Active energy ray curable white ink composition, printing method, printing device, and printed matter

Abstract

To provide an active energy ray-curable white ink composition which is excellent in productivity due to correspondence to high-speed printing (in other words, curability), whiteness for preventing impairing of color development of color ink, concealing property, and discharge property for preventing image failures such as satellite deposition in printing.SOLUTION: An active energy ray-curable white ink composition contains (A) a nitrogen atom-containing monofunctional monomer, (B) a nitrogen atom-free monofunctional monomer having a glass transition point of 15°C or higher, (C) a polyfunctional monomer, (D) a polymerizable oligomer, (E) an acylphosphine oxide-based polymerization initiator, and (F) a white pigment. A content of the component (D) is 0.2 mass% or less with respect to the total amount of the active energy ray-curable white ink composition, a content of the component (E) is 6 mass% or more and 10 mass% or less with respect to the total amount of the active energy ray-curable white ink composition, and a content of the component (F) is 12 mass% or more and 17 mass% or less with respect to the total amount of the active energy ray-curable white ink composition.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to an active energy ray-curable white ink composition, a printing method, a printing apparatus, and a printed matter. [Background technology]

[0002] As the active energy ray-curable ink composition, mainly required are color inks (mainly cyan, magenta, yellow, and black) required for forming an image, white ink required for enhancing the color development of the image when printing on a transparent medium, and clear ink for surface protection and controlling the glossiness of the image.

[0003] The main qualities required of white ink include productivity for high-speed printing, i.e., curing ability, whiteness and hiding power to avoid impairing the color development of color inks, and ejection ability to prevent image defects such as satellite adhesion during printing.

[0004] In view of this, for example, an active energy ray-curable white inkjet ink composition containing a white pigment, a polymerizable monomer, an acylphosphine oxide initiator, and a non-acylphosphine oxide initiator has been proposed, with the objective of achieving both excellent whiteness, hiding properties, and curability (see, for example, Patent Document 1).

[0005] In addition, in order to address issues of ink storage stability and ejection properties such as satellite adhesion and frequency suitability, an active energy ray-curable ink composition has been proposed that contains a dispersion obtained by dispersing a pigment using a basic resin-type dispersant that contains a urethane skeleton and has excellent flow properties (see, for example, Patent Document 2).

[0006] An ink composition has been proposed which contains (component A) a white pigment, (component B) a polymerizable compound, (component C) a thioxanthone compound, and (component D) an acylphosphine compound, in which the content of component C is 0.03 to 0.8 wt % relative to the total weight of the ink composition, and the content of component D is 1 to 15 wt % relative to the total weight of the ink composition (see, for example, Patent Document 3). Summary of the Invention [Problem to be solved by the invention]

[0007] An object of the present invention is to provide an active energy ray-curable white ink composition that is excellent in productivity (i.e., curability) for high-speed printing, whiteness so as not to impair the color development of color inks, hiding power, and ejection ability so as to prevent image defects such as satellite adhesion during printing. Here, satellite adhesion refers to an image defect caused by a microdroplet (satellite) that does not merge with the main ink droplet and flies away, landing at a position that is shifted from the landing position of the main ink droplet, causing the microdroplet to adhere to an unintended area. [Means for solving the problem]

[0008] The active energy ray-curable white ink composition of the present invention as a means for solving the above problems contains (A) a nitrogen atom-containing monofunctional monomer, (B) a nitrogen atom-free monofunctional monomer having a glass transition temperature of 15° C. or higher, (C) a polyfunctional monomer, (D) a polymerizable oligomer, (E) an acylphosphine oxide-based polymerization initiator, and (F) a white pigment, wherein the content of the component (D) is 0.2 mass % or less with respect to the total amount of the active energy ray-curable white ink composition, the content of the component (E) is 6 mass % or more and 10 mass % or less with respect to the total amount of the active energy ray-curable white ink composition, and the content of the component (F) is 12 mass % or more and 17 mass % or less with respect to the total amount of the active energy ray-curable white ink composition. and the mass ratio of the component (A), the component (B), the component (C), and the component (E) [(A):(B):(C):(E)] is 1:3.0-6.5:0.5-1.5:0.3-2.0. . Effect of the Invention

[0009] According to the present invention, it is possible to provide an active energy ray-curable white ink composition that is excellent in productivity (i.e., curability) for high-speed printing, whiteness for not impairing the color development of color inks, hiding power, and ejection properties for preventing image defects such as satellite adhesion during printing. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic diagram showing an example of an image forming apparatus according to the present invention. [Diagram 2] FIG. 2 is a schematic diagram showing another example of an image forming apparatus according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] (Active energy ray curable white ink composition) The active energy ray-curable white ink composition of the present invention contains (A) a nitrogen-atom-containing monofunctional monomer, (B) a nitrogen-atom-free monofunctional monomer having a glass transition temperature of 15° C. or higher, (C) a polyfunctional monomer, (D) a polymerizable oligomer, (E) an acylphosphine oxide-based polymerization initiator, and (F) a white pigment, wherein the content of the component (D) is 0.2% by mass or less, relative to the total amount of the active energy ray-curable white ink composition, the content of the component (E) is 6% by mass or more and 10% by mass or less, relative to the total amount of the active energy ray-curable white ink composition, and the content of the component (F) is 12% by mass or more and 17% by mass or less, relative to the total amount of the active energy ray-curable white ink composition, and further contains other components as necessary.

