Uv-curable coating material, process for the production thereof and use thereof

Abstract

The present disclosure provides a UV-curable coating and a preparation method and use thereof. The UV-curable coating comprises, by weight fraction, 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 silane coupling agent modified silica. The UV-curable coating of the present disclosure takes polyurethane acrylate as the base resin, and adds erucamide, ethoxylated trimethylolpropane triacrylate and modified silica in the polyurethane acrylate, which not only can improve the surface roughness problem caused by silica filling, but also can effectively overcome the negative impact of erucamide on adhesion based on the synergistic effect of silica and ETMPTA.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to the technical field of light-cured coating preparation, in particular to a UV-cured coating and a preparation method and application thereof. BACKGROUND

[0002] In recent years, various optical parts with polyester film (PET) as the substrate have been widely used. PET material has excellent performance, and its better 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 PET material, it is usually necessary to coat a wear-resistant protective coating to improve its service life.

[0003] At present, ultraviolet light (UV) curing coating is usually introduced into the preparation of PET film. Nano-silicon dioxide (SiO2) is widely used in the modification of UV curing coating due to its unique nanoscale effect. However, the addition of nano-silicon dioxide also has many deficiencies, for example, due to its high specific surface area and surface energy, it is easy to agglomerate into micron-sized particles in the coating, which causes problems such as uneven surface after curing, reduced transparency of the coating, and uneven hardness. Therefore, how to optimize the UV curing coating is a problem to be solved at present. SUMMARY

[0004] The purpose of the embodiments of the present disclosure is to provide a UV-cured coating and a preparation method and application 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-cured coating, which comprises, by weight fraction:

[0007] Polyurethane acrylate: 30-60 parts;

[0008] Photoinitiator: 3-6 parts:

[0009] Erdic acid amide: 0.5-2 parts;

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

[0011] Modified silicon dioxide: 2-6 parts;

[0012] The modified silicon dioxide is silane coupling agent modified silicon dioxide.

[0013] As an embodiment, the preparation method of the modified silicon dioxide comprises:

[0014] The silane coupling agent is added to the solvent to dissolve and obtain a mixed solution;

[0015] The silica is added to the mixed solution, and after being sealed, the reaction is stirred at 60-80°C for 2-4 hours;

[0016] After the reaction is completed, the solid is separated by filtration, and the solid is washed and vacuum dried to obtain the modified silica;

[0017] The solvent is an ethanol-water mixed solvent.

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

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

[0020] As an embodiment, the UV-curable coating further comprises: an active diluent: 10-15 parts.

[0021] As an embodiment, the active diluent is at least one of isobornyl acrylate, 1,6-hexanediol diacrylate, trimethylolpropane triacrylate, dipentaerythritol hexaacrylate, or tri-pentaerythritol pentaacrylate.

[0022] In a second aspect, the present disclosure provides a preparation method of the UV-curable coating of the first aspect, the preparation method comprising:

[0023] The above components are weighed by weight fraction, the photoinitiator, the erucic acid amide, the ethoxylated trimethylolpropane triacrylate, and the modified silica are added to the reactor, and stirred uniformly to obtain a first mixture;

[0024] The remaining components are added to the first mixture, and stirred uniformly to obtain the UV-curable coating.

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

[0026] As an embodiment, the curing method of the protective coating comprises:

[0027] The UV-curable coating is sprayed on the surface of the PET substrate, and the UV-curable coating is cured in an ultraviolet light source to obtain the protective coating.

[0028] As an embodiment, 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] The embodiments of the present disclosure use silane coupling agent modified silica, ethoxylated trimethylolpropane triacrylate and erucamide. On the one hand, erucamide is a long-chain nonpolar molecule, which can migrate to the surface of the coating during UV curing to form a low-surface-energy lubricating layer, reducing the friction of silica particles on the surface of the coating and reducing particle aggregation and protrusions. Meanwhile, the crosslinked network formed by ETMPTA during UV curing can "lock" the silica particles, further limiting their migration or aggregation. That is, during UV curing, the lubricating layer of erucamide and the crosslinked network of ETMPTA synergistically act to make the surface of the coating smooth and reduce the surface roughness. On the other hand, the modified silica significantly enhances the adhesion through chemical bonding and has better dispersibility. The modified silica enhances the interfacial bonding strength of the coating-substrate through chemical bonding. As described above, the three functional groups of ETMPTA form a dense three-dimensional network after UV curing, which physically encapsulates the silica particles modified by the silane coupling agent, forming a "nano-reinforced composite structure". That is, the modified silica is combined with the substrate through chemical bonding, and the crosslinked network of ETMPTA further embeds the microstructure 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 ethoxylated segment (-O-CH2CH2-) in the ETMPTA molecule can provide flexibility to avoid brittle fracture of the coating due to excessive crosslinking density.

