JP2022130033A - Water-based ink composition for writing instruments, and writing instrument including the same - Google Patents

Abstract

To provide a water-based ink composition for writing instruments that can form handwritten characters having an excellent stereoscopic appearance and excellent fixability, and a writing instrument including the same.SOLUTION: A water-based ink composition for writing instruments contains water, a colorant, a foamer, a water-dispersible resin with a glass transition temperature of lower than 100°C, and a thickener.SELECTED DRAWING: None

Description

TECHNICAL FIELD The present invention relates to an aqueous ink composition for writing instruments and a writing instrument using the same.

When writing with a writing instrument filled with an ink composition, the ink usually permeates the surface of the paper and a flat handwriting is obtained. However, by making this handwriting three-dimensional, it is possible to enjoy handwriting different from usual.
As one of the methods of forming three-dimensional handwriting, heat-expandable microcapsules are added and the obtained handwriting is treated with a heater such as an iron or a dryer to expand the heat-expandable microcapsules. , proposed an ink composition that gives a three-dimensional handwriting. (For example, Patent Document 1)
However, with conventional ink compositions, the resulting handwriting does not have a sufficient three-dimensional effect, and even if a three-dimensional handwriting is obtained, the handwriting does not expand uniformly, resulting in an uneven three-dimensional effect. However, there is still room for improvement in that the handwriting cannot be sufficiently fixed to the surface to be written and the handwriting is peeled off.
Furthermore, the ejection of ink from the writing tip is unstable, it is difficult to leave uniform handwriting, and it is difficult to leave fine handwriting such as characters in three dimensions.

JP-A-2000-191962

According to the present invention, the above problems are solved, and a water-based ink composition for writing instruments and a writing instrument using the same are provided, which are capable of forming handwritings with excellent three-dimensional effect and fixability. is.

In order to solve the above problems, the present invention
"1. A water-based ink composition for writing instruments comprising water, a coloring agent, a foaming agent, a water-dispersible resin having a glass transition temperature of less than 100°C, and a thickener. A water-based ink composition for writing instruments.
2. 2. The ink composition according to Item 1, wherein the blowing agent is a heat-sensitive blowing agent.
3. 3. The ink composition according to item 1 or 2, wherein the heat-sensitive foaming agent is a thermal expansion foaming agent.
4. 4. The ink composition according to any one of items 1 to 3, wherein the thickener is a shear thinning agent.
5. 5. The ink composition according to any one of items 1 to 4, wherein the content of the foaming agent is 1% by mass to 20% by mass based on the total mass of the ink composition.
6. 6. The ink composition according to any one of items 1 to 5, wherein the content of the water-dispersible resin is 1% by mass to 50% by mass based on the total mass of the ink composition.
7. 7. The ink composition according to any one of items 1 to 6, wherein the ink composition has a solid content ratio of 10% by mass to 50% by mass.
8. 8. The ink composition according to any one of items 1 to 7, wherein the ink composition has a viscosity of 500 mPa·s or more at 20°C and a shear rate of 1.92 sec ^-1 .
9. A writing instrument containing the composition according to any one of items 1 to 8.
10. 10. The writing instrument according to Clause 9, which is a pressurized writing instrument.
”.

To provide a water-based ink composition for writing utensils, which gives handwritings excellent in three-dimensional effect, and furthermore, the handwritings obtained are hard to separate from a writing surface and excellent in fixability, and a writing utensil using the same. can be done.

1 is a longitudinal sectional view of an example of a cap-type pressurized ball-point pen; FIG. Fig. 2 is a longitudinal sectional view of the ballpoint pen of Fig. 1 with the cap removed; FIG. 4 is an explanatory view showing the writing instrument in a state (pressurized state) in which a cap is fitted to the rear end portion of the barrel;

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail. In this specification, "parts", "%", "ratios" and the like indicating formulations are based on mass unless otherwise specified, and the content rate refers to the constituent components based on the mass of the ink composition. is the mass % of

<Water-based ink composition for writing instruments>
The water-based ink composition for writing instruments according to the present invention (hereinafter sometimes referred to as the ink composition) comprises water, a coloring agent, a foaming agent, a water-dispersible resin having a glass transition temperature of less than 100°C, and an and a viscous agent.
It is particularly important that the ink composition of the present invention uses a foaming agent, a water-dispersible resin having a glass transition temperature of less than 100° C., and a thickening agent.
By using these constituent components, a three-dimensional effect can be visually confirmed, and handwriting that is difficult to peel off from the writing surface and has excellent three-dimensional effect and fixability can be obtained.
. The constituent components of the ink composition of the present invention are described in detail below.
<Blowing agent>
The ink composition according to the invention comprises a foaming agent.
The foaming agent swells the handwriting, making it possible to obtain a three-dimensional handwriting.
The foaming agent is a foaming agent that foams by an external stimulus such as heat or light. Specific examples include a heat-sensitive foaming agent that foams by heat and a photosensitive foaming agent that foams by light.
Among these, in the present invention, it is preferable to use a heat-sensitive foaming agent capable of producing a three-dimensional handwriting by heat treatment.
Furthermore, the heat-sensitive foaming agent includes thermal expansion foaming agents (also referred to as physical foaming agents) and thermal decomposition foaming agents (also referred to as chemical foaming agents). It is preferable to use a certain thermal expansion foaming agent.

In the present application, the thermally expandable foaming agent is not particularly limited, but by using it together with a water-dispersible resin having a glass transition temperature of less than 100° C., which will be described later, it is possible to easily form a handwriting with an excellent three-dimensional effect. In addition, it is preferable to use thermally expandable microcapsules because the three-dimensional effect is easily maintained.
Thermally expandable microcapsules are particles with a core-shell structure in which a volume-expanding compound is wrapped in a thermoplastic resin. When heated, the thermoplastic resin in the outer shell begins to soften, and the vapor pressure of the encapsulated volume-expanding compound increases. As a result, the pressure becomes sufficient to deform the particles, and the thermoplastic resin of the outer shell is stretched and expanded.

