Water-based UV (ultraviolet) curing ink-jet ink and preparation method thereof

Abstract

The invention discloses water-based UV (ultraviolet) curing ink-jet ink and a preparation method thereof, and relates to the field of UV curing ink, and the water-based UV curing ink-jet ink comprises the following components: 25-35% of water-based light-cured resin emulsion; 5%-12% of a rosin-based tackifying monomer; 4%-7% of a photoinitiator; 1%-2% of an amine synergistic agent; 3%-8% of a coloring agent; 8%-12% of an organic cosolvent; 0.2%-0.8% of a surfactant; 0.1%-0.3% of a defoaming agent; and the balance of deionized water. The adhesive force of the ink on a non-absorbent substrate is remarkably improved by introducing the rosin-based tackifying monomer, meanwhile, the compatibility and curing efficiency of the ink are effectively improved by optimizing the ratio of the water-based light-cured resin emulsion to the tackifying monomer and compounding the photoinitiator, and the problem of falling off or abrasion of a cured film is avoided.

Description

Technical Field

[0001] This invention relates to the field of UV-curable inks, specifically to a water-based UV-curable inkjet ink and its preparation method. Background Technology

[0002] Water-based UV-curable inkjet inks are advanced materials that combine the environmentally friendly properties of water-based inks with the high efficiency of UV curing technology. They are widely used in packaging, label printing, electronic products, and decorative materials. Due to their low volatile organic compound emissions and rapid curing capabilities, these inks are increasingly used on non-absorbent substrates such as plastics, metals, and glass, but this places higher demands on the ink's adhesion, abrasion resistance, and stability.

[0003] In existing technologies, water-based UV-curable inkjet inks typically consist of water-based UV-curable resins (such as polyurethane acrylates), photoinitiators, colorants, cosolvents, and surfactants. To improve adhesion to non-absorbent substrates, a common practice is to add tackifying resins or reactive monomers, such as epoxy-modified acrylates or styrene-acrylic copolymers. Preparation methods often include pre-dispersion, grinding, and mixing steps to ensure ink uniformity and printing performance.

[0004] However, existing water-based UV-curable inkjet inks still have significant drawbacks: insufficient adhesion to non-absorbent substrates, leading to easy peeling or wear of the cured film and affecting the durability of printed materials; poor compatibility of some tackifiers with resins, potentially causing ink stability issues or reducing curing efficiency; and the organic solvents used in some formulations may be environmentally unfriendly and fail to comply with increasingly stringent environmental regulations. Therefore, there is an urgent need to develop a water-based UV-curable inkjet ink with excellent adhesion, stable curing performance, and environmental friendliness. Summary of the Invention

[0005] Based on this, the purpose of the present invention is to provide an aqueous UV-curable inkjet ink and its preparation method to solve the technical problem of insufficient adhesion on non-absorbent substrates.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a water-based UV-curable inkjet ink, comprising the following components by weight percentage: 25%-35% water-based UV-curable resin emulsion;

[0007] Rosin-based tackifying monomers 5%-12%; photoinitiators 4%-7%; amine synergists 1%-2%; colorants 3%-8%; organic cosolvents 8%-12%; surfactants 0.2%-0.8%; defoamers 0.1%-0.3%; balance: deionized water;

[0008] The rosin-based tackifying monomer is rosin acrylate, and its general molecular structure formula is as follows:

[0009] ;

[0010] Where R is hydrogen or methyl, the addition of this rosin-based tackifying monomer is used to significantly improve the adhesion of the ink-cured film to non-absorbent substrates.

[0011] This invention also provides a method for preparing water-based UV-curable inkjet ink, comprising the following steps: S1, pre-dispersion: under light-protected conditions, the rosin-based tackifying monomer is heated to 50-60°C to make it a transparent liquid, and then the photoinitiator and amine synergist are added under stirring until completely dissolved and mixed to obtain premixed liquid A; S2, color paste preparation: the colorant, all the organic cosolvents and one-third of the total amount of water-based UV-curable resin emulsion are mixed and ground and dispersed using a sand mill until the particle size is less than 200 nm to obtain color paste B; S3, main emulsion preparation: under low-speed stirring, the remaining water-based UV-curable resin emulsion is mixed with deionized water to form a uniform main emulsion C; S4, final mixing: while continuously stirring the main emulsion C, the premixed liquid A is slowly added dropwise to make it uniformly dispersed in the emulsion; then color paste B, surfactant and defoamer are added; S5, post-treatment: the mixture obtained in step (4) is continuously stirred and matured at room temperature for 1 hour, and finally passed through a pore size of 0.8 The high-performance water-based UV-curable inkjet ink is obtained by filtering through a μm filter.

