White photocuring inkjet ink and preparation method thereof

Abstract

The invention provides white photocuring ink-jet ink and a preparation method thereof, and belongs to the technical field of ink-jet ink. The white photocuring ink-jet ink is prepared from the following components in parts by mass: 30 to 60 parts of monofunctional photocuring monomer, 10 to 20 parts of polyfunctional acrylate monomer, 5 to 25 parts of white pigment, 5 to 15 parts of photoinitiator composition and 0 to 15 parts of resin, wherein the photoinitiator composition is prepared from a compound of a light elimination type ketoxime ester photoinitiator and 2, 4, 6-trimethylbenzoyl phenyl ethyl phosphonate, and the photoinitiator composition is prepared from a compound of a light elimination type ketoxime ester photoinitiator and 2, 4, 6-trimethylbenzoyl phenyl ethyl phosphonate. According to the invention, the light elimination type ketoxime ester photoinitiator and the 2, 4, 6-trimethylbenzoyl phenyl ethyl phosphonate are compounded for use, and the synergistic effect of the photoelimination type ketoxime ester photoinitiator and the 2, 4, 6-trimethylbenzoyl phenyl ethyl phosphonate improves the photosensitive efficiency, the deep curing performance and the surface drying performance of the white photocuring ink-jet ink, and the white photocuring ink-jet ink is not easy to yellow.

Description

Technical Field

[0001] This invention relates to the field of inkjet ink technology, and in particular to a white photocurable inkjet ink and its preparation method. Background Technology

[0002] Inkjet printing is a method of ejecting tiny droplets of ink from micro-nozzles and allowing them to adhere to a recording medium. This method is characterized by its ability to record high-resolution, high-quality images at high speeds using relatively inexpensive equipment. Inkjet printing technology involves not only research on the inkjet printing apparatus but also on the inkjet inks used.

[0003] In particular, in the practical application of inkjet printing technology on film or leather materials, most of these materials are roll-to-roll, and the printing process is roll-to-roll, after which they are tightly rolled together. However, existing inkjet inks often have a slow drying speed after printing. During the roll-to-roll winding process, undried ink is prone to sticking and smudging, which not only damages the printed pattern but also causes surface contamination of the material, seriously affecting the processing quality and production efficiency of the product.

[0004] Therefore, it is essential to develop inkjet inks with fast drying properties. Summary of the Invention

[0005] In view of this, in order to at least partially solve the aforementioned technical problems, the present invention provides a white photocurable inkjet ink and a method for preparing the same.

[0006] According to one aspect of the present invention, a white photocurable inkjet ink is provided, comprising, by weight parts: 30-60 parts of a monofunctional photocurable monomer, 10-20 parts of a polyfunctional acrylate monomer, 5-25 parts of a white pigment, 5-15 parts of a photoinitiator composition, and 0-15 parts of a resin; wherein the photoinitiator composition comprises: a compound of a photoeliminating ketoxime ester photoinitiator and ethyl 2,4,6-trimethylbenzoylphenylphosphonate.

[0007] In some embodiments, the photoinitiator composition comprises, by weight, 4.5 to 10 parts of ethyl 2,4,6-trimethylbenzoylphenylphosphonate and 0.5 to 5 parts of a photoeliminating ketooxime ester photoinitiator.

[0008] In some embodiments, the photoeliminator-type ketoxime ester photoinitiator is a photoinitiator having one of the structures shown in formulas (I) to (III) or any mixture thereof:

[0009] Formula (I);

[0010] Formula (II);

[0011] Equation (III).

[0012] In some embodiments, the monofunctional photocurable monomer includes at least one of a nitrogen-containing monofunctional photocurable monomer and a monofunctional acrylate monomer; preferably, the nitrogen-containing monofunctional photocurable monomer includes at least one of an N-vinyl compound, a nitrogen-containing monofunctional acrylate monomer, and an acrylamide monomer.

[0013] In some embodiments, the monofunctional acrylate monomer includes a polyethoxyacrylate monomer or a monofunctional acrylate monomer with a homopolymer glass transition temperature below 50°C.

[0014] In some embodiments, the monofunctional acrylate monomers with a homopolymer glass transition temperature below 50°C include at least one of isobornyl acrylate, cyclotrimethylolpropane methyl acetal acrylate, tetrahydrofuran acrylate, polyethylene glycol o-phenyl ether acrylate, phenoxyethyl acrylate, and benzyl acrylate.

[0015] In some implementations, the structure of the polyethoxyacrylate monomer is as follows: Where 1≤n≤20, and R is C1~C 10 Alkyl, C2~C 10 alkenyl or C6~C 30 Aryl.

