JP2005255952A - Water-based ink composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a water-based ink composition that has no sedimentation with time and excellent long-term stability and is suitable for writing utensils, stamps and corrections. <P>SOLUTION: The water-based ink is obtained by dispersing composite particles obtained by coating the surface of base particle having <1.6 specific gravity with titanium oxide and titanium hydroxide into a liquid medium consisting essentially of water in which the dispersed particles have 50 nm-2 nm average particle diameter. Preferably the thickness of the coating layers of titanium oxide and titanium hydroxide on the composite particle is preferably 1-500 nm. Preferably the base particle is composed of an organic resin particle having ≥60°C Tg (glass transition point). Preferably the surface of the base particle is treated with an anionic surfactant. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a water-based ink composition suitable for writing instruments, stamps, and corrections that has no sedimentation separation with time and has excellent long-term stability over time.

In general, titanium oxide is a pigment capable of imparting whiteness and concealment due to its excellent light scattering effect, and is used as a white pigment and concealment-type modifier. As its usage, an ink composition in which titanium oxide itself is dispersed in a liquid medium composed of water or an organic solvent is prepared and used as a correction liquid or marking ink.
However, the specific gravity of titanium oxide itself is very large, such as 3.8 to 4.1, and has a serious drawback that sedimentation and separation occur even if the particle size in the dispersion is reduced.

  In order to eliminate such drawbacks, in the correction ink, for example, titanium dioxide as an essential component, a dispersant in the water-containing alcohol of the titanium dioxide, a polymer flocculant, a lower alcohol and water are used. In the correction liquid (see Patent Document 1) and writing ink, for example, an aqueous ink composition (see Patent Document 2) consisting of at least a polymeric polysaccharide composed of titanium oxide and succinoglucan and water, and titanium oxide. And a water-based ink for ballpoint pens containing oleic acid as essential components (see Patent Document 3).

However, even with aqueous correction liquids and water-based ink compositions described in each of these documents, initially, titanium oxide sedimentation and separation are somewhat suppressed, but precipitation and separation phenomena occur over time. There are still some issues.
Japanese Patent Laid-Open No. 3-166275 (Claims, Examples, etc.) JP-A-8-113752 (Claims, Examples, etc.) JP-A-10-251588 (Claims, 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. The specific gravity is lower than that of the conventional white pigment titanium oxide particles, and the whiteness and concealment of the titanium oxide particles themselves. To provide a water-based ink composition suitable for writing instruments, stamps, and corrections with excellent stability over time for a long period of time, using particles with specific properties that retain their properties, and having no settling separation over time. Objective.

  In order to solve the above conventional problems, etc., the present inventors have conducted extensive research on good titanium oxide and titanium hydroxide-coated composite particles and water-based ink compositions containing the same. By making full use of the method, the present inventors have found that the above-mentioned objective water-based ink composition can be obtained by overcoming the problems of the conventional titanium oxide oil-containing water-based ink composition, and have completed the present invention.

That is, the present invention resides in the following (1) to (10).
(1) Composite particles in which titanium oxide and titanium hydroxide are coated on the surface of mother particles having a specific gravity of less than 1.6 are dispersed in a liquid medium containing water as a main component, and the average particle size of the dispersed particles is 50 nm to 2 μm. A water-based ink composition characterized by being in a range.
(2) The water-based ink composition according to the above (1), wherein the thickness of the coating layer of titanium oxide and titanium hydroxide on the composite particles is in the range of 1 to 500 nm.
(3) The water-based ink composition according to the above (1), wherein the base particles are composed of organic resin particles having a Tg (glass transition point) of 60 ° C. or higher.
(4) The water-based ink composition according to the above (1), wherein the surface of the mother particle is treated with an anionic surfactant.
(5) In the ink composition, as a particle fixing binder, at least one selected from an acrylic emulsion having a MFT (minimum film forming temperature) of less than 40 ° C., a styrene-butadiene emulsion, and an ethylene-vinyl acetate emulsion. The water-based ink composition according to any one of (1) to (4), which is contained.
(6) The water-based ink composition according to any one of (1) to (4), wherein the ink composition contains water-soluble fibers as a particle fixing binder.
(7) The water-based ink composition according to any one of (1) to (6), wherein a colorant composed of a pigment and a dye is contained in an amount of 0.1 to 15% by weight based on the total amount of the ink composition.
(8) The water-based ink according to any one of (1) to (7), wherein a viscosity value of 1 rpm measured with an EMD viscometer is in a range of 5 to 2000 mPa · s under a condition of 25 ° C. Composition.
(9) The water-based ink according to any one of (1) to (7), wherein a viscosity value at 100 rpm measured with an EMD viscometer is in a range of 4 to 200 mPa · s under a condition of 25 ° C. Composition.
(10) The water-based ink according to any one of (1) to (9), wherein the titanium oxide and titanium hydroxide coating layers of the composite particles are formed by any one of the following methods (a) to (c): Composition.
(A) A method in which titanium alkoxide is hydrolyzed in a film-forming reaction solution to coat titanium oxide and titanium hydroxide on the surface of the mother particle.
(B) A method in which inorganic titanic acid is hydrolyzed in a film-forming reaction solution to coat titanium oxide and titanium hydroxide on the surface of the mother particles.
(C) A method in which peroxotitanium is reacted in a film-forming reaction solution to coat titanium oxide and titanium hydroxide on the surface of the mother particle.

ADVANTAGE OF THE INVENTION According to this invention, while being excellent in the sedimentation-separation inhibitory effect and aging stability which were not in the former, the aqueous ink composition excellent in whiteness and hiding property is provided.
Moreover, according to invention of Claims 5-9, the water-based ink composition excellent in drying property and adhesiveness is provided further.

Hereinafter, embodiments of the present invention will be described in detail.
The water-based ink composition of the present invention (hereinafter sometimes simply referred to as “ink composition”) is composed of composite particles in which titanium oxide and titanium hydroxide are coated on the surface of mother particles having a specific gravity of less than 1.6, and water is the main component. The dispersed particles are dispersed in a liquid medium, and the average particle size of the dispersed particles is in the range of 50 nm to 2 μm.

