JP2017101170A - Production method for aqueous ink - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an aqueous white ink excellent in adhesiveness and concealment property to a resin-made recording medium and a production method therefor and an aqueous fluid dispersion of polyester resin particles suitable for the aqueous ink.SOLUTION: There are provided [1] a production method for an aqueous ink, including the following steps 1 to 4. [2] an aqueous fluid dispersion of polyester resin particles containing white pigment and having a volume median particle diameter of 200 nm to 570 nm and [3] an aqueous ink containing an aqueous fluid dispersion of the [2]. Step 1: a step of melting and kneading a white pigment and a polyester resin at a mass ratio (white pigment/polyester resin) of 10/90 to 55/45 to obtain a kneaded product. Step 2: a step of kneading the kneaded product obtained in the step 1 and a basic compound to obtain an organic solvent-based slurry of the kneaded product. Step 3: a step of adding water to the organic solvent-based slurry obtained in the step 2 and kneading the same to obtain a fluid dispersion. Step 4: a step of removing the organic solvent from the fluid dispersion obtained in the step 3 to obtain an aqueous fluid dispersion of the polyester resin particles containing the white pigment.SELECTED DRAWING: None

Description

  The present invention relates to a method for producing an aqueous ink, an aqueous dispersion, and an aqueous ink.

  White ink is an ink containing an inorganic oxide such as titanium dioxide as a white pigment, and is used in a recording method for obtaining characters and images on a recording medium such as various plastic products and metal products whose base is not white. . When an image is recorded on a transparent resin recording medium, it may be used for the purpose of reducing the transparency of the color image, and a color image with high color development is formed on a colored structure such as a plastic product. It is also used for occasions.

  On the other hand, in the field of commercial printing used for product packaging and advertisement, etc., conventionally with solvent-based inks, UV curable inks, etc. for resin-made recording media such as polyethylene terephthalate, polyvinyl chloride, polyethylene, polypropylene and nylon Printing has been done. On the other hand, from the viewpoints of reducing environmental burden, energy saving, safety, etc., as a printing method using water-based ink, it is required to utilize an inkjet recording method or a flexographic printing method. In particular, the ink jet recording method is a recording method in which ink droplets are directly ejected and adhered to a recording member from very fine nozzles to obtain characters and images, which is easy to make full color, inexpensive, and covered. The spread is remarkable due to the many advantages of non-contact with printed matter. Thus, an attempt has been made to utilize an ink jet recording method for the resin recording medium.

Patent Document 1 describes that a water-based ink characterized by containing a suspension of a polyester adsorbed with a dye or pigment is excellent in fixability to paper to be printed such as paper and an OHP sheet and water resistance. ing.
In Patent Document 2, in order to obtain a high-quality image with high density and no bleeding, and water-resistant and weather-resistant images that can be used even outdoors, an aqueous colored particle dispersion for inkjet recording liquid is hydrophilic. A colored resin in which a pigment is dispersed in a polyester resin obtained by using isophthalic acid in a proportion of 50 to 100 mol% in the total acid component, and having a group and a hydrophobic group. It is described that the dispersion is dispersed in the form of particles.

Patent Document 3 discloses an inkjet ink containing at least titanium oxide, a pigment-dispersing resin, an organic solvent, and water as a water-based white ink for inkjet having a low viscosity, storage stability, and excellent pigment sedimentation using titanium oxide as a pigment. A water-based white ink for ink jet, wherein the pigment-dispersed resin is a resin obtained by copolymerizing at least an α-olefin and maleic acid and / or maleic anhydride. Yes.
Patent Document 4 discloses a white ink for inkjet that can record an excellent image in which at least one of cracking, wear resistance, and adhesion is solved, and includes a white color material and a polyester resin. A white ink for inkjet recording is described, which comprises: a first resin comprising: a second resin comprising at least one of a fluorene resin and a styrene acrylic resin; and a third resin comprising a polyolefin wax.

JP-A-9-183932 JP 2002-256181 A JP 2014-210837 A JP2013-177526A

  However, it is difficult to reduce the particle size of the white pigment by stably dispersing the pigment particles in the water-based ink as compared with other colored materials. Further, the adhesion to the resin recording medium is poor. For this reason, it is difficult for the conventional technology to fix the white pigment on the recording medium at a high density, and as a result, the color of the background of the recording medium or the object on which the recording medium is placed is transmitted. There was a problem.

  The present invention provides a method for producing a white aqueous ink excellent in adhesion and concealment to a resin recording medium, an aqueous dispersion of polyester resin particles suitable for the aqueous ink, and an aqueous ink containing the dispersion. Is an issue.

Regarding the adhesion of the ink, it is considered that the presence of a highly dispersed pigment alone is one of the causes of deterioration, and therefore it is considered effective to cover the pigment by some means. In addition, it was considered that the white pigment particles can be stably reduced in size by modifying the pigment surface to improve the concealability and enhancing the dispersibility in water.
As a result of the study, it was found that the adhesiveness and concealment with respect to the resin-made recording medium can be improved by using an emulsion containing a white pigment in a polyester resin as a color material. In particular, for emulsions containing a white pigment, it has been found effective to disperse a melt-kneaded white pigment and polyester resin in advance.

That is, the present invention provides the following [1] to [3].
[1] A method for producing a water-based ink comprising the following steps 1 to 4.
Step 1: A step of obtaining a kneaded product by melt-kneading a white pigment and a polyester resin at a mass ratio (white pigment / polyester resin) of 10/90 to 55/45 Step 2: A kneaded product obtained in Step 1 is an organic solvent. And a step of obtaining an organic solvent-based slurry of the kneaded product Step 3: Step of adding water to the organic solvent-based slurry obtained in Step 2 and mixing to obtain a dispersion Step 4: Step Step 2 of removing the organic solvent from the dispersion obtained in step 3 to obtain an aqueous dispersion of polyester resin particles containing a white pigment [2] containing a white pigment and having a volume median particle size of 200 nm or more and 570 nm or less An aqueous dispersion of polyester resin particles.
[3] An aqueous ink containing the aqueous dispersion of [2].

  According to the present invention, there is provided a method for producing a white aqueous ink having excellent adhesion and concealment to a resin recording medium, an aqueous dispersion of polyester resin particles suitable for the aqueous ink, and an aqueous ink containing the dispersion. Can be provided.

≪Method for producing water-based ink≫
The method for producing a water-based ink of the present invention includes the following steps 1 to 4.
Step 1: A step of obtaining a kneaded product by melt-kneading a white pigment and a polyester resin at a mass ratio (white pigment / polyester resin) of 10/90 to 55/45 Step 2: A kneaded product obtained in Step 1 is an organic solvent. And a step of obtaining an organic solvent-based slurry of the kneaded product Step 3: Step of adding water to the organic solvent-based slurry obtained in Step 2 and mixing to obtain a dispersion Step 4: Step Step of removing the organic solvent from the dispersion obtained in Step 3 to obtain an aqueous dispersion of polyester resin particles containing a white pigment. The method for producing an aqueous ink of the present invention is not limited to the effect of the present invention. You may have processes other than process 1-4.
In the present specification, “water-based ink” may be simply referred to as “ink”. The “polyester resin particles containing a white pigment” may be referred to as “white pigment-containing polyester resin particles” or simply “white pigment-containing resin particles”.

The reason why the water-based ink of the present invention is excellent in adhesion and concealment to a resin recording medium is not clear, but can be considered as follows.
When the pigment is contained in the water-based ink, a method of dispersing the pigment in water using a surfactant or a water-insoluble resin is often used. However, since the fixability of the pigment on the resin recording medium is low, the pigment is It moves on the recording medium or cannot be fixed to the recording medium in the first place, so that the adhesion of the printed image becomes insufficient, and the concealing property tends to be lowered due to the influence.

