Self-wrinkled UV (ultraviolet) photocuring matte coating and preparation method thereof

Abstract

The invention discloses a self-wrinkled UV light-cured matte coating and a preparation method thereof, and relates to the technical field of UV light-cured coatings. The coating is prepared from the following components in parts by weight: 10 to 20 parts of alicyclic epoxy resin, 10 to 20 parts of polyfunctional epoxy resin, 10 to 15 parts of dual-curing epoxy acrylic resin, 5 to 10 parts of acrylic resin, 0.1 to 0.5 part of flatting agent, 0.5 to 1 part of photoinitiator, 0.3 to 0.8 part of cationic thermal initiator and 40 to 60 parts of solvent. According to the invention, a dual-curing mechanism of thermal cation curing and free radical UV light curing is adopted, complex multi-step curing processes such as an excimer lamp are not needed, and the matte effect of micro-wrinkles on the surface of the coating can be realized only through a conventional UV light source and heat treatment. Compared with the prior art, according to the scheme, the technological process is greatly simplified, the equipment investment cost is reduced, and the production efficiency is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of ultraviolet curable coatings, and specifically to a self-creasing UV curable matte coating and a preparation method thereof. Background Art

[0002] Currently in the market, the coatings that can achieve a matte effect on the coating mainly include two technical solutions: 1. Achieving the matte effect through the scheme of curing the coating with an excimer lamp. 2. Achieving the matte effect through the matte coating with the addition of a matting agent. After testing, the above two technical solutions have the following defects:

[0003] 1. The scheme of curing the coating with an excimer lamp first semi-cures the coating with a LED 395 nm ultraviolet lamp, then superficially cures it with a 254 nm ultraviolet lamp or a 172 nm ultraviolet lamp (in a nitrogen atmosphere) to form wrinkles to generate a matte structure, and finally completely cures the coating with a high-pressure mercury lamp. This scheme has the disadvantages of high equipment investment and complex process.

[0004] 2. The scheme of the matte coating with the addition of a matting agent is achieved by the matting agent arranging on the surface of the coating to form light diffusion. This scheme is a two-phase system of the matting agent and the resin, and there will be problems such as the dispersion and wetting of the matting agent and the resin, the storage stability problem, and the appearance unevenness caused by the solid content deviation, sedimentation, etc. during the downstream construction and coating, resulting in the decline of the material stability. Summary of the Invention

[0005] The purpose of this application is to provide a technical solution to solve the problems raised in the above background art.

[0006] To achieve the above purpose, this application provides the following technical solution:

[0007] A self-creasing UV curable matte coating is composed of the following components in parts by weight: 10-20 parts of alicyclic epoxy resin, 10-20 parts of polyfunctional epoxy resin, 10-15 parts of dual-curing epoxy acrylate resin, 5-10 parts of acrylate resin, 0.1-0.5 part of leveling agent, 0.5-1 part of photoinitiator, 0.3-0.8 part of cationic thermal initiator, and 40-60 parts of solvent.

[0008] Preferably, the alicyclic epoxy resin is any one or a mixture of more than one of 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexanecarboxylate, bis(7-oxabicyclo[4.1.0]heptamethyl)adipate, and diglycidyl 4,5-epoxycyclohexane-1,2-dicarboxylate.

[0009] Preferably, the alicyclic epoxy resin is preferably diglycidyl 4,5-epoxycyclohexane-1,2-dicarboxylate.

[0010] Preferably, the multi-functional epoxy resin is any one or a mixture of more than one of 3-ethyl-3-epoxypropane methanol and N,N,N,N-tetraglycidyl-4,4-diaminodiphenylmethane.

[0011] Preferably, the multi-functional epoxy resin is preferably N,N,N,N-tetraglycidyl-4,4-diaminodiphenylmethane.

[0012] Preferably, the dual-curing epoxy acrylate resin is a resin containing both epoxy groups and acrylic groups.

