Ultraviolet-curable inkjet ink having high color stability and use thereof

Abstract

The present invention relates to the field of photo-curable inks, and in particular to an ultraviolet-curable inkjet ink having high color stability and a use thereof. The ultraviolet-curable inkjet ink comprises a pigment, a diluent, a host resin, a photoinitiator, and an auxiliary agent. The ultraviolet-curable inkjet ink comprises saturated cyclic groups and / or polyether segments. The auxiliary agent at least comprises a photostabilizer. By introducing components having saturated cyclic groups and polyether segments into the ultraviolet-curable inkjet ink, the present invention effectively improves the chemical stability of the ultraviolet-curable inkjet ink, thereby being capable of effectively preventing the problems of fading and discoloration of the ultraviolet-curable inkjet ink caused by external environmental factors after inkjet printing.

Description

A UV-curable inkjet ink with high color stability and its application Technical Field

[0001] This invention relates to the field of UV-curable inks, and more particularly to a UV-curable inkjet ink with high color stability and its applications. Background Technology

[0002] As a crucial link in the building decoration field, the flooring industry's development has closely followed people's pursuit of higher quality living environments. From early solid wood flooring to later composite flooring, and then to the trendy three-dimensional flooring that has emerged in recent years, the evolution of flooring types not only reflects technological progress but also embodies the diversification of consumer demands. Looking to the future, with people's increasing requirements for the decoration of their living and working environments, and the acceleration of urbanization, the development space for the flooring industry is expected to further expand.

[0003] As an innovative member of the flooring family, 3D flooring is unique in that it uses a clever combination of materials and design to create a visual effect that blends reality and illusion, giving the space unprecedented depth and breadth. By utilizing different material properties, color contrasts and texture variations, as well as creatively designed pattern layouts, 3D flooring can bring a sense of three-dimensionality and dynamism to interior spaces, greatly enriching people's visual experience and spatial perception.

[0004] In the current interior and exterior design and decoration industry, the trend towards personalized and artistic decoration is becoming increasingly apparent, and the demand for unique and artistically valuable decorative materials continues to grow. Three-dimensional flooring, with its superior visual appeal and innovative design, is gradually becoming the choice of more and more consumers. Continuous technological advancements and innovations have provided more possibilities for the production of three-dimensional flooring, driving its development to higher levels from material selection to design innovation. Looking to the future, the market position and popularity of three-dimensional flooring will continue to rise, becoming the ideal choice for more and more consumers.

[0005] In the production process of 3D flooring, a two-dimensional wood-like image is formed on the surface of the substrate through printing or printing, thereby visually satisfying people's demand for wood materials. Subsequently, a three-dimensional wear-resistant layer corresponding to the two-dimensional image and having a more similar feel to wood is formed on the upper surface of the wood-like two-dimensional image.

[0006] The relevant technology can be found in the following patent: Patent CN 101659073B discloses a wood grain treatment process for the surface of a waterproof flooring substrate. It involves printing simulated wood grain on the surface of wood-plastic flooring and then adding a wear-resistant layer on top of the simulated wood grain, thereby protecting the wood grain pattern and maintaining the wood grain texture effect for a long time.

[0007] Patent CN 112455110A discloses a process for producing wooden flooring using inkjet printing. This patent enables the formation of a raised, three-dimensional, wear-resistant layer on the surface of a printed pattern by continuously printing additive inks onto the patterned texture.

[0008] Patent CN 112996649A discloses a method for manufacturing a three-dimensional structure on the surface of a flat substrate, the resulting substrate, and an apparatus for producing the substrate according to the method. The method involves first dripping a material for forming wood grain seams onto the surface of the substrate, then applying a curable resin to the area of ​​the substrate surface not covered by the material for forming wood grain seams, and then removing the material for forming wood grain seams after the resin has cured, thereby forming wood grain seams in the cured resin.

[0009] The technical points of existing three-dimensional flooring mainly focus on the following aspects: (1) improving the similarity between the three-dimensional wear-resistant layer and the natural wood grain; (2) improving the correspondence between the three-dimensional wear-resistant layer and the two-dimensional planar image; (3) reducing the problems of wood grain blurring and color variation that occur during the wood grain printing process.

[0010] Previously, the applicant had conducted extensive research and development on the aforementioned technical points and achieved certain results. However, after mass-producing three-dimensional flooring with an appearance and feel similar to solid wood flooring, the applicant accidentally discovered that although these three-dimensional floorings were produced using the same materials and methods, there were significant color differences between different batches, which is clearly unacceptable for the flooring industry. To address the issue of significant color differences between different batches of flooring, the applicant conducted an in-depth investigation into a series of factors during production and storage, discovering that the photothermal stability of the ink has a significant impact on the color difference in the flooring. Summary of the Invention

[0011] The present invention aims to overcome the defects of existing three-dimensional flooring, which may fade and deviate in color during storage and use, resulting in large color differences. Therefore, it provides a UV-curable inkjet ink with high color stability and its application to overcome the above-mentioned shortcomings.

[0012] To achieve the above-mentioned objectives, the present invention is implemented through the following technical solution: In a first aspect, the present invention provides a UV-curable inkjet ink with high color stability, wherein the UV-curable inkjet ink comprises pigment, diluent, main resin, photoinitiator and additives; wherein the UV-curable inkjet ink contains saturated cyclic groups and / or polyether segments; and wherein the additives contain at least a light stabilizer.