[0012] In the conventional technology described in Patent Document 1 (JP Patent No. 5663919), the inventors' investigations revealed that the active energy ray curable white ink composition containing a non-acylphosphine oxide initiator is affected by the yellowish color of the polymerization initiator itself, and the whiteness is insufficient. In addition, since the content of the polymerization initiator, which has a relatively high molecular weight compared to the constituents such as polymerizable monomers, is high, the ligaments (tailing at the rear end of the main droplet) of the ejected droplets become long during printing, and there are concerns about deterioration of image quality due to mist, odor, and safety. Furthermore, in the conventional technology described in Patent Document 2 (JP 2014-214230 A), the evaluation of satellite adhesion is insufficient, and the quality of satellite adhesion required in recent inkjet printers is not achieved.

[0013] Furthermore, in the conventional technology described in Patent Document 3 (JP 2012-140491 A), 1.5 to 2.0 parts by mass of polymerizable oligomer are blended with respect to the total amount of ink in the examples. Polymerizable oligomers are compounds that have relatively high viscoelasticity, and inks containing 1.5 parts by mass or more of polymerizable oligomer tend to cause long tails of ejected ink droplets, resulting in printing problems such as mist.

[0014] As a result of extensive investigations, the present inventors have found that an active energy ray-curable white ink composition that contains a specific combination of (A) a nitrogen-containing monofunctional monomer, (B) a non-nitrogen-containing monofunctional monomer having a glass transition point of 15° C. or higher, and (C) a polyfunctional monomer by controlling the content of (D) a polymerizable oligomer, (E) an acylphosphine oxide polymerization initiator, and (F) a white pigment, has excellent whiteness, hiding power, ejection properties, and curability, and has completed the present invention.

[0015] <(A) Nitrogen atom-containing monofunctional monomer> The nitrogen atom-containing monofunctional monomer of component (A) is not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include (meth)acryloylmorpholine, N-vinylcaprolactam, N-vinyl(meth)acrylamide, etc. These may be used alone or in combination of two or more. The nitrogen atom-containing monofunctional monomer (A) has a relatively high glass transition point (Tg), and therefore the active energy ray-curable white ink composition containing the nitrogen atom-containing monofunctional monomer has good curability. The content of the nitrogen atom-containing monofunctional monomer of the component (A) is preferably 8% by mass or more, more preferably 10% by mass or more, and even more preferably 10% by mass or more and 20% by mass or less, based on the total amount of the active energy ray-curable white ink composition. When the content of the nitrogen atom-containing monofunctional monomer of the component (A) is 8% by mass or more, the curability of the active energy ray-curable white ink composition is good.

[0016] <(B) Nitrogen-free monofunctional monomer having a glass transition temperature (Tg) of 15°C or higher> The nitrogen atom-free monofunctional monomer of component (B) having a glass transition point (Tg) of 15° C. or higher is not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include isobornyl (meth)acrylate (Tg=88° C.), cyclic trimethylolpropane formal (meth)acrylate (Tg=32° C.), cyclohexyl (meth)acrylate (Tg=15° C.), 3,3,5-trimethylcyclohexanol (meth)acrylate (Tg=29° C.), etc. These may be used alone or in combination of two or more. When a monofunctional monomer is used alone, the curing properties are very poor. However, by containing a nitrogen-free monofunctional monomer having a glass transition point (Tg) of 15°C or higher as component (B) in addition to the nitrogen-containing monofunctional monomer as component (A), the ink composition contains multiple types of monofunctional monomers, which results in good curing properties. The glass transition temperature (Tg) of the monofunctional monomer of component (B) means the glass transition temperature of a homopolymer of the monofunctional monomer of component (B). When a catalog value of the monomer manufacturer is available, the value is adopted, and when not available, the value is measured by differential scanning calorimetry (DSC). The glass transition temperature of the homopolymer of the monofunctional monomer of the component (B) is 15°C or higher, and preferably 30°C or higher and 100°C or lower. The content of the nitrogen-free monofunctional monomer having a glass transition temperature (Tg) of 15° C. or higher in the component (B) is preferably 15% by mass or more and 60% by mass or less with respect to the total amount of the active energy ray-curable white ink composition.

[0017] <Other monofunctional monomers> The other monofunctional monomers are not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include 2-phenoxyethyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, 2-(2-ethoxyethoxy)ethyl (meth)acrylate, etc. These may be used alone or in combination of two or more.

[0018] <(C) Polyfunctional Monomer> The polyfunctional monomer of the component (C) is not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include polyethylene glycol (200) di(meth)acrylate, tripropylene glycol di(meth)acrylate, dipropylene glycol di(meth)acrylate, tricyclodecane dimethanol di(meth)acrylate, cyclohexane dimethanol di(meth)acrylate, etc. These may be used alone or in combination of two or more. The polyfunctional monomer of component (C) is expected to have the effect of improving fastness and curability by increasing the degree of crosslinking of the cured ink product. The content of the polyfunctional monomer of the component (C) is preferably 5% by mass or more and 15% by mass or less with respect to the total amount of the active energy ray-curable white ink composition.

