An aqueous coating composition

Abstract

The present application relates to a kind of water-based paint compositions, preparation and application of composition, two-component coating system comprising the composition and its application, and the product obtained using the composition or two-component coating system coating. The water-based paint compositions include: a water-based UV resin;A nano-silicon oxide compound treated by silane;And a photoinitiator;Each kilogram of the solid component of the water-based UV resin contains not less than 3 mol of olefinic unsaturated group, the weight ratio of the solid component of the nano-silicon oxide compound and the solid component of the water-based UV resin is 11:20-73:100. The coating formed by the water-based paint compositions of the present application has high hardness and good adhesion, and is particularly suitable for electronic, electrical and communication equipment in the field of 5G.

Description

TECHNICAL FIELD

[0001] The present application relates to a water-based coating composition, preparation and application of the composition, a two-component coating system comprising the composition and application thereof, and an article coated using the composition or the two-component coating system. The water-based coating composition of the present application forms a coating layer with high hardness and good adhesion, and is particularly suitable for electronic, electrical and communication devices in the 5G field. BACKGROUND

[0002] The 5G era has higher requirements for the communication signal penetration of the shells of electronic, electrical and communication devices, especially small devices and portable devices. The commonly used material for the shells of the above-mentioned devices is metal, which cannot meet the requirements of 5G devices due to its strong shielding and attenuation to communication signals. In the field of portable devices, such as the mobile phone industry, attempts have been made to use plastic, glass or ceramic as back cover materials. Plastic is widely studied due to its advantages such as light weight, wear resistance and not easy to break. Among them, PC / PMMA composite boards are widely welcomed due to their excellent glass-like effect. In order to increase the hardness of the PC / PMMA composite board, a coating is usually coated on the surface thereof.

[0003] UV coatings are widely used in many applications, such as electronics and electrical appliances, e.g. mobile phones, laptops, etc., due to their fast curing speed, high production efficiency, and high film fullness. UV coatings applied to the plastic back cover of a mobile phone can not only achieve a bright or matte effect, but also improve the hardness, wear resistance, scratch resistance, water boiling resistance, solvent resistance, cold and hot resistance, and special chemical resistance of the plastic back cover. There are three types of UV coatings, namely solvent-based UV coatings, solvent-free UV coatings and water-based UV coatings.

[0004] CN106459616A discloses a solvent-based coating agent and a film coated with the same, wherein the coating has enhanced mechanical and chemical resistance and sufficient formability for a 2D film insert molding method. The composition of the coating agent can contain inorganic particles to improve mechanical durability, and the total content of additives including inorganic particles is 0-20% by weight.

[0005] EP2604660A1 discloses a hard coating for a plastic surface, the surface of boehmite nanoparticles is modified by an alkoxysilane compound, and mixed with an acrylate to form an organic / inorganic hybrid material to achieve good comprehensive performance. The system is a solvent-based system.

[0006] CN104736613A discloses a laminated pre-coated film with high hardness and excellent properties, which is a solvent-based system.

[0007] US20070238804A1 discloses a UV coating for protecting various plastic substrates such as ophthalmic lenses, polycarbonate sheets, CR-39 sheets or polystyrene. The UV coating is a solvent-free and water-free system, the whole process is very complex, which is not conducive to large-scale industrial production.

[0008] CN105765002A discloses a formable hard coating composition and a coated film comprising a co-extruded PC / PMMA film and a coating obtained by coating with the hard coating composition. The composition is solvent-based, comprising a binder and a crosslinking agent, the binder comprising at least one acrylate oligomer and at least one monofunctional acrylic monomer, and the crosslinking agent comprising at least one multifunctional acrylic or methacrylic monomer.

[0009] US2010304113A provides a solvent-based coating composition and a coated film formed therefrom, comprising a binder containing UV-curable functional groups, a compound containing UV-curable fluorine-containing functional groups, a photosensitive initiator and nanoparticles. The coated film has excellent wear resistance and stain resistance, such as fingerprint removal and anti-coating writing.

[0010] Solvent-based UV coatings and solvent-free coatings are not conducive to the environment and human body due to the presence of a large amount of low flash point solvents or active monomers. Water-based UV coatings not only have the advantages of fast curing speed, high production efficiency, and high film fullness of UV coatings, but also replace organic solvents with water as a dispersion medium, greatly reducing the volatile amount of VOC, which is harmless to the human body and the environment. However, the existing water-based UV coatings still have a gap compared with solvent-based or solvent-free UV coatings in terms of adhesion to the surface of the substrate, pencil hardness of the coating, and water boiling resistance.

