JP5626520B2 - UV curable ink composition for inkjet - Google Patents

Description

  The present invention relates to an ultraviolet curable inkjet ink composition.

  Conventionally, as a method of forming a coating film having a metallic luster on a printed material, gold powder produced from brass, aluminum fine particles, etc., printing ink using silver powder as a pigment, foil press printing using metal foil, metal foil was used. Thermal transfer systems have been used.

  In recent years, there have been many examples of application to ink jet recording methods in printing, and one of them is metallic printing, and development of ink having metallic luster has been promoted. For the ink having metallic luster, a flat pigment (hereinafter also referred to as “flat aluminum pigment”) in which aluminum particles are thinly extended is often used.

  As a method for producing a flat aluminum pigment, for example, (1) a method in which aluminum particles produced by an atomizer method are crushed and extended by a ball mill, and (2) an ultrasonic cleaner in which aluminum deposited on a film is evaporated in a solvent. (For example, refer to Patent Document 1).

  On the other hand, in recent years, development of ultraviolet curable inks that are cured when irradiated with ultraviolet rays has been promoted. According to this ultraviolet curable ink, an image having high water resistance, solvent resistance, scratch resistance and the like can be recorded on the surface of the recording medium in the ink jet recording method. Therefore, if the above-described flat aluminum pigment is applied to an ultraviolet curable ink, it is expected that an excellent metallic gloss image can be recorded on the surface of a recording medium by an ink jet recording method.

JP 2008-202076 A

  However, in order to apply the flat aluminum pigment as described above to the ultraviolet ray curable ink of the ink jet recording system, there are the following problems.

  One of them is that the storage stability of the ultraviolet curable ink is impaired. When a flat aluminum pigment as described above is applied to an ultraviolet curable ink, since the active surface of the flat aluminum pigment is exposed, it reacts with the monomer used for the ultraviolet curable ink on the active surface, so that In some cases, the ultraviolet curable ink gelled.

  The other is that the size of the flat aluminum pigment is limited. In general, in order to obtain a metallic luster, it is considered that a flat aluminum pigment having a larger diameter is better. However, in the ink jet recording method, it is necessary to use a pigment having a diameter smaller than the nozzle diameter of the ink jet recording apparatus. Therefore, it has been difficult to record a metallic gloss image having a good gloss level.

  In some embodiments according to the present invention, by solving the above-mentioned problems, an ultraviolet curable ink-jet ink that can record a metallic gloss image with good glossiness by an ink-jet recording method and has good storage stability. A composition is provided.

  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 ultraviolet curable inkjet ink composition according to the present invention is:
An aluminum pigment (A) provided with a coating having a structure in which tetraethoxysilane is chemically bonded to the surface of aluminum particles;
Phenoxyethyl (meth) acrylate (B);
It is characterized by containing.

  According to the ultraviolet curable inkjet ink composition of Application Example 1, a metallic gloss image having a good glossiness can be recorded by the inkjet recording method, and the storage stability is improved.

[Application Example 2]
In the ultraviolet curable inkjet ink composition of Application Example 1, the phenoxyethyl (meth) acrylate (B) may be contained in an amount of 10% by mass to 70% by mass with respect to the total mass of the ink composition.

[Application Example 3]
The ultraviolet curable inkjet ink composition of Application Example 1 or Application Example 2 can further contain a monomer (C) represented by the following general formula (1).
_{^{CH 2 = CR 1 -COO-R}} 2 -O-CH = CH-R 3 ... (1)
(In Formula (1), R ¹ represents a hydrogen atom or a methyl group. R ² represents a divalent organic residue having 2 to 20 carbon atoms. R ³ represents a hydrogen atom or 1 to 11 carbon atoms. Represents a monovalent organic residue.)

[Application Example 4]
In the ultraviolet curable inkjet ink composition of Application Example 3, the monomer (C) may be 2- (2-vinyloxyethoxy) ethyl (meth) acrylate.

[Application Example 5]
In the ultraviolet curable inkjet ink composition of Application Example 3 or Application Example 4, the monomer (C) may be contained in an amount of 10% by mass to 70% by mass with respect to the total mass of the ink composition.

[Application Example 6]
The ultraviolet curable inkjet ink composition according to any one of Application Example 1 to Application Example 5 may further contain dipentaerythritol hexaacrylate.

[Application Example 7]
In the ultraviolet curable inkjet ink composition described in Application Example 6, the dipentaerythritol hexaacrylate may be included in an amount of 5% by mass or more based on the total mass of the ink composition.

[Application Example 8]
The ultraviolet curable inkjet ink composition according to any one of Application Example 1 to Application Example 7 may further contain a photopolymerization initiator.

[Application Example 9]
In the ultraviolet curable inkjet ink composition according to any one of Application Example 1 to Application Example 8, the aluminum particles have an average thickness of 5 nm to 30 nm and a 50% average of 0.5 μm to 3 μm. It can be a tabular grain having a particle size.

[Application Example 10]
In the ultraviolet curable inkjet ink composition according to any one of Application Examples 1 to 9, the thickness of the coating film may be 0.5 nm or more and 10 nm or less.

[Application Example 11]
In the ultraviolet curable inkjet ink composition according to any one of Application Examples 1 to 10, the aluminum pigment (A) further includes at least one selected from polycarboxylic acid and a salt thereof on the surface of the coating. Can have.

The SEM image which shows the surface of the aluminum pigment (A) produced in the Example. The TEM image which shows the cross section of the aluminum pigment (A) produced in the Example. The TEM image which shows the cross section of the aluminum pigment (A) produced in the Example. The TEM image which shows the cross section of the aluminum pigment (A) produced in the Example.

  Hereinafter, preferred embodiments of the present invention will be described. The embodiment described below describes an example of the present invention. In addition, the present invention is not limited to the following embodiments, and includes various modifications that are implemented within a range that does not change the gist of the present invention.

  In the present specification, “(meth) acrylate” means at least one of acrylate and its corresponding methacrylate, and “(meth) acryl” means at least one of acrylic and its corresponding methacryl. To do.

1. UV curable ink composition for ink jet UV curable ink composition for ink jet according to an embodiment of the present invention (hereinafter, also simply referred to as “UV curable ink composition”) has tetraethoxysilane on the surface of aluminum particles. It contains an aluminum pigment (A) provided with a film having a chemically bonded structure, and phenoxyethyl (meth) acrylate (B).

  The ultraviolet curable ink composition according to the present embodiment is excellent in that the storage stability can be drastically improved because the active surface can be prevented from being exposed from the surface of the aluminum pigment (A).

  Hereinafter, the additives (components) contained in or contained in the ultraviolet curable ink composition according to the present embodiment will be described in detail.

1.1. Aluminum pigment (A)
The aluminum pigment (A) used in the present embodiment includes a coating (hereinafter, also simply referred to as “silica coating”) having a structure in which tetraethoxysilane is chemically bonded to the surface of aluminum particles. In the present specification, “chemically bonded” means that a hydroxyl group present on the surface of aluminum particles and tetraethoxysilane are bonded by a hydrolysis reaction.

  Such an aluminum pigment (A) can be produced, for example, by the following production method (step (a) to step (f)).

  First, an aluminum particle dispersion in which aluminum particles are dispersed in an organic solvent is prepared by the following steps (a) to (b).

  (A) First, a composite pigment base material having a structure in which a peeling resin layer and an aluminum or aluminum alloy layer (hereinafter simply referred to as “aluminum layer”) are sequentially laminated on a sheet-like substrate surface is prepared.

  The sheet-like substrate is not particularly limited, but may be a polyester film such as polytetrafluoroethylene, polyethylene, polypropylene, or polyethylene terephthalate, a polyamide film such as nylon 66 or nylon 6, a polycarbonate film, a triacetate film, a polyimide film, or the like. An example is a moldable film. Of these, polyethylene terephthalate or a copolymer thereof is preferable.

  The thickness of the sheet-like substrate is not particularly limited, but is preferably 10 to 150 μm. If it is 10 μm or more, there is no problem in handleability in the process or the like, and if it is 150 μm or less, it is rich in flexibility and there is no problem in roll formation, peeling and the like.

  The release resin layer is an undercoat layer of an aluminum layer, and is a peelable layer for improving the peelability from the sheet-like substrate surface. As the resin used for the release resin layer, for example, polyvinyl alcohol, polyvinyl butyral, polyethylene glycol, polyacrylic acid, polyacrylamide, cellulose derivative, acrylic acid polymer, or modified nylon resin is preferable.

  The resin layer for peeling can be formed by applying a solution of one or a mixture of two or more of the exemplified resins to a sheet-like substrate and drying it. After coating, additives such as a viscosity modifier can be added.

  For the application of the release resin layer, known techniques such as gravure coating, roll coating, blade coating, extrusion coating, dip coating, and spin coating, which are generally used, can be used. After coating and drying, the surface can be smoothed by calendaring if necessary.