[0019] <(D) Polymerizable Oligomer> The polymerizable oligomer of component (D) is not particularly limited and may be appropriately selected depending on the purpose, and examples thereof include CN963, CN964, CN965, and CN996 manufactured by Sartomer Corp. The polymerizable oligomer preferably has a structure having an acrylate group terminal, and more preferably has two polymerizable reactive groups in the molecule. The content of the polymerizable oligomer of the component (D) is 0.2% by mass or less, preferably less than 0.1% by mass, more preferably from 0.01% by mass to less than 0.1% by mass, and even more preferably from 0.01% by mass to 0.05% by mass, relative to the total amount of the active energy ray-curable white ink composition. The polymerizable oligomer is a compound that has relatively high viscoelasticity, and ink containing the oligomer tends to cause long tails in the ejected ink droplets, which may result in printing problems such as mist. Therefore, the active energy ray-curable white ink composition of the present invention preferably contains the oligomer in an amount of 0.2% by mass or less.

[0020] <(E) Acylphosphine oxide polymerization initiator> The acylphosphine oxide polymerization initiator of the component (E) is not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, etc. These may be used alone or in combination of two or more. Examples of commercially available acylphosphine oxide polymerization initiators include Omnirad TPO H: 2,4,6-trimethylbenzoyldiphenylphosphine oxide (manufactured by IGM Resins BV), Omnirad 819: bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (manufactured by IGM Resins BV), and the like. The content of the acylphosphine oxide polymerization initiator of the component (E) is from 6 to 10% by mass, and preferably from 6 to 8% by mass, based on the total amount of the active energy ray-curable white ink composition. When the content of the acylphosphine oxide-based polymerization initiator of the component (E) is from 6% by mass to 10% by mass, there is an advantage in that satellite adhesion can be reduced and sufficient curability can be achieved.

[0021] Here, the mass ratio of the component (A), the component (B), the component (C), and the component (E) [(A):(B):(C):(E)] is preferably 1:3.0-6.5:0.5-1.5:0.3-2.0, and more preferably 1:2.5-4.0:0.5-1.2:0.6-1.0. When the mass ratio [(A):(B):(C):(E)] satisfies the above range, there are advantages in that satellite adhesion can be reduced and the ink curing properties are excellent.

[0022] <Non-acylphosphinoxide polymerization initiator> The non-acylphosphine oxide polymerization initiator (a polymerization initiator that is not an acylphosphine oxide) is not particularly limited and can be appropriately selected depending on the purpose. Examples of the non-acylphosphine oxide polymerization initiator include 2,4-diethylthioxanthen-9-one and 2-isopropylthioxanthone. Since non-acylphosphine oxide polymerization initiators are often relatively yellow compounds, and when incorporated into a white ink, the cured ink may also have a yellowish tinge, it is preferable that the active energy ray-curable white ink composition of the present invention is substantially free of such initiators. Here, "substantially free" means that the content of non-acylphosphine oxide polymerization initiators is 0.1% by mass or less.

[0023] <(F) White pigment> The white pigment of the component (F) is not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include titanium oxide, iron oxide, tin oxide, zirconium oxide, iron titanate which is a composite oxide of iron and titanium, etc. Among these, titanium oxide is preferred because it has a high refractive index and can provide high whiteness. The number average primary particle diameter of the white pigment is preferably 100 nm or more and 500 nm or less, and more preferably 200 nm or more and 300 nm or less, from the viewpoints of dispersion stability and ejection stability. The content of the white pigment of the component (F) is from 12% by mass to 17% by mass, and preferably from 13.5% by mass to 15.5% by mass, based on the total amount of the active energy ray-curable white ink composition. When the content of the white pigment of the component (F) is from 12% by mass to 17% by mass, there is an advantage in that satellite adhesion can be reduced and sufficient hiding power can be obtained.

[0024] The white pigment is preferably used as a pigment dispersion by dispersing it with a dispersant. The dispersant is not particularly limited and can be appropriately selected depending on the purpose, but polymer dispersants are preferred, such as BYK JET-9150 and BYK JET-9151 manufactured by BYK.

[0025] <Other ingredients> The active energy ray-curable white ink composition of the present invention may contain other components as necessary. The other components are not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include polymerization inhibitors, leveling agents, defoamers, fluorescent brightening agents, penetration promoters, wetting agents (moisturizing agents), fixing agents, viscosity stabilizers, antifungal agents, preservatives, antioxidants, ultraviolet absorbers, chelating agents, pH adjusters, thickeners, etc.

[0026] <Preparation of active energy ray-curable white ink composition> The active energy ray-curable white ink composition of the present invention can be prepared using the various components described above. The preparation means and conditions are not particularly limited. For example, the ink composition can be prepared by charging a polymerizable monomer, an organic pigment, a dispersant, etc. into a dispersing machine such as a ball mill, a Kitty mill, a disk mill, a pin mill, or a Dyno mill, dispersing the ingredients to prepare a pigment dispersion, and then mixing a polymerization initiator, a polymerization inhibitor, a surfactant, etc. into the pigment dispersion.

