JP6397770B2 - Ink composition - Google Patents

Description

  The present invention relates to an ink composition.

  Conventionally, a color image is formed on a recording medium using color inks such as cyan ink, magenta ink, yellow ink, and black ink. In recent years, ink that can form an image of a color that cannot be expressed by such color ink alone has attracted attention. For example, a white ink composition containing a white color material such as titanium dioxide has attracted attention. The white ink composition can form a white image that cannot be formed by the color ink described above.

  The white ink composition is used to erase the background color in order to improve the color development of the color image when recording a color image on a recording medium such as a plastic product or a metal product where the background color is not necessarily white. May be used for When a color image is recorded on a transparent sheet, it may be used for forming a white shielding layer that lowers the transparency of the color image. For this reason, the white ink composition is required to improve the color developability of whiteness when it is deposited on a recording medium.

  Conventionally, in order to improve whiteness color development when adhered to a recording medium, the concentration of the white color material contained in the white ink composition is increased, or the particle size of the white color material is increased. There has been a way to do it. However, the method of increasing the concentration of the white color material may impair the abrasion resistance of the formed white image. On the other hand, the method of increasing the particle size of the white color material has a problem that the white color material settles in the ink composition. Thus, there was a trade-off relationship between improvement in whiteness color developability and deterioration in sedimentation and abrasion resistance. For such a problem, for example, Patent Documents 1 to 3 disclose the use of porous titanium dioxide particles as a white color material.

JP 2007-2111176 A JP 2006-274214 A JP 2012-233148 A

  When the porous titanium dioxide particles as described above are used, there is an effect of improving the sedimentation of the particles. However, it is still insufficient in terms of enhancing the shielding properties and color developability of the recorded white image, and further improvement in the color developability of whiteness has been demanded.

  Accordingly, some embodiments according to the present invention provide an ink composition that improves the shielding and coloring properties of a white image when deposited on a recording medium by solving at least a part of the problems. To do. In addition to the above characteristics, some embodiments according to the present invention provide an ink composition that can reduce sedimentation of a white color material over time in the ink composition.

  SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following aspects or application examples.

[Application Example 1]
One aspect of the ink composition according to the present invention is:
An ink composition comprising a white color material, polymer particles and a solvent,
The polymer particles include repeating units derived from unsaturated vinyl monomers,
The polymer particles satisfy the relationship of the following formula (1).
Y ≦ 0.33X + 20 (1)
(In the above formula (1), X represents an average particle diameter D50 (nm) and Y represents a melting start temperature (° C.).)

  According to the ink composition of Application Example 1, the shielding property and color developability of the white image when deposited on the recording medium are improved. This mechanism is considered as follows. That is, when the ink composition is deposited on the recording medium, the polymer particles form a large number of voids between the white color materials, and then the polymer particles form a film to form a layer containing voids (gap layer). ) Is formed. Since the light scattering can be enhanced by this void layer, it is considered that the whiteness color developability is further improved.

[Application Example 2]
In the ink composition of Application Example 1,
The toluene dissolution rate of the polymer particles may be 10% by mass or more and 80% by mass or less.

[Application Example 3]
In the ink composition of Application Example 1 or Application Example 2,
The polymer particles may be obtained by polymerization in the presence of a chain transfer agent.

[Application Example 4]
In the ink compositions of Application Examples 1 to 3,
The polymer particle may further include a repeating unit derived from a monomer having two or more polymerizable double bonds.

[Application Example 5]
In the ink composition of Application Example 4,
The content ratio of the repeating unit derived from the monomer having two or more polymerizable double bonds in 100 parts by mass of the polymer particles may be 1 part by mass or more and 10 parts by mass or less.

[Application Example 6]
In the ink composition of any one of Application Examples 1 to 5,
The absorbance when diluted with water so that the solid content concentration of the white color material in the ink composition is 0.01% by mass can be 1.1 or more and 2.2 or less.

[Application Example 7]
In the ink composition of any one of Application Examples 1 to 6,
When the average particle diameter D50 of the white color material is D1 (nm) and the average particle diameter D50 of the polymer particles is D2 (nm), a relationship of D1: D2 = 1: 0.01 to 1: 5 Can be in

[Application Example 8]
In the ink composition of Application Example 7,
The D1 may be 100 nm to 800 nm and the D2 may be 100 nm to 500 nm.

[Application Example 9]
In the ink composition of any one of Application Examples 1 to 8,
When the content of the white color material is W1 and the content of the polymer particles is W2, the relationship can be W1: W2 = 1: 5 to 5: 1.

[Application Example 10]
In the ink composition of any one of Application Examples 1 to 9,
The white color material may be an aggregate of particles having a primary particle diameter of 10 nm to 200 nm.

The graph which shows the relationship between the melting start temperature and average particle diameter of the polymer particle synthesize | combined in the Example. 3 is an SEM image showing a cross-sectional state of an image recorded with ink 1. FIG. 3 is an SEM image showing a cross-sectional state of an image recorded with ink 5. FIG.

  Hereinafter, preferred embodiments according to the present invention will be described in detail. It should be understood that the present invention is not limited only to the embodiments described below, and includes various modifications that are implemented within a scope that does not change the gist of the present invention.

1. Ink Composition The ink composition according to the present embodiment contains a white color material, polymer particles, and a solvent as essential components. Hereinafter, each component contained in the ink composition according to the present embodiment will be described in detail.

1.1. White color material The white color material used in the present embodiment is not particularly limited as long as it is a pigment used in a general white color ink.

Here, the white ink is an ink (ink) capable of recording a color called “white” for the sake of social wisdom, and includes ink that is slightly colored. Moreover, the ink (ink) containing the pigment includes an ink (ink) which is named and sold under a name such as “white ink (ink), white ink (ink)”. Further, for example, when ink (ink) is recorded on Epson genuine photographic paper <Glossy> (manufactured by Seiko Epson Corporation) with an amount of 100% duty or more or an amount sufficient to cover the surface of the photographic paper, the brightness of the ink (L ^* ) and chromaticity (a ^* , b ^* ) are measured using a spectrophotometer Spectrolino (trade name, manufactured by GretagMacbeth), measurement conditions are D50 light source, observation field is 2 °, density is DIN NB, white When the measurement was performed with the reference set to Abs, the filter set to No, and the measurement mode set to Reflectance, the following values were satisfied: 70 ≦ L ^* ≦ 100, −4.5 ≦ a ^* ≦ 2, −6 ≦ b ^* ≦ 2.5 Ink is included to indicate the range.

Examples of the white color material used in the present embodiment include metal oxide, barium sulfate, calcium carbonate, and the like. Examples of the metal oxide include titanium dioxide, zinc oxide, silica, alumina, and magnesium oxide. The white color material also includes particles having a hollow structure. The particles having a hollow structure are not particularly limited, and known particles can be used. As the particles having a hollow structure, for example, particles described in specifications such as US Pat. No. 4,880,465 can be preferably used. Among these, as the white color material used in the present embodiment, titanium dioxide is preferable from the viewpoint of whiteness and abrasion resistance.

  The white color material used in the present embodiment is also preferably secondary particles formed by aggregating a plurality of primary particles having an average primary particle diameter of 10 nm to 200 nm. The secondary particles formed in this manner are formed by aggregating a plurality of primary particles, and a number of pores (voids) are formed on the surface of the secondary particles (hereinafter referred to as such). Secondary particles are also called “porous particles”.) When porous particles are used as the white color material, since the dispersion medium can enter the voids of the porous particles, the dispersion stability of the porous particles (white color material) in the ink composition is improved. Furthermore, since the specific gravity of the porous particles is smaller than that of a white color material having the same particle diameter in which a large number of pores are not formed on the surface, it is advantageous in that it is difficult to settle in the ink composition. Become.

