JP2017048274A - Aqueous ink composition for writing instrument - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an aqueous ink composition for a writing instrument excellent in secular viscosity distribution stability by suppressing the secular viscosity distribution ununiformity (an upper-lower difference in viscosity) of an aqueous ink composition containing oxycellulose.SOLUTION: Provided is an aqueous ink composition for a writing instrument at least comprising oxycellulose and a self-dispersible pigment. The aqueous ink composition for a writing instrument preferably includes at least one kind selected from carboxymethyl cellulose having an etherification degree below 0.8, its salt and succinoglycan as well.SELECTED DRAWING: None

Description

  The present invention relates to an aqueous 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 comprising at least water, a colorant, and fermented cellulose (see, for example, Patent Document 2, 3) Oxidized cellulose (cellulose fiber) having specific physical properties ), At least one of a colorant and a masking agent, and water. (See, for example, Patent Document 3) 4) 0.05 to 1.5% by mass of oxidized cellulose A water-based ink composition for a writing instrument, which contains and has an intrinsic viscosity value of 10 mPa · s or less derived from the Casson formula For example, it is known, such as Patent Document 4).

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. Although it has excellent dispersibility of the masking agent and prevents sedimentation separation during storage, it has the property that non-uniform viscosity distribution (viscosity difference) tends to occur over time. When pigments are used as coloring materials, there are many non-uniformity of viscosity distribution (viscosity difference), and it is still impossible to achieve sufficient viscosity distribution stability over time and eventually dispersion stability over time. The current situation is that there are problems.
Further, the aqueous ink composition for a writing instrument of the above-mentioned Patent Document 4 contains oxidized cellulose in a specific range and further has a limiting intrinsic viscosity value. Unprecedented storage stability, stability over time, Although it is excellent in drawing quality, further improvement in ink quality is desired.

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 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 ( Viscosity difference in viscosity), especially when pigments are used as coloring materials, non-uniformity of viscosity distribution over time (viscosity difference in viscosity) is suppressed, and water-based ink composition for writing instruments with excellent viscosity distribution stability over time The purpose is to provide goods.

  As a result of intensive studies in view of the above-described conventional problems, the present inventors have found that the water-based ink composition for a writing instrument can be obtained by containing a pigment having specific physical properties in addition to 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 writing instruments, comprising at least oxidized cellulose and a self-dispersing pigment.
(2) The aqueous ink composition for a writing instrument according to the above (1), further comprising at least one selected from carboxymethylcellulose having a degree of etherification of less than 0.8 or a salt thereof, and succinoglycan. object.
(3) A writing instrument comprising the water-based ink composition for a writing instrument described in (1) or (2) above.

  ADVANTAGE OF THE INVENTION According to this invention, the aqueous | water-based for writing implements which suppressed the non-uniformity (viscosity difference of a viscosity) with time of the viscosity distribution which is the subject of an oxidized cellulose containing water-based ink composition, and was excellent in the viscosity distribution stability with time. An ink composition 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 and a self-dispersing pigment.

<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, the effect of the present invention can be exerted by using the above-mentioned oxidized cellulose having the above physical properties and the specific saccharide described later, and it is desirable that the number average fiber diameter of oxidized cellulose is 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, 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.

  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>
A water-based ink composition for a writing instrument according to the present invention is characterized by containing at least the oxidized cellulose and a self-dispersing pigment, and is used as an ink composition for a writing instrument such as an aqueous ballpoint pen. .
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%, 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.

The self-dispersing pigment used as a coloring material in the present invention refers to a pigment that can be dispersed or dissolved in an aqueous medium without a dispersant, and without using a dispersant for dispersing the pigment, for example, A pigment in which a hydrophilic group is bonded (grafted) to the surface of the pigment by subjecting the pigment to physical treatment or chemical treatment.
Examples of the hydrophilic group, for _{example, -COOM, -SO 3 M, -SO} 2 M, -CO -, - OM, -SO 2 NH 2, -RSO 2 M, -PO 3 HM, -PO 3 M 2, One or more hydrophilic groups selected from —SO ₂ NHCOR, —NH ₃ , and —NR ₃ are preferable. Note that M in these formulas independently represents a hydrogen atom, an alkali metal, ammonium, a phenyl group which may have a substituent, or organic ammonium. R in these formulas independently represents an alkyl group having 1 to 12 carbon atoms or a naphthyl group which may have a substituent.
Examples of the physical treatment include vacuum plasma treatment, and chemical treatment includes, for example, a wet oxidation method in which oxidation is performed with an oxidizing agent in water, or by bonding p-aminobenzoic acid to the pigment surface. Examples thereof include a method of bonding a carboxyl group through a phenyl group.