[0027] <Viscosity> The viscosity of the active energy ray-curable white ink composition of the present invention may be appropriately adjusted depending on the application and means of application, and is not particularly limited. For example, when an ejection means is used such that the composition is ejected from a nozzle, the viscosity in the range of 20°C to 65°C, desirably the viscosity at 25°C, is 60 mPa·s or less, preferably 3 mPa·s or more and 40 mPa·s or less, more preferably 5 mPa·s or more and 30 mPa·s or less, even more preferably 5 mPa·s or more and 15 mPa·s or less, and particularly preferably 6 mPa·s or more and 12 mPa·s or less. It is particularly preferable that the viscosity range is satisfied without containing the organic solvent. The viscosity can be measured by using a cone rotor (1°34'×R24) with a cone plate type rotational viscometer VISCOMETER TVE-22L manufactured by Toki Sangyo Co., Ltd., at a rotation speed of 50 rpm and by appropriately setting the temperature of the constant temperature circulating water in the range of 20°C to 65°C. A VISCOMATE VM-150III can be used to adjust the temperature of the circulating water.

[0028] The active energy ray-curable white ink composition of the present invention preferably has a tail length (ligament length) of an ink droplet measured by the following method of 120 μsec or less, more preferably 100 μmsec or less, and even more preferably 80 μsec or less. If the tail length is 120 μsec or less, there is an advantage in that satellite adhesion can be reduced. <Measurement method> At a discharge temperature where the viscosity of the active energy ray-curable white ink composition is 11 mPa·s ± 0.5 mPa·s, only a single nozzle in a single row of the discharge head is driven to discharge droplets of 5 pL to 10 pL at an average droplet speed of 7.0 m / s ± 0.5 m / s. The time required for the main droplet to pass a position 1.3 mm from the nozzle face is measured, and this is the tail length of the ink droplet.

[0029] <Curing means> The active energy ray-curable white ink composition of the present invention can be cured by using active energy rays. The active energy rays used to cure the active energy ray curable white ink composition are not particularly limited, and may be any rays capable of imparting energy necessary for promoting the polymerization reaction of the polymerizable component in the active energy ray curable white ink composition, such as ultraviolet rays, electron beams, α rays, β rays, γ rays, and X-rays. In particular, when a high-energy light source is used, the polymerization reaction can be promoted without using a polymerization initiator. In addition, in the case of ultraviolet irradiation, mercury-free devices are strongly desired from the viewpoint of environmental protection, and replacement with GaN-based semiconductor ultraviolet light-emitting devices is very useful industrially and environmentally. Furthermore, ultraviolet light-emitting diodes (UV-LEDs) and ultraviolet laser diodes (UV-LDs) are small, have a long life, are highly efficient, and are low cost, making them preferable as ultraviolet light sources. The conditions for the active energy rays used in printing are, from the viewpoint of whiteness, an illumination intensity of 2,000 mW / cm 2 More than 3,000mW / cm 2 It is preferable that the cumulative energy is 2,000 mJ / cm or less. 2 More than 3,000mJ / cm 2 It is preferable that:

[0030] (Active energy beam curable inkjet ink set) The active energy ray-curable inkjet ink set used in the present invention contains the active energy ray-curable white ink composition of the present invention, and at least one ink composition selected from a cyan ink composition, a magenta ink composition, a yellow ink composition, and a black ink composition. The cyan ink composition, magenta ink composition, yellow ink composition, and black ink composition are all preferably actinic energy ray-curable ink compositions. The actinic radiation curable inkjet ink set can improve the color development of images when printed on transparent media.

[0031] <Application> The use of the active energy ray-curable white ink composition of the present invention is not particularly limited as long as it is in a field in which active energy ray-curable materials are generally used, and can be appropriately selected depending on the purpose. Examples of the use include molding resins, paints, adhesives, insulating materials, release agents, coating materials, sealing materials, various resists, and various optical materials.

[0032] Furthermore, the active energy ray curable white ink composition of the present invention can be used as an ink to form two-dimensional characters and images, and decorative coatings on various substrates, and can also be used as a material for three-dimensional modeling to form a three-dimensional image (three-dimensional object). This material for three-dimensional modeling may be used, for example, as a binder between powder particles used in a powder lamination method in which a three-dimensional modeling is performed by repeatedly curing and laminating powder layers, or may be used as a three-dimensional construction material (model material) or a support member (support material) used in an additive manufacturing method (stereolithography) as shown in FIG. 2. FIG. 2 shows a method of ejecting the active energy ray curable white ink composition of the present invention into a predetermined area, irradiating it with active energy rays, and laminating the cured products to perform three-dimensional modeling (details will be described later).

[0033] As a three-dimensional modeling device for forming a three-dimensional object using the active energy ray-curable white ink composition of the present invention, a known three-dimensional modeling device can be used, and is not particularly limited. For example, the three-dimensional modeling device may be one that is equipped with a means for containing, a supplying means, a discharging means, an active energy ray irradiation means, and the like for the composition. The present invention also includes a molded article obtained by processing a cured product obtained by curing the active energy ray-curable white ink composition or a structure on a substrate on which the cured product is formed. The molded article is, for example, a product obtained by subjecting a cured product or structure formed into a sheet or film shape to a molding process such as heat stretching or punching, and is suitably used for applications requiring molding after surface decoration, such as meters and operation panels for automobiles, office automation equipment, electric and electronic devices, and cameras. The substrate is not particularly limited and can be appropriately selected depending on the purpose. Examples of the substrate include paper, thread, fiber, cloth, leather, metal, plastic, glass, wood, ceramics, and composite materials thereof. From the viewpoint of processability, a plastic substrate is preferred.

