Self-healing transparent coating composition using solar energy and applications thereof

Abstract

The present invention relates to a clear coat with a thermoreversible network capable of self-healing, as a coating composition capable of self-healing scratches on the surface, and a manufacturing method therefor, wherein the composition comprises a multifunctional crosslinker possessing a hindered urea structure and alkylene oxide repeating units and a photo-thermal dye compound that primarily absorbing in the NIR region to generate heat and is adapted to take advantage of reversible bonds generated by the high heat from solar light or UV-induced photo-thermal dyes, whereby when an NIR laser is used to locally generate heat at a scratched area, self-healing can be achieved.

Description

Self-healing transparent coating composition using sunlight and its application

[0001] The present invention relates to a transparent coating product capable of self-healing under sunlight using organic photothermal molecules.

[0002] Physical damage such as scratches that occur on the coating of transportation equipment, electronic products, etc. not only corrodes the metal substrate that the coating is protecting, causing functional damage to the substrate, but also significantly reduces the product's appearance quality.

[0003] One way to address this issue is to use coating compositions with high physical properties that completely eliminate physical damage. However, this method is costly, and developing a coating composition with properties that completely eliminate physical damage is nearly impossible. For this reason, industry and academia have been researching various self-healing coating systems that can recover from physical damage caused by external stimuli such as heat and pressure. Among these, resins containing thermoreversible hindered urea bonds possess a dynamic crosslinking system, making them highly valuable as self-healing technologies suitable for industries requiring high mechanical properties such as transportation, electronics, and architecture.

[0004] Prior art related to a method for producing a self-healing polyurethane includes Korean Patent Publication No. 2018-0078834, which is about a method for producing a self-healing polymer, characterized in that it includes a step of forming a polyurea prepolymer by reacting a diisocyanate with tertiary butyl diamine and a step of forming a polymer by reacting the polyurethane prepolymer and the polyurea prepolymer with a crosslinking agent, and Korean Patent Publication No. 2018-0026417, which is about a self-healing polyurethane obtained by curing a mixture containing a polyurethane prepolymer and an anhydrous sugar alcohol.

[0005] In general, the self-healing performance of reversible self-healing coating systems is determined by the fluidity of the polymer, making it very difficult to simultaneously achieve high mechanical properties and self-healing performance. In addition, most reversible self-healing coating systems reported to date are manufactured by preparing a multifunctional curing agent with reversible self-healing properties and chemically reacting it with a resin containing a reactive functional group. However, this method has a drawback in that as the composition of the self-healing curing agent increases, the degree of curing of the polymer system also rapidly increases, which causes a decrease in the self-healing performance.

[0006] Recently, research on self-healing phenomena by light has been conducted using inorganic photothermal molecules with excellent photothermal effects, such as carbon nanotubes, graphene, and metal nanoparticles. However, they absorb light in the visible light range and exhibit dark colors, making them unsuitable for use as coating materials.

[0007] Therefore, for a self-healing coating system with high transmittance, it is necessary to introduce organic photothermal molecules with low absorption in the visible light range and high photothermal efficiency.

[0008] The purpose of the present invention is to provide a transparent coating composition and clear coat that can self-heal scratches that occur on a surface and have high mechanical properties while being transparent.

[0009] The present invention relates to a polyacrylic resin comprising a hydroxyl group at the terminal of a side chain;

[0010] A polyfunctional alcohol containing two or more hindered urea structures in the molecule and containing hydroxyl groups at both ends of the molecule; a crosslinking agent containing a hydroxyl group or an isocyanate group; and

[0011] A locally self-healing transparent coating composition capable of forming a polymer network including a photothermal dye compound is provided.

[0012] According to one example of the present invention, the hydroxyl group of the polyfunctional alcohol may comprise 10 to 40 mol% of the total hydroxyl groups of the coating composition.

[0013] According to one example of the present invention, the isocyanate group of the crosslinking agent may be included in a molar ratio of 0.8 to 1.2 with respect to the total hydroxyl groups of the coating composition.

[0014] According to one example of the present invention, the hindered urea structure may include a structure represented by the following chemical formula 1 or 2.

[0015] <Chemical Formula 1>

[0016]

[0017] In the above chemical formula 1, A1 is a C4 to C7 branched chain alkyl group.

[0018] <Chemical Formula 2>

[0019]

[0020] In the above chemical formula 2, a is 1 to 4, n is 1 to 3, and R1 is a straight-chain alkyl group of C1 to C3.

[0021] According to one example of the present invention, the polyacrylic resin can be represented by the following chemical formula 3.

[0022] <Chemical Formula 3>

[0023]

[0024] In the above chemical formula 3

[0025] Ar is aryl, R2 and R3 are each independently a straight or branched chain alkyl having 1 to 4 carbon atoms, L1 to L3 are each independently a straight or branched chain alkylene having 1 to 4 carbon atoms, R' and R" are each independently a straight or branched chain alkyl having 1 to 4 carbon atoms. In the above chemical formula 3, m is 0 to 1,000, n is 1 to 1,000, o is an integer from 0 to 100, p to s are integers from 0 to 100, and o and r are not both 0.

[0026] According to one example of the present invention, the polyacrylic resin can be represented by the following chemical formula 4.

[0027]

[0028] <Chemical Formula 4>

[0029]

[0030] In the above chemical formula 4

[0031] m is an integer from 0 to 1,000, n is an integer from 1 to 1,000, o is an integer from 0 to 100, p is an integer from 0 to 100, q to s are integers from 0 to 100, and o and r are not both 0.

[0032] According to one example of the present invention, the polyfunctional alcohol may be synthesized by reacting a precursor including the hindered urea structure formed by reacting a hindered diamine with a polyfunctional isocyanate with a chain or branched diol.

[0033] According to one example of the present invention, the hindered diamine may be N,N'-di-tertbutylethylenediamine or bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate.

[0034] According to one example of the present invention, the polyfunctional isocyanate may include isophorone diisocyanate (IPDI).

[0035] According to one example of the present invention, the chain or branched diol may include ethylene glycol, tetraethylene glycol, and pentaethylene glycol.

[0036] According to one example of the present invention, the precursor comprising the hindered urea structure may comprise a structure represented by Chemical Formulas 5A to 5B.

[0037] <Chemical Formula 5A>

[0038]

[0039] <Chemical Formula 5B>

[0040]

[0041]

[0042]

[0043] In the above chemical formulas 5A to 5B,

[0044] m and n are 1 to 5, o and p are 1 to 3, and b and c are 1 to 5. L5 is C1 to C10 alkylene, L4 and L6 are any one selected from the group consisting of C1 to C10 alkylene and cycloalkylene, and the cycloalkylene of L4 and L6 may be further substituted with C1 to C10 alkyl. R2 and R3 are alkyl groups, and R4 and R5 are C4 to C7 branched-chain alkyl.

