JP2017125136A - Aqueous ink composition for writing instrument - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an aqueous ink composition for writing instrument which suppresses dry-up by a pen point caused by cap-off that is a problem of the aqueous ink composition for writing instrument using oxycellulose without impairing writing performance, and is excellent in pen point drying property.SOLUTION: An aqueous ink composition for writing instrument contains at least oxycellulose, a pigment, and 0.001-1.0 mass% of a polyacrylic acid with respect to the total amount of the ink composition.SELECTED DRAWING: None

Description

  The present invention relates to an aqueous ink composition for a writing instrument containing oxidized cellulose.

Conventionally, as a thickener exhibiting shear thinning used for an ink composition for writing instruments, one using a natural thickener derived from cellulose such as oxidized cellulose, fermented cellulose, crystalline cellulose and the like is known.
For example, Patent Document 1 includes an aqueous ink composition (for example, Patent Document 1) containing oxidized cellulose (cellulose fiber) having specific physical properties, at least one of a colorant and a masking agent, and water. Reference).

The aqueous ink composition containing oxidized cellulose of Patent Document 1 is superior to conventional thickening and gelling agents such as xanthan gum, and is not affected by the temperature, colorant, concealing agent characteristics, etc. The effect of expressing specific rheological properties can be obtained.
On the other hand, since oxidized cellulose has strong cohesiveness, if the dispersion medium (moisture) is insufficient, aggregation between celluloses proceeds and rheological properties greatly vary. Such characteristics impair the fluidity of the ink when the dispersion medium is volatilized at the pen tip of the writing instrument (with the cap removed for a long time), cause dry-up at the pen tip, and cause deterioration in quality. May cause problems. In particular, this tendency is remarkable in an aqueous ink composition to which a pigment is added. The reason for this is not clear, but pigments used for writing instruments usually have polarity on their surfaces by a dispersant or chemical treatment, so the polar groups interact with acidic groups derived from oxidized cellulose and hydroxyl groups. It is inferred that this is happening.
Moreover, although the said patent document 1 only describes that synthetic polymers, such as polyacrylic acid and polyvinyl alcohol, polysaccharide, an inorganic filler, etc. can be used together as a well-known thickener with the said oxidized cellulose. In addition, there is no description, suggestion, or recognition regarding suppression of dry-up at the nib due to cap-off, which is a problem of a water-based ink composition for writing instruments when polyacrylic acid uses oxidized cellulose. .

  On the other hand, as an ink composition for a writing instrument using fermented cellulose and crystalline cellulose, for example, an aqueous ink composition for marking pens comprising water, a pigment, fermented cellulose, and a crosslinking agent for crosslinking the pigment and fermented cellulose (for example, , Patent Document 2), a water-based ballpoint pen ink comprising a coloring material, a solvent, water, a thickener, and 0.01% to 0.5% by weight of crystalline cellulose (for example, Patent Document 3) is known.

The above-mentioned Patent Document 2 adds a cross-linking agent that cross-links a pigment and fermented cellulose for the purpose of improving pigment dispersion stability, and describes polyacrylic acid as an example of the cross-linking agent. Is different from the problem of the invention and the technical idea (configuration and operational effects thereof).
In Patent Document 3, crystalline cellulose is added for the purpose of suppressing the direct current phenomenon of the ink without degrading the writing property by adding crystalline cellulose, and polyacrylic acids and polyvinyl alcohol are used as thickeners. However, the present invention is different from the present invention in terms of the subject of the invention and its technical idea (configuration and operational effects).

JP 2013-181167 A (Claims, paragraph [0053], Examples, etc.) Japanese Patent Laying-Open No. 2015-10114 (claims, paragraph [0010], examples, etc.) JP 2010-1381 A (Claims, paragraph [0007], Examples, etc.)

  The present invention has been made in view of the above-described problems of the prior art, and is intended to solve this problem. Cap-off is a problem of a water-based ink composition for writing instruments when oxidized cellulose is used without impairing writing performance. An object of the present invention is to provide a water-based ink composition for a writing instrument that suppresses dry-up at the nib due to, and is excellent in nib drying resistance.

  As a result of intensive studies in view of the above-described conventional problems and the like, the present inventors have found that a water-based ink composition for a writing instrument can be obtained by containing a specific amount of a specific component together with oxidized cellulose. The headline and the present invention have 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 at least 0.001 to 1.0% by mass of polyacrylic acid based on oxidized cellulose, a pigment, and the total amount of the ink composition.
(2) The aqueous ink composition for a writing instrument as described in (1) above, wherein the polyacrylic acid is an alkali swelling emulsion.
(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, without impairing the writing performance, it is possible to suppress dry-up at the nib due to the cap-off, which is a problem of the aqueous ink composition for writing instruments when using oxidized cellulose, and excellent in nib drying resistance. A water-based ink composition for a writing instrument is provided.

