JP7778465B2 - Photocurable ejection ink - Google Patents

Description

The present invention relates to a photocurable ink for ejection.

Ink used in devices such as inkjet printers and dispensers that eject ink and make it fly and land at the appropriate position must have a viscosity that is similar to that at the time of ejection and when it lands.

For example, Patent Document 1 discloses an ultraviolet-curable composition that is ejected by an inkjet method in order to improve the ejection stability of the ink, the ultraviolet-curable composition comprising a polymerizable compound, a metal powder, and a thixotropy inhibitor, and characterized in that the viscosity η1 [mPa·s] at a shear rate of 1000 s ⁻¹ and the viscosity η2 [mPa·s] obtained by applying a shear stress at a shear rate of 1000 s ⁻¹ for 10 minutes and then measuring the viscosity at ^a shear rate of 10 s −1 satisfy the relationship η2-η1≦3.

JP 2017-88820 A

In inkjet printing and additive manufacturing (for example, methods of producing three-dimensional objects by layering ink with a dispenser), it is preferable that the ink that lands at the printing position has high viscosity and does not wet and spread, in order to improve printing and modeling quality (for example, by suppressing ink bleeding) and modeling speed (for example, by increasing the thickness of ink layered at one time and accelerating the layering speed).

However, as shown in Patent Document 1 and other documents, it has traditionally been impossible to make the viscosity of ink when ejected significantly different from the viscosity of ink when it lands. Therefore, in order to increase the viscosity when it lands, it is necessary to also increase the viscosity when it is ejected. However, ink with a high viscosity when ejected is prone to clogging inside the ejection device and at the ejection ports. In particular, ink with a viscosity of 10,000 mPa·s or higher when it lands is preferable for the production of three-dimensional objects, but it is nearly impossible to properly eject ink with such a viscosity.

In other words, there was a trade-off between ink ejection performance and printability or modeling performance (e.g., print quality, modeling quality, or modeling speed).

In light of the above, the present invention aims to provide a photocurable ejection ink that can be used for printing or shaping while maintaining ejection properties.

The photocurable ejection ink according to a first aspect of the present invention comprises:
Contains a radical polymerizable compound, a photoinitiator, and a thixotropic agent,
The first viscosity measured at a shear rate of 10,000 ^s is 1,000 mPa s or less,
After applying a shear force at a shear rate of 10,000 ^s for 30 seconds, the second viscosity measured at a shear rate of ^{10 s} is 10,000 mPa s or more.
It is characterized by:

The above configuration allows the ink viscosity to be low when ejected and high when it lands, achieving both ink ejection performance and printability or shaping performance.

The radical polymerizable compound may be an acrylate monomer.

The above configuration allows the ink viscosity to be low when ejected and high when it lands, achieving both ink ejection performance and printability or shaping performance.

The thixotropic agent may be fine particles of silicon dioxide.

The above configuration allows the ink viscosity to be low when ejected and high when it lands, achieving both ink ejection performance and printability or shaping performance.

The radical polymerizable compound has a solubility parameter of less than 10, and
The thixotropic agent is a microparticle having a hydrophilic surface.
This may also be the case.

The above configuration allows the ink viscosity to be low when ejected and high when it lands, achieving both ink ejection performance and printability or shaping performance.

The microparticles having a hydrophilic surface are silicon dioxide microparticles whose surfaces are untreated.
This may also be the case.

The above configuration allows the ink viscosity to be low when ejected and high when it lands, achieving both ink ejection performance and printability or shaping properties. Furthermore, silicon dioxide microparticles with untreated surfaces are inexpensive, making them highly economical.

The radical polymerizable compound has a solubility parameter of 10 or more, and
The thixotropic agent is a microparticle having a hydrophobic surface.
This may also be the case.

The above configuration allows the ink viscosity to be low when ejected and high when it lands, achieving both ink ejection performance and printability or shaping performance.

The present invention allows for optimal printing or modeling while maintaining ink ejection properties.

A photocurable ejection ink according to one embodiment of the present invention contains a radically polymerizable compound, a photoinitiator, and a thixotropic agent. As described below, the thixotropic properties of the ink are controlled by the thixotropic agent so that the ink can be easily ejected from an ejection port such as a nozzle, and the ink is prevented from spreading after landing.

