Patent Description:
Transparent polymer films are widely used as core materials in the field of optical, transparent and flexible displays, and in particular have come to replace glass in the display industry due to the light weight, ease of processing and flexibility thereof. However, since transparent polymer films have disadvantages of low surface hardness and abrasion resistance compared to glass, coating techniques for improving the abrasion resistance of polymer films arise as an important issue.

The materials used for polymer films broadly include organic materials, inorganic materials and hybrid organic-inorganic materials. Thereamong, organic materials have advantages of flexibility and moldability due to the inherent characteristics of organic substances, but have the disadvantage of low surface hardness, whereas inorganic materials have the advantages of high surface hardness and transparency, but have the disadvantages of poor flexibility and moldability. For this reason, hybrid organic-inorganic materials having the advantages of both materials are receiving attention at present, and active research thereon is underway. However, it is not possible at present to realize the advantages of both types of materials.

In addition, the most important requirements in order for surface-coated polymer films to be appropriate for use in optical applications are that coating agents should have excellent adhesivity to the films and should be free from curling and rainbow phenomena. Therefore, finding coating materials that are capable of exhibiting all of these advantages has arisen as a key issue for technology development.

There are several patent documents that disclose coating compositions relating to polymer films. For example, <CIT> discloses a high-hardness hard coating film composition including an ultraviolet ray-curable polyurethane acrylate oligomer, and <CIT> discloses a vinyl oligosiloxane hybrid composition including a metal catalyst. The former case can minimize the curling phenomenon and prevent the rainbow phenomenon, which is attributable to optical interference. The latter case reported a low shrinkage rate and excellent optical properties and heat resistance of a composition having an inorganic network structure.

Meanwhile, International Patent Publication No. <CIT> discloses a high-hardness siloxane resin composition containing a cyclic epoxy group, a method for preparing the same, and an optical film including a cured product thereof. This patent suggests that the technical level of the hard coating has improved such that a high hardness of <NUM> is able to be implemented.

Nevertheless, coating materials still have limitations in that drawbacks in terms of hardness and permeability are inevitable when putting emphasis on the advantages of organic materials, and the drawback associated with flexibility cannot be completely overcome when putting emphasis on the advantages of inorganic materials. In particular, organic materials are suitable for surface coating of polymer films due to the advantage of flexibility thereof. However, when the surface hardness of the coating layer is improved by forming a dense network between the molecules, increased shrinkage may result in curling and cracking, which causes the coating layer to peel off due to the deteriorated adhesivity. Therefore, for wider use of polymer films, there is urgent need for techniques capable of preventing deterioration in the flexibility of films due to the coating while increasing the surface hardness thereof. <CIT> relates to a coating resin composition comprising a siloxane resin chemically bonded by compounds including an alkoxy silane containing epoxy or acrylic in the chemical structure; a dialkoxysilane of a silane D structure; or a trialkoxy silane of a silane T structure, and to a coating film comprising a cured article of the resin composition as a coating layer. <CIT> relates to a hard coating film having a multilayer-structure and, specifically, to a hard coating film having a multilayer-structure, which has a low Vickers hardness (Hv) value while having an excellent scratch resistance together with flexibility. <CIT> relates to organosilicon compositions that are reaction products of a polyhydric alcohol and a silane wherein the silicon atom is bonded to at least one organofunctional group and at least two hydrolyzable groups. <CIT> relates to an epoxysiloxane condensate that is modified by means of an in situ reaction with an organic compound, which is di-functional or multifunctional if warranted. <CIT> relates to a curable resin composition comprising a glycol-modified silicon compound and a resin having an average of at least two hydroxyl groups in the molecule, and a method of curing the composition by applying it to a substrate followed by heating. <CIT> relates to an organosilicon compositions useful as adhesion promoters for curable organopolysiloxanes, said organosilicon compositions being formed by reacting (A) a polyhydric alcohol, (B) an organosiloxane containing at least one organofunctional group and one hydroxyl or hydrolyzable group per molecule and (C) a silane containing at least three hydrolyzable groups per molecule.

Therefore, the present disclosure has been made in view of the above problems, and it is one object of the present disclosure to provide a resin composition for coating which has a surface hardness of at least <NUM> as well as excellent flexibility and abrasion resistance. It is another object of the present disclosure to provide a coating film including a cured product of the resin composition as a coating layer.

The technical problems are solved by the appended claims.

