Abstract:
A hard coating composition comprises a dopamine, a plurality of inorganic oxide particles, and a solvent. The dopamine reduces the film forming time of an anti-fogging coating. A hard coating film using the hard coating composition, and a coated article using the hard coating film are also provided.

Description:
FIELD 
       [0001]    The subject matter herein generally relates to a coating composition, and more particularly, to a hard coating composition, a hard coating film using the hard coating composition, and a coated article using the hard coating film. 
       BACKGROUND 
       [0002]    A hard coating film can be attached to a surface of an article, to prevent the article from being damaged. As the hard coating film is set on the surface of the article, the hard coating film needs to keep shape, hardness, or size unchanged, to ensure the article has a good appearance. The hard coating film is generally formed by a hard coating composition. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0003]    Implementations of the present technology will now be described, by way of example only, with reference to the attached figures. 
           [0004]      FIG. 1  is a diagrammatic view of an exemplary embodiment of a coated article of the present disclosure. 
           [0005]      FIG. 2  is a cross-sectional view along line II-II of  FIG. 1 . 
           [0006]      FIG. 3  illustrates a flowchart of a method for making a coated article in accordance with an exemplary embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0007]    It will be appreciated that for simplicity and clarity of illustration, where appropriate, reference numerals have been repeated among the different figures to indicate corresponding or analogous elements. In addition, numerous specific details are set forth in order to provide a thorough understanding of the embodiments described herein. However, it will be understood by those of ordinary skill in the art that the embodiments described herein may be practiced without these specific details. In other instances, methods, procedures, and components have not been described in detail so as not to obscure the related relevant feature being described. Also, the description is not to be considered as limiting the scope of the embodiments described herein. The drawings are not necessarily to scale, and the proportions of certain parts may be exaggerated to illustrate details and features of the present disclosure better. 
         [0008]    Several definitions that apply throughout this disclosure will now be presented. 
         [0009]    The term “comprising” when utilized, means “including, but not necessarily limited to”; it specifically indicates open-ended inclusion or membership in the so-described combination, group, series, and the like. The term “about” when utilized, means “not only includes the numerical value, but also include numbers closest to the numerical value”. 
         [0010]    An exemplary embodiment of a hard coating composition comprises a dopamine, a plurality of inorganic oxide particles, and a solvent. 
         [0011]    The dopamine has a mass percentage of about 1% to about 40% of a total mass of the hard coating composition. The plurality of the inorganic oxide particles has a mass percentage of about 40% to about 80% of the total mass of the hard coating composition. The solvent has a mass percentage of about 5% to about 50% of the total mass of the hard coating composition. 
         [0012]    In at least one exemplary embodiment, the hard coating composition has a PH value of about 8.0 to about 10.5. The PH value is conducive to oxidation of the dopamine. 
         [0013]    A chemical structure formula of the dopamine is: 
         [0000]    
       
                 
         
             
             
         
       