  Although the thickness of the resin layer for peeling is not specifically limited, Preferably it is 0.5-50 micrometers, More preferably, it is 1-10 micrometers. If it is less than 0.5 μm, the amount as a dispersion resin is insufficient, and if it exceeds 50 μm, when it is rolled, it tends to peel off at the interface with the aluminum layer.

  As means for laminating the aluminum layer on the peeling resin layer, it is preferable to apply vacuum deposition, ion plating or sputtering.

  The aluminum layer may be sandwiched between protective layers as exemplified in JP-A-2005-68250. Examples of the protective layer include a silicon oxide layer and a protective resin layer.

  The silicon oxide layer is not particularly limited as long as it contains silicon oxide, but is preferably formed from a silicon alkoxide such as tetraalkoxysilane or a polymer thereof by a sol-gel method. An alcohol solution in which silicon alkoxide or a polymer thereof is dissolved is applied and heated and fired to form a silicon oxide layer coating.

  The protective resin layer is not particularly limited as long as it is a resin that does not dissolve in the dispersion medium, and examples thereof include polyvinyl alcohol, polyethylene glycol, polyacrylic acid, polyacrylamide, and cellulose derivatives. Of these, it is preferably formed from polyvinyl alcohol or a cellulose derivative.

  The protective resin layer can be formed by applying an aqueous solution of one or more of the exemplified resins and drying the mixture. Additives such as viscosity modifiers can be added to the coating solution. The silicon oxide and the resin are applied by the same method as the application of the release resin layer.

  The thickness of the protective layer is not particularly limited, but is preferably in the range of 50 to 150 nm. If it is less than 50 nm, the mechanical strength is insufficient, and if it exceeds 150 nm, the strength becomes too high, so that pulverization / dispersion becomes difficult, and peeling may occur at the interface with the aluminum layer.

  Further, as exemplified in JP-A-2005-68251, a color material layer may be provided between the “protective layer” and the “aluminum layer”. The color material layer is introduced in order to obtain an arbitrary colored composite pigment. In addition to the metallic luster, glitter, and background hiding properties of the aluminum pigment (A) used in the present embodiment, an arbitrary color tone, hue If it can contain the coloring material which can provide, it will not be restrict | limited in particular. The color material used for the color material layer may be either a dye or a pigment. Moreover, as a dye and a pigment, a well-known thing can be used suitably.

  In this case, the “pigment” used in the color material layer means a natural pigment, a synthetic organic pigment, a synthetic inorganic pigment or the like defined in the general engineering field.

  The method for forming the color material layer is not particularly limited, but is preferably formed by coating. Further, when the color material used in the color material layer is a pigment, it is preferable to further include a color material dispersion resin, and as the color material dispersion resin, a pigment, a color material dispersion resin, and as necessary It is preferable that other additives and the like are dispersed or dissolved in a solvent to form a uniform liquid film by spin coating as a solution and then dried to produce a resin thin film. In the production of the composite pigment base material, it is preferable in terms of work efficiency that both the colorant layer and the protective layer are formed by coating.

  As the composite pigment base material, a layer structure having a plurality of sequentially laminated structures of the release resin layer and the aluminum layer is also possible. At that time, the entire thickness of the laminated structure composed of a plurality of aluminum layers, that is, the aluminum layer-the resin layer for peeling-the aluminum layer, or the resin layer for peeling, excluding the sheet-like substrate and the resin layer for peeling immediately above it. -It is preferable that the thickness of an aluminum layer is 5000 nm or less. When it is 5000 nm or less, even when the composite pigment base material is rolled up, it is difficult to cause cracking and peeling and is excellent in storage stability. Further, even when pigmented, it is preferable because it is excellent in metallic gloss. Moreover, although the structure where the peeling resin layer and the aluminum layer were laminated | stacked one by one on both surfaces of the sheet-like base material surface is mentioned, it is not restrict | limited to these.

  (B) Next, the composite pigment base material is peeled in an organic solvent with the interface between the sheet base material surface of the composite pigment base material and the release resin layer as a boundary, and is pulverized or refined. As a result, an aluminum particle dispersion containing coarse particles is prepared. Furthermore, the obtained aluminum particle dispersion is filtered to remove coarse particles, whereby a dispersion containing tabular aluminum particles having a predetermined average particle diameter can be obtained.

  The organic solvent is not limited as long as it does not impair the dispersion stability of aluminum particles and the reactivity with tetraethoxysilane described later, but a polar organic solvent is preferable. Examples of polar organic solvents include alcohols (methyl alcohol, ethyl alcohol, propyl alcohol, butyl alcohol, isopropyl alcohol, fluorinated alcohol, etc.), ketones (acetone, methyl ethyl ketone, cyclohexanone, etc.), carboxylic acid esters (methyl acetate). Ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, etc.), ethers (diethyl ether, dipropyl ether, tetrahydrofuran, dioxane, etc.) and the like.

  Among the polar organic solvents exemplified above, alkylene glycol monoether or alkylene glycol diether which is liquid at normal temperature and pressure is more preferable.

  As alkylene glycol monoether, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether, ethylene glycol monohexyl ether, ethylene glycol monophenyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, Diethylene glycol monobutyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether, tetraethylene glycol monomethyl ether, tetraethylene glycol monoethyl ether, propylene glycol monomethyl ether, propylene group Monoethyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether and the like.

  Examples of the alkylene glycol diether include ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, triethylene glycol dimethyl ether, triethylene glycol diethyl ether, triethylene glycol dibutyl ether, tetra Ethylene glycol dimethyl ether, tetraethylene glycol diethyl ether, tetraethylene glycol dibutyl ether, propylene glycol dimethyl ether, propylene glycol diethyl ether, dipropylene glycol dimethyl ether, dipropylene glycol diethyl ether, etc. It is below.

  Among these, triethylene glycol monobutyl ether and diethylene glycol diethyl ether are more preferable from the viewpoint of excellent dispersion stability of aluminum particles.

  The peeling treatment method from the sheet-like substrate is not particularly limited, but is a method that is performed by immersing the composite pigment raw material in a liquid, or a peeling treatment that is performed by ultrasonic treatment at the same time as the immersion in the liquid. And a method of pulverizing the peeled composite pigment. The plate-like aluminum particles obtained as described above have a release resin layer serving as a protective colloid, and a stable dispersion can be obtained simply by performing a dispersion treatment in an organic solvent.

  Here, the term “tabular particle” refers to an aluminum particle having a substantially flat surface (XY plane) when the major axis on the plane is X, the minor axis is Y, and the thickness is Z. (Z) refers to particles that are substantially uniform. More specifically, the 50% average particle diameter R50 (hereinafter also simply referred to as “R50”) of the equivalent circle diameter determined from the area of the substantially flat surface (XY plane) of the aluminum particles is 0.5 μm to 3 μm. And what satisfies the thickness (Z) of 5 nm to 30 nm.

  The “equivalent circle diameter” is a diameter of a circle when assuming a substantially flat surface (XY plane) of the aluminum particle as a circle having the same projected area as the projected area of the aluminum particle. For example, when the substantially flat surface (XY plane) of an aluminum particle is a polygon, the diameter of the circle obtained by converting the polygonal projection surface into a circle is the equivalent circle diameter of the aluminum particle. That's it.

  R50 is preferably 0.5 μm to 3 μm, and more preferably 0.75 μm to 2 μm, from the viewpoint of ensuring good metallic gloss and ejection stability. When R50 is less than 0.5 μm, the metallic gloss may be insufficient. On the other hand, when R50 exceeds 3 μm, ejection stability may be reduced due to nozzle clogging.

  The maximum particle diameter of the equivalent circle diameter determined from the area of the substantially flat surface (XY plane) of the tabular grains is preferably 10 μm or less. By setting the maximum particle size to 10 μm or less, it is possible to prevent clogging of the tabular particles from a nozzle of an ink jet recording apparatus, a foreign matter removal filter provided in an ink flow path, and the like.

  The major axis X, minor axis Y, and equivalent circle diameter on the plane of the tabular grains can be measured using a particle image analyzer. Examples of the particle image analyzer include a flow-type particle image analyzer “FPIA-2100”, “FPIA-3000”, and “FPIA-3000S” (supplied by Sysmex Corporation).

The particle size distribution (CV value) of the tabular grains can be obtained from the following formula (2).
CV value = standard deviation of particle size distribution / average value of particle diameter × 100 (2)
Here, the CV value obtained is preferably 60 or less, more preferably 50 or less, and particularly preferably 40 or less. By selecting tabular grains having a CV value of 60 or less, an effect of excellent printing stability can be obtained.

  The thickness (Z) is preferably 5 nm or more and 30 nm or less, more preferably 10 nm or more and 25 nm or less, from the viewpoint of securing metallic gloss. When the thickness (Z) is less than 5 nm, the metallic luster tends to decrease when a film is formed on the surface of the aluminum particles. On the other hand, even if the thickness (Z) exceeds 30 nm, the metallic gloss tends to decrease.