[0045]

[0046] According to one example of the present invention, the precursor comprising the hindered urea structure may comprise a structure represented by the following chemical formulae 6A to 6D.

[0047] <Chemical Formula 6A>

[0048]

[0049] <Chemical Formula 6B>

[0050]

[0051] <Chemical Formula 6C>

[0052]

[0053] <Chemical Formula 6D>

[0054]

[0055] According to one example of the present invention, the polyfunctional alcohol may include a structure represented by the following chemical formulas 7A to 7B.

[0056] <Chemical Formula 7A>

[0057]

[0058] <Chemical Formula 7B>

[0059]

[0060] In the above chemical formulas 7A and 7B

[0061] b, c, m and n are 1 to 5, o is 1 to 4, and p and q are 1 to 3. L5 is C1 to C10 alkylene, L4 and L6 are any one selected from the group consisting of C1 to C10 alkylene and cycloalkylene, and the cycloalkylene of L4 and L6 may be further substituted with C1 to C10 alkyl. R2 and R3 are alkyl groups, and R4 and R5 are C4 to C7 branched-chain alkyl.

[0062] According to one example of the present invention, the polyfunctional alcohol may include the following chemical formulas 8A to 8D.

[0063] <Chemical Formula 8A>

[0064]

[0065] <Chemical Formula 8B>

[0066]

[0067] <Chemical Formula 8C>

[0068]

[0069] <Chemical Formula 8D>

[0070]

[0071] In one example of the present invention, the photothermal dye may include a chemical structure represented by Chemical Formula 9.

[0072] <Chemical Formula 9>

[0073]

[0074] In the above chemical formula 9

[0075] R may be the same or different, and may be one composed of a hydrogen atom, an alkyl group, an aryl group, an alkoxy group, a hydroxy group, a phenyl group, or a halogenated alkyl group, X is an anion, and n is 1 or 2.

[0076] In one example of the present invention, the anion may include bis(oxalate)borate.

[0077] In one example of the present invention, the crosslinking agent containing a hydroxy group or an isocyanate group may include a chemical structure represented by the following chemical formula 10.

[0078] <Chemical Formula 10>

[0079]

[0080] In chemical formula 10, R6 is each independently a C1 to C6 alkyl group, and X1 is an isocyanate group or a hydroxy group.

[0081] In one example of the present invention, the polyfunctional alcohol may be included in an amount of 5 to 50 parts by weight based on 100 parts by weight of the polyacrylic resin.

[0082] In one example of the present invention, the hydroxyl group or isocyanate group-containing crosslinking agent may be included in an amount of 25 to 55 parts by weight per 100 parts by weight of the polyacrylic resin.

[0083] In one example of the present invention, the photothermal dye may comprise 0.01 to 0.50 wt%.

[0084] The present invention provides a clear coat having a local self-healing function formed by a crosslinking reaction of the local self-healing transparent coating composition.

[0085] According to one example of the present invention, the thermal decomposition temperature (T) of the local clear coat d ) may include 235 to 260 ℃.

[0086] According to one example of the present invention, the glass transition temperature (T) of the clear coat g ) can be between 20 and 60°C.

[0087] According to one example of the present invention, the near-infrared and visible light transmittance of the clear coat may be 90% or more.

[0088] According to one example of the present invention, the indentation modulus of the clear coat may include 2 to 8 GPa.

[0089] According to one example of the present invention, the indentation hardness of the clear coat may include 110 to 130 MPa.

[0090] A clear coat containing a multifunctional crosslinking agent having a structure including a hindered urea adduct and an alkylene oxide repeating unit according to the present invention can self-heal micro-scratches in a short time by utilizing reversible bonding occurring at high temperatures, and has excellent solvent resistance and mechanical properties of the coating.

[0091] In addition, since the photothermal dye absorbs the NIR (near infrared) range and generates heat, it has the economic advantage of providing long-term stability to the clear coat by focusing sunlight with an NIR laser or magnifying glass to irradiate only the scratched area, enabling self-healing.

[0092] Figure 1 is a precursor of a polyfunctional alcohol including a hindered urea structure of Manufacturing Example 1 of the present invention. 1 This is the result of H-NMR analysis.

[0093] Figure 2 is a result of FT-IR analysis of a precursor of a polyfunctional hindered urea alcohol containing a hindered urea structure of Manufacturing Example 1 of the present invention.

[0094]

[0095] *Figure 3 is a diagram of a multifunctional alcohol according to manufacturing example 2 of the present invention. 1 This is the result of H-NMR analysis.

[0096] Figure 4 shows the results of FT-IR analysis on a multifunctional alcohol according to Manufacturing Example 2 of the present invention.

[0097] Figure 5 shows the results of quantitative analysis of the mechanical properties of clear coating materials manufactured according to Comparative Examples 1 and 5 of the present invention using a TGA device.

[0098] Figure 6 shows the results of quantitative analysis of the mechanical properties of clear coating materials manufactured according to Comparative Examples 1 and 5 of the present invention using a DSC device.

[0099] Figure 7 shows the results of analyzing the penetration depth and indentation hardness during indentation using a nanoindentation device to determine the mechanical properties of a clear coating material manufactured according to Comparative Example 1 of the present invention.

[0100] Figure 8 shows the results of analyzing the mechanical properties of the clear coating material manufactured according to Comparative Examples 1 and 5 of the present invention, including the indentation hardness and indentation elastic modulus, using a nanoindentation device.

[0101] Figure 9 shows the results of quantitative analysis of the transparency of clear coating materials of Comparative Examples 2 to 5 manufactured according to one embodiment of the present invention using a spectrophotometer.

[0102] Figure 10 shows the results of quantitative analysis of the transparency of the clear coating materials of Comparative Example 1 and Examples 1 to 3 manufactured according to one embodiment of the present invention using a spectrophotometer.

[0103] Figure 11 is a clear coat manufactured according to one embodiment of the present invention, wherein the clear coats of Comparative Examples 2 to 5 are coated on a slide glass using a bar coater.

[0104] Figure 12 is a clear coat manufactured according to one embodiment of the present invention, Comparative Example 1 and Examples 1 to 3, using a bar coater to coat a slide glass.

[0105] Figure 13 is a diagram comprehensively showing the self-healing efficiency of the coating materials of Examples 1 to 3 and Comparative Examples 1 to 5 manufactured according to the present invention.

[0106] Figure 14 shows the self-healing effect after scratching with a force of 50 mN on a clear coat that does not contain the photothermal dye of Comparative Example 1.

[0107] Figure 15 shows the self-healing effect after scratching a clear coat containing the photothermal dye of Example 2 with a force of 50 mN.

[0108] Figure 16 shows the self-healing effect after scratching with a force of 50 mN on a clear coat that does not contain the multifunctional alcohol and photothermal dye of Comparative Example 5.

