is preferably at least selected from carboxymethylcellulose (CMC), a salt thereof, and a polysaccharide, from the viewpoint of preventing bleeding of drawn lines together with the vegetable cellulose nanofiber having the above characteristics. It is desirable that one type is contained.
Carboxymethylcellulose (CMC) or a salt thereof to be used is not particularly limited as long as it is used in a water-based ink composition for writing instruments, and any commercially available product can be used. Examples of the salt of carboxymethyl cellulose include alkali metal salts such as sodium and potassium, ammonium salts, and the like.
Preferably, carboxymethylcellulose is desirable from the viewpoint of cost and availability.

  Examples of polysaccharides that can be used include xanthan gum, guar gum, hydroxypropylated guar gum, casein, gum arabic, gelatin, amylose, agarose, agaropectin, arabinan, curdlan, callose, carboxymethyl starch, chitin, chitosan, quince seed , Glucomannan, gellan gum, tamarind seed gum, dextran, nigeran, hyaluronic acid, pustulan, funolan, HM pectin, porphyran, laminaran, lichenan, carrageenan, alginic acid, tragacanth gum, archaic gum, saxinoglycan, locust bean gum, tara gum, etc. These may be used alone or in combination of two or more. Also, if you have these commercial products, you can use them

The total content of these carboxymethylcelluloses or salts thereof and polysaccharides is preferably 0.005 to 5%, more preferably 0.01 to 3%, based on the total amount of the ink composition.
If these contents are less than 0.005%, the further effect of the present invention cannot be exhibited. On the other hand, if it exceeds 5%, the effect of the present invention does not change so much. This will result in poor writing performance and blurred lines.

The aqueous ink composition for a writing instrument of the present invention contains at least a colorant and, if necessary, a water-soluble solvent, in addition to the vegetable cellulose nanofiber having the above characteristics.
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, and the content in the total amount of the water-based 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 the water-soluble solvent that can be used include glycols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, polyethylene glycol, 3-butylene glycol, thiodiethylene glycol, and glycerin, ethylene glycol monomethyl ether, and diethylene glycol monomethyl ether. 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 vegetable cellulose nanofiber, carboxymethyl cellulose (CMC) or a salt thereof, a polysaccharide, a colorant, a water-soluble solvent, and water (tap water) as the balance. Purified water, distilled water, ion-exchanged water, pure water, etc.), as long as the effects of the present invention are not impaired, dispersants, lubricants, pH adjusters, rust preventives, antiseptics or antibacterial agents, etc. It can contain suitably.

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 aqueous ink composition for a writing instrument of the present invention comprises the above plant cellulose nanofiber, carboxymethylcellulose (CMC) or a salt thereof, a polysaccharide, a colorant, a water-soluble solvent, and other components for a writing instrument (for a ballpoint pen, for marking). For pens, etc.) Depending on the intended use of the ink, by mixing with a stirrer such as a homomixer, homogenizer or disper, coarse particles in the ink composition can be removed by filtration or centrifugation as necessary. By doing so, a water-based ink composition for writing instruments can be prepared.
For an aqueous ballpoint pen, the aqueous ink composition for a writing instrument can be prepared by filling an aqueous ballpoint pen provided with a ball 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, for example, a bead mill, a homomixer, and a homogenizer that can apply powerful shearing to each component including the above-described vegetable cellulose nanofibers. A thixotropic ink (for example, a gel ink water-based ballpoint pen ink) can be produced by mixing and stirring with the stirring conditions set to suitable conditions.
Further, the pH (25 ° C.) of the aqueous ink composition for a writing instrument of the present invention is adjusted to 5 to 10 depending on the pH adjuster or the like from the viewpoints of usability, safety, stability of the ink itself, and matching properties 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, when the vegetable cellulose nanofiber having the above-described characteristics to be used is blended in the water-based ink composition for a writing instrument, the vegetable-based ink having the characteristics described above is used. As a thickening and gelling agent for water-based ink compositions for writing instruments, it exhibits rheological properties unique to cellulose nanofibers, that is, it exhibits high viscosity even at low viscosity, and also exhibits a high thixotropy index unique to cellulose. In addition, it exhibits rheology control effects in a smaller amount than conventional fine cellulose and xanthan gum, and has higher viscosity recovery when using the cellulose nanofibers compared to oxidized cellulose. Thus, a water-based ink composition for a writing instrument having no property can be obtained.

  EXAMPLES Next, although an Example and a comparative example demonstrate this invention further in detail, this invention is not limited to the following Example etc.

[Examples 1 to 5 and Comparative Examples 1 to 3]
Non-oxidized vegetable cellulose nanofibers A to D that have the following physical properties, thickeners such as oxidized cellulose, colorants, and the like, each of the aqueous ink compositions for writing instruments according to the formulation shown in Table 1 below. Using a high-pressure wet medialess atomizer (Nanovaita, manufactured by Yoshida Kikai Kogyo Co., Ltd.), a predetermined amount is mixed and stirred by a wet method while appropriately changing the stirring conditions (shearing force, pressure, temperature, stirring time). It was prepared by filtering through a 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 found to be in the range of 7.9 to 8.2.