As the mother particles having a specific gravity of less than 1.6 used in the present invention, organic fine particles obtained by polymerizing a monomer by polymerization, condensation reaction or the like are preferable. Specifically, polyethylene (specific gravity of 0.91 to 0) .97), polyvinyl acetate (specific gravity 1.16 to 1.25), ethylene-vinyl acetate copolymer (specific gravity 1.41 to 1.21), polyisobutylene (specific gravity 1.05 to 1.13), polyamide (specific gravity) 1.02-1.14), styrene-butadiene copolymer (specific gravity 1.01-1.10), polystyrene (specific gravity 1.18-125), polyacryl (specific gravity 1.10-1.28), polyurethane (specific gravity) 1.1 to 1.30), polymethyl methacrylate (specific gravity 1.20 to 1.55) and the like.
In addition, materials such as vinylidene chloride (specific gravity 1.65 to 1.72), vinylidene fluoride (specific gravity 1.68 to 1.85), fluorinated polyethylene (specific gravity 2 or more), which has a specific gravity exceeding 1.6, Preparation of composite particles having a high specific gravity and coated with titanium oxide and titanium hydroxide causes precipitation and separation, and is not suitable as a mother particle.

  The mother particles used in the present invention must not be deformed by heat or stress applied during the production of composite particles coated with titanium oxide and titanium hydroxide, and preferably have a Tg (glass transition temperature) of 60 ° C. or higher. It is desirable to have. More preferably, a stable coating layer can be obtained if a crosslinkable monomer is added at the time of preparation of polymerizable polymer particles and the crosslinkable polymer particles have no glass transition point. In addition, it is not preferable that Tg is less than 60 ° C. because a stable coating layer may not be obtained due to deformation of the mother particle itself due to heat and stress in the coating process.

  The mother particles used in the present invention are preferably wetted and dispersed easily with an aqueous medium such as water or alcohol. Preferably, the surface of the mother particles is desirably surface-treated with an anionic surfactant, and specifically, fatty acid soaps, carboxylates such as polyoxyethylene alkyl ether carboxylic acids, alkyl sulfonates, alkyl benzenes and Surface treatment with anionic surfactants such as sulfonates such as alkylnaphthalene sulfonate and sulfosuccinate, sulfates such as alkyl sulfates and alkyl ether sulfates, alkyl phosphates and alkyl ether phosphates It is desirable to do.

In the aqueous ink composition of the present invention, the average particle size dispersed in the aqueous liquid medium can be adjusted to a range of 50 nm to 2 μm in order to suppress sedimentation and separation of titanium oxide and titanium hydroxide-coated composite particles. is necessary.
When the average particle size is less than 50 nm, the whiteness and hiding properties are lowered. On the other hand, when the average particle size exceeds 2 μm, sedimentation and separation occur, which is not appropriate.
In order to adjust the average particle diameter of the titanium oxide and titanium hydroxide-coated composite particles to the above range (50 nm to 2 μm), it is necessary to adjust the mother particles themselves to 50 nm to 2 μm, for example, emulsion polymerization The particles are prepared by polymerizing methods such as seed polymerization, precipitation polymerization, turbid polymerization, condensation, addition polymerization, etc., and pulverization methods such as jet mills, and classified by centrifugation, precipitation, filtration, etc. It can adjust to the range of a desired average particle diameter.

The titanium oxide and titanium hydroxide coating layer of the titanium oxide and titanium hydroxide coated composite particles used in the present invention is preferably 1 to 500 nm.
When this coating layer is less than 1 nm, the whiteness and concealing properties of titanium oxide are reduced, and when the coating layer exceeds 500 nm, there are whiteness and concealing properties. This is not suitable because the proportion of the composite particles increases, the specific gravity of the composite particles themselves increases, and sedimentation and separation occur.

The method for forming the titanium oxide and titanium hydroxide coating layer of the titanium oxide and titanium hydroxide coated composite particles used in the present invention is not particularly limited, but preferably any of the following (a) to (c) It can be formed by any method.
(A) A method in which titanium alkoxide is hydrolyzed in a film-forming reaction solution to coat titanium oxide and titanium hydroxide on the surface of the mother particle.
(B) A method in which inorganic titanic acid is hydrolyzed in a membrane-forming reaction solution to coat titanium oxide and titanium hydroxide on the surface of the mother particles.
(C) A method in which peroxotitanium is reacted in a film-forming reaction solution to coat titanium oxide and titanium hydroxide on the surface of the mother particle.

The titanium alkoxide solution of the method (a) is not particularly limited as long as it can be represented by the general formula Ti (OR) ₄ , but R is a methyl group (CH ₃ ), an ethyl group (C ₂ H ₅ ), A propyl group (C ₃ H ₇ ) or a butyl group (C ₄ H ₉ ) is generally used.
The coating process of the titanium oxide and titanium hydroxide layers using this titanium alkoxide solution is as follows 1) to 4).
1) A predetermined amount of mother particles are uniformly dispersed in 400 ml of ethyl alcohol and stirred at 700 to 900 rpm. A predetermined amount of titanium alkoxide solution is added to this.
2) Next, a base particle dispersed at a dropping rate of about 1 ml / min is prepared by mixing well the alkali water (ion exchange water adjusted to pH 9 with ammonia water) with the same weight as the added titanium alkoxide solution in 60 ml of ethyl alcohol. Drip into the ethyl alcohol solution.
3) After completion of dropping, stirring is continued for 60 to 180 minutes, and the added titanium alkoxide solution is sufficiently reacted.
4) After completion of the reaction, substitution washing with 100 ml of ethyl alcohol is carried out, and after completion of the washing, drying is performed at a melting point of the mother particles or lower.

In this process, when the dropping rate of alkaline water is faster than 1 ml / min, the titanium alkoxide solution is rapidly hydrolyzed and the separated fine particles of titanium oxide and titanium hydroxide are precipitated, and the titanium oxide and titanium hydroxide coatings are formed. It may become impossible to form a layer. Conversely, even if the dropping rate of alkaline water is slower than about 1 ml / min, there is no effect on the hydrolysis rate of the titanium alkoxide solution, and there is no difference in the properties of the titanium oxide and titanium hydroxide coating layers after the reaction. In view of the efficiency, the alkaline water dropping speed is preferably 1 ml / min.
Further, if the reaction time after the completion of the dropping is shorter than 60 minutes, the added titanium alkoxide solution may not be sufficiently hydrolyzed. On the other hand, even if it is longer than 180 minutes, the added titanium alkoxide solution is not sufficiently hydrolyzed. In view of time efficiency, the aging time is preferably 60 to 180 minutes.