[0011] CN107109101A discloses an optical film coating composition comprising a UV-curable acrylate resin, mixed particles containing inorganic nanoparticles and carbon black, and a photoinitiator. The coating composition can improve visibility and brightness.

[0012] US20090269568A1 improves the effect of water-based UV coatings by introducing inorganic particles, which can achieve a high anti-sticking property of the coating layer formed by UV coating before deformation so that the coating layer can be rolled up without any problem, and a high stretching ratio can still be achieved during deformation. When the amount of inorganic particles added is 1 wt%-60 wt%, the 750g pencil hardness of the coating layer formed by UV coating can reach 2H. However, the coating still cannot meet the hardness requirements of the shell of electronic, electrical and communication equipment, especially the hardness requirements of the coating for the plastic back cover of mobile phones.

[0013] Therefore, it is desirable to develop a waterborne UV coating with good adhesion and high pencil hardness to meet the performance requirements of the coating for 5G device housings, especially plastic back covers of mobile phones. SUMMARY

[0014] The object of the present application is to provide a waterborne coating composition, preparation and use of the composition, a two-component coating system comprising the composition and use thereof, and an article coated using the composition or the two-component coating system.

[0015] The waterborne coating composition according to the present application comprises:

[0016] at least one waterborne UV resin;

[0017] at least one silane-treated nano-silica compound; and

[0018] at least one photoinitiator;

[0019] wherein the waterborne UV resin contains not less than 3 mol of ethylenically unsaturated groups per kilogram of the solid content of the waterborne UV resin, and the weight ratio of the solid content of the nano-silica compound to the solid content of the waterborne UV resin is 11:20-73:100.

[0020] According to one aspect of the present application, there is provided a method for preparing the waterborne coating composition provided by the present application, by mixing the waterborne UV resin, the silane-treated nano-silica compound and the photoinitiator in any manner.

[0021] According to yet another aspect of the present application, there is provided the use of the waterborne coating composition provided by the present application for preparing an article.

[0022] According to still another aspect of the present application, there is provided an article comprising a substrate and a coating layer formed by applying the waterborne coating composition provided by the present application to the substrate.

[0023] According to yet another aspect of the present application, there is provided a method for manufacturing an article, comprising the steps of: applying the waterborne coating composition provided by the present application to a surface of a substrate, drying and curing.

[0024] According to still another aspect of the present application, there is provided a two-component coating system comprising a component A and a component B, the component A being the waterborne coating composition provided by the present application, and the component B being a crosslinking agent.

[0025] According to yet another aspect of the present application, there is provided the use of the two-component coating system provided by the present application for preparing an article.

[0026] According to another aspect of the present application, there is provided an article comprising a substrate and a coating formed by applying the two-component coating system according to the present application to the substrate.

[0027] The waterborne coating composition or the two-component coating system according to the present application has the advantages of low VOC and low odor. The waterborne UV resin and the silane-treated nano-silica compound can form a dense inorganic / organic hybrid system, and the coating formed by the waterborne coating composition or the two-component coating system has the advantages of high pencil hardness, good conventional adhesion and good water boiling adhesion. The good conventional adhesion indicates that the adhesion between the coating and the substrate is good, and the good water boiling adhesion indicates that the adhesion between the coating and the substrate is good and the hydrolysis resistance is good under high temperature and high humidity conditions. The high pencil hardness indicates that the scratch resistance of the coating is good. The waterborne coating composition or the two-component coating system according to the present application can meet the performance requirements of the coating for the 5G device shell, especially the plastic back cover of the mobile phone. DETAILED DESCRIPTION

[0028] The present application provides a waterborne coating composition comprising:

[0029] at least one waterborne UV resin;

[0030] at least one silane-treated nano-silica compound; and

[0031] at least one photoinitiator;

[0032] wherein the waterborne UV resin contains not less than 3 mol of ethylenic unsaturated groups per kilogram of solid content, and the weight ratio of the solid content of the nano-silica compound to the solid content of the waterborne UV resin is 11:20-73:100.

[0033] The present application also provides a preparation method and applications of the composition, in particular applications in the field of coatings, a two-component coating system comprising the composition and applications thereof, and an article obtained by coating using the composition or the two-component coating system.