[0012] In summary, the present invention has the following main beneficial effects:

[0013] This invention significantly improves the adhesion of ink to non-absorbent substrates by introducing rosin-based tackifying monomers. Simultaneously, by optimizing the ratio of waterborne UV-curable resin emulsion to tackifying monomers and the combined use of photoinitiators, it effectively improves ink compatibility and curing efficiency, avoiding problems such as cured film peeling or wear. Furthermore, by employing environmentally friendly organic cosolvents and a water-based system, it reduces volatile organic compound emissions while ensuring ink stability and printing performance, meeting environmental protection requirements. Overall, it solves the defects of insufficient adhesion, poor stability, and environmental unfriendliness in existing technologies. Attached Figure Description

[0014] Figure 1 This is a flowchart illustrating the preparation process of the present invention. Detailed Implementation

[0015] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0016] A water-based UV-curable inkjet ink and its preparation method, such as Figure 1 As shown.

[0017] I. Detailed Explanation of Ink Components and Mechanism of Action

[0018] Waterborne UV-curable resin emulsion (25%-35%)

[0019] It provides basic mechanical properties, abrasion resistance, and flexibility. Its water-based nature ensures the ink's environmental friendliness. This invention preferably uses a water-based polyurethane acrylate emulsion. Its solid content is preferably 40±2%, and its viscosity (25℃) is 50-500 mPa·s. The resin molecule contains both urethane bonds, which provide flexibility and adhesion, and photocurable acrylate double bonds, which participate in the cross-linking reaction. The weight ratio of the resin to the rosin-based tackifying monomer is strictly controlled within the range of 3:1 to 5:1. If the resin ratio is too low (<3:1), the cured ink film may be too hard and brittle; if the ratio is too high (>5:1), the tackifying effect is insufficient, and the adhesion decreases.

[0020] Rosin-based tackifying monomers (5%-12%)

[0021] The hydrogenated phenanthrene ring structure in the molecule exhibits excellent affinity with non-absorbent substrates, significantly improving adhesion. Simultaneously, the terminal acrylate groups can participate in the UV-curable crosslinking network, becoming part of the crosslinking points, preventing small molecule migration and ensuring the durability of the ink film. Its general molecular formula is:

[0022] ;

[0023] Where R is hydrogen or methyl, corresponding to rosin acrylate and rosin methacrylate, respectively.

[0024] The preparation method is as follows: Natural rosin is heated to 180℃ and melted under nitrogen protection. After purification by vacuum distillation, it is reacted with an equimolar amount of acrylic acid or methacrylic acid in the presence of a catalyst (such as p-toluenesulfonic acid, 0.5% of the total mass) and a polymerization inhibitor (such as hydroquinone, 0.05% of the total mass) at 200-220℃ for 4-6 hours. The reaction endpoint is defined as an acid value below 10 mg KOH / g. The resulting product is a light yellow transparent solid with a softening point of approximately 70℃.

[0025] Photoinitiator (4%-7%)

[0026] It is used to absorb ultraviolet light energy, generate active free radicals, and initiate the polymerization and cross-linking reaction of acrylate double bonds in resin and monomer. This invention uses a compound system of phenyl bis(2,4,6-trimethylbenzoyl)phosphine oxide (BAPO, trade name such as Irgacure 819) and 2-hydroxy-2-methyl-1-phenyl-1-propanone (HMPP, trade name such as Darocur 1173), with a weight ratio of 1:1.5.

[0027] BAPO: It belongs to the long-wavelength absorption type (absorption peak of about 370nm) acylphosphine oxide, which has good deep curing effect.

[0028] HMPP: It is a split-type photoinitiator with strong surface curing ability. When combined with BAPO, it can achieve uniform and rapid curing of ink film from the surface to the inside.