[0031] Therefore, the embodiments of the present disclosure simultaneously consider flexibility, low friction coefficient and wear resistance.

[0032] Additional aspects and advantages of the present disclosure will be described in the following description, which will become apparent from the description, or will be learned by practice of the present disclosure. DETAILED DESCRIPTION

[0033] In order to more fully understand the technical content of the present disclosure, the present disclosure will be further introduced and described below in combination with specific embodiments; obviously, the following described embodiments are only some of the embodiments of the present disclosure, not all the embodiments; based on the embodiments in the present disclosure, all other embodiments obtained by those skilled in the art without creative labor are within the protection scope of the present disclosure.

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

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

[0036] "comprise," "contain," "include," "have," or other variations thereof, are intended to be open-ended, not limiting. The terms "comprising," "comprise" and "comprises" do not exclude other steps or ingredients. The term "comprising" also includes the terms "consisting of" and "consisting essentially of." The compositions and methods / processes of the present disclosure can 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 the present embodiment and the preparation method and use thereof are described in detail below.

[0038] First, the UV-curable coating of the first aspect of the present embodiment is described.

[0039] UV-curable coating

[0040] As known by those skilled in the art, nano-silica is widely used in the modification of UV-curable coatings due to its unique nanoscale effect; however, the addition of nano-silica also has many shortcomings, 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 after curing, reduced transparency of the coating, and uneven hardness; at the same time, erucamide as a lubricant will migrate to the surface of the coating during UV curing, forming a low-surface-energy lubricating layer, resulting in a decrease in the interfacial adhesion between the coating and the substrate.

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

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

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

[0044] Specifically, the present embodiment adopts silane coupling agent modified silica, on the one hand, erucamide is a long-chain non-polar molecule, which can migrate to the surface of the coating during UV curing to form a low-surface-energy lubricating layer, reducing the friction of silica particles on the surface of the coating, reducing particle aggregation and protrusion, and at the same time, the crosslinked network formed by ETMPTA during UV curing can "lock" the silica particles, further limiting their migration or aggregation. That is, during UV curing, the lubricating layer of erucamide and the crosslinked network of ETMPTA synergistically act to make the coating surface tend to be flat, and together reduce the surface roughness.

[0045] On the other hand, the modified silica significantly enhances the adhesion by chemical bonding, and has better dispersibility; wherein the modified silica enhances the interfacial bonding force between the coating and the substrate by chemical bonding; as described above, the three functional groups of ETMPTA form a dense three-dimensional network after UV curing, which physically wraps the silica particles modified by silane coupling agent, and can form a "nano-reinforced composite structure"; that is, the modified silica is combined with the substrate by chemical bonding, and the crosslinked network of ETMPTA is further embedded into the microstructure of the substrate surface (such as the physical scratches on the surface of PET), forming a dual effect of "chemical bonding + mechanical interlocking", which further significantly improves the overall strength and adhesion of the coating; at the same time, the ethoxy segment (-O-CH2CH2-) in the ETMPTA molecule can provide flexibility to avoid brittle fracture of the coating due to too high crosslinking density.

[0046] In summary, the coating obtained by the present embodiment simultaneously considers hardness, low friction coefficient, wear resistance and adhesion.

[0047] The related components of the above UV-cured coating will be further described below.

[0048] As described above, the UV-cured coating of the present embodiment also includes a photoinitiator. It can be understood that during curing, a UV light source is needed to provide the energy required for curing, and the photoinitiator can absorb UV light (UV) and decompose into active species, so that the oligomer (polyurethane acrylate) undergoes crosslinking reaction under the action of active species.

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

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

[0051] As mentioned above, the present embodiment can significantly enhance the adhesion by using modified silica which can significantly enhance the adhesion by chemical bonding, and cooperates with the crosslinking network of ETMPTA, thereby significantly improving the overall strength and adhesion of the coating.

[0052] The modified silica can be prepared by using conventional methods known in the art.