As the thermoplastic resin constituting the outer shell (shell), for example, a (meth)acrylonitrile polymer or a copolymer having a high (meth)acrylonitrile content is preferably used. Other monomers (comonomers) for the copolymer include vinyl halides, vinylidene halides, styrene-based monomers, (meth)acrylate-based monomers, vinyl acetate, butadiene, vinylpyridine, chloroprene, and other monomers. .
The thermoplastic resins include divinylbenzene, ethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, 1,3-butylene glycol di(meth)acrylate, allyl (meth) ) cross-linkable with a cross-linking agent such as acrylate, triacrylformal, triallyl isocyanurate; As for the form of cross-linking, it is preferably not cross-linked, but may be partially cross-linked to the extent that the properties as a thermoplastic resin are not impaired.
Also, as the volume expansion compound, a substance that vaporizes under a realistic temperature environment, such as a low boiling point solvent or water, can be used. Examples of low boiling point solvents include hydrocarbons such as n-pentane, isopentane, neopentane, butane, isobutane, hexane, and petroleum ether; chlorinated hydrocarbons such as methyl chloride, methylene chloride, dichloroethylene, trichloroethane, and trichlorethylene; liquids.

A commercially available product can be used as the thermally expandable microcapsule. Examples of the commercially available products include the Advancell series manufactured by Sekisui Chemical Co., Ltd., the Expancell series manufactured by AkzoNovel (sold by Nippon Philite Co., Ltd. in Japan), the Matsumoto Microsphere series manufactured by Matsumoto Yushi Seiyaku Co., Ltd., Examples include the Kureha Microsphere series manufactured by Kureha Corporation.
These may be used individually by 1 type, and may use 2 or more types together.

On the other hand, examples of thermally decomposable foaming agents include organic thermally decomposable foaming agents and inorganic thermally decomposable foaming agents.
Organic pyrolytic foaming agents include, for example, azodicarbonamide complexes (ADCA), azobisisobutyronitrile (AIBN), dinitrosopentamethylenetetramine (DPT), N,N'-dimethyl-N , N′-dinitrosoterephthalamide, benzenesulfonyl hydrazide (BSH), p-toluenesulfonyl hydrazide (TSH), 4,4′-oxybis(benzenesulfonyl hydrazide) (OBSH), 3,3′-disulfone hydrazide diphenyl sulfone, Toluenedisulfonyl hydrazine, p-toluenedisulfonyl hydrazide, p-toluenesulfonyl semicarbazide, diethyl azodicarboxylate and the like.
Examples of inorganic pyrolytic foaming agents include hydrogencarbonates such as sodium hydrogencarbonate, carbonates, and combinations of hydrogencarbonates and organic acid salts.
In addition, as a foaming agent, you may use individually by 1 type, and may use 2 or more types together.

As described above, in the present application, it is particularly preferable to use thermally expandable microcapsules as the foaming agent, and the average particle size of the thermally expandable microcapsules is preferably 1 μm to 50 μm.
If it is 1 μm or more, it is easy to obtain a handwriting with an excellent three-dimensional effect. It is easy to obtain a handwriting having a continuous three-dimensional effect. In addition, the stability of the ink over time can also be improved.
Considering the improvement of the above effect, the average particle size of the thermally expandable microcapsules is more preferably 5 μm or more, more preferably 10 μm or more, more preferably 40 μm or less, and still more preferably 30 μm or less. and more preferably 20 μm or less.

The foaming initiation temperature (Ts) of the thermally expandable microcapsules is preferably 60° C. or higher, more preferably 70° C. or higher, still more preferably 80° C. or higher, and preferably 150° C. or lower. It is preferably 140° C. or lower, still more preferably 120° C. or lower, and particularly preferably 110° C. or lower.
Further, the maximum expansion temperature (Tm) of the thermally expandable microcapsules is preferably 100° C. or higher, more preferably 110° C. or higher, and preferably 200° C. or lower, more preferably 180° C. or lower. The temperature is preferably 150° C. or lower, and particularly preferably 140° C. or lower.
If the foaming start temperature and maximum expansion temperature are within the above numerical ranges, unintended foaming expansion is unlikely to occur under normal storage and use environments, and general-purpose equipment is used for heat treatment. and easy to obtain three-dimensional handwriting.

The content of the foaming agent is preferably 1 to 20% by mass, more preferably 2 to 10% by mass, based on the total mass of the ink composition.
If the content of the foaming agent is within the range of the above numerical value, the ejection property of the ink from the tip of writing is improved, and handwriting with an excellent three-dimensional effect can be obtained. In addition, the stability of the ink over time can be improved.

<Water-dispersible resin>
The ink composition according to the present invention comprises a water-dispersible resin (hereinafter sometimes referred to as water-dispersible resin) having a glass transition temperature (Tg) of less than 100°C.
The water-dispersible resin used in the present invention is a poorly water-soluble resin that can be uniformly dispersed in water, preferably emulsified and dispersed in an aqueous medium. It exists in the form of particles without dissolving inside.

In the present invention, by using a water-dispersible resin having a glass transition temperature of less than 100° C., it is possible to obtain handwriting with an excellent three-dimensional effect due to the effect of the foaming agent. On the other hand, handwriting with excellent fixability can be obtained.
The glass transition temperature of the water-dispersible resin used in the present invention is preferably 80° C. or lower, more preferably 50° C. or lower, still more preferably 20° C. or lower, and particularly preferably 10° C. or lower. , and preferably -10°C or higher, more preferably 0°C or higher.
The glass transition temperature (Tg) can be determined by differential scanning calorimetry.