As the inorganic titanic acid solution in the method (b), for example, a titanyl sulfate solution, a titanium tetrachloride solution, or a titanium trichloride solution can be used. The steps of forming a titanium oxide and titanium hydroxide coating layer using this inorganic titanic acid solution are as described in 1) to 3) below.
1) A predetermined amount of mother particles are dispersed in 400 ml of ion-exchanged water and stirred at 700 to 900 rpm. Further, this dispersion is heated to 40-59 ° C.
2) Next, an inorganic titanic acid aqueous solution obtained by diluting a predetermined amount of an inorganic titanic acid solution 10 to 20 times by weight with ion exchange water is dropped into the mother particle dispersion at a dropping rate of 0.5 to 1.0 ml / min. To do.
3) After completion of dropping, stirring is continued for 60 to 180 minutes, and the dropped inorganic titanic acid aqueous solution is sufficiently reacted. After completion of the reaction, substitution washing is sufficiently performed with 100 ml of ion-exchanged water, and after completion of the washing, drying is performed below the melting point of the mother particles.

If the dilution ratio of the inorganic titanium oxide solution is less than 10 times by weight, the dripping rate of the inorganic titanic acid solution increases, and the concentration of the inorganic titanic acid solution in the reaction solution increases rapidly. Reaction is inhibited. On the contrary, even if the dilution ratio exceeds 20 times by weight, no difference is observed in the properties of the formed titanium oxide and titanium hydroxide coating layers, and the dilution rate of the inorganic titanate solution is considered in consideration of time efficiency. Is preferably 10 to 20 times by weight.
On the other hand, if the dropping rate is higher than 1.0 ml / min, the concentration of the inorganic titanic acid solution in the reaction solution increases rapidly, so that the reaction of the inorganic titanic acid solution may be inhibited. Conversely, even if the dropping rate is slower than 0.5 ml / min, there is no difference in the properties of the formed titanium oxide and titanium hydroxide coating layers, and considering the time efficiency, the dropping rate of the inorganic titanate solution Is preferably 0.5 to 1.0 ml / min.
Furthermore, if the reaction time after the completion of the dropping is less than 60 minutes, the dropped inorganic titanic acid solution may not sufficiently react. The aqueous solution is sufficiently hydrolyzed, and considering the time efficiency, the reaction time is preferably 60 to 180 minutes.

As a titanium source of the peroxotitanic acid solution in the above method (c), a titanium alkoxide solution represented by the general formula Ti (OR) ₄ [R is a methyl group (CH ₃ ), an ethyl group (C ₂ H ₅ ), A propyl group (C ₃ H ₇ ) or a butyl group (C ₄ H ₉ ) is generally used], or an inorganic titanic acid solution such as a titanyl sulfate solution, a titanium tetrachloride solution, or a titanium trichloride solution. Can be used. A peroxotitanic acid solution is prepared using these inorganic titanic acid solutions, and the steps are as described in 1) to 3) below.
1) A basic substance such as excess sodium hydroxide aqueous solution or ammonia water is added to a predetermined amount of inorganic titanium oxide solution to precipitate white titanium hydroxide gel.
2) Next, a predetermined amount of peroxide such as hydrogen peroxide solution is added to dissolve the titanium hydroxide gel to obtain a yellow transparent basic peroxotitanium solution. In addition, as an amount of the peroxide to be added, taking hydrogen peroxide water as an example, an amount containing 5 to 10 times mole number of hydrogen peroxide with respect to titanium oxide in a predetermined amount of inorganic titanic acid solution is added. It is desirable to do. If the amount of the hydrogen peroxide solution is less than 5 times the number of moles, the titanium hydroxide gel is not sufficiently dissolved. Conversely, if the amount of the hydrogen peroxide solution exceeds 10 times the number of moles, The excess of hydrogen oxide water is decomposed, and the liquid is foamed by the generated foam, which produces a precipitate of peroxotitanium hydrate, which is not desirable.
3) After the peroxide is added, a necessary amount of aqueous ammonia is added so that the pH of the basic peroxotitanium solution is 9.0 to 9.6.

Next, the steps of forming a titanium oxide and titanium hydroxide coating layer using a peroxotitanium solution are as described in 4) to 6) below.
4) Dissolve 9.89 g of boric acid, 11.94 g of potassium chloride, and 2.56 g of sodium hydroxide in 560 ml of ion-exchanged water, and adjust the buffer solution at pH 9 or around 10. A predetermined amount of mother particles are added to this buffer solution, and the mixture is uniformly dispersed with an ultrasonic disperser, followed by stirring at 900 rpm. Further, this dispersion is placed in a constant temperature water bath and heated to 40 to 59 ° C.
5) When the mother particle dispersion temperature reaches 40 to 59 ° C., a peroxotitanium solution is dropped into the dispersion at a dropping rate of 0.5 to 1.0 ml / min.
6) After completion of the dropping, stirring is continued for 60 to 180 minutes to sufficiently react the dropped peroxotitanium solution. After completion of the reaction, substitution washing is sufficiently performed with 100 ml of ion-exchanged water, and after completion of the washing, drying is performed below the melting point temperature of the mother particles.

In the above process, when the dropping rate is made higher than 1.0 ml / min, the concentration of the peroxotitanium solution in the reaction solution increases rapidly, so that the precipitated peroxotitanium hydrate does not become a coating layer on the surface of the mother particles. And become free particles. On the other hand, even if the dropping rate is slower than 0.5 ml / min, there is no significant difference in the properties of the formed peroxotitanium hydrated film coating layer, and the dropping rate of the peroxotitanium solution is 0 in consideration of temporal efficiency. 0.5 to 1.0 ml / min is preferable.
Further, in drying the composite particles after coating with peroxotitanium hydrate, unless this drying is performed, the peroxotitanium hydrate does not become titanium hydroxide, and the hue of the coated composite particles remains light yellow. The coating layer can be modified into titanium oxide and titanium hydroxide by dehydration treatment such as drying and heating, and oxidation treatment, and can impart whiteness and hiding properties to the composite particles.

