UV offset printing reverse surface oil system and printing method thereof

Abstract

The invention discloses a UV offset printing reverse surface oil system and a printing method thereof, and belongs to the technical field of packaging printing ink. The UV offset printing reverse surface oil system is composed of bottom surface oil and top surface oil which are functionally layered. The bottom surface oil is rich in a high-functionality monomer and an adhesion promoting component, and specially reacts with the reverse bottom oil to form regular micro-textures and ensure interlayer adhesion; the top layer oil is rich in high-refractive-index resin, high-functionality monomers and wear-resistant components, and is responsible for optical synergy and surface protection. Through a semi-curing-coating-full-curing precise process, the functions of texture forming, bottom layer attachment, optical brightening and surface protection are precisely separated and fused, and a final printed product has strong visual impact force, extremely smooth hand feeling and excellent physical performance at the same time; the industrial problem that a traditional single-layer reverse process cannot give consideration to multiple high-performance indexes is solved.

Description

Technical Field

[0001] This invention relates to the technical field of packaging printing inks, and in particular to a UV offset printing reverse side ink system and its printing method. Background Technology

[0002] UV reverse printing is a key technology for achieving special visual effects such as frosted, ice flower, and pearlescent finishes on high-end packaging. This process typically involves applying a UV reverse base coat and a UV reverse top coat to the substrate. By utilizing the polarity difference or surface energy mismatch between the two, cohesive shrinkage occurs during the curing process, thereby forming unique micro-textures.

[0003] In existing technologies, improvements to UV reverse engineering processes mostly focus on the formulation of base oil and top oil, for example: Chinese patent document CN110183898A discloses a UV reverse matte process, which improves direct adhesion to ordinary offset printing inks by optimizing the resin system and component ratio of the reverse base oil and top oil, eliminating the need for pre-coating with water-based base oil and thus improving printing efficiency. However, the core purpose of this technical solution is still to form a stable matte texture, and its top oil function is singular. It does not propose an effective solution for how to actively enhance the optical effects of underlying pearlescent, metallic, and other special inks.

[0004] Furthermore, another Chinese patent document, CN114103499A, addresses the issue of weak pearlescent effects in offset printing by proposing the addition of fine-particle pearlescent powder to a UV reverse primer. It utilizes the shrinkage of the topcoat on the low surface energy primer to form irregular "small protrusions" that act as "micro-mirrors" to amplify the pearlescent effect. While this approach enhances the pearlescent feel to some extent, it relies on a single topcoat layer to simultaneously achieve both "texture shaping" and "surface protection." This single structure leads to technological compromises: to achieve strong shrinkage, the topcoat requires high shrinkage stress, which often results in poor coating leveling, a rough surface, and poor abrasion resistance; conversely, if a smooth, abrasion-resistant surface is desired, insufficient shrinkage force may result in a bland texture effect and limited optical enhancement.

[0005] In summary, those skilled in the art have long faced a technical dilemma that has not been effectively resolved: how to obtain a high-gloss, extremely smooth, and wear-resistant physical surface while using reverse processes to generate strong visual textures, such as for pearlescent enhancement? Existing single-layer UV reverse surface oil structures, due to their functional limitations, cannot optimally meet both of these requirements simultaneously, which severely restricts their application in the ultra-high-end packaging field.

[0006] Therefore, there is an urgent need for an innovative technical solution that can fundamentally break through the performance bottleneck of single-layer structures and achieve a synergistic leap in visual effects and physical performance. Summary of the Invention

[0007] Based on this, the purpose of this invention is to overcome the above-mentioned shortcomings of existing single-layer UV reverse surface oil technology and to provide a high-performance double-layer composite UV offset printing reverse surface oil system and its printing method.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: A UV offset printing reverse coating system comprising a functionally specific and synergistic bottom coating and a top coating; The underlying surface oil, i.e., the technical means of texture and adhesion layer, includes: a) Use high content, such as 30-40 parts of acrylate hexafunctional monomers, such as DPHA, to ensure strong and uniform shrinkage force during curing, which reacts with the reverse primer to form a regular and delicate micro-convex mirror array, laying the structural foundation for optical enhancement.

[0009] b) Add 1-3 parts of phosphate ester adhesion promoter. This component can effectively migrate to the interface between the bottom layer and the reverse primer / substrate. Through chemical bonding, it fundamentally solves the interlayer adhesion problem. It is especially suitable for non-absorbent substrates such as PET and gold and silver cardboard.