  The aluminum particles are preferably aluminum or an aluminum alloy from the viewpoints of cost and metal gloss. In the case of using an aluminum alloy, examples of other metal elements or non-metal elements added in addition to aluminum include silver, gold, platinum, nickel, chromium, tin, zinc, indium, titanium, and copper.

  Here, you may provide the process of wash | cleaning the aluminum particle contained in an aluminum particle dispersion liquid. The aluminum particle dispersion may contain the aforementioned release resin layer, or the release resin layer may adhere to the aluminum particles. The peeling resin layer may inhibit the reaction between tetraethoxysilane and aluminum particles in the step (c) described later. Therefore, it is preferable to remove the peeling resin layer in the aluminum particle dispersion. The organic solvent described above may be used for cleaning the aluminum particles.

  (C) Next, tetraethoxysilane (hereinafter also referred to as “TEOS”) is added to the aluminum particle dispersion obtained in the step (b) and stirred. Thereby, the hydroxyl group and TEOS which exist on the surface of the said aluminum particle hydrolyze, and the aluminum pigment (A) in which the silica film was formed on the surface of the said aluminum particle is obtained.

  The reaction temperature in the hydrolysis reaction is preferably 10 ° C. or higher and 150 ° C. or lower, more preferably 20 ° C. or higher and 130 ° C. or lower. If it is less than 10 degreeC, advancing of a hydrolysis reaction will become slow and formation of the silica film in the aluminum particle surface will become inadequate easily. If it exceeds 150 ° C, special safety precautions are required.

  The reaction time in the hydrolysis reaction is preferably 0.5 hours or more and 200 hours or less, more preferably 1 hour or more and 180 hours or less. When the reaction time is less than 0.5 hour, the hydrolysis reaction may not be completed sufficiently, and the formation of a silica coating on the aluminum particle surface tends to be insufficient. If it exceeds 200 hours, aluminum particles may aggregate.

  The amount of TEOS added may be determined by calculating an amount such that the thickness of the silica coating is 0.5 nm or more and 10 nm or less, preferably 5 nm. This is because if the thickness of the silica film exceeds 10 nm, the metallic gloss may be lowered.

  Specifically, the addition amount of TEOS is preferably 0.2 parts by mass or more and 5 parts by mass or less, more preferably 0.5 parts by mass or more and 4 parts by mass or less, and still more preferably with respect to 1 part by mass of aluminum particles. 1 part by mass or more and 3 parts by mass or less. When the addition amount of TEOS exceeds 5 parts by mass, the aluminum particle dispersion may become cloudy due to unreacted TEOS. On the other hand, if it is less than 0.2 parts by mass, the active surface present on the surface of the aluminum particles may not be completely covered.

  After adding TEOS to the aluminum particle dispersion, the hydrolysis reaction can be promoted by further adding a basic catalyst. As the basic catalyst, ammonia is suitable. The amount of ammonia added is preferably 1 part by mass or less, more preferably 0.1 part by mass or less, with respect to 10 parts by mass of the aluminum particles. If the amount of ammonia added exceeds the above range, the aluminum particles may aggregate and the metallic luster may not be maintained.

  (D) Next, the organic solvent in the dispersion obtained in the step (c) is removed. Examples of means for separating the organic solvent in the dispersion include filtration, centrifugal sedimentation, and centrifugal separation. By these means, the organic solvent and the aluminum pigment (A) on which the silica film is formed can be separated to remove the organic solvent contained in the dispersion. Among these means, a means for separating by centrifugation and removing the organic solvent is preferable because the operation is simple.

  (E) An aluminum pigment (A) having a silica coating formed by the steps (a) to (d) can be produced. The aluminum pigment (A) used in the present embodiment may have at least one selected from polycarboxylic acids and salts thereof on the surface of the silica coating by further providing the following steps.

  First, an aqueous solution containing at least one selected from a polycarboxylic acid and a salt thereof is added to the aluminum pigment (A) from which the organic solvent has been removed in the step (d) and sufficiently stirred. The stirring time is not particularly limited, but is preferably about 3 hours to 120 hours. When the stirring time is within the above range, an aqueous dispersion of the aluminum pigment (A) having excellent water dispersibility can be obtained without impairing the metallic luster. When the stirring time exceeds 120 hours, metal gloss may be impaired due to aggregation of particles.

  By this step, at least one selected from polycarboxylic acids and salts thereof can be adsorbed on the surface of the silica coating of the aluminum pigment (A) obtained in the step (d). As a result, the aluminum pigment (A) can ensure better dispersion stability and improve storage stability in the ultraviolet curable ink composition.

  The polycarboxylic acid and its salt are preferably at least one selected from the following copolymer A, copolymer B, and copolymer C. Copolymers A to C have a bulky molecular structure. Therefore, when the copolymers A to C are adsorbed on the surface of the aluminum pigment (A), the steric hindrance derived from the molecular structure effectively aggregates the aluminum pigments (A) in the ultraviolet curable ink composition. Can be suppressed.

  The copolymer A is a copolymer having a structural unit represented by the following general formula (3) or (4) and a structural unit represented by the following general formula (5).

  The copolymer B is a copolymer having a structural unit represented by the following general formula (3) or (4) and a structural unit represented by the following general formula (6).

  The copolymer C is a copolymer having a structural unit represented by the following general formula (3) or (4) and a structural unit represented by the following general formula (7). The copolymer C may further have a structural unit represented by the following general formula (6).

  These copolymers may be in any arrangement state of an alternating copolymer, a random copolymer, a block copolymer, and a graft copolymer.

In the formula (5), l is an integer of 1 to 5, and preferably an integer of 1 to 3.

In formula (6), m is an integer of 1-5, and it is preferable that it is an integer of 1-3.

In formula (7), n is an integer of 1-5, and it is preferable that it is an integer of 1-3. R ⁴ represents an alkyl group.

  The weight average molecular weight of the polycarboxylic acid and its salt is preferably 2000 to 500,000, more preferably 10,000 to 100,000. If the weight average molecular weight of the polycarboxylic acid and its salt is within the above range, an increase in the viscosity of the ultraviolet curable ink composition can be suppressed, so that the influence on the ejection stability in the ink jet recording head can be reduced, and an aluminum pigment ( The dispersibility of A) can be improved. In addition, the weight average molecular weight of polycarboxylic acid and its salt can be calculated | required by the polystyrene conversion molecular weight measured by the gel permeation chromatography (GPC) which used tetrahydrofuran as a solvent, for example.

  Specific examples of the copolymer A include Polystar OM (trade name, manufactured by NOF Corporation), which is a copolymer having maleic acid and olefin as structural units. Specific examples of the copolymer B include DSK Discoat N-10 (trade name, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), which is a copolymer having maleic acid and styrene as structural units. Specific examples of the copolymer C include, for example, Marialim AKM-0531 (trade name, manufactured by NOF Corporation), which is a copolymer having maleic anhydride and polyoxypropylene alkyl ether as structural units.

  The addition amount of the polycarboxylic acid and its salt is preferably 0.02 parts by mass or more and 1.5 parts by mass or less, more preferably 0.03 parts by mass or more and 1.3 parts by mass relative to 1 part by mass of the aluminum pigment (A). It is 0.03 mass part or less and 1.2 mass part or less especially preferably. When the addition amount of the polycarboxylic acid and its salt is within the above range, the dispersion stability can be improved without impairing the metallic gloss of the aluminum pigment (A) in the ultraviolet curable ink composition.

  Next, water in the aqueous dispersion of the aluminum pigment (A) is removed. Examples of means for removing water in the aqueous dispersion include filtration, centrifugal sedimentation, and centrifugal separation. By these means, water and the aluminum pigment (A) on which the silica film is formed can be separated. In order to completely remove water adhering to the surface of the aluminum pigment (A) obtained by the separation, a separate drying step may be provided. Or you may provide the washing | cleaning process with the solvent (for example, the organic solvent illustrated above) which can be mixed with both water and a monomer (C). As a result, water is completely removed, and defects are reduced when mixing with various monomers.

  (F) Finally, from the viewpoint of facilitating addition of the aluminum pigment (A) obtained in step (d) or step (e) to the ultraviolet curable ink composition, the aluminum pigment (A) is dispersed in the monomer. Prepare a dispersion. As the monomer, various monomers described later can be used. From the viewpoint of securing the dispersion stability of the aluminum pigment (A), it is preferable to use the monomer (C) represented by the general formula (1).

  If step (e) was not performed, polycarboxylic acid or a salt thereof was directly added to the dispersion of the aluminum pigment (A) prepared in step (f) or to the ultraviolet curable ink composition. And a step of stirring may be provided. By this step, the polycarboxylic acid or a salt thereof can be adsorbed on the surface of the silica coating of the aluminum pigment (A). As a result, the aluminum pigment (A) can ensure better dispersion stability in the ultraviolet curable ink composition and can improve storage stability.