The water-based ink composition of the present invention preferably contains 5 to 50% by weight, more preferably titanium oxide and titanium hydroxide-coated composite particles obtained by the above coating method, based on the total amount of the water-based ink composition. 10 to 40% by weight is desirable.
When the content of the composite particles is less than 5% by weight, predetermined whiteness and hiding properties cannot be obtained. On the other hand, when the content exceeds 50% by weight, the stability of the ink composition over time is improved. This is not preferable because the particles may be aggregated and settled.

In the water-based ink composition of the present invention, it is preferable to include a binder resin as a particle fixing binder component for the purpose of fixing the titanium oxide and titanium hydroxide coated composite particles to the surface of a subject such as writing paper.
The binder resin that can be used is required to have a binding property between the coated particles, a binding property with the contained colorant, adhesion to paper, and flexibility of the coating itself. That is, the binder resin is required that the drawn paint film does not crack when dried, and that the paint film does not break when rewritten on the paint film. Further, the binder resin is also required to be stably present in the ink composition without being precipitated or solidified in a water-soluble organic solvent.
Examples of binder resins that can be used in the water-based ink composition of the present invention include water-dispersed resins such as acrylic emulsions, ethylene-vinyl acetate emulsions, and styrene-butadiene emulsions, or polyvinyl alcohol, polyallylamine, There may be mentioned at least one water-soluble resin such as polysaccharide and water-soluble fiber.

Among the above water-dispersed binder resins, acrylic emulsions, ethylene-vinyl acetate emulsions, and styrene-butadiene emulsions having an MFT (minimum film forming temperature) of less than 40 ° C. have a soft binder film. preferable. A water-dispersed resin having an MFT of over 40 ° C. is not suitable because no film formation occurs at room temperature.
Specific examples of water-dispersed resins having an MFT of less than 40 ° C. include commercially available mobile vinyl 757, 776, 952, and 966 (manufactured by Clariant Japan), Primal B-15, and B- in the acrylic emulsion system. 41, LT-84, AC-2235 (made by Rohm & Haas), Ricabond ES-23 (made by Chuo Rika), Acryt UW-520, 319S, UW-309 (made by Taisei Kako), Worleecri 1771 7712 (manufactured by Worlee-Chemie), NK Polymer AC-11, AC-13, AC-117 (manufactured by Shin-Nakamura Chemical Co., Ltd.), Denace EVA 59, 88, 90 (electrochemical industry) for vinyl acetate type Bon coat 2830, 2835, 2960 (produced by Dainippon Ink and Chemicals), styrene-butadiene Examples include Nippon 4850A, LX112, LX209, 2570X, LX511, LX531 (manufactured by Nippon Zeon Co., Ltd.), etc., which are styrene butadiene rubber latex systems. These may be used alone or in combination of two or more. Can be used.

These water-dispersed resins are preferably contained in the water-based ink composition of the present invention in the range of 1 to 20% by weight in terms of solid content, and more preferably 3 to 15% by weight. .
If the content of the water-dispersed resin is less than 1% by weight, the adhesiveness of the coated composite particles and the colorant to the paper is poor, and it may be detached when the writing line, stamp drawing line or correction part is rubbed. Absent. Moreover, when the content of the water-dispersed resin exceeds 20% by weight, the stability of the ink composition with time decreases, and aggregation and sedimentation of particles, thickening and gelation of the ink composition itself occur. This is not preferable.

Among the above water-soluble binder resins, water-soluble fibers extracted from hydroxyethyl cellulose, hydroxypropyl cellulose, crystalline cellulose, plants, etc. are used for dispersion stability of composite particles in the ink composition and adhesion of the drawn film. From the viewpoint of further enhancing the properties, water-soluble fibers are more preferable.
Specific examples of water-soluble resins that can be used for hydroxycellulose include commercially available SU-25F, SL-25F, SG-25F, SH-25F, SV-25F, SW-25F, SX-25F, and SV-25F. , AL-15F, AG-15F, AH-15F, AV-15F, AW-15F, AX-15F (manufactured by Fuji Chemical Co., Ltd.) and the like, and these can be used alone or in combination of two or more.

Moreover, as hydroxypropyl cellulose, commercially available KLUCEL-H, the same -M, the same -G, the same -J, the same -L, the same -E (manufactured by Sanki Co., Ltd.), etc. are mentioned, and these are independent or 2 More than one type can be used in combination.
Examples of crystalline cellulose include commercially available Avicel, Ceolas KG (manufactured by Asahi Kasei Co., Ltd.), Cell Green PCA, Selish (manufactured by Daicel Chemical Industries), Self-Ar (manufactured by Nippon Shokuhin Kako Co., Ltd.), etc. Cellulose (manufactured by Nippon Shokuhin Kako Co., Ltd.) and the like extracted from corn can be used as the fiber, and these can be used alone or in combination of two or more. This content is preferably 0.1 to 10% by weight in the ink composition.
These water-soluble resins can be used in combination with the above-mentioned water-dispersed resin, or can be contained alone in the ink composition in place of the water-dispersed resin, and the total amount in the ink composition is 0. 0.1 to 10% by weight is preferable.
If the content of the water-soluble resin is less than 0.1% by weight, further dispersion stability and adhesion of the drawn film cannot be enhanced, whereas if it exceeds 10% by weight, the ink composition The stability over time is lowered, and aggregation and sedimentation of particles and thickening and gelation of the ink composition itself may occur, which is not preferable.

The water-based ink composition of the present invention contains composite particles coated with titanium oxide and titanium hydroxide that have the above physical properties, preferably further contains the binder resin, but further contains a coloring agent. It is desirable to contain. By containing this coloring component, it is possible to provide an ink having a marking performance that conceals the hue of the writing material and colors well.
In the present invention, in the use of the correction ink, the coloring component is not an essential component, but a coloring agent can also be included from the viewpoint of clarifying the correction portion. For this correction, the coloring component is included. In addition, it is possible to provide a correction ink having a performance of concealing the drawn line of the cursive object and correcting it better.
As the colorant (component) that can be used, all dyes dissolved or dispersed in water and having a chromatic color within a range not impairing the effects of the present invention, conventionally known inorganic and organic pigments, resin emulsions A pseudo pigment colored with a dye can be used without limitation.
Examples of the dye include C.I. I. Acid Black 2, 24, 26, 48, 50, 52, 58, 62, Eosin, Foxin, Water Yellow # 6-C, Acid Red, Water Blue # 105, Brilliant Blue FCF, Nigrosine NB, etc. Acid dyes of C.I. I. Direct Black17, 19, 22, 32, 38, 51, 71, 74, 75, etc. Direct dyes such as Direct Sky Blue 5B and Violet BB, and basic dyes such as Rhodamine and Methyl Violet Can be mentioned.