  The content (solid content) of the white color material in the ink composition according to the present embodiment is preferably 1% by mass or more and 20% by mass or less, more preferably 5% by mass or more and 15% by mass or less. . When the content of the white color material is within the above range, an image having good white color development can be formed, and occurrence of nozzle clogging and the like of the ink jet recording apparatus can be reduced.

  The average particle diameter D50 of the white color material is preferably from 100 nm to 800 nm, more preferably from 150 nm to 600 nm, and particularly preferably from 200 nm to 400 nm. When the average particle diameter D50 of the white color material is within the above range, the particles may settle and the dispersion stability may be impaired, or nozzle clogging may occur when applied to an ink jet recording apparatus. Can be reduced. Further, when the average particle diameter of the white color material is within the above range, an image having good white color developability tends to be formed.

  The average particle diameter D50 of the white color material can be measured by a particle size distribution measuring apparatus using a dynamic light scattering method as a measurement principle. An example of such a particle size distribution measuring apparatus is “Microtrac UPA” manufactured by Nikkiso Co., Ltd.

  The absorbance (wavelength 500 nm) when diluted with water so that the solid content concentration of the white color material in the ink composition according to the present embodiment is 0.01% by mass is preferably 1.1 or more. 2.2 or less, more preferably 1.4 or more and 1.8 or less. When the absorbance is within the above range, an image having good white color development can be formed, and occurrence of nozzle clogging and the like of the ink jet recording apparatus can be reduced.

1.2. Polymer Particle The polymer particle used in the present embodiment includes a repeating unit derived from an unsaturated vinyl monomer. In addition, the polymer particles used in the present embodiment have a polymerizable double bond in addition to the repeating unit derived from the unsaturated vinyl monomer from the viewpoint of improving the discharge stability by forming a crosslinkable polymer. It is preferable to further include a repeating unit derived from a monomer having two or more.

1.2.1. Repeating units derived from unsaturated vinyl monomers As unsaturated vinyl monomers, (meth) acrylic acid ester monomers, aromatic vinyl monomers, vinyl ester monomers, vinyl generally used in emulsion polymerization Examples include cyanide monomers, halogenated monomers, olefin monomers, diene monomers, vinyl monomers, unsaturated carboxylic acids, acrylamides, and hydroxyl group-containing monomers. . Among these, acrylic ester monomers, methacrylic ester monomers, aromatic vinyl monomers, vinyl ester monomers, vinyl cyanide monomers, unsaturated carboxylic acids, acrylamides, hydroxyl groups Containing monomers are preferred.

  As acrylic acid ester monomers, methyl acrylate, ethyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, n-amyl acrylate, isoamyl acrylate, n-hexyl acrylate, 2-ethylhexyl acrylate, octyl acrylate Decyl acrylate, dodecyl acrylate, octadecyl acrylate, cyclohexyl acrylate, phenyl acrylate, benzyl acrylate, glycidyl acrylate, and the like.

  Methacrylic acid esters include methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, n-amyl methacrylate, isoamyl methacrylate, n-hexyl methacrylate, 2-ethylhexyl methacrylate, octyl methacrylate, decyl methacrylate, dodecyl methacrylate. , Octadecyl methacrylate, cyclohexyl methacrylate, phenyl methacrylate, benzyl methacrylate, glycidyl methacrylate and the like.

  Examples of aromatic vinyl monomers include styrene, p-methylstyrene, α-methylstyrene, 2-methylstyrene, vinyltoluene, t-butylstyrene, chlorostyrene, vinylxylene, vinylnaphthalene, vinylanthracene, vinylanisole, Examples include divinylbenzene.

  Vinyl esters include vinyl acetate and the like; vinylcyan compounds include acrylonitrile and methacrylonitrile; halogenated monomers include vinylidene chloride and vinyl chloride; olefin monomers. Ethylene, propylene, etc .; diene monomers, butadiene, chloroprene, etc .; vinyl monomers, vinyl ether, vinyl ketone, vinyl pyrrolidone, etc .; unsaturated carboxylic acids, acrylic acid, Methacrylic acid, itaconic acid, fumaric acid, maleic acid, etc .; acrylamides include acrylamide, methacrylamide, N, N′-dimethylacrylamide, etc .; hydroxyl group-containing monomers include 2-hydroxyethyl acrylate, 2 -Hydroxypropyl acrylate, 2-hydroxy Ethyl methacrylate, 2-hydroxypropyl methacrylate, and the like, respectively.

  The unsaturated vinyl monomers exemplified above may be used alone or in combination of two or more.

1.2.2. Repeating units derived from monomers having two or more polymerizable double bonds As monomers having two or more polymerizable double bonds, diacrylate compounds, triacrylate compounds, tetraacrylate compounds, hexaacrylate compounds, dimethacrylates Examples thereof include compounds, trimethacrylate compounds, divinylbenzene, and methylene bisacrylamide compounds. By using a crosslinkable polymer obtained by copolymerizing three or more crosslinkable monomers having two or more, preferably three or more polymerizable double bonds during polymerization, the nozzle plate surface has an ink composition. Further, it becomes difficult to get wet by an object, flight bending can be further prevented, and discharge stability can be further improved.

Specific examples of the monomer having two or more polymerizable double bonds include polyethylene glycol diacrylate, triethylene glycol diacrylate, 1,3-butylene glycol diacrylate, 1,6-butylene glycol diacrylate, 1,6 -Hexanediol diacrylate, neopentyl glycol diacrylate, 1,9-nonanediol diacrylate, polypropylene glycol diacrylate, 2,2'-bis (4-acryloxypropyloxyphenyl) propane, 2,2'-bis ( Diacrylate compounds such as 4-acryloxydiethoxyphenyl) propane; triacrylate compounds such as trimethylolpropane triacrylate, trimethylolethane triacrylate, tetramethylolmethane triacrylate Tetraacrylate compounds such as ditrimethylol tetraacrylate, tetramethylolmethane tetraacrylate, pentaerythritol tetraacrylate; hexaacrylate compounds such as dipentaerythritol hexaacrylate; ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, polyethylene glycol di Methacrylate, 1,3-butylene glycol dimethacrylate, 1,4-butylene glycol dimethacrylate, 1,6-hexanediol dimethacrylate, neopentyl glycol dimethacrylate, dipropylene glycol dimethacrylate, polypropylene glycol dimethacrylate, polybutylene glycol dimethacrylate Methacrylate, 2, Dimethacrylate compounds such as 2′-bis (4-methacryloxydiethoxyphenyl) propane; Trimethacrylate compounds such as trimethylolpropane trimethacrylate and trimethylolethane trimethacrylate; methylenebisacrylamide and divinylbenzene.

  The monomers having two or more polymerizable double bonds exemplified above may be used alone or in combination of two or more.

  The content ratio of the repeating unit derived from the monomer having two or more polymerizable double bonds in 100 parts by mass of the polymer particles is preferably 1 part by mass or more and 10 parts by mass or less from the viewpoint of the melting start temperature. More preferably, it is 2 parts by mass or more and 8 parts by mass or less.

1.2.3. Production of polymer particles The polymer particles used in the present embodiment are produced directly by a known emulsion polymerization method using the above-mentioned monomers, or a copolymer produced by another polymerization method is used as a mechanical emulsion method. Based on this, it can be produced by finely dispersing in a liquid medium.

  Examples of the method using the emulsion polymerization method include a method in which various monomers are charged at once in the presence of a dispersant and a polymerization initiator, and a method in which polymerization is performed while continuously supplying monomers. The polymerization at that time is usually carried out in a temperature range of 30 to 90 ° C., and polymer particles that are substantially an aqueous dispersion of copolymer particles generally called an emulsion are obtained.

  The aqueous dispersion of copolymer particles obtained by the emulsion polymerization method is excellent in that it is very stable in a small amount of a dispersant and a particle having a very small particle diameter can be easily obtained.

  Examples of the dispersant used in the emulsion polymerization method include nonionic surfactants, anionic surfactants, nonionic water-soluble polymers, anionic water-soluble polymers, and the like. You can select and use.