[0010] The technical means for the top layer oil, i.e., the optical and protective layer, include: a) A high content, such as 20-30 parts, of high-refractive-index polyurethane acrylate, wherein the refractive index of the polyurethane acrylate is >1.55, is used, supplemented with 15-25 parts of hexafunctional monomers. The high-refractive-index resin actively improves the light reflection efficiency of the underlying layer, while the hexafunctional monomers work synergistically with the underlying layer to ensure that the top layer itself can also form a dense network with high cross-linking density.

[0011] b) Adding 2-5 parts of nano-silica abrasion-resistant agent significantly enhances the scratch resistance and wear resistance of the final surface.

[0012] This invention also provides a printing method using the above-mentioned topcoat system, the key of which lies in the precision process of semi-curing-coating-full curing: (1) The bottom layer oil is semi-cured. The UV energy of the semi-curing is 50-100 millijoules per square centimeter, which can fix the micro-texture of the surface, but retain some internal reactivity.

[0013] (2) Apply the top coat immediately and allow it to fully cure. During this process, the active monomers in the top coat can slightly swell the incompletely cross-linked parts of the bottom coat, forming a strong interpenetrating network structure, achieving chemical bonding between the two layers and eliminating the risk of delamination.

[0014] Compared with the prior art, the beneficial effects of the present invention include: 1. Synergistic effect and performance breakthrough: The bottom layer focuses on building optimal texture and ensuring adhesion, while the top layer focuses on optical brightening and surface protection. The clear division of labor between the two produces a synergistic effect greater than the sum of its parts. The final printed product has a strong visual shimmer, an extremely smooth surface, and excellent abrasion resistance.

[0015] 2. Fundamental solution to adhesion: The adhesion promoter in the base layer, combined with a special semi-curing process, ensures the firm adhesion of the entire coating system from both the interface chemistry and physical structure levels, solving the problem of interlayer separation on complex substrates.

[0016] 3. Ultimate Optical Effects: The combination of the high-refractive-index resin on the top layer and the regular micro-texture on the bottom layer achieves ultimate control over light, resulting in brightness and vibrancy of pearlescent and metallic effects that far surpass traditional single-layer processes.

[0017] 4. Technological innovation and controllable results: The semi-curing process is the key to achieving a perfect bond between the two layers. By controlling the semi-curing energy, the texture and interlayer bonding force can be precisely adjusted, realizing the programmability of the process. Attached Figure Description

[0018] Figure 1 This is a process flow diagram of the preparation method of the UV offset printing reverse surface oil system of the present invention. Detailed Implementation

[0019] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to specific examples and accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0020] Specifically, in the following embodiments, all parts of the components are parts by weight.

[0021] Before evaluating the performance of the following embodiments and comparative examples, the test methods used in this application should be clarified first: 1. Pearl gloss: Use a 60-degree gloss meter, such as BYK-Gardnermicro-TRI-gloss, to measure the specular gloss (GU) of the pearlescent area after applying the topcoat. The higher the value, the better the reflective effect.

[0022] 2. Adhesion: Tested according to standard GB / T9286-1998 using a cross-cut adhesion tester and 3M tape. Ratings range from 0 to 5, with 0 being the best (no peeling) and 5 being the worst.

[0023] 3. Abrasion resistance: Using an abrasion tester, such as JN-5336, with a 500g standard rubber load, after 100 abrasion cycles, measure the gloss retention rate. The unit of this gloss retention rate is _____.

[0024] 4. Leveling / Surface Feel: A combination of visual inspection and tactile examination is used to assess surface smoothness, orange peel effect, and gloss. The evaluation is divided into four levels: "Excellent," "Good," "Average," and "Poor." "Excellent" indicates a mirror-like smooth surface; "Good" indicates smooth but with a slightly textured feel; "Average" indicates perceptible roughness; and "Poor" indicates noticeable orange peel or pinholes.

[0025] Examples 1-3: This set of examples aims to demonstrate the effect of changes in the content of high-functionality monomers and adhesion promoters in the bottom coat on performance; and the top coat in this set of examples all uses a fixed formulation, that is, the same as the top coat in Example 4.

[0026] Table 1: Weight proportions and properties of the base coat

[0027] Based on the analysis in Table 1, it can be seen that: Example 1 achieved the best balance; Example 2, due to its low DPHA content, resulted in insufficient shrinkage and a shallower texture; although Example 3 had a deep texture, its formulation cost was slightly higher. When the adhesion promoter content was below 1 part, the adhesion began to decrease.

[0028] Examples 4-6: This set of examples aims to demonstrate the effect of changes in the content of high refractive index resin and wear-resistant agent in the top coat on performance; the bottom coats in this set of examples all use a fixed formulation, the same as the bottom coat formulation in Example 1.