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

[0054] (1) adding a silane coupling agent into a solvent to 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 amount of the silane coupling agent is 1-5% of the mass of the silica; wherein the solvent is an ethanol-water mixed solvent; preferably, in the solvent, ethanol: water = 9: 1 (volume ratio).

[0056] (2) adding silica into the mixed solution, sealing and stirring at 60-80°C for 2-4 hours.

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

[0058] During the reaction, continuous stirring is required to prevent particle agglomeration.

[0059] (3) after the reaction is completed, the solid is separated by filtration, and the solid is washed and vacuum dried to obtain the modified silica.

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

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

[0062] In the present embodiment, the content of the above components is respectively: polyurethane acrylate: 30-60 parts; photoinitiator: 3-6 parts; erucic acid amide: 0.5-2 parts; ethoxylated trimethylolpropane triacrylate: 5-9 parts; modified silica: 2-6 parts.

[0063] As the preferred technical solution of the embodiment, the content of the above components is respectively: polyurethane acrylate: 40-55 parts; photoinitiator: 4-5 parts; erucic acid amide: 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 the 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 the 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 the erucic acid amide 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 the 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 the 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 the embodiment also contains a reactive diluent; it can be understood that the addition of the reactive diluent to the UV-curable coating can adjust the viscosity and participate in the curing reaction, and after curing, it becomes part of the coating.

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

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

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

[0075] The UV-curable coating of the present embodiment comprises, in addition to the various components listed above, conventional components such as leveling agents, and reasonable addition of the above conventional components does not impair the effects of the present embodiment.

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

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

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

[0079] Preparation method

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

[0081] Exemplarily, the preparation method comprises:

[0082] (1) The above components are weighed by weight fraction, and the photoinitiator, erucamide, ethoxylated trimethylolpropane triacrylate and modified silica are added into the reactor and stirred uniformly to obtain a first mixture;

[0083] (2) The remaining components are added to the first mixture and stirred uniformly 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 the present embodiment can be carried out in a stirred tank.

[0086] In step (1), in order to ensure 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 speed of 500-800 r / min for 10-20 min to obtain the UV-curable coating.

[0088] Next, the use of the third aspect of the present embodiment will be described.

[0089] Use

[0090] Based on the description in the first aspect, the coating obtained by the UV-curable coating in this embodiment simultaneously takes into account flexibility, low coefficient of friction and wear resistance; therefore, the UV-curable coating provided in this embodiment can be used to prepare a protective coating for PET substrates to meet the requirements of PET packaging boxes for aesthetics, functionality or protection.

[0091] As one embodiment, the curing method of the protective coating includes:

[0092] A UV-curable coating is sprayed onto the surface of a PET substrate and then placed in a UV light source to cure the coating, thus obtaining a protective coating.

[0093] The ultraviolet light source can be a mercury lamp UV curing machine or an LED-UV curing machine.

[0094] As one implementation method, the UV curing energy of the ultraviolet light source is 800-1200 mJ / cm². 2 .

[0095] The present disclosure is further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the disclosure.

[0096] Unless otherwise specified, all materials, reagents and instruments used in the following embodiments are commercially available.

[0097] In the following examples, the modified silica was prepared using the following method:

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

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

[0100] (3) After the reaction was completed, the solid was separated by filtration. The solid was washed three times with ethanol and dried under vacuum (65°C) to constant weight to obtain modified silica.

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

[0102] Examples 1-5

[0103] In the present embodiment, UV-curable coatings with the following formulations were prepared, and the specific components are shown in Table 1.

[0104] Table 1: Composition and content (parts) of UV-curable coatings of Examples 1-5

[0105]

[0106]

[0107] The preparation method of the UV-curable coatings of the above Examples 1-5 includes:

[0108] (1) The above components are weighed by weight fraction, and the photoinitiator, erucamide, ethoxylated trimethylolpropane triacrylate and modified silica are added into a stirring kettle, and stirred at 2500 r / min for 45 min to obtain a first mixture;

[0109] (2) The remaining components are added into the first mixture, and stirred at a speed of 650 r / min for 20 min to obtain a UV-curable coating.

[0110] Comparative examples 1-4

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

[0112] Table 2: Composition and content (parts) of UV-curable coatings of Comparative Examples 1-4

[0113]

[0114] The preparation method of the UV-curable coatings of Comparative Examples 1-4 includes:

[0115] (1) The above components are weighed by weight fraction, and the photoinitiator, erucamide, ethoxylated trimethylolpropane triacrylate and modified silica (or silica) are added into a stirring kettle, and stirred at 2500 r / min for 45 min to obtain a first mixture;

[0116] (2) Add the remaining components into the first mixture, stir at 650 r / min for 20 min to obtain the UV-curable coating.