[0034] The term "curing" as used herein refers to the process of the waterborne coating composition or the two-component coating system comprising the composition from a liquid state to a solid state.

[0035] The term "coating" as used herein refers to a chemical substance capable of being coated on the surface of an object by different application processes to form a solid coating layer which is firmly adhered, has certain strength and is continuous.

[0036] The term "waterborne UV resin" refers to a waterborne ultraviolet light curing resin.

[0037] The term ultraviolet light curable resin refers to a polymer which, upon exposure to ultraviolet (UV) radiation, is capable of forming covalent bonds with the functional groups of chain extenders, crosslinkers and other polymer molecules to form a crosslinked polymer network.

[0038] The term "polyurethane" as used herein refers to polyurethane urea and / or polyurethane polyurea and / or polyurea and / or polythiourethane.

[0039] The term "silane treated nanosilica compound" as used herein refers to a nanosilica compound which has been pre-treated with a silane.

[0040] Aqueous coating composition

[0041] The amount of organic solvent in the composition is preferably not more than 5 wt%, most preferably not more than 0.5 wt%, relative to the total weight of the composition.

[0042] The composition is aqueous based and has the feature of being low VOC.

[0043] The weight ratio of the solid fraction of the nanosilica compound to the solid fraction of the aqueous UV resin is preferably 3:5 to 17:25.

[0044] Aqueous UV resin

[0045] The aqueous UV resin of the present invention is present as a dispersion or emulsion, wherein water is comprised.

[0046] The solid fraction of the aqueous UV resin of the present invention refers to the solid or effective components of the aqueous UV resin.

[0047] The solid fraction of the aqueous UV resin comprises not less than 3 mol, further preferably not less than 3.5 mol, most preferably not less than 4 mol of ethylenically unsaturated groups per kg of the aqueous UV resin.

[0048] The aqueous UV resin is preferably an aqueous UV polyurethane acrylate dispersion.

[0049] The amount of the solid fraction of the aqueous UV resin is preferably 30 wt% to 50 wt%, relative to the total weight of the aqueous UV resin.

[0050] The amount of the aqueous UV resin is preferably 45 wt% to 50 wt%, relative to the total weight of the aqueous coating composition.

[0051] The amount of residual organic solvent in the aqueous UV resin is preferably less than 1.0 wt%, relative to the total weight of the solid fraction of the aqueous UV resin.

[0052] The aqueous UV polyurethane acrylate dispersions are preferably one or more of the following: Bayhydrol UV 2689 / 2 and Bayhydrol UV 2720 / 1.

[0053] Silane-treated nanosilica compound

[0054] The solid fraction of the nano-silicon oxide compound refers to the solid component or effective component of the nano-silicon oxide compound.

[0055] The particle size of the nano-silicon oxide compound is preferably 8 nm to 18 nm, most preferably 8 nm to 10 nm.

[0056] The nano-silicon oxide compound is preferably one or more of the following: fumed nano-silicon dioxide, aqueous nano-silicon dioxide dispersion, aqueous nano-silicon sol, solvent-based nano-silicon dioxide solution, and solvent-based nano-silicon sol; further preferably one or more of the following: aqueous nano-silicon dioxide dispersion and aqueous nano-silicon sol; most preferably aqueous nano-silicon dioxide dispersion.

[0057] The nano-silicon oxide compound is preferably neutral or alkaline.

[0058] The nano-silicon oxide compound is preferably an aqueous nano-silicon dioxide dispersion with a neutral or alkaline surface treated with silane, further preferably an aqueous nano-silicon dioxide dispersion with a neutral or alkaline surface treated with silane having a particle size of 8 nm to 18 nm, most preferably Dispercoll S 3030 / 1.

[0059] The amount of the nano-silicon oxide compound is 37 to 44% by weight, relative to the total weight of the aqueous coating composition.

[0060] Photoinitiator

[0061] The photoinitiator is preferably one or more of the following: monomolecular initiator and bimolecular initiator.

[0062] The monomolecular initiator is preferably an aromatic ketone compound, most preferably one or more of the following: benzophenone in combination with a tertiary amine, alkylbenzophenone, 4,4'-bis(dimethylamino)benzophenone (Michler's ketone), anthrone, and halogenated benzophenone.

