A uv coating adhesive for embossing printing and a preparation method thereof

Abstract

The application provides a UV laminating glue for embossing printing and a preparation method thereof. The glue comprises the following components: photocuring resin 45-55%, high molecular pressure sensitive resin 5-10%, photoinitiator 2-5%, active diluent 30-40% and auxiliary agent 0.5-2%. The photocuring resin and the high molecular pressure sensitive resin are used in cooperation, initial adhesion is provided before curing to prevent film displacement bubbles, and the flexibility of the glue film is improved after curing to avoid cracking of the embossing part. The active diluent is compounded by a single functional group diluent and a double functional group diluent to balance the wetting permeability and the cohesive strength. The photoinitiator is used to realize second-level deep curing, and post-processing can be carried out without standing, thereby significantly improving the film lamination degree, bending resistance and production efficiency of the embossing printed product.

Description

[Technical Field] This invention belongs to the field of printing technology, and in particular relates to a UV coating adhesive for embossed printing and its preparation method. [Background Technology] Lamination, a crucial post-printing finishing process, traditionally employs water-based or solvent-based adhesive systems. While water-based adhesives offer environmental advantages, their curing relies on the physical evaporation of moisture. This is particularly problematic when used with deep embossing processes, where the raised structure hinders moisture diffusion, requiring a resting period of at least 24 hours before proceeding to the next step. This severely restricts the achievement of short-cycle delivery (7-10 days). Furthermore, water-based adhesives suffer from insufficient initial tack and final bond strength, with laminated products typically exhibiting a film-to-paper peel strength of only 1.5-2.2 N, failing to meet the demands of subsequent complex processing such as die-cutting and box gluing. Additionally, to prevent smudging when stacking large areas of dark-colored printed material, approximately 4 g / m² of anti-stick powder is applied during printing. Residual powder interferes with the adhesive layer's wetting and anchoring of the paper, further weakening adhesion and affecting the positioning accuracy of precision processes like embossing and die-cutting. Water-based films, containing hydrophilic components, are prone to absorbing moisture and plasticizing in high-humidity environments, leading to decreased interfacial bonding and delamination, compromising long-term reliability. Although solvent-based adhesives dry slightly faster, they emit high levels of volatile organic compounds (VOCs), pose significant safety hazards, and do not align with the trend of green manufacturing.

[0001] Ultraviolet (UV) curing technology, with its advantages of second-level curing, solvent-free evaporation, and excellent film-forming properties, provides a new path for accelerating the lamination process. However, existing UV laminating adhesives are mostly designed for planar printed products and are severely inadequate for three-dimensional embossed structures such as reliefs. On the one hand, the rigid resin system used to pursue high crosslinking density results in brittle films that are prone to cracking due to stress concentration in raised and bent areas. On the other hand, conventional UV adhesives have insufficient initial tack before curing, making it difficult to maintain a tight bond between the film and complex curved surfaces, and causing bubbles and displacement during the lamination process. [Summary of the Invention] The purpose of this invention is to provide a UV coating adhesive for embossed printing, which solves the technical problems of existing coating adhesives being prone to cracking, having insufficient initial adhesion leading to poor bonding, and having low peel strength after curing when coating three-dimensional embossed printed materials.

[0002] This invention is achieved by the following technical solution: A UV coating adhesive for embossing printing, comprising the following components by weight percentage: UV-curable resin 45-55%; 5-10% high molecular weight pressure-sensitive resin; Photoinitiator 2-5%; 30-40% reactive diluent; Additives 0.5-2%.

[0003] This invention uses a UV-curable resin as the matrix, combined with a high-molecular-weight pressure-sensitive resin. During the coating roll pressing process, the adhesive rapidly impregnates and anchors within the embossed texture. The high-molecular-weight pressure-sensitive resin provides initial tack, effectively preventing micro-displacement or rebound of the film before UV curing. After curing, the long-chain flexible structure of the high-molecular-weight pressure-sensitive resin, combined with the synergistic effect of the reactive diluent, effectively reduces the rigidity of the cross-linked network, increasing the elongation at break of the film. This allows the adhesive layer to release stress as the embossed paper deforms during die-cutting and bending, preventing brittle cracking due to stress concentration at the raised areas. Simultaneously, a photoinitiator enables second-level curing, eliminating the need for post-coating drying before immediate entry into subsequent processing steps, significantly shortening the production cycle and meeting the demands of short-cycle delivery.

[0004] Preferably, the active diluent includes monofunctional diluents and difunctional diluents.

[0005] Preferably, the monofunctional diluent is one of tetrahydrofuran acrylate, isobornyl acrylate, or cyclotrimethylolpropane methyl acetal acrylate.