[0109] Figure 17 shows the repetitive self-healing effect of Example 2.

[0110] Figure 18 shows the repetitive self-healing effect of Comparative Example 3.

[0111] Figure 19 shows the self-healing effect of a model car to which the coating of Example 2 of the present invention is applied by sunlight.

[0112] Hereinafter, the present invention will be described in detail. Terms and words used in this specification and claims should not be construed as limited to their conventional or dictionary meanings. Based on the principle that the inventor can appropriately define the concept of a term to best explain his or her invention, they should be interpreted in a way that aligns with the technical spirit of the present invention.

[0113] The term “self-healing” used throughout this specification broadly means the ability of a damaged material to automatically and autonomously heal (recover) to its original state without any external intervention, and narrowly means the ability to recover to some extent to its original state after damage caused by an external force.

[0114] The present invention relates to a polyacrylic resin comprising a hydroxyl group at the terminal of a side chain;

[0115] The present invention relates to a local self-healing transparent coating composition comprising: a polyfunctional alcohol having two or more hindered urea structures in the molecule and including hydroxyl groups at both terminals of the molecule; a crosslinking agent containing a hydroxyl group or an isocyanate group; and a photothermal dye compound.

[0116] According to one example of the present invention, the content of the hydroxyl group of the polyfunctional alcohol is preferably 5 to 50 mol%, specifically 10 to 40 mol%, of the total content of hydroxyl groups of the coating composition including the hydroxyl group of the polyacrylate, the hydroxyl group of the polyfunctional alcohol, and the hydroxyl group of the crosslinking agent.

[0117] According to another example of the present invention, it is preferable that the content of the isocyanate group of the crosslinking agent be included in a molar ratio of 0.8 to 1.2 with respect to the content of the entire hydroxyl group of the coating composition including the hydroxyl group of the polyacrylate, the hydroxyl group of the polyfunctional alcohol, and the hydroxyl group of the crosslinking agent.

[0118] By including the hydroxyl group of the above-mentioned polyfunctional alcohol and the isocyanate group of the crosslinking agent in the above-mentioned content with respect to the total hydroxyl groups, the self-healing properties and hardness properties of the clear coat manufactured with the present coating composition can be controlled.

[0119] The hindered urea structure included in the polyfunctional alcohol of the present invention may include a structure represented by the following chemical formula 1 or chemical formula 2.

[0120] <Chemical Formula 1>

[0121]

[0122] In the above chemical formula 1, A1 is a branched chain alkyl group of C1 to C10, specifically C4 to C7.

[0123] <Chemical Formula 2>

[0124]

[0125] In the above chemical formula 2, a may be 1 to 7, specifically 1 to 4, n may be 1 to 5, specifically 1 to 3, and R1 is a straight-chain alkyl group of C1 to C7, specifically C1 to C3.

[0126] Since the multifunctional alcohol of the present invention includes the hindered urea functional group, a urea bond is reversibly formed by the heat generated by the photothermal dye compound, thereby generating a self-healing effect of the coating.

[0127] According to an example of the present invention, the polyfunctional alcohol can be prepared by reacting a precursor including a hindered urea structure, which is prepared by reacting an amine group of a hindered diamine with an isocyanate group of a polyfunctional isocyanate in an equivalent amount of 1:5 to 1:3, specifically in an equivalent amount of 1:4 to 1:3, preferably in an equivalent amount of 1:2, and then reacting the precursor with a chain or branched diol.

[0128] The chain or branched diol may be an aliphatic diol, specifically a diol, triol or tetraol having a total number of carbon atoms of 3 to 15, and more specifically, may contain at least two ether groups in its molecular structure, such as ethylene glycol, triethylene glycol, ethylene glycol, or triethylene glycol. The chain or branched diol includes a chain structure repeating unit in a crosslinked structure, thereby increasing flexibility of the clear coat, and includes an ether group, thereby improving solubility in a solvent, which provides an advantage in the process when manufacturing a clear coat using a coating composition.

[0129] The hindered diamine may be any one of N,N'-di-tertbutylethylenediamine or bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate, and the polyfunctional isocyanate may be any one of an aliphatic, aromatic, alicyclic, or araliphatic compound containing two or more isocyanate groups in its molecular structure.

[0130] The above aliphatic polyfunctional isocyanate compounds include ethylene diisocyanate, trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate (HMDI), octamethylene diisocyanate, nonamethylene diisocyanate, dodecamethylene diisocyanate, 2,2-dimethylpentane diisocyanate, 2,2,4-trimethyl hexamethylene diisocyanate, decamethylene diisocyanate, butene diisocyanate, 1,3-butadiene-1,4-diisocyanate, 2,4,4-trimethyl hexamethylene diisocyanate, 1,6,11-undecane triisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, lysine diisocyanate, 2,6-diisocyanatemethylcaproate, Bis(2-isocyanateethyl)fumarate, bis(2-isocyanateethyl)carbonate, 2-isocyanateethyl-2,6-diisocyanatehexanoate, 1,3,6-hexamethylenetriisocyanate, 1,8-diisocyanato-4-isocyanatomethyl octane, 2,5,7-trimethyl-1,8-diisocyanato-5-isocyanatomethyl octane, bis(isocyanatoethyl)carbonate, bis(isocyanatoethyl)ether, 1,4-butyleneglycoldipropyl ether-ω,ω'-diisocyanate, lysine diisocyanato methyl ester, lysine triisocyanate, 2-isocyanatoethyl-2,6-diisocyanatoethyl-2,6-diisocyanato At least one aliphatic selected from the group consisting of hexanoate, 2-isocyanatopropyl-2,6-diisocyanatohexanoate, xylylene diisocyanate, bis(isocyanatoethyl)benzene, bis(isocyanatopropyl)benzene, α,α,α',α'-tetramethyl xylylene diisocyanate, bis(isocyanatobutyl)benzene, bis(isocyanatomethyl)naphthalene, bis(isocyanatomethyl)diphenyl ether, bis(isocyanatoethyl)phthalate, 2,6-di(isocyanatomethyl)furan, 1,3,-bis(6-isocyanatohexyl)-urethidine-2,4-dione, 1,3,5-tris(6-isocyanatohexyl)isocyanurate It could be an isocyanate.