[0063] The bimolecular initiator is preferably one or more of the following: benzoin, derivative of benzoin, benzil ketals, acyl phosphine oxide, bisacyl phosphine oxide, phenylglyoxylate, camphorquinone, alpha-aminoalkylphenone, alpha, alpha-dialkoxyacetophenone, and alpha-hydroxyalkylphenone. The acyl phosphine oxide is preferably 2,4,6-trimethylbenzoyldiphenylphosphine oxide.

[0064] The photoinitiator is most preferably one or more of the following: Omnirad, Irgacure, Darocur, and Esacure.

[0065] The amount of the photoinitiator is preferably 0.5% by weight to 5.0% by weight, most preferably 0.5% by weight to 1.0% by weight, relative to the total weight of the water-based coating composition.

[0066] Other

[0067] The water-based coating composition preferably further comprises one or more of the following: a silane coupling agent, other water-based polymer dispersions or emulsions, a reactive diluent, and an additive.

[0068] The silane coupling agent is preferably one or more of the following: an alkyl silane coupling agent, an unsaturated group-containing silane coupling agent, an amino silane coupling agent, an epoxy silane coupling agent, a mercapto silane coupling agent, an ether silane coupling agent, and a silane oligomer; most preferably an unsaturated group-containing silane coupling agent.

[0069] The unsaturated group-containing silane coupling agent is preferably one or more of the following: a vinyl silane coupling agent, an acryloxy silane coupling agent, and a methacryloxy silane coupling agent, further preferably one or more of the following: an acryloxy silane coupling agent and a methacryloxy silane coupling agent, most preferably one or more of the following: 3-acryloxypropyltrimethoxysilane and 3-methacryloxypropyltrimethoxysilane.

[0070] The amount of the silane coupling agent is preferably 0.1% by weight to 3.0% by weight, relative to the total weight of the water-based coating composition.

[0071] The other water-based polymer dispersions or emulsions are preferably one or more of the following: a polyurethane dispersion, a polyacrylate primary dispersion, a polyacrylate secondary dispersion, an ethylene-vinyl acetate copolymer emulsion, a petroleum resin polymer emulsion, a rosin polymer emulsion, a polybutadiene dispersion, a propylene phenyl copolymer emulsion, a butylene styrene copolymer emulsion, a terpene phenol aldehyde polymer emulsion, a polychloroprene dispersion, and a polyvinylidene chloride dispersion.

[0072] The amount of the other water-based polymer dispersions or emulsions is preferably 0 to 50% by weight, relative to the total weight of the water-based coating composition.

[0073] The active diluent is preferably an acrylate monomer active diluent, further preferably a tri- or higher functionality acrylate monomer, most preferably one or more of the following: trimethylolpropane triacrylate (TMPTA), ethoxylated trimethylolpropane triacrylate (EOTMPTA), glyceryl-propoxylated triacrylate (GPTA), pentaerythritol tetraacrylate (PETA), ethoxylated pentaerythritol tetraacrylate (EOPETA), and dipentaerythritol hexaacrylate (DPHA).

[0074] The amount of the active diluent is preferably 1.0 wt% - 20.0 wt%, relative to the total weight of the waterborne coating composition.

[0075] The additive is preferably one or more of the following: defoamer, wetting agent, leveling agent, anti-blocking agent, anti-staining aid, anti-fingerprint aid, and thickening agent.

[0076] The amount of the additive can be an amount well known to one skilled in the art, preferably 0 wt% - 20 wt%, further preferably 0 wt% - 10 wt%, most preferably 0.1 wt% - 10 wt%, relative to the total weight of the waterborne coating composition.

[0077] Process for the preparation of an aqueous coating composition

[0078] The method of preparing the waterborne coating composition preferably comprises the following steps: mixing the waterborne UV resin, the silane-treated nano-silica compound, the photoinitiator, the optional silane coupling agent, the optional other waterborne polymer dispersion or emulsion, the optional active diluent, and the optional additive in any manner.

[0079] The article is preferably a housing of a 5G product, further preferably a front cover or back cover of a 5G product, most preferably a back cover of a mobile phone.

[0080] The substrate is preferably made of a thermoplastic polymer. The substrate can exist in the form of a sheet or in the form of a laminated film. The laminated film can be double-layered or multi-layered.

