Uv inkjet printing ink for metal substrates and method of preparation

Abstract

The application discloses a kind of UV inkjet printing ink for metal substrate and preparation method, belong to UV curing material technical field.The present UV inkjet ink is insufficient in adhesion on metal substrate, and poor in high temperature resistance performance, difficult to meet the technical defects of metal printing application demand, the application is prepared by molecular structure design, and the acrylic functional monomer with high efficient free radical polymerization activity and strong metal interface combination ability is obtained;The functional monomer is compatible with prepolymer system, photo-initiator, functional additive and the like components, to form UV inkjet ink composition.The UV inkjet printing ink prepared by the application can realize the high adhesion of ink on metal substrate, while having heat shock resistance performance and good thermal stability, can accurately meet the reliability application demand of high-end metal printing field.

Description

Technical Field

[0001] This invention belongs to the field of UV curing material technology, specifically relating to a UV inkjet printing ink for metal substrates with high adsorption capacity, high temperature resistance and thermal stability. It is especially suitable for metal substrates (such as aluminum, stainless steel, copper substrates, etc.) and is a general-purpose UV inkjet printing ink technology for metals that meets the requirements of high precision and high reliability. Background Technology

[0002] UV inkjet printing technology, with its advantages of fast curing speed, low VOC emissions, high printing precision, and strong digital adaptability, has gradually replaced traditional screen printing technology in the application of printing on metal substrates. However, the smooth surface, low polarity, and easy formation of oxide layers on metal substrates (such as aluminum, stainless steel, and copper substrates) result in generally insufficient adhesion of conventional UV inkjet inks, leading to coating peeling and flaking during subsequent high-temperature processes such as electronic device assembly and metal component processing. Furthermore, high-end metal substrate printing places special demands on inks, such as high-temperature resistance (260℃, no abnormalities after 10 seconds of short-term service). In related technologies, UV inkjet inks often suffer from unreasonable cross-linking structures of film-forming resins and poor compatibility of functional components, making it difficult to balance high adhesion with the high-temperature resistance required for high-end metal printing, thus limiting their large-scale application in the high-end metal printing field.

[0003] Specifically, in existing technologies, the main methods for improving the adhesion of UV inks to metals include substrate pretreatment and ink formulation optimization. Substrate pretreatment, such as plasma treatment and sandblasting, can improve the surface roughness of the substrate, but it requires additional investment in specialized equipment, increasing production processes and costs. Moreover, the surface activity of the substrate is easily attenuated after treatment, resulting in poor adhesion stability. In terms of ink formulation optimization, existing technologies mostly improve adhesion by adding coupling agents and adjusting the proportion of prepolymers. However, coupling agents have poor compatibility with the ink system, which can easily lead to inkjet clogging. Excessive addition of epoxy prepolymers will increase the brittleness of the coating and reduce its thermal shock resistance.

[0004] Acrylic monomers / oligomers are the core film-forming components of UV-curable inks, and their structure directly determines the ink's curing performance, film-forming performance, and interfacial bonding ability. However, traditional acrylate monomers lack specific groups that form strong interactions with metal substrates (such as aluminum, stainless steel, and copper substrates), making it impossible to solve the problems of adhesion and high-temperature resistance on metal substrates.

[0005] Therefore, it is necessary to design a UV inkjet printing ink formulation with high adhesion, high temperature resistance, and good thermal stability suitable for metal substrates, which can solve the technical problems that urgently need to be solved in the current field of metal substrate processing. Summary of the Invention

[0006] To address the technical shortcomings of existing UV inkjet inks in terms of insufficient adhesion, inadequate high-temperature resistance, and poor thermal stability on metal substrates (such as aluminum, stainless steel, and copper), this invention provides a UV inkjet printing ink. Through the structural design of the core functional unit and the synergistic formulation of each component, the ink achieves high adhesion on metal substrates while also possessing excellent adhesion, high-temperature resistance, and good thermal stability, precisely meeting the reliability application requirements of high-end metal printing fields.

[0007] To achieve the above objectives, the present invention proposes a UV inkjet printing ink for metal substrates, comprising the following components by weight: 1-4 parts of high-adhesion acrylic functional monomers for metals, 2-6 parts of silicone acrylate oligomers, 8-20 parts of epoxy acrylates, 30-75 parts of acrylate comonomers, 1-7 parts of pigments, 3-7 parts of mixed photoinitiators, and 0.1-1 parts of composite additives.

[0008] Furthermore, the chemical structural formula of the metal high-adhesion acrylic functional monomer is shown in formula (I):

[0009] The definitions of each group are as follows: It consists of acrylate / methacrylate groups that can be cured by free radicals. It is hydrogen (H) or methyl ( ); Y is an adhesion functional group, selected from... or ; m is the curing functionality, i.e. the number of acrylate / methacrylate groups, which is a positive integer and m≥1; n is the number of adhesion functional groups, which is a positive integer and n≥1; R is a connecting bridging group, selected from one of aliphatic alkylene, alicyclic alkylene, aromatic arylene, polyoxyethylene segment, polyoxypropylene segment, polyester segment, or epoxy-modified polyether segment. The connecting bridging group is only used to connect the curing group and the adhesion functional group, and does not directly participate in free radical curing and metal adhesion reactions.

[0010] Furthermore, the acid value of the high-adhesion acrylic functional monomer is 50-250 mgKOH / g.

[0011] Furthermore, the high-adhesion acrylic functional monomer is selected from 2-acryloyloxyethyl succinate or di(acryloyloxyethyl) phosphate monoester.

[0012] Further, the 2-acryloyloxyethyl succinic acid monoester is prepared by the following method: Step (1) Feeding and Nitrogen Replacement: Succinic acid, hydroxyethyl acrylate (HEA), p-toluenesulfonic acid (PTSA), and hydroquinone (HQ) are added to the reaction apparatus in sequence, and toluene is added as a dehydrating agent; stirring is started, and high-purity nitrogen is introduced to replace the air in the apparatus to maintain a slightly positive nitrogen pressure and prevent the double bonds of acrylate from self-polymerizing; wherein, the molar ratio of succinic acid to hydroxyethyl acrylate is 1:1, p-toluenesulfonic acid is 0.02 times the molar amount of succinic acid, and hydroquinone is 0.005-0.01 times the molar amount of succinic acid; Step (2) Reflux water separation reaction: Heat the system to 105-110℃ and maintain reflux. Use toluene to form an azeotrope with the water generated in the reaction to remove water. After condensation and separation, the water is separated. Take a sample every 1 hour to test the acid value. Stop the reaction when the acid value is stable at 230-240mgKOH / g. The reaction time is ≤5h. Step (3) Desolventizing under reduced pressure: Cool the reaction system to below 75°C, control the vacuum degree to -0.095MPa, and distill off toluene and trace amounts of unreacted hydroxyethyl acrylate until no distillate flows out; Step (4) Refining: Add hydroquinone polymerization inhibitor to the crude product, stir to dissolve, and then filter through a microporous membrane to obtain 2-acryloyloxyethyl succinic acid monoester.