     
         [0014]    The dopamine has a catechol functional group. When the hard coating composition is put in an alkaline or an oxidizing condition, the catechol functional group of the dopamine can be oxidized to form a dopamine quinone containing a benzoquinone structure. The dopamine quinone can disproportionately react with the dopamine to form a semi-quinone radical, and couple to form a cross-linking bond, thereby a polymer with a cross-linking structure is formed. Thereby, a hard coating film can be formed. The inorganic oxide particles are dispersed in the cross-linking structure. 
         [0015]    The plurality of inorganic oxide particles may be selected from particles of silica, zirconia, alumina, titanium, or any combination thereof. The inorganic oxide particle can increase a hardness and a refractive index of a hard coating film formed by the hard coating composition. 
         [0016]    A particle diameter of the inorganic oxide particle may be about 1 nm to about 1000 nm. Preferably, the particle diameter of the inorganic oxide particle is about 1 nm to about 300 nm. 
         [0017]    The solvent may be water, an alcohol aqueous solution, or an oxidizing aqueous solution. The alcohol aqueous solution may be a methanol aqueous solution, an ethanol aqueous solution, or a propanol aqueous solution. The oxidizing aqueous solution may be sodium periodate (NaIO 4 ) aqueous solution. When the solvent is alcohol aqueous solution or oxidizing aqueous solution, the PH of the hard coating composition may be adjusted to in a range of about 8.0 to about 10.5 by a sodium hydroxide solution. 
         [0018]    The hard coating composition does not include an organic solvent, so the hard coating composition is environmentally friendly. 
         [0019]      FIG. 1  and  FIG. 2  illustrate a coated article  100 . The coated article  100  includes a substrate  20  and a hard coating film  10  attached to at least one surface of the substrate  20 . The hard coating film  10  is formed by coating the hard coating composition on the surface of the substrate  20 , and drying the hard coating composition. 
         [0020]    The hard coating film  10  comprises a polymer of dopamine. The polymer has a cross-linking structure. The hard coating film  10  further comprises a plurality of inorganic oxide particles dispersed in the cross-linking structure. The hard coating film  10  is resistant to yellowing in the sunlight. 
         [0021]    A material of the substrate  20  may be glass, resin, metal, oxide, semiconductor, ceramic, polymer, or wood. 
         [0022]    The coated article  100  may be a lens, a window glass, or a lamp shell. 
         [0023]      FIG. 3  illustrates a flowchart of a method for making the coated article  100  in accordance with an exemplary embodiment. The exemplary method is provided by way of example, as there are a variety of ways to carry out the method. Each block shown in  FIG. 3  represents one or more processes, methods or subroutines, carried out in the exemplary method. Furthermore, the illustrated order of blocks is by example only, and the order of the blocks can change. Additional blocks may be added, or fewer blocks may be utilized, without departing from this disclosure. The exemplary method may begin at block  301 . 
         [0024]    At block  301 , a substrate  20  is provided. The substrate  20  may be made of glass, resin, metal, oxide, semiconductor, ceramic, polymer, or wood. 
         [0025]    At block  302 , a hard coating composition is provided. The hard coating composition comprises a dopamine, a plurality of inorganic oxide particles, and a solvent. The dopamine has a mass percentage of about 1% to about 40% of a total mass of the hard coating composition. The plurality of the inorganic oxide particles has a mass percentage of about 40% to about 80% of the total mass of the hard coating composition. The solvent has a mass percentage of about 5% to about 50% of the total mass of the hard coating composition. 
         [0026]    At block  303 , at least one surface of the substrate  20  is coated with the hard coating composition, and then put in the air or an oxidizing condition to have the dopamine in the hard coating composition react, to form a hard coating film  10  on the substrate  20 . 
         [0027]    The hard coating film  10  and the substrate  20  are bonded together by a covalent bond, an intermolecular interaction force, a hydrogen bond, a π-π bond, or any combination thereof. Thereby an adhesion strength between the hard coating film  10  and the substrate  20  is strong. 
         [0028]    An oxidation rate of the dopamine in the alkaline or oxidizing condition is rapid, thereby the hard coating film  10  can be formed on the surface of the substrate  20  quickly. 
         [0029]    In at least one exemplary embodiment, the hard coating composition is coated on the at least one surface of the substrate  20  by spray coating process or spin coating process. In another exemplary embodiment, the hard coating composition is coated on the surface of the substrate  20  by immersing the substrate  20  into the hard coating composition, and then taking the substrate  20  out, thereby a portion of the hard coating composition is adsorbed on the surface of the substrate  20 . 
       Example 1 
       [0030]    The hard coating composition comprised dopamine, silica particles, zirconia particles, and methanol aqueous solution. 
         [0031]    The dopamine had a mass percentage of 13.05% of the total mass of the hard coating composition. The silica particles had a mass percentage of 29.88% of the total mass of the hard coating composition. The zirconia particles had a mass percentage of 36.53% of the total mass of the hard coating composition. The methanol aqueous solution had a mass percentage of 10% of the total mass of the hard coating composition. 
         [0032]    The substrate  20  was immersed into the hard coating composition for 2 hours, and then taken out, a hard coating film  10  was formed on the surface of the substrate  20 . 
         [0033]    The hard coating film  10  was subjected to a surface hardness test and an adhesion strength test under ASTM standard. The surface hardness test was carried out by a pencil hardness test method, the surface hardness test result showed that the surface hardness of the hard coating film  10  was 2H. The adhesion strength test result showed the ASTM standard was 5B. In other words, the hard coating film  10  was not liable to peeling. 
       Example 2 
       [0034]    The hard coating composition comprised dopamine, silica particles, zirconia particles, titanium particles, and sodium periodate aqueous solution. 
         [0035]    The dopamine had a mass percentage of 21.06% of the total mass of the hard coating composition. The silica particles had a mass percentage of 23.136% of the total mass of the hard coating composition. The zirconia particles had a mass percentage of 26.028% of the total mass of the hard coating composition. The titanium particles had a mass percentage of 8.676% of the total mass of the hard coating composition. The sodium periodate aqueous solution had a mass percentage of 21.1% of the total mass of the hard coating composition. 
         [0036]    The substrate  20  was immersed into the hard coating composition for 0.5 hour, and then taken out, a hard coating film  10  was formed on the surface of the substrate  20 . 
         [0037]    The hard coating film  10  was subjected to a surface hardness test and an adhesion strength test under ASTM standard. The surface hardness test was carried out by a pencil hardness test method, the surface hardness test result showed that the surface hardness of the hard coating film  10  was 2H. The adhesion strength test result showed the ASTM standard was 5B. In other words, the hard coating film  10  was not liable to peeling. 
         [0038]    Referring to the examples 1-2, the hard coating film  10  has a high surface hardness and a strong adhesion strength. A high surface hardness means a high scratch resistance. 
         [0039]    The embodiments shown and described above are only examples. Even though numerous characteristics and advantages of the present technology have been set forth in the foregoing description, together with details of the structures and function of the present disclosure, the disclosure is illustrative only, and changes can be made in the detail, including in matters of shape, size, and arrangement of the parts within the principles of the present disclosure, up to and including, the full extent established by the broad general meaning of the terms used in the claims.