(discharge device)
The present ink is used by any ejection device capable of ejecting the present ink, particularly an ejection device that ejects the present ink in order to print the present ink onto a printing target (for example, a printing medium such as paper, a raw material roll such as cloth, or a building material such as a glass plate or a wooden board), or to form a three-dimensional object by layering the present ink.

The ejection device can be any device that can eject the ink from the ejection port and land it at a specific position. For example, it can be an inkjet printer equipped with an ejection mechanism (e.g., a print head) of an inkjet type (e.g., continuous type, on-demand type (piezo type, or thermal type)), or a dispenser equipped with an ejection mechanism (e.g., a syringe) of another liquid fixed-amount ejection type (e.g., a lead screw type, pneumatic type, etc.).

The ejection device preferably includes a mechanism for applying shear force to the ink by vibration, agitation, compression, or other means to prevent clogging of the ink from its storage unit (e.g., a tank, cartridge, etc.) to the ejection port (particularly at the ejection port). Examples of mechanisms for applying shear force include those described in JP-A-2005-212412, JP-A-2008-149594, and JP-A-8-216425.

(Radical polymerizable compound)
The radical polymerizable compound is not particularly limited as long as it is a compound having radical polymerizability, but acrylate is preferred in terms of polymerizability, durability of the cured product, solubility of the initiator and sensitizer, etc. In particular, acrylate monomers are preferred as the radical polymerizable compound.

Examples of the acrylate include monofunctional acrylates such as phenol EO-modified acrylate, nonylphenol EO-modified acrylate, and ethoxydiethylene glycol acrylate;
bifunctional acrylates such as hexanediol diacrylate, hexanediol EO-modified diacrylate, hydroxypivalic acid neopentyl glycol diacrylate, neopentyl glycol PO-modified diacrylate, tripropylene glycol diacrylate, dipropylene glycol diacrylate, bisphenol A EO-modified diacrylate, polyethylene glycol diacrylate, and polypropylene glycol diacrylate;
Examples of the polyfunctional acrylate include trimethylolpropane triacrylate, trimethylolpropane EO-modified triacrylate, trimethylolpropane PO-modified triacrylate, glycerin propoxy triacrylate, pentaerythritol triacrylate, pentaerythritol EO-modified tetraacrylate, ditrimethylolpropane tetraacrylate, and dipentaerythritol hexaacrylate.

These radical polymerizable compounds can be used alone or in combination.

Among these, bifunctional acrylates are preferred in terms of the mechanical properties of the resulting molded object, such as durability and rigidity, and a combination of PO-modified neopentyl glycol PO-modified diacrylate and bisphenol A EO-modified diacrylate is more preferred.

Examples of monofunctional acrylates that can be used include phenol EO-modified (n=2) acrylate (trade name: Miramer M142), phenol EO-modified (n=4) acrylate (trade name: Miramer M144), nonylphenol EO-modified (n=8) acrylate (trade name: Miramer M166), and ethoxydiethylene glycol acrylate (trade name: Miramer M170), all manufactured by Bigen Specialty Chemical Co., Ltd.

Bifunctional acrylates include hexanediol diacrylate (trade name: Miramer M200), hexanediol EO-modified diacrylate (trade name: Miramer M202), hydroxypivalic acid neopentyl glycol diacrylate (trade name: Miramer M210), neopentyl glycol PO-modified (n=2) diacrylate (trade name: Miramer M216), tripropylene glycol diacrylate (trade name: Miramer M220), dipropylene glycol diacrylate (trade name: Miramer M222), bisphenol A EO-modified (n=4) diacrylate (trade name: Miramer M240), and bisphenol A EO-modified (n=10) diacrylate (trade name: Miramer M240), all manufactured by Bigen Specialty Chemical Co., Ltd. Examples of materials that can be used include polyethylene glycol (molecular weight 400) diacrylate (abbreviated name: PEG400DA, trade name: Miramer M280), polyethylene glycol (molecular weight 300) diacrylate (abbreviated name: PEG300DA, trade name: Miramer M284), and polypropylene glycol diacrylate (trade name: Miramer M2040).