  Specific examples of the nonionic surfactant include polyoxyethylene lauryl ether, polyoxyethylene alkyl ethers such as polyoxyethylene stearyl ether, polyoxyalkylene alkyl ethers, polyoxyethylene polyoxypropylene alkyl ethers, Polyoxyethylene styrenated phenyl ether, polyoxyethylene distyrenated phenyl ether, polyoxyethylene octyl phenyl ether, polyoxyethylene oleyl phenyl ether, polyoxyethylene nonyl phenyl ether, oxyethylene / oxypropylene block copolymer, t-octylphenoxy Examples thereof include ethyl polyethoxyethanol, nonylphenoxyethyl polyethoxyethanol, and the like. It can be selected and used more.

  Specific examples of the anionic surfactant include sodium dodecylbenzenesulfonate, sodium lauryl sulfate, sodium alkyldiphenyl ether disulfonate, sodium alkylnaphthalenesulfonate, sodium dialkylsulfosuccinate, sodium stearate, potassium oleate, sodium. Dioctyl sulfosuccinate, sodium polyoxyethylene alkyl ether sulfate, sodium polyoxyethylene alkyl ether sulfate, sodium polyoxyethylene alkyl phenyl ether sulfate, sodium dialkylsulfosuccinate, sodium stearate, sodium oleate, t-octylphenoxyethoxy Polyethoxyethyl sulfate sodium salt, etc. are listed, and one or more of these are selected. It is possible to use Te.

  Nonionic water-soluble polymers include polyvinyl alcohol or derivatives thereof; starch derivatives such as oxidized starch, etherified starch and phosphate esterified starch; polyvinylpyrrolidone or polyvinylpyrrolidone derivatives such as polyvinylpyrrolidone copolymerized with vinyl acetate; Derivatives Cellulose derivatives such as carboxymethyl cellulose and hydroxymethyl cellulose; polyacrylamide or derivatives thereof; polymethacrylamide or derivatives thereof; gelatin, casein and the like can be mentioned, and one or more of these can be selected and used.

  Anionic water-soluble polymers include polyalginic acid and its metal salt, carboxymethylcellulose and its metal salt, polyacrylic acid and its metal salt, polyacrylamide partial hydrolyzate and its metal salt, maleic acid copolymer, lignin sulfone Acids and their metal salts and their derivatives, oxyorganic acids and their metal salts, alkylallyl sulfonic acids and their metal salts, polyoxyalkyl allyl ethers, polyol complexes, higher polyhydric alcohol sulfonic acids and their metal salts, gelatin Examples thereof include water-soluble proteins such as glue, metal salts thereof and derivatives thereof, and one or more of these can be selected and used.

  The amount of the dispersant used is not particularly limited, but is usually 0.02 to 20% by mass, more preferably 0.02 to 10% by mass, and particularly preferably 0.02 to 5% based on the total weight of the monomers to be copolymerized. % By mass.

  In the present embodiment, among the above-described dispersants, it is preferable to obtain polymer particles by an aqueous emulsion into which a nonionic surfactant having an HLB value of 13 to 16 is introduced.

  Nonionic surfactant introduction methods include addition to water before polymerization, addition to emulsion, addition at the time of polymerization, addition after polymerization, etc. Addition method, batch addition, divided addition, continuous addition Etc. These introduction methods can be arbitrarily combined and are not particularly limited.

As the initiator used for copolymerization, a normal radical initiator can be used, for example, hydrogen peroxide; persulfates such as ammonium persulfate, sodium persulfate, potassium persulfate; cumene hydroperoxide, t-butyl. Organic peroxides such as hydroperoxide, benzoyl peroxide, t-butylperoxy-2-ethylhexanoate, t-butylperoxybenzoate, lauroyl peroxide; azobisisobutyronitrile, 2,2′- Azobis (2-amidinopropane) dihydrochloride, 2,2′-azobis [2- (N-phenylamidino) propane] dihydrochloride, 2,2′-azobis {2- [N- (4-chlorophenyl) amidino ] Propane} dihydrochloride, 2,2′-azobis {2- [N- (4-hydroxyphenyl) amidino] propane} Dihydrochloride, 2,2′-azobis [2- (N-benzylamidino) propane] dihydrochloride, 2,2′-azobis [2- (N-allylamidino) propane] dihydrochloride, 2,2 ′ -Azobis {2- [N- (2-hydroxyethyl) amidino] propane} dihydrochloride, 2,2'-azobis {2-methyl-N- [1,1-bis (hydroxymethyl) -2-hydroxyethyl ] Propionamide}, 2,2′-azobis {2-methyl-N- [1,1-bis (hydroxymethyl) ethyl] propionamide}, 2,2′-azobis [2-methyl-N- [2- Hydroxyethyl) propionamide], 2,2′-azobis (isobutyramide) dihydrate, and the like; or these and metal ions such as iron ions and sodium sulfoxylate, formaldehyde, Examples thereof include redox initiators in combination with reducing agents such as sodium bisulfite, sodium hydrogen sulfite, L-ascorbic acid, Rongalite, etc., and one or more of these can be selected and used.

  The usage amount of a general initiator is 0.01 to 20% by mass based on the total mass of monomers to be copolymerized.

  In this Embodiment, it is preferable to superpose | polymerize in presence of 0.1-5 mass% chain transfer agent with respect to the monomer whole quantity. By adding a chain transfer agent, the weight average molecular weight Mw (toluene solubility) of the polymer particles can be adjusted to an appropriate range. As the chain transfer agent, a chain transfer agent generally used for radical polymerization can be used. Examples of chain transfer agents include butanethiol, octanethiol, decanethiol, dodecanethiol, hexadecanethiol, thiophenol, octyl thioglycolate, octadecanethiol, cyclohexyl mercaptan, octyl 2-mercaptopropionate, 2-mercaptoethyl ester of octanoate 1,8-dimercapto-3,6-dioxaoctane, 3-mercaptopropyltrimethoxysilane, β-mercaptopropionic acid, methyl-3-mercaptopropionate, 2-ethylhexyl-3-mercaptopropionate, n -Octyl-3-mercaptopropionate, n-octyl mercaptan, n-dodecyl mercaptan, trimethylolpropane tris (3-mercaptopropionate), tris-[(3-me Organic thiol compounds such as captopropionyloxy) -ethyl] -isocyanurate, tetraethylene glycol bis (3-mercaptopropionate), dipentaerythritol hexakis (3-mercaptopropionate) decane trithiol, dodecyl mercaptan; Halogen compounds such as carbon chloride, carbon tetrabromide, methylene chloride, bromoform and bromotrichloroethane; and unsaturated hydrocarbon compounds such as α-methylstyrene dimer, α-terpinene, γ-terpinene, dipentene and terpinolene. These chain transfer agents may be used individually by 1 type, and may use 2 or more types together. Among these, it is preferable to use an organic thiol compound having a hydrocarbon group having 3 or more carbon atoms.

  Furthermore, a pH adjuster can also be used as needed. Examples of the pH adjuster include sulfuric acid, hydrochloric acid, nitric acid, sodium hydroxide, potassium hydroxide, magnesium sulfate, potassium sulfate, aluminum sulfate, sodium acetate, magnesium acetate, potassium acetate, ammonia, triethanolamine, diethanolamine, monoethanol. An amine etc. are mentioned.

1.2.4. Characteristics of polymer particles <Melting start temperature>
The melting start temperature of the polymer particles used in the present embodiment is preferably 65 ° C. or less, more preferably 55 ° C. or less, still more preferably 50 ° C. or less, and particularly preferably 45 ° C. or less. When the ink composition is deposited on the recording medium, the polymer particles form a number of voids between the white color materials. When the melting start temperature of the polymer particles is 65 ° C. or lower, the polymer particles are melted at a temperature equal to or higher than the melting start temperature to form a void layer. It is considered that the color development of whiteness is improved because light scattering can be enhanced by this void layer.