[0029] Table 2: Topcoat Oil (by weight) formulation and properties

[0030] Based on the analysis in Table 2, it can be seen that Example 4 achieved a perfect balance between optical effect and tactile feel. Example 5, due to the insufficient amount of high refractive index resin, resulted in a significant decrease in gloss; although Example 6 had high gloss, the high content of nanoparticles resulted in a slightly hard feel and increased cost.

[0031] Example 7: This example combines the results above and uses the optimal combination of bottom and top coats, i.e., bottom coat formula: same as in Example 1; top coat formula: same as in Example 4.

[0032] The preparation method of Example 7 is as follows: the base and top coat oils are mixed according to conventional methods, and then stirred and dispersed at a speed of 1000-1200 r / min for 30-40 minutes until uniform.

[0033] Example 8: This example uses the same topcoat system as Example 7, but systematically tests the effect of semi-curing energy on the final effect; its printing method is the same as Example 2, only the semi-curing energy in step (2) is changed.

[0034] Table 3: Effect of semi-curing energy on performance as shown in Example 7

[0035] Based on the analysis in Table 3, it can be seen that the semi-curing energy is one of the key steps in the process of this invention. If the energy is too low, such as 30 millijoules per square centimeter, the underlying texture cannot be stably formed and the adhesion is poor. If the energy is too high, such as 150 millijoules per square centimeter, the excessive cross-linking of the underlying layer affects the molecular interpenetration with the top layer, resulting in decreased leveling and a poorer feel. Therefore, an energy of about 70 millijoules per square centimeter can achieve the best balance between texture shaping and interlayer bonding.

[0036] Furthermore, the present invention provides the following comparative examples: Comparative Example 1, i.e., single-layer structure: A single-sided printing process was performed using a simple mixture of the bottom layer formulation from Example 1 and the top layer formulation from Example 4. Specifically: 12 parts epoxy acrylate, 13 parts polyurethane acrylate, 25 parts high refractive index PUA, 55 parts DPHA, 25 parts TMPTA, 2 parts phosphate ester accelerator, and nano... The mixture contained 15 parts photoinitiator and 3 parts leveling agent; Comparative Example 1 used a full curing process.

[0037] Comparative Example 2, i.e. no adhesion promoter: the topcoat system of Example 7 was used, but no phosphate ester adhesion promoter was added to the bottom topcoat.

[0038] Comparative Example 3, i.e. without high refractive index resin: The topcoat system of Example 7 was used, but the high refractive index PUA in the top coat was replaced by an equal amount of ordinary polyurethane acrylate, such as using a polyurethane acrylate with a refractive index of 1.48.

[0039] Comparative Example 4, i.e. fully cured base layer: The topcoat system of Example 7 was used, but the semi-curing step was omitted. The base layer was fully cured with an energy of 400 millijoules per square centimeter before the top layer was applied.

[0040] Furthermore, Examples 7 and 8 were semi-cured at 70 millijoules per square centimeter and printed under the same conditions as the comparative examples, and their performance was tested. The results are as follows: Table 4: Comparison of Comprehensive Performance Test Results

[0041] The comparison data in Table 4 shows that: 1. Synergistic effect of dual-layer structure: The performance of Examples 7 / 8 is superior to that of Comparative Example 1, proving that the dual-layer design that separates texture attachment and optical protection functions solves the inherent contradiction that a single-layer system cannot take into account multiple high-performance indicators.

[0042] 2. Necessity of adhesion promoters: Comparative Example 2 showed extremely poor adhesion, proving that phosphate ester adhesion promoters are key components and indispensable for ensuring a strong bond between the two-layer system and the difficult-to-adhere substrate.

[0043] 3. The core role of high refractive index resin: The gloss of Comparative Example 3 dropped significantly to 75 GU, proving that high refractive index resin is the core of producing excellent optical effects, and its ability to control light is irreplaceable by ordinary resin.

[0044] 4. The criticality of the semi-curing process: Comparative Example 4 is inferior to the embodiment of the present invention in terms of gloss, adhesion and feel, which proves that the semi-curing process is the decisive step to achieve the ideal combination of the bottom layer and the top layer and ensure the final comprehensive performance.

[0045] Specifically, please refer to Figure 1 The UV offset printing reverse coating system of the present invention comprises two functionally independent components: a bottom coating, i.e., a texture and adhesion layer, and a top coating, i.e., an optical and protective layer; the preparation methods are as follows: 1. Preparation of the base coat oil Function: Specifically designed to react with the reverse primer to form a regular microtexture and provide excellent interlayer adhesion.