[0131] The above alicyclic polyfunctional isocyanate compounds include isophorone diisocyanate (IPDI), 4,4'-dicyclohexylmethane diisocyanate, cyclohexylene diisocyanate, methylcyclohexylene diisocyanate, bis(2-isocyanateethyl)-4-cyclohexene-1,2-dicarboxylate, 2,5-norbornane diisocyanate, 2,6-norbornane diisocyanate, 2,2-dimethyl dicyclohexylmethane diisocyanate, bis(4-isocyanato-n-butylidene) pentaerythritol, dimer acid diisocyanate, 2-isocyanatomethyl-3-(3-isocyanatopropyl)-5-isocyanatomethyl-bicyclo[2,2,1]-heptane, 2-Isocyanatomethyl-3-(3-isocyanatopropyl)-6-isocyanatomethyl-bicyclo[2,2,1]-heptane, 2-Isocyanatomethyl-2-(3-isocyanatopropyl)-5-isocyanatomethyl-bicyclo[2,2,1]-heptane, 2-Isocyanatomethyl-2-(3-isocyanatopropyl)-6-isocyanatomethyl-bicyclo[2,2,1]-heptane, 2-Isocyanatomethyl-3-(3-isocyanatopropyl)-6-(2-isocyanatoethyl)-bicyclo[2,2,1]-heptane, 2-Isocyanatomethyl-3-(3-isocyanatopropyl)-6-(2-isocyanatoethyl)-bicyclo[2,1,1]-heptane, It may be at least one alicyclic isocyanate selected from the group consisting of 2-isocyanatomethyl-2-(3-isocyanatopropyl)-5-(2-isocyanatoethyl)-bicyclo[2,1,1]-heptane, 2-isocyanatomethyl-2-(3-isocyanatopropyl)-6-(2-isocyanatoethyl)-bicyclo[2,2,1]-heptane, norbornane bis(isocyanatomethyl).

[0132] The above-mentioned aromatic aliphatic polyfunctional isocyanate compounds include 1,3-bis(isocyanatomethyl)benzene (m-xylene diisocyanate, m-XDI), 1,4-bis(isocyanatomethyl)benzene (p-xylene diisocyanate, p-XDI), 1,3-bis(2-isocyanatopropan-2-yl)benzene (m-tetramethyl xylene diisocyanate, m-TMXDI), 1,4-bis(2-isocyanatopropan-2-yl)benzene (p-tetramethyl xylene diisocyanate, p-TMXDI), 1,3-bis(isocyanatomethyl)-4-methylbenzene, 1,3-bis(isocyanatomethyl)-4-ethylbenzene, 1,3-bis(isocyanatomethyl)-5-methylbenzene, 1,3-Bis(isocyanatomethyl)-4,5-dimethylbenzene, 1,4-bis(isocyanatomethyl)-2,5-dimethylbenzene, 1,4-bis(isocyanatomethyl)-2,3,5,6-tetramethylbenzene, 1,3-bis(isocyanatomethyl)-5-tert-butylbenzene, 1,3-bis(isocyanatomethyl)-4-chlorobenzene, 1,3-bis(isocyanatomethyl)-4,5-dichlorobenzene, 1,3-bis(isocyanatomethyl)-2,4,5,6-tetrachlorobenzene, 1,4-bis(isocyanatomethyl)-2,3,5,6-tetrachlorobenzene, 1,4-bis(isocyanatomethyl)-2,3,5,6-tetrabromobenzene, It may be at least one aromatic aliphatic isocyanate selected from the group consisting of 1,4-bis(2-isocyanatoethyl)benzene, 1,4-bis(isocyanatomethyl)naphthalene.

[0133] The above polyfunctional isocyanate is preferably one of hexamethylene diisocyanate (HMDI) and isophorone diisocyanate (IPDI).

[0134] The precursor comprising the hindered urea structure according to one embodiment of the present invention can be specifically represented by the following chemical formula 5A or chemical formula 5B, and more specifically, can be chemical formulas 6A to 6D.

[0135] <Chemical Formula 5A>

[0136]

[0137] <Chemical Formula 5B>

[0138]

[0139] In the above chemical formulas 5A to 5B,

[0140] m and n are 1 to 7, specifically 1 to 5, o and p are 1 to 5, specifically 1 to 3, b and c are 1 to 7, specifically 1 to 5. L5 is a C1 to C15, specifically C1 to C10, alkylene, L4 and L6 are any one selected from the group consisting of a C1 to C15, specifically C1 to C10, alkylene and cycloalkylene, and the cycloalkylene of L4 and L6 may be further substituted with a C1 to C15, specifically C1 to C10, alkyl. R2 and R3 are a C1 to C5, specifically C1 to C3, alkyl group, and R4 and R5 are a C4 to C10, specifically C4 to C7, branched-chain alkyl.

[0141] <Chemical Formula 6A>

[0142]

[0143] <Chemical Formula 6B>

[0144]

[0145] <Chemical Formula 6C>

[0146]

[0147] <Chemical Formula 6D>

[0148]

[0149]

[0150] According to an example of the present invention, the polyfunctional alcohol formed by the reaction of a precursor including the hindered urea structure with a chain or branched diol may include a structure represented by the following chemical formula 7A or 7B, and more specifically, may include structures 8A to 8D.

[0151] <Chemical Formula 7A>

[0152]

[0153] <Chemical Formula 7B>

[0154]

[0155] In the above chemical formulas 7A and 7B

[0156] m and n are 1 to 7, specifically 1 to 5; b and c are 1 to 7, specifically 1 to 5; o is 1 to 6, specifically 1 to 4; and p and q are 1 to 5, specifically 1 to 3. L5 is C1 to C15, specifically C1 to C10 alkylene; L4 and L6 are any one selected from the group consisting of C1 to C15, specifically C1 to C10 alkylene and cycloalkylene, wherein the cycloalkylene of L4 and L6 may be further substituted with C1 to C15, specifically C1 to C10 alkyl. R4 and R5 are C4 to C10, specifically C4 to C7 branched chain alkyl.

[0157]

[0158] <Chemical Formula 8A>

[0159]

[0160] <Chemical Formula 8B>

[0161]

[0162]

[0163] <Chemical Formula 8C>

[0164]

[0165] <Chemical Formula 8D>

[0166]

[0167] The polyacrylic resin according to an example of the present invention may be a homopolymer or copolymer resin typically including polyacrylate resin, polymethacrylate resin, and various acrylate and methacrylate monomers, and preferably includes a hydroxyl group (-OH) at the terminal of the side chain. Specifically, the polyacrylate resin may be represented by the following chemical formula 3, and more specifically, may have a structure represented by the following chemical formula 4.

[0168] <Chemical Formula 3>

[0169]

[0170]

[0171] In the above chemical formula 3, m is 0 to 2,000, specifically 0 to 1000, n is 1 to 2000, specifically 1 to 1000, o to s are integers of 0 to 200, specifically 0 to 100, and o and r are not both 0. Ar is aryl, R2 to R3 are each independently C1 to C7, specifically C1 to C4 alkyl, L1 to L3 are each independently C1 to C4, specifically C2 to C3 alkylene, and R' and R" are each independently C1 to C7, specifically C1 to C4 alkyl.

[0172] <Chemical Formula 4>

[0173]

[0174] In the above chemical formula 4, m is 0 to 2,000, specifically 0 to 1000, n is 1 to 2000, specifically 1 to 1000, o to s are integers of 0 to 200, specifically 0 to 100, and o and r are not 0 at the same time.

