UV curing coating as well as preparation method and application thereof

Abstract

The invention provides a UV curing coating as well as a preparation method and application thereof. The UV curing coating comprises the following components in parts by weight: 30-60 parts of urethane acrylate; 3 to 6 parts of a photoinitiator; 0.5 to 2 parts of erucyl amide; 5 to 9 parts of ethoxylated trimethylolpropane triacrylate; 2-6 parts of modified silicon dioxide; wherein the modified silicon dioxide is silane coupling agent modified silicon dioxide. According to the UV curing coating disclosed by the embodiment of the invention, urethane acrylate is taken as basic resin, erucyl amide, ethoxylated trimethylolpropane triacrylate and modified silicon dioxide are added into urethane acrylate, so that the problem of surface roughness caused by silicon dioxide filling can be improved; and the negative influence of erucyl amide on the adhesive force can be effectively overcome based on the synergistic effect of silicon dioxide and ETMPTA.

Description

Technical Field

[0001] The present disclosure relates to the technical field of the preparation of photocurable coatings, and particularly relates to a UV-curable coating, a preparation method thereof, and uses thereof. Background Art

[0002] In recent years, various optical parts based on polyester film (PET) substrates have been widely used. The PET material has excellent properties, and its good mechanical properties, heat resistance, and high transmittance are superior to many other materials. However, due to the low surface hardness and poor wear resistance of the PET material, it is usually necessary to coat a wear-resistant protective coating to improve its service life.

[0003] Currently, ultraviolet (UV) curable coatings are usually introduced into the preparation of PET films. Among them, nano-silica (SiO2) is widely used for the modification of UV curable coatings due to its unique nano-scale effect. However, there are also many deficiencies in the addition of nano-silica. For example, due to its high specific surface area and surface energy, it is easy to agglomerate into micron-sized particles in the coating, resulting in problems such as uneven surface, reduced coating transparency, and uneven hardness after curing. Therefore, how to optimize the UV curable coating is an urgent problem to be solved at present. Summary of the Invention

[0004] The purpose of the embodiments of the present disclosure is to provide a UV-curable coating, a preparation method thereof, and uses thereof.

[0005] To achieve the above technical purpose, the embodiments of the present disclosure provide the following technical solutions:

[0006] In a first aspect, the embodiments of the present disclosure provide a UV-curable coating. By weight, the UV-curable coating includes:

[0007] Polyurethane acrylate: 30 - 60 parts;

[0008] Photoinitiator: 3 - 6 parts;

[0009] Erucamide: 0.5 - 2 parts;

[0010] Ethoxylated trimethylolpropane triacrylate: 5 - 9 parts;

[0011] Modified silica: 2 - 6 parts;

[0012] Among them, the modified silica is silica modified with a silane coupling agent.

[0013] As an implementation manner, the preparation method of the modified silica includes:

[0014] Adding a silane coupling agent to a solvent and dissolving to obtain a mixed solution;

[0015] Add silica into the mixed solution, seal it, and stir and react at 60 - 80 °C for 2 - 4 hours;

[0016] After the reaction, filter and separate to obtain a solid, and the solid is washed and vacuum dried to obtain modified silica;

[0017] Among them, the solvent is an ethanol - water mixed solvent.

[0018] As an implementation manner, the silane coupling agent is KH - 550 or KH - 560.

[0019] As an implementation manner, the photoinitiator is at least one of 2,4,6 - trimethylbenzoyl diphenylphosphine oxide, bis-(2,4,6 - trimethylbenzoyl)phenylphosphine oxide, 1 - hydroxycyclohexyl phenyl ketone, benzophenone, 2 - hydroxy - 2 - methyl - 1 - phenyl - 1 - propanone.

[0020] As an implementation manner, the UV - curable coating further includes: Reactive diluent: 10 - 15 parts.

[0021] As an implementation manner, the reactive diluent is at least one of isobornyl acrylate, 1,6 - hexanediol diacrylate, trimethylolpropane triacrylate, dipentaerythritol hexaacrylate or tripentaerythritol pentaacrylate.