[0016] In some embodiments, the multifunctional acrylate monomers include at least one of 1,6-hexanediol diacrylate, 1,4-butanediol diacrylate, dipropylene glycol diacrylate, tripropylene glycol diacrylate, 3-ethyl-3-oxabutane methanol acrylate, octene glycol diacrylate, tetraethylene glycol diacrylate, trihydroxypropane triacrylate, pentaerythritol triacrylate, dipentaerythritol pentaacrylate, or dipentaerythritol hexaacrylate.

[0017] In some embodiments, the white photocurable inkjet ink includes a resin, in parts by weight, ranging from 0.1 to 15 parts, including acrylate resins.

[0018] In some embodiments, the white pigment includes at least one of titanium dioxide, composite titanium dioxide, lithopone, zinc oxide, lead white, and antimony white.

[0019] In some implementations, the average particle size of the white pigment is <1 μm.

[0020] Preferably, the average particle size of the white pigment is 0.1~0.3μm.

[0021] In some embodiments, the white light-curing inkjet ink further includes: additives, including at least one of dispersant, light stabilizer, polymerization inhibitor, defoamer, and leveling agent; by mass parts, the dispersant is 1 to 5 parts, and the total of the light stabilizer, polymerization inhibitor, defoamer, and leveling agent is 0.1 to 3 parts.

[0022] In some embodiments, the photoinitiator composition optionally includes an α-hydroxy ketone photoinitiator, wherein the α-hydroxy ketone photoinitiator is present in 0 to 4 parts by weight; preferably, the α-hydroxy ketone photoinitiator includes at least one of 1-hydroxycyclohexylphenyl ketone and 2-hydroxy-2-methyl-1-phenyl-1-propanone.

[0023] According to another aspect of the present invention, a method for preparing a white photocurable inkjet ink is provided, comprising: mixing and grinding a white pigment and a portion of a monofunctional photocurable monomer to obtain a color paste; mixing and stirring another portion of a monofunctional photocurable monomer, a polyfunctional acrylate monomer, a photoinitiator composition, and an optional resin to obtain a mixture; mixing the color paste with the mixture to obtain a white photocurable inkjet ink; wherein the photoinitiator composition comprises: a compound of a photoeliminating ketoxime ester photoinitiator and ethyl 2,4,6-trimethylbenzoylphenylphosphonate.

[0024] In some embodiments, a first additive is added during the mixing and grinding process, the first additive including at least one of a dispersant, a polymerization inhibitor, and a light stabilizer; and a second additive is added during the mixing and stirring process, the second additive including at least one of a defoamer and a leveling agent.

[0025] According to embodiments of the present invention, a photo-eliminating ketoxime ester photoinitiator is used in combination with ethyl 2,4,6-trimethylbenzoylphenylphosphonate. Both have photobleaching properties and are suitable for white photocurable inkjet inks. Their synergistic effect helps to broaden the light absorption range of the photoinitiator composition (e.g., irradiation by an LED light source with a wavelength of 365-405 nm), thereby improving its photosensitivity, further enhancing the curing rate and adhesion of the white photocurable inkjet ink, while also ensuring both deep curing and surface drying performance, and minimizing the risk of yellowing. Detailed Implementation

[0026] The embodiments of the present invention will now be further described. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of the invention. In the following detailed description, numerous specific details are set forth to provide a thorough understanding of the embodiments of the invention for ease of explanation. However, it will be apparent that one or more embodiments may be practiced without these specific details. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concepts of the invention.

[0027] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. The term "comprising" as used herein indicates the presence of features, steps, or operations, but does not exclude the presence or addition of one or more other features.

[0028] When using expressions such as "at least one of A, B or C", they should generally be interpreted in accordance with the meaning that is commonly understood by those skilled in the art (e.g., "a system having at least one of A, B or C" should include, but is not limited to, a system having A alone, a system having B alone, a system having C alone, a system having A and B, a system having A and C, a system having B and C, and / or a system having A, B, and C, etc.).

[0029] The initiation system plays a crucial role in the rapid drying of inkjet inks. With the development of ultraviolet (UV) curing technology, traditional mercury lamp light sources, which produce ozone and harmful ultraviolet radiation, are gradually being replaced by safer, cheaper, and energy-efficient light-emitting diode (LED) light sources. 395nm UV-LED light sources have become the mainstream light source for inkjet printing technology. Photoinitiators with good absorption in this wavelength range, such as thioxanthone photoinitiators, have a deep color due to their absorption of the blue end of visible light and cannot be used for white or light-colored materials.

[0030] Trimethylbenzoyl-diphenylphosphine oxide (TPO), a photoinitiator of the photobleaching type, is currently a well-matched photoinitiator with UV-LEDs, but its reproductive toxicity issues limit its application. The current alternative initiator is ethyl 2,4,6-trimethylbenzoylphenylphosphonate (TPO-L), which, while possessing low toxicity and low yellowing properties, reduces initiation efficiency by 30%, with a particularly significant decrease in sensitivity for white systems. In inkjet applications requiring rapid curing, reduced initiation efficiency is unacceptable. Therefore, in the evolution of initiators, ensuring the photosensitivity efficiency of the initiator to guarantee the curing performance of inkjet inks is crucial.