Examples of polyfunctional acrylates include trimethylolpropane triacrylate (trade name: Miramer M300), trimethylolpropane EO-modified (n=3) triacrylate (trade name: Miramer M3130), trimethylolpropane EO-modified (n=6) triacrylate (trade name: Miramer M3160), trimethylolpropane EO-modified (n=9) triacrylate (trade name: Miramer M3190), trimethylolpropane PO-modified (n=3) triacrylate (trade name: Miramer M360), glycerin propoxy triacrylate (trade name: Miramer M320), pentaerythritol triacrylate (trade name: Miramer M340), and pentaerythritol EO-modified tetraacrylate (trade name: Miramer M360), all manufactured by Bigen Specialty Chemical Co., Ltd. Examples of suitable acrylates include ditrimethylolpropane tetraacrylate (trade name: Miramer M4004), ditrimethylolpropane tetraacrylate (trade name: Miramer M410), and dipentaerythritol hexaacrylate (trade name: Miramer M600).

The content of the radical polymerizable compound in the ink is not particularly limited, but is preferably 70 to 99% by mass, more preferably 75 to 90% by mass, and particularly preferably 80 to 85% by mass.

(Photoinitiator/sensitizer)
The photoinitiator is not particularly limited as long as it generates radicals and cures the radical polymerizable compound when irradiated with light of a specific wavelength (for example, ultraviolet light).

Examples of initiators include aminoalkylphenone initiators and phosphine oxide initiators. Initiators can be used alone or in combination.

Among aminoalkylphenone initiators, α-aminoalkylphenone initiators are preferred, with 2-benzyl-2-(dimethylamino)-4'-morpholinobutyrophenone being more preferred.

Examples of aminoalkylphenone initiators that can be used include 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one (trade name: Omnirad 907 (formerly BASF's trade name: Irgacure 907)), 2-benzyl-2-(dimethylamino)-4'-morpholinobutyrophenone (trade name: Omnirad 369 (formerly BASF's trade name: Irgacure 369)), and 2-dimethylamino-2-(4-methylbenzyl)-1-(4-morpholin-4-yl-phenyl)butan-1-one (trade name: Omnirad 379EG (formerly BASF's trade name: Irgacure 379EG)), all manufactured by IGM Resins.

The phosphine oxide initiator is preferably an acylphosphine oxide photopolymerization initiator, with 2,4,6-trimethylbenzoyl-diphenylphosphine oxide and bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide being more preferred.

Examples of phosphine oxide initiators that can be used include 2,4,6-trimethylbenzoyl-diphenylphosphine oxide (trade name: Omnirad TPO H (formerly BASF's trade name: Irgacure TPO)) and bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (trade name: Omnirad 819 (formerly BASF's trade name: Irgacure 819)), both manufactured by IGM Resins.

In addition to the initiator, a sensitizer may also be blended into the ink. The sensitizer imparts photosensitivity to wavelength regions to which the initiator is not photosensitive, or increases the photosensitivity of the initiator.

For example, sensitizers include thioxanthone-based sensitizers, 2-isopropylthioxanthone, and 2,4-diethylthioxanthen-9-one. Sensitizers can be used alone or in combination.

Examples of thioxanthone sensitizers include thioxanthone, 2,4-diethyl-9H-thioxanthen-9-one, and 2-isopropylthioxanthone.

Examples of thioxanthone-based sensitizers that can be used include thioxanthone manufactured by Tokyo Chemical Industry Co., Ltd., 2,4-diethyl-9H-thioxanthen-9-one manufactured by Wako Pure Chemical Industries, Ltd., and 2-isopropylthioxanthone manufactured by Tokyo Chemical Industry Co., Ltd.

If only aminoalkylphenone initiators and thioxanthone sensitizers, or only phosphine oxide initiators and thioxanthone sensitizers, are used as initiators and sensitizers in the ink, there is a limit to the amount of each initiator that can be dissolved, which may result in an insufficient amount of initiator and insufficient internal curing of the ink. However, if an aminoalkylphenone initiator, a phosphine oxide initiator, and a thioxanthone sensitizer are used in combination in the ink, the total amount of initiator dissolved in the ink can be increased, and by incorporating a sufficient amount of initiator that generates a sufficient amount of radicals for curing when exposed to light with a wavelength that easily penetrates the ink (for example, light with a wavelength of 405 nm), the internal curing of the ink can be improved.