Examples of water-dispersible resins include acrylic resins, urethane resins, vinyl resins, and styrene resins.
Among them, in the present application, it is preferable to select and use one or more of acrylic resins, styrene resins, and vinyl resins, and it is more preferable to use styrene resins or vinyl resins. This is because the effects of the foaming agent are obtained, and handwriting with excellent stereoscopic effect can be easily obtained, and further, handwriting with excellent fixability can be easily obtained.
As the styrene resin, a styrene-olefin polymer composed of styrene and an olefin such as butadiene, isoprene, ethylene/butylene, or ethylene/propylene is preferably used.
Vinyl acetate resin is preferably used as the vinyl resin.
Furthermore, since it is easy to improve the above effects, the feeling of the handwriting obtained has elasticity (flexibility), and it is easy to obtain a handwriting with a continuous three-dimensional effect. Preferably coalescence is used, more preferably styrene-butadiene polymers are used.
Although the reason for this is not clear, it is considered as follows. When a styrene-olefin polymer is used, the film formed on the handwriting surface tends to have excellent elasticity. For this reason, the handwriting can receive the force of the blowing agent sufficiently without being affected by the film on the surface of the handwriting.Furthermore, the elasticity of the film is maintained, and the handwriting itself after foaming is a flexible foam with elasticity. becomes. Therefore, the obtained handwriting is continuous and has a sufficient three-dimensional effect, and is rich in elasticity (flexibility).
Considering the improvement of the above effect, the styrene-butadiene polymer preferably has a styrene content of 60 mol% or less, more preferably 50 mol% or less, relative to the total amount constituting the styrene-butadiene polymer. preferable.

The weight average molecular weight of the water-dispersible resin is preferably 10,000 to 10,000,000, more preferably 30,000 to 3,000,000, and still more preferably 100,000 to 1,000,000. Here, in the present invention, the weight average molecular weight can be measured by an ordinary method using gel permeation chromatography. The same applies to the subsequent mass average molecular weights.

The water-dispersible resin preferably has an average particle size of 500 nm or less, more preferably 300 nm or less, and still more preferably 200 nm or less. When the average particle diameter is 500 nm or less, the dispersion stability of the resin particles is improved, and the ink ejection property is improved and easily stabilized, so that the three-dimensional effect is excellent, and uniform and continuous handwriting can be easily obtained. In addition, sedimentation of resin particles is suppressed, and ink dispersion stability is improved.
Incidentally, the average particle size can be measured by a dynamic light scattering method.

When producing the ink composition according to the present invention, the water-dispersible resin may be added in the form of a dispersion, such as an emulsion, in water (using a dispersant if necessary). In one preferred form, the aqueous dispersion is added to the ink composition in the form of an emulsion.

Examples of commercially available emulsions containing a water-dispersible resin include Movinyl 718A (trade name, manufactured by Nippon Synthetic Chemical Industry Co., Ltd.) as an acrylic resin emulsion, Vinyblan 1002 as a vinyl acetate resin emulsion, 1008 (trade name, manufactured by Nissin Chemical Industry Co., Ltd.), and styrene-butadiene polymer emulsions include L-1924 and L-1432 (trade name, manufactured by Asahi Kasei Chemicals Co., Ltd.).

The content of the water-dispersible resin is preferably 1 to 50% by mass based on the total mass of the ink composition. If the content of the water-dispersible resin is within the above numerical range, the ink jettability can be improved, and handwriting with excellent three-dimensional effect and excellent fixability can be obtained. In addition, the stability of the ink over time can be improved.
Furthermore, considering the improvement of the above effects, the content is more preferably 5 to 40% by mass, still more preferably 10 to 30% by mass, and particularly preferably 15 to 30% by mass.
In addition, water-dispersible resin can also combine multiple types.

<Thickener>
The ink composition of the present invention comprises a thickening agent.
The thickener makes it easy to suppress sedimentation and aggregation of the foaming agent and the water-dispersible resin in the ink when the ink is left standing, thereby obtaining excellent dispersibility of the foaming agent and the water-dispersible resin. Therefore, the three-dimensional effect of the handwriting after the foaming treatment is less likely to be uneven, and the handwriting excellent in three-dimensional effect and fixability can be obtained.
As the thickening agent, conventionally known substances can be used, but it is preferable to use a substance capable of imparting shear thinning properties to the ink composition (shear thinning agent). By using such a substance, the viscosity of the ink composition can be easily lowered when an external force is applied, while maintaining the ink viscosity at which the foaming agent, the water-dispersible resin, etc. do not readily settle or aggregate when left standing. . Therefore, it is possible to further improve ink discharge from the writing tip during writing while suppressing ink sedimentation and aggregation during standing. Therefore, it is possible to obtain a handwriting with a more excellent three-dimensional effect.
In particular, when such an ink composition is used in a pressurized writing instrument, a strong shearing force is applied to the ink when pressurized, and the viscosity of the ink tends to be lower. For this reason, the ink ejection from the tip of the writing is likely to be improved, and it is possible to secure a sufficient amount of ink in the handwriting before the foaming treatment, and the handwriting after the foaming treatment has a further excellent three-dimensional effect. Become.
Furthermore, among pressurized writing implements, when it is used in a pressurized ballpoint pen, a strong shearing stress is likely to be applied to the ink as the ball rotates, making it easier to obtain the above effects. Furthermore, since the ink ejection amount can be stabilized, uniform and continuous handwriting having a three-dimensional effect can be easily obtained, and even fine handwriting such as characters can be easily left three-dimensionally.