[0031] In the process of realizing this invention, it was discovered that the complex of photoeliminating ketoxime ester photoinitiator and ethyl 2,4,6-trimethylbenzoylphenylphosphonate exhibits a synergistic effect in white photocurable inkjet inks. Through spectral complementarity, complementary initiation mechanisms, and complementary performance, it improves the curing performance, chemical resistance, and anti-yellowing performance of white photocurable inkjet inks.

[0032] Specifically, according to one aspect of the present invention, a white photocurable inkjet ink is provided, comprising, by weight parts: 30-60 parts of a monofunctional photocurable monomer, 10-20 parts of a polyfunctional acrylate monomer, 5-25 parts of a white pigment, 5-15 parts of a photoinitiator composition, and 0-15 parts of a resin; wherein the photoinitiator composition comprises: a compound of a photoeliminating ketoxime ester photoinitiator and ethyl 2,4,6-trimethylbenzoylphenylphosphonate.

[0033] According to embodiments of the present invention, a combination of a photoeliminating ketoxime ester photoinitiator and ethyl 2,4,6-trimethylbenzoylphenylphosphonate provides a more comprehensive response to light sources, a broader absorption spectrum, and improved photosensitivity. The photoeliminating ketoxime ester photoinitiator can rapidly cure the surface layer of white UV-curable inkjet inks, preventing surface sticking and scratches; ethyl 2,4,6-trimethylbenzoylphenylphosphonate can penetrate white pigment and other masking layers to achieve deep curing. The synergistic effect of these two components balances deep curing and surface drying performance, improving the adhesion, abrasion resistance, and chemical resistance of white UV-curable inkjet inks, while reducing the risk of yellowing.

[0034] Optionally, the photoinitiator composition may be, for example, 5 parts, 8 parts, 10 parts, 12 parts or 15 parts by weight, or a range between any two of the above values.

[0035] It is understood that white UV-curable inkjet inks may or may not include resin. The resin content is 0 to 15 parts by weight. When resin is included in the white UV-curable inkjet ink, the addition of resin can improve the density of the cured film, thereby improving its adhesion and strength.

[0036] Optionally, the resin may be, for example, 0 parts, 0.1 parts, 1 part, 3 parts, 5 parts, 8 parts, 10 parts, 12 parts or 15 parts by weight, or a range of any two of the above values.

[0037] In some embodiments, the photoinitiator composition contains 4.5 to 10 parts by weight of ethyl 2,4,6-trimethylbenzoylphenylphosphonate and 0.5 to 5 parts by weight of photoeliminating ketoxime ester photoinitiator. This configuration helps to control the initiation efficiency and reduces the likelihood of yellowing. If the proportion of ethyl 2,4,6-trimethylbenzoylphenylphosphonate is too low, internal uncured areas may occur, posing a risk of yellowing. If the proportion of photoeliminating ketoxime ester photoinitiator is too low, surface curing may be delayed, leading to smudging issues.

[0038] Optionally, by weight, ethyl 2,4,6-trimethylbenzoylphenylphosphonate may be, for example, 4.5 parts, 5 parts, 6 parts, 7 parts, 8 parts, 9 parts or 10 parts, and photoeliminating ketooxime ester photoinitiator may be, for example, 0.5 parts, 1 part, 2 parts, 3 parts, 4 parts or 5 parts, or a range consisting of any two of the above values.

[0039] In some embodiments, the photoeliminator-type ketoxime ester photoinitiator is a photoinitiator having one of the structures shown in formulas (I) to (III) or any mixture thereof:

[0040] Formula (I);

[0041] Formula (II);

[0042] Formula (III).

[0043] According to embodiments of the present invention, the use of the above-mentioned photoeliminating ketoxime ester photoinitiator combined with ethyl 2,4,6-trimethylbenzoylphenylphosphonate can further improve the surface-deep synergistic curing performance of white photocurable inkjet inks, avoiding the situation where the surface is cured but the interior is not, thus improving its adhesion, abrasion resistance, and hardness, and reducing problems such as peeling and cracking. Simultaneously, it can further reduce the risk of yellowing of white photocurable inkjet inks and maintain color stability.

[0044] In some embodiments, the monofunctional photocurable monomer includes at least one of a nitrogen-containing monofunctional photocurable monomer and a monofunctional acrylate monomer. The nitrogen-containing monofunctional photocurable monomer can improve the scratch resistance of the coating film; the monofunctional acrylate monomer has excellent tensile properties; the combination of the above two monomers can give white photocurable inkjet ink good tensile properties.