The melting start temperature of the polymer particles used in the present embodiment is a high-flow type flow tester (for example, flow tester “CFT-500D” manufactured by Shimadzu Corporation), and the pore diameter of the die: 1 mmφ × 1 mm It means the outflow start point temperature (° C.) when 1 g of sample is flowed out under the conditions of pressurization: 30 kg / cm ² and heating rate: 5 ° C./min.

<Glass transition temperature>
The glass transition temperature of the polymer particles used in the present embodiment is preferably −30 ° C. to 0 ° C. When the glass transition temperature of the polymer particles is within the above range, the polymer particles are formed into a film at room temperature to form a void layer. The glass transition temperature can be adjusted by the blending ratio of the monomers described above. The glass transition temperature of the polymer particles used in the present embodiment can be determined from the DSC curve by a method based on JIS K7121.

<Average particle diameter D50>
The average particle diameter D50 (volume basis) of the polymer particles used in the present embodiment is preferably 50 nm or more and 1,000 nm or less, more preferably 100 nm or more and 800 nm or less, and 100 nm or more and 500 nm or less. Is particularly preferred. When the average particle diameter D50 of the polymer particles is in the above range, the polymer particles can form voids between the white color materials when the ink composition is adhered onto the recording medium. Moreover, when discharging an ink composition using an inkjet printer, the discharge stability from a nozzle head is securable.

  The average particle diameter D50 of the polymer particles is controlled by the usage amount of the surfactant and the polymerization initiator. Increasing the amount of surfactant used decreases the particle size, and decreasing the amount of polymerization initiator decreases the particle size.

  The average particle diameter D50 of the polymer particles can be measured by a particle size distribution measuring apparatus using a dynamic light scattering method as a measurement principle. As such a measuring device, for example, a particle size analyzer FPAR-1000 (Otsuka Electronics Co., Ltd.), a laser particle size analysis system LPA-3000 / 3100 (Otsuka Electronics Co., Ltd.), a laser diffraction particle size distribution measuring device SALD-2000A ( Shimadzu Corporation).

<Relationship between average particle size and melting start temperature>
The polymer particles used in the present embodiment must have a range in which the relationship between the average particle diameter D50 and the melting start temperature is represented by the following formula (1).
Y ≦ 0.33X + 20 (1)
(In the above formula (1), X represents an average particle diameter D50 (nm) and Y represents a melting start temperature (° C.).)
The above formula (1) is a law found by experience through repeated experiments by the present inventors. By using specific polymer particles in the range represented by the above formula (1), the effect of the present invention can be obtained in which the shielding property and color development of a white image when deposited on a recording medium are good. . The mechanism by which this effect occurs can be considered as follows. That is, when the relationship between the average particle diameter D50 of the polymer particles and the melting start temperature is within the range represented by the following formula (1), the polymer particles are white when the ink composition is deposited on the recording medium. A large number of voids are formed between the color materials, and the polymer particles are melted to form a layer containing voids (void layer). Since the light scattering can be enhanced by this void layer, it is considered that the whiteness color developability is further improved.

<Toluene dissolution rate>
The toluene dissolution rate of the polymer particles used in the present embodiment is preferably 10% by mass to 80% by mass, more preferably 10% by mass to 60% by mass, and particularly preferably 10% by mass.
It is not less than 40% by mass. The toluene dissolution rate of the polymer particles correlates with the weight average molecular weight (Mw) of the polymer particles. When the toluene dissolution rate is within the above range, the polymer particles are easily melted on the recording medium, and the above-described void layer is easily formed. Therefore, the white image has a shielding property and color developability when adhered on the recording medium. The advantageous effects of the present invention are easily obtained.

The “toluene dissolution rate” in the present invention can be determined as follows. An aqueous dispersion of polymer particles used in the present embodiment was applied onto a glass plate, dried at room temperature for 24 hours, and then vacuum dried for 12 hours to obtain a film. 1 g of the film thus obtained was immersed in toluene and allowed to stand for 16 hours in a sealed container at 23 ° C. atmosphere. Next, the toluene phase was filtered through a 300-mesh wire mesh to separate the insoluble matter, and the mass (Y (g)) of the residue obtained by evaporating and removing the dissolved toluene was measured from the following formula ( The toluene dissolution rate was determined by 2).
Toluene dissolution rate (mass%) = (Y / 1) × 100 (2)

1.3. Solvent The ink composition according to the present embodiment contains a solvent. As the solvent, at least one of water and an organic solvent (described later) can be contained. When the ink composition contains water as a solvent, it is used as a so-called aqueous ink. On the other hand, when the white ink composition does not substantially contain water, it is used as a so-called non-aqueous ink. The ink composition according to the present embodiment is preferably a water-based ink from the viewpoint of the stability of the polymer particles.

  In the present invention, “substantially free of A” means that A is not intentionally added in the production of ink, or exceeds the amount that sufficiently achieves the significance of adding A. Meaning not to be added. Specific examples of “substantially free” include, for example, 1.0% by mass or more, preferably 0.5% by mass or less, more preferably 0.1% by mass or less, and still more preferably 0% by mass. 0.05% by mass or less, particularly preferably 0.01% by mass or less, more preferably 0.001% by mass or less.

<Water>
When water is contained, it is preferable to use water from which ionic impurities have been removed as much as possible, such as pure water such as ion exchange water, ultrafiltration water, reverse osmosis water, and distilled water, and ultrapure water. . Further, when water sterilized by ultraviolet irradiation or addition of hydrogen peroxide is used, generation of mold and bacteria can be prevented when the pigment dispersion and ink using the same are stored for a long period of time.

  When the ink composition is a water-based ink, for example, the water content can be 50% by mass or more based on the total mass of the ink composition. An organic solvent described later can be added to the water-based ink.

<Organic solvent>
The ink composition according to the present embodiment may contain an organic solvent. Such an ink composition may contain a plurality of types of organic solvents. The organic solvent is not particularly limited, and examples thereof include 1,2-alkanediols, polyhydric alcohols (excluding the 1,2-alkanediols), pyrrolidone derivatives, lactones, glycol ethers, and the like.

Examples of 1,2-alkanediols include 1,2-propanediol, 1,2-butanediol, 1,2-pentanediol, 1,2-hexanediol, 1,2-octanediol, and the like. Since 1,2-alkanediols are excellent in the action of increasing the wettability of the ink with respect to the recording medium and uniformly wetting it, an image having excellent adhesion may be formed on the recording medium in some cases. When 1,2-alkanediols are contained, the content thereof can be 1% by mass or more and 20% by mass or less with respect to the total mass of the ink composition.

  Examples of the polyhydric alcohols include ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, trimethylolpropane, and glycerin. . Polyhydric alcohols can be preferably used from the viewpoint of suppressing clogging, ejection failure, and the like by suppressing ink drying and solidification on the nozzle forming surface of the recording head of the ink jet recording apparatus. When polyhydric alcohols are contained, the content can be 2% by mass or more and 20% by mass or less based on the total mass of the ink composition.

  Examples of pyrrolidone derivatives include N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, N-vinyl-2-pyrrolidone, 2-pyrrolidone, N-butyl-2-pyrrolidone, and 5-methyl-2-pyrrolidone. Is mentioned. The pyrrolidone derivative can act as a good solubilizer for the resin component. When the pyrrolidone derivative is contained, the content thereof can be 0.5 mass% or more and 10 mass% or less with respect to the total mass of the ink composition.

  In the present invention, “lactone” is a general term for cyclic compounds having an ester group (—CO—O—) in the ring. The lactone is not particularly limited as long as it is included in the above definition, but is preferably a lactone having 2 to 9 carbon atoms. Specific examples of such lactones include α-ethyl lactone, α-acetolactone, β-propiolactone, γ-butyrolactone, δ-valerolactone, ε-caprolactone, ζ-enantiolactone, η-caprolactone, γ-valerolactone, γ-heptalactone, γ-nonalactone, β-methyl-δ-valerolactone, 2-butyl-2-ethylpropiolactone, α, α-diethylpropiolactone, and the like. Of these, γ-butyrolactone is particularly preferred. When the recording medium is a film such as a vinyl chloride resin, the lactone can improve the adhesion by allowing the ink to penetrate into the recording medium. In particular, lactone is preferably used when the ink composition is a non-aqueous ink, and the content in this case is 5% by mass to 30% by mass with respect to the total mass of the white ink composition. Can do.