[0175] According to an example of the present invention, the coating composition of the present invention may include a crosslinking agent containing a hydroxyl group or an isocyanate group. The crosslinking agent has the effect of imparting hardness to the coating composition of the present invention, and the type of the crosslinking agent may be, but is not limited to, an acrylic polymer containing a hydroxyl group or an isocyanate group and an aliphatic aromatic compound.

[0176] Examples of the crosslinking agent containing the above hydroxyl group or isocyanate group include polyethylene glycol, polypropylene glycol, polybutanediol, glycerin, monoethanolamine, diethanolamine, triethanolamine, trimethylol propane, pentaerythritol, oxypropylated ethylene diamine, xylylene diisocyanate (XDI), tolylene diisocyanate (TDI), tetramethylene diisocyanate, hexamethylene diisocyanate (HMDI), isophorone diisocyanate (IPDI), hydrogenated tolylene diisocyanate, diphenylmethane diisocyanate, hydrogenated diphenylmethane diisocyanate, and polyisocyanates obtained by adding these to trimethylol propane, etc. Examples thereof include compounds, isocyanurates, addition compounds, known polyether polyols, polyester polyols, acrylic polyols, and polybutadiene polyols.

[0177] According to one example of the present invention, a crosslinking agent containing a hydroxyl group or an isocyanate group may include the following chemical formula 10.

[0178] <Chemical Formula 10>

[0179]

[0180] In chemical formula 10, R6 is each independently an alkyl group of C1 to C10, specifically C1 to C6, and X1 is an isocyanate group or a hydroxy group.

[0181] According to one embodiment of the present invention, the photothermal dye may include a diimmonium dye. The diimmonium dye has the effect of absorbing light in the NIR (Near Infrared) region to generate high-temperature heat, thereby forming cross-linking in the reversible self-healing system of the coating composition.

[0182] It is preferable that the photothermal dye above uses a compound having a maximum absorption wavelength of 850 to 1500 nm, as shown in the following chemical formula 9. The maximum absorption wavelength may be specifically 1000 to 1500 nm, and more specifically 1000 to 1400 nm.

[0183] <Chemical Formula 9>

[0184]

[0185]

[0186] R may be the same or different and may be one composed of a hydrogen atom, an alkyl group, an aryl group, an alkoxy group, a hydroxy group, a phenyl group or a halogenated alkyl group, X represents a monovalent or divalent organic or inorganic anion and n is 1 or 2.

[0187] The above R is an alkyl group, and is selected from the group consisting of methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, sec-butyl, t-butyl, n-pentyl, iso-pentyl, neo-pentyl, cyclopentyl, 1,2-dimethyl propyl, n-hexyl, cyclohexyl, 1,3-dimethyl butyl, 1-iso-propyl propyl, 1,2-dimethyl butyl, Examples of straight-chain, branched-chain or alicyclic alkyl groups having 1 to 20 carbon atoms include n-heptyl, 1,4-dimethyl pentyl, 2-methyl-1-iso-propyl propyl, 1-ethyl-3-methyl butyl, n-octyl, 2-ethyl hexyl, 3-methyl 1-iso-propyl butyl, 2-methyl-1-iso-propyl, 1-t-butyl-2-methyl propyl, n-nonyl, and 3,5,5-trimethyl hexyl. In addition, examples of the aryl group include a phenyl group, a naphthyl group, a tolyl group, a furyl group, a pyridyl group, etc., and examples of the halogenated alkyl group include at least one selected from a fluorinated alkyl group, a chloride alkyl group, and a brominated alkyl group.

[0188] In addition, examples of the alkoxy group include methoxy, ethoxy, propoxy, butoxy, etc., and examples of the alkoxy alkyl group include methoxy methyl, methoxy ethyl, ethoxy ethyl, propoxy ethyl, butoxy ethyl, 3-methoxy propyl, 3-ethoxy propyl, methoxyethoxy methyl, ethoxyethoxy ethyl, dimethoxy methyl, diethoxy methyl, dimethoxy ethyl, and diethoxy ethyl. More preferably, R may be n-butane and X may be bis(oxalate)borate.

[0189] The anion may be a known monovalent or divalent organic or inorganic acid anion, but is not limited thereto. Examples of the anion include organic carboxylic acid ions such as acetate ion, lactate ion, trifluoroacetate ion, propionate ion, benzoate ion, oxalate ion, succinate ion, and stearate ion; organic sulfonic acid ions such as methanesulfonate ion, toluene sulfonate ion, naphthalene monosulfonate ion, chlorobenzene sulfonate ion, nitrobenzene sulfonate ion, dodecylbenzene sulfonate ion, benzene sulfonate ion, ethane sulfonate ion, and trifluoromethane sulfonate ion; and organic borate ions such as tetraphenylborate ion and bisoxalateborate ion, fluoride ion, chloride ion, bromide ion, and iodide ion; It includes thiocyanate ion, hexafluoroantimonate ion, perchlorate ion, periodate ion, nitrate ion, tetrafluoroborate ion, hexafluorophosphate ion, molybdate ion, tungstate ion, titanate ion, vanadate ion, phosphate ion, and according to one example of the present invention, the anion is most preferably bisoxalateborate.

[0190] The present invention provides a clear coat having a local self-healing function manufactured using the above-described local self-healing transparent coating composition.

[0191] The high thermal and mechanical properties of the clear coat including the above-described local self-healing function are advantageous effects that occur because the above-described local self-healing transparent coating composition has a balanced chemical structure including a polyfunctional alcohol, which is a flexible unit including an alkylene oxide repeating structure, and a rigid crosslinker including an isocyanate group or a hydroxyl group.

[0192] According to an example of the present invention, the thermal decomposition temperature (T) of the clear coat d) can be 200 to 300 ℃. Specifically, it can be 220 to 280 ℃.

[0193] According to an example of the present invention, the indentation hardness of the clear coat may be 100 to 150 GPa, and specifically, 110 to 130 GPa.

[0194] According to an example of the present invention, the indentation modulus of the clear coat may be 1 to 10 MPa, and specifically, 2 to 8 MPa.

[0195] According to one example of the present invention, the glass transition temperature (T) of the clear coat g ) is 10 to 70 ℃, and specifically, may be 20 to 60 ℃. The local self-healing transparent coating composition has a glass transition temperature (T g ), a thermoreversible system can be operated by the heat generated by the photothermal dye, thereby exhibiting a self-healing effect.

[0196] According to one embodiment of the present invention, the near-infrared and visible light transmittance of the clear coat may be at least 80%. More specifically, the transmittance may be at least 90%. The local self-healing transparent coating composition may provide a high-quality clear coat with high transmittance and maintain a transparent color by including a diimmonium-based photothermal dye.