[0081] The thermoplastic polymer is preferably one or more of the following: polymethyl methacrylate (PMMA), polyester, rigid PVC, cellulose ester, polystyrene (PS), polystyrene copolymer, polyacrylonitrile (PAN), ABS plastic, acrylonitrile methyl methacrylate (AMMA), acrylonitrile-styrene-acrylate (ASA), polyurethane (PUR), polyethylene (PE, PE-HD, -LD, -LLD, -C), polypropylene (PP), polyamide (PA), polycarbonate (PC) and polyethersulfone (PES) (abbreviations according to DIN 7728 part 1), further preferably one or more of the following: polycarbonate sheet and PC / PMMA composite sheet, most preferably PC / PMMA composite sheet.

[0082] The PC / PMMA composite sheet is also known as PC / acrylic composite sheet.

[0083] The polyester is preferably one or more of the following: PET (polyethylene terephthalate), PEN (polyethylene naphthalate), PBTP (polybutylene terephthalate) and UP (unsaturated polyester resin).

[0084] The polystyrene copolymer is preferably one or more of the following: SAN (styrene-acrylonitrile copolymer), SB (styrene-butadiene copolymer) and MBS (methyl methacrylate-butadiene-styrene copolymer).

[0085] The preferred method of manufacturing an article, which is a housing of a 5G product, further preferably a face cover or back cover of a 5G product, most preferably a back cover of a mobile phone, comprises the following steps:

[0086] i) applying the aqueous coating composition of the present invention to the PMMA face of a PC / PMMA composite sheet;

[0087] ii) drying at 50°C - 100°C for 3 minutes - 10 minutes; and

[0088] iii) photocuring at a curing rate of 1 m / min - 10 m / min and a radiation intensity of 100 mJ / cm 2 - 2000 mJ / cm 2 .

[0089] The application is preferably one or more of the following: curtain coating, spray coating, roller coating, knife coating, screen printing and transfer printing.

[0090] The drying can be a method commonly used in the industry, preferably using an oven or a tunnel.

[0091] The dry film thickness of the coating is preferably 5 pm - 20 pm, most preferably 8 pm - 20 pm.

[0092] The drying temperature of step ii) is preferably 60°C to 80°C and the drying time is preferably 5 minutes to 10 minutes.

[0093] The curing is preferably UV-curing, further preferably UV radiation, most preferably using a UV device of the type M-40-2x1-URS-TR-SS by IST.

[0094] The curing dose of step iii) is measured using an EIT UV Power Pack II dosimeter by EIT.

[0095] Step iii) is preferably a one-pass through the UV device at a curing speed of 5 m / min, cured at a radiation intensity of 700 mJ / cm 2

[0096] The amount of organic solvent of the two-component coating system is preferably not more than 5 wt.-%, most preferably not more than 0.5 wt.-%, relative to the total weight of the two-component coating system.

[0097] The two-component coating system is waterborne and has a low VOC content.

[0098] The A-component and the B-component are preferably stored separately and mixed before use.

[0099] The weight ratio of the A-component to the B-component is preferably 2:1 to 100:1, further preferably 5:1 to 100:1, most preferably 50:1 to 65:1.

[0100] The crosslinker is preferably one or more of the following: isocyanate group containing compounds and carbodiimides.

[0101] The isocyanate group containing compounds are preferably water-dispersible aliphatic polyisocyanates, most preferably one or more of the following: water-dispersible HDI-based polyisocyanates and water-dispersible IPDI-based polyisocyanates.

[0102] The NCO group content of the isocyanate group containing compounds is preferably 10 wt.-% to 20 wt.-%.

[0103] The carbodiimides are preferably waterborne carbodiimides.

[0104] The NCN group content of the carbodiimides is preferably 3 wt.-% to 5 wt.-%.

[0105] Example

[0106] ​Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. If there is a conflict between the definitions of terms in this specification and those of the prior art or with other statutes, the definitions in this specification shall control.

[0107] Unless otherwise indicated, all numbers expressing quantities of ingredients, reaction conditions, and so forth used in the specification and claims are to be understood as approximations based on the desired properties sought to be obtained by the employ of the terms "about." Therefore, unless otherwise indicated, the numerical parameters set forth in the specification and claims are approximations that can vary from the numerical values stated.

[0108] As used herein, "and / or" means one or all of the listed items.

[0109] As used herein "comprises" and "comprising" are to be construed as including only the recited elements among the "only" and "at least the recited elements.

[0110] All percentages in the present application are percent by weight, unless otherwise stated.