Examples of glycol ethers include ethylene glycol monoisobutyl ether, ethylene glycol monohexyl ether, ethylene glycol monoisohexyl ether, diethylene glycol monohexyl ether, triethylene glycol monohexyl ether, diethylene glycol monoisohexyl ether, triethylene glycol monoisohexyl. Ether, ethylene glycol monoisoheptyl ether, diethylene glycol monoisoheptyl ether, triethylene glycol monoisoheptyl ether, ethylene glycol monooctyl ether, ethylene glycol monoisooctyl ether, diethylene glycol monoisooctyl ether, triethylene glycol monoisooctyl ether, ethylene Recall mono-2-ethylhexyl ether, diethylene glycol mono-2-ethylhexyl ether, triethylene glycol mono-2-ethylhexyl ether, diethylene glycol mono-2-ethylpentyl ether, ethylene glycol mono-2-ethylpentyl ether, ethylene glycol mono-2 -Ethylhexyl ether, diethylene glycol mono-2-ethylhexyl ether, ethylene glycol mono-2-methylpentyl ether, diethylene glycol mono-2-methylpentyl ether, propylene glycol monobutyl ether, dipropylene glycol monobutyl ether, tripropylene glycol monobutyl ether, propylene glycol Monopropyl ether, dipropylene glycol mono Ropirueteru, and tripropylene glycol monomethyl ether, and the like. These can be used individually by 1 type or in mixture of 2 or more types. Glycol ethers can control the wettability and permeation rate of the ink to the recording medium. Therefore, a clear image with little shading unevenness can be recorded. When the ink composition is used as a water-based ink, the content of glycol ethers can be 0.05% by mass or more and 6% by mass or less with respect to the total mass of the ink composition. On the other hand, when the ink composition is used as a non-aqueous ink, the content thereof can be 70% by mass or more and 90% by mass or less with respect to the total mass of the ink composition.

1.4. Surfactant The ink composition according to the present embodiment may contain a surfactant. The surfactant has a function of reducing surface tension and improving wettability with a recording medium. Among the surfactants, for example, acetylene glycol surfactants, silicone surfactants, and fluorine surfactants can be preferably used.

  Although it does not specifically limit as acetylene glycol type surfactant, For example, Surfynol 104,104E, 104H, 104A, 104BC, 104DPM, 104PA, 104PG-50,104S, 420,440,465,485, SE, SE- F, 504, 61, DF37, CT111, CT121, CT131, CT136, TG, GA, DF110D (all are trade names, manufactured by Air Products and Chemicals. Inc.), Olphin B, Y, P, A, STG, SPC , E1004, E1010, PD-001, PD-002W, PD-003, PD-004, EXP. 4001, EXP. 4036, EXP. 4051, AF-103, AF-104, AK-02, SK-14, AE-3 (all trade names, manufactured by Nissin Chemical Industry), acetylenol E00, E00P, E40, E100 (all trade names, river Ken Fine Chemical Co., Ltd.).

  Although it does not specifically limit as a silicone type surfactant, A polysiloxane type compound is mentioned preferably. Although it does not specifically limit as the said polysiloxane type compound, For example, polyether modified organosiloxane is mentioned. Commercially available products of the polyether-modified organosiloxane include, for example, BYK-306, BYK-307, BYK-333, BYK-341, BYK-345, BYK-346, BYK-348 (above trade names, manufactured by BYK). KF-351A, KF-352A, KF-353, KF-354L, KF-355A, KF-615A, KF-945, KF-640, KF-642, KF-643, KF-6020, X-22-4515 , KF-6011, KF-6012, KF-6015, KF-6017 (above trade names, manufactured by Shin-Etsu Chemical Co., Ltd.).

  As the fluorine-based surfactant, a fluorine-modified polymer is preferably used, and specific examples thereof include BYK-340 (manufactured by BYK Japan).

  These surfactants can be used singly or in combination of two or more. When the surfactant is contained, the content thereof is preferably 0.1% by mass or more and 1.5% by mass or less with respect to the total mass of the ink composition.

1.5. Other Components The ink composition according to the present embodiment may contain a thickener, a pH adjuster, an antiseptic / antifungal agent, a rust inhibitor, a chelating agent, and the like as necessary.

<Thickener>
The thickener can be used for adjusting the viscosity of the ink. Examples of the thickener include polyvinyl alcohols, poly (meth) acrylic acids, polyethers, polyvinyl pyrrolidones, polyvinyl formals, proteins (for example, gelatin, casein, and glue), polysaccharides (for example, pullulan, Dextran, dextrin, cyclodextrin, carrageenan, pectin, glucomannan, sodium alginate, xanthan gum, arabic gum, locust bean gum, tragacanth gum, guar gum, tamarind gum, etc.), starches (eg starch, oxidized starch, carboxyl starch, dialdehyde starch) Etc.), cellulose or derivatives thereof (for example, methylcellulose, ethylcellulose, carboxymethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, hydroxypropyl) Pills methyl cellulose), alginates (e.g., sodium alginate, potassium alginate, ammonium alginate, etc.) alginates (e.g., propylene glycol alginate, etc.) and the like.

  In the case of containing a thickener, the content can be appropriately set according to the viscosity of the ink composition. can do.

<PH adjuster>
Examples of the pH adjuster include potassium dihydrogen phosphate, disodium hydrogen phosphate, sodium hydroxide, lithium hydroxide, potassium hydroxide, ammonia, diethanolamine, triethanolamine, tripropanolamine, potassium carbonate, sodium carbonate, carbonate Sodium hydrogen etc. are mentioned.

<Preservatives and fungicides>
Examples of antiseptics and fungicides include sodium benzoate, sodium pentachlorophenol, sodium 2-pyridinethiol-1-oxide, sodium sorbate, sodium dehydroacetate, 1,2-dibenzisothiazolin-3-one, etc. Is mentioned. Examples of commercially available products include Proxel XL2, Proxel GXL (above trade name, manufactured by Avicia), Denside CSA, NS-500W (above trade name, manufactured by Nagase ChemteX Corporation), and the like.

<Rust preventive>
Examples of the rust preventive include benzotriazole.

<Chelating agent>
Examples of the chelating agent include ethylenediaminetetraacetic acid and salts thereof (ethylenediaminetetraacetic acid dihydrogen disodium salt and the like).

1.5. Method for Producing Ink Composition The ink composition according to the present embodiment is obtained by mixing the above-described components (materials) in an arbitrary order, performing filtration or the like as necessary, and removing impurities. Can do. Here, when a white color material is added, it is preferable to prepare the white color material in a state of being uniformly dispersed in a solvent before mixing, because the handling becomes simple. As a method for mixing each material, a method in which materials are sequentially added to a container equipped with a stirring device such as a mechanical stirrer or a magnetic stirrer and stirred and mixed is preferably used. As a filtration method, for example, centrifugal filtration or filter filtration can be performed as necessary.

1.6. Physical properties of ink composition <Relationship between average particle size of white color material and polymer particles>
In the ink composition according to the present embodiment, when the average particle diameter D50 of the white color material is D1 (nm) and the average particle diameter D50 of the polymer particles is D2 (nm), D1: D2 = 1: A relationship of 0.01 to 1: 5 is preferable, and a relationship of D1: D2 = 1: 0.1 to 1: 1 is more preferable. When the relationship between the average particle size of the white color material and the average particle size of the polymer particles is within the above range, the polymer particles are placed between the white color materials when the ink composition is deposited on the recording medium. It is easy to enter and many voids are easily formed. Thereby, the color development of the whiteness of the recorded image can be further improved.