The present disclosure can maximize flexibility during curing through incorporation of a linear diol structure in a polymer-bonding structure, while securing surface hardness and scratch resistance through dense crosslinking of the siloxane network derived from siloxane molecules.

In one aspect, the present disclosure is directed to a coating film comprising a cured resin composition including a siloxane resin chemically bonded by a silane compound represented by the following Formula <NUM> and a diol compound represented by the following Formula <NUM>:.

<Formula <NUM>>     R<NUM>nSi(OR<NUM>)<NUM>-n.

wherein R<NUM> is a C1-C3 linear, branched or cyclic alkylene group substituted with epoxy or acryl, R<NUM> is a C1-C8 linear, branched or cyclic alkyl group, and n is an integer of <NUM> to <NUM>,.

wherein n is an integer of <NUM> to <NUM>.

The silane compound represented by Formula <NUM> may include at least one selected from <NUM>-glycidoxypropyl trimethoxysilane, <NUM>-glycidoxypropyl triethoxysilane, <NUM>-glycidoxypropyl tripropoxysilane, <NUM>-methacryloxypropyl trimethoxysilane, <NUM>-methacryloxypropyl triethoxysilane, <NUM>-acryloxypropyl trimethoxysilane, <NUM>-acryloxypropyl triethoxysilane, <NUM>-acryloxypropyl tripropoxysilane, <NUM>-(<NUM>,<NUM>-epoxycyclohexyl)ethyltrimethoxysilane, <NUM>-(<NUM>,<NUM>-epoxycyclohexyl)ethyltriethoxysilane and <NUM>-(<NUM>,<NUM>-epoxycyclohexyl)ethyltripropoxysilane, but is not limited thereto.

However, when the siloxane resin is synthesized using the silane compound alone, high surface hardness can be secured, but there is a limitation on securing flexibility, since the bonding structure is formed only through dense siloxane crosslinking. Accordingly, by polymerizing a siloxane resin using a silane compound containing an alkoxy silane represented by Formula <NUM> along with a diol compound represented by Formula <NUM>, the present disclosure is capable of incorporating the linear diol structure in the polymer chain of the siloxane resin and thereby imparting excellent flexibility to the cured product of the resin composition for coating including the siloxane resin.

More specifically, the diol compound represented by Formula <NUM> according to the present disclosure has a linear structure. The reason for this is that, when the linear diol compound has a linear structure, flexibility can be maximized due to free rotation in the molecule.

In the diol compound represented by Formula <NUM>, n is an integer of <NUM> to <NUM>, preferably an integer of <NUM> to <NUM>. When n is within the range defined above, the decrease in hardness can be minimized.

The diol compound represented by Formula <NUM> has a molar ratio of <NUM>:<NUM> to <NUM>:<NUM>, preferably <NUM>:<NUM> to <NUM>:<NUM>, and more preferably <NUM>:<NUM> to <NUM>:<NUM>, relative to the silane compound represented by Formula <NUM>.

When the molar ratio of the diol compound represented by Formula <NUM> is less than <NUM>, there is a limitation in realizing bendability because the increase in flexibility is insufficient, and when the molar ratio exceeds <NUM>, the decrease in viscosity resulting from the diol residue makes it difficult to determine the reaction time, which causes problems in the process of preparing the siloxane resin.

The siloxane resin may further include a silane compound represented by the following Formula <NUM>, which is chemically bonded together with the silane compound represented by Formula <NUM> and the diol compound represented by Formula <NUM>.

wherein R<NUM> is a C1-C4 linear or branched alkyl group.

The silane compound represented by Formula <NUM> forms a silane Q structure having no alkoxy functional group in Si in the polymer chain of the siloxane resin, so that the resin composition for coating can be cured to thus provide hardness comparable to that of glass.

The silane compound represented by Formula <NUM> is preferably contained in a molar ratio of <NUM>:<NUM> or more relative to the silane compound represented by Formula <NUM>.

When the molar ratio of the silane compound represented by Formula <NUM> is less than <NUM>, a silane Q structure having no alkoxy functional group in Si cannot be sufficiently formed in the polymer chain of the siloxane resin, and hardness and scratch resistance may thus be lowered.