Examples of the inorganic pigment include metal powder, and examples of the organic pigment include azo lake, insoluble azo pigment, chelate azo pigment, phthalocyanine pigment, perylene and perinone pigment, anthraquinone pigment, quinacridone pigment, dye lake, nitro Examples thereof include pigments and nitroso pigments. More specifically, carbon black such as channel black, furnace black, and thermal black, titanium black, iron black, graphite, copper chrome black, cobalt black, brown, chromium oxide, cobalt blue, iron oxide yellow, viridian, cadmium yellow, Zinc, cadmium red, yellow lead, molybdate orange, zinc chromate, strontium chromate, inorganic pigments such as ultramarine, barite powder, bitumen, manganese violet, aluminum powder, pearl powder, aniline black, perylene black, cyanine black, resin emulsion A pseudo pigment colored with a black dye, C.I. I. Pigment Blue 1, Same Blue 15, Same Blue 17, Same Blue 27, Same Red 5, Same Red 22, Same Red 38, Same Red 48, Same Red 49, Same Red 53, Same Red 57, Same Red 81, Same Red 104, Red 146, Red 245, Yellow 1, Yellow 3, Yellow 4, Yellow 12, Yellow 13, Yellow 14, Yellow 17, Yellow 34, Yellow 55, Yellow 74, Yellow 83, Yellow 95, Yellow 166, Yellow 167, Orange 5, Orange 13, Orange 16, Violet 1, Violet 3, Violet 19, Violet 23, Violet 50, Green 7 etc., and one or more of these are selected and used as a good colorant It is possible.
The content of these colorants is preferably 0.1 to 15% by weight with respect to the total amount of the ink composition.

The water-based ink composition of the present invention uses water (purified water, ion-exchanged water, pure water, deep sea water, etc.) as a main medium, but from the viewpoint of imparting water retention and improving writing feeling as a solvent. Preferably, a water-soluble polar solvent having a polar group compatible with water can be used.
Examples of the water-soluble polar solvent that can be used include methyl alcohol, ethyl alcohol, isopropyl alcohol, ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, ethylene glycol monomethyl ether, glycerin, and pyrrolidone. These can be used alone or in admixture of two or more.
The content of these water-soluble polar solvents is preferably 1 to 30% by weight, more preferably 5 to 25% by weight, based on the total amount of the ink composition.

Further, in the present invention, it is preferable to further contain an alkylene oxide adduct of glycerin or diglycerin as a moisturizing property or a lubricant imparting agent (water-soluble liquid medium).
As the alkylene oxide adduct of glycerin or diglycerin, for example, at least one selected from ethylene oxide or propylene oxide adduct of glycerin and ethylene oxide or propylene oxide adduct of diglycerin, preferably diglycerin propylene Oxide (4 to 30) mole adduct, diglycerin ethylene oxide (5 to 40) mole adduct, and more preferably, polyoxyethylene 13 mole addition diglyceryl ether, polyoxypropylene 9 mole addition diglyceryl ether, It is desirable to use polyoxyethylene 10 mol addition glyceryl ether and polyoxypropylene 9 mol addition glyceryl ether.
The content of these water-soluble liquid media is preferably 1 to 20% by weight, more preferably 5 to 15% by weight, based on the total amount of the ink composition.
If the content is less than 1% by weight, further improvement in moisture retention and lubricity cannot be exhibited, and if it exceeds 20% by weight, the drying property of the writing line is impaired. Absent.

In the water-based ink composition of the present invention, additives (arbitrary components) that are widely used in water-based ink compositions can be appropriately used as components other than the above as long as the effects of the present invention are not impaired.
Additives include, as preservatives or antifungal agents, phenol, sodium omadin, sodium pentachlorophenol, 1,2-benzisothiazolin-3-one, 2,3,5,6-tetrachloro-4 (methylsulfonyl) Examples include pyridine, sodium benzoate, benzoic acid, sorbitan acid, alkali metal salts of dehydroacetic acid, benzimidazole compounds, and the like.
Examples of the rust inhibitor include benzotriazole, dicyclohexylammonium nitrite, diisopropylammonium nitrite, tolyltriazole, and saponins. Examples of the pH adjuster include urea, aqueous ammonia, monoethanolamine, triethanolamine, aminomethylpropanol, alkali metal salts of phosphoric acid such as sodium tripolyphosphate, alkali metal hydroxides such as sodium hydroxide, and the like. .
Examples of the lubricant include polyalkylene glycol derivatives such as polyoxyethylene lauryl ether, polyether-modified silicones such as fatty acid alkali salts and polyethylene glycol adducts of dimethylene polysiloxane.
Furthermore, various additives can be added for the purpose of imparting a dispersion effect. Examples thereof include nonionic surfactants such as alkyl ethers and alkyl esters of polyoxyethylene, glycerin fatty acid esters, and fluorosurfactants.

Further, in the present invention, when used as a writing ink, a more stable aqueous ink composition can be obtained by incorporating a water-soluble viscosity modifier.
Examples of the viscosity modifier that can be used include at least one selected from the group consisting of synthetic polymers, cellulose, and polysaccharides (each alone or a mixture of two or more thereof).
Examples of the synthetic polymer include polyacrylic acids, polyvinyl alcohol, polyethylene oxide, polyvinyl pyrrolidone, polyvinyl methyl ether, and polyacrylamide. Examples of cellulose include ethyl cellulose, methyl cellulose, hydroxymethyl cellulose, and carboxymethyl cellulose. Examples of the polysaccharide include xanthan gum, guar gum, casein, gum arabic, gelatin, carrageenan, alginic acid, tragacanth gum, locust bean gum and the like.

The water-based ink composition of the present invention can be suitably used as an ink composition for writing instruments, in particular, a water-based ballpoint pen, by appropriately containing the above viscosity modifier and the like.
As a viscosity value in this case, a viscosity value of 1 rpm measured with an EMD type viscometer under a condition of 25 ° C. is preferably in the range of 5 to 2000 mP · s, more preferably in the range of 10 to 1000 mP · s. It is desirable to do. By setting the viscosity value at 1 rpm in the range of 5 to 2000 mP · s, ink separation with time does not occur, and ink with good writing feeling can be obtained. Furthermore, the viscosity value at 100 rpm measured with an EMD viscometer under the condition of 25 ° C. is preferably 4 to 200 mPa · s, and more preferably 5 to 100 mPa · s. By setting the viscosity value at 100 rpm to be in the range of 4 to 200 mPa · s, it is possible to realize a better drawn line with no blurring.