[0013] Furthermore, the di(acryloyloxyethyl) phosphate monoester is prepared by the following method: Step (1) Low-temperature feeding pretreatment: Dihydroxyethyl acrylate, hydroquinone as a polymerization inhibitor, and p-toluenesulfonic acid as a catalyst are added sequentially to a dry three-necked reactor under nitrogen protection. Mechanical stirring is started at 200 rpm. The temperature is lowered to 0-5℃ by an external ice bath, and nitrogen is maintained at a slight positive pressure of 0.01 MPa for 30 min to remove oxygen. Step (2) Phosphorylation reaction: Phosphorus oxychloride is slowly added dropwise at a rate of 1-2 mL / min. During the addition process, the temperature is precisely controlled by an ice bath to ensure that the system temperature is stable at 3±1℃. The addition time is 95-110 min. Step (3) Insulation reaction and hydrolysis: After the addition is complete, remove the ice bath and naturally raise the temperature to 25-30℃ and keep it at a constant temperature for 3-4 hours; then add deionized water at a rate of 0.5-1 mL / min, control the hydrolysis temperature at 25-28℃, and absorb hydrogen chloride in the tail gas through 5-10% dilute alkali solution. After the addition is complete, continue to keep it at a constant temperature and stir for 1 hour. Step (4) Post-processing purification: Adjust the pH of the system to 4-5 with 5-10% dilute alkali solution, turn on the vacuum distillation device, control the vacuum degree ≥0.09MPa and the temperature to 40-50℃; then purify by silica gel column chromatography, collect the target fraction, and obtain a light yellow transparent liquid product.

[0014] Furthermore, the organosilicon acrylate oligomer is selected from at least one of polydimethylsiloxane acrylate oligomer, epoxy-modified organosilicon acrylate oligomer, amino-modified organosilicon acrylate oligomer, methylphenylsiloxane acrylate oligomer, hydroxyl-modified organosilicon acrylate oligomer, and polyether-modified organosilicon acrylate oligomer. The epoxy acrylate is selected from at least one of bisphenol A epoxy acrylate, phenolic epoxy acrylate, and alicyclic epoxy acrylate.

[0015] Further, the acrylate comonomer is at least one of monofunctional acrylate monomers, difunctional acrylate monomers, and polyfunctional acrylate monomers; wherein the monofunctional acrylate monomer is selected from at least one of 4HBA, IDA, PHEA, IBOA, ACMO, THF(EO)A, 2-EHA, LMA, EOEOEA, TCDNA, THFA, and IBOMA; the difunctional acrylate monomer is selected from at least one of PO-NPGDA, HDDA, TPGDA, PEGDMA, PO2-NPGDA, 1,4-BDDA, NPGDA, PEGDA, TEGDMA, PDDA, EO10-BPADA, and EO4-BPADA; and the polyfunctional acrylate monomer is selected from at least one of PO-TMPTA, TMPTA, GPTA, PMPTA, THEICTA, EO3-TMPTA, TMPTMA, and PET4A.

[0016] Furthermore, the pigment is selected from one or a mixture of two or more of azo red, phthalocyanine blue, carbon black, and titanium dioxide; The mixed photoinitiator is selected from two or more of the following: 2,4,6-trimethylbenzoylphenylphosphine oxide, 2-methyl-1-(4-methylthiophenyl)-2-morpholino-1-propanone, 1-hydroxycyclohexylphenyl ketone, 2-isopropylthioxanthraphenone, aromatic diazonium salt, diaryliodothionium salt, triarylthionium salt, alkylthionium salt, triarylsiloxane, and iron aromatic salt. The composite additive includes at least one of leveling agent, defoamer, polymerization inhibitor, and wetting and dispersing agent.

[0017] The present invention utilizes a synergistic effect of high metal adhesion acrylic functional monomer, silicone acrylate oligomer, and epoxy acrylate: the functional monomer provides chemical anchoring of the metal, the silicone enhances flexibility and leveling, and the epoxy acrylate enhances heat resistance and crosslinking density. The combination of the three produces unexpected technical effects, as it is impossible to achieve the technical requirements of high adhesion, high temperature resistance, and thermal stability by using any one of the components alone.

[0018] The present invention also proposes a method for preparing the above-mentioned UV inkjet printing ink, comprising the following steps: mixing metal high-adhesion acrylic functional monomer, organosilicon acrylate oligomer, epoxy acrylate, acrylate comonomer, pigment, mixed photoinitiator and composite additive in the following weight proportions, stirring at 1000-1500 rpm for 1-3 hours, and then filtering with a 1μm precision filter to remove large-particle solid impurities, thereby obtaining the UV inkjet printing ink. Detailed Implementation

[0019] The following will provide a clear and complete description of the technical solutions involved in the embodiments of the present invention with reference to specific examples. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the protection scope of the present invention.

[0020] In related technologies, functional inks used in UV inkjet printing processes generally suffer from varying degrees of detachment defects due to insufficient interfacial adhesion between the ink and the substrate during the film-forming process, especially for applications involving metal substrates (such as copper, aluminum alloys, and stainless steel substrates). This is accompanied by problems such as poor thermal stability of the system.

[0021] To address the aforementioned technical problems, this invention proposes a UV inkjet printing ink for metal substrates, comprising the following components by weight: 1-4 parts of a high-adhesion acrylic functional monomer for metals, 2-6 parts of an organosilicon acrylate oligomer, 8-20 parts of an epoxy acrylate, 30-75 parts of an acrylate comonomer, 1-7 parts of a pigment, 3-7 parts of a mixed photoinitiator, and 0.1-1 parts of a composite additive. The synergistic function of each raw material imparts excellent adhesion to metal substrates, high-temperature resistance, and thermal stability to the ink.