  On the other hand, in the present invention, the polyester resin particles containing a white pigment contain a white pigment and a polyester resin in a mass ratio (white pigment / polyester resin) of 10/90 to 55/45. By making the pigment-containing resin particles covered with a polyester resin, the polyester resin has high affinity with a resin recording medium such as a PET (polyethylene terephthalate) film, so that the movement of the pigment on the medium is suppressed. At the same time, since the white pigment is coated with a polyester resin, it is considered that the white pigment is excellent in adhesion to a resin recording medium such as a PET film.

  However, when manufacturing polyester resin particles containing a pigment, if a forced emulsification method using mechanical force is used to disperse a white pigment that easily aggregates in water, there is a risk that the resin may deteriorate, There is a risk of dispersion without being sufficiently covered with the resin.

In the present invention, a kneaded product of a white pigment and a polyester resin is mixed with an organic solvent and a basic compound to obtain an organic solvent-based slurry of the kneaded product, and then water is added to the polyester containing the white pigment. An aqueous dispersion of resin particles can be produced with good dispersion stability.
In particular, in the present invention, a white pigment and a polyester resin are previously melt-kneaded to obtain a kneaded product. Thereby, since the white pigment can be reduced in particle size and dispersed in the polyester resin, there is no variation in the white pigment content among the obtained polyester resin particles containing the white pigment. Therefore, the aqueous ink of the present invention It is considered that the printed image by is excellent in concealment.
In the present invention, the water-based ink refers to an ink using water as a main solvent (an amount of solvent exceeding 50% by mass with respect to the total mass of the solvent).

<Step 1>
In step 1, the white pigment and the polyester resin are melt-kneaded at a mass ratio (white pigment / polyester resin) of 10/90 to 55/45 to obtain a kneaded product.
Prior to obtaining an aqueous dispersion of polyester resin particles containing a white pigment, the white pigment and the polyester resin are melted and kneaded in advance to reduce the particle size by shearing the white pigment and easily disperse in the polyester resin. Become.

  The mass ratio of white pigment to polyester resin (white pigment / polyester resin) improves the dispersion stability of the white pigment-containing resin particles in the aqueous dispersion, and improves the adhesion and concealment to the resin recording medium. In view of the above, it is 10/90 or more, preferably 15/85 or more, more preferably 20/80 or more, still more preferably 30/70 or more, and 55/45 or less, preferably 52/48. Below, more preferably 50/50 or less.

[White pigment]
In the present invention, a white pigment is used as the colorant.
The white pigment may be either an inorganic white pigment or an organic white pigment.
Examples of inorganic white pigments include inorganic oxides, barium sulfate, and calcium carbonate. Examples of the inorganic oxide include titanium oxide, zinc oxide, magnesium oxide, silica, and alumina. Among these, from the viewpoint of high whiteness and improving concealability, inorganic oxides are preferable, and titanium oxide is more preferable.
Among the titanium oxides, rutile type titanium oxide is preferable. Further, as the titanium oxide, those subjected to surface treatment such as silica treatment, alumina treatment, zirconia treatment, and silane coupling agent treatment may be used. As commercially available products of titanium oxide, “JR-800”, “JR-805”, “JR-806”, “JR-301”, “JR-403”, “JR-6035”, “ "JR-701", Ishihara Sangyo Co., Ltd.'s Taipei series "CR-50", "CR-50-2", "CR-57", "CR-58", "CR-80", "CR-" 90 ”,“ R-780 ”,“ R-830 ”,“ R-630 ”and the like.
Specific examples of the organic white pigment include hollow resin particles.

Among these white pigments, at least one surface treatment selected from silica treatment, alumina treatment, and silane coupling agent treatment is performed from the viewpoint of obtaining excellent adhesion and concealment to a resin recording medium. Is preferred, and titanium oxide treated with an alumina treatment and a silane coupling agent is more preferred.
Said white pigment can be used individually or in mixture of 2 or more types in arbitrary ratios.

[Polyester resin]
The polyester resin is a polycondensate obtained by polycondensation of at least an alcohol component and a carboxylic acid component.

[Alcohol component]
The alcohol component, which is a raw material monomer of the polyester resin, preferably contains an aromatic diol from the viewpoint of improving adhesion to a resin recording medium.
The aromatic diol is preferably an alkylene oxide adduct of bisphenol A.
In the present invention, the alkylene oxide adduct of bisphenol A means the entire structure in which an oxyalkylene group is added to 2,2-bis (4-hydroxyphenyl) propane.
Specifically, the alkylene oxide adduct of bisphenol A is preferably a compound represented by the following general formula (I).

In the general formula (I), OR ¹ and R ² O are both oxyalkylene groups, preferably each independently an oxyalkylene group having 1 to 4 carbon atoms, more preferably an oxyethylene group. Or it is an oxypropylene group.
x and y correspond to the number of added moles of alkylene oxide. Furthermore, from the viewpoint of reactivity with the carboxylic acid component, the average value of the sum of x and y is preferably 2 or more. Further, from the same viewpoint, the average value of the sum of x and y is preferably 7 or less, more preferably 5 or less, and still more preferably 3 or less.
Further, x OR ¹ and y R ² O may be the same or different from each other, but are preferably the same from the viewpoint of improving the adhesion to the resin recording medium. The alkylene oxide adduct of bisphenol A may be used alone or in combination of two or more. The alkylene oxide adduct of bisphenol A is preferably a propylene oxide adduct of bisphenol A or an ethylene oxide adduct of bisphenol A, and more preferably a propylene oxide adduct of bisphenol A.
The content of the alkylene oxide adduct of bisphenol A in the alcohol component that is the raw material monomer of the polyester resin is preferably 50 mol% or more, more preferably 80 mol%, from the viewpoint of improving the adhesion to the resin recording medium. As mentioned above, More preferably, it is 90 mol% or more, and 100 mol% or less is preferable.

In addition to the alkylene oxide adduct of bisphenol A, the alcohol component that is a raw material monomer of the polyester resin may contain the following alcohol components.
Specifically, as the alcohol component of the raw material monomer of the polyester resin, for example, ethylene glycol, propylene glycol (1,2-propanediol), glycerin, pentaerythritol, trimethylolpropane, hydrogenated bisphenol A, sorbitol, or these Alkylene (2 to 4 carbon atoms) oxide adduct (average number of added moles of 1 to 16). You may use the said alcohol component individually or in combination of 2 or more types.

[Carboxylic acid component]
In the production of the polyester resin, a carboxylic acid component is used as a raw material monomer in addition to the alcohol component.
The carboxylic acid component includes carboxylic acids, anhydrides of those acids, and alkyl (1 to 3 carbon atoms) esters thereof.
As the carboxylic acid component that is a raw material monomer of the polyester resin, aromatic dicarboxylic acid, aliphatic dicarboxylic acid, alicyclic dicarboxylic acid, and trivalent or higher polyvalent carboxylic acid are preferable, and adhesion to a recording medium made of resin and concealment From the viewpoint of improving the properties and the reactivity with the alcohol component, aromatic dicarboxylic acids and aliphatic dicarboxylic acids are more preferable, and aliphatic dicarboxylic acids are more preferable.
As the aromatic dicarboxylic acid, phthalic acid, isophthalic acid, and terephthalic acid are preferable, and terephthalic acid is more preferable.
Examples of the aliphatic dicarboxylic acid include unsaturated aliphatic dicarboxylic acid and saturated aliphatic dicarboxylic acid, from the viewpoint of improving the adhesion and concealment to the resin recording medium, and from the viewpoint of reactivity with the alcohol component, Unsaturated aliphatic dicarboxylic acids are preferred.
As the unsaturated aliphatic dicarboxylic acid, fumaric acid and maleic acid are preferable from the same viewpoint, and fumaric acid is more preferable.
As the saturated aliphatic dicarboxylic acid, adipic acid and succinic acid (succinic acid may be substituted with an alkyl group and / or an alkenyl group) are preferable.
As the alicyclic dicarboxylic acid, cyclohexane dicarboxylic acid, decalin dicarboxylic acid, and tetrahydrophthalic acid are preferable.
Trimellitic acid and pyromellitic acid are preferable as the trivalent or higher polyvalent carboxylic acid.
The said carboxylic acid component may be individual or 2 or more types may be contained.