[0111] The analytical measurements of the present application are all carried out at 23°C, unless otherwise stated.

[0112] As used in the specification and claims, the articles "a", "an", "the", and "said” are intended to include both “only one” as well as “one or more” unless otherwise indicated. For example, "a component" means one or more components.

[0113] The solids of the dispersions are determined according to DIN-EN ISO 3251 using a Mettler Toledo's HS153 moisture determinator by weighing 1 g of sample.

[0114] The particle size is determined using laser spectroscopy (Malvern Instruments' Zatasizer Nano ZS 3600 laser particle size instrument) after dilution with deionized water at 23°C.

[0115] The pH is measured using a Sartorius' PB-10 pH meter at 23°C.

[0116] Raw materials and reagents

[0117] Bayhydrol UV 2689 / 2: Aqueous UV resin, solid content 41.4%, pH value 7.0-8.5, moles of ethylenically unsaturated groups per kg of aqueous UV resin solids 4-8 mol, available from Covestro (China) Co., Ltd.

[0118] Bayhydrol UV 2282: Aqueous UV resin, solid content 39.6%, pH value 7.0-8.5, moles of ethylenically unsaturated groups per kg of aqueous UV resin solids less than 3.0 mol, available from Covestro (China) Co., Ltd.

[0119] Bayhydrol UH XP 2648: Aqueous UV resin, solid content 35.6%, pH value 8.0, no ethylenically unsaturated groups, available from Covestro (China) Co., Ltd.

[0120] Dispercoll S 3030 / 1: Aqueous nanosilica dispersion with silane-treated surface, solid content 30.9%, pH value 10.5, particle size 8-9 nm, available from Covestro (China) Co., Ltd.

[0121] Dispercoll S 2020: Aqueous nanosilica dispersion with untreated surface, solid content 20.3%, pH value 3, particle size 15 nm, available from Covestro (China) Co., Ltd.

[0122] SNOWTEX-40: Aqueous nanosilica dispersion with untreated surface, solid content 40.2%, pH value 9-10.5, particle size 20-25 nm, available from Nissan Chemical.

[0123] Omnirad 500: Alpha-hydroxyketone, surface curing initiator, available from IGM Resins.

[0124] BYK 093: Defoamer, available from BYK-Chemie.

[0125] BYK 333: Polyether-modified silicone, wetting agent, available from BYK-Chemie.

[0126] BYK 346: Polyether-modified silicone solution, wetting agent, available from BYK-Chemie.

[0127] TEGO Twin 4100: Wetting agent, available from Evonik Industries.

[0128] TEGO Glide 410: Wetting agent anti-blocking agent, available from Evonik Industries.

[0129] Borchi Gel 0621: thickener, available from Borchi (Shanghai) Trading Co., Ltd.

[0130] Desmodur XP 2802: hydrophilically modified carbodiimide crosslinker, 40 wt% solids, NCN group content 4.2 wt%, available from Covestro.

[0131] Bayhydur 305: polyisocyanate curing agent, water-dispersible HDI-based hydrophilic aliphatic polyisocyanate, NCO group content 16.2 wt%, available from Covestro.

[0132] Performance test methods

[0133] 1. Conventional adhesion

[0134] The cross-hatch test was performed on the UV cured coating according to the national standard GB / T 9286-1998 “Cross-hatch test for paint films”. The tape used was 3M Scotch 600. The adhesion rating method was based on the standard of GB / T 9286-1998 “Cross-hatch test for paint films” and the method B of ASTM D 3359 “Standard method for testing adhesion by tape”. Table 1 shows the rating standard of conventional adhesion. The pass value of conventional adhesion was 5B.

[0135] Table 1 Rating standard of conventional adhesion

[0136] Conventional adhesion Description 5B Cut edges completely smooth with no flaking 4B Minor flaking of coating at intersection of cuts but the area of the crosscut affected cannot be significantly greater than 5% 3B Flaking of coating at intersection of cuts and / or along edges of cuts, the area of the crosscut affected cannot be significantly greater than 5% but can be significantly greater than 15% 2B Coating partially or completely flaked in large pieces along edges of cuts and / or partially or completely flaked from different parts of the grid, the area of the crosscut affected cannot be significantly greater than 15% but can be significantly greater than 35% 1B Coating flaked in large pieces along edges of cuts and / or some parts of the grid partially or completely flaked, the area of the crosscut affected cannot be significantly greater than 35% but can be significantly greater than 65% 0B Flaking to an extent greater than 1B