[0045] In some embodiments, the nitrogen-containing monofunctional photocurable monomer includes at least one of N-vinyl compounds, nitrogen-containing monofunctional acrylate monomers, and acrylamide monomers. The N-vinyl compounds include at least one of N-vinylcaprolactam (NVC), vinylmethyl oxazolidinone (VMOX), N-vinylformamide, N-vinylcarbazole, N-vinylacetamide, and N-vinylpyrrolidone; the nitrogen-containing monofunctional acrylate monomers include at least one of acrylamide (ACMO); and the acrylamide monomers include at least one of (meth)acrylamide, N-hydroxymethyl (meth)acrylamide, diacetone acrylamide, N,N-dimethyl (meth)acrylamide, acryloyloxyethyl dimethylbenzylammonium chloride, and other (meth)acrylamides. It should be noted that in this invention, "N-vinyl compounds" do not include nitrogen-containing monofunctional acrylate monomers and acrylamide monomers.

[0046] Preferably, the nitrogen-containing monofunctional photocurable monomer includes any one of monomers with a nitrogen-containing heterocyclic structure, such as N-vinylcaprolactam (NVC), vinylmethyl oxazolidinone (VMOX), N-vinylcarbazole, N-vinylpyrrolidone, or acrylomorpholine (ACMO); more preferably, it includes acrylomorpholine (ACMO).

[0047] Optionally, the monofunctional acrylate monomers include polyethoxyacrylate monomers. Polyethoxyacrylate monomers have lower viscosity and less shrinkage, which is beneficial for improving the spreadability and adhesion of white UV-curable inkjet inks during inkjet printing, as well as improving the flexibility of white UV-curable inkjet inks after film formation.

[0048] Optionally, the monofunctional acrylate monomers also include monofunctional acrylate monomers whose homopolymers have low glass transition temperatures, such as monofunctional acrylate monomers with homopolymer glass transition temperatures below 50°C. These monofunctional acrylate monomers can improve the flexibility of the polymer molecular chain, resulting in white photocurable inkjet inks with better flexibility and tensile properties after curing.

[0049] Optionally, the monofunctional acrylate monomer with a homopolymer glass transition temperature below 50°C may include at least one of isobornyl acrylate (IBOA), cyclotrimethylolpropane methyl acetal acrylate (CTFA), tetrahydrofuran acrylate (THFA), polyethylene glycol o-phenyl ether acrylate (OPPEA), phenoxyethyl acrylate (meth)acrylate, and benzyl acrylate (meth)acrylate.

[0050] In some implementations, the mass percentage of monofunctional photocurable monomers in the white photocurable inkjet ink is 30% to 60%, preferably 40% to 60%.

[0051] In some implementations, the structure of the polyethoxyacrylate monomer is as follows: Where 1≤n≤20, and R is alkyl, alkenyl or aryl.

[0052] In some implementations, R is C1~C 10 Alkyl, C2~C 10 alkenyl or C6~C 30 Aryl groups, such as methyl, vinyl, and phenyl, are used. This configuration helps to further balance viscosity and crosslinking density, and can alleviate the internal stress of white photocurable inkjet inks after curing, reducing brittle cracking.

[0053] Optionally, the polyethoxyacrylate monomer includes ethyl 2-ethyleneoxyethoxyacrylate (VEEA).

[0054] In some embodiments, the multifunctional acrylate monomers include at least one of 1,6-hexanediol diacrylate (HDDA), 1,4-butanediol diacrylate (BDDA), dipropylene glycol diacrylate (DPGDA), tripropylene glycol diacrylate (TPGDA), 3-ethyl-3-oxabutanemethylethanol acrylate (EOEOEA), octene glycol diacrylate, tetraethylene glycol diacrylate (TEGDA), trihydroxypropane triacrylate (TMPTA), pentaerythritol triacrylate (PETA), dipentaerythritol pentaacrylate, or dipentaerythritol hexaacrylate (DPHA). These multifunctional acrylate monomers contribute to the formation of a three-dimensional cross-linked network structure, while balancing flexibility and hardness, thus improving the adhesion, abrasion resistance, and chemical resistance of white photocurable inkjet ink films.

[0055] In some implementations, the mass percentage of multifunctional acrylate monomers in the white photocurable inkjet ink is 5-20%, preferably 10-20%.

[0056] In some embodiments, the resin includes acrylate resins. Adding an appropriate amount of the aforementioned acrylate resin can effectively improve the adhesion of the white UV-curable inkjet ink film, as well as enhance the strength and toughness of the cured film, reducing the possibility of tensile cracking.

[0057] Optionally, the acrylate resin includes at least one of polyurethane acrylate, epoxy acrylate, and polyester acrylate.

[0058] Optionally, the number-average molecular weight of the acrylate resin is 500~3000, for example, 700~2000. This avoids the phenomenon of excessively low viscosity of white UV-curable inkjet ink, which would cause droplets, due to excessively low molecular weight, and avoids the phenomenon of excessively high viscosity of white UV-curable inkjet ink, which would cause ink sticking and affect the uniformity of inkjet printing, due to excessively high molecular weight.