  The content of the aluminum pigment (A) is preferably 0.5% by mass or more and 7% by mass or less as a solid content with respect to the total mass of the ink composition. When the content of the aluminum pigment (A) is less than the above range, the metallic gloss of the recorded image may be insufficient. When the content of the aluminum pigment (A) exceeds the above range, the viscosity of the ultraviolet curable ink composition may increase and precipitation of the aluminum pigment (A) may occur.

1.2. Phenoxyethyl (meth) acrylate (B)
The ultraviolet curable ink composition according to the present embodiment contains phenoxyethyl (meth) acrylate (B). Phenoxyethyl (meth) acrylate (B) is a monomer added for the purpose of recording an image excellent in flexibility and elongation durability on a recording medium.

  Moreover, phenoxyethyl (meth) acrylate (B) is excellent also in the capability to melt | dissolve the photoinitiator mentioned later. Therefore, when the ink composition contains phenoxyethyl (meth) acrylate, more photopolymerization initiator can be dissolved in the ink composition than in the case of containing other monomers. It can be cured with ultraviolet rays. Furthermore, phenoxyethyl (meth) acrylate (B) has a feature that it is very easy to use because of its good dilutability with respect to other monomers.

  The content of phenoxyethyl (meth) acrylate (B) is preferably 10% by mass or more and 70% by mass or less, more preferably 20% by mass or more and 60% by mass or less, and particularly preferably with respect to the total mass of the ink composition. 30% by mass or more and 55% by mass or less. When the content of phenoxyethyl (meth) acrylate (B) is in the above range, good curability is exhibited and a good image without a tacky feeling can be recorded. In the present specification, “curability” refers to a property of polymerizing and curing in the presence or absence of a photopolymerization initiator by ultraviolet irradiation.

1.3. Monomer (C)
The ultraviolet curable ink composition according to the present embodiment may contain a monomer (C) represented by the following general formula (1).
_{^{CH 2 = CR 1 -COO-R}} 2 -O-CH = CH-R 3 ... (1)
(In Formula (1), R ¹ represents a hydrogen atom or a methyl group. R ² represents a divalent organic residue having 2 to 20 carbon atoms. R ³ represents a hydrogen atom or 1 to 11 carbon atoms. Represents a monovalent organic residue.)

  The ultraviolet curable ink composition according to the present embodiment can improve the curability of the ink by containing the monomer (C).

In the general formula (1), the divalent organic residue represented by R ² is a linear, branched or cyclic alkylene group having 2 to 20 carbon atoms, an ether bond and / or an ester in the structure. An alkylene group having 2 to 20 carbon atoms having an oxygen atom due to a bond and an optionally substituted divalent aromatic group having 6 to 11 carbon atoms are preferable. Among these, structures such as alkylene groups having 2 to 6 carbon atoms such as ethylene group, n-propylene group, isopropylene group and butylene group, oxyethylene group, oxy n-propylene group, oxyisopropylene group and oxybutylene group Among them, an alkylene group having 2 to 9 carbon atoms having an oxygen atom by an ether bond is preferably used.

In the general formula (1), the monovalent organic residue having 1 to 11 carbon atoms represented by R ³ is a linear, branched or cyclic alkyl group having 1 to 10 carbon atoms, or 6 carbon atoms. ˜11 optionally substituted aromatic groups are preferred. Among these, C6-C2 aromatic groups, such as a C1-C2 alkyl group which is a methyl group or an ethyl group, a phenyl group, and a benzyl group, are used suitably.

  Specific examples of the monomer (C) represented by the general formula (1) include, for example, 2-vinyloxyethyl (meth) acrylate, 3-vinyloxypropyl (meth) acrylate, and 1-methyl (meth) acrylate. 2-vinyloxyethyl, 2-vinyloxypropyl (meth) acrylate, 4-vinyloxybutyl (meth) acrylate, 1-methyl-3-vinyloxypropyl (meth) acrylate, 1-vinyloxymethylpropyl (meth) acrylate 2-methyl-3-vinyloxypropyl (meth) acrylate, 1,1-dimethyl-2-vinyloxyethyl (meth) acrylate, 3-vinyloxybutyl (meth) acrylate, 1-methyl-2 (meth) acrylate -Vinyloxypropyl, 2- (vinyloxybutyl) (meth) acrylate, 4-vinyloxy (meth) acrylate Hexyl, 6-vinyloxyhexyl (meth) acrylate, 4-vinyloxymethylcyclohexylmethyl (meth) acrylate, 3-vinyloxymethylcyclohexylmethyl (meth) acrylate, 2-vinyloxymethylcyclohexyl (meth) acrylate Methyl, (meth) acrylic acid p-vinyloxymethylphenylmethyl, (meth) acrylic acid m-vinyloxymethylphenylmethyl, (meth) acrylic acid o-vinyloxymethylphenylmethyl, (meth) acrylic acid 2- (2 -Vinyloxyethoxy) ethyl, 2- (vinyloxyisopropoxy) ethyl (meth) acrylate, 2- (vinyloxyethoxy) propyl (meth) acrylate, 2- (vinyloxyethoxy) isopropyl (meth) acrylate, (Meth) acrylic acid 2- (vinyloxyisopropo Cis) propyl, 2- (vinyloxyisopropoxy) isopropyl (meth) acrylate, 2- (vinyloxyethoxyethoxy) ethyl (meth) acrylate, 2- (vinyloxyethoxyisopropoxy) ethyl (meth) acrylate, 2- (vinyloxyisopropoxyethoxy) ethyl (meth) acrylate, 2- (vinyloxyisopropoxyisopropoxy) ethyl (meth) acrylate, 2- (vinyloxyethoxyethoxy) propyl (meth) acrylate, (meth ) 2- (vinyloxyethoxyisopropoxy) propyl acrylate, 2- (vinyloxyisopropoxyethoxy) propyl (meth) acrylate, 2- (vinyloxyisopropoxyisopropoxy) propyl (meth) acrylate, (meth) Acrylic acid 2- (vinyloxyethoxyethoxy) Isopropyl, 2- (vinyloxyethoxyisopropoxy) isopropyl (meth) acrylate, 2- (vinyloxyisopropoxyethoxy) isopropyl (meth) acrylate, 2- (vinyloxyisopropoxyisopropoxy) isopropyl (meth) acrylate 2- (vinyloxyethoxyethoxyethoxy) ethyl (meth) acrylate, 2- (vinyloxyethoxyethoxyethoxyethoxy) ethyl (meth) acrylate, 2- (isopropenoxyethoxy) ethyl (meth) acrylate, ( 2- (isopropenoxyethoxyethoxy) ethyl (meth) acrylate, 2- (isopropenoxyethoxyethoxyethoxy) ethyl (meth) acrylate, 2- (isopropenoxyethoxyethoxyethoxyethoxy) ethyl (meth) acrylate, (Meta Polyethylene glycol monovinyl ether acrylate, and (meth) acrylic acid polypropylene glycol monovinyl ether.

  Among the monomers (C) exemplified above, 2-vinyloxyethyl (meth) acrylate, 3-vinyloxypropyl (meth) acrylate, (meth) from the viewpoint of obtaining an advantageous effect that the curability is better. 1-methyl-2-vinyloxyethyl acrylate, 2-vinyloxypropyl (meth) acrylate, 4-vinyloxybutyl (meth) acrylate, 4-vinyloxycyclohexyl (meth) acrylate, 5-vinyloxy (meth) acrylate Pentyl, 6-vinyloxyhexyl (meth) acrylate, 4-vinyloxymethylcyclohexylmethyl (meth) acrylate, p-vinyloxymethylphenylmethyl (meth) acrylate, 2- (2-vinyl) (meth) acrylate Roxyethoxy) ethyl, (meth) acrylic acid 2- (vinyloxyethoxyethoxy) Le, (meth) acrylic acid 2- (vinyloxy ethoxy ethoxy) ethyl are preferred.

  Among these, 2- (2-vinyloxyethoxy) ethyl (meth) acrylate is more preferable from the viewpoint of obtaining an advantageous effect that the viscosity of the ink can be designed to be low, and 2- (2-vinyloxyethoxy) acrylate is more preferable. ) Ethyl is particularly preferred.

  The content of the monomer (C) is preferably 10% by mass or more and 70% by mass or less, more preferably 40% by mass or more and 60% by mass or less, with respect to the total mass of the ink composition. When the monomer (C) content is in the above range, an advantageous effect of low viscosity and good curability can be obtained.