[0029] This compound ratio can effectively balance the curing speed and curing depth, avoiding surface oxygen inhibition or incomplete curing of the underlying layer.

[0030] Amine synergists (1%-2%)

[0031] Used as a co-initiator, it can undergo electron transfer with photoinitiators (especially HMPP) to generate additional free radicals, significantly enhancing curing efficiency. Especially on the surface of ink films, it can effectively overcome the oxygen inhibition effect. Diethanolamine or triethanolamine can be selected.

[0032] Colorant (3%-8%)

[0033] For providing color, organic pigments, inorganic pigments, or mixtures thereof can be used. To ensure smooth inkjet printing and color saturation, the pigments must undergo ultrafine dispersion treatment, with a final particle size of less than 200 nm. For example, phthalocyanine blue PB15:3 can be used for cyan, PR122 for magenta, PY74 for yellow, and carbon black PBK7 for black.

[0034] Organic cosolvents (8%-12%)

[0035] It is used to regulate ink evaporation rate and viscosity, prevent printhead drying, and improve printing performance. It also aids in the dissolution and compatibility of various components.

[0036] The compounding solution is a mixed solvent of 1,2-propanediol and propylene glycol methyl ether acetate (PMA) in a weight ratio of 2:1. 1,2-propanediol has a high boiling point (188℃) and good moisturizing properties; PMA has a moderate boiling point (146℃) and excellent solubility and moderate evaporation rate. The combination of the two can create a stable evaporation gradient during the printing process.

[0037] Surfactants (0.2%-0.8%)

[0038] To reduce the surface tension of ink, enabling it to effectively wet various substrates and improve spreadability and print quality, nonionic surfactants, such as polyether-modified siloxanes, can be used.

[0039] Defoamer (0.1%-0.3%)

[0040] Mineral oil-based defoamers, such as BYK-024, can be used to suppress and eliminate foam during preparation and use, and to prevent printing line breakage.

[0041] Deionized water

[0042] Used as the main medium in aqueous systems.

[0043] II. Detailed Explanation of Preparation Method

[0044] The preparation method will be explained step by step in detail below with reference to specific embodiments.

[0045] Examples 1-3 & Comparative Example 1

[0046] To verify the effectiveness of this invention, the following four ink formulations were prepared, and their specific formulas (by weight percentage) are shown in the table below:

[0047] Components Example 1 Example 2 Example 3 Comparative Example 1 (without rosin monomer) Aqueous WPUA emulsion (35%) 30.0 32.0 28.0 35.0 Acrylated rosin ester 8.0 6.0 10.0 0.0 Photoinitiator BAPO 1.6 1.6 1.6 1.6 Photoinitiator HMPP 2.4 2.4 2.4 2.4 Diethanol amine 1.5 1.5 1.5 1.5 Carbon black color paste (20% solid content) 25.0 25.0 25.0 25.0 1,2-propanediol 6.0 6.0 6.0 6.0 Propylene glycol methyl ether acetate (PMA) 3.0 3.0 3.0 3.0 Surfactant BYK-3455 0.5 0.5 0.5 0.5 Defoamer BYK-024 0.2 0.2 0.2 0.2 Deionized water To 100 To 100 To 100 To 100 Resin / monomer ratio 3.75 5.33 2.8 -

[0048] The preparation steps are as follows (taking Example 1 as an example):

[0049] S1. Pre-dispersion: This is carried out in a brown, light-proof reaction flask equipped with heating and magnetic stirring. 8.0 g of rosin acrylate is added to the flask, and the temperature is raised to 55°C (according to the preferred embodiment of claim 8), while stirring continuously until it is completely melted into a transparent liquid. Subsequently, under continuous stirring, 1.6 g of BAPO, 2.4 g of HMPP, and 1.5 g of diethanolamine are added sequentially. The temperature is maintained at 50-60°C, and the mixture is stirred at 300 rpm for approximately 30 minutes until all solids are completely dissolved, yielding a homogeneous, transparent premix A.