The water-based ink composition of the present invention comprises composite particles obtained by coating titanium oxide and titanium hydroxide on mother particles having a specific gravity of less than 1.6 in an aqueous medium comprising water or a water-soluble solvent and having an average particle diameter of 50 nm to 2 μm. It can be produced by dispersing within a range and preparing preferred additive components and the like in the same manner as in known methods for producing writing, stamping or correcting ink compositions.
The ink composition of the present invention can be suitably applied to writing instrument inks such as ballpoint pen inks, correction inks, and stamp inks for various applications.
Below, the preparation example of the water-based ink composition for writing instruments, stamps, or corrections for each use in this invention is shown.
In an ink composition for a writing instrument such as a ballpoint pen, 5 to 50% by weight of composite particles having the above physical properties, a water-dispersed resin and / or a water-soluble resin serving as a particle fixing binder, and a colorant comprising a pigment and / or a dye The ink composition can be prepared by containing water and other additives for writing ink. More preferably, the ink composition has a viscosity value of 1 rpm measured with an EMD viscometer under the condition of 25 ° C. It is desirable to adjust the viscosity value of 10 to 1000 mPa · s and the viscosity value at 100 rpm to the range of 5 to 100 mPa · s.
For stamps, 5-50% by weight of the composite particles having the above physical properties, a binder resin such as a water-dispersed resin or a water-soluble resin as a particle fixing binder, a colorant comprising a pigment and / or a dye, and water And other additives for stamping, and for correction, 5 to 50% by weight of the composite particles having the above physical properties, a water-dispersed resin as a particle fixing binder, and water-soluble It can be prepared by containing a binder resin such as a resin, water, and other correction additives (including the colorant).

The reason why the water-based ink composition of the present invention configured as described above is superior to the present invention is presumed as follows.
Conventionally, a water-based ink composition using a titanium oxide pigment cannot be stably dispersed in the ink composition for a long period of time because of its large specific gravity.
On the other hand, the water-based ink composition of the present invention coats titanium oxide and titanium hydroxide on low specific gravity mother particles, uses composite particles having a small specific gravity, concealability, and whiteness, in an aqueous medium. To provide a water-based ink composition suitable for a writing instrument having a whiteness and a hiding property that is stable and does not settle for a long period of time, or for stamping or correction. Will be able to.
As described above, the water-based ink composition of the present invention can be suitably applied to writing instrument inks such as ballpoint pen inks, correction inks, and stamp inks that are used for various applications. In addition to the effect, an ink composition that produces a marking color tone without being affected by the color tone of the writing surface can be obtained. In addition, for correction, in addition to the above-mentioned effects, it is possible to correct oil ink or water-based ink handwriting, printing with an ink jet printer or the like, or copying images with a copying machine without blurring. .

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

[Preparation Examples 1 to 3 of Composite Particles]
Titanium oxide-coated composite particles were prepared by the following methods.
(Preparation Example 1 of Composite Particles, Titanium Oxide Coating with Titanium Alkoxide Solution)
(1) 2.0 g of ion exchange water adjusted to pH 9 using aqueous ammonia was mixed with 60 ml of ethyl alcohol.
(2) 24 g of mother particles (PM-030 manufactured by Ganz Kasei Co., Ltd.) made of polymethyl methacrylate having an average particle size of 0.3 μm and a specific gravity of 1.5 were dispersed in 400 ml of ethyl alcohol, and ultrasonic dispersion was applied for 60 seconds. Thereafter, this solution was stirred at 900 rpm.
(3) 2.0 g of titanium-tetra-iso-propoxide solution (TPT solution “A-1” manufactured by Nippon Soda Co., Ltd.) was added thereto.
(4) Here, 62 ml of alkaline water prepared in (1) above was dropped into the mother particle-dispersed alcohol solution at a dropping rate of 1.0 ml / min.
(5) After completion of the dropping, stirring was continued for 60 minutes, and the titanium-tetraiso-propoxide solution was sufficiently reacted.
(6) After a predetermined time, 80 ml of ethyl alcohol was further added, and stirring was continued for 10 minutes to complete the reaction.
(7) After completion of the stirring, replacement washing with 100 ml of ethyl alcohol was performed twice.
(8) After completion of the substitution washing, the mixture was left at room temperature and dried to obtain titanium oxide-coated composite particles.
The spectral reflectance of the obtained titanium oxide-coated composite particles was measured with a spectrophotometer V-570 manufactured by JASCO Corporation. The titanium oxide-coated composite particles showed absorption by titanium oxide in the vicinity of a wavelength of 300 nm, and it was confirmed that the titanium oxide was coated. The thickness of the titanium oxide coating layer was 10 nm.