(Production method of polyester resin)
The polyester resin is obtained by polycondensation of an alcohol component and a carboxylic acid component. The polyester resin is preferably obtained by polycondensation of an alcohol component and a carboxylic acid component containing an aliphatic dicarboxylic acid. Suitable structures and suitable contents of the alcohol component and the carboxylic acid component are as described above.

  The equivalent ratio (COOH group / OH group) of the carboxyl group (COOH group) of the carboxylic acid component to the hydroxy group (OH group) of the alcohol component in the polyester resin improves the adhesion and concealment to the resin-made recording medium. From the viewpoint, it is preferably 0.65 or more, more preferably 0.80 or more, and preferably 1.2 or less, more preferably 1.1 or less.

The polyester resin is produced, for example, by polycondensing the alcohol component and the carboxylic acid component at a temperature of 150 ° C. or higher and 250 ° C. or lower using an esterification catalyst as necessary in an inert gas atmosphere. Can do.
Examples of the esterification catalyst include metal compounds such as a tin catalyst, a titanium catalyst, antimony trioxide, zinc acetate, and germanium dioxide. From the viewpoint of the reaction efficiency of the esterification reaction in the synthesis of the polyester, a tin catalyst is preferable. As the tin catalyst, dibutyltin oxide, di (2-ethylhexanoic acid) tin (II), salts thereof and the like are preferably used, and di (2-ethylhexanoic acid) tin (II) is more preferably used. If necessary, an esterification cocatalyst such as gallic acid may be further used. The amount of the esterification catalyst used is preferably 0.01 parts by mass or more, more preferably 0.1 parts by mass or more, and preferably 1 part per 100 parts by mass of the total amount of the alcohol component and the carboxylic acid component. It is not more than part by mass, more preferably not more than 0.8 part by mass.
Moreover, you may use together radical polymerization inhibitors, such as tert- butyl catechol and hydroquinone. The amount of the radical polymerization inhibitor used is preferably 0.001 parts by mass or more, more preferably 0.005 parts by mass or more, and preferably 100 parts by mass or more with respect to the total amount of the alcohol component and the carboxylic acid component. 0.5 parts by mass or less, more preferably 0.1 parts by mass or less.

(Physical properties of polyester resin)
From the viewpoint of improving the adhesion to the recording medium made of resin and the concealing property, the softening point of the polyester resin is preferably 85 ° C. or higher, more preferably 90 ° C. or higher, further preferably 95 ° C. or higher, and preferably It is 120 degrees C or less, More preferably, it is 115 degrees C or less, More preferably, it is 110 degrees C or less, More preferably, it is 105 degrees C or less.
From the viewpoint of improving adhesion to the recording medium made of resin and concealing property, the glass transition temperature (Tg) of the polyester resin is preferably 50 ° C. or higher, more preferably 55 ° C. or higher, and preferably 75 ° C. or lower. More preferably, it is 70 degrees C or less, More preferably, it is 65 degrees C or less, More preferably, it is 60 degrees C or less.

From the viewpoint of improving the adhesion to the recording medium made of resin and the concealing property, and from the viewpoint of improving the dispersion stability of the polyester resin particles, the acid value of the polyester resin is preferably 15 mgKOH / g or more, more preferably 17 mgKOH / g. More preferably, it is 20 mgKOH / g or more, preferably 30 mgKOH / g or less, more preferably 25 mgKOH / g or less, and further preferably 23 mgKOH / g or less.
Obtain the desired softening point, glass transition temperature, and acid value of the polyester resin by appropriately adjusting the type of monomer used in the production of the polyester resin, the blending ratio, the polycondensation temperature, and the reaction time. Can do.

  In the present invention, the polyester includes not only unmodified polyester but also polyester modified to such an extent that the properties are not substantially impaired. Examples of the modified polyester include, for example, a polyester having a segment made of an addition polymerization resin, JP-A-11-133668, JP-A-10-239903, by the method described in JP-A-2015-124353. Examples thereof include polyesters grafted or blocked with phenol, urethane, epoxy or the like by the method described in JP-A-8-20636 and composite resins having two or more resin units including polyester units.

  As resin which comprises the polyester resin particle containing a white pigment, in the range which does not impair the effect of this invention, a styrene-acryl copolymer, a polycarbonate, a polyurethane etc. can be used other than polyester, for example. The content of the polyester in the resin constituting the polyester resin particles containing the white pigment is preferably 90% by mass or more, more preferably in the resin from the viewpoint of improving the adhesion to the resin recording medium and the concealing property. It is 95 mass% or more, More preferably, it is 98 mass% or more, More preferably, it is 100 mass%.

(Production of kneaded product)
In step 1, a white pigment and a polyester resin are melt-kneaded to obtain a kneaded product.
The kneaded material contains components other than the white pigment and the polyester resin, for example, various additives such as a penetrant, a dispersant, a surfactant, a viscosity modifier, an antifoaming agent, an antiseptic, an antifungal agent, and a rust inhibitor. The total content of the white pigment and the polyester resin in the kneaded material is preferably 80% by mass or more, more preferably 90%, from the viewpoint of improving the adhesion to the recording medium made of resin and the concealing property. It is at least mass%, and preferably at most 100 mass%. The total content of the white pigment and the polyester resin in the kneaded product is more preferably 100% by mass.

Step 1 preferably includes a mixing step of mixing the white pigment and the polyester resin in advance before the white pigment and the polyester resin are melt-kneaded.
Dispersibility of the white pigment in the polyester resin can be enhanced by mechanically mixing the white pigment and the polyester resin in advance before the melt-kneading. The mechanical mixing of the white pigment and the polyester resin can be performed under known conditions using a mixer such as a Henschel mixer or a ball mill, and the method is not particularly limited. For example, when a Henschel mixer is used as the mixer, a method of stirring the white pigment and the polyester resin at a stirring speed of 1000 rpm to 2000 rpm can be mentioned.
In the mixing step, components other than the white pigment and the polyester resin, for example, various additives such as a penetrant, a dispersant, a surfactant, a viscosity modifier, an antifoaming agent, an antiseptic, an antifungal agent, and a rust inhibitor are further added. You may mix.

[Melting and kneading]
The melt kneading is performed using, for example, a kneader. Alternatively, an aqueous paste of a colorant containing a white pigment and a resin may be kneaded and the water removed by flashing, that is, a so-called flushing method, and the white pigment and resin may be melt-kneaded to obtain a kneaded product.
Preferably, after completion of the mixing step, a mixture of a white pigment and a polyester resin is supplied to a kneader and melt kneaded.
As a kneader for performing melt kneading, a known kneader such as a single or biaxial extruder, a batch kneader by a roll mill, an open roll kneader, a closed kneader, etc. can be used, preferably They are a twin screw extruder, a roll mill type batch type extruder, and an open roll type kneader. For example, KTK type twin screw extruder manufactured by Kobe Steel Co., Ltd., TEM type extruder manufactured by Toshiba Machine Co., Ltd., twin screw extruder manufactured by K.K.C.K. An extruder, an open roll type continuous kneader or the like is preferably used.
The melt kneader is more preferably a twin screw extruder from the viewpoint of reducing the temperature during melt kneading and efficiently dispersing the white pigment in the resin.