[0006] This invention employs a monofunctional diluent, utilizing its low viscosity to reduce the overall viscosity of the system, thereby enhancing the wetting and capillary penetration capabilities of the UV coating adhesive on the printing ink substrate. This ensures the adhesive layer can fully fill the embossed texture. Furthermore, because its molecular structure contains only one polymerizable double bond, the cross-linked network formed after curing has a relatively low density and stronger chain segment mobility, effectively releasing curing shrinkage stress and imparting excellent flexibility to the film. This not only strengthens the interfacial bonding between the coating film (e.g., BOPP film) and the printing ink but also prevents the adhesive layer from cracking or peeling due to stress concentration at the embossed areas.

[0007] Preferably, the difunctional diluent is one of 1,6-hexanediol diacrylate or tripropylene glycol diacrylate.

[0008] This invention uses a difunctional diluent to introduce double bond crosslinking points, which can rapidly form a dense three-dimensional crosslinking network under photoinitiation. This significantly improves the UV curing speed and the cohesive strength of the coating adhesive, ensuring that the coating adhesive has excellent aging resistance and bonding strength, thereby preventing the coating paper from bubbling or peeling off in subsequent processes.

[0009] Preferably, the mass ratio of the monofunctional diluent to the difunctional diluent is 2:1.

[0010] Preferably, the photocurable resin is polyurethane acrylate.

[0011] The photocurable resin is selected from polyurethane acrylates with a low glass transition temperature (Tg) and a Tg range of -50 to 20°C.

[0012] Preferably, the polymeric pressure-sensitive resin is a hot-melt pure acrylate resin.

[0013] Preferably, the photoinitiator is 2-hydroxy-2-methyl-1-phenyl-1-propanone.

[0014] This invention uses 2-hydroxy-2-methyl-1-phenyl-1-propanone as a photoinitiator. It has an α-hydroxy ketone structure and rapidly decomposes upon absorbing ultraviolet light to generate highly reactive free radicals, initiating the polymerization reaction of the system. This enables second-level deep curing of the adhesive layer, significantly improving UV curing efficiency and monomer conversion rate, ensuring excellent curing speed and cohesive crosslinking of the laminating adhesive. Simultaneously, this photoinitiator exhibits good solubility in acrylate monomers / oligomers, good compatibility with the system, and low yellowing properties due to its lack of amine groups. This prevents the laminated paper from becoming sticky or peeling off before curing in subsequent processes, ensuring the color reproduction and appearance quality of embossed printing, and meeting the process requirements for short-cycle delivery.

[0015] Preferably, the additive is an antifoaming agent and / or a wetting agent.

[0016] The method for preparing the UV coating adhesive for embossing printing includes the following steps: S1. Premixing: Add the reactive diluent to the mixing container and stir at 400 r / min for 30 min until uniform; S2. Main mixing: Add the photocurable resin, high molecular weight pressure-sensitive resin, photoinitiator and additives to the reactive diluent mentioned in step S1 in sequence, and stir and disperse at 600 r / min for 60 min until uniform to obtain the crude product; S3. Impurity Removal: The crude product described in step S2 is filtered through a filter bag to remove impurities, thereby obtaining the UV coating adhesive.

[0017] This invention proposes a UV coating adhesive for embossed printing, comprising a UV-curable resin, a high-molecular-weight pressure-sensitive resin, a photoinitiator, a reactive diluent, and additives. First, the UV-curable resin serves as the strength framework; its high reactivity and the soft / hard segment structure of polyurethane endow the adhesive film with excellent instant curing ability and flexural toughness. The high-molecular-weight pressure-sensitive resin acts as a functional synergistic layer, providing initial tack before curing to ensure tight adhesion between the film and the three-dimensional embossed surface, preventing air bubbles and displacement. After curing, it synergizes with the UV-curable resin to further enhance the film's flexibility and interfacial bonding strength. Second, the reactive diluent, through a combination of monofunctional and difunctional diluents, reduces the system viscosity to enhance wetting and penetration of printing inks while precisely controlling the crosslinking density—the monofunctional component inhibits excessive crosslinking to maintain flexibility, while the difunctional component introduces appropriate crosslinking points to ensure cohesive strength. Together, they achieve peel strength after bending in the embossed area. The photoinitiator ensures surface drying within seconds. Finally, the additives effectively suppress coating bubbles and reduce surface tension, thereby improving the wetting ability of the anti-stick powder coating paper surface.