About the water-based ink composition for writing instruments obtained in the said Examples 1-5 and Comparative Examples 1-3, the viscosity value was measured with the following method.
For measurement of the viscosity value, a shear rate of 3.83 ^{−1 at} 25 ° C. was measured with an EMD viscometer (manufactured by Tokyo Keiki Co., Ltd.) using each ink stored in a glass bottle at room temperature for 24 hours and for one month. and the viscosity was measured values of ^{383 -1.}

About the water-based ink composition for writing instruments obtained in Examples 1 to 5 and Comparative Examples 1 to 3, an aqueous ball-point pen is prepared by the following method, and the ink dripping property and the bleeding property of the drawn line are evaluated by the following evaluation methods. It was.
These results are shown in Table 1 below.

[Production of vegetable cellulose nanofibers A to D which are not subjected to oxidation treatment used in Examples 1 to 5]
1) Cellulose nanofibers A to C
5% of crystalline cellulose (Theolas RC-591S, manufactured by Asahi Kasei Chemicals Corporation) was blended in water, and stirred with a stirrer for 1 hour. Next, using a high-pressure wet-medialess atomizer (Nanovaita, manufactured by Yoshida Kikai Kogyo Co., Ltd.), the stirring conditions (shearing force, pressure, temperature, stirring time) are appropriately changed and mixed and stirred by a wet method to obtain each number average fiber. Short diameter cellulose nanofibers A to C were prepared.

2) Cellulose nanofiber D
5% carboxymethylcellulose (SLD-FM, manufactured by Nippon Paper Industries Co., Ltd.) was mixed in water and stirred with a stirrer for 1 hour. Next, the cellulose nanofiber D was mixed and stirred by a wet method by appropriately changing the stirring conditions (shearing force, pressure, temperature, stirring time) using a high-pressure wet medialess atomizer (Nanovaita manufactured by Yoshida Kikai Kogyo Co., Ltd.). Was made.

[Oxidized cellulose used in Comparative Examples 1 to 3]
Oxidized cellulose (number average fiber minor axis: about 140 nm, I) obtained by the same production method, crystal structure confirmation, etc. as the oxidized cellulose used in Examples 1 to 5 described in JP-A-2015-67722 by the applicant of the present application Type crystal structure). In addition, the oxidized cellulose shown to Comparative Examples 1-3 of Table 1 displays what was manufactured above by the solid content density | concentration of each comparative example.

The number average fiber short diameter of the vegetable cellulose nanofiber obtained above was confirmed and measured by the following method.
That is, a sample obtained by adding water to plant cellulose nanofiber and diluting it 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 subjected to a transmission electron microscope. The number average fiber short diameter was measured and calculated from the image obtained by observation with (TEM). The above oxidized cellulose was also measured and calculated in the same manner.

(Production of water-based ballpoint pen)
A water-based ballpoint pen was produced using each ink composition obtained above. Specifically, using an axis 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, a polypropylene ink containing tube, and a stainless steel 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 ink sag]
A ballpoint pen was filled with each of the aqueous ink compositions for writing instruments prepared as described above and passed for 24 hours, and then the pen body was left facing downward for 24 hours in an environment of 25 ° C. and 60% RH, and ink direct current phenomenon from the pen tip Was evaluated according to the following evaluation criteria.
Evaluation criteria:
○: No leakage or slight wetness is observed.
Δ: An ink reservoir having a diameter of 0.5 mm or more is observed.
X: Ink dripped.

[Evaluation method for bleeding of drawn lines]
After the ball ink was filled with the water-based ink composition for writing instruments prepared as described above and passed for 24 hours, spiral writing was performed on writing paper by hand, and the degree of bleeding of the drawn lines was visually evaluated according to the following evaluation criteria.
Evaluation criteria:
○: Clear handwriting without bleeding.
Δ: Slightly blurred handwriting with some blurring.
X: Blurred and unclear handwriting.

  As is clear from the results of Table 1 above, the aqueous ink compositions for writing instruments of Examples 1 to 5 according to the present invention have high viscosity recoverability compared to Comparative Examples 1 to 3, which are outside the scope of the present invention. It has been found that a water-based ink composition for a writing instrument having no ink sag and no drawn line bleeding is obtained.

  A water-based ink composition for writing tools suitable for writing tools such as water-based ballpoint pens and marking pens can be obtained.

Claims (3)

  A water-based ink composition for a writing instrument, comprising at least vegetable cellulose nanofibers not subjected to oxidation treatment, wherein the cellulose nanofibers have a number average fiber short diameter of 10 to 200 nm.   The aqueous ink composition for a writing instrument according to claim 1, further comprising at least one selected from carboxymethylcellulose, a salt thereof, and a polysaccharide.   A writing instrument comprising the aqueous ink composition for a writing instrument according to claim 1 or 2 mounted thereon.