  A twin-screw extruder generally has a closed structure in which a barrel covers two screws. A twin-screw extruder can usually be equipped with a heater in any or all of the parts corresponding to the supply part, compression part, and metering part of the screw, and the part corresponding to the supply part, compression part, and metering part. The barrel temperature (temperature of the inner wall surface of the twin screw extruder) can be adjusted. The melt kneading temperature can be adjusted by adjusting the barrel temperature.

The conditions for melt kneading are not particularly limited, but from the viewpoint of efficiently dispersing the white pigment in the resin, the kneading temperature is preferably 70 ° C. or higher, more preferably 80 ° C. or higher, and preferably 140 ° C. or lower. More preferably, it is 120 degrees C or less. When a twin screw extruder is used, the kneading temperature is a barrel temperature.
When a twin screw extruder is used, the peripheral speed of the shaft rotation is preferably 0.1 m / sec or more, more preferably 1 m / sec or less, from the viewpoint of efficiently dispersing the white pigment in the resin.
The feed rate of the mixture to the twin-screw extruder is appropriately adjusted according to the allowable capacity of the kneader used, the barrel temperature and the peripheral speed of the shaft rotation.

The kneaded product is preferably pulverized after being cooled to such an extent that it can be pulverized. The kneaded product is cooled, for example, by extruding the melt-kneaded kneaded product to a cooling belt, a cooling roller, or the like.
For pulverization, the kneaded product is roughly pulverized to about 1 to 5 mm using a pulverizer. As a pulverizer suitably used for coarse pulverization, a hammer mill, an atomizer, a rotoplex, and the like can be given. The pulverization may be further pulverized to reduce the particle size, or may be classified as necessary.

<Process 2>
In step 2, the kneaded product obtained in step 1 is mixed with an organic solvent and a basic compound to obtain an organic solvent-based slurry of the kneaded product.
By mixing the kneaded material with an organic solvent and a basic compound to form an organic solvent-based slurry, the white pigment that has been reduced in particle size by melt-kneading and dispersed in the polyester resin is further uniformly dispersed and obtained later. The content state of the white pigment in the polyester resin particles containing the white pigment can be made uniform among the particles. Here, the organic solvent-based slurry refers to a slurry in which the main component of the dispersion medium (a component whose content in all the solvents is more than 50% by mass) is an organic solvent. Therefore, the organic solvent-based slurry may contain, for example, water in a smaller amount than the organic solvent.
The organic solvent used in step 2 is preferably water-soluble, for example, an alcohol-based organic solvent such as methanol, ethanol, isopropanol, or butanol, a ketone-based organic solvent such as acetone or methyl ethyl ketone, or an ether-based organic solvent such as tetrahydrofuran. Can be mentioned. Among them, preferred is a ketone organic solvent, and more preferred is methyl ethyl ketone from the viewpoint of efficiently dispersing a white pigment in a resin.
Examples of the basic compound include monovalent alkali metal hydroxides such as potassium hydroxide and sodium hydroxide, ammonia, various amines, and preferably sodium hydroxide, potassium hydroxide, and ammonia.
The basic compound is preferably used as an aqueous solution. The concentration of the basic compound in the basic compound aqueous solution is preferably 1% by mass or more, more preferably 3% by mass or more, and preferably 20% by mass or less, more preferably 10% by mass or less, and still more preferably 7%. It is below mass%.

  In step 2, the kneaded product may be mixed with various additives in addition to the organic solvent and the basic compound. From the viewpoint of efficiently dispersing the white pigment in the resin, the kneaded product, the organic solvent, and the base are mixed. It is preferable not to use a surfactant, a dispersant, and an antifoaming agent for mixing with the active compound. Specifically, when any one or more of a surfactant, a dispersant, and an antifoaming agent is used in Step 2, the total amount of these is preferably 1 with respect to 100 parts by mass of the kneaded product. It is 0.5 parts by mass or less, more preferably 0.5 parts by mass or less.

In step 2, the mixing ratio of the kneaded product and the organic solvent (kneaded product / organic solvent) is preferably 100/200 or more, more preferably 100/170 or more, and still more preferably 100/150 or more, based on mass. And, Preferably it is 100/30 or less, More preferably, it is 100/50 or less.
In Step 2, the mixing ratio of the kneaded product and the basic compound (kneaded product / basic compound) is preferably 100/5 or more, more preferably 100/3 or more, and preferably on a mass basis. Is 100 / 0.5 or less, more preferably 100/1 or less.

The mixing method of the kneaded material, the organic solvent and the basic compound is not particularly limited, but after mixing the polyester resin in the kneaded material in the organic solvent, further adding the basic compound aqueous solution and stirring and mixing. It is preferable. From the viewpoint of efficiently and highly dispersing the white pigment in the polyester resin, the mixing time of the kneaded product, the organic solvent and the basic compound is preferably 0.2 hours or more, more preferably 0.4 hours or more, and still more preferably. 0.5 hours or more, and preferably 8 hours or less, more preferably 6 hours or less, and further preferably 5 hours or less.
Further, the mixing time after the addition of the basic compound is preferably 0.2 hours or more, more preferably 0.3 hours or more, still more preferably 0.4 hours or more, and preferably 4 hours or less, more Preferably it is 2 hours or less, More preferably, it is 1 hour or less.

  The mixing temperature of the kneaded product and the organic solvent, and the mixing temperature after addition of the basic compound are preferably 20 ° C. or higher, more preferably 25 ° C. or higher, more preferably 27 ° C. or higher, from the viewpoint of mixing the components uniformly. And preferably 40 ° C. or lower, more preferably 35 ° C. or lower, still more preferably 33 ° C. or lower.

<Step 3>
In step 3, water is added to the organic solvent slurry obtained in step 2 and mixed to obtain a dispersion.
From the viewpoint of improving the dispersion stability of the white pigment-containing resin particles in the aqueous dispersion, and from the viewpoint of improving the adhesion to the recording medium made of the resin and the concealing property, the addition rate of water to the organic solvent-based slurry is polyester resin 100. It is preferably 1 part by mass / min or more, more preferably 2 parts by mass / min or more, still more preferably 3 parts by mass / min or more, still more preferably 5 parts by mass / min or more with respect to parts by mass, and Preferably it is 20 mass parts / min or less, More preferably, it is 18 mass parts / min or less, More preferably, it is 15 mass parts / min or less, More preferably, it is 13 mass parts / min or less, More preferably, it is 10 mass parts / min or less. It is. The addition rate of water to the organic solvent-based slurry is 1 part by mass / min or more with respect to 100 parts by mass of the polyester resin, so that the productivity of the polyester resin particles containing the white pigment becomes higher, and 20 parts by mass / By being below min, white pigment-containing resin particles having excellent dispersion stability in water can be obtained more easily even after the organic solvent is removed in the subsequent step 4.
The amount of water added is preferably 100 parts by mass or more, more preferably 150 parts by mass or more, with respect to 100 parts by mass of the kneaded material, from the viewpoint of improving the dispersion stability of the white pigment-containing resin particles in the aqueous dispersion. More preferably, it is 200 mass parts or more, Preferably it is 1000 mass parts or less, More preferably, it is 500 mass parts or less, More preferably, it is 250 mass parts or less.