[0034] <<Composition storage container>> The composition-storing container used in the present invention means a container in which the active energy ray-curable white ink composition of the present invention is stored, and is suitable for use in the above-mentioned applications. For example, when the composition of the present invention is used for ink, a container storing the ink can be used as an ink cartridge or ink bottle, which eliminates the need to directly touch the ink during ink transport, ink replacement, and other operations, and can prevent hands, fingers, and clothing from getting dirty. In addition, it is possible to prevent foreign matter such as dust from getting mixed into the ink. The shape, size, material, and the like of the container itself may be any suitable one for the application and usage, and are not particularly limited, but it is preferable that the material be a light-shielding material that does not transmit light, or that the container be covered with a light-shielding sheet or the like.

[0035] <Image forming method and image forming apparatus (printing method and printing apparatus)> In the printing method of the present invention, the active energy ray-curable white ink composition of the present invention is ejected using an ejection head. The printing device of the present invention has the active energy ray-curable white ink composition of the present invention and an ejection head that ejects the active energy ray-curable white ink composition.

[0036] The printing method of the present invention may use active energy rays or heating. In order to cure the active energy ray-curable white ink composition of the present invention with active energy rays, an irradiation step of irradiating active energy rays is provided, and the image forming apparatus of the present invention includes an irradiation means for irradiating active energy rays and a storage section for storing the active energy ray-curable white ink composition of the present invention, and the storage section may store the container. Furthermore, the image forming apparatus may include a discharge step of discharging the active energy ray-curable white ink composition and a discharge means. The discharge method is not particularly limited, and examples thereof include a continuous jet type and an on-demand type. Examples of the on-demand type include a piezo type, a thermal type, and an electrostatic type.

[0037] FIG. 1 is an example of an image forming apparatus equipped with an inkjet ejection means. The ink is ejected onto a recording medium 22 supplied from a supply roll 21 by printing units 23a, 23b, 23c, and 23d each equipped with an ink cartridge and an ejection head for each color of active energy ray curable ink of yellow, magenta, cyan, and black. Then, the ink is cured by irradiating the ink with active energy rays from light sources 24a, 24b, 24c, and 24d for curing the ink, forming a color image. Then, the recording medium 22 is conveyed to a processing unit 25 and a print winding roll 26. Each printing unit 23a, 23b, 23c, and 23d may be provided with a heating mechanism so that the ink is liquefied in the ink ejection section. If necessary, a mechanism for cooling the recording medium to about room temperature by contact or non-contact may be provided. In addition, the inkjet recording method can be either a serial method in which the ejection head is moved to eject ink onto the recording medium, which moves intermittently according to the width of the ejection head, or a line method in which the recording medium is moved continuously and ink is ejected onto the recording medium from a head held at a fixed position. The actinic energy ray-curable white ink composition is preferably discharged at a temperature such that the viscosity of the ink composition during discharge is 11 mPa·s±0.5 mPa·s. The ejection head ejects 5 pL to 35 pL of droplets of the active energy ray-curable white ink composition at an average droplet speed of 7.0 m / s ± 0.5 m / s, and ejects 5 pL to 9 pL of droplets of the active energy ray-curable white ink composition at an average droplet speed of 7.0 m / s ± 0.5 m / s. As the ejection head, it is preferable to use, for example, Ricoh Company, Ltd.'s MH5420 (7 pL (single drop)), MH5440 (7 pL to 35 pL (multi-drop)), MH5320 (5 pL (single drop)), or MH5340 (5 pL to 15 pL (multi-drop)), from the standpoints of high ink resistance resulting in a long head life, the ability to eject high viscosity ink due to the inclusion of a heater, good waveform response, and a large maximum ejectable droplet volume resulting in high productivity. The recording medium 22 is not particularly limited, but may be paper, film, ceramics, glass, metal, a composite material thereof, or the like, and may be in sheet form. The recording medium may be configured to allow only one-sided printing, or may be configured to allow both-sided printing. The recording medium is not limited to those generally used as recording media, and may be cardboard, building materials such as wallpaper and flooring, concrete, cloth for clothing such as T-shirts, textiles, leather, or the like, as appropriate. The present invention is particularly effective with transparent media, since it is effective in hiding satellite adhesion, etc. Furthermore, the irradiation of active energy rays from the light sources 24a, 24b, and 24c may be weakened or omitted, and after printing multiple colors, the active energy rays may be irradiated from the light source 24d, which can save energy and reduce costs.

[0038] Recorded items recorded with the active energy ray-curable white ink composition of the present invention include not only items printed on smooth surfaces such as ordinary paper or resin films, but also items printed on uneven printing surfaces and items printed on printing surfaces made of various materials such as metals and ceramics. In addition, by laminating two-dimensional images, it is also possible to form an image with a partially three-dimensional effect (an image consisting of two and three dimensions) or a three-dimensional object. Fig. 2 is a schematic diagram showing an example of another image forming apparatus (apparatus for forming a three-dimensional solid image) according to the present invention. The image forming apparatus 39 in Fig. 2 uses a head unit (movable in the AB direction) in which inkjet heads are arranged, and ejects a first active energy ray-curable composition from ejection head unit 30 for a model and ejects a second active energy ray-curable white ink composition having a different composition from the first active energy ray-curable white ink composition from ejection head units 31 and 32 for a support, and laminates these compositions while curing them with adjacent ultraviolet ray irradiation means 33 and 34. More specifically, for example, the second active energy ray curable composition is discharged from the support discharge head units 31 and 32 onto the object support substrate 37, and the first support layer having a reservoir is formed by irradiating the composition with active energy rays to solidify the composition, and then the first active energy ray curable composition is discharged from the object discharge head unit 30 into the reservoir, and the first object layer is formed by irradiating the composition with active energy rays to solidify the composition. This process is repeated several times while lowering the stage 38 movable in the vertical direction according to the number of layers to laminate the support layer and the object layer to produce a three-dimensional object 35. Thereafter, the support layer 36 is removed as necessary. Note that, although only one object discharge head unit 30 is provided in FIG. 2, two or more object discharge head units 30 may be provided.