Hereinafter, embodiments of the present invention will be described in detail.
The aqueous ink composition for a writing instrument according to the present invention is characterized by containing at least oxidized cellulose, a pigment, and 0.001 to 1.0% by mass of polyacrylic acid based on the total amount of the ink composition. is there.

<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 include those obtained by oxidizing at least the hydroxyl group (—OH group) at the C6 position of glucose to an aldehyde group (—CHO) and a carboxyl group (—COOH group).

  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 and miniaturizing it to 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, at least the above-mentioned physical properties of oxidized cellulose and polyacrylic acid can be used to exhibit the effects of the present invention. Preferably, the oxidized cellulose has a number average fiber diameter of 2 to 150 nm. .
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.
In addition, 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, 2 theta can be identified from having typical peaks at two positions near 22 to 23 °.

  The production of the 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, isolated from 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.

  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 is in the range of about 10% to 50% by weight as the solid content (cellulose) concentration 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 a part 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 water-based ink composition for a writing instrument of the present invention contains at least the oxidized cellulose, a pigment, and 0.001 to 1.0% by mass of polyacrylic acid based on the total amount of the ink composition. For example, it is used as an ink composition for writing instruments such as water-based ballpoint pens.
In the present invention, the content (solid content) of the oxidized cellulose is preferably 0.05 to 1.5% by mass (hereinafter simply referred to as “%”) with respect to the total amount of the aqueous ink composition for writing instruments. ), More preferably 0.1 to 1.0%.
If the content of oxidized cellulose is less than 0.05%, rheological characteristics peculiar to oxidized cellulose are not exhibited, and precipitation of solids such as pigments may occur over time, whereas it exceeds 1.5%. In this case, the viscosity becomes high, so that the phenomenon of broken lines in the writing lines and the fluidity of the ink may be lowered.

<Pigment>
The pigment used in the present invention is used as a colorant, and the type of the pigment is not particularly limited, and any of inorganic and organic pigments conventionally used for writing instruments such as water-based ballpoint pens can be used. Can be used.
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.
The pigment content is preferably 0.5 to 30%, more preferably 1 to 15%, based on the total amount of the ink composition.

<Polyacrylic acid>
The polyacrylic acid used in the present invention is used to suppress dry-up at the nib due to cap-off, which is a problem caused by using oxidized cellulose, and to exhibit a function excellent in nib drying resistance. When used in combination with oxidized cellulose, the effect of the present invention can be effectively exhibited without causing deterioration in writing performance even when blended in an aqueous ink composition for writing instruments.
As polyacrylic acid that can be used, crosslinked and uncrosslinked polyacrylic acid or a salt thereof can be used. The cations constituting the polyacrylate are not particularly limited, but alkali metals, alkaline earth metals, and ammonium are preferable. In this invention, polyacrylic acid or its salt can be used 1 type or in combination of 2 or more types.
As the polyacrylic acid that can be used, commercially available products can be used. For example, “Hibiswaco # 104”, “Hibiswaco # 103” (trade name) manufactured by Wako Pure Chemical Industries, Ltd., manufactured by Toa Gosei Co., Ltd. "Julimar AC-10SHP", "Julimar AC-10LHPK" (above, trade name), "Viscomate NP-800", "Viscomate NP-800" (above, trade name) manufactured by Showa Denko KK and the like.

As a preferred polyacrylic acid, it is desirable to use an alkali swelling emulsion from the viewpoint of more effectively exhibiting resistance to nib drying. The alkali-swelled emulsion is neutralized with an alkali in a dispersion medium, swells, spreads throughout the dispersion medium while molecules are entangled with each other, and polar groups on the surface of the pigment, acidic groups derived from oxidized cellulose, and hydroxyl groups. It alleviates the interaction.
In the present invention, commercially available products can be used as such alkali-swelled emulsions, for example, “Primal ASE60”, “Primal TT615”, “Primal RM5” (trade name) manufactured by Rohm & Haas. And “RHEOTECH 3800”, “RHETECH 4800”, etc. manufactured by Arkema.

The content of these polyacrylic acids is preferably 0.001 to 1.0%, more preferably 0.05 to 1.0%, based on the total amount of the ink composition.
If the content is less than 0.01%, the effects of the present invention cannot be exhibited. On the other hand, if the content exceeds 1.0%, the phenomenon of broken lines in the writing lines and the fluidity of the ink decrease. Sometimes.

The water-based ink composition for a writing instrument of the present invention may contain a colorant other than the pigment and a water-soluble solvent in addition to the oxidized cellulose, pigment, and polyacrylic acid.
Examples of colorants other than pigments that can be used include water-soluble dyes. There is no restriction | limiting in particular about the kind of water-soluble dye, Arbitrary things can be used from the water-soluble dye conventionally used for writing instruments, such as a water-based ballpoint pen.

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.).

  Coloring agents other than these pigments 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 0.05 to 30%, preferably It is in the range of 1 to 15%.

  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. 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.