[0022] In a second aspect, an embodiment of the present disclosure provides a preparation method of the UV - curable coating as described in the first aspect, and the preparation method includes:

[0023] Weigh the above components by weight, add the photoinitiator, erucamide, ethoxylated trimethylolpropane triacrylate and modified silica into a reactor, and stir evenly to obtain a first mixture;

[0024] Add the remaining components into the first mixture, and stir evenly to obtain the UV - curable coating.

[0025] In a third aspect, an embodiment of the present disclosure provides the use of the UV - curable coating as described in the first aspect in the preparation of a protective coating for a PET substrate.

[0026] As an implementation manner, the curing method of the protective coating includes:

[0027] Spray the UV - curable coating on the surface of the PET substrate, place it in an ultraviolet light source to cure the UV - curable coating, and obtain a protective coating.

[0028] As an implementation manner, the UV - curing energy of the ultraviolet light source is 800 - 1200 mJ / cm 2 .

[0029] The embodiments of the present disclosure have at least the following beneficial effects:

[0030] In the embodiments of the present disclosure, silica is modified with a silane coupling agent, ethoxylated trimethylolpropane triacrylate (ETMPTA), and erucamide. On the one hand, erucamide is a long-chain non-polar molecule that can migrate to the coating surface during the UV curing process to form a lubricating layer with a low surface energy, reducing the frictional force of the silica particles on the coating surface, reducing particle agglomeration and protrusions. At the same time, the cross-linked network formed by ETMPTA during the UV curing process can "lock" the silica particles, further restricting their migration or aggregation. That is, during the UV curing process, the lubricating layer of erucamide and the cross-linked network of ETMPTA act synergistically to make the coating surface tend to be flat and jointly reduce the surface roughness. On the other hand, the modified silica significantly enhances the adhesion through chemical bonding and has better dispersibility; among them, the modified silica enhances the interfacial bonding force between the coating and the substrate through chemical bonding; as described above, the trifunctional group structure of ETMPTA forms a dense three-dimensional network after UV curing, physically encapsulating the silica particles modified with the silane coupling agent, and a "nano-enhanced composite structure" can be formed; that is, the modified silica is combined with the substrate through chemical bonding, and the cross-linked network of ETMPTA further embeds into the microscopic structure of the substrate surface (such as the physical scratches on the PET surface), forming a dual effect of "chemical bonding + mechanical interlocking", thereby significantly improving the overall strength and adhesion; at the same time, the ethoxy chain segment (-O-CH2CH2-) in the ETMPTA molecule can provide flexibility to avoid coating cracking caused by too high cross-linking density.

[0031] Therefore, the embodiments of the present disclosure take into account flexibility, low friction coefficient, and wear resistance at the same time.

[0032] Additional aspects and advantages of the present disclosure will be given in part in the following description, which will become apparent from the following description, or can be understood through the practice of the present disclosure. Detailed Embodiments

[0033] To more fully understand the technical content of the present disclosure, the present disclosure will be further introduced and described below in conjunction with specific embodiments; obviously, the embodiments described below are only a part of the embodiments of the present disclosure, rather than all of the embodiments; based on the embodiments in the present disclosure, all other embodiments obtained by those skilled in the art without creative efforts belong to the scope of protection of the present disclosure.

[0034] For those skilled in the art, the features, beneficial effects, and advantages of the present disclosure will become obvious by reading the content disclosed in this specification.

[0035] The term "mass content" in this article can be represented by the symbol "parts".

[0036] As used herein, "comprising", "including", "containing", "having" or other variants are intended to cover non-closed inclusion, and there is no distinction between these terms. The term "including" means that other steps and components can be added without affecting the final result. The term "including" also includes the terms "consisting of" and "consisting essentially of". The compositions and methods / processes of the present disclosure may comprise, consist of, and consist essentially of the essential elements and limitations described herein, as well as any additional or optional ingredients, components, steps, or limitations described herein.

[0037] The UV curable coating of this embodiment, its preparation method and uses will be described in detail below.

[0038] First, the UV curable coating of the first aspect of this embodiment will be described.