[0013] Preferably, the acrylic resin is a polyurethane acrylate resin with a functional group ≥ 6 or an acrylic monomer with a functional group ≥ 3.

[0014] Preferably, the leveling agent is any one or a mixture of more than one of polyester-modified silicone leveling agent, polyether-modified silicone leveling agent, and polyacrylic acid leveling agent.

[0015] Preferably, the photoinitiator is any one or a mixture of more than one of homolytic photoinitiators and cleavage photoinitiators.

[0016] Preferably, the solvent is any one or a mixture of more than one of ketones, alcohols, and esters.

[0017] A preparation method of a self-creasing UV-curable matte coating, comprising adding 10-20 parts of alicyclic epoxy resin, 10-20 parts of multi-functional epoxy resin, 10-15 parts of dual-curing epoxy acrylate resin, 5-10 parts of acrylic resin, 0.1-0.5 parts of leveling agent, 0.5-1 part of photoinitiator, 0.3-0.8 part of cationic thermal initiator, and 40-60 parts of solvent into a light-shielding stirring kettle, physically stirring evenly, and then discharging after vacuum defoaming.

[0018] In summary, the technical effects and advantages of the present invention are as follows:

[0019] 1. The present invention adopts a dual-curing mechanism of thermal cationic curing and free radical UV curing, without relying on complex multi-step curing processes such as excimer lamps. Only through a conventional UV light source and heat treatment, a matte effect with micro-creases on the coating surface can be achieved. Compared with the prior art, this solution greatly simplifies the process flow, reduces the equipment investment cost, and improves the production efficiency.

[0020] 2. By precisely controlling the ratio of epoxy resin in the thermal cationic curing system to acrylic resin in the free radical UV curing system and optimizing the synergistic effect of thermal curing and UV curing, the present invention can obtain matte effects with different haze levels, making the optical properties of the coating more controllable and significantly improving the applicability of the material in different application scenarios.

[0021] 3. The present invention endows the coating with a matte effect through a dual-curing mechanism, without relying on matting agents, fundamentally eliminating the construction coating instability caused by problems such as uneven dispersion and sedimentation of matting agents. Therefore, the coating has better dispersion uniformity during storage, higher appearance consistency of the coating after construction, and at the same time eliminates the coating quality instability problem caused by the deviation of solid content.

[0022] In summary, during the high-temperature baking stage of the coating of the present invention, first, the rheology of the coating is regulated by solvent volatilization, and then the internal system of the coating is gradually and slowly thermally cured. At the same time, a gel-like structure is formed on the surface layer due to faster thermal curing reaction. During the UV curing process of the high-pressure mercury lamp, an oxygen inhibition polymerization effect is formed on the surface gel layer, making the curing rate of the inner layer of the coating faster than that of the surface layer, resulting in the shrinkage stress of the inner layer being greater than that of the surface layer, and then pulling the surface gel layer to form a micro-crease structure, achieving a high-quality matte effect. Detailed implementation mode

[0023] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work shall fall within the protection scope of the present invention.

[0024] Example 1:

[0025] 10 parts of diglycidyl 4,5-epoxycyclohexane-1,2-dicarboxylate, 20 parts of N,N,N,N-tetraglycidyl-4,4-diaminodiphenylmethane, 12.5 parts of dual-curing epoxy acrylate resin Changxing ETERCURE6270, 7.5 parts of acrylate resin DPHA, 0.25 part of leveling agent TEGO370, 0.5 part of photoinitiator 184, 0.25 part of photoinitiator TPO, 0.5 part of cationic thermal initiator Donghua DH081, 20 parts of solvent butyl acetate, and 30 parts of solvent propylene glycol monomethyl ether are added to a stirring kettle and physically stirred evenly.

[0026] Preparation of performance test samples: The above self-creasing UV-curable matte coating is coated on a PET base film by a precision coating method, dried at a temperature of about 120°C for 5 minutes, the curing energy is ≥500 mJ / cm2, post-cured at 50°C for 12 hours, and the dry thickness of the coating is 3 - 4 μm.