It is preferable to add water to the organic solvent-based slurry while stirring the organic solvent-based slurry. The stirring speed (peripheral speed at the blade tip) is preferably 0.8 m / sec or more, more preferably 1.0 m / sec or more, and even more preferably 1.2 m / sec or more, from the viewpoint of uniformly mixing the components. And, it is preferably 2.0 m / sec or less, more preferably 1.7 m / sec or less, still more preferably 1.5 m / sec or less.
The temperature at the time of addition of water to the organic solvent-based slurry is preferably 20 ° C. or higher, more preferably 25 ° C. or higher, further preferably 27 ° C. or higher, and preferably 40 ° C. from the viewpoint of mixing the components uniformly. It is below, More preferably, it is 35 degrees C or less, More preferably, it is 33 degrees C or less.

<Step 4>
In step 4, the organic solvent is removed from the dispersion obtained in step 3 to obtain an aqueous dispersion of polyester resin particles containing a white pigment.
The volume-median particle size of the polyester resin particles (white pigment-containing resin particles) containing the white pigment obtained in Step 4 is a viewpoint of improving the dispersion stability of the white pigment-containing resin particles in the aqueous dispersion, and is recorded from the resin. From the viewpoint of improving the adhesion to the medium and the concealing property, it is preferably 200 nm or more, more preferably 250 nm or more, further preferably 300 nm or more, still more preferably 350 nm or more, still more preferably 380 nm or more, and preferably Is 570 nm or less, more preferably 550 nm or less, still more preferably 500 nm or less.
Here, the “volume median particle size” means a particle size at which the cumulative volume frequency measured by the volume fraction becomes 50% cumulative from the smaller particle size. The measuring method is as described in the examples.

The method for removing the organic solvent from the dispersion is not particularly limited, but is preferably performed by at least one of heating the dispersion and reducing the pressure, and more preferably heating the dispersion and then distilling off the organic solvent. . The pressure reduction is preferably performed stepwise.
The heating temperature of the dispersion is preferably 35 ° C. or higher, more preferably 45 ° C. or higher, still more preferably 55 ° C. or higher, and preferably 85 ° C. or lower, more preferably 75 ° C. or lower, still more preferably 65 ° C. or lower. It is.

(Aqueous dispersion)
In the aqueous dispersion of polyester resin particles containing a white pigment, the content of the white pigment is preferably 2% by mass or more, more preferably 5% by mass or more, still more preferably 10% by mass or more, and preferably It is 40 mass% or less, More preferably, it is 20 mass% or less.
In the aqueous dispersion of polyester resin particles containing a white pigment, the content of the polyester resin is preferably 2% by mass or more, more preferably 5% by mass or more, still more preferably 10% by mass or more, and preferably It is 40 mass% or less, More preferably, it is 20 mass% or less.

In the aqueous dispersion of polyester resin particles containing a white pigment, the water content is preferably 20% by mass or more, more preferably 40% by mass or more, and preferably 96% by mass or less, more preferably 90%. It is not more than mass%, more preferably not more than 80 mass%.
The mass ratio [white pigment / polyester resin] between the white pigment and the polyester resin is as described above.
The organic solvent in the aqueous dispersion is preferably substantially removed, but may remain as long as the object of the present invention is not impaired. The amount of the residual organic solvent is preferably 0.1% by mass or less, more preferably 0.01% by mass or less.

≪Water-based ink≫
The obtained aqueous dispersion of polyester resin particles containing a white pigment can be used as it is as an aqueous ink. The aqueous dispersion of the present invention in which the white pigment is encapsulated in the polyester resin is obtained by the method for producing the aqueous ink of the present invention described above. As the constituent components such as the white pigment and the polyester resin that can be used in the aqueous dispersion and the aqueous ink of the present invention, the components mentioned in the method for producing the aqueous ink of the present invention can be used, and preferred embodiments are also the same. Moreover, it is preferable that the form of the polyester resin particle (white pigment containing resin particle) containing a white pigment is also the form demonstrated with the manufacturing method of the water-based ink of this invention.
The water-based ink is preferably used by mixing with various additives as optional components as required.
Various additives that are optional components include organic solvents, penetrants, dispersants, surfactants, viscosity modifiers, antifoaming agents, antiseptics, antifungal agents, rust preventives, pH adjusters, antioxidants, An ultraviolet absorber etc. are mentioned.

Examples of the organic solvent include polyhydric alcohol, polyhydric alcohol alkyl ether, polyhydric alcohol aryl ether, cyclic carbonate, nitrogen-containing heterocyclic compound, amide, amine, and sulfur-containing compound.
Examples of the polyhydric alcohol include ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, polypropylene glycol, 1,3-propanediol, 1,2-butanediol, 1,3- Butanediol, 2,3-butanediol, 1,4-butanediol, 3-methyl-1,3-butanediol, 1,5-pentanediol, 1,2-hexanediol, 1,6-hexanediol, 2 -Methyl-2,4-pentanediol, tetraethylene glycol, glycerin, 1,2,6-hexanetriol, 1,2,4-butanetriol, 1,2,3-butanetriol, 3-methyl-1,3 , 5-Pentanetriol, 2-D Le-1,3-hexanediol, 2,2,4-trimethyl-1,3-pentanediol.

Examples of the polyhydric alcohol alkyl ether include ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, triethylene glycol monomethyl ether, triethylene glycol monoisobutyl ether, tetraethylene glycol monomethyl ether. , Propylene glycol monoethyl ether, dipropylene glycol monobutyl ether, dipropylene glycol monomethyl ether, tripropylene glycol monomethyl ether, tripropylene glycol monobutyl ether, and the like.
Examples of the polyhydric alcohol aryl ether include ethylene glycol monophenyl ether and ethylene glycol monobenzyl ether.
Examples of the cyclic carbonate include ethylene carbonate and propylene carbonate.

Examples of the nitrogen-containing heterocyclic compound include N-methyl-2-pyrrolidone, N-hydroxyethyl-2-pyrrolidone, 2-pyrrolidone, 1,3-dimethylimidazolidinone, and ε-caprolactam.
Examples of the amide include formamide, N-methylformamide, N, N-dimethylformamide and the like.
Examples of the amine include monoethanolamine, diethanolamine, triethanolamine, monoethylamine, diethylamine, triethylamine and the like.
Examples of the sulfur-containing compound include dimethyl sulfoxide, sulfolane, thiodiethanol, thiodiglycol and the like.
Although an organic solvent may be used individually or in combination of 2 or more types, it is preferable to use 2 or more types in combination.

  Among these, at least one or more selected from polyhydric alcohols, polyhydric alcohol alkyl ethers, and nitrogen-containing heterocyclic compounds are preferable, and diethylene glycol, propylene glycol, dipropylene glycol, 1,2-butanediol, , 2-hexanediol, glycerin, diethylene glycol monomethyl ether, dipropylene glycol monomethyl ether, and 2-pyrrolidone are more preferable.

  From the viewpoint of improving the dispersion stability of the ink, the content of the organic solvent is preferably 5% by mass or more, more preferably 10% by mass or more, and preferably 40% by mass or less, more preferably in the ink. Is 35% by mass or less.

Examples of the surfactant include nonionic surfactants, anionic surfactants, amphoteric surfactants, silicone surfactants, and fluorine surfactants.
Examples of the nonionic surfactant include acetylene glycol; glycol ether such as polyoxyethylene alkyl ether; polyoxyethylene alkyl phenyl ether, polyoxyethylene alkyl ester, polyoxyethylene sorbitan fatty acid ester, and the like.

Examples of the anionic surfactant include polyoxyethylene alkyl ether acetate, dodecyl benzene sulfonate, oxalate sulfonate, laurate, polyoxyethylene alkyl ether sulfate salt, and the like.
Examples of amphoteric surfactants include lauryl aminopropionate, lauryl dimethyl betaine, stearyl dimethyl betaine, lauryl dihydroxyethyl betaine, lauryl dimethylamine oxide, myristyl dimethylamine oxide, stearyl dimethylamine oxide, dihydroxyethyl lauryl amine oxide, and the like. Is mentioned.