[0013] After studying the problem of ink fading, the inventors of this application discovered that the main reason for ink fading is the redox reaction of the resin in the ink. When the ink is stimulated by external factors such as heat and ultraviolet rays, the molecular bonds in the resin are excited and broken, which changes its physicochemical properties, thus macroscopically manifesting as ink fading and discoloration.

[0014] In order to overcome the above-mentioned defects in the prior art, this application makes targeted selections of the chemical structure of the components in the UV-curable inkjet ink.

[0015] Specifically, the inventors of this application discovered in experiments that the organic components of existing UV-curable inkjet inks typically consist of a linear structure of main resin, diluent, and additives. However, these linear molecules have a high degree of freedom in their molecular chains, resulting in weak intermolecular forces. This makes it easier for chain segments to move and rotate within the ink system, leading to poor fixation of pigment molecules around them. Furthermore, the internal chemical bonds of these linear molecules are usually highly reactive, making them susceptible to external environmental factors, resulting in oxidation, hydrolysis, and other chemical reactions that cause molecular chain breakage or structural changes. These changes in molecular chain structure further affect the interaction between the pigment and chain segments, altering the pigment's chemical environment and accelerating fading or discoloration, thus reducing the ink's color stability.

[0016] In this application, the color stability of the ink was unexpectedly significantly improved after selectively adding saturated cyclic groups to at least one component of the UV-curable inkjet ink. Further research revealed that saturated cyclic groups, compared to linear segments in existing technologies, possess advantages such as stable molecular structure, stable chemical bonds, and efficient energy transfer and dissipation.

[0017] First, regarding structural stability, the inventors discovered that the ring structure of these saturated cyclic groups keeps the bond angles and bond lengths between atoms within the molecule relatively fixed, resulting in low ring strain. Taking cyclohexane as an example, its chair conformation has carbon-carbon bond angles close to tetrahedral angles, resulting in low molecular energy and structural stability. This stable structure is less prone to bond breakage or deformation under external environmental factors such as light, temperature changes, and contact with chemical substances, thus ensuring the relative stability of the chemical environment of the pigment molecules connected to it, which is beneficial for maintaining color stability. Furthermore, the saturated cyclic groups possess a certain spatial three-dimensional structure, which can effectively hinder the steric hindrance of pigment molecules. On one hand, it can prevent excessive proximity and aggregation between pigment molecules, maintaining good dispersion of the pigment in the ink; on the other hand, when external substances attempt to approach the pigment molecules, the steric hindrance of the cyclic groups will impede their contact with the pigment molecules, reducing the possibility of chemical reactions between the pigment molecules and external substances, thereby improving color stability.

[0018] Furthermore, regarding the stability of its chemical bonds: generally speaking, the chemical bonds in saturated cyclic groups are mostly single bonds, with a relatively uniform electron cloud distribution, unlike unsaturated bonds which exhibit large differences in electron cloud density. This makes cyclic groups highly resistant to external chemical attacks, such as oxidation and reduction reactions, and less prone to bond breakage and new bond formation due to electron transfer, thus reducing the possibility of changes in pigment molecular structure and color caused by chemical bond alterations. In addition, the bond energies of common saturated cyclic structures, such as carbon-carbon and carbon-hydrogen bonds, are relatively high, requiring significant energy to break. Under normal use and storage conditions, the saturated cyclic groups in the ink maintain the integrity of their chemical bonds, preventing bond breakage or recombination due to the absorption of small amounts of energy, ensuring the chemical stability of the ink system and contributing to the maintenance of pigment color stability.

[0019] Finally, regarding the rationality of its energy transfer and dissipation: saturated cyclic groups exhibit selectivity when absorbing external energy, typically preferentially absorbing energy forms or wavelength ranges that have less impact on pigment molecules. For example, some saturated cyclic groups can absorb some energy from ultraviolet light and dissipate it as harmless heat, rather than transferring the energy to pigment molecules. This reduces the risk of color changes due to photochemical reactions caused by excessive ultraviolet light absorption. After saturated cyclic groups absorb a certain amount of energy, they can effectively dissipate it through various mechanisms. For instance, some cyclic structures can convert absorbed energy into heat and dissipate it into the surrounding environment through intramolecular vibrations and rotations, or transfer energy to other molecules through intermolecular energy transfer. This effective energy dissipation mechanism allows the ink system to release excess absorbed energy promptly, preventing energy accumulation within the system from damaging pigment molecules and contributing to color stability.

[0020] Besides the addition of saturated cyclic groups, this application has discovered that incorporating polyether segments into a portion of the ink material can also effectively maintain color stability. This is because polyether segments themselves possess certain antioxidant properties, capable of resisting the oxidation of the ink system by oxygen, free radicals, and other external environmental factors. Polyether segments can absorb and dissipate some of the energy from high-energy rays such as ultraviolet light, reducing their direct irradiation and damage to pigment molecules. Furthermore, when the ink is exposed to light, the polyether segments can convert the absorbed light energy into heat or other harmless forms of energy, thereby reducing the probability of photochemical reactions in pigment molecules. Therefore, the presence of polyether segments provides a relatively stable chemical environment for pigment molecules, preventing color changes due to chemical reactions with other substances and improving color stability.