[0050] S2. Preparation of Coloring Paste: In another container, add 25.0g of carbon black coloring paste (which already contains some dispersing resin), 6.0g of 1,2-propanediol, 3.0g of PMA, and 10.0g (one-third of the total) of aqueous WPUA emulsion. Pre-disperse using a high-speed disperser at 1500 rpm for 10 minutes, then transfer to a basket mill and grind and disperse using 0.4mm zirconia beads for 2 hours. Sample and test the particle size every 30 minutes until the D90 particle size of the pigment particles in the paste is less than 200nm, obtaining coloring paste B.

[0051] S3. Preparation of the main emulsion: In a 500ml beaker, add the remaining 20.0g of aqueous WPUA emulsion and approximately 15.0g of deionized water (reserve some water for adjusting the final viscosity). Mix at low speed (400 rpm) for 15 minutes to form a uniform, slightly bluish main emulsion C.

[0052] S4. Final Mixing: While continuously stirring the main emulsion C, increase the stirring speed to 900 rpm. Using a constant pressure dropping funnel, slowly and evenly add the premix A dropwise to the main emulsion C over 20 minutes. After the addition is complete, continue stirring at this speed for 15 minutes to ensure complete emulsification and dispersion of solution A. Subsequently, add colorant B, 0.5g of surfactant BYK-3455, and 0.2g of defoamer BYK-024 in sequence.

[0053] S5. Post-processing: The mixture obtained in step S4 is continuously stirred and matured at 500 rpm for 1 hour at room temperature (25±2℃) to fully stabilize the system and remove micro-bubbles. Finally, the ink is pressurized using an inert gas (such as nitrogen) and filtered through a polyvinylidene fluoride (PVDF) filter with a pore size of 0.8 μm to obtain the final high-performance water-based UV-curable inkjet ink.

[0054] III. Performance Testing and Effect Verification

[0055] The inks prepared in Examples 1-3 and Comparative Example 1 were filled into a Ricoh G5 printhead printing tester and printed on untreated polyethylene (PE) plastic sheets. The printed pattern was passed through a UV curing machine at a speed of 5 m / min under an 80 W / cm mercury lamp. The performance of the cured ink film was tested, and the results are shown in the table below.

[0056] Table 2: Ink Performance Test Results of Examples and Comparative Examples

[0057] Test item Test method / standard Example 1 Example 2 Example 3 Comparative Example 1 Viscosity (25℃, mPa·s) Brookfield DV2T rotational viscometer 10.5 9.8 11.2 8.5 Surface tension (25℃, mN / m) Platinum plate method, Krius K100 surface tension meter 26.2 26.8 25.5 28.5 Adhesion (crosshatch method) GB / T 9286-1998, 3M 610 tape peeling 0 level 0 level 1 level 4 level Degree of curing Acetone rubbing method (50 times back and forth) No change No change Slight loss of gloss Ink film peeling off Storage stability (50℃, 7 days) Observation state, test viscosity change rate No precipitation, viscosity +3% No precipitation, viscosity +5% Slight delamination, can be restored after shaking No precipitation, viscosity +8%

[0058] Examples 1 and 2 exhibited the best performance in all aspects, with resin-to-monomer ratios (3.75 and 5.33, respectively) falling within the optimal range of 3:1 to 5:1 protected by claim 3. Therefore, they demonstrated Grade 0 adhesion and complete curing on PE substrates, and were also storage stable. Example 2, due to its slightly higher resin content, showed slightly better adhesion than Example 3.

[0059] The resin / monomer ratio (2.8) in Example 3 was slightly lower than the lower limit of the preferred range, resulting in a slight decrease in adhesion (level 1) and slight stratification after storage, indicating that the long-term stability of the system may be challenged when the ratio is close to the lower limit.

[0060] Comparative Example 1, without the addition of the core component of this invention, rosin-based tackifying monomer, exhibited extremely poor adhesion to non-absorbent PE substrates despite its acceptable viscosity and surface tension. Furthermore, it was incompletely cured and easily rubbed off with acetone, failing to meet usage requirements. This conversely demonstrates the crucial role of rosin-based tackifying monomers in improving adhesion to non-absorbent substrates.