[0022] It should be noted that this invention employs a metal high-adhesion acrylic functional monomer (general formula) with a specific structural design. This high-adhesion acrylic functional monomer is prepared through a specific chemical synthesis reaction, wherein Y is a carboxylic acid group ( ) or free dihydroxyphosphate group ( This synthetic route allows for the targeted preparation of monofunctional (m=1), bifunctional (m=2), and multifunctional (m≥3) systems through precise control of raw material types, with mild reaction conditions and high reproducibility. The preparation process involves multiple steps including esterification and ring-opening, as well as purification treatment. While preserving the core function of the free radical solidification, it endows the functional monomer with excellent high metal adhesion properties, belonging to the category of chemical synthesis preparation methods.

[0023] The high-metal-adhesion acrylic functional monomer prepared by this invention retains the excellent free radical polymerization activity of acrylate monomers, and the specific functional group Y and ester group contained in its molecular structure can provide additional reaction sites. It can achieve molecular-level uniform mixing in epoxy resin or acrylate resin systems, effectively avoiding potential sedimentation and uneven dispersion problems. Simultaneously, the functional group Y (selected from…) or The synergistic effect of the functional group and the ester group can further reduce the curing initiation temperature of the curing system and improve the curing efficiency. Moreover, the functional group Y can form a stable chemical anchoring effect with the surface of the metal substrate (such as POM metal bond). The introduction of this monomer not only increases the functionality of the curing system, but also allows the functional group Y and the ester group to participate in the cross-linking reaction during curing, in addition to the free radical polymerization reaction of the acrylate double bond, forming a denser and more stable cross-linking network. This significantly improves the bonding strength between the cured coating and the metal substrate, while also giving the coating excellent durability properties such as water resistance and salt spray resistance.

[0024] The technical solution of the present invention will be further described in detail below with reference to specific preferred embodiments, so as to fully verify the technical effect of the present invention.

[0025] In one embodiment, the high-adhesion acrylic functional monomer is preferably 2-acryloyloxyethyl succinate monoester. As functional monomer A, the structure of the preferred compound 2-acryloyloxyethyl succinate monoester falls into general formula (I). The range, corresponding to the following groups:

[0026] (Acryloyl, non-methacryloyl)

[0027] (Contains 1 acryloyloxy ester group)

[0028] (The alkylene group containing the ester bond originates from the link between succinic acid and hydroxyethyl acrylate)

[0029] (Carboxyl group, retain 1 active carboxyl group)

[0030] (Contains 1 carboxyl functional group)

[0031] Its simplified structural formula is:

[0032] The method for preparing 2-acryloyloxyethyl succinic acid monoester of the present invention includes the following steps: (1) Feeding and nitrogen replacement: Succinic acid, hydroxyethyl acrylate (HEA), p-toluenesulfonic acid (PTSA), and hydroquinone (HQ) are added to the reaction apparatus in sequence, and toluene is added as a dehydrating agent; stirring is started, and high-purity nitrogen is introduced to replace the air in the apparatus to maintain a slightly positive nitrogen pressure and prevent the self-polymerization of acrylate double bonds; wherein, the molar ratio of succinic acid to hydroxyethyl acrylate is 1:1, p-toluenesulfonic acid is 0.02 times the molar amount of succinic acid, and hydroquinone is 0.005-0.01 times the molar amount of succinic acid; (2) Reflux water separation reaction: Heat the system to 105-110℃ and maintain reflux. Use toluene and the water generated in the reaction to form an azeotrope to remove water. After condensation and separation, the water is separated. Take a sample every 1 hour to test the acid value. Stop the reaction when the acid value is stable at 230-240mgKOH / g. The reaction time is ≤5h. (3) Desolventizing under reduced pressure: Cool the reaction system to below 75°C, control the vacuum degree to -0.095MPa, and distill off toluene and trace amounts of unreacted hydroxyethyl acrylate until no distillate flows out; (4) Refining: Hydroquinone polymerization inhibitor is added to the crude product, stirred and dissolved, and then filtered through a microporous membrane to obtain 2-acryloyloxyethyl succinic acid monoester.

[0033] The specifications of the raw materials are as follows: succinic acid purity ≥99.0% (analytical grade), hydroxyethyl acrylate is industrial grade and contains 0.1% hydroquinone polymerization inhibitor, p-toluenesulfonic acid purity ≥98.5% (analytical grade), hydroquinone purity ≥99.0% (analytical grade), toluene is anhydrous analytical grade, and nitrogen purity ≥99.99%.

[0034] The reaction apparatus is a 500mL three-necked flask equipped with a water separator and reflux condenser, a precision thermometer with a range of 0-200℃, a nitrogen inlet tube extending below the liquid surface, and a mechanical stirrer with a rotation speed of 200rpm; the nitrogen micro-positive pressure is specifically 0.01 MPa.

[0035] The amount of toluene dehydrating agent added is 200 mL (corresponding to 1.0 mol succinic acid), and the cumulative water separation during the azeotropic dehydration process is 17-19 mL, which is close to the theoretical water production.

[0036] In the purification step, the added hydroquinone mass is 0.2g, the microporous filter membrane pore size is 0.45μm, the product yield is ≥86% (calculated based on succinic acid), and the product is a colorless to pale yellow transparent liquid with a molecular weight of 217±0.2g / mol.

[0037] The desolvation time under reduced pressure is 1.5 hours. During the desolvation process, the system temperature is strictly controlled to not exceed 75°C to prevent thermal decomposition of the product and breakage of double bonds.

[0038] The product characterization of functional monomer A: 2-acryloyloxyethyl succinic acid monoester is shown in the table below:

[0039] The invention obtained Acryloyloxyethyl succinic acid monoester (functional monomer A) has the following significant advantages: Firstly, Acryloyloxyethyl succinic acid monoester contains free carboxyl ( This monomer can form hydrogen bonds, coordination bonds, and even chemical bonds with metal surfaces, belonging to the chemically anchored adhesion monomer category. Secondly, it has better compatibility with metal oxides, primers, and pigments. The carboxyl groups have high polarity, resulting in stronger wetting, dispersibility, and adhesion to metal surface oxide layers, inorganic fillers, and pigments. It can improve the overall interfacial adhesion of inks, reducing pinholes, edge shrinkage, and adhesion failure. Thirdly, it has better cohesion and resistance to thermal shock in the cured film. This monomer is monofunctional but has a large molecular weight and strong polarity, resulting in higher cohesion in the cured coating and making it less prone to softening. Fourthly, it has better resistance to damp heat and aging. The carboxyl groups bond tightly to the metal interface, providing stronger resistance to hydrolysis and damp heat peeling. It is suitable for industrial-grade metal printing, post-processing, and high-temperature and high-humidity environments. It can improve the wettability of inks on substrates. The high-polarity structure results in better spreadability on metal surfaces, which is beneficial for inkjet droplet formation and adhesion.