[0021] In addition to its role in ink color stability, the inventors also discovered that polyether segments possess good flexibility, enabling the base resin to exhibit better elasticity and impact resistance after film formation. During the ink curing process, polyether segments can alleviate stress caused by volume shrinkage or external forces, reducing film cracking and peeling, thereby maintaining the integrity and stability of the ink film, which is crucial for the final printed pattern layer. Furthermore, the presence of polyether segments enhances the compatibility of the base resin with other components such as pigments and diluents. Specifically, it can form weak interactions with pigment molecules, such as hydrogen bonds and van der Waals forces, keeping the pigment molecules relatively fixed in position within the ink and less susceptible to interference from external chemicals. Through intermolecular interactions, it allows different components to mix better, forming a stable ink system. Good compatibility helps prevent pigment aggregation and precipitation in the ink, ensuring uniform pigment dispersion and smooth ink jetting, further avoiding problems such as uneven inkjeting and color deviation.

[0022] Therefore, in some preferred embodiments, if saturated cyclic groups and polyether segments are introduced into the ink at the same time, a synergistic effect can be further achieved between the two, thereby having a crucial impact on the stability of the ink color.

[0023] Preferably, at least one of the host resin and diluent contains saturated cyclic groups and / or polyether segments.

[0024] This application does not specify which component introduced the cyclic groups and / or polyether segments. However, since the color stability of the ink is mainly determined by the resin in the ink, in a preferred embodiment, the main resin and at least one of the diluent may contain saturated cyclic groups and / or polyether segments.

[0025] Preferably, the UV-curable inkjet ink contains, by weight percentage, 5.0-25.0% pigment, 15.0-30.0% diluent, 20.0-40.0% base resin, 8.0-15.0% photoinitiator, and 0.5-10% additives.

[0026] Preferably, the cyclic group is any one or more combinations of alkane rings, ester rings, and heterocycles.

[0027] In this application, the choice of cyclic groups plays a crucial role in its performance. The alkane ring is a ring structure formed by carbon atoms linked by single bonds. Its carbon-carbon and carbon-hydrogen bonds are saturated bonds, with a uniform electron cloud distribution and a relatively stable molecular structure. This stability allows the main resin, diluent, or additive containing the alkane ring to better maintain its chemical structure in the ink system, making it less prone to chemical reactions, thus providing a fundamental guarantee for the color stability of the ink. The steric hindrance effect of the alkane ring can effectively restrict the movement and aggregation of pigment molecules, ensuring uniform dispersion of pigments in the ink. During ink storage and use, even under the influence of environmental factors such as temperature and humidity, pigment molecules are less likely to agglomerate due to collisions, thus maintaining color uniformity and stability. Furthermore, the stable structure of the alkane ring can reduce the interference of external factors on the ink system, preventing color changes caused by changes in molecular structure.

[0028] Ester rings are cyclic structures containing ester groups, such as lactones. The ester groups in an ester ring possess a certain polarity, allowing them to interact with other polar groups in the ink system. Simultaneously, the cyclic structure of the ester ring imparts a degree of stability. This structural characteristic of both polar interaction and relative stability allows components containing ester rings to play a unique role in inks. The polarity of the ester ring enables it to form good compatibility with pigment molecules, contributing to the stable dispersion of pigments in the ink. At the same time, the cyclic structure of the ester ring provides steric hindrance, preventing excessive aggregation of pigment molecules. When ink is affected by external factors, the stable structure of the ester ring can reduce chemical changes, protecting the chemical environment of pigment molecules and thus improving the color stability of the ink. Furthermore, the ester ring structure may also affect the ink curing process, contributing to the formation of a more stable ink film and further enhancing color stability.

[0029] Heterocyclic rings are cyclic compounds in which the atoms constituting the ring include other atoms besides carbon, such as oxygen, nitrogen, and sulfur. Heterocyclic rings are diverse in type and structure, with different rings exhibiting different electron cloud distributions and chemical properties. Generally, heteroatoms in a heterocyclic ring can influence the ring's electron cloud density and chemical reactivity, giving it certain unique properties. In this application, the inventors discovered that heterocyclic rings containing specific heteroatoms can absorb the energy of ultraviolet light and dissipate it through specific electronic transitions, thereby reducing the damaging effects of ultraviolet light on pigment molecules. Furthermore, the heterocyclic structure can form conjugated systems or other interactions with pigment molecules, enhancing the stability of the pigment molecules and preventing fading or discoloration due to oxidation, photolysis, or other reactions. Simultaneously, the steric hindrance effect of the heterocyclic ring also helps maintain the dispersed state of the pigment molecules, improving the color stability of the ink.

[0030] Preferably, the heterocycle contains heteroatoms other than carbon and hydrogen atoms.

[0031] Preferably, the heteroatom is any one or a combination of oxygen, nitrogen, phosphorus, boron, and silicon.