[0197] Hereinafter, preferred embodiments of the present invention will be described in detail, with reference to the accompanying drawings, so that those with general knowledge in the technical field to which the present invention pertains can easily implement the invention. In particular, the technical concept of the present invention, its core structure, and its operation are not limited by this. Furthermore, the present invention can be implemented in various different types of equipment and is not limited to the implementation examples and embodiments described herein.

[0198]

[0199] [Manufacturing Example 1]

[0200] In a 250 mL round-bottomed flask, 7.74 g (34.82 mol) of isophorone diisocyanate was added, 20 mL of methylethylketone was added, and the mixture was heated to 35°C under nitrogen gas. Then, 3 g (17.41 mmol) of ditertiary butylethylenediamine dissolved in 10 mL of methylethylketone was slowly added dropwise to the flask and stirred for 2 hours to synthesize a precursor of a polyfunctional alcohol containing a hindered urea structure.

[0201]

[0202] [Manufacturing Example 2]

[0203] In a 250 mL round bottom flask, add 6.76 g (34.28 mmol) of tetraethylene glycol and 0.11 g (0.17 mmol) of dibutyltin dilaurate, add 10 mL of methylethylketone, and heat to 70°C under nitrogen gas. Then, slowly add the mixture dropwise to the flask of Manufacturing Example 1 and stir for 2 hours to form a chemical bond with tetraethylene glycol having a structure including an ethylene oxide repeating unit, thereby producing a polyfunctional alcohol having a hydroxyl group at the terminal.

[0204] [Manufacturing Example 3]

[0205] A stock solution was prepared by dissolving 0.1 g of the photothermal dye compound in 1 mL of methylethylketone.

[0206]

[0207] [Example 1]

[0208] A coating composition was prepared comprising 1.43 g of a commercial polyacrylic resin; 0.27 g of the polyfunctional alcohol prepared in Preparation Example 2; a commercial curing agent; and 3.9 μl of a photothermal dye (0.05 wt%, Demodur N330, Norubi Co., Ltd.).

[0209]

[0210] [Example 2]

[0211] A coating composition was prepared in the same manner as in Example 1, except that it contained 7.8 μl (0.10 wt%) of a photothermal dye.

[0212]

[0213] [Example 3]

[0214] A coating composition was prepared in the same manner as in Example 1, except that it contained 39.3 μl (0.50 wt%) of a photothermal dye.

[0215]

[0216] [Comparative Example 1]

[0217] A coating composition was prepared in the same manner as in Example 1, except that the photothermal dye was not included.

[0218]

[0219] [Comparative Example 2]

[0220] A coating composition was prepared comprising 1.43 g of commercial polyacrylic resin; 0.33 g of commercial curing agent; and 3.4 μl (0.05 wt%) of photothermal dye.

[0221]

[0222] [Comparative Example 3]

[0223] A coating composition was prepared in the same manner as in Comparative Example 2, except that it contained 6.8 μl (0.10 wt%) of a photothermal dye.

[0224]

[0225] [Comparative Example 4]

[0226] A coating composition was prepared in the same manner as in Comparative Example 2, except that it contained 33.8 μL (0.50 wt%) of a photothermal dye.

[0227]

[0228] [Comparative Example 5]

[0229] A coating composition containing 1.43 g of commercial polyacrylic resin and 0.33 g of commercial curing agent was prepared.

[0230]

[0231] [Experimental Example 1] Photothermal Experiment of a Thermoreversible Clear Coat

[0232] After coating the coating compositions of Examples 1 to 3 and Comparative Examples 1 to 5 on a slide glass, a photothermal experiment was conducted.

[0233] The photothermal experiment was conducted using a near-infrared laser (NIR) with an output of 1 W and a wavelength of 1064 nm, and a near-infrared beam was irradiated under conditions of a diameter of 1.5 mm and a height of 15 cm, and the temperature of the coating on the slide glass was measured using a thermal imaging camera. The results of the experiment are shown in Tables 1 and 2 below.

[0234]

[0235]

[0236] Example Photothermal Temperature (℃) Time Example 1 (0.05 wt%) Example 2 (0.10 wt%) Example 3 (0.50 wt%) (s) 0 26.6 26.9 28.4 10 40.45 4.3 126 20 44.36 0.7 139 30 46.26 5.21 42 40 48.26 7.9 140 50 49.17 0.21 37 60 49.67 1.1 135 90 51.37 3.8 135 120 52.27 5.4 133 1 5052.775.813018053.176.212724054.178.512530054.678.112536054.779.011942054.479.412048054.679.511854055.479.711860055.479.6120Temperature change (℃)28.852.8113.6

[0237] Example Photothermal Temperature (℃) Time Comparative Example 1 (0.0 wt%) Comparative Example 2 (0.05 wt%) Comparative Example 3 (0.10 wt%) Comparative Example 4 (0.50 wt%) Comparative Example 5 (0.0 wt%)(s)026.526.626.928.425.91028.840.454.312628.12030.344.360.713929.73031.346.265.214231.04031.548 .267.914031.65031.849.170.213732.26032.349.671.113532.39032.751.373.813533.112033.752.275.413333.51 5033.752.775.813034.518033.953.176.212734.524034.254.178.512534.930034.354.678.112535.436033.954.779.011935.642034.354.479.412035.748034.554.679.511835.754034.755.479.711835.260035.055.479.612035.7Temperature change (℃)9.827.444.2114.69.8

[0238] *In the above table, Examples 1 to 3 had the highest temperatures of 55.4, 79.7, and 142°C, respectively, and increased by 28.8, 52.8, and 113.6°C relative to the initial temperature.

[0239] Comparative Example 1 had a maximum temperature of 35°C, which was 9.8°C higher than the initial starting temperature. Similarly, Comparative Examples 2 to 5 had maximum temperatures of 54.1, 71.1, 141, and 35.7°C, respectively, which were 27.4, 44.2, 114.6, and 9.8°C higher than the initial temperature, respectively.

[0240] When the above Table 1 is summarized, it was confirmed that the surface temperature of the coating rapidly increases as the laser exposure time increases in the initial stage and then reaches a state of thermal equilibrium, and also that the difference between room temperature and the coating surface temperature gradually increases as the content of the photothermal compound increases.

[0241] Therefore, it was confirmed that the temperature-increasing effect of the coating when the photothermal dye was included was higher than when the photothermal dye was not included, and that the temperature increased linearly depending on the content of the photothermal dye.

[0242]

[0243] [Experimental Example 2] Mechanical Properties Test of Clear Coat

[0244] For the hardness tests of Example 2 and Comparative Example 3, the hardness and modulus of the coating were measured using an indentation hardness tester (nanoindentation-NI). The results of the experiment are shown in Table 3 below.