  The method for producing the monomer (C) represented by the general formula (1) is not limited to the following, but is a method of esterifying (meth) acrylic acid and a hydroxyl group-containing vinyl ether (production method B), (meth) acrylic. Method of esterifying acid halide and hydroxyl group-containing vinyl ether (Production method C), Method of esterifying (meth) acrylic anhydride and hydroxyl group-containing vinyl ether (Production method D), (meth) acrylic acid esters and Method of transesterifying hydroxyl group-containing vinyl ethers (Production method E), Method of esterifying (meth) acrylic acid and halogen-containing vinyl ethers (Production method F), (meth) acrylic acid alkali (earth) metal salt and halogen Method for Esterification of Containing Vinyl Ether (Production Method G), Hydroxyl-Containing (Meth) Acrylic Acid Esters and Carvone How to vinyl exchange and vinyl (Procedure H), hydroxyl group-containing (meth) How to ether exchange and acrylic acid esters and alkyl vinyl ethers (formula I). Among these, since the desired effect can be further exhibited in this embodiment, the production method E is preferable.

1.4. Other Monomers The ultraviolet curable ink composition according to the present embodiment may contain other monomers other than the phenoxyethyl (meth) acrylate (B) and the monomer (C). As other monomers, conventionally known monofunctional, bifunctional and trifunctional or higher polyfunctional monomers and oligomers can be used. Examples of the monomer include unsaturated carboxylic acids such as (meth) acrylic acid, itaconic acid, crotonic acid, isocrotonic acid and maleic acid and salts or esters thereof, urethane, amide and anhydride thereof, acrylonitrile, styrene, various Unsaturated polyesters, unsaturated polyethers, unsaturated polyamides, and unsaturated urethanes. Examples of the oligomer include oligomers formed from the above monomers such as linear acrylic oligomers, epoxy (meth) acrylate, oxetane (meth) acrylate, aliphatic urethane (meth) acrylate, and aromatic urethane (meth). Examples include acrylate and polyester (meth) acrylate.

  Moreover, an N-vinyl compound may be included as another monofunctional monomer or polyfunctional monomer. Examples of the N-vinyl compound include N-vinylformamide, N-vinylcarbazole, N-vinylacetamide, N-vinylpyrrolidone, N-vinylcaprolactam, acryloylmorpholine, and derivatives thereof.

  Of the other monomers, esters of (meth) acrylic acid, that is, (meth) acrylates are preferred.

  Among the above (meth) acrylates, monofunctional (meth) acrylates include, for example, isoamyl (meth) acrylate, stearyl (meth) acrylate, lauryl (meth) acrylate, octyl (meth) acrylate, decyl (meth) acrylate, iso Myristyl (meth) acrylate, isostearyl (meth) acrylate, 2-ethylhexyl-diglycol (meth) acrylate, 2-hydroxybutyl (meth) acrylate, butoxyethyl (meth) acrylate, ethoxydiethylene glycol (meth) acrylate, methoxydiethylene glycol ( (Meth) acrylate, methoxypolyethylene glycol (meth) acrylate, methoxypropylene glycol (meth) acrylate, tetrahydrofurfuryl (meth) a Relate, isobornyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 2-hydroxy-3-phenoxypropyl (meth) acrylate, lactone-modified flexible (meth) acrylate, t -Butylcyclohexyl (meth) acrylate, dicyclopentenyl (meth) acrylate, dicyclopentanyl (meth) acrylate, benzyl (meth) acrylate, and dicyclopentenyloxyethyl (meth) acrylate.

  Among the (meth) acrylates, examples of the bifunctional (meth) acrylate include triethylene glycol di (meth) acrylate, tetraethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, and tripropylene glycol di ( (Meth) acrylate, polypropylene glycol di (meth) acrylate, 1,4-butanediol di (meth) acrylate, 1,6-hexanediol di (meth) acrylate, 1,9-nonanediol di (meth) acrylate, neopentyl Glycol di (meth) acrylate, dimethylol tricyclodecane di (meth) acrylate, EO (ethylene oxide) adduct of bisphenol A di (meth) acrylate, PO of bisphenol A (propylene oxide) ) Adduct di (meth) acrylate, hydroxypivalic acid neopentyl glycol di (meth) acrylate, and polytetramethylene glycol di (meth) acrylate.

  Among the above (meth) acrylates, trifunctional or more polyfunctional (meth) acrylates include, for example, trimethylolpropane tri (meth) acrylate, EO-modified trimethylolpropane tri (meth) acrylate, and pentaerythritol tri (meth) acrylate. , Pentaerythritol tetra (meth) acrylate, dipentaerythritol hexa (meth) acrylate, ditrimethylolpropane tetra (meth) acrylate, glycerin propoxytri (meth) acrylate, cowprolactone modified trimethylolpropane tri (meth) acrylate, pentaerythritol Examples include ethoxytetra (meth) acrylate and caprolactam-modified dipentaerythritol hexa (meth) acrylate. When the ink composition contains dipentaerythritol hexaacrylate as a polyfunctional monomer, the curability can be further improved. The content of dipentaerythritol hexaacrylate is preferably 5% by mass or more, more preferably 5% by mass or more and 20% by mass or less with respect to the total mass of the ink composition. Curability can be improved more as content of dipentaerythritol hexaacrylate is 5 mass% or more.

  Among these, it is preferable that another monomer contains a monofunctional (meth) acrylate. In this case, the ink composition has a low viscosity, is excellent in solubility of the photopolymerization initiator and other additives, and is easy to obtain ejection stability during ink jet recording. Furthermore, since the toughness, heat resistance, and chemical resistance of the coating film are increased, it is more preferable to use a monofunctional (meth) acrylate and a bifunctional (meth) acrylate in combination.

  Furthermore, the monofunctional (meth) acrylate preferably has at least one skeleton selected from the group consisting of an aromatic ring skeleton, a saturated alicyclic skeleton, and an unsaturated alicyclic skeleton. When the other monomer is a monofunctional (meth) acrylate having the skeleton, the viscosity of the ink composition can be reduced.

  Examples of the monofunctional (meth) acrylate having an aromatic ring skeleton include 2-hydroxy-3-phenoxypropyl (meth) acrylate. Examples of the monofunctional (meth) acrylate having a saturated alicyclic skeleton include isobornyl (meth) acrylate, t-butylcyclohexyl (meth) acrylate, and dicyclopentanyl (meth) acrylate. Examples of the monofunctional (meth) acrylate having an unsaturated alicyclic skeleton include dicyclopentenyloxyethyl (meth) acrylate.

  It is also preferable to contain amino (meth) acrylate. When the ink composition contains amino (meth) acrylate, the copolymerization reaction is promoted, and the curability can be further improved.

  Said other monomer may be used individually by 1 type, and may use 2 or more types together.

1.5. Photopolymerization initiator The ultraviolet curable ink composition according to the present embodiment may contain a photopolymerization initiator. The photopolymerization initiator is not particularly limited as long as it generates active species such as radicals and cations by ultraviolet irradiation and initiates the polymerization reaction of the monomer. As the photopolymerization initiator, a radical photopolymerization initiator or a cationic photopolymerization initiator can be used, but it is preferable to use a radical photopolymerization initiator.

  In addition, it is excellent in safety | security by using an ultraviolet-ray (UV) among radiation, and the cost of a light source lamp can be held down. Therefore, the photopolymerization initiator preferably has an absorption peak in the ultraviolet region.

  Examples of the photo radical polymerization initiator include aromatic ketones, acylphosphine oxide compounds, aromatic onium salt compounds, organic peroxides, thio compounds (thioxanthone compounds, thiophenyl group-containing compounds, etc.), hexaarylbiimidazole compounds, and the like. Ketoxime ester compounds, borate compounds, azinium compounds, metallocene compounds, active ester compounds, compounds having a carbon halogen bond, and alkylamine compounds.

  Among these, at least one selected from an acylphosphine oxide compound and a thioxanthone compound is preferable from the viewpoint of obtaining an advantageous effect of good solubility in monomers and curability, and the acylphosphine oxide compound and the thioxanthone compound are used in combination. More preferably.

  Specific examples of the photo radical polymerization initiator include acetophenone, acetophenone benzyl ketal, 1-hydroxycyclohexyl phenyl ketone, 2,2-dimethoxy-2-phenylacetophenone, xanthone, fluorenone, benzaldehyde, fluorene, anthraquinone, triphenylamine. , Carbazole, 3-methylacetophenone, 4-chlorobenzophenone, 4,4′-dimethoxybenzophenone, 4,4′-diaminobenzophenone, Michler's ketone, benzoin propyl ether, benzoin ethyl ether, benzyldimethyl ketal, 1- (4-isopropylphenyl) ) -2-Hydroxy-2-methylpropan-1-one, 2-hydroxy-2-methyl-1-phenylpropan-1-one, thioxanthone, diethyl Oxanthone, 2-isopropylthioxanthone, 2-chlorothioxanthone, 2-methyl-1- [4- (methylthio) phenyl] -2-morpholino-propan-1-one, bis (2,4,6-trimethylbenzoyl) -phenyl Phosphine oxide, 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide, 2,4-diethylthioxanthone, and bis- (2,6-dimethoxybenzoyl) -2,4,4-trimethylpentylphosphine oxide Can be mentioned.