As the shear thinning agent, a crosslinked acrylic acid polymer, an associative thickener, a polysaccharide, or the like can be used.
Examples of associative thickeners include polyester-based, polyether-based, urethane-modified polyether-based, polyaminoplast-based, alkali-swelling associative thickeners, and nonionic associative thickeners, depending on the associative hydrophobic group. Polysaccharides include xanthan gum, welan gum, succinoglycan, guar gum, locust bean gum, λ-carrageenan, cellulose derivatives, diutan gum and the like. These shear thinning agents can be used alone or in combination of two or more.
Among these, polysaccharides or crosslinked acrylic acid polymers are preferably used, and polysaccharides are more preferable. It is resistant to shearing by a stirrer, can be stably produced, and has good compatibility with water-dispersible resins and foaming agents, and can be adjusted to an ink with excellent stability over time. because it is easy. Furthermore, among polysaccharides, succinoglycan has a higher viscosity in a static state (at low shear) than other polysaccharides, so it is easy to stably disperse water-dispersed resins and foaming agents, and it is highly stable. It is more preferable because it provides an excellent ink composition.

The content of the thickener is preferably 0.01% by mass to 5% by mass, more preferably 0.05% by mass to 1% by mass, based on the total mass of the water-based ink composition. More preferably, it is 1 to 0.8% by mass.
If the content of the thickening agent is within the above numerical range, excellent dispersibility of the foaming agent, water-dispersible resin, etc. can be obtained, and ink ejection from the tip of writing can be improved, resulting in three-dimensional effect and fixation. It is easy to obtain a handwriting excellent in quality. Furthermore, the ink stability over time can also be improved.

In addition, considering that the ink has excellent stability over time, improves and stabilizes the ink ejection property, has a uniform and continuous three-dimensional effect, and gives excellent fixability, the foaming ratio for the content of the thickener The ratio of the total content of the agent and the water-dispersible resin is preferably 50 to 120, more preferably 60 to 100, on a mass basis.

<Colorant>
The ink composition according to the invention comprises a colorant. Any of conventionally known pigments and dyes can be used.

Dyes are not particularly limited. Examples thereof include various dyes such as acid dyes, basic dyes, reactive dyes, direct dyes, disperse dyes and food colorings, and these can be used alone or in combination of two or more.

Specifically, as the acid dye, C.I. I. Acid Red 18, C.I. I. Acid Red 51, C.I. I. Acid Red 52, C.I. I. Acid Red 87, C.I. I. Acid Red 92, C.I. I. Acid Red 289, C.I. I. Acid Orange 10, C.I. I. Acid Yellow 3, C.I. I. Acid Yellow 7, C.I. I. Acid Yellow 23, C.I. I. Acid Yellow 42, C.I. I. acid green 3, C.I. I. Acid Green 16, C.I. I. acid blue 1, C.I. I. Acid Blue 9, C.I. I. Acid Blue 22, C.I. I. Acid Blue 90, C.I. I. Acid Blue 239, C.I. I. Acid Blue 248, C.I. I. Acid violet 15, C.I. I. Acid Violet 49, C.I. I. Acid Black 1, C.I. I. Acid Black 2 and basic dyes such as C.I. I. Basic Orange 2, C.I. I. Basic Orange 14, C.I. I. Basic Green 4, C.I. I. Basic Blue 9, C.I. I. Basic Blue 26, C.I. I. Basic Violet 1, C.I. I. Basic Violet 3, C.I. I. Basic Violet 10, and as a direct dye, C.I. I. Direct Red 28, C.I. I. Direct Yellow 44, C.I. I. Direct Blue 86, C.I. I. Direct Blue 87, C.I. I. Direct Violet 51, C.I. I. Direct Black 19, food coloring such as C.I. I. Food Yellow 3, C.I. I. Food Black 2 and the like.

Pigments are not particularly limited. For example, carbon black, aniline black, ultramarine, yellow lead, titanium oxide, iron oxide, phthalocyanine pigments, azo pigments, quinacridone pigments, quinophthalone pigments, styrene pigments, triphenylmethane pigments, perinone pigments, perylene pigments, dioxazine pigments, luster pigments, microcapsule pigments, colored resin pigments, and the like. As the pigment, a water-dispersible pigment product or the like that is previously dispersed in a medium using a pigment dispersant such as a surfactant may be used.

In the present application, the coloring agent is preferably a pigment, since it is easy to obtain a handwriting with good color development and excellent three-dimensional effect.
Among pigments, it is preferable to use colored resin pigments. Since colored resin pigments tend to have excellent heat resistance and weather resistance, they tend to maintain good color developability even after the handwriting is subjected to foaming treatment. In addition, since it tends to be possible to obtain stable ink ejection from the tip of writing, it is easy to obtain uniform and continuous handwriting excellent in three-dimensional effect. In addition, the temporal stability of the ink tends to be improved.
In the present invention, the term "colored resin pigment" refers to resin particles colored with a coloring agent. The colorant is not particularly limited as long as it can color the resin particles, and any pigment or dye can be used. The resin particles are excellent in alkali resistance, acid resistance, and heat resistance, and have high stability even in the presence of various additives. Therefore, styrene-acrylonitrile resin particles (hereinafter sometimes referred to as SA resin particles). is preferably
Examples of commercially available products containing colored resin particles include, specifically, Shinroihi Color series (manufactured by Shinroihi Co., Ltd.), Lumicol series (manufactured by Nihon Shokuryo Kagaku Co., Ltd.), and LM series (Fuji Pigment Co., Ltd.). (manufactured by Nippon Shokubai Co., Ltd.). Specifically, the Lumicol series includes NKW-2317H, NKW-6307H, NKW-2308H, NKW-2302H, NKW-2305H, and NKW-6305H.
In addition, as the Shinrohi color series, the Shinrohi color base SW-11, the same SW-12, the same SW-13, the same SW-14, the same SW15, the same SW-16, the same SW-17, the same SW-18, the same SW-27, SW-37, SW-47, SF-1012, SF-1013, SF-1014, SF-1015, SF-1017, SF-1027, SF-1038, SF- 5015 etc. are also mentioned.