The self-dispersing pigment that can be used is not particularly limited as long as it is a pigment contained in the above-mentioned self-dispersing pigment, and examples thereof include self-dispersing carbon black and self-dispersing organic pigments.
Examples of commercially available products include Microjet series manufactured by Orient Chemical Industry Co., Ltd., CAB-O-JET series manufactured by Cabot Corporation, Aqua-Black series manufactured by Tokai Carbon Corporation, and the like.
These self-dispersing pigments can be used alone or in admixture of two or more.

The content of these self-dispersing pigments is preferably in the range of 0.5 to 15%, particularly preferably in the range of 1 to 10%, based on the total amount of the aqueous ink composition for writing instruments. .
If the content is less than 0.5%, the function as a coloring material is not sufficient. On the other hand, if it exceeds 15%, the stability of the ink is impaired, which is not preferable.

In the present invention, in addition to the above self-dispersing pigment, resin dispersed pigments and water-soluble dyes (direct dyes, acid dyes, food dyes, basic dyes, etc.) are used in appropriate amounts within a range not impairing the effects of the present invention. Can do.
The resin-dispersed pigment that can be used is not particularly limited as long as it is a pigment that can be dispersed by a dispersant (resin dispersion), and examples thereof include inorganic pigments such as carbon black, general organic pigments, and titanium oxide. be able to. The dispersant such as a resin (polymer) used for the resin-dispersed pigment will be described later.
When the resin-dispersed pigment is used in combination, the total content can be adjusted within the range of the content of the self-dispersed pigment (0.5 to 15%). From the viewpoint of ink stability, the resin-dispersed pigment is used. The content of the pigment is preferably within a range of 1/2 or less (50% by mass or less) by mass ratio with respect to the self-dispersing pigment, and particularly preferably 1/4 or less (25% by mass) by mass ratio. The following range is desirable.

  The water-based ink composition for a writing instrument of the present invention preferably has carboxymethyl cellulose having a degree of etherification of less than 0.8, in addition to the above oxidized cellulose and self-dispersing pigment, in order to further exert the effects of the present invention. It is desirable to contain at least one selected from the salt and succinoglycan, more preferably any one of these.

Carboxymethylcellulose (CMC) or a salt thereof having a degree of etherification of less than 0.8 used in the present invention further improves the non-uniformity of viscosity distribution over time (up / down difference in viscosity) of the ink when oxidized cellulose is used. It is a component to be suppressed, and any carboxymethyl cellulose or a salt thereof having a degree of etherification of less than 0.8 (0 <degree of etherification <0.8) can be used without particular limitation. .
Examples of the salt of carboxymethylcellulose include alkali metal salts such as sodium and potassium, ammonium salts, and the like, and sodium carboxymethylcellulose is preferable from the viewpoint of cost and availability.

In the present invention, the “degree of etherification” of carboxymethylcellulose or a salt thereof refers to the degree of substitution of the carboxymethyl group with respect to the hydroxyl group present in the anhydroglucose unit of cellulose. Since there are three hydroxyl groups in the unit, the degree of etherification can theoretically be “3.0”.
The degree of etherification can be obtained, for example, according to a CMC industry association analysis method (ashing method). Weigh precisely 1 g of sodium carboxymethylcellulose, put it in a magnetic crucible, incinerate at 600 ° C., titrate sodium oxide produced by incineration with N / 10 sulfuric acid using phenolphthalein as an indicator, and add 1 g of sodium carboxymethylcellulose (CMCNa). The titration amount of YmL can be calculated by putting it in the following formula, and the obtained degree of etherification can be shown.
Degree of etherification = (162 × Y) / (10,000-80 × Y)
In the present invention, in the case of carboxymethyl cellulose having a degree of etherification of 0.8 or more or a salt thereof, sufficient effects of the invention may not be obtained, which is not preferable.

As carboxymethylcellulose or a salt thereof having a degree of etherification of less than 0.8, commercially available Sunrose F10LC (etherification degree: 0.55 to 0.65), F05MC (etherification) manufactured by Nippon Paper Industries Co., Ltd. Degrees 0.65-0.75), B3B (etherification degree 0.45-0.55), SLD-FM (CMCNa, etherification degree 0.2-0.3), etc. Serogen PR (degree of etherification 0.6-0.7), PL-15 (degree of etherification 0.45-0.55), F-SH (degree of etherification 0.6- 0.7) etc., and those selected from the serogen series, and the like can be mentioned, and these can be used as one kind or a mixture of two or more kinds.
Preferably, when the oxidized cellulose is used, the non-uniformity of the viscosity distribution with time (difference in viscosity) is further suppressed to further improve the effect of the present invention. It is desirable to use carboxymethyl cellulose or a salt thereof that is 75 or less, more preferably carboxymethyl cellulose or a salt thereof that is 0.7 or less.