[0040] In another embodiment, the high-adhesion acrylic functional monomer for metals is preferably bis(acryloyloxyethyl) phosphate monoester as functional monomer B. In this embodiment, the structure of the preferred compound bis(acryloyloxyethyl) phosphate monoester falls into general formula (I). The range, corresponding to the following groups:

[0041]

[0042]

[0043]

[0044]

[0045]

[0046] Its simplified structural formula is:

[0047] A method for preparing a di(acryloyloxyethyl) phosphate monoester includes the following steps: (1) Low-temperature feeding pretreatment: Dihydroxyethyl acrylate, hydroquinone inhibitor and p-toluenesulfonic acid catalyst were added sequentially to a 1000mL nitrogen-protected dry three-necked reactor. Mechanical stirring was started at 200rpm. The temperature was lowered to 3℃ (within the range of 0-5℃) by an external ice bath. The nitrogen pressure was maintained at 0.01MPa and oxygen was removed for 30min.

[0048] (2) Phosphorylation reaction: Phosphorus oxychloride was slowly added dropwise at a rate of 1.5 mL / min (within the range of 1-2 mL / min). During the dropwise addition, the temperature was precisely controlled by an ice bath to ensure that the system temperature was stable at 3±1℃, so as to avoid the decomposition of phosphorus oxychloride and double bond polymerization caused by a sudden temperature rise. The dropwise addition took about 102 min.

[0049] (3) Heat preservation reaction and hydrolysis: After the addition is completed, remove the ice bath and naturally raise the temperature to 28℃ (within the range of 25-30℃), and keep the temperature constant for 3.5h (within the range of 3-4h); then add deionized water dropwise at a rate of 0.8mL / min (within the range of 0.5-1mL / min), and control the hydrolysis temperature at 25-28℃. The tail gas absorbs hydrogen chloride through 8% sodium bicarbonate solution (5-10% sodium carbonate solution or sodium bicarbonate solution or other dilute alkaline solution). After the addition is completed, continue to keep the temperature and stir for 1h to ensure complete hydrolysis of phosphorus oxychloride.

[0050] (4) Post-treatment purification: Adjust the pH of the system to 4.5 (within the range of 4-5) with 8% sodium bicarbonate solution, turn on the vacuum distillation apparatus, control the vacuum degree to -0.092MPa (≥0.09MPa) and the temperature to 45℃ (within the range of 40-50℃) to remove residual hydrogen chloride and trace solvents; then purify by silica gel column chromatography (eluent: ethyl acetate / petroleum ether = 1:2), collect the target fraction, and obtain a light yellow transparent liquid product.

[0051] In this embodiment, the polyhydroxy acrylate intermediate is selected from dihydroxyethyl acrylate, the polymerization inhibitor is hydroquinone, the catalyst is p-toluenesulfonic acid, and the dilute alkaline solution is a sodium carbonate solution or sodium bicarbonate solution with a mass fraction of 5-10%.

[0052] In this example, the nitrogen gas is high-purity nitrogen with a purity of ≥99.8%, and a slight positive pressure (0.01MPa) is maintained inside the reactor throughout the process. The hydrogen chloride gas in the tail gas is treated by absorption with dilute alkaline solution to avoid environmental pollution.

[0053] The phosphorus oxychloride is added at a rate of 1-2 mL / min, and the temperature is precisely controlled by an external cooling device during the addition process to ensure that the temperature fluctuation of the system does not exceed ±1℃.

[0054] In the hydrolysis reaction, the deionized water is added at a rate of 0.5-1 mL / min. After the addition is complete, the mixture is kept warm and stirred for 1 hour to ensure that phosphorus oxychloride is completely hydrolyzed to generate free dihydroxyphosphate groups.

[0055] The vacuum distillation conditions are: vacuum degree ≥ 0.09 MPa, temperature 40-50℃; the eluent used for column chromatography purification is a mixture of ethyl acetate and petroleum ether in a volume ratio of 1:2.

[0056] Functionality can be controlled by adjusting the types and ratios of raw materials: when dihydroxy acrylate is used as an intermediate, it reacts with 1 equivalent of phosphorus oxychloride to obtain a bifunctional compound with m=2 and n=1, and reacts with 2 equivalents of phosphorus oxychloride to obtain a bifunctional compound with m=2 and n=2; when polyhydroxy acrylate is used as an intermediate, it reacts with n equivalents of phosphorus oxychloride to obtain a polyfunctional compound with m≥3 and n being the corresponding feed equivalent.

[0057] The product characterization and results of functional monomer B: bis(acryloyloxyethyl)phosphate monoester are shown in the table below:

[0058] The di(acryloyloxyethyl) phosphate monoester (compound B) prepared by this invention has the following significant advantages: First, its molecular structure contains phosphate anchoring groups, which have strong polarity and chelating properties, enabling them to form chemical coordination bonds with aluminum, copper, stainless steel, electroplating layers, etc., significantly improving the adhesion and bonding strength of inks on metal surfaces; Second, it is a bifunctional acrylate monomer, resulting in a higher crosslinking density after curing, effectively improving the defects of traditional monofunctional monomer cured films such as poor heat resistance, insufficient thermal shock resistance, and weak cohesion; Third, the cured film exhibits superior chemical resistance, mechanical strength, and aging resistance, meeting the stringent requirements of high-end metal printing for inks to withstand high temperatures, humidity, and thermal shock.