[0039] (Printed material) The printed matter of the present invention is printed using the active energy ray-curable white ink composition of the present invention. The printed matter has a cured product of the active energy ray-curable white ink composition of the present invention on a recording medium.

[0040] In the present invention, the terms image formation, recording, printing, printing, etc. are all synonymous. Recording medium, media, and printed material are all synonymous. EXAMPLES

[0041] Examples of the present invention will be described below, but the present invention is not limited to these examples.

[0042] (Preparation Example of White Pigment Dispersion) -Preparation of White Pigment Dispersion A- White pigment dispersion A was prepared by mixing 50 mass% of white pigment (product name: JR301, number average primary particle size: 300 nm, manufactured by Teika Corporation) with 45 mass% of PEA (phenoxyethyl acrylate, manufactured by Osaka Organic Chemical Industry Co., Ltd.) as a dispersion medium and 5 mass% of BYK JET-9151 (manufactured by BYK) as a dispersant using zirconia beads and a bead mill disperser.

[0043] (Examples 1 to 14 and Comparative Examples 1 to 10) - Manufacturing of white ink - Based on the ink compositions shown in Tables 1 to 5, each raw material was mixed and an ink mixture was obtained using a three-one motor. The ink mixture was then filtered using a capsule filter with an absolute filtration accuracy of 1.0 μm and filled into a clean bottle to obtain the white inks of Examples 1 to 14 and Comparative Examples 1 to 10.

[0044] Next, various properties of each of the obtained white inks were evaluated as follows. The results are shown in Tables 1 to 5.

[0045] <Length of the tail of the discharged droplet (ligament length)> An ink ejection test was carried out as follows using a printing device (EV2500, manufactured by Ricoh Co., Ltd.) equipped with an ejection head MH5420 manufactured by Ricoh Co., Ltd. Note that as the ejection head, MH5440, MH5320, and MH5340 (all manufactured by Ricoh Co., Ltd.) can be used instead of MH5420. A single nozzle in a single row of the ejection head was driven to eject droplets of 7 pL ± 2 pL at an average droplet speed of 7.0 m / s ± 0.5 m / s, at an ejection temperature where the viscosity of each white ink was 11 mPa·s ± 0.5 mPa·s. The point at which the main droplet of the ejected ink passed 1.3 mm from the nozzle face was defined as 0 μsec. The time it took for the trailing edge of the trailing ink behind the main droplet to pass 1.3 mm from the nozzle face was then defined as the length of the trailing ink droplet, and it was evaluated according to the following criteria. A score of △ or better was considered to be feasible. [Evaluation Criteria] ◎: 80μsec or less 〇: More than 80μsec but less than 100μsec △: More than 100μsec but less than 120μsec ×: More than 120μsec

[0046] <Curability> As a non-permeable substrate, a polyethylene terephthalate (PET) film with a smooth surface was used. Each white ink was applied to the surface of a PET film using a bar coater so that the dry film thickness was 10 μm±2 μm. The light source is an LED with a central wavelength of 395 nm, and the illuminance is 1,000 ± 100 mW / cm 2 The white ink layer on the PET film prepared above was irradiated with any desired cumulative energy by adjusting the irradiation time under the irradiation conditions above. When the ink film surface was touched with a finger 10 seconds after irradiation with the LED, the minimum integrated energy value at which the ink did not feel sticky was taken as the measurement of curability, and it was evaluated according to the following criteria. Note that a rating of △ or higher is a workable level. [Evaluation Criteria] ○: 1,000mJ / cm 2 below △: 1,000mJ / cm 2 Super 1,500mJ / cm 2 below ×: More than 1,500mJ / cm2

[0047] <Whiteness> At a resolution of 600 dpi x 1,200 dpi, the ink was applied to the surface of a transparent substrate made of Mitsubishi Gas Chemical Company's Iupilon NF2000 with an ink deposition amount of 1.7 mg / cm 2 ±0.1mg / cm 2 Each white ink was printed so as to obtain the following: The conditions for the active energy rays used in printing are an illumination intensity of 2,000 mW / cm 2 More than 3,000mW / cm 2 Less than or equal to 2,000mJ / cm 2 More than 3,000mJ / cm 2It was decided. The a of each print was measured using X Rite exact (manufactured by X Rite). * , b * From the value of c * ={(a * ) 2 +(b * ) 2} 1 / 2 The saturation c calculated using the formula * The results were measured and evaluated according to the following criteria. A score of △ or higher was considered to be feasible. [Evaluation Criteria] 〇:c * is 1.5 or less △:c * is greater than 1.5 and less than 3.0 ×:c * is over 3.0

[0048] <Concealment> At a resolution of 600 dpi x 1,200 dpi, the ink was applied to the surface of a transparent substrate made of Mitsubishi Gas Chemical Company's Iupilon NF2000 with an ink deposition amount of 4.6 mg / cm 2 ±0.1mg / cm 2 Each white ink was printed so as to obtain the following: The black transmission density was measured using an X-Rite939 (manufactured by X-Rite) using the printed white ink image and black paper, and evaluated according to the following criteria. △ or better is a workable level. [Evaluation Criteria] ◎: Black transmission density is 0.10 or less ○: Black transmission density is more than 0.10 and less than 0.13 △: Black transmission density is more than 0.13 and less than 0.15 ×: Black transmission density is more than 0.15

[0049] [Table 1]

[0050] [Table 2]

[0051] [Table 3]

[0052] [Table 4]

[0053] [Table 5] *In Table 5, "-" for the whiteness and hiding power of Comparative Example 8 means that it could not be measured.