Examples of the silicone surfactant include polyester-modified silicone and polyether-modified silicone.
Examples of the fluorosurfactant include perfluoroalkyl sulfonic acid compounds, perfluoroalkyl carboxylic acid compounds, perfluoroalkyl phosphate compounds, and perfluoroalkyl ethylene oxide adducts.
Surfactants may be used alone or in combination of two or more.

  Among these, at least one selected from nonionic surfactants and silicone surfactants is preferable, and at least one selected from acetylene glycol, glycol ether, polyester-modified silicone, and polyether-modified silicone is more preferable, and acetylene. Glycol and glycol ether are more preferable, and at least one selected from acetylene glycol and polyoxyethylene alkyl ether is still more preferable.

  The content of the surfactant is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, and preferably 5% by mass in the ink from the viewpoint of improving the dispersion stability of the ink. % Or less, more preferably 2% by mass or less.

There is no restriction | limiting in particular as an antifoamer, According to the objective, it can select suitably, For example, a silicone type antifoamer, a polyether type antifoamer, a fatty-acid-ester type antifoamer, etc. are mentioned.
Examples of the antiseptic and antifungal agent include 1,2-benzisothiazolin-3-one, sodium dehydroacetate, sodium sorbate, sodium 2-pyridinethiol-1-oxide, sodium benzoate, sodium pentachlorophenol, etc. Is mentioned.

Examples of the rust inhibitor include acidic sulfite, sodium thiosulfate, ammonium thiodiglycolate, diisopropylammonium nitrite, pentaerythritol tetranitrate, and the like.
The pH adjuster is not particularly limited as long as the pH can be adjusted to 7 or more without adversely affecting the ink to be prepared, and any substance can be used according to the purpose. For example, diethanolamine, Amines such as triethanolamine; hydroxides of alkali metals such as lithium hydroxide, sodium hydroxide, potassium hydroxide; carbonates of alkali metals such as lithium carbonate, sodium carbonate, potassium carbonate; ammonium hydroxide, quaternary An ammonium hydroxide etc. are mentioned.

Examples of the antioxidant include phenolic antioxidants (including hindered phenolic antioxidants), amine antioxidants, sulfurous antioxidants, phosphorus antioxidants, and the like.
Examples of the UV absorber include benzophenone UV absorbers, benzotriazole UV absorbers, salicylate UV absorbers, and the like.

Next, the suitable example in the case of mixing with an arbitrary component is demonstrated.
First, water such as ion-exchanged water and deionized water is mixed with at least one of an optional organic solvent and various additives as necessary, and stirred as necessary to obtain a mixed solution.
Next, this mixed liquid is mixed with an aqueous dispersion of polyester resin particles containing a white pigment, and filtered with a filter or the like as necessary, whereby an aqueous ink can be suitably obtained.

The content of the polyester resin particles containing the white pigment contained in the water-based ink is preferably 2% by mass or more, more preferably in the water-based ink from the viewpoint of improving the adhesion to the resin recording medium and the concealing property. It is 5% by mass or more, more preferably 8% by mass or more, and preferably 25% by mass or less, more preferably 20% by mass or less.
The content of water contained in the water-based ink is not particularly limited and can be arbitrarily set depending on the use mode of the water-based ink. However, when the water-based ink of the present invention is used for inkjet recording, the water-based ink has good dischargeability. Therefore, in the water-based ink, it is preferably 20% by mass or more, more preferably 30% by mass or more, further preferably 40% by mass or more, and preferably 95% by mass or less, more preferably 90% by mass or less. More preferably, it is 80 mass% or less.

≪Usage≫
The aqueous ink of the present invention can be used as an ink for ink jet recording. As a preferred embodiment when the aqueous ink of the present invention is used in an ink jet recording method, the aqueous recording ink of the present invention is attached to a resin recording medium by an ink jet recording method, and then the resin recording medium to which the aqueous ink adheres is used. Heat to 40 ° C or higher and 100 ° C or lower.
The water-based ink of the present invention can be used for both office printing and commercial and industrial printing of catalogs, flyers, packages, labels and the like. Suitable for use in resin recording media such as polyethylene terephthalate (PET), polyvinyl chloride (PVC), polyethylene (PE), polypropylene (PP), and nylon (NY), which are suitable for commercial and industrial label printing. It is suitable for commercial and industrial printing.

Examples of the resin recording medium include polyethylene terephthalate, polyvinyl chloride, polyethylene, polypropylene, and nylon.
Among these, it can use suitably for the method of attaching the aqueous ink of this invention with respect to the recording medium made from a polyethylene terephthalate, and forming an image.
The recording medium is preferably a resin film. Examples of the film include a polyester film, a polyvinyl chloride film, a polypropylene film, a polyethylene film, and a nylon film. Among these, a polyester film is preferable, and a polyethylene terephthalate film is more preferable.
These films may be subjected to surface treatment such as corona treatment as necessary.

  Hereinafter, the present invention will be described more specifically with reference to examples and the like. In the following examples and the like, each physical property was measured by the following method.

[Acid value of resin]
It measured according to JIS K0070. However, the measurement solvent was a mixed solvent of acetone and toluene [acetone: toluene = 1: 1 (volume ratio)].

[Softening point of resin]
Using a flow tester “CFT-500D” (manufactured by Shimadzu Corporation), a 1 g sample was heated at a heating rate of 6 ° C./min, a load of 1.96 MPa was applied by a plunger, a diameter of 1 mm, and a length of 1 mm. Extruded from the nozzle. The amount of plunger drop of the flow tester was plotted against the temperature, and the temperature at which half of the sample flowed out was taken as the softening point.

[Glass transition temperature of resin]
Using a differential scanning calorimeter “Q-20” (manufactured by TA Instruments Japan Co., Ltd.), 0.01 g of a sample was weighed into an aluminum pan, heated to 200 ° C., and the temperature decreasing rate was 10 ° C./min. At 0 ° C. Next, the sample was heated at a temperature rising rate of 10 ° C./min, and the amount of heat was measured. Among the observed endothermic peaks, the peak temperature with the maximum peak area is taken as the maximum peak temperature of the endotherm, the extension of the baseline below the maximum peak temperature of the endotherm, and the maximum slope from the peak of the peak to the peak apex The temperature at the intersection with the tangent line indicating the glass transition temperature.

[Volume Median Particle Size (D ₅₀ ) of Resin Particles]
(1) Measuring apparatus: Laser diffraction type particle size measuring instrument “LA-920” (manufactured by Horiba, Ltd.)
(2) Measurement conditions: Distilled water was added to the measurement cell, and the volume-median particle size (D ₅₀ ) was measured at a concentration at which the absorbance was in an appropriate range.