[0117] It can be understood that, if the corresponding component is not contained in the comparative example (e.g., erucamide is not contained in Comparative Example 1), the corresponding component need not be weighed and added.

[0118] Effect verification

[0119] The UV-curable coatings prepared in Examples 1-5 and Comparative Examples 1-4 above were respectively coated on the surface of a substrate layer to obtain a coating layer.

[0120] The specific steps are as follows:

[0121] PET substrates were taken, the surface of the substrate layer was cleaned and dried, and the corresponding UV-curable coating (Examples 1-5 and Comparative Examples 1-4) was roll-coated on the surface of the corresponding substrate layer. The UV-curing machine was used to cure it, and the UV-curing energy was 1000 mJ / cm 2 . PET substrates with a coating layer (thickness about 10 μm) on the surface were obtained.

[0122] The coating layer of the PET substrate prepared above was tested for related effects, including coating hardness test, adhesion test, friction coefficient and coating appearance.

[0123] The coating hardness was determined according to GB6739-1996; the adhesion test was performed by the Cross-Cut Test: a knife with a hardness of 6H was used to cut 11 parallel lines on the surface of the coating layer at an interval of 1 mm, and then 11 perpendicular intersecting lines were cut to form 100 1 mm 2 squares, the blade angle was 30°-45°, ensuring that the coating layer was cut through to the PET substrate, 3M 600 adhesive tape was pasted, 5N force was used to flatten, and after standing for 90 s, it was quickly peeled off at an angle of 60°. According to the GB / T 9286 standard, the result was 0 level (completely detached) to 5 level (no detachment).

[0124] The friction coefficient was determined according to the ASTM D1894 standard, and the coating appearance was directly observed to determine whether the coating was transparent and whether there were any pinholes.

[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) Friction coefficient Coating appearance Example 1 4 4 0.08 Transparent, no fish eyes Example 2 5 5 0.05 Transparent, no fish eyes Example 3 5 5 0.04 Transparent, no fish eyes Example 4 5 5 0.05 Transparent, no fish eyes Example 5 5 5 0.06 Transparent, no fish eyes Comparative example 1 4 4 0.18 Transparent, some fish eyes Comparative example 2 2 2 0.04 Transparent, no fish eyes Comparative example 3 2 1 0.15 Transparent, some fish eyes Comparative example 4 3 3 0.1 Transparent, few fish eyes

[0128] Note: In Table 3, part of the pinholes were larger than the small pinholes, according to the number of pinholes.

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

[0130] Specifically, the present embodiment uses silane coupling agent modified silica, on the one hand, erucamide is a long-chain non-polar molecule, which can migrate to the coating surface during UV curing to form a low-surface-energy lubricating layer, reducing the friction of silica particles on the coating surface, reducing particle agglomeration and protrusions, and at the same time, the crosslinked network formed by ETMPTA during UV curing can "lock" the silica particles, further limiting their migration or aggregation. That is, during UV curing, the lubricating layer of erucamide and the crosslinked network of ETMPTA work together to make the coating surface smooth, and together reduce the surface roughness (lower friction coefficient, transparent appearance without pitting).

[0131] On the other hand, the modified silica significantly enhances the adhesion through chemical bonding and has better dispersibility; wherein the modified silica enhances the interfacial bonding force between the coating and the substrate through chemical bonding; at the same time, the three functional group structure of ETMPTA forms a dense three-dimensional network after UV curing, which physically wraps the silica particles modified by the silane coupling agent, forming a "nano-reinforced composite structure"; that is, the modified silica is combined with the substrate through chemical bonding, and the crosslinked network of ETMPTA further embeds the microstructure of the substrate surface (such as the physical scratches on the PET surface), forming a "chemical bonding + mechanical interlocking" dual effect, thereby significantly improving the overall strength and adhesion of the coating (better coating hardness and adhesion).