[0039] UV curable coating

[0040] As known to those skilled in the art, nano-silica is widely used in the modification of UV curable coatings due to its unique nano-scale effect; however, the addition of nano-silica also has many deficiencies. For example, due to its high specific surface area and surface energy, it is easy to agglomerate in the coating to form micron-sized particles, resulting in problems such as uneven surface, reduced coating transparency, and uneven hardness after curing; at the same time, erucamide, as a lubricant, will migrate to the coating surface during the UV curing process to form a lubricating layer with low surface energy, resulting in a decrease in the interfacial bonding force between the coating and the substrate.

[0041] In view of this, this embodiment proposes a UV curable coating; the raw materials of the UV curable coating provided in this embodiment include polyurethane acrylate, photoinitiator, erucamide, ethoxylated trimethylolpropane triacrylate (ETMPTA), and modified silica; wherein, the modified silica is silica modified with a silane coupling agent.

[0042] In the following examples, silica is all fumed silica, and the CAS number of erucamide is 112-84-5.

[0043] It can be understood that the UV curable coating of this embodiment uses polyurethane acrylate as the base resin (oligomer), and adding erucamide, ethoxylated trimethylolpropane triacrylate, and modified silica to polyurethane acrylate can not only improve the surface roughness problem caused by silica filling, but also effectively overcome the negative impact of erucamide on adhesion based on the synergistic effect of modified silica and ETMPTA.

[0044] Specifically, in this embodiment, silica is modified with a silane coupling agent. On the one hand, erucamide is a long-chain non-polar molecule, which can migrate to the coating surface during the UV curing process to form a lubricating layer with a low surface energy, reducing the friction force of silica particles on the coating surface, reducing particle agglomeration and protrusions. At the same time, the cross-linked network formed by ETMPTA during the UV curing process can "lock" the silica particles, further restricting their migration or aggregation. That is, during the UV curing process, the lubricating layer of erucamide and the cross-linked network of ETMPTA act synergistically to make the coating surface tend to be flat and jointly reduce the surface roughness.

[0045] On the other hand, the modified silica significantly enhances the adhesion through chemical bonding and has better dispersibility; among them, the modified silica enhances the interfacial bonding force between the coating and the substrate through chemical bonding; as mentioned above, the trifunctional group structure of ETMPTA forms a dense three-dimensional network after UV curing, physically encapsulating the silica particles modified by the silane coupling agent, and a "nano-enhanced composite structure" can be formed; that is, the modified silica is combined with the substrate through chemical bonding, and the cross-linked network of ETMPTA further embeds the microscopic structure of the substrate surface (such as the physical scratches on the PET surface), forming a dual effect of "chemical bonding + mechanical interlocking", thereby significantly improving the overall strength and adhesion of the coating; at the same time, the ethoxy chain segment (-O-CH2CH2-) in the ETMPTA molecule can provide flexibility to avoid coating cracking due to excessive cross-linking density.

[0046] In summary, the coating obtained in this embodiment takes into account hardness, low friction coefficient, wear resistance and adhesion at the same time.

[0047] Next, the related components of the above UV-curable coating will be further described.

[0048] As mentioned above, the UV-curable coating of this embodiment further includes a photoinitiator. It can be understood that during curing, an ultraviolet light source is required to provide the energy required for curing, and the photoinitiator can absorb ultraviolet light (UV) and decompose into active species, causing the oligomer (polyurethane acrylate) to undergo a cross-linking reaction under the action of the active species.

[0049] The photoinitiator used in this embodiment is a conventional photoinitiator known in the art. For example, the photoinitiator is at least one of 2,4,6-trimethylbenzoyl diphenylphosphine oxide (TPO), bis-(2,4,6-trimethylbenzoyl)phenylphosphine oxide, 1-hydroxycyclohexyl phenyl ketone, benzophenone, 2-hydroxy-2-methyl-1-phenyl-1-propanone (HMPP).

[0050] Preferably, the photoinitiator is 2,4,6-trimethylbenzoyl diphenylphosphine oxide (TPO) and / or 2-hydroxy-2-methyl-1-phenyl-1-propanone (HMPP).