The total content of initiator and sensitizer in the ink is not particularly limited, but is preferably 1% to 25% by mass, more preferably 5% to 20% by mass, and particularly preferably 10% to 15% by mass. A curing agent content within this range is preferable in terms of the reactivity of the radical polymerizable compound.

(thixotropic agent)
The thixotropic agent is not particularly limited as long as it is a compound that imparts the desired thixotropy to the ink, but fine particles of silicon dioxide are preferred in terms of compatibility with radical polymerizable compounds (especially acrylate monomers).

Such silicon dioxide fine particles include fumed silica such as hydrophilic fumed silica and hydrophobic fumed silica, silica such as mesoporous silica, and alumina.

Furthermore, when the thixotropic agent is composed of fine particles, it is desirable to appropriately select the surface affinity based on the Hildebrand solubility parameter (SP value) of the radical polymerizable compound. The SP value of the radical polymerizable compound or a mixture thereof can be calculated according to conventional methods.

When the SP value of the radical polymerizable compound is less than approximately 10 (e.g., 9.5 or less, 9 or less), the thixotropic agent is preferably a fine particle with a hydrophilic surface. For example, such a fine particle can be hydrophilic fumed silica. Examples of hydrophilic fumed silica that can be used include Aerosil A255, Aerosil A300, and Aerosil A380 manufactured by Aerosil Co., Ltd. Furthermore, silicon dioxide fine particles with untreated surfaces can also be used as fine particles with a hydrophilic surface.

When the SP value of the radical polymerizable compound is approximately 10 or higher (e.g., 10.5 or higher, 11 or higher), the thixotropic agent is preferably a fine particle with a hydrophobic surface. For example, such a fine particle may be hydrophobic fumed silica. Examples of hydrophobic fumed silica that can be used include Aerosil R972, Aerosil R974, and Aerosil R104 manufactured by Aerosil Co., Ltd.

When the thixotropic agent is in the form of fine particles, the particle size can be any size as long as it can impart thixotropy to the ink and enable ejection, but it is preferable that the _D50 measured by laser diffraction method is 0.1 to 0.5 μm. For example, this D50 can be measured using a laser diffraction/scattering particle size distribution analyzer LA960 (manufactured by HORIBA).

The amount of thixotropic agent contained in the ink is not particularly limited, but the amount of thixotropic agent consisting of fine particles with hydrophilic surfaces is preferably 2 to 12% by mass, and more preferably 4 to 8% by mass, and the amount of thixotropic agent consisting of fine particles with hydrophobic surfaces is preferably 4 to 16% by mass, and more preferably 6 to 12% by mass.

(thixotropy)
The thixotropy of the ink is controlled by the thixotropic agent described above so that the ink can be easily ejected from an ejection port such as a nozzle and the ink is prevented from spreading after landing.

In particular, the thixotropy of the ink is preferably ^adjusted so that, when the viscosity of the ink measured at a shear rate of 10,000 s ⁻¹ is defined as a first viscosity and the viscosity of the ink measured at a shear rate of 10 ⁻¹ s ⁻¹ after applying a shear force continuously at a shear rate of 10,000 s −1 for 30 seconds is defined as a second viscosity, the second viscosity is higher than the first viscosity.

The first viscosity is preferably 1000 mPa·s or less, 500 mPa·s or less, or 100 mPa·s or less.

The second viscosity is preferably 10,000 mPa·s or more, 50,000 mPa·s or more, or 100,000 mPa·s or more.

The viscosity recovery time of the ink is preferably shorter than the time it takes for the ink to harden upon light irradiation after landing. For example, the recovery time is preferably 10 seconds or less, 5 seconds or less, or 2 seconds or less. The shorter the recovery time, the more the ink can be prevented from wetting and spreading before light irradiation. This further reduces ink bleeding and defects in the formation of three-dimensional objects.