[0059] In some embodiments, the mass percentage of acrylate resin in the white photocurable inkjet ink is 0-15%, preferably 0-10%, and more preferably 0-5%.

[0060] In some implementations, the white pigment includes at least one of titanium dioxide, composite titanium dioxide, lithopone, zinc oxide, lead white, and antimony white; the average particle size of the white pigment is <1 μm. This configuration provides better tinting strength and dispersibility, resulting in more uniform color of the inkjet-printed film and reducing the likelihood of discoloration, thus effectively improving the durability of the film color.

[0061] Preferably, the average particle size of the white pigment is 0.1~0.3μm.

[0062] In some embodiments, the white UV-curable inkjet ink further includes: additives, including at least one of dispersant, light stabilizer, polymerization inhibitor, defoamer, and leveling agent; by weight, the dispersant is 1-5 parts, and the total of the light stabilizer, polymerization inhibitor, defoamer, and leveling agent is 0.1-3 parts. Additives can be used to further improve the performance of the white UV-curable inkjet ink. Dispersants can effectively improve the dispersion of each component in the white UV-curable inkjet ink, prevent sedimentation or agglomeration, and make the distribution of each component more uniform. Light stabilizers can shield or absorb the energy of ultraviolet light, slow down the photocuring process, and prevent monofunctional photocurable monomers from curing prematurely, thereby effectively extending the service life of the white UV-curable inkjet ink. Polymerization inhibitors help prevent the white UV-curable inkjet ink from polymerizing during storage, improving its storage stability. Defoamers can significantly reduce the possibility of foam formation in the white UV-curable inkjet ink, reduce film unevenness or porosity caused by foaming, thereby improving the film-forming performance of the white UV-curable inkjet ink after inkjet printing. Leveling agents can effectively reduce the surface tension of the liquid surface during inkjet printing, improve the leveling and uniformity of white UV-curable inkjet inks, reduce the possibility of spots and blemishes, make the film formation more uniform, and reduce the phenomenon of stress concentration at uneven areas during stretching, which can lead to cracks.

[0063] Optionally, the dispersant includes at least one selected from polyether block copolymers, polyurethane block copolymers, polyester block copolymers, marinic acid block copolymers, acrylic block copolymers, and organically modified polysiloxanes. More preferably, the dispersant includes at least one selected from Lubrizol Solsperse 36000, Lubrizol Solsperse 32000, Degussa Disperse 685, Degussa Disperse 655, BYK Disperbyk 2200, and BYK Disperbyk 2205.

[0064] Optionally, the dispersant may be, for example, 1 part, 2 parts, 3 parts, 4 parts or 5 parts by mass, or a range of any two of the above values.

[0065] Optionally, the polymerization inhibitor includes at least one of phenolic polymerization inhibitors, quinone polymerization inhibitors, or aromatic nitro compound polymerization inhibitors; more preferably, it includes at least one of p-tert-butylcatechol, di-tert-butyl-p-cresol, and p-hydroxyanisole.

[0066] Optionally, the defoamer includes at least one of polyethylene glycol, fatty acid antifoaming agent, silica-based defoamer, mineral oil, polyethylene wax, higher fatty alcohol, tributyl phosphate, and emulsified methyl silicone oil.

[0067] Optionally, the leveling agent includes at least one of organosiloxane, sodium carboxymethyl cellulose, polyamide, modified amide copolymer, polyvinyl alcohol, and modified acrylic copolymer.

[0068] Optionally, the total amount of light stabilizer, polymerization inhibitor, defoamer, and leveling agent, by weight, may be, for example, 0.1 parts, 0.5 parts, 1 part, 2 parts, or 3 parts, or a range between any two of the above values.

[0069] In some implementations, the total mass percentage of light stabilizer, polymerization inhibitor, defoamer, and leveling agent in the white light-curing inkjet ink is 0.3% to 3%, for example, it can be 0.3%, 1%, 2%, or 3%.

[0070] In some embodiments, the photoinitiator composition optionally includes an α-hydroxyketone photoinitiator, in parts by weight of 0 to 4 parts. α-hydroxyketone photoinitiators help to rapidly initiate the polymerization reaction, increase the curing rate, and prevent uncured monomer residues that could cause stickiness.

[0071] Preferably, the α-hydroxy ketone photoinitiator includes at least one of 1-hydroxycyclohexylphenyl ketone (184) and 2-hydroxy-2-methyl-1-phenyl-1-propanone (1173).

[0072] Optionally, the α-hydroxyketone photoinitiator can be, for example, 0 parts, 0.1 parts, 0.5 parts, 1 part, 2 parts, 3 parts or 4 parts by mass, or a range consisting of any two of the above values.