It is also a preferred embodiment to use a reversible thermochromic microcapsule pigment as the colorant. By using a reversible thermochromic microcapsule pigment as a coloring agent, it is possible not only to obtain a three-dimensional handwriting, but also to achieve both a three-dimensional shape change and a color change of the handwriting, making the handwriting more beautiful. You can enjoy it even more.
The reversible thermochromic microcapsule pigment includes at least (a) an electron-donating color-forming organic compound, (b) an electron-accepting compound, and (c) a reaction medium that determines the temperature at which the color reaction of both of them occurs. and those encapsulating a reversible thermochromic composition consisting of.

The content of the colorant varies depending on its type, but is preferably 0.1 to 30% by mass, more preferably 1 to 20% by mass, more preferably 1 to 20% by mass, based on the total mass of the ink composition. 2 to 10% by mass.
Colorants may be used singly or in combination of two or more.

<Water>
The ink composition according to the invention comprises water. Water is not particularly limited, and for example, tap water, ion-exchanged water, ultrafiltered water, distilled water, or the like can be used.
The water content is preferably 10 to 90% by weight based on the total weight of the ink composition.

<Other additives>
The ink composition of the present invention essentially comprises the above-described components (foaming agent, water-dispersible resin, thickener, colorant and water), but may contain other components as necessary.

<Strengthening agent>
The ink composition according to the present invention may further comprise a extender.
By using the extender, the shape of the handwriting before the foaming treatment is easily maintained, and the handwriting with excellent three-dimensional effect is easily obtained after the foaming treatment.
Examples of extenders include inorganic extenders such as calcium carbonate, kaolin, talc, silica, aluminum silicate, alumina and barium sulfate, as well as organic extenders such as resin particles.
The content of the extender is preferably 0.1 to 20% by mass based on the total mass of the ink composition. It is 1 to 10% by mass in consideration of the effect of the extender, which makes it easy to obtain a handwriting with excellent three-dimensional effect, the stability of the ink over time, the ink ejection stability, and the maintenance of good color development of the handwriting. is more preferable.

<Water-soluble organic solvent>
The ink composition according to the present invention preferably further contains a water-soluble organic solvent. In general, when it contains components such as foaming agents, water-dispersible resins, and pigments that can exist in an insoluble state in water, which is the main solvent, water will be absorbed by the nib of a writing instrument filled with the ink. The ink may evaporate and dry and solidify, clogging the ink flow path. When such a phenomenon occurs, it is difficult to clear the clogging with ink that is followed later, and the writing instrument may become unable to write again, although there is ink remaining. Therefore, it is preferable to improve the dry-up resistance performance. Since the ink composition of the present invention contains the components as described above and has a high content thereof, it is highly necessary to improve the dry-up resistance performance. Therefore, the ink composition of the present application preferably further contains a water-soluble organic solvent capable of improving the dry-up resistance performance.
Examples of the water-soluble organic solvent include polyhydric alcohols, glycol ethers, etc. Among them, it is preferable to select and use polyhydric alcohols such as ethylene glycol, diethylene glycol, and glycerin. These solvents have little effect on the foaming agent and the water-dispersible resin, do not significantly affect the dispersion stability of the ink composition, and impart the hygroscopic effect of polyhydric alcohols to the ink composition. This is because the dry-up resistance performance can be improved. Among them, it is preferable to use glycerin in the present application.

The content of the water-soluble organic solvent is preferably 0.1 to 20 mass % based on the total mass of the ink composition. Furthermore, considering that handwriting with a three-dimensional effect can be easily obtained while improving dry-up resistance, the amount is 1 to 10% by mass.

In addition, the ink composition of the present invention may contain various additives such as pH adjusters, rust preventives, antiseptics, and chelating agents for the purpose of improving the physical properties and functions of the ink.

Examples of pH adjusters include basic inorganic compounds such as ammonia, sodium carbonate, sodium phosphate and sodium hydroxide, basic organic compounds such as sodium acetate, triethanolamine and diethanolamine, lactic acid, acetic acid and citric acid. .

Preservatives include phenol, sodium benzoate, sodium dehydroacetate, potassium sorbate, propyl parahydroxybenzoate, 2,3,5,6-tetrachloro-4-(methylsulfonyl)pyridine, 2-pyridinethiol-1- sodium oxide, 1,2-benzisothiazolin-3-one, 2-methyl-4-isothiazolin-3-one, 2-n-octyl-4-isothiazolin-3-one, orthophenylphenol or a salt thereof; .

Rust inhibitors include benzotriazole and its derivatives, tolyltriazole, dicyclohexylammonium nitrite, diisopropylammonium nitrite, sodium thiosulfate, saponin, dialkylthiourea, and the like.

Chelating agents include ethylenediaminetetraacetic acid (EDTA), hydroxyethylenediaminetriacetic acid (HEDTA), glycol etherdiaminetetraacetic acid (GEDTA), nitrilotriacetic acid (NTA), hydroxyethyliminodiacetic acid (HIDA), dihydroxyethylglycine (DHEG ), diethylenetriaminepentaacetic acid (DTPA), triethylenetetraminehexaacetic acid (TTHA) and their alkali metal salts, ammonium salts or amine salts.

Moreover, in the present invention, a moisturizing agent other than the water-soluble organic solvent may be further included. Examples thereof include urea, sorbitol, dextrin, N,N,N-trialkylamino acids such as trimethylglycine, hyaluronic acids, and the like, which can be preferably used.