The viscosity of the ink was measured at a temperature of 25°C, at a shear rate of 10 ^-1 (1/s) and a shear rate of 10 ⁴ (1/s), after a sufficient amount of time had passed and the viscosity (mPa·s) had stabilized. A rheometer (trade name: MCR302, manufactured by Anton Paar) or the like can be used to measure the viscosity. The viscosity recovery time of the ink was measured by shearing the ink at a low shear rate (10 ^-1 (1/s)) for 10 seconds at a temperature of 25°C while measuring the viscosity (mPa·s) over time, then rapidly increasing the shear rate to a high shear rate (10 ⁴ (1/s)) and shearing for 30 seconds, and then decreasing the shear rate to the low shear rate, and measuring the time it took for the ink viscosity to recover to 80% of the viscosity at the initial low shear rate. The viscosity recovery time can be measured using a rheometer (trade name: MCR302, manufactured by Anton Paar) or the like.

(Other ingredients)
The ink may contain other components within the scope of the present invention. Examples of other components include fillers, colorants, dispersants, initiators, plasticizers, surfactants, surface conditioners, leveling agents, antifoaming agents, antioxidants, charge-imparting agents, bactericides, preservatives, deodorizers, charge control agents, wetting agents, antiskinning agents, fragrances, pigment derivatives, and solvents. Some of these components may have a slight effect on the thixotropy of the ink, but such effects can be offset by appropriately adjusting the content of the thixotropic agent described above.

Examples of the filler include titanium oxide, zinc oxide (ZnO), zinc dioxide (ZnO ₂ ), antimony trioxide, indium tin oxide, aluminum oxide, and barium titanate.

Known dyes and pigments can be used as colorants. Pigments include inorganic and organic pigments.

Examples of inorganic pigments include titanium oxide, zinc oxide, zinc oxide, tripon, iron oxide, aluminum oxide, silicon dioxide, kaolinite, montmorillonite, talc, barium sulfate, calcium carbonate, cadmium red, red iron oxide, molybdenum red, chrome vermilion, molybdate orange, yellow lead, chrome yellow, cadmium yellow, yellow iron oxide, titanium yellow, chromium oxide, pyridian, cobalt green, titanium cobalt green, cobalt chrome green, ultramarine blue, Prussian blue, cobalt blue, cerulean blue, manganese violet, cobalt violet, and mica.

Examples of organic pigments include azo pigments, azomethines, polyazo pigments, phthalocyanines, quinacridone pigments, anthraquinone pigments, indigo pigments, thioindigo pigments, quinophthalone pigments, benzimidazolone pigments, isoindolines, isoindolinone pigments, and carbon black.

When using this ink as a cyan ink, C.I. Pigment Blue 1, 2, 3, 15:3, 15:4, 15:34, 16, 22, 60, etc. can be blended as colorants.

When using this ink as a magenta ink, colorants such as C.I. Pigment Red 5, 7, 12, 48 (Ca), 48 (Mn), 57 (Ca), 57:1, 112, 122, 123, 168, 184, 202, 209, and C.I. Pigment Violet 19 can be blended.

When this ink is used as a yellow ink, C.I. Pigment Yellow 1, 2, 3, 12, 13, 14C, 16, 17, 73, 74, 75, 83, 93, 95, 97, 98, 109, 110, 114, 120, 128, 129, 130, 138, 150, 151, 154, 155, 180, 185, etc. can be blended as colorants.

When using this ink as a black ink, it can be blended with HCF, MCF, RCF, LFF, SCF manufactured by Mitsubishi Chemical Corporation, Monarch and Regal manufactured by Cabot Corporation, Color Black, Special Black, and Printex manufactured by Degussa-Huls, Toka Black manufactured by Tokai Carbon, and Raven manufactured by Columbia.

The content of colorant in the optical ink is not particularly limited, but if a colorant is used, it is preferably 1 to 20% by mass, and more preferably 1 to 10% by mass in the ink.

When a pigment is used as the colorant, the ink may contain a dispersant to disperse the pigment.

Dispersants include low-molecular-weight dispersants and polymer-based dispersants, and more specifically, nonionic, cationic, and anionic surfactants, polyester-based polymer dispersants, acrylic-based polymer dispersants, and polyurethane-based polymer dispersants.

The ink can be prepared by any method, including, but not limited to, mixing and stirring various initiators, radical polymerizable compounds, and other components as needed.

Mixers include lead screw type feeders, three-one motors, magnetic stirrers, dispersers, homogenizers, ball mills, centrifugal mills, container-driven media mills such as planetary ball mills, high-speed rotating mills such as sand mills, media-agitated mills such as stirred tank mills, bead mills, high-pressure injection mills, dispersers, etc.