(Preparation Example 2 of Composite Particles, Titanium Oxide Coating with Peroxotitanium Solution)
(1) 0.93 g of titanium tetrachloride solution was mixed with 5.58 g of ion-exchanged water.
(2) Ammonia water (1.51 g) was added thereto to precipitate a white titanium hydroxide gel.
(3) Next, 3.31 g of hydrogen peroxide was added to dissolve the white titanium hydroxide gel to obtain a yellow transparent peroxotitanium solution.
(4) Finally, 0.17 g of aqueous ammonia was added to adjust the pH, and the pH of the peroxotitanium solution was adjusted to 0.58.
(5) 16 g of mother particles (PM-030 manufactured by Ganz Kasei Co., Ltd.) made of polymethyl methacrylate having an average particle size of 0.3 μm and a specific gravity of 1.5 are added to 100 ml of ion-exchanged water, and uniformly dispersed and stirred at 900 rpm did. Thereafter, 2 g of an anionic reactive surfactant Adekari Soap (SE-100N, manufactured by Asahi Denka Co., Ltd.) was added, and the whole dispersion was kept at 55 ° C. and stirred for 1 hour. Then, it dried at the temperature below resin melting | fusing point.
(6) In 560 ml of ion-exchanged water, 9.89 g of boric acid, 1.94 g of potassium chloride and 2.56 g of sodium hydroxide were dissolved to prepare a pH 9.12.
In this buffer solution, 16 g of mother particles treated with the anionic surfactant in (5) above were dispersed, and ultrasonic dispersion was applied for 60 seconds. The dispersion was heated to 50 ° C. while stirring at 900 rpm.
(7) After the dispersion reached 50 ° C., the peroxotitanium solution prepared in (3) above was dropped at a dropping rate of 1 ml / min.
(8) After completion of the dropwise addition, stirring was further continued for 120 minutes to sufficiently react the peroxotitanium solution.
(9) After completion of the reaction, substitution washing with 250 ml of ion-exchanged water was sufficiently performed, and the remaining liquid of the reaction solution was removed.
(10) After completion of the substitution reaction, the mixture was allowed to stand in a dryer at 58 ° C. for 6 hours and dried to obtain titanium oxide-coated composite particles.
The spectral reflectance of the obtained titanium oxide-coated composite particles was measured with a spectrophotometer V-570 manufactured by JASCO Corporation. The titanium oxide-coated composite particles showed absorption by titanium oxide in the vicinity of a wavelength of 300 nm, and it was confirmed that the titanium oxide was coated. The thickness of the titanium oxide coating layer was 7 nm.

[Composite Particle Preparation Example 3 (for Comparative Example), Titanium Oxide Coating with Titanium Alkoxide Solution]
(1) A solution was prepared by mixing 9.6 g of ion-exchanged water adjusted to pH 9 with aqueous ammonia and 60 ml of ethyl alcohol.
(2) 16 g of mother particles (manufactured by Mitsui Kinzoku Co., Ltd.) made of magnetite having an average particle size of 2.34 μm and a specific gravity of 4.94 were dispersed in 400 ml of ethyl alcohol, and ultrasonic dispersion was applied for 60 seconds. Thereafter, this solution was stirred at 900 rpm.
(3) 9.6 g of a titanium-tetra-iso-propoxide solution (TPT solution “A-1” manufactured by Nippon Soda Co., Ltd.) was added thereto.
(4) Here, 62 ml of alkaline water prepared in (1) above was dropped into the mother particle-dispersed alcohol solution at a dropping rate of 1.0 ml / min.
(5) After completion of the dropping, stirring was continued for 60 minutes, and the titanium-tetraiso-propoxide solution was sufficiently reacted.
(6) After a predetermined time, 80 ml of ethyl alcohol was further added, and stirring was continued for 10 minutes to complete the reaction.
(7) After completion of the stirring, replacement washing with 100 ml of ethyl alcohol was performed twice.
(8) After completion of the substitution washing, the mixture was left at room temperature and dried to obtain titanium oxide-coated composite particles.
The spectral reflectance of the obtained titanium oxide-coated composite particles was measured with a spectrophotometer V-570 manufactured by JASCO Corporation. The titanium oxide-coated composite particles showed absorption by titanium oxide in the vicinity of a wavelength of 300 nm, and it was confirmed that the titanium oxide was coated. The thickness of the titanium oxide coating layer was 12 nm.

[Examples 1-3 and Comparative Examples 1-5, water-based ink composition for writing instruments]
Each water-based ink composition for writing was prepared according to the formulation shown in Table 1 below.
The physical properties (average particle diameter, viscosity) and sedimentation separation test, time-dependent stability test, drying test, ink ejection test, and line drawing quality evaluation of the aqueous ink compositions for writing of the obtained Examples and Comparative Examples are as follows. It was measured and evaluated by the method.
These results are shown in Table 1 below.

(Measurement method of average particle size)
The obtained aqueous ink compositions of Examples and Comparative Examples were diluted 100 times in ion-exchanged water, and the average particle diameter of each particle was measured using NICOM 370 (manufactured by Nozaki Sangyo Co., Ltd.) using the photon correlation method. Was measured.
(Measurement method of viscosity)
The viscosity of 1 rpm and 100 rpm was measured with the EMD type viscometer [VISCOMETER RE110R (made by Toki Sangyo Co., Ltd.)] of the obtained water-based ink compositions of Examples and Comparative Examples at 25 ° C.

(Settling separation test)
25 ml of each of the obtained aqueous ink compositions of Examples and Comparative Examples was collected in a 30 ml sedimentation test tube and allowed to stand at 50 ° C. for 1 month, and the state of separation was evaluated according to the following evaluation criteria.
Evaluation criteria ○: No separation or aggregation occurred.
Δ: A slight change in shading is observed in the upper layer.
[Delta] [Delta]: The concentration in the rising part and the lower rear part are clearly different, and a separation tendency is observed.
X: Separation or aggregation is clearly recognized.

(Aging stability test)
Each ink obtained was filled in a 15 ml glass lidded bottle, sealed, and stored at 50 ° C. for 1 month. Moreover, about each ink, the state of isolation | separation was confirmed visually, the viscosity value after the passage of time and initial time was measured similarly to the said conditions, and the following evaluation criteria evaluated.
Evaluation criteria:
A: Viscosity values at 1 rpm and 100 rpm are within ± 10% compared to the initial value, and the ink stability over time is good.
○: Viscosity values at 1 rpm and 100 rpm are within ± 25% of the initial values, and the ink stability over time is good.
X: Viscosity values at 1 rpm and 100 rpm are ± 100% or more compared to the initial value, and the ink changes with time.

(Drying test)
A film appliquor having a width of 6 mm and a gap of 50 μm was obtained on a paper (writing instrument paper A) defined in JIS-P3201-1989 at a temperature of 25 ° C. and a relative humidity of 65% (writing instrument paper A). When it was applied using the evening and was written using an oil-based ballpoint pen, the time until the film could be written without tearing was measured and evaluated according to the following evaluation criteria.
Evaluation criteria:
○: Less than 1 minute △: More than 1 minute and less than 5 minutes ×: More than 5 minutes

Moreover, the obtained water-based ink composition of each Example and Comparative Example was filled in an ink containing tube of a water-based ballpoint pen body (manufactured by Mitsubishi Pencil Co., Ltd., uni-ball Signo) having the following configuration.
Ink receiving tube:
Shape: cylindrical, inner diameter: 4.0 mm, made of polypropylene, length 11 mm, ball diameter: 1.0 mm, ball material: carbide

(Ink ejection test)
Using each of the obtained water-based ballpoint pens, writing was performed with a ballpoint pen writing tester (writing conditions: writing speed; approximately 4.5 m / min, writing angle; 60 °, writing load: 100 g), and after 100 m writing. The ink consumption (mg / 100 m) was measured.