[0027] Example 2:

[0028] Add 20 parts of diglycidyl 4,5-epoxycyclohexane-1,2-dicarboxylate, 10 parts of N,N,N,N-tetraglycidyl-4,4-diaminodiphenylmethane, 10 parts of double-curing epoxy acrylate resin Changxing ETERCURE6270, 10 parts of acrylate resin DPHA, 0.25 part of leveling agent TEGORAD2010, 0.5 part of photoinitiator 184, 0.25 part of photoinitiator TPO, 0.5 part of cationic thermal initiator Donghua DH081, 20 parts of solvent butyl acetate, and 30 parts of solvent propylene glycol methyl ether into a stirring kettle and stir physically until evenly mixed.

[0029] Preparation of performance test samples: Coating the above self-creasing UV-curable matte coating on a PET base film by means of precision coating, with a drying temperature of about 120 °C * 5 min, a curing energy ≥ 500 mJ / cm2, post-curing at 50 °C for 12 h, and a dry film thickness of the coating of 3 - 4 μm.

[0030] Example 3:

[0031] Add 15 parts of diglycidyl 4,5-epoxycyclohexane-1,2-dicarboxylate, 15 parts of N,N,N,N-tetraglycidyl-4,4-diaminodiphenylmethane, 15 parts of double-curing epoxy acrylate resin Changxing ETERCURE6270, 5 parts of acrylate resin Zahn EB8415, 0.5 part of leveling agent TEGORAD2200N, 0.5 part of photoinitiator 184, 0.5 part of photoinitiator TPO, 0.5 part of cationic thermal initiator Donghua DH081, 20 parts of solvent butyl acetate, and 30 parts of solvent propylene glycol methyl ether into a stirring kettle and stir physically until evenly mixed.

[0032] Preparation of performance test samples: Coating the above self-creasing UV-curable matte coating on a PET base film by means of precision coating, with a drying temperature of about 120 °C * 5 min, a curing energy ≥ 500 mJ / cm2, post-curing at 50 °C for 12 h, and a dry film thickness of the coating of 7 - 8 μm.

[0033] Example 4:

[0034] Add 10 parts of diglycidyl 4,5-epoxycyclohexane-1,2-dicarboxylate, 20 parts of N,N,N,N-tetraglycidyl-4,4-diaminodiphenylmethane, 10 parts of double-curing epoxy acrylate resin Changxing ETERCURE6278, 10 parts of acrylate resin Zahn EB8415, 0.5 part of leveling agent TEGORAD2200N, 0.5 part of photoinitiator 184, 0.5 part of photoinitiator TPO, 0.5 part of cationic thermal initiator Donghua DH081, 20 parts of solvent butyl acetate, and 30 parts of solvent propylene glycol methyl ether into a stirring kettle and stir physically until evenly mixed.

[0035] Performance test sample preparation: Coat the above self-creasing UV-curable matte coating on a PET base film by precision coating, with a drying temperature of about 120°C for 5 minutes, a curing energy of ≥500 mJ / cm2, and post-curing at 50°C for 12 hours. The dry thickness of the coating is 3 - 4 μm.

[0036] The performance is shown in the following table:

[0037] Project Example 1 Example 2 Example 3 Example 4 Transmittance 90.9 91.0 90.8 90.7 Haze 40.2 25.0 32.0 55.0 Hardness 2H 2H 2H 2H Adhesion Grade 0 Grade 0 Grade 0 Grade 0

[0038] Transmittance and haze: Measured according to ASTM D1003;

[0039] Hardness: Tested according to GB / T 6739-2006;

[0040] Adhesion: Tested according to GB / T 9286-1998.