[0051] As described above, in this embodiment, by using modified silica, the adhesion can be significantly enhanced through chemical bonding, and it acts together with the crosslinked network of ETMPTA, thereby significantly improving the overall strength and adhesion of the coating.

[0052] Among them, the modified silica can be prepared by existing known conventional methods.

[0053] Exemplarily, the preparation method of the modified silica includes:

[0054] (1) Add a silane coupling agent to a solvent to dissolve and obtain a mixed solution.

[0055] In step (1), the concentration of the silane coupling agent is usually 5%-20 wt%, based on the total mass of the mixed solution; the dosage of the silane coupling agent is 1%-5% of the mass of the silica; among them, the solvent is an ethanol-water mixed solvent; preferably, in the solvent, ethanol:water = 9:1 (volume ratio).

[0056] (2) Add the silica to the mixed solution, seal it, and stir and react at 60-80 °C for 2-4 hours.

[0057] The preparation method of this embodiment can be carried out in a reaction kettle (with a stirring function). Step (1) can be directly carried out in the reaction kettle, or it can be configured and then added to the reaction kettle; after adding the silica and the mixed solution to the reaction kettle together, seal it and stir (300-600 r / min) and react at 60-80 °C for 2-4 hours.

[0058] Among them, continuous stirring is required during the reaction to prevent particle agglomeration.

[0059] (3) After the reaction is completed, filter and separate to obtain a solid, and the solid is washed and vacuum dried to obtain the modified silica.

[0060] In step (3), after filtering to obtain the solid, the solid can be washed with ethanol 2-3 times to remove the unreacted silane coupling agent; then vacuum dried (60-80 °C) to constant weight to obtain the modified silica.

[0061] As an implementation manner, the silane coupling agent is KH-550 or KH-560, preferably KH-550.

[0062] In this embodiment, by weight, the contents of the above components are respectively: polyurethane acrylate: 30-60 parts; photoinitiator: 3-6 parts: erucamide: 0.5-2 parts; ethoxylated trimethylolpropane triacrylate: 5-9 parts; modified silica: 2-6 parts.

[0063] As a preferred technical solution of this embodiment, the contents of the above components are as follows: polyurethane acrylate: 40-55 parts; photoinitiator: 4-5 parts; erucamide: 1-1.5 parts; ethoxylated trimethylolpropane triacrylate: 6.5-9 parts; modified silica: 3-5 parts.

[0064] For example, in the embodiments of the present disclosure:

[0065] The content of polyurethane acrylate includes but is not limited to: 30 parts, 35 parts, 40 parts, 43 parts, 46 parts, 50 parts, 52 parts, 54 parts, 55 parts, 58 parts, 60 parts.

[0066] The content of photoinitiator includes but is not limited to: 3 parts, 3.5 parts, 3.8 parts, 4 parts, 4.4 parts, 5 parts, 5.5 parts, 5.6 parts, 6 parts.

[0067] The content of erucamide includes but is not limited to: 0.5 parts, 0.6 parts, 1 part, 1.2 parts, 1.4 parts, 1.5 parts, 1.8 parts, 2 parts.

[0068] The content of ethoxylated trimethylolpropane triacrylate includes but is not limited to: 5 parts, 6 parts, 7 parts, 8 parts, 9 parts, 10 parts.

[0069] The content of modified silica includes but is not limited to: 2 parts, 2.4 parts, 2.6 parts, 2.8 parts, 3 parts, 3.5 parts, 4 parts, 4.6 parts, 5 parts, 5.7 parts, 6 parts.

[0070] Other components

[0071] The UV-curable coating of this embodiment further contains an active diluent; it can be understood that adding the active diluent to the UV-curable coating can adjust the viscosity and participate in the curing reaction, and it becomes a part of the coating after curing.

[0072] Exemplarily, the active diluent is at least one of isobornyl acrylate (IBOA), 1,6-hexanediol diacrylate (HDDA), trimethylolpropane triacrylate, dipentaerythritol hexaacrylate or pentaerythritol pentaacrylate (PE5A).