[Solid content concentration of resin particles]
Using an infrared moisture meter “FD-230” (manufactured by Kett Science Laboratory Co., Ltd.), 5 g of a measurement sample was dried at 150 ° C. and in measurement mode 96 (monitoring time 2.5 minutes / variation width 0.05%). The moisture (mass%) was measured. The solid content concentration was calculated according to the following formula.
Solid content concentration (% by mass) = 100-water content (% by mass)

[Evaluation of concealment]
Inkjet printer “IPSiO GX 2500” (Ricoh Co., Ltd., Piezo method) is filled with water-based ink, and biaxially stretched PET film “Lumirror 75T60” (Toray Industries, Inc.) “Glossy paper, clean, no color matching” Under the conditions, an A4 solid image was printed.
The printed matter was dried for 10 minutes in a dryer at 80 ° C., and left to stand in an environmental room at room temperature of 25 ° C. and relative humidity of 50% for one day to prepare a sample. Thereafter, “black paper <black paper> A4” (manufactured by Tochiman Co., 116 g paper) was laid under the printed material, and image density measurement was performed from above the printed material.
The spectrophotometer “Spectro Eye” (manufactured by Gretag Macbeth Co.) is used to measure the image density, the measurement condition is the observation light source D65, the observation field of view is 2 degrees, the density reference is DIN 16536, and the numerical value of the black color density component is read. It was. The number of times of measurement was changed, and 5 points were selected at random from the portion printed in the forward path of bidirectional printing, and 5 points were selected from the portion printed on the return path, and an average value of a total of 10 points was obtained. The image density when black paper laid under the printed material is measured is 1.90. The image density measured from above the printed material is concealed by the white printed material, and the lower the image density, the higher the concealment of the printed material and the better It is.
The concealment rate was obtained from the obtained image density by the following formula, and the concealability of the white ink was evaluated.
Concealment rate [%] = 100 − ((image density of printed material measured with black paper laid down) / (image density of black paper)) × 100

[Evaluation of adhesion]
Inkjet printer “IPSiO GX 2500” (Ricoh Co., Ltd., Piezo method) is filled with water-based ink, and biaxially stretched PET film “Lumirror 75T60” (Toray Industries, Inc.) “Glossy paper, clean, no color matching” Under the conditions, an A4 solid image was printed. The printed matter was dried for 10 minutes with a dryer at 80 ° C., and allowed to stand for 1 day in an environmental room at a room temperature of 25 ° C. and a relative humidity of 50% to prepare a sample. After that, a 4 cm long tape “Cello Tape CT15” (registered trademark) (manufactured by Nichiban Co., Ltd.) was applied to the printing surface of the sample, and the tape was peeled off at an angle of 90 ° at a speed of 10 cm / sec. The remaining area was visually evaluated in the following three stages.
<Evaluation criteria>
A: No peeling or peeling, but peeling area less than 10% B: peeling area 10% or more and less than 50% C: peeling area 50% or more

Production Example X1
(Production of polyester resin A)
The inside of the four-necked flask equipped with a nitrogen introduction tube, a dehydration tube, a stirrer, and a thermocouple was replaced with nitrogen, and 3004 g of polyoxypropylene (2.2) -2,2-bis (4-hydroxyphenyl) propane, 996 g of fumaric acid, 2 g of tert-butylcatechol and 8 g of dibutyltin oxide were added, heated to 210 ° C. over 5 hours with stirring in a nitrogen atmosphere, held at 210 ° C. for 2 hours, and then at 8.3 kPa. Then, the reaction was performed until the softening point reached 100 ° C. to obtain a polyester resin A. The characteristics of the polyester resin A are shown in Table 1.

Production Example X2
(Production of polyester resin B)
The inside of a four-necked flask equipped with a nitrogen introduction tube, a dehydration tube, a stirrer, and a thermocouple was replaced with nitrogen, and 3374 g of polyoxypropylene (2.2) -2,2-bis (4-hydroxyphenyl) propane, Put 33 g of polyoxyethylene (2.0) -2,2-bis (4-hydroxyphenyl) propane, 672 g of terephthalic acid, and 10 g of dibutyltin oxide, and raise the temperature to 230 ° C. with stirring in a nitrogen atmosphere. After holding for 5 hours, the pressure in the flask was further lowered and held at 8.3 kPa for 1 hour. Then, after cooling to 210 ° C. and returning to atmospheric pressure, 696 g of fumaric acid and 0.49 g of tert-butylcatechol were added and held at 210 ° C. for 5 hours, and then the pressure in the flask was further reduced to 8.3 kPa. For 4 hours to obtain polyester resin B. Table 1 shows the characteristics of the polyester resin B.

Production Example Y1
(Production of kneaded material 1)
Using a 20 L Henschel mixer, 2000 g of polyester resin A and 2000 g of white pigment “Typaque CR-50-2” (Ishihara Sangyo Co., Ltd., titanium oxide treated with alumina treatment and silane coupling agent) were rotated at 1500 rpm (circumference). After mixing for 3 minutes at a stirring speed of 21 m / sec), the barrel temperature was 100 ° C. and the shaft speed was 200 rpm (shaft peripheral speed 0.30 m / sec) using a twin screw extruder “PCM-30” (manufactured by Ikegai Co., Ltd.). ), And melt-kneaded at a mixture supply rate of 10 kg / hr. The obtained kneaded product was cooled with a cooling belt and then coarsely crushed with a Rotoplex (manufactured by Toa Machine Industry Co., Ltd.) to obtain a kneaded product of white pigment and resin (kneaded product 1).

Production Example Y2
(Production of kneaded material 2)
In Production Example Y1, white pigment “Typek CR-50-2” (Ishihara Sangyo Co., Ltd., titanium oxide treated with alumina treatment and silane coupling agent) was replaced with white pigment “Typek CR-80” (Ishihara Sangyo Co., Ltd.). A white pigment-resin kneaded product (kneaded product 2) was obtained in the same manner except that the titanium oxide was treated with silica and alumina.

Production Example Y3
(Production of kneaded product 3)
In the same manner as in Production Example Y1, except that 2000 g of the polyester resin A was changed to 2400 g and the white pigment “Taipeku CR-50-2” (manufactured by Ishihara Sangyo Co., Ltd.) 2000 g was changed to 1600 g, respectively. (Kneaded product 3) was obtained.

Production Example Y4
(Production of kneaded material 4)
In the same manner as in Production Example Y1, except that 2000 g of the polyester resin A was changed to 2800 g and the white pigment “Taipeku CR-50-2” (manufactured by Ishihara Sangyo Co., Ltd.) 2000 g was changed to 1200 g, respectively. (Kneaded product 4) was obtained.

Production Example Y5
(Production of kneaded product 5)
A white pigment-resin kneaded product (kneaded product 5) was obtained in the same manner as in Production Example Y1, except that the polyester resin A was changed to the polyester resin B.

Production Example Z1
(Production of dispersion of white pigment-containing polyester resin particles 1)
A four-necked flask equipped with a nitrogen inlet tube, a reflux condenser, a stirrer (“Three-One Motor BL300” (manufactured by Shinto Kagaku Co., Ltd.)) and a thermocouple was charged with 1200 g of the kneaded material, and methyl ethyl ketone (MEK) at 30 ° C. The resin was dissolved by mixing with 200 g for 3 hours. Subsequently, 31.9 g of 5 mass% sodium hydroxide aqueous solution was added, and it stirred for 30 minutes, and obtained the organic-solvent type slurry. Thereafter, 467 g of deionized water was added dropwise at a rate of 7.8 parts by mass / min to 100 parts by mass of the polyester resin with stirring at 30 ° C. and 1.37 m / sec. Then, after heating up at 60 degreeC, methyl ethyl ketone was distilled off, reducing pressure in steps to 80 kPa-30 kPa. After cooling to 25 ° C., the mixture was filtered through a 150-mesh wire mesh, the solid content concentration was adjusted to 30% by mass with deionized water, and an aqueous dispersion containing white pigment-containing polyester resin particles 1 was obtained. Table 3 shows the volume median particle size of the white pigment-containing polyester resin particles 1 in the aqueous dispersion obtained.

Production Examples Z2 to Z5
(Production of aqueous dispersion of white pigment-containing polyester resin particles 2 to 5)
An aqueous dispersion containing white pigment-containing polyester resin particles was prepared in the same manner as in Production Example Z1, except that the type of kneaded product and the amount of 5% by mass aqueous sodium hydroxide added were changed to those shown in Table 3. Obtained. Table 3 shows the volume median particle size (D ₅₀ ) of the white pigment-containing polyester resin particles in the obtained aqueous dispersion.