[0061] This invention details a water-based UV-curable inkjet ink and its preparation method. The core of this invention lies in using a specific ratio of water-based UV-curable resin emulsion and a well-defined rosin-based tackifying monomer to form the main framework, supplemented by a compounded photoinitiator system, amine synergists, and mixed organic cosolvents. Through a strictly controlled preparation process, the ink achieves excellent adhesion, rapid and uniform deep curing, and superior storage stability on non-absorbent substrates. This achieves the beneficial effects of improved adhesion, guaranteed curing efficiency, and environmental friendliness as expected by this invention. Furthermore, all technical features in the claims are fully supported and verified in the embodiments.

[0062] Although embodiments of the present invention have been shown and described, these specific embodiments are merely explanations of the invention and are not intended to limit it. The specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. After reading this specification, those skilled in the art may make modifications, substitutions, and variations to the embodiments as needed without departing from the principles and spirit of the invention, but such modifications, substitutions, and variations are protected by patent law as long as they are within the scope of the claims of the present invention.

Claims

1. A water-based UV-curable inkjet ink, characterized in that: By weight percentage, it includes the following components: Waterborne UV-curable resin emulsion 25%-35%; Rosin-based thickening monomers 5%-12%; Photoinitiator 4%-7%; Amine synergists 1%-2%; Colorant 3%-8%; Organic co-solvents 8%-12%; Surfactant 0.2%-0.8%; Defoamer 0.1%-0.3%; The remainder is deionized water; The rosin-based tackifying monomer is rosin acrylate, and its general molecular structure formula is as follows: ； Where R is hydrogen or methyl, the addition of this rosin-based tackifying monomer is used to significantly improve the adhesion of the ink-cured film to non-absorbent substrates.

2. The water-based UV-curable inkjet ink according to claim 1, characterized in that: The rosin-based tackifying monomer is obtained by esterification of natural rosin with acrylic acid or methacrylic acid after purification, and its acid value is less than 10 mg KOH / g.

3. The water-based UV-curable inkjet ink according to claim 1, characterized in that: The aqueous photocurable resin emulsion is an aqueous polyurethane acrylate, and its weight ratio with the rosin-based tackifying monomer is in the range of 3:1 to 5:

1.

4. The water-based UV-curable inkjet ink according to claim 1, characterized in that: The photoinitiator is a compound of phenylphosphine dioxide and 2-hydroxy-2-methyl-1-phenyl-1-propanone, with a weight ratio of 1:1.

5.

5. The water-based UV-curable inkjet ink according to claim 1, characterized in that: The organic co-solvent is a mixture of 1,2-propanediol and propylene glycol methyl ether acetate, with a weight ratio of 2:

1.

6. The water-based UV-curable inkjet ink according to claim 1, characterized in that: The viscosity of the ink is 8-12 mPa·s at 25°C, and the surface tension is 24-28 mN / m.

7. A method for preparing an aqueous UV-curable inkjet ink as described in any one of claims 1 to 6, characterized in that: Includes the following steps: S1. Pre-dispersion: Under light-protected conditions, the rosin-based tackifying monomer is heated to 50-60°C to make it a transparent liquid. Then, the photoinitiator and amine synergist are added under stirring until they are completely dissolved and mixed to obtain premixed liquid A. S2. Preparation of color paste: Mix the colorant, all the organic cosolvents and one-third of the total amount of water-based photocurable resin emulsion, and grind and disperse them using a sand mill until the particle size is less than 200 nm to obtain color paste B. S3. Preparation of main emulsion: Under low-speed stirring, mix the remaining water-based light-curing resin emulsion with deionized water to form a uniform main emulsion C; S4. Final mixing: While continuously stirring the main emulsion C, slowly add the premixed liquid A dropwise to evenly disperse it in the emulsion; then add the coloring paste B, surfactant and defoamer; S5. Post-processing: The mixture obtained in step (4) is continuously stirred and matured at room temperature for 1 hour, and finally filtered through a filter with a pore size of 0.8 μm to obtain the high-performance water-based UV curing inkjet ink.

8. The preparation method according to claim 7, characterized in that: The heating temperature in step S1 is 55°C.

9. The preparation method according to claim 7, characterized in that: The low-speed stirring speed in step S4 is 300-500 rpm, and the continuous stirring speed is 800-1000 rpm.

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