[0018] This invention also proposes a method for preparing UV coating adhesive for embossing printing. Through a three-step process of "premixing-primary mixing-impurity removal", the photoinitiator is prevented from being thermally polymerized in advance and the high molecular pressure-sensitive resin is fully swollen and dispersed. The final product is a coating adhesive system that combines instant curing, high peel strength, excellent three-dimensional compatibility and high humidity environment stability. This solves the technical problems of traditional water-based adhesives in terms of drying efficiency, bonding reliability and compatibility with embossing processes, and supports the short-cycle delivery requirement of 7-10 days.

Detailed Implementation Methods

[0019] Example 2 A method for preparing a UV coating adhesive for embossing printing includes the following steps: S1. Premixing: Add the reactive diluent, which is a mixture of isoborneol acrylate and 1,6-hexanediol diacrylate in a mass ratio of 2:1, into a stirring container and stir at 400 r / min for 30 min until uniform. S2. Main mixing: Add 50% photocurable resin, 10% high molecular weight pressure-sensitive resin, 4% photoinitiator and 1% additives to 35% of the reactive diluent mentioned in step S1, and stir and disperse at 600 r / min for 60 min until uniform to obtain the crude product. S3. Impurity Removal: The crude product described in step S2 is filtered through a 200-mesh filter bag to remove impurities and obtain the UV coating adhesive.

[0020] Example 3 A method for preparing a UV coating adhesive for embossing printing includes the following steps: S1. Premixing: Add the reactive diluent, which is a mixture of cyclotrimethylolpropane methyl acetal acrylate and tripropylene glycol diacrylate in a mass ratio of 2:1, into a stirring container and stir and disperse at 400 r / min for 30 min until uniform. S2. Main mixing: Add 50% photocurable resin, 7% high molecular weight pressure-sensitive resin, 4% photoinitiator and 1% additives to 38% of the reactive diluent mentioned in step S1, and stir and disperse at 600 r / min for 60 min until uniform to obtain the crude product. S3. Impurity Removal: The crude product described in step S2 is filtered through a 200-mesh filter bag to remove impurities and obtain the UV coating adhesive.

[0021] Comparative Example 1 A method for preparing a UV coating adhesive includes the following steps: S1. Premixing: Add tetrahydrofuran acrylate to a mixing container and stir at 400 r / min for 30 min until uniform; S2. Main mixing: Add 52% photocurable resin, 8% high molecular weight pressure-sensitive resin, 4% photoinitiator and 1% additive to 35% of the reactive diluent mentioned in step S1, and stir and disperse at 600 r / min for 60 min until uniform to obtain the crude product. S3. Impurity Removal: The crude product described in step S2 is filtered through a 200-mesh filter bag to remove impurities and obtain the UV coating adhesive.

[0022] Comparative Example 2 A method for preparing a UV coating adhesive for embossing printing includes the following steps: S1. Premixing: Add 1,6-hexanediol diacrylate to a mixing container and stir at 400 r / min for 30 min until uniform; S2. Main mixing: Add 52% photocurable resin, 8% high molecular weight pressure-sensitive resin, 4% photoinitiator and 1% additive to 35% of the reactive diluent mentioned in step S1, and stir and disperse at 600 r / min for 60 min until uniform to obtain the crude product. S3. Impurity Removal: The crude product described in step S2 is filtered through a 200-mesh filter bag to remove impurities and obtain the UV coating adhesive.

[0023] Comparative Example 3 Traditional water-based adhesives Table 1 Components of Examples 1-3 and Comparative Examples 1-2

[0024] The UV coating adhesives of Examples 1-3 and Comparative Examples 1-2 are used to coat the substrate, including the following steps: A1. Ink printing: Printing on the substrate with quick-drying ink, letting it stand to allow the ink to dry to the surface, and then obtaining the printed product. A2. Base coat application: Apply the base coat to the surface of the printed material described in step A1, allowing the base coat to penetrate the printed material. A3. Simultaneous lamination and UV curing: Apply UV coating adhesive to the surface of the printed material described in step A2, and simultaneously press the BOPP film together and perform UV curing to obtain a UV-coated test sample.

[0025] Using the conventional water-based adhesive from Comparative Example 3, a film is applied to the substrate, including the following steps: B1. Ink printing: Print the substrate with quick-drying ink, let it stand to allow the ink to dry to the surface, and obtain the printed product; B2. Base coat application: Apply the base coat to the surface of the printed material described in step B1, allowing the base coat to penetrate the printed material. B3. Simultaneous lamination and UV curing: Apply UV coating adhesive to the surface of the printed material described in step B2, and simultaneously press the BOPP film together and perform hot air drying to obtain the water-based lamination test sample.

[0026] The performance of the UV-coated test samples of Examples 1-3 and Comparative Examples 1-2, and the water-based coated test sample of Comparative Example 3 were tested under the following standards and conditions: Peel test: Refer to GB / T27934.1-2011 Control and test methods for lamination process of paper printed matter. Cut a lamination test sample with a width of 25mm and a length of ≥150mm. Perform a 180° peel test at a speed of 300mm / min in an environment of 23±2℃ and 50±5%RH and record the peel force.