[0132] Further comparing Example 3 with Comparative Example 1, the friction coefficient of Comparative Example 1 significantly increases and part of the coating appears pitting when erucamide is absent; this may be due to the absence of erucamide, which cannot better reduce the agglomeration and protrusion of modified silica particles, resulting in higher surface roughness and part of the coating appearing pitting. At the same time, due to the agglomeration of modified silica particles, they cannot better combine with ETMPTA, 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, the coating hardness and adhesion of Comparative Example 2 and Comparative Example 3 both decrease significantly, indicating that through the dual effect between ETMPTA and modified silica particles, the overall strength and adhesion of the coating can be significantly improved, therefore, the absence of modified silica in Comparative Example 2 and the absence of 3EO-TMPTA in Comparative Example 3 result in a decrease in the interfacial bonding force between the coating and the substrate.

[0134] In the above-mentioned examples, the friction coefficient of the coating is significantly reduced, and the hardness and adhesion of the coating are also improved. In the comparative example 2, the friction coefficient of the comparative example 2 does not change significantly in the absence of the modified silica, indicating that the lubricating layer of the erucamide and the crosslinked network of the ETMPTA synergistically act to make the surface of the coating tend to be flat, and to jointly reduce the surface roughness. In the comparative example 3, not only is the friction coefficient significantly increased in the absence of the 3EO-TMPTA, but also the coating has some pockmarks, indicating that in the present examples, the ETMPTA not only can synergistically improve the surface roughness problem caused by the silica filling with the erucamide, but also can synergistically act with the modified silica to effectively overcome the negative impact of the erucamide on the adhesion.

[0135] Further comparing the example 3 and the comparative example 4, the coating hardness and adhesion of the comparative example 4 are obviously decreased, and the friction coefficient is obviously increased, in the comparative example 4 in which the modified silica of the example 3 is replaced by the ordinary silica, indicating that the dispersion performance of the ordinary silica is poor, and the agglomeration and protrusion of the silica particles are more obvious. At the same time, the ordinary silica cannot better combine with the 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 the present examples uses the polyurethane acrylate as the base resin, and adds the erucamide, the ethoxylated trimethylolpropane triacrylate and the modified silica in the polyurethane acrylate, which not only can improve the surface roughness problem caused by the silica filling, but also can effectively overcome the negative impact of the erucamide on the adhesion based on the synergistic effect of the silica and the ETMPTA.

[0137] The technical solutions provided by the embodiments of the present disclosure are described in detail above, and the principles and implementation manners of the embodiments of the present disclosure are described by applying specific examples. The above description of the embodiments is only applicable to help understand the principles of the embodiments of the present disclosure; at the same time, for those skilled in the art, according to the embodiments of the present disclosure, the specific implementation manners and application ranges will be changed, and the above description of the embodiments should not be understood as a limitation of the present disclosure.

Claims

1. A UV-cured coating for the preparation of a protective coating of a PET substrate, characterized in that, The raw materials of the UV-curable coating include, by weight fraction: Polyurethane acrylate: 30-60 parts; Photoinitiator: 3-6 parts; Ethyoxylated trimethylolpropane triacrylate: 5-9 parts; Modified silica: 2-6 parts; Active diluent: 10-15 parts; The modified silica is silane coupling agent modified silica; and the active diluent is at least one of isobornyl acrylate, 1,6-hexanediol diacrylate, trimethylolpropane triacrylate, dipentaerythritol hexaacrylate or tripentaerythritol pentaacrylate. The preparation method of the modified silica includes:

2. The UV-cured coating of claim 1, wherein, adding the 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, filtering and separating to obtain a solid, and washing and vacuum drying the solid to obtain the modified silica; The solvent is an ethanol-water mixed solvent. The silane coupling agent is KH-550 or KH-560.

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

4. The UV-cured coating of claim 1, wherein, The preparation method includes:

5. A process for the preparation of a UV-curable coating as claimed in any one of claims 1 to 4, characterized in that taking the above components by weight fraction, adding the photoinitiator, the erucic acid amide, the ethyoxylated trimethylolpropane triacrylate and the modified silica into a reactor, stirring uniformly to obtain a first mixture; adding the remaining components into the first mixture, stirring uniformly to obtain the UV-curable coating.

6. Use of the UV-curable coating according to any one of claims 1-4 in preparing a protective coating for a PET substrate. The curing method of the protective coating includes:

7. Use according to claim 6, characterized in that, spraying the UV-curable coating on the surface of the PET substrate, placing it in an ultraviolet light source to cure the UV-curable coating, and obtaining the protective coating. ​ 8. Use according to claim 7, characterized in that, The UV curing energy of the ultraviolet light source is 800-1200 mJ / cm 2 .

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