<Quantitative relationship between white color material and polymer particles>
In the ink composition according to the present embodiment, when the content of the white color material is W1 and the content of the polymer particles is W2 (nm), the relationship of W1: W2 = 1: 5 to 5: 1. It is preferable that the relationship is W1: W2 = 2: 1 to 3: 1. When the quantitative relationship between the white color material and the polymer particles is within the above range, when the ink composition is deposited on the recording medium, the polymer particles easily enter between the white color materials and a large number of voids. Is easily formed. Thereby, the color development of the whiteness of the recorded image can be further improved.

<Surface tension>
The ink composition according to the present embodiment has a surface tension at 20 ° C. of 20 mN / m or more and 40 mN / m from the viewpoint of a balance between image quality and reliability as an ink when applied to an ink jet recording apparatus. It is more preferable that it is 25 mN / m or more and 35 mN / m or less. The surface tension is measured by, for example, measuring the surface tension when the platinum plate is wetted with ink in an environment of 20 ° C. using an automatic surface tension meter CBVP-Z (trade name, manufactured by Kyowa Interface Science Co., Ltd.). It can be measured by checking.

<Viscosity>
From the same viewpoint, the viscosity at 20 ° C. of the ink composition according to the present embodiment is preferably 3 mPa · s or more and 10 mPa · s or less, and more preferably 3 mPa · s or more and 8 mPa · s or less. preferable. The viscosity can be measured, for example, by using a viscoelasticity tester MCR-300 (trade name, manufactured by Pysica) under a 20 ° C. environment.

2. EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples, but the present invention is not limited to these examples.

2.1. Preparation of pigment dispersion <Preparation of pigment 1 dispersion>
160 g of commercially available titanium dioxide powder (rutile type, primary particle size: 80 nm) was added to 480 g of ion-exchanged water, and 160 g of a 10 wt% sodium hexametaphosphate aqueous solution was further added and stirred at room temperature. To this slurry solution, 83.7 g of zirconium chloride oxide octahydrate was added. A sodium hydroxide aqueous solution was slowly added to the slurry solution to adjust the pH to 3.5 to 4.0, and the mixture was stirred as it was for 20 hours. The obtained slurry solution was filtered under pressure at 0.4 MPa, the solid content was redispersed with 480 mL of ion-exchanged water, filtered again at 0.4 MPa, and left as it was at room temperature under a pressurized atmosphere. And dried in a filtration device. The obtained powder was heated at a rate of 5 ° C. per minute from room temperature to 500 ° C. in an air atmosphere using an electric furnace, and further baked at 500 ° C. for 2 hours to obtain a powder. The powder thus obtained was designated as Pigment 1. The average secondary particle diameter of Pigment 1 was 288 nm. By sufficiently mixing and stirring 20 parts by mass of this pigment 1 and 80 parts by mass of ion-exchanged water, a dispersion of pigment 1 having a solid content concentration of 20% by mass was obtained.

<Preparation of pigment 2 to pigment 4 dispersion>
The type of titanium dioxide powder was changed to that shown in Table 1, the adjusted pH, drying or firing conditions were changed as appropriate, and the addition amount of titanium dioxide, 10 wt% sodium hexametaphosphate aqueous solution and zirconium chloride octahydrate Was carried out in the same manner as in the preparation of the dispersion liquid of Pigment 1 except that the pigments having the compositions shown in Table 1 were obtained.

<Dispersion of Pigment 5>
As a non-porous titanium dioxide dispersion, a slurry containing trade name “NanoTek (R) Slurry” manufactured by C-I Kasei Co., Ltd. and titanium dioxide particles having an average secondary particle size of 330 nm at a solid content concentration of 15% was used.

<Preparation of dispersion of pigment 6>
As a cyan pigment, 50 parts by weight of Pigment Blue 15: 3 and 13 parts by weight of styrene-acrylic resin (weight average molecular weight 78,000, resin acid value 100) were added with ion-exchanged water to make 100 parts by weight as a whole. The mixture was stirred. This mixture was subjected to a dispersion treatment for 6 hours together with zirconia beads (diameter 1.5 mm) using a sand mill (manufactured by Yaskawa Seisakusho Co., Ltd.). Thereafter, the zirconia beads were separated by a separator to obtain a non-porous cyan pigment dispersion (average secondary particle size 110 nm).

<Measurement of average particle diameter D50 (D1)>
The measurement was performed under the following conditions using a dynamic light scattering nanotrack particle size distribution meter (manufactured by Nikkiso Co., Ltd., Microtrac UPA). In addition, MV value was employ | adopted as average particle diameter D50.・ Measurement time: 120s
-Number of measurements: average of 3 times-Particle permeability: transmission-Particle refractive index: 2.52
-Particle shape: non-spherical-Density: 4.23
-Solvent name: water-Solvent refractive index: 1.33
・ Filter: Standard
・ Sensitivity: Standard

2.2. Synthesis of polymer particles <Synthesis of polymer particles 1>
A reaction vessel equipped with a stirrer, a reflux condenser, a dropping device, and a thermometer was charged with 700 g of ion exchange water and 5 g of sodium dodecyl diphenyl ether disulfonate, and the temperature was raised to 75 ° C. while purging with nitrogen under stirring. The internal temperature is kept at 75 ° C., 10 g of potassium persulfate is added as a polymerization initiator, and after dissolution, 500 g of ion-exchanged water, 5 g of sodium dodecyl diphenyl ether disulfonate, 300 g of styrene, 550 g of 2-ethylhexyl acrylate, 2-hydroxyethyl methacrylate An emulsion prepared by adding 150 g and 1 g of n-dodecyl mercaptan under stirring was dropped into the reaction solution over 4 hours continuously. After completion of the dropwise addition, aging was performed for 3 hours. The obtained aqueous emulsion was cooled to room temperature, and then ion-exchanged water was added to adjust the solid content to 45% by weight.

<Synthesis of polymer particle 2>
A reaction vessel equipped with a stirrer, a reflux condenser, a dropping device, and a thermometer was charged with 900 g of ion-exchanged water and 20 g of the aqueous emulsion obtained in Synthesis Example 1, and the temperature was raised to 75 ° C. while purging with nitrogen under stirring. The internal temperature was kept at 75 ° C., and an aqueous solution in which 10 g of ammonium persulfate was dissolved as a polymerization initiator in 100 g of ion-exchanged water in advance was added, 500 g of ion-exchanged water in advance, 5 g of sodium dodecyl diphenyl ether disulfonate, 150 g of styrene, 50 g of methyl methacrylate, An emulsion prepared by adding 650 g of n-butyl acrylate, 150 g of 2-hydroxyethyl methacrylate, and 1 g of n-dodecyl mercaptan was added dropwise to the reaction solution over 4 hours continuously. After completion of the dropwise addition, aging was performed for 3 hours. The obtained aqueous emulsion was cooled to room temperature, and then ion-exchanged water was added to adjust the solid content to 45% by weight.

<Synthesis of polymer particles 3>
A reaction vessel equipped with a stirrer, a reflux condenser, a dropping device, and a thermometer was charged with 800 g of ion-exchanged water and 5 g of sodium dodecyl diphenyl ether disulfonate, and the temperature was raised to 75 ° C. while purging with nitrogen under stirring. The internal temperature is kept at 75 ° C., 10 g of potassium persulfate is added as a polymerization initiator, and after dissolution, 500 g of ion exchange water, 5 g of sodium dodecyl diphenyl ether disulfonate, 200 g of styrene, 100 g of methyl methacrylate, 600 g of 2-ethylhexyl acrylate, and An emulsion prepared by adding 100 g of 2-hydroxyethyl methacrylate under stirring was dropped into the reaction solution over a continuous period of 4 hours. After completion of the dropwise addition, aging was performed for 3 hours. The obtained aqueous emulsion was cooled to room temperature, and then ion-exchanged water and an aqueous sodium hydroxide solution were added to adjust the solid content to 45% by weight and pH 7.