[0046] step: a. Feeding and mixing: Under light-protected conditions, polymeric prepolymer A, acrylate hexafunctional monomers and phosphate adhesion promoters are added to a stirred tank in parts by weight; the polymeric prepolymer A can be epoxy acrylate or polyurethane acrylate.

[0047] b. High-speed dispersion: Start stirring and disperse at a speed of 1000-1300 rpm for 15-30 minutes.

[0048] c. Adding additives: Reduce the rotation speed to 400-600 rpm, and add photoinitiator A and leveling agent A in sequence.

[0049] d. Stir until homogeneous: Continue stirring at this speed for 30-45 minutes until all components are evenly mixed to obtain a uniform, transparent liquid, i.e., the bottom layer oil.

[0050] e. Discharge: filtration, discharge, and packaging.

[0051] 2. Preparation of Topcoat Oil Function: Responsible for providing a high refractive index to enhance optical effects and forming a smooth, wear-resistant protective layer.

[0052] step: a. Feeding and mixing: Under light-protected conditions, high-refractive-index polyurethane acrylate and acrylate monomers, including hexafunctional and monofunctional monomers, are added to the stirred tank in parts by weight.

[0053] b. High-speed dispersion: Start stirring and disperse at a speed of 1000-1300 rpm for 15-30 minutes to ensure that the prepolymer is completely dissolved.

[0054] c. Adding additives: While maintaining the rotation speed, add photoinitiator B, nano silica wear-resistant agent and leveling agent B in sequence.

[0055] d. Fine dispersion: Increase the rotation speed to 1200-1500 rpm and continue dispersing for 30-40 minutes until the fineness reaches below 5μm, ensuring that the nanoparticles are fully dispersed to obtain a uniform and transparent liquid, i.e., topcoat oil.

[0056] e. Discharge: filtration, discharge, and packaging.

[0057] In summary, the different embodiments of the UV offset reverse surface oil system of the present invention fully verify the feasibility, reproducibility and technical superiority of the dual-layer composite surface oil system and its printing method; each component can work effectively within its claimed protection scope, and through synergistic effect, they jointly achieve technical effects far exceeding those of the prior art.

[0058] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0059] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A UV offset printing reverse surface oil system, characterized in that, Includes functionally independent base coat and top coat; The base coat is composed of the following components in parts by weight: 20-30 parts of polymerizable prepolymer, 30-40 parts of acrylate hexafunctional monomer, 1-3 parts of phosphate ester adhesion promoter, 5-10 parts of photoinitiator A, and 0.5-2 parts of leveling agent A; The topcoat oil is composed of the following components in parts by weight: 20-30 parts of high refractive index polyurethane acrylate, 15-25 parts of acrylate hexafunctional monomers, 20-30 parts of acrylate monofunctional monomers, 2-5 parts of nano silica abrasion resistant agent, 5-10 parts of photoinitiator B, and 1-3 parts of leveling agent B.

2. The UV offset printing reverse side ink system according to claim 1, characterized in that: The polymeric prepolymer in the bottom coat is a mixture of epoxy acrylate and polyurethane acrylate.

3. The UV offset printing reverse side ink system according to claim 2, characterized in that: The weight ratio of epoxy acrylate to polyurethane acrylate is 1:1 to 1:1.

5.

4. The UV offset printing reverse side ink system according to claim 1, characterized in that: The high-refractive-index polyurethane acrylate in the topcoat oil has a refractive index greater than 1.

55.

5. The UV offset printing reverse side ink system according to claim 1, characterized in that: The acrylate hexafunctional monomer is dipentaerythritol hexaacrylate.

6. A printing method using the UV offset reverse side ink system as described in any one of claims 1-5, characterized in that, Includes the following steps: a. Print a UV reverse primer on the substrate and then UV cure it; b. Apply the base coat onto the cured UV reverse primer; c. Use UV light with an energy of 50-100 millijoules per square centimeter to semi-cur the base coat; d. Apply the top coat to the semi-cured bottom coat surface; e. The composite coating is fully cured using UV light with an energy of 300-600 millijoules per square centimeter.

7. The printing method of the UV offset reverse side ink system according to claim 6, characterized in that: The UV light energy of the semi-cured material described in step c is 60-80 millijoules per square centimeter.

8. The printing method of the UV offset reverse side ink system according to claim 6, characterized in that: The printing substrate is PET or gold / silver cardboard.

9. A printed matter, characterized in that, It is prepared by the printing method of the UV offset reverse side oil system according to any one of claims 6 to 8.

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