[0059] The 2-acryloyloxyethyl succinate and di(acryloyloxyethyl) phosphate monoesters prepared in this invention are both functional monomers for adhesion to metal substrates. Each has its own advantages: 2-acryloyloxyethyl succinate monoester contains a carboxyl anchoring group, which provides excellent adhesion to substrates such as copper, aluminum, iron, and electroplated metals. It also has good compatibility with UV inkjet systems and excellent ink stability, making it suitable for most conventional metal printing. Di(acryloyloxyethyl) phosphate monoester contains a phosphate chelating group, which provides stronger chemical anchoring for inert and difficult-to-adhere metals such as stainless steel and dense aluminum alloys. It also exhibits superior resistance to high temperatures, damp heat, and thermal shock.

[0060] In one embodiment, the acid value range of the high-adhesion acrylic functional monomer is limited to 50-250 mg KOH / g. It is understood that the functional monomer is (general formula...) The preferred acid values ​​of the compound can be 50 mg KOH / g, 100 mg KOH / g, 150 mg KOH / g, 200 mg KOH / g, or 250 mg KOH / g, but are not limited to the values ​​listed above. Other unlisted values ​​within the above range are also applicable.

[0061] It should be noted that the acid value of the acrylic functional monomers with high adhesion to metals mainly affects the active sites on the surface of the metal substrate. The acid value serves as a functional monomer for high adhesion to metals, acting as an active site on the surface of the metal substrate. The theoretical dosage and reactivity of the functional monomer are determined. By limiting the acid value, it is ensured that the adhesion groups of the functional monomer form an ink-metal substrate interface bonding layer with a suitable density with the active sites on the surface of the metal substrate. At the same time, the double bonds in the functional monomer participate in the cross-linking of the system, forming a cured product with a suitable cross-linking density and a complete network structure, thereby obtaining the designed metal adhesion, high heat resistance, and long-term thermal stability.

[0062] It should also be noted that when the acid value of the functional monomer is greater than 250 mg KOH / g, the cured composition is prone to layering, turbidity, and phase separation due to increased polarity, which may cause printhead clogging and is detrimental to inkjet printing. When the acid value of the functional monomer is less than 50 mg KOH / g, the reaction density between the cured composition and the active sites on the surface of the metal substrate decreases, resulting in a significant drop in adhesion. Only when the acid value of the acrylic functional monomer with high metal adhesion is in the range of 50-250 mg KOH / g can the composition achieve excellent metal adhesion, thermal shock resistance, and long-term thermal stability.

[0063] As a further preferred embodiment, the silicone acrylate oligomer is selected from silicone polyurethane acrylate oligomers; specifically, the silicone polyurethane acrylate oligomer includes at least one of Changxing DR-U187B, Sartoma CN990, polydimethylsiloxane acrylate oligomer, epoxy-modified silicone acrylate oligomer, amino-modified silicone acrylate oligomer, methylphenylsiloxane acrylate oligomer, hydroxyl-modified silicone acrylate oligomer, and polyether-modified silicone acrylate oligomer. It should be noted that the silicone polyurethane acrylate oligomer has a dual function of functional enhancement and surface performance optimization in UV inks. This oligomer combines the flexibility of polyurethane with the low surface energy characteristics of silicone, giving the ink higher flexibility, folding resistance, and abrasion resistance after curing, making it suitable for flexible substrates or products requiring post-processing such as stamping or bending. The silicone component significantly reduces the surface tension of the ink system, helping to improve ink leveling, reduce defects such as pinholes and orange peel, and improve the gloss and smoothness of the printed film.

[0064] As a further preferred embodiment, the epoxy acrylate comprises at least one of the following components: bisphenol A epoxy acrylate, phenolic epoxy acrylate, alicyclic epoxy acrylate Sartoma CN120, and Changxing 6250. In one embodiment, the epoxy acrylate comprises a combination of bisphenol A type epoxy acrylate resin and Novolacs type epoxy acrylate resin; or, in a preferred embodiment, the epoxy acrylate comprises a combination of fluorene backbone epoxy acrylate resin and bisphenol S type epoxy acrylate resin; or, in a preferred embodiment, the epoxy acrylate comprises a combination of biphenyl type epoxy acrylate resin and bisphenol F type epoxy acrylate resin. The combination is not limited to those listed above; other combinations not listed within the above range are also applicable.

[0065] As a further preferred embodiment, the acrylate comonomer can be one or more of the following: monofunctional, difunctional, or multifunctional.

[0066] In one specific embodiment, the monofunctional acrylate monomer may be at least one of 4-hydroxybenzoic acid (4HBA), iminodiacetic acid (IDA), 2-phenoxyethyl acrylate (PHEA), isobornyl acrylate (IBOA), acrylmorpholine (ACMO), tetrahydrofuran (ethylene oxide) acrylate (THF (EO) A), 2-ethylhexyl acrylate (2-EHA), lauryl methacrylate (LMA), ethoxyethoxyethyl acrylate (EOEOEA), tricyclodecanediethanol diacrylate (TCDNA), tetrahydrofuran acrylate (THFA), and isobornyl methacrylate (IBOMA).

[0067] In one specific embodiment, the bifunctional acrylate monomer may be at least one of the following: propoxylated neopentyl glycol diacrylate (PO-NPGDA), 1,6-hexanediol diacrylate (HDDA), tripropylene glycol diacrylate (TPGDA), polyethylene glycol dimethacrylate (PEGDMA), dipropoxylated neopentyl glycol diacrylate (PO2-NPGDA), 1,4-butanediol diacrylate (1,4-BDDA), neopentyl glycol diacrylate (NPGDA), polyethylene glycol diacrylate (PEGDA), triethylene glycol dimethacrylate (TEGDMA), 1,3-propanediol diacrylate (PDDA), 10-ethoxylated bisphenol A diacrylate (EO10-BPADA), and 4-ethoxylated bisphenol A diacrylate (EO4-BPADA).

[0068] In one specific embodiment, the multifunctional acrylate monomer may be at least one of propoxylated trimethylolpropane triacrylate (PO-TMPTA), trimethylolpropane triacrylate (TMPTA), pentaerythritol triacrylate (GPTA), pentaerythritol triacrylate (PMPTA), tris(2-hydroxyethyl) isocyanurate triacrylate (THEICTA), 3-ethoxylated trimethylolpropane triacrylate (EO3-TMPTA), trimethylolpropane trimethacrylate (TMPTMA), and pentaerythritol tetraacrylate (PET4A). However, it is not limited to the combinations listed above; other combinations not listed within the above range are also applicable.

[0069] As a further preferred embodiment, the pigment is selected from one or a mixture of two or more of azo red, phthalocyanine blue, carbon black, and titanium dioxide.