[0032] In this application, heteroatoms such as oxygen, nitrogen, phosphorus, boron, and silicon are selected. These heteroatoms possess high thermal and chemical stability and can participate in the formation of conjugated systems, thereby altering the electron cloud distribution of the ring and enabling coordination and other interactions with other substances. For example, the coexistence of oxygen and nitrogen atoms can simultaneously enhance the polarity and conjugation effect of the heterocycle, strengthening its interaction with pigment molecules and its stabilizing effect on the pigment molecules. The combination of phosphorus and silicon atoms can improve the stability of the heterocycle while leveraging their respective steric hindrance and electronic effects, further optimizing the pigment dispersion state and energy dissipation mechanism, thus more effectively improving the color stability of the ink. Therefore, we can adjust the types and proportions of different heteroatoms according to specific ink formulations and usage requirements to achieve precise optimization of ink performance.

[0033] Preferably, the pigment is an organic pigment.

[0034] Preferably, the organic pigment is selected from one or more combinations of monoazo raw materials, diazo pigments, condensed azo pigments, and phthalocyanine pigments.

[0035] Preferably, the organic pigment is phthalocyanine blue.

[0036] Preferably, the pigment has a particle size of D50 < 200 nm and D99 < 500 nm.

[0037] This application specifies a certain limit on the particle size of the ink. Smaller ink particles are used because larger particles result in grainy prints with unclear details, unnatural color gradations, and compromised print quality. Meanwhile, ink particles within a suitable size range can be evenly distributed on the printing medium, resulting in clear pattern details, smooth color gradations, and a more realistic overall effect. Furthermore, excessively small particles may cause ink clogging or the formation of a uniform film during printhead ejection, affecting print quality and speed. Finally, appropriately sized ink particles facilitate uniform pigment dispersion within the ink, protecting the pigment from oxidation or fading due to direct sunlight.

[0038] Preferably, the diluent is one or a combination of monofunctional active diluents and difunctional active diluents.

[0039] Preferably, the diluent is selected from one or more combinations of 1,6-hexanediol diacrylate, dipropylene glycol diacrylate, tripropylene glycol diacrylate, cyclohexanediol diacrylate, N-acryloylmorpholine, tetrahydrofuran methacrylate, methyltetrahydrofuran 2,5-diacrylate, cyclohexanediethanol diacrylate, 1,3-adamantanediol diacrylate, hydrogenated bisphenol A diacrylate, and cyclic phosphorus-containing acrylates.

[0040] Preferably, the light stabilizer includes any one of light shielding agents, ultraviolet absorbers, quenchers, free radical scavengers, and hydroperoxide decomposers.

[0041] Further preferably, the light-shielding agent is a substance that can block or reflect ultraviolet rays, preventing light from penetrating into the polymer and thus protecting the polymer. Specifically, it can be selected from inorganic pigments such as carbon black and titanium dioxide, or organic pigments such as phthalocyanine blue and phthalocyanine green.

[0042] Further preferably, the ultraviolet absorber can effectively absorb ultraviolet light with a wavelength of 290-410nm, and according to its chemical structure, it can be mainly divided into any one or more combinations of o-hydroxybenzophenones, benzotriazoles, salicylates, triazines, and substituted acrylonitriles.

[0043] Further preferably, the quencher can accept the energy absorbed by the chromophores in the plastic and dissipate this energy in the form of heat, fluorescence, or phosphorescence, thereby protecting the polymer from ultraviolet damage, such as divalent organonickel chelates.

[0044] Further preferably, the free radical scavenger can capture the active free radicals generated in the polymer, thereby inhibiting the photo-oxidation process and achieving photostability. It can be mainly selected from hindered amine photostability stabilizers (HALS).

[0045] Further preferably, the hydroperoxide decomposer can be a type of hindered amine light stabilizer. During storage and processing, polymers can generate hydroperoxides, leading to photo-oxidative degradation. The hydroperoxide decomposer can decompose the peroxides, generating stable nitrogen-oxygen free radicals, and further capture these free radicals, thereby inhibiting polymer degradation.

[0046] Preferably, the photoinitiator includes a primary initiator and a co-initiator; wherein the primary initiator includes any one of 2-hydroxy-2-methyl-1-phenylpropanone, 1-hydroxycyclohexyl-phenyl ketone, 1-[4-(2-hydroxyethoxy)phenyl]-2-hydroxy-2-methyl-1-propanone, 2-benzyl-2-dimethylamino-1-(4-morpholinylphenyl)-1-butanone, 2-methyl-1-[(4-methylthio)phenyl]-2-morpholinyl-1-propanone, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, ethyl 2,4,6-trimethylbenzoylphenylphosphine, di(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, 2,4,6-trimethylbenzophenone, 2-isopropylthioxanthanone, 2,4-diethylthioxanthanone, and methyl benzoylcarbamate; The co-initiator is selected from at least one of the following: CN371NS, CN550, CN551NS, CN386 from SARTOMER and Omnirad EDB, Omnirad EHA, and Omnipol ASA from IGM.

[0047] Secondly, the present invention also provides the application of the ultraviolet curable inkjet ink with high color stability in inkjet printing.

[0048] Thirdly, the present invention also provides a three-dimensional solid sheet, the three-dimensional solid sheet comprising a base layer and a two-dimensional pattern layer disposed above the base layer, and further comprising a three-dimensional wear-resistant layer disposed above the two-dimensional pattern layer and corresponding to the two-dimensional pattern layer, and at least one topcoat layer disposed on the upper surface of the three-dimensional wear-resistant layer; the two-dimensional pattern layer is obtained by printing with an ultraviolet curable inkjet ink with high color stability as described above.