Production Example Z6
(Production of aqueous dispersion of white pigment-containing polyester resin particles 6)
A four-necked flask equipped with a nitrogen inlet tube, a reflux condenser, a stirrer [“Three-One Motor BL300” (manufactured by Shinto Kagaku Co., Ltd.)] and a thermocouple, 100 g of polyester resin A and a white pigment “TYPECR CR50-2” (100 g of titanium oxide manufactured by Ishihara Sangyo Co., Ltd.) was added and mixed with 200 g of methyl ethyl ketone at 30 ° C. to dissolve the resin. Next, 31.9 g of 5% by weight aqueous sodium hydroxide solution was added and stirred for 30 minutes, and then at a rate of 7.8 parts by weight per 100 parts by weight of the polyester resin with stirring at 30 ° C. and 1.37 m / sec. At 467 g of deionized water was added dropwise. Then, after heating up at 60 degreeC, methyl ethyl ketone was distilled off, reducing pressure in steps to 80 kPa-30 kPa. After cooling to 25 ° C., the mixture was filtered through a 150-mesh wire mesh, the solid content concentration was adjusted to 30% by mass with deionized water, and an aqueous dispersion containing white pigment-containing polyester resin particles 6 was obtained. Table 3 shows the volume-median particle size (D ₅₀ ) of the white pigment-containing polyester resin particles 6 in the obtained aqueous dispersion.

Production Example Z7
(Production of aqueous dispersion of polyester resin particles 7)
In a four-necked flask equipped with a nitrogen inlet tube, a reflux condenser, a stirrer [“Three-One Motor BL300” (manufactured by Shinto Kagaku Co., Ltd.)], and a thermocouple, 200 g of polyester resin A is placed at 30 ° C. with 200 g of methyl ethyl ketone. Mix to dissolve the resin. Subsequently, after adding 63.9 g of 5 mass% sodium hydroxide aqueous solution and stirring for 30 minutes, it is a speed | rate of 7.8 mass parts / min with respect to 100 mass parts of polyester resins under stirring of 30 degreeC and 1.37 m / sec. At 467 g of deionized water was added dropwise. Then, after heating up at 60 degreeC, methyl ethyl ketone was distilled off, reducing pressure in steps to 80 kPa-30 kPa. After cooling to 25 ° C., the mixture was filtered through a 150-mesh wire mesh, the solid content concentration was adjusted to 30% by mass with deionized water, and an aqueous dispersion containing polyester resin particles 7 was obtained. Table 3 shows the volume-median particle size (D ₅₀ ) of the polyester resin particles 7 in the obtained aqueous dispersion.

Examples 1 to 5 and Comparative Example 1
(Manufacture of water-based ink)
In a 100 mL screw tube, 20.0 parts by mass of propylene glycol (manufactured by Wako Pure Chemical Industries, Ltd.), 10.0 parts by mass of 1,2-butanediol (manufactured by Wako Pure Chemical Industries, Ltd.), wetting agent (product name: “ Olfine E1010 "(Orphine is a registered trademark), active ingredient: acetylene glycol surfactant, manufactured by Nissin Chemical Industry Co., Ltd. (1.0 part by mass) and deionized water (26.6 parts by mass) are mixed, and a magnetic stirrer is mixed. And stirred at room temperature (25 ° C.) for 15 minutes to obtain a mixed solution.
Next, 40.0 parts by mass of an aqueous dispersion containing the white pigment-containing polyester resin particles shown in Table 4 (12 parts by mass in terms of the total amount of white pigment and resin (in 100 parts by mass of the aqueous ink)) was dropped with a dropper. The mixture was stirred and mixed with a magnetic stirrer. Finally, the mixture was filtered with a filter having a pore diameter of 1.2 μm (product name: “Minisalto” (registered trademark), manufactured by Sartorius Stedim Biotech) to obtain a water-based ink. Table 4 shows the evaluation results of the obtained water-based ink.

Comparative Example 2
(Manufacture of water-based ink 7)
In a 100 mL screw tube, 20.0 parts by mass of propylene glycol (manufactured by Wako Pure Chemical Industries, Ltd.), 10.0 parts by mass of 1,2-butanediol (manufactured by Wako Pure Chemical Industries, Ltd.), wetting agent (product name: “ Olfine E1010 "(Orphine is a registered trademark), active ingredient: 1.0 part by mass of acetylene glycol surfactant, manufactured by Nissin Chemical Industry Co., Ltd., and 46.6 parts by mass of deionized water are mixed together, and a magnetic stirrer is mixed. And stirred at room temperature (25 ° C.) for 15 minutes to obtain a mixed solution.
Next, while dropping 20.0 parts by mass of the aqueous dispersion containing polyester resin particles 7 obtained in Production Example Z7 (6 parts by mass in terms of resin (in 100 parts by mass of aqueous ink)) with a dropper, the magnetic The mixture was stirred and mixed with a stirrer. Finally, the mixture was filtered with a filter having a pore diameter of 1.2 μm (product name: “Minisalto” (registered trademark), manufactured by Sartorius Stedim Biotech), and water-based ink 7 was obtained. Table 4 shows the evaluation results of the obtained water-based ink.

From the results of Table 4, it can be seen that the water-based inks of Examples 1 to 5 are more excellent in adhesion and concealment to the polyethylene terephthalate film than Comparative Example 1 in which the white pigment and the polyester resin were not previously melt-kneaded. .
Even if the results of Comparative Example 2 and the results of Examples 1 to 5 are compared using the water-based ink of Comparative Example 2 that does not use a white pigment as a reference value, according to the present invention, the result is due to the addition of the white pigment. It can be seen that the decrease in adhesion is suppressed and the adhesion is excellent even when a white pigment is contained.

Claims (8)

A method for producing a water-based ink comprising the following steps 1 to 4.
Step 1: A step of obtaining a kneaded product by melt-kneading a white pigment and a polyester resin at a mass ratio (white pigment / polyester resin) of 10/90 to 55/45 Step 2: A kneaded product obtained in Step 1 is an organic solvent. And a step of obtaining an organic solvent-based slurry of the kneaded product Step 3: Step of adding water to the organic solvent-based slurry obtained in Step 2 and mixing to obtain a dispersion Step 4: Step Removing the organic solvent from the dispersion obtained in 3 to obtain an aqueous dispersion of polyester resin particles containing a white pigment   2. The water-based ink according to claim 1, wherein in Step 3, 100 to 1000 parts by mass of water is added at a rate of 1 to 20 parts by mass / min with respect to 100 parts by mass of the polyester resin. Production method.   3. The method for producing an aqueous ink according to claim 1, wherein in step 2, the mixing ratio of the kneaded product and the organic solvent (kneaded product / organic solvent) is 100/200 or more and 100/30 or less on a mass basis.   The method for producing a water-based ink according to any one of claims 1 to 3, wherein the mixing time of the kneaded material, the organic solvent and the basic compound is 0.2 hours or more and 8 hours or less in Step 2.   The method for producing a water-based ink according to any one of claims 1 to 4, wherein the acid value of the polyester resin is 15 mgKOH / g or more and 30 mgKOH / g or less.   The method for producing an aqueous ink according to any one of claims 1 to 5, wherein the polyester resin is a polycondensate of an alcohol component and a carboxylic acid component containing an aliphatic dicarboxylic acid.   An aqueous dispersion of polyester resin particles containing a white pigment and having a volume median particle size of 200 nm or more and 570 nm or less.   An aqueous ink comprising the aqueous dispersion according to claim 7.