[0070] As a further preferred embodiment, the photoinitiator is selected from any one or a combination of at least two of the following: 2,4,6-trimethylbenzoylphenylphosphine oxide, 2-methyl-1-(4-methylthiophenyl)-2-morpholino-1-propanone, 1-hydroxycyclohexylphenyl ketone, 2-isopropylthioxanthraphenone, acylphosphide photoinitiators, anthrone photoinitiators, benzoin photoinitiators, or alkylphenyl ketone photoinitiators, aromatic diazonium salts, diaryliodomonium salts, triarylthiomonium salts, alkylthiomonium salts, triarylsiloxanes, and iron aromatic salts. In a preferred embodiment, the photoinitiator can be a combination of alkylphenyl ketone photoinitiators and acylphosphide photoinitiators; in a preferred embodiment, the photoinitiator can be a combination of anthrone photoinitiators and acylphosphide photoinitiators; in a preferred embodiment, the photoinitiator can be a combination of alkylphenyl ketone photoinitiators and benzoin photoinitiators; the combination is not limited to those listed above, and other combinations not listed within the above range are also applicable.

[0071] As a further preferred embodiment, the additive includes at least one of a wetting and dispersing agent, a leveling agent, a defoamer, or a film-forming aid. It is understood that the additive can be a combination of a leveling agent and a defoamer, a combination of a defoamer and a film-forming aid, or a combination of a leveling agent and a film-forming aid, but is not limited to the combinations listed above; other unlisted combinations are also applicable.

[0072] The UV inkjet printing ink prepared by this invention exhibits high adhesion to metal substrates, overcoming the technical defect of insufficient adhesion of existing UV inkjet inks to metal substrates (such as aluminum, stainless steel, and copper). It performed excellently in material adhesion tests, showing no signs of peeling.

[0073] In one application, the UV inkjet printing ink has a viscosity of 9-12 mPa.s at 50°C and a surface tension of 21-24 mN / m at 50°C. The surface tension matches the wetting of the metal substrate, overcoming the technical problem of the rheological properties of the ink caused by the unreasonable selection and ratio of components such as organosilicon acrylate oligomers and epoxy acrylates.

[0074] In one application, the UV inkjet printing ink was repeatedly tested at a temperature of 288°C and showed no color change, peeling, or bulging. It meets the short-term service conditions of 260°C and has excellent high-temperature resistance.

[0075] Examples 1-6 and Comparative Examples 1-6 Examples 1-6 and Comparative Examples 1-6 are UV inkjet printing inks with different raw material ratios. The types and ratios of the raw materials are different, as shown in Tables 1 and 2 (unit: parts by weight).

[0076] Examples 1-6 disclose the specific formulation of UV inkjet printing ink for metal substrates. The manufacturers, models and dosages of each component are shown in the table below. Among them, the functional monomer is a self-made high-adhesion acrylic functional monomer for metal, with the general chemical formula of Y, where Y is a carboxylic acid group or a phosphate group.

[0077] Table 1. Raw material ratios for UV inkjet printing inks in Examples 1-6

[0078] Table 2. Raw material ratios for UV inkjet printing inks in Comparative Examples 1-6

[0079] The preparation methods of the UV inkjet printing inks in Examples 1-6 and Comparative Examples 1-6 include the following steps: According to the weight ratio, the high-adhesion acrylic functional monomer, silicone acrylate oligomer, epoxy acrylate, acrylate comonomer, pigment, photoinitiator and composite additive are mixed sequentially and stirred at 1000-1500 rpm for 1-3 hours. Then, the large-particle solid impurities are removed by filtering with a 1μm precision filter to obtain UV inkjet printing ink.

[0080] Performance testing (1) Viscosity measurement: Samples of UV inkjet printing inks from Examples 1-6 and Comparative Examples 1-6 were placed in the sleeve of a Burleffs DV2T viscometer. The samples were heated and maintained at 50°C. After 15 minutes, the viscosity data were recorded.

[0081] Evaluation criteria: Acceptable: Viscosity within the range of 9-12 mPas; Unacceptable: Viscosity outside the range of 9-12 mPas.

[0082] Surface tension test: Samples of UV inkjet printing inks from Examples 1-6 and Comparative Examples 1-6 were placed in a BZY-2 surface tension meter. The temperature was set to room temperature. The sample was added to half the height of the glass dish. The platinum plate was brought close to the sample. When the sample came into contact with the platinum plate and stabilized, the surface tension data was recorded.

[0083] The testing standards are as follows: Acceptable: Surface tension is within the range of 21-24 mN / m; Unacceptable: Surface tension is not within the range of 21-24 mN / m.

[0084] (3) Printing performance test: The UV inks used in Examples 1-6 and Comparative Examples 1-6 were injected into the ink cartridges of an inkjet printer. A 395nm LED lamp was used, and the exposure lamp energy was set to 300-500mJ / cm². 2 The printhead temperature was set to 45-55℃, the substrate was an FR-4 substrate, and inkjet printing was performed using the inkjet printing mode. Samples were then produced, and the performance of the ink coating was evaluated. Pass: Printer prints normally, without oblique spraying or clogging; Fail: Printing is oblique, or the printer is clogged.

[0085] (4) Adhesion test on metal materials: The UV inkjet printing inks of Examples 1-6 and Comparative Examples 1-6 were injected into the ink cartridges of the inkjet printer. A 395nm LED lamp was used, and the exposure lamp energy was set to 300-500mJ / cm. 2 The printhead temperature is set to 45-55℃, the substrate is a copper substrate, the inkjet printing mode is enabled to form an ink layer, and the adhesion test is performed by using the cross-cut method. The ink coating is cut to the surface of the metal substrate with a cross-cut tool to form a 10×10 grid pattern with a grid spacing of 1mm. Then, 3M 600 tape is used to stick it and then quickly peeled off to observe the coating peeling.

[0086] The testing standards are as follows: Excellent: No signs of peeling; Good: Peeling rate less than 5%, with slight corner chipping but no large areas of peeling; Unsatisfactory: Peeling rate more than 5%, with large areas of peeling.

[0087] (5) Solder thermal shock resistance test: The inkjet-printed sample was placed in a solder bath at a temperature of 288°C. The sample was immersed in the solder bath for 10 seconds and then taken out and cooled to room temperature. This was repeated three times in total.