(Effects of this ink)
Conventionally, in inkjet printing and additive manufacturing (for example, a method of manufacturing a three-dimensional object by layering ink with a dispenser), it is preferable that the ink that lands at the printing position has high viscosity and does not wet and spread in order to improve the quality of printing and modeling (for example, by suppressing ink bleeding) and the speed of modeling (for example, by increasing the thickness of ink layered at one time and increasing the layering speed), but such high-viscosity ink is prone to ink clogging, and depending on the viscosity, it has even been impossible to eject it. In other words, there has been a trade-off between the ejectability of the ink and the printability or modeling ability.

However, according to the present invention, the thixotropy of the ink is suitably adjusted, so that when the ink is ejected and high shear force is applied, the viscosity is low enough to allow ejection, and when the ink is landed and no shear force is applied (or only extremely low shear force is applied), the viscosity is high enough that the ink barely spreads. This allows for both ink ejection properties and printability or modeling properties. Therefore, this ink allows for suitable printing or modeling while maintaining ejection properties.

(Example)
The present invention will be described below based on examples, but the present invention is not limited to these examples. Performance tests of various ink samples were carried out in the following manner.

(Thixotropy test)
(1-1) Viscosity/shear rate Using a rheometer (trade name: MCR302, manufactured by Anton Paar), the viscosity (mPa·s) was measured at a temperature of 25°C at a shear rate of 10 ⁻¹ (1/s) and a shear rate of 10 ⁴ (1/s) after sufficient time had passed and the viscosity had stabilized.
(1-2) Recovery Time Using a rheometer (trade name: MCR302, manufactured by Anton Paar), the ink was sheared at a low shear rate (10 ⁻¹ (1/s)) for 10 seconds at a temperature of 25°C while measuring the viscosity (mPa·s) over time. The shear rate was then suddenly increased to a high shear rate (10 ⁴ (1/s)) and sheared for 30 seconds, and then the shear rate was decreased to a low shear rate. The time until the viscosity of the ink recovered to 80% of the viscosity at the initial low shear rate was measured.

Example 1
1.5 parts of 2-benzyl-2-(dimethylamino)-4'-morpholinobutyrophenone (manufactured by BASF, trade name: Irgacure 369) as an aminoalkylphenone initiator, 1.5 parts of 2,4,6-trimethylbenzoyl-diphenylphosphine oxide (manufactured by BASF, trade name: TPO) and 1.5 parts of bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (manufactured by IGM Resins, trade name: Omnir) as phosphine oxide initiators, ad819) 2.5 parts, 2,4-diethylthioxanthen-9-one (manufactured by LAMBSON, trade name: DETX) 1.0 part as a thioxanthone-based sensitizer, functionalized amine coagent (manufactured by DSM, trade name: AgiSyn008) 2.0 parts as an amine-based initiator aid, neopentyl glycol PO-modified diacrylate (abbreviation name: NPG(PO)2DA) (manufactured by Bigen Specialty Chemical Co., Ltd., trade name: Miramer) as a radical polymerizable compound, M216, abbreviated name: PONPGDA M216, viscosity 30 mPa·s (25°C), acid value 0.3 mgKOH/g, hydroxyl value 20 mgKOH/g, molecular weight 328, refractive index 1.447) 52.93 parts, and bisphenol A EO-modified (n = 10) diacrylate (manufactured by Bigen Specialty Chemical Co., Ltd., trade name: Miramer M2100, abbreviated name: BPE10A M2100, viscosity 700 mPa·s (25°C), acid value 0.2 mgKOH/g, hydroxyl value 20 mgKOH/g, molecular weight 770, refractive index 1.516) 30.0 parts, and fumed silica (surface-untreated silica, manufactured by evonik, trade name: Aerosil) as a thixotropic agent. A300), and 0.07 parts of a fully crosslinked silicone polyether acrylate (manufactured by Evonik Resource Efficiency GmbH, trade name: TEGO RAD2100, short-chain siloxane skeleton/long-chain organically modified highly crosslinked additive) as a surface conditioner were added and mixed to obtain Ink E1.