[0049] Therefore, the present invention has the following beneficial effects: By introducing components with saturated cyclic groups and / or polyether segments into UV-curable inkjet inks, the present invention effectively improves the chemical stability of UV-curable inkjet inks, thereby effectively preventing fading and discoloration caused by external environmental factors after inkjet printing. Simultaneously, it also improves the elasticity and impact resistance of the ink film after formation, thereby alleviating stress caused by volume shrinkage or external forces, reducing film cracking and peeling, and thus maintaining the integrity and stability of the ink film. Attached Figure Description

[0050] Figure 1 shows a photograph of the printed solid color block before it is exposed to ultraviolet light.

[0051] Figure 2 shows a photograph of the printed solid color block after 24 hours of ultraviolet light exposure. Detailed Implementation

[0052] The present invention will be further described below with reference to specific embodiments. Those skilled in the art will be able to implement the present invention based on these descriptions. Furthermore, the embodiments of the present invention described below are generally only some, not all, of the embodiments of the present invention. Therefore, all other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

[0053] The UV-curable inkjet ink with high color stability involved in this embodiment includes pigments, diluents, main resins, photoinitiators, and additives.

[0054] (1) Main Resin: The main resin in UV-curable inkjet ink is a key component, playing multiple roles including film formation, pigment dispersion and stabilization, viscosity and flowability adjustment, enhanced adhesion to the printing medium, and influence on curing speed and efficiency. Under ultraviolet light, it cross-links to form a film, uniformly disperses and stabilizes the pigment in the ink, regulates the ink viscosity and flowability to facilitate inkjet printing, enhances adhesion to the printing medium, and its own characteristics determine the ink curing speed and efficiency, which has a very important impact on print quality, color stability, and product performance.

[0055] Generally speaking, the main resin used in UV-curable inkjet inks can be any one of epoxy acrylic resin, polyurethane acrylic resin, polyester acrylic resin, acrylate oligomer, or silicone-modified acrylic resin.

[0056] In some preferred embodiments, the main resin may also be a photocurable resin containing polyether segments, wherein the introduction of polyether segments can be obtained by acrylate esterification or epoxidation of polyethylene glycol.

[0057] A typical method for preparing polyether-modified acrylates includes the following steps: Ethylene oxide or propylene oxide is anionicly ring-opened polymerized with a diol or polyol in a strong alkali environment to obtain a hydroxyl-terminated polyether, which is then esterified with acrylate to obtain polyether acrylate or polyether-modified epoxy resin. The process generally involves mixing the hydroxyl-terminated polyether with excess ethyl acrylate and a polymerization inhibitor, heating the mixture, and undergoing a transesterification reaction under the action of a catalyst (such as triisopropyl titanate). The resulting ethanol and ethyl acrylate form an azeotrope and are distilled off. The ethyl acrylate fraction is returned to the reactor via a fractionation column, while the ethanol fraction is distilled off, ensuring the transesterification reaction is complete. Excess ethyl acrylate is then removed by vacuum distillation, ultimately yielding the polyether-modified acrylate.

[0058] In some other preferred embodiments, the host resin may further comprise a photocurable resin with cyclic groups, including any one of hydrogenated bisphenol A groups, tetrahydrofuran groups, alicyclic groups, piperidine groups, and pyrrole groups.

[0059] (2) Diluent The main diluent in UV curable inkjet ink plays two main roles: first, it reduces the viscosity of the ink, allowing the ink to flow and spray better during the inkjet process, ensuring smooth inkjet printing and preventing problems such as nozzle clogging or uneven inkjet printing; second, it participates in the curing cross-linking reaction, forming a cured ink film together with the main resin and other components, affecting the performance of the ink film, such as flexibility, hardness, abrasion resistance, and chemical resistance, thereby improving the quality and durability of the printed pattern.

[0060] Common diluents typically include acrylate monomers, epoxy monomers, ketone solvents, and reactive diluents with special functions.

[0061] Among them, acrylate monomers, such as methyl methacrylate and butyl acrylate, have low viscosity, good dilution effect, and fast curing speed, which can effectively reduce the viscosity of the ink, making it easier to inkjet print. At the same time, during the UV curing process, acrylate monomers can participate in the cross-linking reaction, forming a cured ink film together with the host resin, which helps to improve the hardness, abrasion resistance, and chemical resistance of the ink film.

[0062] Epoxy monomers typically include monofunctional, difunctional, and trifunctional glycidyl ethers, such as butyl glycidyl ether, phenyl glycidyl ether, C12-14 alcohol aliphatic glycidyl ether, benzyl glycidyl ether, neodecanoic acid glycidyl ester, 1,4-butanediol diglycidyl ether, ethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, neopentyl glycol diglycidyl ether, and 1,6-hexanediol diglycidyl ether. They are characterized by high reactivity, rapidly undergoing polymerization under the action of photoinitiators. Epoxy monomers can react with epoxy groups or other active groups in the host resin, increasing the crosslinking density of the ink film, thereby improving the adhesion, hardness, and heat resistance of the ink film, making the printed pattern more robust and durable.