[0073] According to another aspect of the present invention, a method for preparing a white photocurable inkjet ink is provided, comprising steps 1 to 3.

[0074] In step 1, white pigment and a portion of monofunctional photocurable monomers are mixed and ground to obtain a color paste.

[0075] In step 2, another portion of the monofunctional photocurable monomer, the polyfunctional acrylate monomer, the photoinitiator composition, and the optional resin are mixed and stirred to obtain a mixture.

[0076] In step 3, the colorant is mixed with the mixture to obtain white light-curing inkjet ink.

[0077] The photoinitiator composition includes a complex of a photoeliminating ketooxime ester photoinitiator and ethyl 2,4,6-trimethylbenzoylphenylphosphonate.

[0078] According to embodiments of the present invention, the mixing, dispersion, and stabilization processes are controlled in stages according to the characteristics of the components, which helps to reduce problems such as uneven dispersion, viscosity fluctuations, component incompatibility, and storage instability. Grinding can refine the particle size of the white pigment, thereby making the color distribution of the white UV-curable inkjet ink more uniform during inkjet printing. Adding a photoinitiator composition of a photoeliminating ketoxime ester photoinitiator and ethyl 2,4,6-trimethylbenzoylphenylphosphonate improves the curing rate, chemical resistance, and anti-yellowing properties of the white UV-curable inkjet ink.

[0079] In some embodiments, a first additive, including at least one of a dispersant, a polymerization inhibitor, and a light stabilizer, is added during the mixing and grinding process; a second additive, including at least one of a defoamer and a leveling agent, is added during the mixing and stirring process. The additives are precisely added according to the characteristics of the components to maximize their respective performance while avoiding localized accumulation of the additives.

[0080] In some specific implementations, the preparation method of white photocurable inkjet ink includes the following steps.

[0081] The first step involves mixing white pigment, a portion of monofunctional photocurable monomer, and a first additive, then adding zirconium beads to a grinder and grinding the mixture to obtain a color paste. Optionally, the particle size of the ground white pigment can be less than 1 μm. The quality of the color paste can also be improved by filtering the ground color paste to remove some excessively large white pigment particles and other impurities.

[0082] The second step involves mixing another portion of monofunctional photocurable monomers, polyfunctional acrylate monomers, photoinitiator compositions, acrylate resins, and a second additive, and stirring until homogeneous to obtain a mixture.

[0083] The third step involves mixing the colorant and the mixture to obtain white light-curing inkjet ink.

[0084] According to another aspect of the present invention, an application of a white light-curable inkjet ink is provided, particularly in the application of radiation-curable inks. This radiation curing can be, for example, curing by ultraviolet (UV), electron beam, alpha rays, beta rays, gamma rays, etc. From the viewpoint of curability and convenience, UV curing is preferred.

[0085] In some implementations, white photocurable inkjet ink is suitable for forming patterns on packaging materials by inkjet printing, such as forming QR code information on cigarette packs by inkjet digital printing, and is compatible with a variety of different inkjet printing devices, such as Epson inkjet printheads, Brother inkjet printheads, Canon inkjet printheads, etc.

[0086] Examples of printing substrates include: paper substrates used for food packaging materials, catalogs, posters, flyers, CD sleeves, direct mail, brochures, cosmetics, beverages, pharmaceuticals, toys, equipment, etc.; films, aluminum foil, and synthetic paper used for various food packaging materials such as polypropylene film and polyethylene terephthalate (PET) film; and other substrates that have been used as printing substrates for a long time.

[0087] The technical solution of the present invention will be further illustrated below through specific embodiments. It should be noted that the specific embodiments described below are merely illustrative examples, and the scope of protection of the present invention is not limited thereto.

[0088] In the embodiments of the present invention, cyclotrimethylolpropane methyl acetal acrylate (CTFA) is from Guangdong Lankeluo New Materials Co., Ltd., acrylamide morpholine (ACMO) is from Guangzhou Sanwang Chemical Materials Co., Ltd., ethyl 2-ethyleneoxyethoxyacrylate (VEEA) is from Guangzhou Shanghe Chemical Technology Co., Ltd., 1,6-hexanediol diacrylate (HDDA) and trimethylolpropane triacrylate (TMPTA) are both from Sartoma Chemical Co., Ltd., tetrafunctional polyester acrylate 6325-100 is from Changxing Chemical Co., Ltd., trimethylbenzoyl-diphenylphosphine oxide (TPO) and ethyl 2,4,6-trimethylbenzoylphenylphosphonate (TPO-L) are both from Changzhou Qiangli Electronic New Materials Co., Ltd., titanium dioxide is from Nanjing Titanium Dioxide Chemical Co., Ltd., dispersant Solsperse 36000 is from Lubrizol Specialty Chemicals Manufacturing, light stabilizer HS508 is from Beijing Tiangang Additives Co., Ltd., leveling agent BYK307 and defoamer BYK052 are both from BYK Chemical. Unless otherwise stated, "%" indicates % by mass, and "parts" indicates parts by mass.