Example 2
Ink E2 was obtained in the same manner as in Example 1, except that only 8.0 parts of 2,4,6-trimethylbenzoyl-diphenylphosphine oxide and 2.0 parts of 2,4-diethylthioxanthen-9-one, which are phosphine oxide initiators, were used as the initiators, 74.9 parts of neopentyl glycol PO-modified diacrylate was used as the radical polymerizable compound, the content of the thixotropic agent was 15.00 parts, and the content of the surface conditioner was 0.10 parts.

Example 3
[0111] Ink E3 was obtained in the same manner as in Example 1, except that the content of the thioxanthone sensitizer was changed to 2.0 parts, 100 parts of phenoxyethyl acrylate (manufactured by MIWON Corporation, trade name: Miramer M140) and 10.0 parts of pentaerythritol triacrylate (manufactured by MIWON Corporation, trade name: Miramer M340) were used as the radical polymerizable compounds, and 8.0 parts of fumed silica (surface-treated silica, manufactured by evonik GmbH, trade name: Aerosil R974) was used as the thixotropic agent.

(Comparative Example 1)
Ink CE1 was obtained in the same manner as in Example 3, except that the content of phenoxyethyl acrylate was 108 parts and no thixotropic agent was added.

(Comparative Example 2)
Ink CE2 was obtained in the same manner as in Example 3, except that the content of phenoxyethyl acrylate was 68.93 parts and 8.0 parts of fumed silica (surface-untreated silica, manufactured by Evonik, trade name: Aerosil A300) was used as the thixotropic agent.

Table 1 shows the viscosity measurements of the resulting inks E1, E2, E3, CE1, and CE2 at shear rates of 1 (1/s) and 1000 (1/s). The calculated SP values of the acrylates in inks E1 and E2 were less than 10, while the calculated SP values of the acrylates in inks E3, CE1, and CE2 were 10 or greater. Table 1 reveals that inks E1, E2, and E3 exhibit thixotropy, with a viscosity of approximately ¹⁰⁵ mPa·s at low shear rates, but decreasing to several hundred mPa·s as the shear rate increased. Furthermore, while ink E3 exhibits thixotropy, inks CE1 and CE2 do not. This suggests that when the solubility parameter of the radical polymerizable compound is 10 or greater, the thixotropic agent must have a hydrophobic surface.

*Ink CE1 of Comparative Example 1 did not exhibit thixotropy, so recovery time could not be measured.

The present invention allows for various embodiments and modifications without departing from the broad spirit and scope of the present invention. Furthermore, the above-described embodiments are intended to explain the present invention and do not limit the scope of the present invention. In other words, the scope of the present invention is defined by the claims, not the embodiments. Various modifications made within the scope of the claims and within the meaning of the equivalent inventions are considered to be within the scope of the present invention.

Claims (4)

A photocurable ejection ink containing a radical polymerizable compound, a photoinitiator, and a thixotropic agent,
When the solubility parameter of the radical polymerizable compound is less than 10, the thixotropic agent is a fine particle having a hydrophilic surface,
when the solubility parameter of the radical polymerizable compound is 10 or more, the thixotropic agent is a fine particle having a hydrophobic surface;
the ink has a first viscosity of 1000 mPa s or less when measured at a shear rate of 10000 ^s ;
a second viscosity measured after applying a shear force to the ink at a shear rate of 10,000 ^s for 30 seconds and then reducing the shear rate ^{to 10} s is 10,000 mPa s or more;
The ink is sheared at a shear rate of 10 ⁻¹ s ⁻¹ for 10 seconds at a temperature of 25° C., then the shear rate is increased to 10,000 s ⁻¹ and sheared for 30 seconds, and then the shear rate is reduced again to 10 ⁻¹ s ⁻¹ , and the viscosity of the ink subsequently recovers to 80% of the viscosity when initially sheared at a shear rate of 10 ⁻¹ s ⁻¹ in 10 seconds or less.
Photocurable ejection ink. The ink according to claim 1, wherein the radical polymerizable compound is an acrylate monomer. The ink described in claim 1 or 2, wherein the thixotropic agent is fine particles of silicon dioxide. the solubility parameter of the radical polymerizable compound is less than 10;
the thixotropic agent is a fine particle having a hydrophilic surface,
The microparticles having a hydrophilic surface are silicon dioxide microparticles whose surfaces are untreated.
The ink of claim 1 .