[0137] 2. Pencil hardness

[0138] The pencil hardness test was performed according to the national standard GB / T 6739-1996 “Pencil hardness test for paint films”. The MITSUBISHI UNI pencil was used, which was mounted on a special pencil hardness tester. The load on the tip of the pencil was 1 kg, the angle of the pencil to the horizontal was 45°, and the pencil was pushed forward to slide about 10 mm long. A total of 5 lines were drawn at different positions, and then the pencil marks were wiped clean with an eraser. The coating surface was checked for any scratches, and the requirement was that no more than 1 scratch was allowed on the coating surface. The pencil hardness was not less than 3H to pass.

[0139] 3. Boiling water adhesion

[0140] The UV cured coating film was completely immersed in hot water at 80°C for 30 minutes, and then taken out and gently blotted to remove the surface water. The appearance change of the coating was observed and the cross-hatch test was performed. The adhesion rating method and standard were the same as those of the conventional adhesion. The boiling water adhesion was not less than 4B to pass.

[0141] Table 2 is the composition of the aqueous coating composition or two-component coating system of the examples and comparative examples, and the performance test results of the coating formed by the composition or two-component coating system.

[0142] Process for the preparation of the aqueous coating compositions of Comparative Examples 1-5, 7, 9-11 and Examples 1-2

[0143] According to the content of the components shown in Table 2, the resin, photoinitiator, optional aqueous nanosilica dispersion, optional additives and deionized water were added into a container, and stirred until all components were uniformly dispersed to obtain the composition of the examples and comparative examples.

[0144] Process for the preparation of the two-component coating systems of Comparative Examples 6, 8 and Examples 3-4

[0145] Preparation of A component: according to the content of the components shown in Table 2, the resin, photoinitiator, optional aqueous nanosilica dispersion, optional additives and deionized water were added into a container, and stirred until all components were uniformly dispersed.

[0146] Mix A component with B component, and stir at 200-500 rpm for 5 min-10 min, filter with 200 mesh filter screen after uniform mixing to obtain the two-component coating system of the examples and comparative examples, ready for use.

[0147] Process for the preparation of the coating

[0148] The aqueous coating composition or two-component coating system was uniformly roll-coated on the PMMA side of the PC / PMMA film, and the dry film thickness of the coating was about 8-15 µm; dried in an oven at 60-80 °C for about 5 minutes; cured using a UV device from IST of M-40-2x1-URS-TR-SS type (the curing dose was measured by EIT UV Power Pack II dosimeter), once through the above UV device at a continuous curing rate of 5 m / min, and the coating was obtained at a radiation intensity of about 600 mJ / cm 2 -800 mJ / cm 2 .

[0149] Table 2 Composition, two-component coating system of the examples and comparative examples and performance test results

[0150]

[0151] Note: The weight ratio refers to the weight ratio of the solid content of the nanosilica compound to the solid content of the aqueous UV resin.

[0152] The water-based coating compositions or two-component coating systems of embodiments 1-4 of the present application have good conventional adhesion, water boiling adhesion and pencil hardness. Among them, embodiments 3-4 are two-component coating systems, and polyisocyanate type curing agent and carbodiimide curing agent are selected respectively. From the coating performance test results in Table 2, different curing agents can achieve high pencil hardness, conventional adhesion and water boiling adhesion.

[0153] The composition of Comparative Example 1 does not contain a silane-treated nano-silica compound, and the conventional adhesion, water boiling adhesion and pencil hardness of the coating prepared from the composition are all unqualified.

[0154] The weight ratio of the solid content of the nano-silica compound to the solid content of the water-based UV resin in the compositions or coating systems of Comparative Examples 2-3 and 6-8 is less than 11:20, and the weight ratio of the solid content of the nano-silica compound to the solid content of the water-based UV resin in the compositions of Comparative Examples 4-5 is greater than 73:100. The coatings formed by the above-mentioned compositions or coating systems cannot simultaneously achieve conventional adhesion, water boiling adhesion and pencil hardness.