[0027] Embossing and denting test: The coated test sample is embossed and indented using an embossing machine. The surface of the coated test sample is observed for bubbles and whether the BOPP film is delaminated.

[0028] Aging test: The coated test specimens that have undergone embossing and indentation processing are placed in a constant temperature and humidity chamber and aged at 60℃ and 80%RH for 72 hours. The presence of bubbles on the surface of the coated test specimens and whether the BOPP film has delaminated are observed.

[0029] Powder application rate: The minimum amount of powder required in the printing process to prevent smudging caused by overlapping printed sheets and to ensure that there are no white spots on the film surface due to poor adhesion caused by powder residue after lamination. 。

[0030] Table 2 Performance Tests of Examples 1-3 and Comparative Examples 1-3

[0031] As shown in Table 2, the peel force of Examples 1-3 was stable at 3.2-4.3N, and no bubbles or delamination were observed in the bending test and aging test. This indicates that the present invention constructs a flexible cross-linked network with a balance between flexibility and cohesive strength through the synergistic effect of high molecular pressure-sensitive resin and reactive diluent. This network can effectively release stress, bend and deform with the relief structure without brittle cracking, and has excellent long-term reliability in high humidity environments.

[0032] In contrast, Comparative Example 1, using a single monofunctional diluent, exhibited low cohesive strength due to insufficient crosslinking density, with a peel strength of only 1.5N. It showed a few bubbles in the die-cutting test and a large number of bubbles in the aging test, indicating poor adhesion, flexibility, and aging resistance. Comparative Example 2, using a single difunctional diluent, had the highest peel strength, but its excessively high crosslinking density resulted in brittle film, leading to delamination in the die-cutting test and severe delamination in the aging test, indicating insufficient overall reliability. Comparative Example 3, using a traditional water-based adhesive, suffered from the lowest peel strength due to the water evaporation curing mechanism and hydrophilic components. Furthermore, it was prone to hygroscopic plasticization in high humidity environments, resulting in numerous bubbles, and required a higher powder coating to prevent contamination, demonstrating poor process adaptability.

[0033] The above description is one implementation method provided in conjunction with specific content. It is not intended that the specific implementation of the present invention is limited to these descriptions. Any technical deductions, substitutions, improvements, etc., that are similar to or based on the present invention should be considered within the scope of protection of this patent.

Claims

1. A UV coating adhesive for embossed printing, characterized in that: By mass percentage, it includes the following components: UV-curable resin 45-55%; 5-10% high molecular weight pressure-sensitive resin; Photoinitiator 2-5%; 30-40% reactive diluent; Additives 0.5-2%.

2. The UV coating adhesive for relief printing according to claim 1, characterized in that: The reactive diluents include monofunctional diluents and difunctional diluents.

3. The UV coating adhesive for relief printing according to claim 2, characterized in that: The monofunctional diluent is one of tetrahydrofuran acrylate, isobornyl acrylate, or cyclotrimethylolpropane methyl acetal acrylate.

4. The UV coating adhesive for relief printing according to claim 2, characterized in that: The difunctional diluent is one of 1,6-hexanediol diacrylate or tripropylene glycol diacrylate.

5. The UV coating adhesive for relief printing according to claim 2, characterized in that: The mass ratio of the monofunctional diluent to the difunctional diluent is 2:

1.

6. The UV coating adhesive for relief printing according to claim 1, characterized in that: The photocurable resin is polyurethane acrylate.

7. The UV coating adhesive for relief printing according to claim 1, characterized in that: The high molecular weight pressure-sensitive resin is a hot-melt pure acrylic resin.

8. The UV coating adhesive for relief printing according to claim 1, characterized in that: The photoinitiator is 2-hydroxy-2-methyl-1-phenyl-1-propanone.

9. The UV coating adhesive for embossing printing according to claim 1, characterized in that: The additives are defoamers and / or wetting agents.

10. The method for preparing UV coating adhesive for relief printing according to any one of claims 1-9, characterized in that: Includes the following steps: S1. Premixing: Add the reactive diluent to the mixing container and stir at 400 r / min for 30 min until uniform; S2. Main mixing: Add the photocurable resin, high molecular weight pressure-sensitive resin, photoinitiator and additives to the reactive diluent mentioned in step S1 in sequence, and stir and disperse at 600 r / min for 60 min until uniform to obtain the crude product; S3. Impurity Removal: The crude product described in step S2 is filtered through a filter bag to remove impurities, thereby obtaining the UV coating adhesive.

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