  In the water-based ink composition for writing instruments of the present invention, in addition to the oxidized cellulose, pigment, polyacrylic acid, colorant other than the pigment, water-soluble solvent, the balance is water (tap water, purified water, distilled water, In addition to ion-exchanged water, pure water, etc.), a dispersant, lubricant, pH adjuster, rust preventive, preservative, antibacterial, and the like can be appropriately contained as long as the effects of the present invention are not impaired.

When a pigment is used, 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 a writing instrument of the present invention is a combination of the above oxidized cellulose, pigment, polyacrylic acid, water-soluble solvent, and other components as appropriate according to the application of the ink for a writing instrument (for ballpoint pens, marking pens, etc.). 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 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, a homogenizer, and the like, each of which includes the above-described oxidized cellulose, pigment, polyacrylic acid, a mixer, and the like. A thixotropic ink (for example, gel ink water-based ballpoint pen ink) is produced by mixing and stirring with a high-pressure homogenizer, an ultrasonic homogenizer, a high-pressure wet medialess atomizer, etc. while setting the stirring conditions to suitable conditions. be able to.
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 aqueous ink composition for writing instruments of the present invention configured as described above, when the oxidized cellulose to be used is blended in the aqueous ink composition for writing instruments, the rheological characteristics peculiar to oxidized cellulose are exhibited, that is, the low viscosity. However, it exhibits a high viscosity and a high thixotropy index unique to cellulose. As a thickening / gelling agent for water-based ink compositions for writing instruments, it has a rheology control effect in a smaller amount than conventional fine cellulose or xanthan gum. In addition, the polyacrylic acid is added in an amount of 0.001 to 1.0% by mass with respect to the total amount of the ink composition, thereby exhibiting the effect of preventing pigment sedimentation over time and without impairing the writing performance. Suppresses dry-up at the pen tip due to cap-off in the case of using the oxidized cellulose. Excellent emission destination drying properties, so that the writing instrument aqueous ink composition capable of expressing a further improvement in ink quality is 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 1-6 and Comparative Examples 1-2]
Using oxidized cellulose having the following physical properties, a predetermined amount of each water-based ink composition for a writing instrument is atomized by high-pressure wet-medialess atomization according to the composition shown in Table 1 below, specifically, a composition such as pigment and polyacrylic acid. Using a device (Yoshida Kikai Kogyo Co., Ltd., Nanovaita), the stirring conditions (shearing force, pressure, stirring time) were appropriately changed, mixed and stirred by a wet method, and prepared by filtration through a 10 μm bag filter. When 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), it was in the range of 6-9.

About the water-based ink composition for writing instruments obtained in Examples 1 to 6 and Comparative Examples 1 and 2, an aqueous ballpoint pen was prepared by the following method, and the pen-drying resistance and writing property (upper and lower drawn line density by the following evaluation methods were used. (Difference) was evaluated.
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, The reaction was started by adding sodium hypochlorite to a 13 wt% sodium hypochlorite aqueous solution so that the amount of sodium hypochlorite was 2.5 mmol per 1 g of pulp. 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, there are typical peaks at two positions near 2 theta = 14 to 17 ° and 2 theta = 22 to 23 °. 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 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 nib resistance]
Each water-based ballpoint pen was left for 1 month in a state where the cap was removed under the conditions of 25 ° C. and 60% RH, and then a straight line was written on a writing paper conforming to the ISO standard and evaluated according to the following evaluation criteria.
Evaluation criteria:
◎: Can be written without problems from the beginning.
○: The line density at the beginning of writing is low, but it returns immediately.
Δ: The state where the drawn line density is low continues for a while, but can be recovered.
×: Writable

[Evaluation method of writability (difference in density of drawn lines)
Each obtained water-based ball-point pen was allowed to stand at room temperature for 1 month, and then was written to the final writing, and the density difference between the strokes at the beginning and end of writing was compared and evaluated according to the following evaluation criteria.
Evaluation criteria:
○: There is no density difference.
Δ: Some density difference is observed.
X: A density difference is clearly recognized.

  As is clear from the results of Table 1 above, the water-based ink compositions for writing instruments of Examples 1 to 6 according to the present invention are more resistant to nib drying than Comparative Examples 1 and 2, which are outside the scope of the present invention. It has been found that it has excellent writing performance and can further improve ink quality. Examples 1, 2, 5 and 6 in which polyacrylic acid becomes an alkali-swelling emulsion were found to be more excellent in nib drying resistance and writing performance than Examples 3 and 4.

  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 writing instruments, comprising at least 0.001 to 1.0% by mass of polyacrylic acid based on oxidized cellulose, a pigment, and the total amount of the ink composition.   2. The aqueous ink composition for a writing instrument according to claim 1, wherein the polyacrylic acid is an alkali swelling emulsion.   A writing instrument comprising the aqueous ink composition for a writing instrument according to claim 1 or 2 mounted thereon.