Furthermore, nonionic surfactants, anionic surfactants, cationic surfactants, surfactants having acetylene bonds in their structures, and fluorine-based surfactants can also be added.
An antifoaming agent can also be added. Lubricants such as phosphate surfactants and fatty acids may also be added. A water-soluble resin that has a hydrophilic group and can be uniformly dissolved in water can also be added.

<Water-based ink composition for writing instruments>
The viscosity of the ink composition according to the present invention is preferably 500 mPa·s or more, more preferably 1000 mPa·s or more, at 20° C. and a shear rate of 1.92 sec ⁻¹ (0.5 rpm). It is preferably 2000 mPa·s or more, preferably 10000 mPa·s or less, and more preferably 5000 mPa·s or less.
If the viscosity is within the above numerical range, it is possible to stably obtain a handwriting with excellent ink jetting properties, excellent three-dimensional effect, and excellent fixability while having excellent dispersion stability.
Further, the solid content ratio of the ink composition is preferably 10 to 50% by mass, more preferably 15 to 40% by mass, and still more preferably 20 to 40% by mass, based on the total mass of the ink composition. is.
If the solid content ratio is within the above numerical range, the viscosity of the ink under conditions of 20° C. and a shear rate of 1.92 sec ⁻¹ can be easily set within the above numerical range, and handwriting with excellent three-dimensional effect and fixability can be formed. .
As described above, the ink composition according to the present invention tends to have a higher viscosity and a higher solid content ratio than the ink composition for writing instruments normally used as described above, in order to obtain handwriting with excellent three-dimensional effect and excellent fixability. Preferably.

The ink composition according to the present invention is used for writing implements, and a preferred form of the present invention is a pressurized writing implement, and further a pressurized ball-point pen. In this case, it is preferable to obtain good ink jettability during writing.
Therefore, the viscosity of the ink composition is preferably 500 mPa·s or less, more preferably 400 mPa·s or less, and still more preferably 300 mPa under conditions of 20° C. and a shear rate of 76.8 sec ⁻¹ (20 rpm).・It is less than or equal to s.
In addition, considering the dispersion stability of the ink when it is still and the ability to obtain good ink ejection from the tip of the writing, and to obtain a handwriting with a stable and uniform three-dimensional effect, It is preferable that the viscosity and the viscosity gradient during flow are above a certain level, that is, the viscosity ratio of the ink composition during high shearing and low shearing is above a certain level.
Therefore, the viscosity ratio of the ink composition at high shear and low shear (viscosity at 20° C., shear rate 1.92 sec ⁻¹ (0.5 rpm)/20° C. shear rate 76.8 sec ⁻¹ (20 rpm) is preferably 5 or more, more preferably 10 or more, and preferably 20 or less.

<Method for producing ink composition>
The ink composition according to the present invention can be produced by any conventionally known method. Specifically, the necessary amounts of the above components are blended and mixed with various stirrers such as a magnetic hot stirrer, propeller stirrer, homogenizer stirrer, homodisper, homomixer, and planetary stirrer, and various dispersers such as a bead mill. , can be manufactured.

<Writing implements>
A writing instrument according to the present invention contains the above ink composition.
The structure and shape of the writing instrument to be filled with the ink composition according to the present invention are not particularly limited, and conventional general-purpose writing instruments can be applied, but pressure writing instruments are particularly preferred. This is because the ink composition according to the present invention tends to have a high viscosity and a high solid content ratio, so that the ink ejection property can be improved by accommodating it in a pressure writing instrument and using it. For this reason, it is possible to ensure a sufficient amount of ink in the handwriting before the foaming treatment, and the handwriting after the foaming treatment has a more excellent three-dimensional effect and excellent fixability.
Further, it is preferably used in a pressurized ball-point pen having a ball-point tip as a pen point. By using a pressurized ballpoint pen, the ink ejection property is easily stabilized, and uniform and three-dimensional handwriting can be easily obtained. In addition, even fine handwriting can be made three-dimensional.
As the pressurized ballpoint pen, a pressurized ballpoint pen in which a pressurized gas is enclosed in the ink container and the pressure of the pressurized gas presses the ink composition toward the tip end side, or a pressurized ballpoint pen that presses the ink composition toward the tip end side by the pressure of the pressurized gas, or a pressurized ballpoint pen that presses the ink composition to the tip end side by the pressure of the pressurized gas, or a pressurized ballpoint pen that presses the ink composition to the tip end side by the pressure of the pressurized gas A knock-type pressurized ballpoint pen that compresses the space existing on the rear end side of the ink composition by moving the pen tip due to the writing pressure of , and presses the ink composition toward the tip end side by the pressure generated by this compression. A cap-type pressurized ball-point pen having a cap that covers the pen tip, and a pen-pressure pressurized ball-point pen may be mentioned.
Since the ink composition according to the present invention tends to have a high solid content ratio, a pressurized ballpoint pen with a cap that can seal the tip is more preferable in consideration of dry-up resistance.

The pressure applied from the rear end side of the ink container cylinder to the ink composition filled inside is preferably greater than the atmospheric pressure, specifically greater than the atmospheric pressure, ie, 1.5 times the pressure. The following are preferred. More specifically, when the atmospheric pressure is 1000 hPa, it is preferably higher than 1000 hPa and 1500 hPa or lower, more preferably higher than 1000 hPa and 1200 hPa or lower. As a result, it is possible to suppress ink leakage from the leading end of the tip while optimizing the amount of ink consumed, and it is possible to improve handwriting quality and handwriting density, such as obtaining a sufficient three-dimensional effect.