[0245] Indentation modulus (EIT, MPa)Indentation hardness (HIT, GPa)20mN30mN40mN50mN20mN30mN40mN50mNExample 21221221241244.55.25.96.5Comparative example 31141161201213.84.34.65.5

[0246] Modulus and hardness were measured as average values ​​from five experiments. It was confirmed that the hardness (HIT) and elastic modulus (EIT) tended to increase as the indentation strength increased when indenting the coatings of Example 2 and Comparative Example 3 under load conditions of 20, 30, 40, and 50 mN. In addition, it was confirmed that the coating of Example 2 had similar hardness and elastic modulus at the same indentation strength compared to the coating of Comparative Example 3 even when a polyfunctional alcohol containing a hindered urea structure was introduced.

[0247] [Experimental Example 3] Measurement of transparency of clear coat

[0248] After coating the above Examples 1 to 3 and Comparative Examples 1 to 5 on slide glass, transparency was measured. Transparency was measured using a spectrophotometer (spetrophotometer-JASCO V-770) and transmittance was analyzed under conditions from 300 nm to 2500 nm. The results are shown in Tables 4 and 5.

[0249] Example 1 (0.05 wt%) Example 2 (0.1 wt%) Example 3 (0.50 wt%) Transmittance (%) 97.8 95.1 80.9

[0250] Comparative Example 1 (0.0 wt%) Comparative Example 2 (0.05 wt%) Comparative Example 3 (0.1 wt%) Comparative Example 4 (0.50 wt%) Comparative Example 5 (0.0 wt%) Transmittance (%) 99.7 97.5 94.5 79.3 99.9

[0251] Transmittance represents the average of the results of five experiments. As shown in Tables 4-1 and 4-2, the results of transmittance measurements showed that the coatings of Example 3 and Comparative Example 4, in which the content of the photothermal dye compound was 0.5 wt%, exhibited a transparency of approximately 90% or more.

[0252] It was found that as the content of the photothermal dye compound increased, the transmittance gradually decreased in both the NIR region (800 to 1900 nm) and the visible light region (350 to 750 nm). In addition, it was found that when the content of the photothermal dye compound exceeded 0.1 wt%, the color of the coating changed to pale yellow due to a strong adsorption band in the visible light region.

[0253]

[0254] [Experimental Example 4] Self-healing test of a thermoreversible clear coat

[0255] For the self-healing tests of the above Example 2, Comparative Example 1, and Comparative Example 5, a micro scratch tester (MST) was used to create a scratch with a load of 40 mN, and then a 1064 nm NIR laser was irradiated on the scratched position for 1 minute to enable self-healing due to heat generation of the photothermal dye compound, and the recovery of the scratch was confirmed using an optical microscope equipped on the MST. The experimental results are shown in FIGS. 14 to 16, and Table 6 shows the self-healing efficiency according to the load by creating a scratch with a load of 20, 30, 40, or 50 mN on the coatings of Examples 1 to 3 and Comparative Examples 1 to 5, and then irradiating the scratched position with a 1064 nm NIR laser for 1 minute.

[0256] Referring to Fig. 14, in the case of Comparative Example 1, which did not include a photothermal dye, no self-healing effect was observed at all. This was confirmed to be because the glass transition temperature of Comparative Example 1 was 38°C, and the maximum temperature of the system was observed at 32.3°C, which is lower than that, so the polymer could not have sufficient fluidity.

[0257] Referring to FIGS. 15 and 16, in the case of Example 2, when a load of 40 mN was applied and then NIR laser was irradiated, a self-healing effect of 100% was observed, whereas in the case of Comparative Example 5, since it did not contain a polyfunctional alcohol and a photothermal dye, it was confirmed that the self-healing effect was significantly lower than that of Example 1. This was confirmed to be due to the increase in fluidity of the polymer chain above the glass transition temperature and the increase in the self-healing effect due to the reversible bonding of the hindered urea group.

[0258] Example Fn (mN) Scratch width (㎛) % WSHE initial final Example 1 20 22. 20 100 30 25. 40 100 40 29. 60 100 50 32. 56. 48 0. 2 Example 2 20 20. 40 100 30 24. 10 100 40 29. 20 100 50 33. 10 100 Example 3 20 20. 80 100 30 24. 50 100 40 28. 70 100 50 32. 40 100 Comparative Example 1 20 19. 40 30 24. 124. 10 40 31. 43 1. 40 50 34. 0 34. 00 Comparative Example 22020.820.803025.425.404030.330.305034.034.00Comparative Example 32022.216.326.63025.416.136.64029.619.125.55031.921.333.2Comparative Example 42018.501003024.101004027.88.967.85033.813.360.6Comparative Example 52021.701003027.301004030.101005033.58.375.3

[0259] *[Experimental Example 5] Self-healing repetition experiment of a thermoreversible clear coat

[0260] In order to determine the repetitive self-healing effects of Examples 1 to 3 and Comparative Examples 1 to 5, Example 2 and Comparative Example 3, which had the best transparency and physical properties, were subjected to a micro scratch tester (MST) in the same manner as the self-healing test. The heat generated by the photothermal dye compound was measured using a thermal imaging camera. The experimental results are shown in Tables 7 and 8.

[0261] Example 2 Results of photothermal repetition test of coating Time (s) Number of repetitions 1234 Temperature (℃) 0 23.0 22.9 22.2 25.2 10 52.6 53.3 51.0 50.8 20 56.3 56.8 57.5 57.4 30 60.9 59.5 60.8 58.4 40 62.2 61.6 63.8 62.1 50 64.0 62.5 64.8 64.2 60 66.8 65.4 66.9 65.9

[0262] Comparative Example 3 Results of photothermal repetition test of coating Comparative Example 3 Time (s) Number of repetitions 1234 Temperature (℃) 0 23.0 25.3 25.5 23.7 10 58.9 58.3 55.9 54.6 20 64.0 64.16 3.0 61.5 30 67.5 67.7 67.6 5.24 070.4 70.2 70.4 8.15 072.2 71.0 72.7 71.0 6073.6 72.2 73.7 77 2.6

[0263] As a result of the self-healing repetition test above, in the first repetition, as the applied load increased in the same manner as in the self-healing test above, both the scratch depth and the degree of rupture of the coating increased, and when the scratch area was irradiated with a 1 W NIR laser for 1 minute, it was confirmed that the self-healing efficiency of Example 2 was higher than that of Comparative Example 3. In addition, referring to FIGS. 17 and 18, it was confirmed that even in the experiment where a high load (40 mN) was applied, the coating of Example 2 showed a higher self-healing efficiency than the coating of Comparative Example 3.

Claims

1. Polyacrylic resin containing a hydroxyl group at the end of the side chain; A polyfunctional alcohol containing two or more hindered urea structures in the molecule and containing hydroxy groups at both terminals of the molecule; A crosslinking agent containing a hydroxyl group or an isocyanate group; and A locally self-healing transparent coating composition capable of forming a polymer network comprising a photothermal dye compound.