(Drawing line quality evaluation method)
The drawn lines written in the ink ejection test were evaluated according to the following criteria.
Evaluation criteria:
A: Good.
○: Scratch occurred within 5 places.
Δ: Scratch occurred within 10 places.
Δ △: Less than 15 spots are generated.
X: Scratch generation exceeds 15 places.
Xx: The flip-flop property of a drawn line is inferior, or there is a point inferior in other various performances.

* 1 to * 10 in Table 1 are as follows.
* 1: Lactimine color Grenn FLB conc (aqueous green pigment dispersion: manufactured by Dainichi Seika Co., Ltd.)
* 2: Titanic JR-701 (titanium oxide pigment particles, primary particle size 0.4 μm, manufactured by DuPont Japan)
* 3: PM-030 (polymethyl methacrylate particles, primary particle size: 0.3 μm, manufactured by Ganz Kasei Co., Ltd.)
* 4: Mobile 756 (acryl-styrene emulsion, minimum film-forming temperature −10 ° C., solid content 52%, manufactured by Clariant Japan)
* 5: Acronal VJ-1110D (acrylic dispersion, minimum film-forming temperature 64 ° C., solid content 46%, manufactured by BASF Dispersion)
* 6: Polysol EVA AD-2 (ethylene-vinyl acetate emulsion, minimum film-forming temperature 2 ° C., solid content 55%, Showa Polymer Co., Ltd.)
* 7: Cell Ace (water-soluble plant fiber, manufactured by Nippon Shokuhin Kako)
* 8: Jonkrill J62 (polyacrylic acid, average molecular weight: 8500, glass transition point: 85 ° C., manufactured by Johnson Polymer Co., Ltd.)
* 9: Kelzan RD (manufactured by Sankisha)
* 10: Hibiswako # 105 (manufactured by Wako Pure Chemical Industries)

As is clear from the results of Table 1 above, Examples 1 to 3, which are within the scope of the present invention, are superior in whiteness to the drawn lines compared to Comparative Examples 1 to 5 that are outside the scope of the present invention. As a result, it was found that it was excellent in stability over time, and also excellent in drying property, ink ejection property, and line drawing quality.
Comparative Example 1 is a blend in which the titanium oxide coating layer on the base particles is eliminated from Example 1. It is recognized that there is no concealment.
Comparative Example 2 is a blend using titanium oxide pigments having the same particle diameter as in Example 1. It is clear that the sedimentation separability of particles and the stability over time are inferior.
Comparative Example 3 is a blend using mother particles having larger specific gravity and particle diameter than Example 2. It is clear that the sedimentation separability and stability over time of the particles are inferior, and the discharge flow rate is small and the drawn quality is inferior.
Comparative Example 4 uses a titanium oxide pigment having the same particle diameter as in Example 2, and uses an acrylic emulsion having a minimum film-forming temperature of 40 ° C. or higher as the fixing binder, and a viscosity at 1 rpm of 1000 mPa · s or higher. It is a set recipe. It is clear that the sedimentation separability and stability with time of the particles are inferior, and that the drying property and the quality of drawn lines are inferior.
Comparative Example 5 is a composition in which the titanium oxide coating layer on the base particles is eliminated from Example 3, and an acrylic emulsion having a minimum film-forming temperature of 40 ° C. or higher is used as the fixing binder. The viscosity is set to 1000 mPa · s or more. It is clear that the sedimentation / separation property of the particles is slightly inferior, the stability with time and the drying property are inferior, and the drawing quality is also inferior.

  The water-based ink composition of the present invention can be suitably applied for writing instruments, stamps, and corrections as industrial applicability, and among them, for writing instruments without being affected by the color tone of the writing surface, It is suitably used as a color that produces an excellent marking color tone.

Claims (10)

  Composite particles in which titanium oxide and titanium hydroxide are coated on the surface of mother particles having a specific gravity of less than 1.6 are dispersed in a liquid medium mainly composed of water, and the average particle size of the dispersed particles is in the range of 50 nm to 2 μm. A water-based ink composition characterized by the above.   The water-based ink composition according to claim 1, wherein the thickness of the coating layer of titanium oxide and titanium hydroxide on the composite particles is in the range of 1 to 500 nm.   The water-based ink composition according to claim 1, wherein the base particles are composed of organic resin particles having a Tg (glass transition point) of 60 ° C. or higher.   The water-based ink composition according to claim 1, wherein the surface of the base particle is treated with an anionic surfactant.   The ink composition contains at least one selected from an acrylic emulsion having a MFT (minimum film forming temperature) of less than 40 ° C., a styrene-butadiene emulsion, and an ethylene-vinyl acetate emulsion as a particle fixing binder. The water-based ink composition as described in any one of Claims 1-4.   The water-based ink composition according to any one of claims 1 to 4, wherein the ink composition contains water-soluble fibers as a particle-fixing binder.   The water-based ink composition according to any one of claims 1 to 6, wherein a colorant comprising a pigment and / or a dye is contained in an amount of 0.1 to 15% by weight based on the total amount of the ink composition.   The water-based ink composition according to any one of claims 1 to 7, wherein a viscosity value of 1 rpm measured with an EMD viscometer is in a range of 5 to 2000 mPa · s under a condition of 25 ° C.   The water-based ink composition according to any one of claims 1 to 7, wherein a viscosity value at 100 rpm measured with an EMD viscometer is in a range of 4 to 200 mPa · s under a condition of 25 ° C. The water-based ink composition according to any one of claims 1 to 9, wherein the titanium oxide and titanium hydroxide coating layers of the composite particles are formed by any one of the following methods (a) to (c).
(A) A method in which titanium alkoxide is hydrolyzed in a film-forming reaction solution to coat titanium oxide and titanium hydroxide on the surface of the mother particle.
(B) A method in which inorganic titanic acid is hydrolyzed in a film-forming reaction solution to coat titanium oxide and titanium hydroxide on the surface of the mother particles.
(C) A method in which peroxotitanium is reacted in a film-forming reaction solution to coat titanium oxide and titanium hydroxide on the surface of the mother particle.