[0073] Preferably, the active diluent is 1,6-hexanediol diacrylate (HDDA) and / or pentaerythritol pentaacrylate (PE5A).

[0074] In this embodiment, by weight, the content of the active diluent is 10-15 parts. Exemplarily, the content of the active diluent includes but is not limited to: 10 parts, 11 parts, 12 parts, 13 parts, 14 parts, 15 parts.

[0075] In addition to the various components listed above, the UV curable coating of this embodiment also contains conventional components such as leveling agents, and the reasonable addition of the above-mentioned conventional components does not damage the effect of this embodiment.

[0076] It can be understood that adding leveling agents (such as BYK-354, BYK-358N) can reduce surface defects of the coating (reduce flow marks) and improve surface flatness.

[0077] Generally, by weight, the content of the leveling agent is 0.3 - 1 part; exemplarily, the content of the leveling agent includes but is not limited to: 0.3 part, 0.4 part, 0.5 part, 0.6 part, 0.7 part, 0.8 part, 0.9 part, 1 part.

[0078] Secondly, the preparation method of the second aspect of this embodiment will be described.

[0079] Preparation method

[0080] The UV curable coating of this embodiment can be prepared by using conventional preparation methods known in the art.

[0081] Exemplarily, the preparation method includes:

[0082] (1) Weigh the above components by weight, add the photoinitiator, erucamide, ethoxylated trimethylolpropane triacrylate and modified silica into a reactor, and stir evenly to obtain a first mixture;

[0083] (2) Add the remaining components to the first mixture and stir evenly to obtain the UV curable coating.

[0084] Next, the above steps will be further described.

[0085] It can be understood that the UV curable coating of this embodiment can be carried out in a stirring kettle.

[0086] In step (1), in order to ensure the uniform dispersion of the modified silica, high-speed stirring (1000 - 3000 r / min) can be used, and the stirring time is 20 - 60 min.

[0087] In step (2), stirring can be carried out at a rotation speed of 500 - 800 r / min for 10 - 20 min to obtain the UV curable coating.

[0088] Then, the use of the third aspect of this embodiment will be described.

[0089] Use

[0090] Based on the description of the first aspect, the coating obtained from the UV-curable coating in this embodiment takes into account flexibility, low coefficient of friction, and wear resistance at the same time. Therefore, the UV-curable coating provided in this embodiment can be used to prepare a protective coating for a PET substrate to meet the requirements of a PET packaging box for aesthetics, functionality, or protection.

[0091] As an implementation method, the curing method of the protective coating includes:

[0092] Spray the UV-curable coating on the surface of the PET substrate, and place it in an ultraviolet light source to cure the UV-curable coating to obtain a protective coating.

[0093] Among them, the ultraviolet light source can use a mercury lamp UV curing machine or an LED-UV curing machine.

[0094] As an implementation method, the UV curing energy of the ultraviolet light source is 800-1200 mJ / cm 2 .

[0095] The following further elaborates on the present disclosure in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present disclosure and not to limit the scope of the present disclosure.

[0096] In the following embodiments, the materials, reagents, and instruments used can be obtained from commercial sources without special instructions.

[0097] In the following embodiments, the modified silica is prepared by the following method:

[0098] (1) Take fumed silica ( UV70C), silane coupling agent KH-550, and a solvent. The amount of the silane coupling agent is 3% of the mass of the silica, and the solvent is ethanol:water = 9:1 (volume ratio); add the silane coupling agent KH-550 to the solvent and dissolve to obtain a mixed solution; the concentration of the silane coupling agent in the mixed solution is 10 wt%.

[0099] (2) Place the silica and the above mixed solution in a reaction kettle, seal it, and stir (350 r / min) at 70 °C for 3.5 hours;

[0100] (3) After the reaction is completed, filter and separate to obtain a solid, and wash the solid 3 times with ethanol and vacuum dry (65 °C) to constant weight to obtain modified silica.