[0054] Details of each component in Tables 1 to 5 are as follows. <(A) Nitrogen atom-containing monofunctional monomer> ACMO: Acryloylmorpholine (KJ Chemicals Co., Ltd.) NVC: N-vinylcaprolactam (Ashland)

[0055] <(B) Nitrogen-free monofunctional monomer having a glass transition temperature (Tg) of 15°C or higher> IBXA: Isobornyl acrylate (Osaka Organic Chemical Industry Ltd., Tg = 88°C) CHA: Cyclohexyl acrylate (Osaka Organic Chemical Industry Ltd., Tg = 15°C) CTFA: Cyclic trimethylolpropane formal acrylate (Osaka Organic Chemical Industry Ltd., Tg = 32°C)

[0056] <<Measurement of glass transition temperature (Tg)>> The polymerization of the nitrogen-free monofunctional polymerizable monomer (B) was carried out by a general solution polymerization method. a: A toluene solution of 10% by mass of the nitrogen atom-free monofunctional polymerizable monomer (B) b: 5% by mass of azobisisobutyronitrile as a polymerization initiator The above a and b were purged with nitrogen, sealed in a test tube, and shaken in a warm bath at 60° C. for 6 hours to synthesize a polymer. Thereafter, the polymer was reprecipitated in a solvent in which the non-nitrogen-atom-containing monofunctional polymerizable monomer was soluble and the polymer was insoluble (eg, methanol, petroleum ether, etc.), and the polymer was isolated by filtration. The obtained polymer was subjected to DSC measurement. The DSC measurement was performed using a Seiko Instruments DSC120U at a measurement temperature of 30° C. to 300° C. and a heating rate of 2.5° C. per minute.

[0057] <Other monofunctional monomers> THFA: Tetrahydrofurfuryl acrylate (Osaka Organic Chemical Industry Ltd.) PEA: 2-phenoxyethyl acrylate (Osaka Organic Chemical Industry Ltd.)

[0058] <(C) Polyfunctional Monomer> DPGDA: Dipropylene glycol diacrylate (manufactured by Sartomer) ·TPGDA: Tripropylene glycol diacrylate (manufactured by Sartomer)

[0059] <(D) Polymerizable Oligomer> CN963: Polyester acrylate oligomer (manufactured by Sartomer)

[0060] <(E) Acylphosphine oxide polymerization initiator> Omnirad TPO H: 2,4,6-trimethylbenzoyldiphenylphosphine oxide (IGM Resins BV) Omnirad 819: Bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (IGM Resins BV)

[0061] <Non-acylphosphine oxide polymerization initiator> ITX: 2-isopropylthioxanthone (IGM Resins BV) DETX: 2,4-diethylthioxanthen-9-one (IGM Resins BV)

[0062] For example, aspects of the present invention are as follows. <1> (A) a nitrogen atom-containing monofunctional monomer, (B) a nitrogen atom-free monofunctional monomer having a glass transition temperature of 15°C or higher, (C) a polyfunctional monomer, (D) a polymerizable oligomer, (E) an acylphosphine oxide-based polymerization initiator, and (F) a white pigment, the content of the component (D) is 0.2% by mass or less relative to the total amount of the active energy ray-curable white ink composition, the content of the component (E) is 6% by mass or more and 10% by mass or less with respect to the total amount of the active energy ray-curable white ink composition, The content of the component (F) is from 12% by mass to 17% by mass, based on the total amount of the active energy ray-curable white ink composition. <2> the mass ratio of the component (A), the component (B), the component (C), and the component (E) [(A):(B):(C):(E)] is 1:3.0-6.5:0.5-1.5:0.3-2.0; <1> 2. The active energy ray-curable white ink composition according to claim 1 . <3> The content of the component (E) is 6% by mass or more and 8% by mass or less with respect to the total amount of the active energy ray-curable white ink composition. <1> from <2> 10. The active energy ray-curable white ink composition according to claim 9, <4> The content of the component (F) is 13.5% by mass or more and 15.5% by mass or less with respect to the total amount of the active energy ray-curable white ink composition. <1> from <3> 10. The active energy ray-curable white ink composition according to claim 9, <5> The above-mentioned polymerization initiator is substantially free of a non-acylphosphine oxide-based polymerization initiator. <1> from <4> 10. The active energy ray-curable white ink composition according to claim 9, <6> The content of the component (D) is less than 0.1% by mass based on the total amount of the active energy ray-curable white ink composition. <1> from <5> 10. The active energy ray-curable white ink composition according to claim 9, <7> The content of the component (A) is 10% by mass or more based on the total amount of the active energy ray-curable white ink composition. <1> from <6> 10. The active energy ray-curable white ink composition according to claim 9, <8> The ink droplet tail length measured by the following method is 120 μsec or less. <1> from <7> 10. The active energy ray-curable white ink composition according to claim 9, <Measurement method> At a discharge temperature where the viscosity of the active energy ray-curable white ink composition is 11 mPa·s ± 0.5 mPa·s, only a single nozzle in a single row of the discharge head is driven to discharge droplets of 5 pL to 10 pL at an average droplet speed of 7.0 m / s ± 0.5 m / s. The time required for the main droplet to pass a position 1.3 mm from the nozzle face is measured, and this is the tail length of the ink droplet. <9> The above <1> from <8> and discharging the active energy ray-curable white ink composition according to any one of the above items from a discharge head. <10> and ejecting 7 pL±2 pL of droplets of the active energy ray-curable white ink composition at an average droplet speed of 7.0 m / s±0.5 m / s at a temperature at which the viscosity of the active energy ray-curable white ink composition during ejection is 11 mPa·s±0.5 mPa·s. <9> 2 is a printing method according to the present invention. <11> The above <1> from <8> and an active energy ray-curable white ink composition according to any one of the preceding claims. an ejection head that ejects the active energy ray-curable white ink composition; The printing device is characterized by having: <12> The above <1> from <8> 2. A printed matter printed using the active energy ray-curable white ink composition according to claim 1.