[0063] Ketone solvents, such as acetone, butanone, and methyl isobutyl ketone, possess strong dissolving power and moderate evaporation rates. Ketone solvents can effectively dilute the base resin, reduce ink viscosity, and promote pigment dispersion stability within the ink. During the curing process, their volatility contributes to ink film formation and performance enhancement.

[0064] Specialty reactive diluents: Some reactive diluents with special structures or functions are also used in UV-curable inkjet inks, such as fluorinated acrylate monomers and silicone-modified acrylate monomers. Fluorinated acrylate monomers can impart lower surface energy to the ink film, giving the printed pattern good water, oil, and stain resistance; silicone-modified acrylate monomers can improve the flexibility, weather resistance, and smoothness of the ink film, improving its feel and appearance quality.

[0065] Therefore, in some embodiments, the diluent is selected from one or more combinations of 1,6-hexanediol diacrylate, dipropylene glycol diacrylate, and tripropylene glycol diacrylate.

[0066] In some preferred embodiments, the diluent may further comprise a diluent with a cyclic group, such as one or more combinations of 2-methyl-1-(piperidin-1-yl)but-1-one, cyclohexene, 2-vinyl-2-methyl-5-(1-methylvinyl)tetrahydrofuran, 3-vinyltetrahydrofuran-3-ol, 2-isopropenyl-5-methyl-5-vinyltetrahydrofuran, 4-vinyltetrahydrofuran-3-ol, N-vinylpiperidinone, N-vinylpyrrolidone, isobornyl acrylate, dicyclopentenyl acrylate, cyclohexanediol diacrylate, N-acryloylmorpholine, tetrahydrofuran methacrylate, 2,5-diacrylate methyltetrahydrofuran, cyclohexanediol diacrylate, 1,3-adamantanediol diacrylate, hydrogenated bisphenol A diacrylate, and cyclic phosphorus-containing acrylates.

[0067] The structure of the cyclic phosphorus-containing acrylate used in subsequent embodiments of this application is as follows:

[0068] (3) The organic pigments mentioned are selected from monoazo pigments, diazo pigments, condensed azo pigments, and phthalocyanine pigments. Specifically, the monoazo pigments include Hansa Yellow G, Pigment Orange 5, and Pigment Red 3. Diazo pigments include Pigment Yellow 12, Permanent Yellow GR, and Pigment Orange 13. Condensed azo pigments include Macromolecular Yellow GRL, Pigment Red 166, and Pigment Brown 23. Phthalocyanine pigments include Phthalocyanine Blue and Phthalocyanine Green G.

[0069] (4) Photoinitiator The photoinitiator includes a primary initiator and a co-initiator.

[0070] The main initiator includes any one of 2-hydroxy-2-methyl-1-phenylpropanone, 1-hydroxycyclohexyl-phenyl ketone, 1-[4-(2-hydroxyethoxy)phenyl]-2-hydroxy-2-methyl-1-propanone, 2-benzyl-2-dimethylamino-1-(4-morpholinylphenyl)-1-butanone, 2-methyl-1-[(4-methylthio)phenyl]-2-morpholinyl-1-propanone, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, ethyl 2,4,6-trimethylbenzoylphenylphosphine, di(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, 2,4,6-trimethylbenzophenone, 2-isopropylthioxanthanone, 2,4-diethylthioxanthanone, and methyl benzoylcarbamate.

[0071] The co-initiator is selected from at least one of the following: CN371NS, CN550, CN551NS, CN386 from SARTOMER and Omnirad EDB, Omnirad EHA, and Omnipol ASA from IGM.

[0072] (5) Additives The additives in UV-curable inkjet inks mainly include the following categories: 1) Light stabilizers, which are mainly used to improve the stability of the ink during storage and use, prevent the ink from deteriorating, polymerizing, or decomposing due to factors such as light, heat, and oxygen, and extend the shelf life of the ink. The light stabilizers include any one of light shielding agents, UV absorbers, quenchers, free radical scavengers, and hydroperoxide decomposers. Among them, the light shielding agents are substances that can block or reflect ultraviolet light, preventing light from penetrating the polymer and thus protecting the polymer. Specifically, they can be selected from inorganic pigments such as carbon black and titanium dioxide, or organic pigments such as phthalocyanine blue and phthalocyanine green. The UV absorbers effectively absorb ultraviolet light with a wavelength of 290–410 nm. According to their chemical structure, they can be mainly divided into any one or more combinations of o-hydroxybenzophenones, benzotriazoles, salicylates, triazines, and substituted acrylonitriles. The quencher can accept the energy absorbed by the chromophores in the plastic and dissipate this energy in the form of heat, fluorescence, or phosphorescence, thereby protecting the polymer from ultraviolet damage, such as divalent organonickel chelates. The free radical scavenger can capture active free radicals generated in the polymer, thereby inhibiting the photo-oxidation process and achieving photostability; it is mainly selected from hindered amine light stabilizers (HALS). Hydroperoxide decomposers can be a type of hindered amine light stabilizer. During storage and processing, polymers can generate hydroperoxides, leading to photo-oxidative degradation. Hydroperoxide decomposers can decompose peroxides, generating stable nitrogen-oxygen free radicals, and further capture these free radicals, thereby inhibiting polymer degradation.