[0041] Based on the dual-curing mechanism of thermal cationic polymerization-radical photopolymerization, the present invention constructs a matte coating system with high crosslinking density and stress-induced microstructure regulation, realizing the controllable construction of the micro-creased morphology on the coating surface. A stable and uniform matte effect can be obtained without relying on the traditional matting powder system. The core innovation of this system lies in the heterogeneous synergistic crosslinking system of alicyclic epoxy resin - multi-functional epoxy resin - epoxy acrylate - acrylate, which precisely regulates the curing rate gradient, thereby inducing the accumulation of surface shear stress under the action of mismatched curing kinetics, driving interface phase transformation and subsurface plastic deformation, and finally forming a periodic micro-creased structure with controllable scale.

[0042] First of all, the dual-curing epoxy acrylate resin acts as a bridging phase, possessing the reaction activities of both epoxy groups and acrylate groups, participating in cationic thermal curing and radical photopolymerization respectively at different curing stages to form a spatially distributed heterogeneous curing crosslinking network, improving the compatibility between interfaces, and simultaneously constructing a layered crosslinking structure with a free volume gradient at the microscale. The acrylate resin serves as the main chain flexibility regulator, optimizing the relaxation rate of local shear stress during the curing process, preventing the structural brittleness caused by over-crosslinking, and enhancing the controllability of stress-induced microstructures.

[0043] During the curing process, the system first undergoes a thermal cationic curing stage, in which the cationic thermal initiator induces the epoxy groups to crosslink slowly through ring-opening polymerization. Due to the high reactivity of the cycloaliphatic epoxy resin, the surface region first enters the critical state of the gel phase, causing a certain degree of microscale crosslinking shrinkage in the local area of the system. At the same time, since the photoinitiator has not been fully activated and the acrylate part has not entered the free radical photopolymerization process, the overall system still has a high internal molecular mobility, manifested as the interior of the coating still being in a sol state, while the surface layer has an increased elastic modulus and reduced local free volume due to preliminary crosslinking, laying the foundation for the accumulation of stress differences in the subsequent UV light curing stage.

[0044] When entering the UV light curing stage, the high-pressure mercury lamp provides strong short-wave ultraviolet irradiation (254 nm and 365 nm). At this time, the photoinitiator rapidly decomposes to generate highly reactive free radicals, initiating the free radical polymerization of acrylate monomers to form a high-density crosslinked structure. Since the reaction kinetics of free radical polymerization is much higher than that of cationic polymerization, the curing rate inside the coating is much higher than that of the surface layer, forming a gradient distribution of curing rate. During this process, volume shrinkage stress is generated inside the coating due to rapid crosslinking. However, due to the locally high crosslinking degree induced by the previous thermal curing, the curing rate of the surface layer lags behind, resulting in a dynamic mismatch between the shear modulus of the surface layer and the tensile modulus inside, thereby inducing the evolution of the stress-driven micro-folded morphology on the surface layer.

[0045] Specifically, during the UV curing process, the interior of the coating undergoes rapid shrinkage, while the surface layer still maintains a certain fluidity due to the limited curing rate. This causes the stress of crosslinking shrinkage in the inner layer to be transmitted to the surface layer, enabling the molecular chains on the surface layer to undergo controlled slippage and form a periodic folding structure along the path of the minimum free energy at the microscale. This process is similar to the buckling instability mechanism in the regulation of polymer surface microstructures, that is, when the shear stress accumulation on the surface layer exceeds the yield threshold and the ratio of the elastic modulus between the surface layer and the inner layer reaches the critical instability point, the surface layer undergoes stress release and forms a regular microscopic periodic undulating structure.

[0046] Furthermore, through the introduction of a leveling agent in the present invention, the surface energy of the coating is precisely regulated, thereby optimizing the rheology in advance during the spreading process of the coating to ensure that the formation of micro-folds is controlled by the curing stress gradient rather than being affected by external factors (such as the surface roughness of the substrate and air disturbance). In addition, as a temporary dispersion medium, the solvent forms a uniform solvent release rate gradient during the evaporation process in the high-temperature baking stage to prevent local stress concentration in the early stage of curing, making the formation of the fold structure more uniform.