[0088] The testing standards are as follows: Excellent: No color change, peeling, or bulging; Good: Color change, but no peeling or bulging; Unqualified: Obvious color change, peeling, or bulging on the surface.

[0089] (6) Thermal stability test: The test was conducted according to HG / T 3330-2012 "UV curable ink". The UV inks of Examples 1-6 and Comparative Examples 1-6 were sampled and the initial viscosity was measured as W1. They were placed in a sealed bottle and put into a 60°C oven. After two weeks, the viscosity was measured as W2. The viscosity change rate S = (W2-W1) / W1 was calculated.

[0090] The evaluation criteria are as follows: Pass: S < 20%; Fail: S ≥ 20%.

[0091] The measurement results are shown in Tables 3 and 4.

[0092] Table 3 Performance testing of inks in Examples 1-6

[0093] Table 4 Performance testing of inks in Comparative Examples 1-6

[0094] Analysis of the data in Tables 3 and 4 shows that the present invention combines a high-adhesion acrylic functional monomer for metals prepared by a specific dosage and preparation method with epoxy acrylic resin and silicone acrylate resin to produce a UV inkjet printing ink that possesses both high metal adhesion, high temperature resistance, and good thermal stability. The functional monomer used in Comparative Example 2 is SR203 from Arkema's Sartomer brand, chemically named tetrahydrofuran methacrylate (THFMA, CAS: 2455-24-5), a monofunctional methacrylate monomer. This monomer's molecular structure contains only a tetrahydrofuran ring, and it can only rely on the weak polarity of the tetrahydrofuran ring to form physical adsorption with the metal substrate. It does not contain anchoring groups that can form strong interactions with the metal substrate. Its core advantages are low viscosity, good flexibility, and excellent compatibility with various prepolymers and photoinitiators in UV inkjet ink systems. It can be used as a general-purpose reactive diluent to improve the inkjet printing smoothness. However, this monomer has significant technical limitations. Its adhesion to metal substrates is weak, and its heat resistance and thermal shock resistance are insufficient. It cannot meet the stringent requirements of high-end metal printing for ink adhesion and durability. Compared with the two core functional monomers 2-acryloyloxyethyl succinate and bis(acryloyloxyethyl) phosphate, which are defined by the general formula protected in this invention, the core performance is significantly different.

[0095] The purpose of this Comparative Example 2 is to compare the performance of Arkema SR203 (THFMA), a commonly used general-purpose acrylate monomer in the prior art, with the general-purpose acrylate functional monomers 2-acryloyloxyethyl succinate and bis(acryloyloxyethyl) phosphate, which are the core protected monomers of this invention. This clearly highlights the significant advantages of the core monomers of this invention in key indicators such as metal adhesion and thermal shock resistance, thanks to their unique anchoring groups (carboxyl and phosphate groups) that form hydrogen bonds, coordination bonds, and even strong chemical chelation with metal substrates. It also clarifies that Arkema SR203, as a conventional monomer in the prior art, cannot meet the application requirements of UV inkjet inks with high metal adhesion.

[0096] The functional monomer Aladdin Reagent M303308 used in Comparative Example 6, chemically named mono-2-(methacryloyloxy)ethyl phthalate (CAS: 27697-00-3), belongs to the monofunctional acrylate monomers. This monomer contains a free carboxyl (-COOH) anchoring group in its molecular structure, which can form hydrogen bonds and coordination with active sites on the surface of metal substrates, exhibiting a certain degree of metal adhesion. Simultaneously, the benzene ring structure in its molecule can improve the rigidity and cohesion of the cured film to a certain extent, and it has good compatibility with prepolymers, photoinitiators, functional additives, and other components in UV inkjet ink systems. However, due to its own molecular structure characteristics, this monomer still has significant shortcomings in adhesion to inert, dense metal substrates such as stainless steel, and its high-temperature and damp-heat resistance does not meet the stringent requirements of high-end metal printing. Compared with the two core functional monomers, 2-acryloyloxyethyl succinate and bis(acryloyloxyethyl) phosphate, which are defined by the general formula protected in this invention, its overall performance is significantly insufficient.

[0097] The purpose of this comparative example is to compare the performance of Aladdin reagent M303308, a typical carboxyl-type adhesion promoter monomer in the prior art, with the general formula-defined acrylic functional monomers 2-acryloyloxyethyl succinate and bis(acryloyloxyethyl) phosphate, which are the core protected monomers of this invention. The aim is to clarify the differences among the four monomers in core technical indicators such as adhesion to metal substrates, high-temperature resistance, and broad-spectrum metal substrate compatibility. This highlights the significant technical advantages of the core monomer of this invention in overcoming the inherent limitations of M303308 (insufficient adhesion to inert metals and poor heat and humidity resistance), demonstrating that the core monomer of this invention is more suitable for the preparation of UV inkjet inks with high metal adhesion and is not a conventional replacement of existing technologies.

[0098] The above description is merely an exemplary embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformations made using the contents of the present invention under the technical concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A UV inkjet printing ink for metal substrates, characterized in that, It includes the following components by weight: 1-4 parts of high-adhesion acrylic functional monomers, 2-6 parts of silicone acrylate oligomers, 8-20 parts of epoxy acrylates, 30-75 parts of acrylate comonomers, 1-7 parts of pigments, 3-7 parts of mixed photoinitiators, and 0.1-1 parts of composite additives.

2. The UV inkjet printing ink for metal substrates as described in claim 1, characterized in that, The chemical structural formula of the high-adhesion acrylic functional monomer is shown in formula (I): , The definitions of each group are as follows: It consists of acrylate / methacrylate groups that can be cured by free radicals. It is hydrogen (H) or methyl ( ); Y is an adhesion functional group, selected from... or ; m is the curing functionality, i.e. the number of acrylate / methacrylate groups, which is a positive integer and m≥1; n is the number of adhesion functional groups, which is a positive integer and n≥1; R is a connecting bridging group, selected from one of aliphatic alkylene, alicyclic alkylene, aromatic arylene, polyoxyethylene segment, polyoxypropylene segment, polyester segment, or epoxy-modified polyether segment. The connecting bridging group is only used to connect the curing group and the adhesion functional group, and does not directly participate in free radical curing and metal adhesion reactions.

3. The UV inkjet printing ink for metal substrates as described in claim 2, characterized in that, The acid value of the high-adhesion acrylic functional monomer is 50-250 mgKOH / g.