[0073] 2) Leveling agents reduce the surface tension of the ink, allowing ink droplets to spread and level better on the printing substrate, forming a smooth, flat ink film and improving the quality and gloss of the printed image. Common leveling agents include silicone-based agents, such as polydimethylsiloxane, which have good leveling and slip properties. They also include acrylate-based leveling agents, such as acrylate copolymers, which have good compatibility with the ink system, effectively improving the leveling effect of the ink film while having minimal impact on its performance.

[0074] 3) Defoamers, whose function is to eliminate air bubbles in the ink, preventing them from causing uneven ink droplet ejection, clogging the printhead, or forming defects in the ink film during inkjet printing, thus ensuring print quality. They typically include mineral oil-based defoamers, silicone-based defoamers, and polyether-based defoamers.

[0075] 4) Adhesion promoters enhance the adhesion between the ink film and the printing substrate, making the printed pattern more durable, less prone to peeling or wear, and improving the durability of the printed product. Types include: Silane coupling agents: such as γ-aminopropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane, which form chemical bonds between the ink film and the substrate, significantly improving adhesion. Titanate coupling agents: These improve the compatibility and adhesion of the ink film with metal, plastic, and other substrates, enhancing the quality and stability of the printed product.

[0076] The formulations of the UV-curable inkjet inks in the specific embodiments and comparative examples of this application are shown in Table 1 and Table 2 respectively. The color stability of the inks is evaluated and compared by the color difference values ​​before and after UV irradiation.

[0077] Table 1

[0078] Table 2

[0079] The UV-curable inkjet inks listed in Tables 1 and 2 were placed in an inkjet printer and mixed with other pigments to print solid color blocks. The printed solid color blocks were then irradiated with UV light (UVA-340 light source) for 24 hours and 300 hours respectively. The color changes of the blocks before and after printing were observed, and a color difference test was performed on the printed solid color blocks using a colorimeter.

[0080] The test results are shown in Figures 1 and 2. Figure 1 shows the state of the solid color block before UV irradiation, and Figure 2 shows the state of the solid color block after 24 hours of UV irradiation. Comparing these two figures, we can see that the solid color block will fade to some extent after UV irradiation. The specific values ​​of the color difference test results for each UV-curable inkjet ink are shown in Table 3 below.

[0081] Table 3. Color difference test results of UV-curable inkjet inks

[0082] As shown in the table above, in Comparative Examples 1 and 2, which used phthalocyanine blue as pigment, no components containing saturated cyclic groups or polyether segments were added to the ink. Therefore, both examples faded rapidly under ultraviolet light, and the color difference increased with prolonged ultraviolet irradiation. This phenomenon was also observed in Comparative Examples 4 and 5, which used pigment red 3 and macromolecular yellow GRL as pigments. Therefore, using Comparative Example 1 as a benchmark, we found that Comparative Example 3, which only added a certain amount of polyether acrylate containing polyether segments to the main resin, exhibited significantly better fading resistance under ultraviolet light than Comparative Examples 1 and 2. This indicates that the introduction of polyether segments can, to some extent, enhance the UV-curable ink's blocking effect on ultraviolet light, thereby improving its fading resistance. Comparative Examples 6 and 7 introduced components containing saturated cyclic groups into the ink (specifically, Comparative Example 6 introduced saturated cyclic groups into both the diluent and the main resin, while Comparative Example 7 introduced saturated cyclic groups only into the diluent). The results showed that their colorfastness was significantly improved compared to Comparative Example 1, indicating that the introduction of saturated cyclic groups significantly contributes to the color stability of UV-curable inks. In Examples 1-9 of this application, both saturated cyclic groups and polyether segments were introduced into the ink. Therefore, compared to the comparative examples that introduced polyether segments and saturated cyclic groups alone, the color stability was qualitatively improved. This indicates that the simultaneous introduction of polyether segments and saturated cyclic groups has a synergistic effect on improving the chemical and color stability of the ink, effectively preventing fading and discoloration of UV-curable inkjet inks after inkjet printing due to external environmental factors.

[0083] Furthermore, from the above results, we also know that, compared with Examples 4-7 which use Pigment Red 3 and Macromolecular Yellow GRL as pigments, the cyan inks in Examples 1-3, 8, and 9 containing Phthalocyanine Blue as pigments exhibit superior anti-fading effects. This indicates that different pigment compositions also have a significant impact on the color stability of inks.

[0084] Furthermore, the applicant discovered in practical applications that cyan ink has a more significant impact on the fading of 3D printing plates and batch-to-batch color differences. This is because cyan is one of the three primary colors in digital printing, allowing it to be mixed with other colors to create numerous smaller colors. For example, the three primary colors can be mixed to create six inks, and the varying shades of these six inks, combined with other colors, can create a myriad of colors. However, when the crucial cyan ink fades and becomes ineffective, the originally rich color palette is disrupted, resulting in a more uniform color and consequently, batch-to-batch color differences.