[0063] The above <1> from <8> The active energy ray-curable white ink composition according to any one of the preceding claims. <9> from <10> The printing method according to any one of the preceding claims. <11> and the printing device according to the above. <12> According to the printed matter described in the above, the conventional problems can be solved and the object of the present invention can be achieved. [Explanation of symbols]

[0064] 21 Supply roll 22 Recording media 23a, 23b, 23c, 23d Printing units 24a, 24b, 24c, 24d light source 25 Processing Unit 26 Printed matter winding roll 30. Discharge head unit for modeling 31, 32 Support ejection head unit 33, 34 Ultraviolet irradiation means 35 Three-dimensional sculpture 36 Support layer section 37 Object support substrate [Prior art documents] [Patent documents]

[0065] [Patent Document 1] Patent No. 5663919 [Patent Document 2] JP 2014-214230 A [Patent Document 3] JP 2012-140491 A

Claims

1. (A) a nitrogen atom-containing monofunctional monomer, (B) a nitrogen atom-free monofunctional monomer having a glass transition temperature of 15° C. or higher, (C) a polyfunctional monomer, (D) a polymerizable oligomer, (E) an acylphosphine oxide-based polymerization initiator, and (F) a white pigment, the content of the component (D) is 0.2% by mass or less relative to the total amount of the active energy ray-curable white ink composition, the content of the component (E) is 6% by mass or more and 10% by mass or less with respect to the total amount of the active energy ray-curable white ink composition, the content of the component (F) is 12% by mass or more and 17% by mass or less with respect to the total amount of the active energy ray-curable white ink composition, an active energy ray-curable white ink composition, wherein a mass ratio of the component (A), the component (B), the component (C), and the component (E) [(A):(B):(C):(E)] is 1:3.0 to 6.5:0.5 to 1.5:0.3 to 2.

0.

2. 2 . The active energy ray-curable white ink composition according to claim 1 , wherein a content of the component (E) is 6% by mass or more and 8% by mass or less with respect to a total amount of the active energy ray-curable white ink composition.

3. 3. The active energy ray-curable white ink composition according to claim 1, wherein a content of the component (F) is 13.5 mass % or more and 15.5 mass % or less with respect to a total amount of the active energy ray-curable white ink composition.

4. The active energy ray-curable white ink composition according to claim 1 , which is substantially free of a non-acylphosphine oxide polymerization initiator.

5. 5. The active energy ray-curable white ink composition according to claim 1, wherein the content of the component (D) is less than 0.1 mass % with respect to the total amount of the active energy ray-curable white ink composition.

6. 6. The active energy ray-curable white ink composition according to claim 1, wherein the content of the component (A) is 10 mass % or more with respect to the total amount of the active energy ray-curable white ink composition.

7. 7. The active energy ray-curable white ink composition according to claim 1, wherein the tail length of the ink droplets measured by the following method is 120 μsec or less. <Measurement method> At a discharge temperature at which the viscosity of the active energy ray-curable white ink composition becomes 11 mPa·s±0.5 mPa·s, only a single nozzle in a single row of the discharge head is driven to discharge droplets of 5 pL to 10 pL at an average droplet speed of 7.0 m / s±0.5 m / s. The time required for the main droplet to pass a position 1.3 mm from the nozzle face is measured, and this is defined as the tail length of the ink droplet.

8. A printing method comprising ejecting the active energy ray-curable white ink composition according to claim 1 using an ejection head.

9. 9. The printing method according to claim 8, wherein droplets of 7 pL±2 pL of the active energy ray-curable white ink composition are ejected at an average droplet speed of 7.0 m / s±0.5 m / s at a temperature at which the viscosity of the active energy ray-curable white ink composition during ejection is 11 mPa·s±0.5 mPa·s.

10. The active energy ray-curable white ink composition according to claim 1 , an ejection head that ejects the active energy ray-curable white ink composition; A printing device comprising:

11. A printed matter printed using the active energy ray-curable white ink composition according to claim 1 .

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