  Examples of commercially available photo radical polymerization initiators include IRGACURE 651 (2,2-dimethoxy-1,2-diphenylethane-1-one), IRGACURE 184 (1-hydroxy-cyclohexyl-phenyl-ketone), DAROCUR 1173. (2-hydroxy-2-methyl-1-phenyl-propan-1-one), IRGACURE 2959 (1- [4- (2-hydroxyethoxy) -phenyl] -2-hydroxy-2-methyl-1-propane- 1-one), IRGACURE 127 (2-hydroxy-1- {4- [4- (2-hydroxy-2-methyl-propionyl) -benzyl] phenyl} -2-methyl-propan-1-one), IRGACURE 907 (2-Methyl-1- (4-methylthiophenyl) -2-morph Linopropan-1-one), IRGACURE 369 (2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) -butanone-1), IRGACURE 379 (2- (dimethylamino) -2-[(4- Methylphenyl) methyl] -1- [4- (4-morpholinyl) phenyl] -1-butanone), DAROCUR TPO (2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide), IRGACURE 819 (bis (2, 4,6-trimethylbenzoyl) -phenylphosphine oxide), IRGACURE 784 (bis (η5-2,4-cyclopentadien-1-yl) -bis (2,6-difluoro-3- (1H-pyrrole-1-) Yl) -phenyl) titanium), IRGACURE OXE 0 (1.2-octanedione, 1- [4- (phenylthio)-, 2- (O-benzoyloxime)]), IRGACURE OXE 02 (ethanone, 1- [9-ethyl-6- (2-methylbenzoyl) -9H-carbazol-3-yl]-, 1- (O-acetyloxime)), IRGACURE 754 (oxyphenylacetic acid, 2- [2-oxo-2-phenylacetoxyethoxy] ethyl ester and oxyphenylacetic acid, 2- (Mixture of (2-hydroxyethoxy) ethyl ester), Lucirin TPO, LR8883, LR8970 (above, manufactured by BASF Japan), KAYACURE DETX-S (2,4-diethylthioxanthone) (manufactured by Nippon Kayaku Co., Ltd.), Ubekrill P36 (Manufactured by UCB), Speedcure TPO Nil-2,4,6-trimethylbenzoylphosphine oxide), Speedcure DETX (2,4-diethylthioxanthen-9-one) (manufactured by Lambson).

  The said photoinitiator may be used individually by 1 type, and may be used in combination of 2 or more type.

  The content of the photopolymerization initiator is preferably 0.5% by mass or more and 10% by mass or less with respect to the total mass of the ink composition. When the content of the photopolymerization initiator is within the above range, the ultraviolet curing rate is sufficiently high, and the photopolymerization initiator is hardly dissolved and there is almost no color derived from the photopolymerization initiator. As described above, when the photopolymerization initiator contained in the ink composition is an acyl phosphine oxide compound and / or a thioxanthone compound, the content of the acyl phosphine oxide compound is based on the total mass of the ink composition. It is preferable that it is 2 mass% or more. On the other hand, the content of the thioxanthone compound is preferably 1% by mass or more based on the total mass of the ink composition.

  Although the addition of a photopolymerization initiator can be omitted by using a photopolymerizable compound as the above-mentioned monomer, the use of a photopolymerization initiator can easily adjust the start of polymerization. Can be preferred.

1.6. Dispersant The ultraviolet curable ink composition according to the present embodiment may further contain a dispersant from the viewpoint of improving the dispersibility of the aluminum pigment (A). Although it does not specifically limit as a dispersing agent, For example, the dispersing agent currently used in preparing pigment dispersion liquids, such as a polymer dispersing agent, is mentioned. Specific examples thereof include polyoxyalkylene polyalkylene polyamines, vinyl polymers and copolymers, acrylic polymers and copolymers, polyesters, polyamides, polyimides, polyurethanes, amino polymers, silicon-containing polymers, sulfur-containing polymers, fluorine-containing polymers, and The thing which has 1 or more types as a main component among epoxy resins is mentioned. Commercially available polymer dispersants include Ajinomoto Fine Techno Co., Ltd., Ajisper series, Solspers series (Solsperse 36000, etc.) available from Avecia, BYK Chemie, Dispersic series, Enomoto Kasei Co., Ltd. Ron series.

  Further, the ultraviolet curable ink composition according to the present embodiment may contain polycarboxylic acid or a salt thereof as a surfactant. Thereby, the dispersion stability of the aluminum pigment (A) in the ink composition is improved, and as a result, the storage stability of the ink composition is also improved. As polycarboxylic acid or its salt, copolymer A, B, C etc. which were illustrated above are mentioned, for example.

1.7. Slip agent (leveling agent)
The ultraviolet curable ink composition according to the present embodiment may further contain a slip agent because an advantageous effect that the surface of the printed material becomes smooth due to the leveling action and the scratching property is improved can be obtained. The slip agent is not particularly limited. For example, as the silicone surfactant, polyester-modified silicone or polyether-modified silicone can be used, and polyether-modified polydimethylsiloxane or polyester-modified polydimethylsiloxane is preferably used. . Specific examples include BYK-347, BYK-348, BYK-UV3500, 3510, 3530, 3570 (manufactured by Big Chemie Japan).

1.8. Other Additives The ultraviolet curable ink composition according to the present embodiment may contain additives (components) other than the additives listed above. Such a component is not particularly limited, and examples thereof include conventionally known polymerization accelerators, polymerization inhibitors, penetration enhancers, wetting agents (humectants), and other additives. Examples of the other additives include conventionally known fixing agents, antifungal agents, preservatives, antioxidants, chelating agents, and thickeners.

2. 2. Inkjet recording method 2.1. Recording medium The ultraviolet curable ink composition according to the present embodiment can be recorded on a recording medium by an inkjet recording method to be described later. Examples of the recording medium include an absorptive or non-absorbable recording medium. The ink jet recording method using the ultraviolet curable ink composition according to the present embodiment ranges from a non-absorbable recording medium in which water-soluble ink is difficult to penetrate to an absorbent recording medium in which water-soluble ink is easily penetrated. It can be widely applied to recording media having various absorption performances. However, when the ink composition is applied to a non-absorbable recording medium, it may be necessary to provide a drying step after being cured by irradiation with ultraviolet rays.

  The absorbent recording medium is not particularly limited. For example, plain paper such as electrophotographic paper having high water-based ink permeability, inkjet paper (an ink absorbing layer composed of silica particles or alumina particles, or polyvinyl alcohol). Art paper and coats used for general offset printing with relatively low permeability of water-based ink from (PVA) and inkjet pyrrole (PVP) and other ink-absorbing layers composed of hydrophilic polymers such as polyvinylpyrrolidone (PVP). Examples thereof include paper and cast paper.

  The non-absorbable recording medium is not particularly limited. For example, films and plates of plastics such as polyvinyl chloride, polyethylene, polypropylene, and polyethylene terephthalate (PET), and metals such as iron, silver, copper, and aluminum are used. Examples thereof include a plate, a metal plate produced by vapor deposition of these various metals, a plastic film, a plate made of an alloy such as stainless steel or brass.

2.2. Inkjet Recording Method The ultraviolet curable ink composition according to this embodiment can be applied to an inkjet recording method. Such an ink jet recording method includes a discharge step of discharging the ink composition onto a recording medium, a curing step of curing the ink composition by irradiating the ink composition discharged in the discharge step with ultraviolet rays, including. In this way, a coating film (cured film) is formed from the ink composition cured on the recording medium.

2.2.1. Discharging Step In the discharging step, a conventionally known ink jet recording apparatus can be used. When the viscosity of the ink composition is preferably 20 mPa · s or less, more preferably 3 to 15 mPa · s, good ejection stability is realized. An ink composition having a high viscosity exceeding 20 mPa · s at 20 ° C. may be ejected by heating the head and / or the ink composition to lower the apparent viscosity.

  Since the ultraviolet curable ink composition of the present embodiment has a higher viscosity than the water-based ink composition used in ordinary ink jet recording inks, the viscosity fluctuation due to temperature fluctuation during ejection is large. Such ink viscosity fluctuation has a great influence on the change in the droplet size and the change in the droplet discharge speed, and can cause image quality deterioration. Therefore, it is preferable to keep the temperature of the ink during ejection as constant as possible.

2.2.2. Curing Step Next, in the curing step, the ink composition ejected on the recording medium is cured by ultraviolet irradiation. This is because the photopolymerization initiator contained in the ink composition is decomposed by ultraviolet irradiation to generate active species such as radicals and cations, and the monomer polymerization reaction is promoted by the function of the active species. It is. Or it is because the polymerization reaction of a photopolymerizable compound starts by ultraviolet irradiation. At this time, if a sensitizing dye is present together with the photopolymerization initiator in the ink composition, the sensitizing dye in the system absorbs actinic radiation to be in an excited state and comes into contact with the photopolymerization initiator. Degradation can be accelerated and a more sensitive curing reaction can be achieved.