[0047] So far, based on the dual curing mechanisms of hot cationic polymerization and free radical UV curing, the coating system of the present invention can achieve the spontaneous formation of surface micro-crease structures without the need for an external matting powder system, achieving a uniform matte effect. Compared with traditional matte coatings that rely on the light scattering effect of matting powder, the system of the present invention has higher optical uniformity and overcomes the storage stability problems caused by uneven dispersion and sedimentation of matting powder.

[0048] In summary, through precise construction of a heterogeneous cross-linked structure, dynamic regulation of the curing rate gradient, and utilization of stress-driven microstructural evolution, the present invention obtains a uniform, controllable, and long-term stable matte coating without introducing matting powder, breaking through the limitations of existing matte technologies in terms of optical consistency, storage stability, equipment cost, etc., and providing a reliable technical solution for high-performance industrial coatings.

[0049] Finally, it should be noted that the above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, for those skilled in the art, they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A self-wrinkling UV light-curing matte coating, characterized in that: The invention is composed of the following components in parts by weight: 10-20 parts of alicyclic epoxy resin, 10-20 parts of multifunctional epoxy resin, 10-15 parts of dual-curing epoxy acrylic resin, 5-10 parts of acrylic resin, 0.1-0.5 parts of leveling agent, 0.5-1 parts of photoinitiator, 0.3-0.8 parts of cationic thermal initiator and 40-60 parts of solvent.

2. A self-wrinkling UV light-curing matte coating according to claim 1, characterized in that: The alicyclic epoxy resin is a mixture of any one or more of 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexylcarboxylate, bis(7-oxabicyclo[4.1.0]-heptylmethyl)adipate, and 4,5-epoxycyclohexane-1,2-dicarboxylic acid diglycidyl ester.

3. A self-wrinkling UV light-curing matte coating according to claim 2, characterized in that: The alicyclic epoxy resin is preferably 4,5-epoxycyclohexane-1,2-dicarboxylic acid diglycidyl ester.

4. The self-wrinkling UV light-curing matte coating according to claim 1, characterized in that: The multifunctional epoxy resin is a mixture of any one or more of 3-ethyl-3-epoxypropane methanol and N,N,N,N-tetraepoxypropyl-4,4-diaminodiphenylmethane.

5. A self-wrinkling UV light-curing matte coating according to claim 4, characterized in that: The multifunctional epoxy resin is preferably N,N,N,N-tetraepoxypropyl-4,4-diaminodiphenylmethane.

6. The self-wrinkling UV light-curing matte coating according to claim 1, characterized in that: The dual-curing epoxy acrylic resin is a resin containing both epoxy groups and acrylic groups.

7. The self-wrinkling UV light-curing matte coating according to claim 1, characterized in that: The acrylic resin is a polyurethane acrylic resin with a functional group of ≥6 or an acrylic monomer with a functional group of ≥3.

8. The self-wrinkling UV light-curing matte coating according to claim 1, characterized in that: The leveling agent is a mixture of any one or more of a polyester modified organic silicon leveling agent, a polyether modified organic silicon leveling agent and a polyacrylic acid leveling agent.

9. The self-wrinkling UV light-curing matte coating according to claim 1, characterized in that: The photoinitiator is a mixture of any one or more of a homolytic photoinitiator and a cleavage photoinitiator.

10. A method for preparing a self-wrinkling UV light-curing matte coating, comprising a self-wrinkling UV light-curing matte coating according to any one of claims 1 to 9, characterized in that: Add 10-20 parts of alicyclic epoxy resin, 10-20 parts of multifunctional epoxy resin, 10-15 parts of dual-cure epoxy acrylic resin, 5-10 parts of acrylic resin, 0.1-0.5 parts of leveling agent, 0.5-1 parts of photoinitiator, 0.3-0.8 parts of cationic thermal initiator and 40-60 parts of solvent into a light-shielding stirring kettle, stir evenly, and then vacuum degassing and discharge the material.