[0101] In the following embodiments, the fumed silica is UV70C, the photoinitiator TPO is selected from Tianjin Jiuri New Materials Co., Ltd.; the polyurethane acrylate is specifically selected as aliphatic polyurethane acrylate B-374 (selected from Guangdong Boxin New Materials Technology Co., Ltd.), and the ethoxylated trimethylolpropane triacrylate is specifically selected as 3EO-TMPTA (selected from Guangzhou Jingpu Trading Co., Ltd.); erucamide is purchased from Nantong Dongli New Materials, and the total amide content is ≥99.5%.

[0102] Examples 1 - 5

[0103] In this example, UV-curable coatings with the following formulations were respectively prepared, and the specific compositions are shown in Table 1.

[0104] Table 1: Compositions and contents (parts) of the UV-curable coatings in Examples 1-5

[0105]

[0106]

[0107] The preparation methods of the UV-curable coatings in the above Examples 1-5 include:

[0108] (1) Weigh the above components by weight parts. Add the photoinitiator, erucamide, ethoxylated trimethylolpropane triacrylate and modified silica into a stirring kettle, and stir at 2500 r / min for 45 min to obtain a first mixture;

[0109] (2) Add the remaining components into the first mixture, and stir at a rotation speed of 650 r / min for 20 min to mix evenly to obtain the UV-curable coating.

[0110] Comparative Examples 1 - 4

[0111] In Comparative Examples 1-4, UV-curable coatings with the following formulations were respectively prepared, and the specific compositions are shown in Table 2.

[0112] Table 2: Compositions and contents (parts) of the UV-curable coatings in Comparative Examples 1-4

[0113]

[0114] The preparation methods of the UV-curable coatings in Comparative Examples 1-4 include:

[0115] (1) Weigh the above components by weight parts. Add the photoinitiator, erucamide, ethoxylated trimethylolpropane triacrylate and modified silica (or silica) into a stirring kettle, and stir at 2500 r / min for 45 min to obtain a first mixture;

[0116] (2) Add the remaining components to the first mixture and stir for 20 min at a rotation speed of 650 r / min to obtain a uniformly mixed UV-curable coating.

[0117] It is understandable that if the comparative example does not contain the corresponding component (for example, comparative example 1 does not contain erucic acid amide), there is no need to weigh and add the corresponding component.

[0118] Effect verification

[0119] Apply the UV-curable coatings prepared in the above Examples 1-5 and Comparative Examples 1-4 to the surface of the substrate layer respectively, and cure to obtain a coating.

[0120] The specific steps are as follows:

[0121] Take a PET substrate, clean and dry the surface of the substrate layer; roll coat the corresponding UV-curable coatings (Examples 1-5 and Comparative Examples 1-4) on the corresponding substrate layer surface respectively, and cure it with a mercury lamp UV curing machine, and the UV curing energy is 1000 mJ / cm 2 ; Obtain a PET substrate with a coating (thickness about 10 μm) on the surface.

[0122] Conduct relevant effect tests on the coatings of the above-prepared PET substrates, including coating hardness test, adhesion test, friction coefficient and coating appearance.

[0123] Among them, the method for determining the coating hardness refers to GB6739-1996; the adhesion test adopts the cross-cut test: use a tool with a hardness of 6H, cut 11 parallel lines with a spacing of 1 mm on the coating surface, and then cut 11 perpendicular cross-lines to form 100 1 mm 2 squares, the blade angle is 30°-45°, ensure that the coating is cut through to the PET substrate, paste 3M No. 600 tape, press it flat with a 5N force, stand still for 90 s and then quickly peel it off at a 60° angle. Referring to the GB / T 9286 standard, the result is from grade 0 (complete peeling) to grade 5 (no peeling).

[0124] The method for determining the friction coefficient refers to the ASTM D1894 standard, and the coating appearance is to directly observe whether the coating is transparent and whether there are any pits.

[0125] The test results of Examples 1-5 and Comparative Examples 1-4 are shown in Table 3.