  As the ultraviolet light source, a mercury lamp, a gas / solid laser, or the like is mainly used, and as a light source used for curing the ultraviolet curable ink composition, a mercury lamp or a metal halide lamp is widely known. On the other hand, there is a strong demand for mercury-free from the viewpoint of environmental protection, and replacement with a GaN-based semiconductor ultraviolet light-emitting device is very useful industrially and environmentally. Furthermore, ultraviolet light-emitting diodes (UV-LEDs) and ultraviolet laser diodes (UV-LDs) are small, have a long lifetime, high efficiency, and are low in cost, and are expected as light sources for ultraviolet curable ink jets. Among these, UV-LED is preferable.

  Here, it is preferable to use an ultraviolet curable ink composition that can be cured by irradiation with an irradiation energy with an emission peak wavelength of preferably 350 to 420 nm. In this case, it is preferable to use a UV-LED. Such an ink composition can be obtained by including a photopolymerization initiator that decomposes upon irradiation with ultraviolet rays in the above wavelength range and / or a monomer that initiates polymerization upon irradiation with ultraviolet rays in the above wavelength range.

3. Examples Hereinafter, embodiments of the present invention will be described more specifically with reference to examples and comparative examples. However, the present embodiment is not limited to only these examples.

3.1. Preparation of aluminum pigment dispersion 1 3.1.1. Preparation of Aluminum Particle Dispersion On a PET film having a film thickness of 100 μm, cellulose acetate butyrate (butylation rate: 35 to 39%, manufactured by Kanto Chemical Co., Ltd.) 3.0% by mass and diethylene glycol diethyl ether (manufactured by Nippon Emulsifier Co., Ltd.) A resin layer thin film was formed on a PET film by uniformly applying a resin layer coating solution comprising 97% by mass by a bar coating method and drying at 60 ° C. for 10 minutes. Next, an aluminum vapor deposition layer having an average film thickness of 20 nm was formed on the resin layer using a vacuum vapor deposition device (“VE-1010 type vacuum vapor deposition device”, manufactured by Vacuum Device Co., Ltd.). Next, the laminate formed by the above method is simultaneously peeled, refined, and dispersed in diethylene glycol diethyl ether using a VS-150 ultrasonic disperser (manufactured by ASONE Co., Ltd.), and integrated ultrasonic dispersion An aluminum particle dispersion having a treatment time of 12 hours was prepared. The obtained aluminum particle dispersion was filtered with a SUS mesh filter having an opening of 5 μm to remove coarse particles. Further, the filtrate was put into a round bottom flask, and diethylene glycol diethyl ether was distilled off using a rotary evaporator. Thereby, the aluminum particle dispersion was concentrated, and then the concentration of the aluminum particle dispersion was adjusted to obtain a 5 mass% aluminum particle dispersion (hereinafter also referred to as “original dispersion”).

3.1.2. Next, 5.0 g of the obtained raw dispersion was put into a beaker, and 0.57 g of TEOS as a silica raw material and 0.1 g of 1 mol / L ammonia water as a basic catalyst were added thereto. The hydrolysis reaction was carried out by stirring at room temperature for a day. In this way, a dispersion of aluminum pigment (A) having a silica coating formed on the surface of aluminum particles was obtained. The 50% average particle diameter (R50) of the aluminum pigment (A) was measured using a flow type particle image analyzer (manufactured by Sysmex Corporation, model “FPIA-3000S”) and found to be 1.9 μm.

3.1.3. Washing Step The obtained dispersion of the aluminum pigment (A) was centrifuged (12,000 rpm, 60 minutes) to remove the solvent. Thereafter, the same amount of diethylene glycol diethyl ether as the removed solvent was added and stirred sufficiently. Further, this was centrifuged (12,000 rpm, 60 minutes) to remove the solvent, and 2- (2-vinyloxyethoxy) ethyl acrylate (made by Nippon Shokubai Co., Ltd., trade name “VEEA”) was added. By replacing the solvent and stirring sufficiently, an aluminum pigment dispersion 1 having a solid content of 10% by mass was obtained.

3.2. Preparation of Aluminum Pigment Dispersion 2 Aluminum Pigment Dispersion 2 was prepared in the same manner as in “3.1. Preparation of Aluminum Pigment Dispersion 1” except that “3.1.2. Silica Film Formation Step” was omitted. Prepared. That is, no silica coating is formed on the surface of the aluminum particles in the aluminum pigment dispersion 2.

3.3. Preparation of Aluminum Pigment Dispersion 3 Aluminum Pigment Dispersion 3 was prepared using an aluminum powder obtained by an atomization method. First, the aluminum ingot is melted in a melting furnace and kept at a temperature of 900 ° C., then the molten aluminum is poured into a crucible attached to an atomizer, and an aluminum rapidly solidified powder (average particle size: about 10 μm) is obtained by a gas atomization method. It was. The average particle diameter was measured using a laser diffraction particle size distribution measurement method. Next, the obtained aluminum rapidly solidified powder was crushed with a ball mill to obtain flat aluminum particles. Finally, the obtained flat aluminum particles and 2- (2-vinyloxyethoxy) ethyl acrylate (manufactured by Nippon Shokubai Co., Ltd., abbreviated name “VEEA”) were mixed and sufficiently stirred to obtain a solid content. A 10 mass% aluminum pigment dispersion 3 was obtained.

3.4. Surface observation with an electron microscope 3.4.1. Observation by Scanning Electron Microscope (SEM) The aluminum pigment (A) obtained in “3.1. Preparation of Aluminum Pigment Dispersion 1” was used as a photographic paper (“PM Photo Paper (Glossy) Model Number: KA450PSK”, Seiko Epson Corporation). And dried for 1 day at room temperature. Then, the surface of the aluminum pigment (A) was observed using a scanning electron microscope (manufactured by Hitachi High-Technologies Corporation, model “S-4700”). The SEM image is shown in FIG. According to FIG. 1, it was confirmed that the flat aluminum pigment was disposed on the recording medium so as to overlap. Thereby, it was shown that the shape of the aluminum pigment (A) obtained in “3.1. Preparation of Aluminum Pigment Dispersion 1” is a flat plate shape.

3.4.2. Observation by Transmission Electron Microscope (TEM) About the aluminum pigment (A) obtained in “3.1. Preparation of Aluminum Pigment Dispersion 1”, a transmission electron microscope (manufactured by Philips, model “TecnaiG2f30”) was used. The cross section was observed. The TEM images are shown in FIGS. In FIG. 2, it was confirmed that a plurality of aluminum pigments (A) overlapped. FIG. 3 is an image obtained by enlarging the area (a) of FIG. According to FIG. 3, it was confirmed that a silica film having a thickness of about 4.5 nm was formed on the surface of the aluminum pigment (A). From FIG. 3, it was also confirmed that a layer having a thickness of about 4.5 nm was formed between the aluminum layer and the silica coating. This layer is considered to be a layer having aluminum oxide. The layer is considered to be generated after the hydrolysis reaction between the hydroxyl groups present on the surface of the aluminum particles and TEOS, and derived from the hydroxyl groups present on the surface of the aluminum particles that have not reacted with TEOS. FIG. 4 is a TEM image showing a region different from FIG. The region (b) in FIG. 4 shows the end of the aluminum pigment (A), and it was confirmed that the silica coating was well formed at the end.

3.5. Preparation of UV curable ink composition Monomer, polymerization inhibitor, slip agent, photopolymerization initiator, and surfactant as necessary are mixed and dissolved completely so that the composition (mass%) shown in Table 1 is obtained. Then, any one of the aluminum pigment dispersions 1 to 3 was added dropwise thereto while stirring so that the concentrations shown in Table 1 were obtained. After completion of the dropwise addition, the mixture was mixed and stirred at room temperature for 1 hour, and further filtered through a 5 μm membrane filter to obtain each ultraviolet curable ink composition. However, when the aluminum pigment dispersion 3 was used, the step of filtering with a membrane filter was omitted.