The content of carboxymethyl cellulose having a degree of etherification of less than 0.8 or a salt thereof is 0.005 to 5%, preferably 0.01 to 3%, based on the total amount of the aqueous ink composition. Is desirable.
If the content is less than 0.005%, the further effect of the present invention is insufficient. On the other hand, if it exceeds 5%, 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, the mass ratio of the oxidized cellulose to the carboxymethyl cellulose or a salt thereof is preferably 1: 5 to 5: 1, and more preferably 1 : 3 to 3: 1 is desirable.

The succinoglycan used in the present invention is a component that further suppresses the non-uniformity of viscosity distribution over time (difference in viscosity) when oxidized cellulose is used, and is a polysaccharide derived from microorganisms. In addition to the saccharide units derived from galactose and glucose, they contain units derived from succinic acid and pyruvic acid and optionally acetic acid or salts of these acids.
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 further effects of the present invention are 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 be ˜1: 2.

The aqueous ink composition for a writing instrument of the present invention comprises the above oxidized cellulose, a self-dispersing pigment, preferably carboxymethyl cellulose having a degree of etherification of less than 0.8 or a salt thereof, and succinoglycan. In addition to what is selected, at least a water-soluble solvent is contained.
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. Etc. 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 has the effects of the present invention in addition to each of the above-mentioned components, and the remaining water as a solvent (tap water, purified water, distilled water, ion-exchanged water, pure water, etc.). A dispersant, lubricant, pH adjuster, rust inhibitor, preservative, or antibacterial agent can be appropriately contained within the range not impaired.

When the resin dispersion type 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 writing instruments of the present invention is a combination of the above oxidized cellulose, self-dispersing pigment, 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). Then, by mixing with a stirrer such as a homomixer, a homogenizer, or a disper, and further removing coarse particles in the ink composition by filtration or centrifugation, if necessary, an aqueous ink composition for a writing instrument is prepared. can do.
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, a high pressure, and the like, each of which contains the above-described oxidized cellulose and a self-dispersing pigment. A thixotropic ink (for example, gel ink water-based ballpoint pen ink) is produced by mixing and stirring the stirring conditions to a suitable condition using a homogenizer, ultrasonic homogenizer, high-pressure wet medialess atomizer, etc. Can do.
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 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 aqueous ink composition for a writing instrument, it has a high viscosity. 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 as a pigment. By using a self-dispersing pigment, the non-uniformity of viscosity distribution over time (viscosity difference) when using the above-mentioned oxidized cellulose is suppressed, and the water for writing instruments has excellent viscosity distribution stability over time. An ink composition will be obtained.
Further, by containing at least one selected from carboxymethyl cellulose having a degree of etherification of less than 0.8 or a salt thereof and succinoglycan, the viscosity distribution over time in the case of using the oxidized cellulose is not uniform. Therefore, the water-based ink composition for writing instruments can be obtained which further suppresses the property (difference in the upper and lower sides of the viscosity) and is further excellent in the stability of the viscosity distribution over time.

  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 Example 1]
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 a self-dispersing pigment. It was prepared by changing the stirring conditions (shearing force, pressure, stirring time) as appropriate using (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 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 the comparative example 1, the viscosity value was measured with 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 ⁻¹ at 25 ° C. was measured with an EMD viscometer (manufactured by Tokyo Keiki Co., Ltd.). In addition, in this invention, as a favorable viscosity distribution, on the said conditions, what has the upper / lower ratio (up / down) of a viscosity in the range of 0.9-2 will become a preferable thing.

Next, for the water-based ink composition for writing instruments obtained in Examples 1 to 5 and Comparative Example 1, an aqueous ballpoint pen is prepared by the following method, and the evaluation of writing property (upper and lower drawn line density difference) is performed by the following evaluation method. went.
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 writability (upper and lower drawn line density difference)]
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 apparent from the results in Table 1 above, the water-based ink compositions for writing instruments of Examples 1 to 5 according to the present invention have a satisfactory viscosity distribution over time as compared with Comparative Example 1 that is outside the scope of the present invention. It was found that the uniformity was maintained, and there was no difference in the upper and lower drawn line density, and the writing property was excellent.

  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 oxidized cellulose and a self-dispersing pigment.   The aqueous ink composition for a writing instrument according to claim 1, further comprising at least one selected from carboxymethylcellulose having a degree of etherification of less than 0.8 or a salt thereof, and succinoglycan.   A writing instrument comprising the aqueous ink composition for a writing instrument according to claim 1 or 2 mounted thereon.