[0126] Table 3: Test results of Examples 1-5 and Comparative Examples 1-4

[0127] Sample group Coating hardness (H) Adhesion (grade) Coefficient of friction Coating appearance Example 1 4 4 0.08 Transparent, without pits Example 2 5 5 0.05 Transparent, without pits Example 3 5 5 0.04 Transparent, without pits Example 4 5 5 0.05 Transparent, without pits Example 5 5 5 0.06 Transparent, without pits Comparative Example 1 4 4 0.18 Transparent, with some pits Comparative Example 2 2 2 0.04 Transparent, without pits Comparative Example 3 2 1 0.15 Transparent, with some pits Comparative Example 4 3 3 0.1 Transparent, with a small number of pits

[0128] Note: In Table 3, calculated by the number of pits, some pits are larger than a small number of pits.

[0129] According to the test results in Table 3, in Examples 1-5, by adding erucamide, ethoxylated trimethylolpropane triacrylate, and modified silica to polyurethane acrylate, the prepared coating has better coating hardness and adhesion, lower friction coefficient, and more excellent appearance.

[0130] Specifically, in this example, silica is modified with a silane coupling agent. On the one hand, erucamide is a long-chain non-polar molecule that can migrate to the coating surface during the UV curing process to form a lubricating layer with low surface energy, reducing the friction force of silica particles on the coating surface, reducing particle agglomeration and protrusions. At the same time, the cross-linked network formed by ETMPTA during the UV curing process can "lock" the silica particles, further restricting their migration or aggregation. That is, during the UV curing process, the lubricating layer of erucamide and the cross-linked network of ETMPTA work together to make the coating surface tend to be flat, jointly reducing the surface roughness (lower friction coefficient, transparent appearance without pits).

[0131] On the other hand, the modified silica significantly enhances the adhesion through chemical bonding and has better dispersibility. Among them, the modified silica enhances the interfacial bonding force between the coating and the substrate through chemical bonding. At the same time, the trifunctional group structure of ETMPTA forms a dense three-dimensional network after UV curing, physically encapsulating the silica particles modified by the silane coupling agent, and a "nano-reinforced composite structure" can be formed. That is, the modified silica is combined with the substrate through chemical bonding, and the cross-linked network of ETMPTA further embeds into the microscopic structure of the substrate surface (such as the physical scratches on the PET surface), forming a dual effect of "chemical bonding + mechanical interlocking", thereby significantly improving the overall strength and adhesion of the coating (better coating hardness and adhesion).

[0132] Further comparing Example 3 and Comparative Example 1, when erucamide is lacking in Comparative Example 1, the friction coefficient of Comparative Example 1 increases significantly and there are partial pits on the coating. This may be because without erucamide, it cannot better reduce the agglomeration and protrusions of the modified silica particles, resulting in a higher surface roughness of Comparative Example 1 and partial pits on the coating. At the same time, due to the agglomeration of the modified silica particles, they cannot be combined with ETMPTA better, resulting in a decrease in the coating hardness and adhesion of Comparative Example 1.

[0133] Further comparing Example 3, Comparative Example 2, and Comparative Example 3, modified silica is lacking in Comparative Example 2 and 3EO-TMPTA is lacking in Comparative Example 3. The coating hardness and adhesion of Comparative Example 2 and Comparative Example 3 both decrease significantly, indicating that through a dual effect between ETMPTA and the modified silica particles, the overall strength and adhesion of the coating can be significantly improved. Therefore, when modified silica is lacking in Comparative Example 2 and 3EO-TMPTA is lacking in Comparative Example 3, the interfacial bonding force between the coating and the substrate decreases.

[0134] Among them, in Comparative Example 2 where modified silica is absent, the friction coefficient of Comparative Example 2 shows no obvious change, indicating that the lubricating layer of erucamide and the crosslinking network of ETMPTA act synergistically to make the coating surface tend to be flat and jointly reduce the surface roughness; while in Comparative Example 3 where 3EO-TMPTA is absent, not only does the friction coefficient increase significantly, but also some pockmarks appear on the coating, indicating that in this embodiment, ETMPTA can not only cooperate with erucamide to improve the surface roughness problem caused by silica filling, but also cooperate with modified silica to effectively overcome the negative impact of erucamide on adhesion.