2. In paragraph 1, A local self-healing transparent coating composition, wherein the hydroxyl group of the above polyfunctional alcohol comprises 10 to 40 mol% of the total hydroxyl groups of the coating composition.

3. In paragraph 1, A local self-healing transparent coating composition in which the isocyanate group of the crosslinking agent is included in a molar ratio of 0.8 to 1.2 with respect to the total hydroxyl group of the coating composition.

4. In paragraph 1, The above hindered urea structure is a local self-healing transparent coating composition comprising a structure of the following chemical formula 1 or 2. <Chemical Formula 1> In the above chemical formula 1, A1 is a C4 to C7 branched chain alkyl group. <Chemical Formula 2> In the above chemical formula 2, a is 1 to 4, n is 1 to 3, and R1 is a straight-chain alkyl group of C1 to C3.

5. In paragraph 1, The above polyacrylic resin is a local self-healing transparent coating composition comprising a chemical structure represented by the following chemical formula 3. <Chemical Formula 3> In the above chemical formula 3 Ar is aryl, R2 and R3 are each independently a straight or branched chain alkyl having 1 to 4 carbon atoms, L1 to L3 are each independently a straight or branched chain alkylene having 1 to 4 carbon atoms, R' and R" are each independently a straight or branched chain alkyl having 1 to 4 carbon atoms. In the above chemical formula 3, m is 0 to 1,000, n is 1 to 1,000, o is an integer from 0 to 100, p to s are integers from 0 to 100, and o and r are not simultaneously 0.

6. In paragraph 1, The above polyacrylic resin is a local self-healing transparent coating composition having a chemical structure represented by the following chemical formula 4. <Chemical Formula 4> In the above chemical formula 4 m is an integer from 0 to 1,000, n is an integer from 1 to 1,000, o is an integer from 0 to 100, p is an integer from 0 to 100, q to s are integers from 0 to 100, and o and r are not both 0.

7. In paragraph 1, The above polyfunctional alcohol is a locally self-healing transparent coating composition synthesized by reacting a precursor including the hindered urea structure formed by reacting a hindered diamine and a polyfunctional isocyanate with a chain or branched diol.

8. In paragraph 7, The above hindered diamine is a local self-healing transparent coating composition comprising N,N'-di-tertbutylethylenediamine or bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate.

9. In paragraph 7, The above multifunctional isocyanate is a local self-healing transparent coating composition comprising isophorone diisocyanate (IPDI).

10. In paragraph 7, The above chain or branched diol is a local self-healing transparent coating composition comprising ethylene glycol, tetraethylene glycol, and pentaethylene glycol.

11. In paragraph 7, A locally self-healing transparent coating composition comprising a precursor comprising the above hindered urea structure, wherein the precursor comprises a structure represented by chemical formulas 5A to 5B. <Chemical Formula 5A> <Chemical Formula 5B> In the above chemical formulas 5A to 5B, m and n are 1 to 5, o and p are 1 to 3, and b and c are 1 to 5. L5 is C1 to C10 alkylene, L4 and L6 are any one selected from the group consisting of C1 to C10 alkylene and cycloalkylene, and the cycloalkylene of L4 and L6 may be further substituted with C1 to C10 alkyl. R2 and R3 are alkyl groups, and R4 and R5 are C4 to C7 branched-chain alkyl.

12. In paragraph 7, A locally self-healing transparent coating composition comprising a precursor comprising the above-mentioned hindered urea structure, wherein the precursor comprises a structure represented by the following chemical formulae 6A to 6D. <Chemical Formula 6A> <Chemical Formula 6B> <Chemical Formula 6C> <Chemical Formula 6D> 13. In paragraph 1, A local self-healing transparent coating composition wherein the above polyfunctional alcohol comprises a structure represented by the following chemical formulas 7A to 7B. <Chemical Formula 7A> <Chemical Formula 7B> In the above chemical formulas 7A and 7B b, c, m and n are 1 to 5, o is 1 to 4, and p and q are 1 to 3. L5 is C1 to C10 alkylene, L4 and L6 are any one selected from the group consisting of C1 to C10 alkylene and cycloalkylene, and the cycloalkylene of L4 and L6 may be further substituted with C1 to C10 alkyl. R2 and R3 are alkyl groups, and R4 and R5 are C4 to C7 branched-chain alkyl.

14. In paragraph 1, The above multifunctional alcohol is a local self-healing transparent coating composition comprising the following chemical formulas 8A to 8D. <Chemical Formula 8A> <Chemical Formula 8B> <Chemical Formula 8C> <Chemical Formula 8D> 15. In paragraph 1, The above photothermal dye is a local self-healing transparent coating composition comprising a chemical structure represented by chemical formula 9. <Chemical Formula 9> In the above chemical formula 9 R may be the same or different, and may be one composed of a hydrogen atom, an alkyl group, an aryl group, an alkoxy group, a hydroxy group, a phenyl group, or a halogenated alkyl group, X is an anion, and n is 1 or 2.

16. In paragraph 15, The above anion is a local self-healing transparent coating composition containing bis(oxalate)borate.

17. In paragraph 1, A local self-healing transparent coating composition, wherein the crosslinking agent containing a hydroxyl group or an isocyanate group has a chemical structure represented by the following chemical formula 10. <Chemical Formula 10> In chemical formula 10, R6 is each independently a C1 to C6 alkyl group, and X1 is an isocyanate group or a hydroxy group.

18. In paragraph 1, A local self-healing transparent coating composition comprising 5 to 50 parts by weight of the above polyfunctional alcohol relative to 100 parts by weight of the polyacrylic resin.

19. In paragraph 1, A local self-healing transparent coating composition comprising 25 to 55 parts by weight of the hydroxyl group or isocyanate group-containing crosslinking agent relative to 100 parts by weight of the polyacrylic resin.

20. In paragraph 1, A local self-healing transparent coating composition comprising 0.01 to 0.50 wt% of the photothermal dye 21. A clear coat comprising a local self-healing function formed by a crosslinking reaction of a local self-healing transparent coating composition described in any one of claims 1 to 20.

22. In paragraph 21, Thermal decomposition temperature (T) of the above local clear coat d ) is a clear coat having a local self-healing function of 235 to 260°C.

23. In paragraph 21, The glass transition temperature (T) of the above clear coat g ) is a clear coat containing a local self-healing function at 20 to 60°C.

24. In paragraph 21, A clear coat having a local self-healing function with a near-infrared and visible light transmittance of 90% or more.

25. In paragraph 21, A clear coat having a local self-healing function with an indentation modulus of 2 to 8 GPa.

26. In paragraph 21, A clear coat having a local self-healing function with an indentation hardness of 110 to 130 MPa.

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