EXAMPLES The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

<Example 1>
The following ingredients other than the thickening agent are mixed in the following amounts with a magnetic stirrer at room temperature to prepare a base ink. The ink composition of Example 1 was obtained by thoroughly mixing and stirring using a homogenizer stirrer until a uniform state was obtained.

- Foaming agent (thermally expandable foaming agent (thermally expandable microcapsules), trade name: EXPANCEL031 WUF40, Nippon Ferrite Co., Ltd., average particle size: 10 to 16 µm, foaming start temperature: 80 to 95°C, maximum expansion temperature: 120 ~ 135 ° C., solid content 76 mass%) 5.0 parts by mass Water-dispersible resin (styrene-butadiene copolymer emulsion, trade name: L1924, manufactured by Asahi Kasei Chemicals Corporation, glass transition temperature 5 ° C., solid content 46 mass %, styrene content: 45 mol%, average particle size: 150 nm) 50.0 parts by mass Thickener (succinoglycan) 0.3 parts by mass Colorant (44% by mass of colored resin particles (pink) dispersed in water Body, trade name: Lumicol NKW-2317H, manufactured by Nihon Shokuryo Kagaku Co., Ltd.) 10.0 parts by mass Water-soluble organic solvent (glycerin) 5.0 parts by mass Water 29.7 parts by mass

<Examples 2 to 11 and Comparative Examples 1 to 3>
In Examples 2 to 11 and Comparative Examples 1 to 3, water-based ink compositions were prepared in the same manner as in Example 1, except that the types and blending amounts of the components contained in the ink composition were changed to those shown in the table. Obtained. Numerical values for compositions in the table indicate parts by mass.

Description is made along the note numbers of the materials in the table.
(1) Trade name: Advancel EMH204, manufactured by Sekisui Chemical Co., Ltd., average particle size: 36-44 μm, foaming start temperature: 110-130°C, maximum expansion temperature: 160-180°C
(2) Trade name: EXPANCEL031 WUF40, Nippon Ferrite Co., Ltd., average particle size: 10-16 μm, foaming start temperature: 80-95° C., maximum expansion temperature: 120-135° C., solid content: 76% by mass
(3) 4,4′-oxybis(benzenesulfonyl hydrazide), trade name: Neo Cellvon #5000, manufactured by Eiwa Chemical Industry Co., Ltd. (4) Trade name: Cellpaste 101, manufactured by Eiwa Chemical Industry Co., Ltd. (5) Trade name: L1924, manufactured by Asahi Kasei Chemicals Corporation, glass transition temperature 5 ° C., solid content 46% by mass, styrene content: 45 mol%, average particle size: 150 nm
(6) Product name: L1432, manufactured by Asahi Kasei Chemicals Corporation, glass transition temperature 18°C, solid content 46% by mass, styrene content: 50 mol%, average particle size: 200 nm
(7) Product name: Vinyblan 1008, manufactured by Shin-Etsu Chemical Co., Ltd., glass transition temperature 30 ° C., solid content 46% by mass
(8) Product name: Movinyl 718A, manufactured by Nippon Synthetic Chemical Industry Co., Ltd., glass transition temperature -6°C, solid content 46% by mass
(9) Product name: Movinyl 972, manufactured by Nippon Synthetic Chemical Industry Co., Ltd., glass transition temperature 100°C, solid content 50% by mass
(10) Trade name: Hibis Wako 104, manufactured by Wako Pure Chemical Industries, Ltd. (11) Trade name: SG-95, manufactured by Nippon Talc Co., Ltd. (12) Trade name: BF-40E, manufactured by Sakai Chemical Industry Co., Ltd. (13) ) Product name: Lumicol NKW-2317H, manufactured by Nihon Shokuryo Kagaku Co., Ltd., solid content 44%
(14) Product name: Water Yellow 6C, manufactured by Orient Chemical Industry Co., Ltd.

Preparation of reversible thermochromic microcapsule pigment 1 1.0 parts of 3,6-bis (diphenylamino) fluorane as an electron-donating color-changing organic compound and a component, 1,1-bis (4-hydroxy as an electron-accepting compound 3.0 parts of phenyl)-2-ethylhexane, 5.0 parts of 2,2-bis(4'-hydroxyphenyl)-hexafluoropropane, and 50.0 parts of 4-benzyloxyphenylethyl caprate as a reaction medium. A reversible thermochromic microcapsule pigment 1 was prepared by encapsulating a reversible thermochromic composition having color memory properties in microcapsules.
Microcapsule Pigment 1 had an average particle size of 1.8 μm, a complete decolorization temperature of 55° C., and a complete color development temperature of −20° C. The color changed from blue to colorless as the temperature changed.

<Evaluation>
The ink compositions of Examples and Comparative Examples were filled in the ball-point pen refill 7 of the cap-type pressurized ball-point pen 1, and writing was performed under pressure. For the subsequent handwriting evaluation, writing was performed using the pressurized ballpoint pen, and the resulting handwriting was evaluated.

Here, the cap-type pressurized ball-point pen 1 is shown in FIGS. 1 to 3. FIG.
A cap-type pressurized ball-point pen 1 has a ball-point pen refill 7 disposed in a barrel body connecting a front barrel 2 with a grip member 14 attached to a grip portion and a rear barrel 3 .
The cap-type pressurized ballpoint pen 1 has a translucent cap 4 obtained by injection molding of PP resin. It is detachably attached by fitting over the fitting protrusion. When a cap is attached to the front barrel 2, the ball-point pen tip 10 is sealed by a sealing member provided in the cap.

A ball-point pen tip 10 rotatably holding a ball with a diameter of 1.0 mm is attached via a tip holder 9 to the front end of an ink container 8 provided in the ball-point pen refill 7 .
A tail plug 11 having an air hole communicating between the inside and the outside is attached to the rear end portion of the ink containing cylinder 8 .
The interior of the ink container 8 is filled with the water-based ink composition 12 for writing instruments and the ink follower 13, which are composed of the above-described ink formulations.
Although not shown, a coil spring is provided behind the ball to constantly press the ball against the inner wall of the front end of the chip.