In this regard, when the molar ratio of the silane compound represented by Formula <NUM> is <NUM> or more, a polymerization product having a satisfactory Q structure can be produced and thus the desired hardness and scratch resistance of the present disclosure can be secured, and when the silane compound represented by Formula <NUM> is present in an excessive amount of higher than <NUM> or more, the desired effects are not improved any further, and thus the increased content is meaningless in terms of improvement of hardness and scratch resistance.

In the present disclosure, the synthesis of the siloxane resin may be carried out through an alkoxy-diol substitution reaction or through condensation-polymerization. The reaction may be carried out at room temperature, but may alternatively be carried out while performing stirring at <NUM> to <NUM> for <NUM> to <NUM> hours. The catalyst for conducting the substitution reaction of alkoxy with diol (hydrolysis with water) and condensation polymerization may be an acid catalyst such as hydrochloric acid, acetic acid, hydrogen fluoride, nitric acid, sulfuric acid or iodic acid, a base catalyst such as ammonia, potassium hydroxide, sodium hydroxide, barium hydroxide or imidazole, and an ion exchange resin such as Amberite. These catalysts may be used alone or in combination thereof. The amount of the catalyst may be about <NUM> parts to about <NUM> parts by weight, based on <NUM> parts by weight of the siloxane resin, but is not particularly limited thereto.

When the substitution reaction and the condensation polymerization are conducted, water or alcohol is produced as a byproduct. When removing this water or alcohol, the reverse reaction can be suppressed and the forward reaction can be performed more quickly, so that control of the reaction rate is possible through this principle. After completion of the reaction, the byproduct may be removed by heating under reduced pressure.

The siloxane resin of the present disclosure thus synthesized has a weight average molecular weight of <NUM>,<NUM> to <NUM>,<NUM> and a polydispersion index (PDI) of <NUM> to <NUM>. The molecular weight (Mw) and polydispersion index (PDI) correspond to the weight average molecular weight (Mw) and the number average molecular weight (Mn) determined for polystyrene through gel permeation chromatography (GPC, Waters Alliance, Model: e2695). The polymer to be measured was dissolved at a concentration of <NUM>% in tetrahydrofuran and was injected in an amount of <NUM>µl into GPC. The mobile phase of GPC was tetrahydrofuran and was fed at a flow rate of <NUM>/min, and analysis was conducted at <NUM>. The column used herein was purchased from Waters Styragel HR3, and two columns were connected in series. The detector herein used was an RI detector (Waters Alliance, <NUM>) and measurement was conducted at <NUM>. At this time, the molecular weight distribution (PDI) was calculated by dividing the measured weight average molecular weight by the number average molecular weight.

Meanwhile, in addition to the siloxane resin, the resin composition for coating may further include, as another component, at least one additive selected from the group consisting of an organic solvent, a photoinitiator, a thermal initiator, an antioxidant, a leveling agent and a coating aid. In this case, it is possible to provide a resin composition for coating suitable for various applications by controlling the kind and content of the additive that is used. In the present disclosure, a resin composition for coating capable of improving hardness, abrasion resistance, flexibility and curling resistance is preferably provided.

The initiator according to the present disclosure is, for example, a photopolymerization initiator such as an organometallic salt and a photopolymerization initiator such as amine and imidazole. In this case, the amount of the initiator that is added is preferably about <NUM> to <NUM> parts by weight based on <NUM> parts by weight of the total amount of the siloxane resin. When the content of the initiator is less than <NUM> parts by weight, the curing time of the coating layer required to obtain sufficient hardness is lengthened and efficiency is thus deteriorated. When the content of the initiator is more than <NUM> parts by weight, the yellowness of the coating layer may be increased, thus making it difficult to obtain a transparent coating layer.

Also, the organic solvent may include at least one selected from the group consisting of ketones such as acetone, methyl ethyl ketone, methyl butyl ketone and cyclohexanone, cellosolves such as methyl cellosolve and butyl cellosolve, ethers such as ethyl ether and dioxane, alcohols such as isobutyl alcohol, isopropyl alcohol, butanol and methanol, halogenated hydrocarbons such as dichloromethane, chloroform and trichlorethylene, and hydrocarbons such as normal hexane, benzene and toluene. In particular, since the viscosity of the siloxane resin can be controlled by controlling the amount of the organic solvent that is added, workability can be further improved, or the thickness of the coating film can be controlled.