[0089] Examples and Comparative Examples

[0090] The formulations of Examples 1 to 7 and Comparative Examples 1 to 2 are shown in Table 1.

[0091] Table 1. Formulations (parts) of Examples 1 to 7 and Comparative Examples 1 to 2

[0092]

[0093] Prepare white photocurable inkjet ink according to the following steps.

[0094] Step 1: Preparation of Pigment A

[0095] Step (1): Use a disperser to stir the monofunctional photocurable monomer CTFA, dispersant Solsperse36000 and light stabilizer HS508 at 300 rpm for 30 min, then add titanium dioxide and continue stirring at 450 rpm for 1 h.

[0096] Step (2): First, use a grinder for rough grinding. The preferred rotor material is zirconium oxide. The rotor structure is a screenless vertical grinder with turbine pins and inner rotor pins. The zirconium bead filling amount is 85wt%, the zirconium bead type is 0.3mm, the air humidity is 60RH%, the temperature is 28℃, the grinding speed is 1500rpm, the grinding flow rate is 1.2kg / min, and the grinding time is 1.5h.

[0097] Step (3): After filtering with 1μm polypropylene (PP) filter paper, grind finely with a grinder with a separator. A ceramic rod pin type bedroom grinder is preferred. Zirconium bead filling amount: 85wt%, zirconia bead type: 0.1mm, grinder separator gap: 0.05mm, air humidity: 60RH%, temperature: 28℃, grinding speed: 1500rpm, grinding flow rate: 1.2kg / min, grinding time: 2h.

[0098] Step 2: Preparation of Mixture B

[0099] Mixture B is obtained by mixing monofunctional photocurable monomers ACMO and VEEA, polyfunctional acrylate monomers HDDA and TMPTA, photoinitiator, acrylate resin 6325-100, leveling agent BYK307 and defoamer BYK052 and stirring evenly.

[0100] Step 3: Preparation of white UV-curable inkjet ink

[0101] Mixture B and pigment A in a yellow light chamber and stir at 1500 rpm for 30 min. Finally, filter the white photocurable inkjet ink through a microporous membrane with a filtration accuracy of 1~3 μm.

[0102] Test Case: Performance Evaluation

[0103] 1. Coating preparation

[0104] The aforementioned white photocurable inkjet ink was coated onto a tinplate substrate using a 30μm wire rod to obtain a coating with a wet film thickness of approximately 15μm.

[0105] 2. Solidification evaluation

[0106] A 405nm LED (RW-LED-YT200S) exposure machine was used, with the power meter placed on the conveyor belt. The measured power was 5W / cm². 2 The coating was subjected to ultraviolet irradiation at a conveyor belt speed of 5 m / min. After passing through the machine once, the surface dryness was assessed by touch, and the coating was graded based on the following evaluation criteria:

[0107] Grade 1: Surface oil, not solidified;

[0108] Level 2: Surface sticky, showing a tendency to harden;

[0109] Level 3: Basic surface texture, but heavy fingerprints are visible when pressed;

[0110] Level 4: Basically dry, slightly rough surface, light fingerprints when pressed;

[0111] Level 5: Completely dry, smooth surface with no fingerprints.

[0112] 3. Evaluation of solvent resistance to wiping

[0113] An exposure machine with a 405nm LED (RW-LED-YT200S) and a power of 5W / cm was used. 2 The coating was irradiated with 2500mJ ultraviolet light, and its resistance to toluene was tested using a solvent-resistant wiper. The number of wipes was recorded until the ink was wiped off and the substrate began to show. The higher the number of wipes, the better the curing degree.

[0114] 4. Yellowing evaluation

[0115] An exposure machine with a 405nm LED (RW-LED-YT200S) and a power of 5W / cm was used. 2 After the above coating was exposed to 2500mJ of ultraviolet light, the color of the coating after exposure was tested using an X-Rite colorimeter. The color value b represents the degree of yellowing, and the larger the value, the more yellow the coating.

[0116] The performance was evaluated using the above evaluation method, and the evaluation results are shown in Table 2.

[0117] Table 2 Performance of Examples 1-7 and Comparative Examples 1-2

[0118]

[0119] As shown in Tables 1 and 2, the white photocurable inkjet inks of Examples 1 to 7, which use TPO-L in combination with the above-mentioned photoeliminating ketoxime ester photoinitiator, have improved sensitivity and solvent wiping resistance compared with Comparative Example 2 using TPO-L alone. They even exceed the level of Comparative Example 1 using TPO alone, and the yellowing is lower than that of using TPO alone, resulting in better overall performance.