<Synthesis of polymer particles 4>
A reaction vessel equipped with a stirrer, a reflux condenser, a dropping device, and a thermometer was charged with 750 g of ion exchange water and 10 g of sodium dodecyl sulfate, and the temperature was raised to 75 ° C. while purging with nitrogen under stirring. The internal temperature was kept at 75 ° C., 10 g of potassium persulfate was added as a polymerization initiator, and after dissolution, 500 g of ion-exchanged water, 5 g of sodium dodecyl diphenyl ether disulfonate, 350 g of styrene, 100 g of methyl methacrylate, 450 g of 2-ethylhexyl acrylate, and An emulsion prepared by adding 100 g of 2-hydroxyethyl methacrylate under stirring was dropped into the reaction solution over a continuous period of 4 hours. After completion of the dropwise addition, aging was performed for 3 hours. The obtained aqueous emulsion was cooled to room temperature, and then ion-exchanged water and an aqueous sodium hydroxide solution were added to adjust the solid content to 45% by weight and pH 7.

<Synthesis of polymer particles 5>
A reaction vessel equipped with a stirrer, a reflux condenser, a dropping device, and a thermometer was charged with 1500 g of ion-exchanged water and 20 g of the aqueous emulsion obtained in Synthesis Example 3, and the temperature was raised to 75 ° C. while purging with nitrogen under stirring. The internal temperature was kept at 75 ° C., and an aqueous solution in which 10 g of ammonium persulfate was previously dissolved as a polymerization initiator in 100 g of ion-exchanged water was added. In advance, 500 g of ion-exchanged water, 5 g of sodium dodecyl sulfate, 260 g of styrene, and n-butyl acrylate 67
An emulsion prepared by adding 0 g, 20 g of acrylic acid, 50 g of acrylamide, and 20 g of polyethylene glycol dimethacrylate with stirring was added dropwise to the reaction solution over 4 hours. After completion of the dropwise addition, aging was performed for 3 hours. The obtained aqueous emulsion was cooled to room temperature, and then ion-exchanged water was added to adjust the solid content to 32% by weight.

<Synthesis of polymer particles 6>
A reaction vessel equipped with a stirrer, a reflux condenser, a dropping device, and a thermometer was charged with 1500 g of ion-exchanged water and 20 g of the aqueous emulsion obtained in Synthesis Example 4, and the temperature was raised to 75 ° C. while purging with nitrogen under stirring. Maintaining the internal temperature at 75 ° C., an aqueous solution in which 10 g of ammonium persulfate was dissolved as a polymerization initiator in 100 g of ion-exchanged water in advance was added, and 350 g of styrene, 560 g of n-butyl acrylate in 500 g of ion-exchanged water and 5 g of sodium dodecyl sulfate in advance. An emulsion prepared by adding 35 g of methacrylic acid, 55 g of acrylamide, and 20 g of polyethylene glycol dimethacrylate under stirring was added dropwise to the reaction solution over 4 hours. After completion of the dropwise addition, aging was performed for 3 hours. The obtained aqueous emulsion was cooled to room temperature, and then ion-exchanged water was added to adjust the solid content to 32% by weight.

<Synthesis of polymer particles 7>
In a reaction vessel equipped with a stirrer, a reflux condenser, a dropping device, and a thermometer, 3000 g of ion-exchanged water and 10 g of sodium dodecyl sulfate were charged, and the temperature was raised to 75 ° C. while purging with nitrogen under stirring. The internal temperature was kept at 75 ° C., 10 g of potassium persulfate was added as a polymerization initiator, and after dissolution, 500 g of ion exchange water, 5 g of sodium dodecyl diphenyl ether disulfonate, 360 g of styrene, 500 g of n-butyl acrylate, 20 g of methacrylic acid, 2 -An emulsion prepared by adding 10 g of hydroxyethyl methacrylate, 20 g of acrylamide, and 80 g of polyethylene glycol dimethacrylate under stirring was dropped into the reaction solution over 4 hours continuously. After completion of the dropwise addition, aging was performed for 3 hours. The obtained aqueous emulsion was cooled to room temperature, and then ion-exchanged water and an aqueous sodium hydroxide solution were added to adjust the solid content to 18% by weight and pH 8.

<Synthesis of polymer particles 8>
A reaction vessel equipped with a stirrer, a reflux condenser, a dropping device, and a thermometer was charged with 1500 g of ion-exchanged water and 20 g of the aqueous emulsion obtained in Synthesis Example 6, and the temperature was raised to 75 ° C. while purging with nitrogen under stirring. The internal temperature was kept at 75 ° C., and an aqueous solution in which 10 g of ammonium persulfate was previously dissolved in 100 g of ion-exchanged water as a polymerization initiator was added, and 260 g of styrene, 630 g of n-butyl acrylate, 500 g of ion-exchanged water, 5 g of sodium dodecyl sulfate in advance, An emulsion prepared by adding 30 g of methacrylic acid, 40 g of acrylamide, and 40 g of polyethylene glycol dimethacrylate with stirring was added dropwise to the reaction solution over 4 hours. After completion of the dropwise addition, aging was performed for 3 hours. The obtained aqueous emulsion was cooled to room temperature, and then ion-exchanged water and an aqueous sodium hydroxide solution were added to adjust the solid content to 32% by weight and pH 7.5.

<Synthesis of polymer particles 9>
A reaction vessel equipped with a stirrer, a reflux condenser, a dropping device, and a thermometer was charged with 1500 g of ion-exchanged water and 20 g of the aqueous emulsion obtained in Synthesis Example 6, and the temperature was raised to 75 ° C. while purging with nitrogen under stirring. The internal temperature was kept at 75 ° C., and an aqueous solution in which 10 g of ammonium persulfate was previously dissolved as a polymerization initiator in 100 g of ion-exchanged water was added. In advance, 500 g of ion-exchanged water, 5 g of sodium dodecyl sulfate, 260 g of styrene, 590 g of n-butyl acrylate, An emulsion prepared by adding 30 g of methacrylic acid, 40 g of acrylamide, and 80 g of polyethylene glycol dimethacrylate under stirring was dropped into the reaction solution over 4 hours continuously. After completion of the dropwise addition, aging was performed for 3 hours. After cooling the obtained aqueous emulsion to room temperature, ion exchange water and aqueous sodium hydroxide solution were added to obtain a solid content of 32% by weight, p
Adjusted to H7.5.

<Measurement of melting start temperature>
When using a flow tester CFT-500D manufactured by Shimadzu Corporation, 1 g of a sample was melted and discharged under the conditions of a pore diameter of a die of 1 mmφ × 1 mm, a pressure of 30 kg / cm ² , and a heating rate of 5 ° C./min. The outflow start temperature (° C.) was defined as the melting start temperature (Ti).

<Measurement of glass transition temperature (Tg)>
It calculated | required from the DSC curve by the method based on JISK7121.

<Measurement of toluene dissolution rate>
An aqueous dispersion of polymer particles was applied on a glass plate, dried at room temperature for 24 hours, and then vacuum dried for 12 hours to obtain a film. 1 g of the film thus obtained was immersed in toluene and allowed to stand for 16 hours in a sealed container at 23 ° C. atmosphere. Next, the toluene phase was filtered through a 300-mesh wire mesh to separate the insoluble matter, and the mass (Y (g)) of the residue obtained by evaporating and removing the dissolved toluene was measured from the following formula ( The toluene dissolution rate was determined by 2).
Toluene dissolution rate (mass%) = (Y / 1) × 100 (2)

<Measurement of average particle diameter D50 (D2)>
It measured on condition of the following using the particle size distribution measuring apparatus (The Otsuka Electronics Co., Ltd. make, particle diameter analyzer FPAR-1000) which makes a dynamic light scattering method a measurement principle.
・ Measurement time: 180s
-Number of measurements: 3 times average-Measurement temperature: 25.0 ° C
-Solvent name: water-Solvent refractive index: 1.3313
Solvent viscosity: 0.8852
-Scattering intensity: 30000 ± 5000

  Table 2 shows the melting start temperature, glass transition temperature, toluene dissolution rate, and average particle diameter D50 of the polymer particles synthesized in Synthesis Examples 1 to 9.