In addition, the component used in Table 1 is as follows.
・ 2- (2-hydroxyethoxy) ethyl acrylate (made by Nippon Shokubai Co., Ltd., trade name “VEEA”)
・ Phenoxyethyl acrylate (manufactured by Osaka Organic Chemical Industry Co., Ltd., trade name “V # 192”)
・ Dicyclopentenyl acrylate (trade name “FA511ASL” manufactured by Hitachi Chemical Co., Ltd.)
・ Dicyclopentenyloxyethyl acrylate (manufactured by Hitachi Chemical Co., Ltd., trade name “FA512AS”)
・ Benzyl methacrylate (Kyoeisha Chemical Co., Ltd., trade name “Light Ester BZ”)
・ Dipentaerythritol hexaacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd., trade name “A-DPH”)
Amino acrylate (Daicel Cytec Co., Ltd., trade name “EBECRYL7100”)
・ Dimethylol tricyclodecane diacrylate (manufactured by Sartomer, trade name “SR833”)
IRGACURE 819 (manufactured by BASF Japan, bis (2,4,6-trimethylbenzoyl) -phenylphosphine oxide, photopolymerization initiator)
Speedcure TPO (manufactured by Lambson, diphenyl-2,4,6-trimethylbenzoylphosphine oxide, photopolymerization initiator)
Speedcure DETX (manufactured by Lambson, 2,4-diethylthioxanthen-9-one, photopolymerization initiator)
-BYK-UV3500 (by Big Chemie Japan Co., Ltd., polydimethylsiloxane having a polyether-modified acrylic group, slip agent)
・ P-methoxyphenol (Kanto Chemical Co., Ltd., trade name “MEHQ”, polymerization inhibitor)
・ Polystar OM (manufactured by NOF Corporation, high molecular sodium polycarboxylate)

3.6. Evaluation of UV-curable ink composition 3.6.1. Preparation of Evaluation Sample Using an inkjet printer PX-G5000 (manufactured by Seiko Epson Corporation), each of the nozzle rows was filled with the above ultraviolet curable ink composition. An A4 solid pattern image with an ink dot diameter of medium dots and an ink coating film thickness of 2 μm was recorded on a PET film at room temperature and normal pressure. The UV-LED was irradiated with ultraviolet light having a wavelength of 395 nm to cure the A4 solid pattern image. As described above, an evaluation sample in which an A4 solid pattern image was recorded on a PET film was produced.

3.6.2. Evaluation of curability As described above, the curability was evaluated by determining the irradiation energy when tack-free when performing the curing process of the solid pattern image recorded on the PET film. The irradiation energy [mJ / cm ² ] was determined from the product of the irradiation intensity [mW / cm ² ] on the irradiated surface irradiated from the light source and the irradiation duration [s]. The measurement of the irradiation intensity was performed using an ultraviolet intensity meter “UM-10” and a light receiving unit “UM-400” (both manufactured by Konica Minolta Sensing). Whether or not it can be said to be tack-free was determined under the following conditions. That is, the determination was made based on whether the ink sticks to the cotton swab or whether the cured ink on the recording medium is scratched. The cotton swab used at that time was a Johnson swab manufactured by Johnson & Johnson. The number of rubbing was 10 reciprocations and the rubbing strength was 100 g load. Moreover, the film thickness of the ink coating film (cured film) at the time of sclerosis | hardenability evaluation was 2 micrometers. The evaluation criteria are as follows. Of the evaluation criteria, “AA” and “A” are practically acceptable criteria. The evaluation results are also shown in Table 1 below.
“AA”: Tack-free irradiation energy of less than 800 mJ / cm ² “A”: Tack-free irradiation energy of 800 mJ / cm ² or more and less than 1200 mJ / cm ² “B”: Tack-free irradiation energy of 1200 mJ / cm ² or more Less than 1600 mJ / cm ² “C”: Irradiation energy when tack-free 1600 mJ / cm ² or more Note that this item of evaluating curability with irradiation energy when tack-free is a test for evaluating whether or not it is cured. No, it indicates an indication of good curability (whether or not it shows a predetermined state when rubbed with a cotton swab). Even if it is not scratched when rubbed, it is not always completely cured, and even if it is scratched, it may be somewhat cured.

3.6.3. Evaluation of Glossiness For the image recorded in “3.6.1. Preparation of Evaluation Sample”, the glossiness at 60 ° was measured using a gloss meter (manufactured by Konica Minolta, model “MULTI Gloss 268”). did. The evaluation criteria for the glossiness of the obtained image are as follows. Of the evaluation criteria, “A” is a practically acceptable criterion. The evaluation results are also shown in Table 1 below.
"A": Glossiness of 300 or more (clear metallic luster)
“B”: glossiness of 250 to less than 300 (matte metallic luster)
"C": Glossiness less than 250 (no metallic luster)

3.6.4. Evaluation of ejection stability The images recorded in “3.6.1. Preparation of evaluation sample” were visually observed for the presence or absence of ejection defects (nozzle omission), and ejection stability was evaluated according to the following evaluation criteria. “Nozzle missing” means that the ink that should normally be ejected from the nozzles attached to the print head is not ejected due to nozzle clogging and affects the printing result. Evaluation criteria for ejection stability are as follows. Of the evaluation criteria, “A” and “B” are practically acceptable criteria. The evaluation results are also shown in Table 1 below. For reference, the viscosity at 20 ° C. of each ink composition is also shown in Table 1 below.
“A”: No occurrence of ejection defects (nozzle missing) was observed.
“B”: There is a portion where a part of the solid image is not buried.
“C”: A plurality of solid images are not filled in.

3.6.5. Evaluation of Storage Stability The ultraviolet curable ink composition was placed in a sample bottle and completely sealed. The sample bottle was stored at 60 ° C. for 7 days, and then the viscosity when returned to 20 ° C. was measured. The storage stability was evaluated by determining the rate of change in viscosity (Δη) between the viscosity at 20 ° C. before storage and the viscosity at 20 ° C. after storage. The viscosity was measured with a viscoelasticity tester MCR-300 (manufactured by Pysica) after placing the sample bottle in a constant temperature bath at 20 ° C. for 1 hour. The evaluation criteria for storage stability are as follows. Among the evaluation criteria, “AA”, “A” and “B” are practically acceptable criteria. The evaluation results are also shown in Table 1 below.
“AA”: Viscosity change rate before and after storage at 60 ° C. for 7 days Δη = less than 5% “A”: Viscosity change rate before and after storage at 60 ° C. for 7 days Δη = 5% to less than 10% “B”: 60 ° C. 7 Viscosity change rate before and after daily storage Δη = 10% or more and less than 15% “C”: Viscosity change rate before and after storage at 60 ° C. for 7 days Δη = 15% or more and less than 20% “D”: Before and after storage at 60 ° C. for 7 days Viscosity change rate Δη = 20% or more

3.6.6. Evaluation Results As shown in Table 1, the ultraviolet curable ink compositions of Examples 1 to 11 are excellent in curability and gloss, and can be ejected without any problem in an ink jet recording apparatus. It was. Also, the storage stability was good.

  On the other hand, according to the ultraviolet curable ink composition of Comparative Example 1, since the silica coating is not formed on the surface of the aluminum particles, the active surface is exposed, and the active surface reacts with the monomer over time. Gelled and viscosity increased. Therefore, other evaluation tests could not be performed.

  According to the ultraviolet curable ink composition of Comparative Example 2, since the particle diameter of the aluminum particles was too large, the nozzles were clogged, and the ink could not be ejected.

  The present invention is not limited to the above-described embodiments, and various modifications can be made. 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 (10)

A coating film having a structure in which tetraethoxysilane is chemically bonded to the surface of aluminum particles which are flat particles having an average thickness of 5 nm to 30 nm and a 50% average particle diameter of 0.5 μm to 3 μm. An aluminum pigment (A) comprising:
Phenoxyethyl (meth) acrylate (B);
An ultraviolet curable ink jet ink composition comprising:   The ultraviolet curable inkjet ink composition according to claim 1, wherein the phenoxyethyl (meth) acrylate (B) is contained in an amount of 10% by mass to 70% by mass with respect to the total mass of the ink composition. Furthermore, the ultraviolet curable inkjet ink composition of Claim 1 or Claim 2 containing the monomer (C) shown by following General formula (1).
_{^{CH 2 = CR 1 -COO-R}} 2 -O-CH = CH-R 3 ... (1)
(In Formula (1), R ¹ represents a hydrogen atom or a methyl group. R ² represents a divalent organic residue having 2 to 20 carbon atoms. R ³ represents a hydrogen atom or 1 to 11 carbon atoms. Represents a monovalent organic residue.)   The ultraviolet curable inkjet ink composition according to claim 3, wherein the monomer (C) is 2- (2-vinyloxyethoxy) ethyl (meth) acrylate.   The ultraviolet curable inkjet ink composition according to claim 3 or 4, wherein the monomer (C) is contained in an amount of 10% by mass to 70% by mass with respect to the total mass of the ink composition.   The ultraviolet curable inkjet ink composition according to any one of claims 1 to 5, further comprising dipentaerythritol hexaacrylate.   The ultraviolet curable inkjet ink composition according to claim 6, wherein the dipentaerythritol hexaacrylate is contained in an amount of 5% by mass or more based on the total mass of the ink composition.   Furthermore, the ultraviolet curable inkjet ink composition as described in any one of Claim 1 thru | or 7 containing a photoinitiator. The ultraviolet curable inkjet ink composition according to any one of claims 1 to 8 , wherein the thickness of the coating film is 0.5 nm or more and 10 nm or less. The aluminum pigment (A) has at least one selected from more polycarboxylic acids and salts thereof on the surface of the film, an ultraviolet curable inkjet according to any one of claims 1 to 9 Ink composition.