[0120] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A white light curable inkjet ink, comprising, in parts by mass: 30-60 parts of a monofunctional curable monomer, 10-20 parts of a multifunctional acrylate monomer, 5-25 parts of a white pigment, 5-15 parts of a photoinitiator composition, and 0-15 parts of a resin. The photoinitiator composition comprises a complex of a photobleachable ketone oxime ester photoinitiator and ethyl 2,4,6-trimethylbenzoylphenylphosphinate. wherein In the photoinitiator composition, ethyl 2,4,6-trimethylbenzoylphenylphosphinate is 4.5-10 parts by mass, and the photobleachable ketone oxime ester photoinitiator is 0.5-5 parts by mass.

2. The white light curable inkjet ink according to claim 1, wherein, The photobleachable ketone oxime ester photoinitiator is a photoinitiator having one of the structures shown in the following formulas (I)-(III) or any mixture thereof:

3. The white light curable inkjet ink according to claim 1, wherein, The monofunctional curable monomer comprises at least one of a nitrogen-containing monofunctional curable monomer and a monofunctional acrylate monomer; preferably, the nitrogen-containing monofunctional curable monomer comprises at least one of an N-vinyl compound, a nitrogen-containing monofunctional acrylate monomer, and an acrylamide monomer. Formula (I); Formula (II); Formula (III).

4. The white light curable inkjet ink according to claim 1, wherein, The monofunctional acrylate monomer comprises a polyethoxylated acrylate monomer or a monofunctional acrylate monomer having a homopolymer glass transition temperature of less than 50°C.

5. The white light curable inkjet ink according to claim 4, wherein, Preferably, the monofunctional acrylate monomer having a homopolymer glass transition temperature of less than 50°C comprises at least one of isobornyl acrylate, cyclotrimethylolpropane formal acrylate, tetrahydrofurfuryl acrylate, polyethylene glycol o-phenylphenylether acrylate, phenoxyethyl (meth)acrylate, and benzyl (meth)acrylate. The polyethoxylated acrylate monomer has the following structure:

6. The white light curable inkjet ink according to claim 5, wherein, The multifunctional acrylate monomer comprises at least one of 1,6-hexanediol diacrylate, 1,4-butanediol diacrylate, dipropylene glycol diacrylate, tripropylene glycol diacrylate, 3-ethyl-3-oxabicyclohexylmethyl acrylate, octanediol diacrylate, tetraethylene glycol diacrylate, trihydroxypropane triacrylate, pentaerythritol triacrylate, dipentaerythritol pentaacrylate, and dipentaerythritol hexaacrylate. wherein 1 < n < 20, R is a C1-C 10 alkyl, C2-C 10 alkenyl or C6-C 30 aryl group.

7. The white light curable inkjet ink according to claim 1, wherein, The white light curable inkjet ink comprises a resin, and the resin comprises an acrylate resin. The white pigment comprises at least one of titanium white, composite titanium white, lithopone, zinc oxide, lead white, and antimony white; the average particle size of the white pigment is <1 μm, and preferably 0.1-0.3 μm.

8. The white light curable inkjet ink according to claim 1, wherein, The white light curable inkjet ink further comprises an auxiliary agent, and the auxiliary agent comprises at least one of a dispersant, a light stabilizer, a polymerization inhibitor, an antifoaming agent, and a leveling agent.

9. The white light curable inkjet ink according to claim 1, wherein, The dispersant is 1-5 parts by mass, and the total amount of the light stabilizer, the polymerization inhibitor, the antifoaming agent, and the leveling agent is 0.1-3 parts by mass. The photoinitiator composition optionally further comprises an α-hydroxy ketone photoinitiator, and the α-hydroxy ketone photoinitiator is 0-4 parts by mass.

10. The white light curable inkjet ink according to claim 1, wherein, Preferably, the α-hydroxy ketone photoinitiator comprises at least one of 1-hydroxycyclohexyl phenyl ketone and 2-hydroxy-2-methyl-1-phenyl-1-propanone. ​ 11.A method for preparing a white light-curable inkjet ink, comprising: mixing and grinding a white pigment and a part of monofunctional light-curable monomers to obtain a color paste; mixing and stirring another part of monofunctional light-curable monomers, multifunctional acrylate monomers, a photoinitiator composition, and optionally a resin to obtain a mixture; mixing the color paste and the mixture to obtain the white light-curable inkjet ink; wherein the photoinitiator composition comprises a complex of a photobleaching ketoxime ester photoinitiator and 2,4,6-trimethylbenzoylphenyl ethyl phosphonate.

12. The method of making according to claim 11, wherein, In the mixing and grinding, a first additive is further added, the first additive comprising at least one of a dispersant, a polymerization inhibitor, and a light stabilizer; In the mixing and stirring, a second additive is further added, the second additive comprising at least one of a defoaming agent and a leveling agent.

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