[0135] Further comparing Example 3 and Comparative Example 4, in Comparative Example 4, the modified silica in Example 3 is replaced with ordinary silica. The hardness and adhesion of the coating in Comparative Example 4 decrease significantly, and the friction coefficient increases significantly, indicating that when ordinary silica is used, its dispersion performance is poor, and the agglomeration and protrusion of silica particles are more obvious; at the same time, it cannot combine better with ETMPTA to form a coating with better strength and adhesion, resulting in a decrease in the interfacial bonding force between the coating and the substrate.

[0136] In summary, the UV-curable coating of this embodiment uses polyurethane acrylate as the base resin, and erucamide, ethoxylated trimethylolpropane triacrylate, and modified silica are added to the polyurethane acrylate. It can not only improve the surface roughness problem caused by silica filling, but also effectively overcome the negative impact of erucamide on adhesion based on the synergistic effect of silica and ETMPTA.

[0137] The technical solutions provided by the embodiments of the present disclosure have been introduced in detail above. Specific examples are used in this article to elaborate on the principles and implementation manners of the embodiments of the present disclosure. The descriptions of the above embodiments are only applicable to help understand the principles of the embodiments of the present disclosure; at the same time, for those of ordinary skill in the art, according to the embodiments of the present disclosure, there will be changes in the specific implementation manners and application scopes. In summary, the content of this specification should not be construed as a limitation to the present disclosure.

Claims

1. A UV-curable coating, characterized in that, By weight parts, the UV curable coating comprises: Polyurethane acrylate: 30 - 60 parts; Photoinitiator: 3 - 6 parts; Erucamide: 0.5 - 2 parts; Ethoxylated trimethylolpropane triacrylate: 5 - 9 parts; Modified silica: 2 - 6 parts; Wherein, the modified silica is silica modified with a silane coupling agent.

2. The UV curable coating according to claim 1, characterized in that, The preparation method of the modified silica comprises: Adding a silane coupling agent into a solvent to dissolve and obtain a mixed solution; Adding silica into the mixed solution, sealing and stirring at 60 - 80 °C for 2 - 4 hours; After the reaction ends, filtering and separating to obtain a solid, and the solid is washed and vacuum dried to obtain the modified silica; Wherein, the solvent is an ethanol - water mixed solvent.

3. The UV curable coating according to claim 1 or 2, characterized in that, The silane coupling agent is KH - 550 or KH - 560.

4. The UV curable coating according to claim 1, characterized in that, The photoinitiator is at least one of 2,4,6 - trimethylbenzoyl diphenylphosphine oxide, bis-(2,4,6 - trimethylbenzoyl)phenylphosphine oxide, 1 - hydroxycyclohexyl phenyl ketone, benzophenone, 2 - hydroxy - 2 - methyl - 1 - phenyl - 1 - propanone.

5. The UV curable coating according to claim 1, characterized in that, The UV curable coating further comprises: Reactive diluent: 10 - 15 parts.

6. The UV curable coating according to claim 5, characterized in that, The reactive diluent is at least one of isobornyl acrylate, 1,6 - hexanediol diacrylate, trimethylolpropane triacrylate, dipentaerythritol hexaacrylate or tripentaerythritol pentaacrylate.

7. A method for preparing a UV-curable coating according to any one of claims 1-6, characterized in that, The preparation method comprises: Weighing the above components by weight parts, adding the photoinitiator, erucamide, ethoxylated trimethylolpropane triacrylate and modified silica into a reactor, and stirring evenly to obtain a first mixture; Adding the remaining components into the first mixture and stirring evenly to obtain the UV curable coating.

8. Use of the UV curable coating according to any one of claims 1 - 6 in the preparation of a protective coating for a PET substrate.

9. The use according to claim 8, characterized in that, The curing method of the protective coating comprises: Spraying the UV curable coating on the surface of the PET substrate, and placing it in an ultraviolet light source to cure the UV curable coating to obtain a protective coating.

10. The use according to claim 9, characterized in that, The UV curing energy of the ultraviolet light source is 800 - 1200 mJ / cm 2 .

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