  A graph showing the relationship between the melting start temperature (° C.) of polymer particles and the average particle diameter D50 (nm) is shown in FIG.

2.3. Preparation of ink composition Inks 1 to 18 were obtained by mixing and stirring the components so as to have the compositions shown in Tables 3 to 4 and further filtering through a membrane filter having a pore size of 5 μm. Among the components described in Table 3 and Table 4, the components other than the compound names are as follows. In Tables 3 and 4, the pigment and polymer particle content is a value in terms of solid content, and the numerical values in Table 3 and Table 4 represent the content (% by mass) in the ink.

・ Surfinol DF110D (trade name, manufactured by Air Products and Chemicals. Inc., acetylene glycol surfactant)
・ BYK-348 (trade name, manufactured by BYK, silicone surfactant)

  In Tables 3 and 4, “absorbance in ink” means absorbance (wavelength 500 nm) when diluted with water so that the solid content concentration of the pigment component in the ink composition is 0.01% by mass. ).

2.4. Evaluation test 2.4.1. Discharge stability The ink composition obtained as described above was filled into an ink jet printer (trade name “PX-G930”, manufactured by Seiko Epson Corporation). An image composed of the ink composition was formed on a recording medium. Subsequently, with the ejection head of the ink jet printer capped, the ink jet printer was left at 40 ° C. for 14 days, and the cleaning recoverability thereafter was evaluated according to the following criteria.
A: Recovered after one cleaning or less.
B: Recovered after cleaning 2 times or more and 3 times or less.
C: Recovered after cleaning 4 times or more and 10 times or less.
D: Not recovered by cleaning.

2.4.2. Whiteness The ink composition obtained as described above was filled in an ink jet printer (trade name “PX-G930”, manufactured by Seiko Epson Corporation). Then, an image made of the ink composition was formed on a film (trade name “Clearproof Film”, manufactured by Seiko Epson Corporation, cut to A4 size). As an image print pattern, a fill pattern that can be printed with a resolution of 1440 dpi in width and 1440 dpi in length and 100% duty is formed.

The whiteness (L *) of the image obtained as described above was measured with a spectrocolorimeter Gretag Macbeth Spectrolino (product name, manufactured by X-RITE). At the time of measurement, a black mount having an OD value of 2.1 was used as a base. The evaluation criteria are as follows.
A: L * value 75 or more B: L * value 70 or more and less than 75 C: L * value 60 or more and less than 70 D: L * value 60 or less

2.4.3. Shielding property The ink composition obtained as described above was filled into an ink jet printer (trade name “PX-G930”, manufactured by Seiko Epson Corporation). Then, an image made of the ink composition was formed on a film (trade name “Clearproof Film”, manufactured by Seiko Epson Corporation, cut to A4 size). As an image print pattern, a fill pattern that can be printed with a resolution of 1440 dpi in width and 1440 dpi in length and 100% duty is formed.

The image obtained as described above was obtained by integrating transmitted light up to a wavelength of 380 to 800 nm with an angle colorimeter (product name “ARM-500V”, manufactured by JASCO). The evaluation criteria are as follows.
A: Less than 500 B: 500 or more and less than 1000 C: 1000 or more and less than 2500 D: 2500 or more

2.4.4. Sedimentability The ink composition obtained as described above was placed in a 10 mL graduated cylinder and allowed to stand in a constant temperature room at 20 ° C. for 1 week. 2 mL of the supernatant was collected, and the absorbance WA at a wavelength of 500 nm and the absorbance W0 at a wavelength of 500 nm of the ink composition before standing were measured, and the residual ratio S was calculated by the following formula.
Residual rate S (%) = ((absorbance WA) / (absorbance W0)) × 100

And the sedimentation property was evaluated based on the following evaluation criteria for the calculated residual rate S (%).
A: Residual rate S is 80% or more B: Residual rate S is 50% or more and less than 80% C: Residual rate S is 20% or more and less than 50% D: Residual rate S is less than 20%

2.5. Evaluation results The results of the above evaluation tests are also shown in Tables 3 and 4.

  From the results shown in Tables 3 and 4, according to the ink composition of the present invention, the ejection stability is good, and the white image is well-shielded and colored when deposited on a recording medium. I understood. Further, it was found that when porous titanium dioxide was used as the white color material, the storage stability was improved without precipitation in the ink composition.

  Apart from the above evaluation tests, the cross-sectional states of the recorded images of ink 1 and ink 5 obtained by the above whiteness evaluation were observed by SEM.

  FIG. 2 is an SEM image showing a cross-sectional state of an image recorded with ink 1. FIG. 3 is an SEM image showing a cross-sectional state of an image recorded with the ink 5.

  As shown in FIG. 2, it can be seen that an image recorded using the ink composition according to the present invention has many fine voids formed therein. Since this void layer can intensify the scattering of light, it is considered that the shielding property and coloring property of the white image are improved.

  On the other hand, as shown in FIG. 3, it can be seen that an image recorded using the ink composition corresponding to the comparative example of the present invention has almost no internal voids and is almost solid. In such a dense layer, light scattering is weak, and thus it is considered that the white image has insufficient shielding and coloring properties.

  The present invention is not limited to the embodiments described above, and various modifications are possible. For example, the present invention includes substantially the same configuration (for example, a configuration having the same function, method, and result, or a configuration having the same purpose and effect) as the configuration described in the embodiment. In addition, the invention includes a configuration in which a non-essential part of the configuration described in the embodiment is replaced. In addition, the present invention includes a configuration that achieves the same effect as the configuration described in the embodiment or a configuration that can achieve the same object. In addition, the invention includes a configuration in which a known technique is added to the configuration described in the embodiment.

Claims (9)

An ink composition comprising a white color material, polymer particles and a solvent,
The polymer particle includes a repeating unit derived from an unsaturated vinyl monomer and a repeating unit derived from a monomer having two or more polymerizable double bonds ,
An ink composition, wherein the polymer particles satisfy a relationship represented by the following formula (1).
Y ≦ 0.33X + 20 (1)
(In the above formula (1), X represents an average particle diameter D50 (nm) and Y represents a melting start temperature (° C.).)   The ink composition according to claim 1, wherein the polymer particles have a toluene dissolution rate of 10% by mass or more and 80% by mass or less.   The ink composition according to claim 1, wherein the polymer particles are obtained by polymerization in the presence of a chain transfer agent. The content ratio of the repeating unit derived from the monomer having two or more polymerizable double bonds in 100 parts by mass of the polymer particles is 1 part by mass or more and 10 parts by mass or less . The ink composition according to any one of the above. The absorbance at a wavelength of 500 nm is 1.1 or more and 2.2 or less when diluted with water so that the solid content concentration of the white color material in the ink composition is 0.01% by mass. The ink composition according to any one of claims 1 to 4 . When the average particle diameter D50 of the white color material is D1 (nm) and the average particle diameter D50 of the polymer particles is D2 (nm), a relationship of D1: D2 = 1: 0.01 to 1: 5 The ink composition according to any one of claims 1 to 5 , wherein The ink composition according to claim 6 , wherein the D1 is 100 nm to 800 nm and the D2 is 100 nm to 500 nm. In the case where the content of the content of the white-colored colorant and W1 the polymer particles was W2, W1: W2 = 1: 5~5: in one relationship, any one of claims 1 to 7 The ink composition according to one item. The ink composition according to any one of claims 1 to 8 , wherein the white color material is an aggregate of particles having a primary particle diameter of 10 nm or more and 200 nm or less.