4. The UV inkjet printing ink for metal substrates as described in claim 2, characterized in that, The high-adhesion acrylic functional monomer is selected from 2-acryloyloxyethyl succinate or di(acryloyloxyethyl) phosphate monoester.

5. The UV inkjet printing ink for metal substrates as described in claim 4, characterized in that, The 2-acryloyloxyethyl succinic acid monoester was prepared by the following method: Step (1) Feeding and Nitrogen Replacement: Succinic acid, hydroxyethyl acrylate (HEA), p-toluenesulfonic acid (PTSA), and hydroquinone (HQ) are added to the reaction apparatus in sequence, and toluene is added as a dehydrating agent; stirring is started, and high-purity nitrogen is introduced to replace the air in the apparatus to maintain a slightly positive nitrogen pressure and prevent the double bonds of acrylate from self-polymerizing; wherein, the molar ratio of succinic acid to hydroxyethyl acrylate is 1:1, p-toluenesulfonic acid is 0.02 times the molar amount of succinic acid, and hydroquinone is 0.005-0.01 times the molar amount of succinic acid; Step (2) Reflux water separation reaction: Heat the system to 105-110℃ and maintain reflux. Use toluene to form an azeotrope with the water generated in the reaction to remove water. After condensation and separation, the water is separated. Take a sample every 1 hour to test the acid value. Stop the reaction when the acid value is stable at 230-240mgKOH / g. The reaction time is ≤5h. Step (3) Desolventizing under reduced pressure: Cool the reaction system to below 75°C, control the vacuum degree to -0.095MPa, and distill off toluene and trace amounts of unreacted hydroxyethyl acrylate until no distillate flows out; Step (4) Refining: Add hydroquinone polymerization inhibitor to the crude product, stir to dissolve, and then filter through a microporous membrane to obtain 2-acryloyloxyethyl succinic acid monoester.

6. The UV inkjet printing ink for metal substrates as described in claim 4, characterized in that, The di(acryloyloxyethyl) phosphate monoester was prepared by the following method: Step (1) Low-temperature feeding pretreatment: Dihydroxyethyl acrylate, hydroquinone as a polymerization inhibitor, and p-toluenesulfonic acid as a catalyst are added sequentially to a dry three-necked reactor under nitrogen protection. Mechanical stirring is started at 200 rpm. The temperature is lowered to 0-5℃ by an external ice bath, and nitrogen is maintained at a slight positive pressure of 0.01 MPa for 30 min to remove oxygen. Step (2) Phosphorylation reaction: Phosphorus oxychloride is slowly added dropwise at a rate of 1-2 mL / min. During the addition process, the temperature is precisely controlled by an ice bath to ensure that the system temperature is stable at 3±1℃. The addition time is 95-110 min. Step (3) Insulation reaction and hydrolysis: After the addition is complete, remove the ice bath and naturally raise the temperature to 25-30℃ and keep it at a constant temperature for 3-4 hours; then add deionized water at a rate of 0.5-1 mL / min, control the hydrolysis temperature at 25-28℃, and absorb hydrogen chloride in the tail gas through 5-10% dilute alkali solution. After the addition is complete, continue to keep it at a constant temperature and stir for 1 hour. Step (4) Post-processing purification: Adjust the pH of the system to 4-5 with 5-10% dilute alkali solution, turn on the vacuum distillation device, control the vacuum degree ≥0.09MPa and the temperature to 40-50℃; then purify by silica gel column chromatography, collect the target fraction, and obtain a light yellow transparent liquid product.

7. The UV inkjet printing ink for metal substrates as described in any one of claims 1-6, characterized in that, The organosilicon acrylate oligomer is selected from at least one of polydimethylsiloxane acrylate oligomer, epoxy-modified organosilicon acrylate oligomer, amino-modified organosilicon acrylate oligomer, methylphenylsiloxane acrylate oligomer, hydroxyl-modified organosilicon acrylate oligomer, and polyether-modified organosilicon acrylate oligomer. The epoxy acrylate is selected from at least one of bisphenol A epoxy acrylate, phenolic epoxy acrylate, and alicyclic epoxy acrylate.

8. The UV inkjet printing ink for metal substrates as described in any one of claims 1-5, characterized in that, The acrylate comonomer is selected from at least one of monofunctional acrylate monomers, difunctional acrylate monomers, and polyfunctional acrylate monomers; wherein the monofunctional acrylate monomer is selected from at least one of 4HBA, IDA, PHEA, IBOA, ACMO, THF(EO)A, 2-EHA, LMA, EOEOEA, TCDNA, THFA, and IBOMA; the difunctional acrylate monomer is selected from at least one of PO-NPGDA, HDDA, TPGDA, PEGDMA, PO2-NPGDA, 1,4-BDDA, NPGDA, PEGDA, TEGDMA, PDDA, EO10-BPADA, and EO4-BPADA; and the polyfunctional acrylate monomer is selected from at least one of PO-TMPTA, TMPTA, GPTA, PMPTA, THEICTA, EO3-TMPTA, TMPTMA, and PET4A.

9. The UV inkjet printing ink for metal substrates as described in claim 1, characterized in that, The pigment is selected from one or a mixture of two or more of azo red, phthalocyanine blue, carbon black, and titanium dioxide; The mixed photoinitiator is selected from two or more of the following: 2,4,6-trimethylbenzoylphenylphosphine oxide, 2-methyl-1-(4-methylthiophenyl)-2-morpholino-1-propanone, 1-hydroxycyclohexylphenyl ketone, 2-isopropylthioxanthraphenone, aromatic diazonium salt, diaryliodothionium salt, triarylthionium salt, alkylthionium salt, triarylsiloxane, and iron aromatic salt. The composite additive includes at least one of leveling agent, defoamer, polymerization inhibitor, and wetting and dispersing agent.

10. A method for preparing UV inkjet printing ink for metal substrates as described in any one of claims 1-9, characterized in that, Includes the following steps: According to the weight ratio, the high-adhesion acrylic functional monomer, silicone acrylate oligomer, epoxy acrylate, acrylate comonomer, pigment, mixed photoinitiator and composite additive are mixed sequentially and stirred at 1000-1500 rpm for 1-3 hours. Then, the ink for UV inkjet printing is obtained by filtering with a 1μm precision filter to remove large-particle solid impurities.

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