The rear end portion of the ink containing cylinder 8 provided in the ballpoint pen refill 7 is press-fitted into the rear end portion of the rear barrel 3, and the portion of the ink containing cylinder 8 filled with the ink composition 12 and the ink follower 13. The space following the rear barrel 3 communicates with the outside air only through a communication hole 3A provided at the rear end of the rear barrel 3, which communicates the inside and the outside of the writing instrument.

The pressurizing mechanism that operates when the cap 4 is fitted will be described in detail below.
By fitting the cap 4 to the rear barrel 3 of the writing instrument main body, pressure can be applied via the ink follower 13 to the ink composition 12 filled in the ballpoint pen refill 7 .
Specifically, when the rear end portion of the rear barrel 3 is inserted into the open end side of the cap body 5 in the direction of arrow F in the drawing, the inner wall 5A of the cap body 5 and the side wall 3B of the rear barrel 3 first come into contact.
At this time, the spaces of the cap body 5, the rear barrel 3, and the ink container 8 communicate with each other in a sealed state through a communication hole 3A provided at the rear end portion of the rear barrel 3, which communicates the inside and the outside.
Further, when the cap 4 is advanced in the direction of the arrow F in the figure, the sealed space is compressed until the fitting is completed. As a result, pressure can be applied via the ink follower 13 to the water-based ink composition for writing instruments filled in the ball-point pen refill 7 . Incidentally, the pressure was 1050 hPa.

<Handwriting evaluation>
The ink compositions of Examples and Comparative Examples were written on writing paper (JIS P 3201 writing paper A), allowed to stand overnight, and then heat-treated with a dryer (1200 W) for 10 minutes. Fixability and elasticity were evaluated. Each evaluation criterion is as follows. The results obtained are shown in the table.
Three-dimensional effect ◯: Swelling of the handwriting could be sufficiently confirmed by visual observation.
Δ: Swelling of the handwriting could be confirmed by visual observation, but it was somewhat lacking.
x: No swelling of the handwriting could be confirmed by visual observation.
Fixability ◯: The ink was not peeled off from the writing surface even when the handwriting was touched.
Δ: When the handwriting was touched, the handwriting was partially peeled off from the writing surface.
x: When the handwriting was touched, it peeled off from the writing surface.
Elasticity ◯: The handwriting has elasticity (flexibility).
Δ: The handwriting has elasticity (flexibility), but is somewhat poor.
x: No elasticity (flexibility) in handwriting.

The ink composition of Example 1 was placed in a sealed glass test tube with a diameter of 15 mm and allowed to stand at room temperature for 3 days, and the state of the ink composition was visually observed. The stability over time was good.

The viscosities of the obtained ink compositions of Examples 1 and 8 were measured at 20° C. using an E-type rotational viscometer (model: DV-II+Pro, rotor: CPE-42, manufactured by Brookfield). The ink viscosities measured at a shear rate of 1.92 sec ^-1 (rotational speed of 0.5 rpm) were 3020 mPa·s and 3328 mPa·s.

[Viscosity ratio]
The viscosities of the obtained ink compositions of Examples 1 and 8 were measured using an E-type rotational viscometer (model: DV-II+Pro, rotor: CPE-42, manufactured by Brookfield) under shear conditions at 20°C. Ink viscosity was measured at a speed of 76.8 sec ⁻¹ (rotational speed of 20 rpm).
The viscosity at a shear rate of 1.92 sec ^-1 (0.5 rpm) and the viscosity at a shear rate of 76.8 sec ^-1 (20 rpm) were calculated, and the viscosity ratio (0.5 rpm/20 rpm) was obtained. there were.

As described above, an ink composition comprising water, a coloring agent, a foaming agent, a water-dispersible resin having a glass transition temperature of less than 100° C., and a thickener has sufficient three-dimensional effect. Moreover, it was found that a writing instrument using this ink composition was excellent as a writing instrument.

1 cap-type pressurized ballpoint pen 2 front barrel 3 rear barrel 3A communication hole 3B side wall 4 cap 5 cap main body 5A inner wall 6 seal member 7 ballpoint refill 8 ink container 9 tip holder 10 ballpoint pen tip 11 tail plug 11A air hole 12 ink for writing instrument Composition 13 Ink Follower 14 Grip

Claims (10)

An aqueous ink composition for writing instruments, comprising water, a coloring agent, a foaming agent, a water-dispersible resin having a glass transition temperature of less than 100°C, and a thickening agent. 2. The ink composition of claim 1, wherein said blowing agent is a thermal blowing agent. 3. The ink composition according to claim 1, wherein the heat-sensitive foaming agent is a thermal expansion foaming agent. The ink composition according to any one of claims 1 to 3, wherein the thickener is a shear thinning agent. The ink composition according to any one of claims 1 to 4, wherein the content of said foaming agent is 1% by mass to 20% by mass based on the total mass of said ink composition. The ink composition according to any one of claims 1 to 5, wherein the content of the water-dispersible resin is 1% by mass to 50% by mass based on the total mass of the ink composition. The ink composition according to any one of claims 1 to 6, wherein the ink composition has a solid content ratio of 10% by mass to 50% by mass. The ink composition according to any one of claims 1 to 7, wherein the ink composition has a viscosity of 500 mPa·s or more at 20°C and a shear rate of 1.92 sec ^-1 . A writing instrument containing the composition according to any one of claims 1 to 8. 10. The writing instrument according to claim 9, which is a pressurized writing instrument.

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