[0085] After actual testing, it was found that the cyan ink should have a color difference value ΔE < 6 after 300 hours of light exposure. Only when the cyan ink meets the above characteristics can the problem of obvious color difference between different batches of three-dimensional panels be avoided, and at the same time, no color change will occur in the three-dimensional panels of the same batch before and after storage. Therefore, the test results show that the UV-curable inkjet ink of this application can effectively meet the usage requirements and reduce the degree of fading and discoloration of the flooring.

[0086] The specific embodiments described herein are merely illustrative of the spirit of the invention. Those skilled in the art to which this invention pertains may make various modifications or additions to the described specific embodiments or use similar methods to substitute them, without departing from the spirit of the invention or exceeding the scope defined by the appended claims.

Claims

1. A UV-curable inkjet ink with high color stability, characterized in that, The UV-curable inkjet ink comprises pigments, diluents, a main resin, a photoinitiator, and additives; wherein... The UV-curable inkjet ink contains saturated cyclic groups and / or polyether segments; and, The additives contain at least a light stabilizer.

2. The UV-curable inkjet ink with high color stability according to claim 1, characterized in that, At least one of the main resin and diluent contains saturated cyclic groups and / or polyether segments.

3. A UV-curable inkjet ink with high color stability according to claim 1 or 2, characterized in that, The UV-curable inkjet ink contains, by weight percentage, 5.0-25.0% pigment, 15.0-30.0% diluent, 20.0-40.0% base resin, 8.0-15.0% photoinitiator, and the balance being additives.

4. The UV-curable inkjet ink with high color stability according to claim 3, characterized in that, The cyclic group is any one or more combinations of alkane rings, ester rings, and heterocycles.

5. The UV-curable inkjet ink with high color stability according to claim 4, characterized in that, The heterocycle contains heteroatoms other than carbon and hydrogen atoms.

6. The UV-curable inkjet ink with high color stability according to claim 5, characterized in that, The heteroatom is any one or more combinations of oxygen, nitrogen, phosphorus, boron, and silicon.

7. A UV-curable inkjet ink with high color stability according to claim 1 or 2, characterized in that, The pigment is an organic pigment.

8. The UV-curable inkjet ink with high color stability according to claim 7, characterized in that, The organic pigment is selected from one or more combinations of monoazo raw materials, diazo pigments, condensed azo pigments, and phthalocyanine pigments.

9. The UV-curable inkjet ink with high color stability according to claim 7, characterized in that, The organic pigment is phthalocyanine blue.

10. A UV-curable inkjet ink with high color stability according to claim 1 or 2, characterized in that, The pigment has a particle size of D50 < 200 nm and D99 < 500 nm.

11. A UV-curable inkjet ink with high color stability according to claim 1 or 2, characterized in that, The diluent is one or more of the following: monofunctional reactive diluents and difunctional reactive diluents.

12. The UV-curable inkjet ink with high color stability according to claim 11, characterized in that, The diluent is selected from one or more combinations of 1,6-hexanediol diacrylate, dipropylene glycol diacrylate, tripropylene glycol diacrylate, cyclohexanediol diacrylate, N-acryloylmorpholine, tetrahydrofuran methacrylate, methyltetrahydrofuran 2,5-diacrylate, cyclohexanediethanol diacrylate, 1,3-adamantanediol diacrylate, hydrogenated bisphenol A diacrylate, and cyclic phosphorus-containing acrylates.

13. A UV-curable inkjet ink with high color stability according to claim 1 or 2, characterized in that, The light stabilizer includes any one of the following: light shielding agent, ultraviolet absorber, quencher, free radical scavenger, and hydroperoxide decomposer.

14. A UV-curable inkjet ink with high color stability according to claim 1 or 2, characterized in that, The additives also include any one of antioxidants, surfactants, leveling agents, and defoamers.

15. The UV-curable inkjet ink with high color stability according to claim 1, characterized in that, The photoinitiator includes a main initiator and a co-initiator; wherein... The main initiator includes any one of 2-hydroxy-2-methyl-1-phenylpropanone, 1-hydroxycyclohexyl-phenyl ketone, 1-[4-(2-hydroxyethoxy)phenyl]-2-hydroxy-2-methyl-1-propanone, 2-benzyl-2-dimethylamino-1-(4-morpholinylphenyl)-1-butanone, 2-methyl-1-[(4-methylthio)phenyl]-2-morpholinyl-1-propanone, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, ethyl 2,4,6-trimethylbenzoylphenylphosphine, di(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, 2,4,6-trimethylbenzophenone, 2-isopropylthioxanthanone, 2,4-diethylthioxanthanone, and methyl benzoylcarbamate. The co-initiator is selected from at least one of the following: CN371NS, CN550, CN551NS, CN386 from SARTOMER and Omnirad EDB, Omnirad EHA, and Omnipol ASA from IGM.

16. The application of a UV-curable inkjet ink with high color stability according to any one of claims 1-15 in inkjet printing.

17. A three-dimensional solid sheet, characterized in that, The three-dimensional solid plate includes a base layer and a two-dimensional pattern layer disposed on the base layer, and also includes a three-dimensional wear-resistant layer disposed on the two-dimensional pattern layer and corresponding to the two-dimensional pattern layer, and at least one topcoat layer disposed on the upper surface of the three-dimensional wear-resistant layer. The two-dimensional pattern layer is printed using an ultraviolet-curable inkjet ink containing a high color stability as described in any one of claims 1-15.

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