[0155] Comparing Comparative Example 9 with Comparative Example 10, Comparative Example 9 uses a water-based nano-silica dispersion with a basic pH value and without silane treatment, and Comparative Example 10 uses a water-based nano-silica dispersion with an acidic pH value and without silane treatment. The conventional adhesion, water boiling adhesion and pencil hardness of the coating prepared from the water-based coating composition of Comparative Example 9 are all unqualified. The coating prepared from the water-based coating composition of Comparative Example 10 has visible small particles with the naked eye, i.e. the composition is incompatible and cannot be tested for coating performance.

[0156] Comparing Comparative Example 1 with Comparative Example 11, Comparative Example 11 uses Bayhydrol UV 2282 as the resin, and the number of moles of ethylenic unsaturated groups in the solid components of Bayhydrol UV 2282 per kilogram is less than 3.0 mol. The conventional adhesion, water boiling adhesion and pencil hardness of the coating prepared from the composition containing the same are all unqualified.

[0157] It is easy for those skilled in the art to know that the present application is not limited to the foregoing specific details, and the present application can be implemented in other specific forms without departing from the spirit or main characteristics of the present application. Therefore, the embodiments should be considered illustrative rather than limiting in any way, and the scope of the present application should be indicated by the claims rather than the foregoing description, and therefore any changes falling within the meaning and scope of the claims should be considered as belonging to the present application.

Claims

1. A water-based coating composition comprising: At least one water-based UV resin; At least one nano-silica compound treated with silane; and At least one photoinitiator; in, Each kilogram of the aqueous UV resin contains at least 3 mol of olefinic unsaturated groups in its solids content. The weight ratio of the solids of the nano-silica compound to the solids of the aqueous UV resin is 11:20-73:100, and the aqueous UV resin is an aqueous UV polyurethane acrylate dispersion.

2. The water-based coating composition according to claim 1, characterized in that, Each kilogram of the waterborne UV resin contains not less than 3.5 mol of olefinic unsaturated groups in its solids content.

3. The water-based coating composition according to claim 1, characterized in that, Each kilogram of the waterborne UV resin contains at least 4 mol of olefinic unsaturated groups in its solids content.

4. The water-based coating composition according to any one of claims 1-3, characterized in that, The amount of the waterborne UV resin is 45%-50% by weight, relative to the total weight of the waterborne coating composition.

5. The water-based coating composition according to claim 1, characterized in that, The amount of the waterborne UV resin is 45%-50% by weight, relative to the total weight of the waterborne coating composition.

6. The water-based coating composition according to any one of claims 1-3, characterized in that, The weight ratio of the solids of the nano-silica compound to the solids of the aqueous UV resin is 3:5-17:

25.

7. The water-based coating composition according to any one of claims 1-3, characterized in that, The particle size of the nano-silica compound is 8nm-18nm.

8. The water-based coating composition according to any one of claims 1-3, characterized in that, The nano-silica compound is neutral or alkaline.

9. The water-based coating composition according to any one of claims 1-3, characterized in that, The amount of the photoinitiator is 0.5% to 5.0% by weight, relative to the total weight of the waterborne coating composition.

10. The water-based coating composition according to any one of claims 1-3, characterized in that, The waterborne coating composition further comprises one or more of the following: silane coupling agents, other waterborne polymer dispersions or emulsions, reactive diluents, and additives.

11. The waterborne coating composition according to claim 10, characterized in that, The amount of the other aqueous polymer dispersions or emulsions shall not exceed 50% by weight, relative to the total weight of the aqueous coating composition.

12. A method of manufacturing an article, comprising the steps of: applying an aqueous coating composition as described in any one of claims 1-11 to a substrate surface, drying and curing.

13. A two-component coating system comprising component A and component B, wherein component A is an aqueous coating composition according to any one of claims 1-11, and component B is a crosslinking agent.

14. The two-component coating system as described in claim 13, characterized in that, The crosslinking agent is one or more of the following: compounds containing isocyanate groups and carbodiimide.

15. Use of the waterborne coating composition according to any one of claims 1-11 or the two-component coating system according to claim 13 or 14 for the preparation of articles.

16. An article comprising a substrate and a coating formed by applying an aqueous coating composition according to any one of claims 1-11 to the substrate, or comprising a substrate and a coating formed by applying a two-component coating system according to claim 13 or 14 to the substrate.

17. The article of claim 16, characterized in that, The substrate is a PC / PMMA composite board.

18. The article of claim 16 or 17, characterized in that, The product in question is the casing of a 5G product.

19. The article of claim 16 or 17, characterized in that, The product in question is a front or back cover for a 5G product.

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