In particular, the present disclosure is directed to a coating film including a base film and a coating layer laminated on at least one surface of the base film and including a cured product of the resin composition for coating as a coating layer. The coating film may have a surface hardness in the direction in which the coating layer is formed, measured in accordance with ASTM D3363, of at least <NUM>. The coating film may have a distance (curl) from an edge of the film to the bottom, of <NUM> or less, based on a coating thickness of <NUM>. The coating film has a radius of curvature, measured using a radius mode of a bending tester (JIRBT-<NUM>-<NUM>), of <NUM> or less, based on a coating thickness of <NUM>. This means that the resin composition has hardness as well as considerably excellent curl characteristics and flexibility.

In the present disclosure, when the resin composition for coating is polymerized, the amount of light suitable for photopolymerization may be not less than <NUM> mJ/cm<NUM> and not more than <NUM>,<NUM> mJ/cm<NUM>, and heat treatment may be performed at a temperature not lower than <NUM> and not higher than about <NUM> so as to obtain a uniform surface before the photopolymerization. In addition, a temperature suitable for thermal polymerization is not lower than <NUM> and not higher than <NUM>, but is not limited thereto.

Hereinafter, the present disclosure will be described in more detail with reference to the following Examples. The examples are only provided only for better understanding of the present disclosure and should not be construed as limiting the scope of the present disclosure.

KBM-<NUM> (Shin-Etsu Chemical Co. ; <NUM>-glycidoxypropyl trimethoxysilane) and ethylene glycol (Sigma-Aldrich Corporation) were mixed at a ratio of <NUM> : <NUM> (200mmol : 300mmol), the resulting mixture was injected into a <NUM>,<NUM> double-jacket reactor, and <NUM> of sodium hydroxide was dissolved in <NUM> of distilled water in a <NUM> vial using a magnetic stirrer. Then, an aqueous sodium hydroxide solution was added as a catalyst, and the mixture was stirred at <NUM> RPM with a mechanical stirrer at <NUM> for <NUM> hours using a thermostat. Then, the resulting mixture was diluted with <NUM>-butanone to a solid content of <NUM> wt% and then filtered through a <NUM> Teflon filter to obtain a siloxane resin. The molecular weight of the resin was measured using GPC, and the result showed that the resin had a number average molecular weight of <NUM>, a weight average molecular weight of <NUM>,<NUM>, and a polydispersity index (PDI, Mw/Mn) of <NUM>.

Next, <NUM> parts by weight of IRGACURE <NUM> (BASF Corporation), which is a photoinitiator, with respect to <NUM> parts by weight of the siloxane resin, was added to the siloxane resin diluted in the solvent to finally obtain a resin composition for coating.

This composition was coated on the polyimide surface using a bar, dried at <NUM> for <NUM> minutes and then exposed to an ultraviolet lamp having a wavelength of <NUM> for <NUM> seconds to prepare a <NUM> coating film.

KBM-<NUM> (Shin-Etsu Chemical Co. ), ethylene glycol (Sigma-Aldrich Corporation) and distilled water were mixed at a ratio of <NUM> : <NUM> : <NUM> (200mmol : 270mmol : 30mmol), the resulting mixture was injected into a <NUM>,<NUM> double-jacket reactor, and <NUM> of sodium hydroxide was dissolved in <NUM> of distilled water in a <NUM> vial using a magnetic stirrer. Then, an aqueous sodium hydroxide solution was added as a catalyst, and the mixture was stirred at <NUM> RPM with a mechanical stirrer at <NUM> for <NUM> hours using a thermostat. Then, the resulting mixture was diluted with <NUM>-butanone to a solid content of <NUM> wt% and then filtered through a <NUM> Teflon filter to obtain a siloxane resin. The molecular weight of the resin was measured using GPC, and the result showed that the resin had a number average molecular weight of <NUM>,<NUM>, a weight average molecular weight of <NUM>,<NUM> and a polydispersity index (PDI, Mw/Mn) of <NUM>. Then, a resin composition for coating was prepared in the same manner as in Example <NUM>, and was coated on a polyimide film to prepare a <NUM> coating film.

KBM-<NUM> (Shin-Etsu Chemical Co. ), ethylene glycol (Sigma-Aldrich Corporation) and distilled water were mixed at a ratio of <NUM> : <NUM> : <NUM> (200mmol : 210mmol : 90mmol), the resulting mixture was injected into a <NUM>,<NUM> double-jacket reactor, and <NUM> of sodium hydroxide was dissolved in <NUM> of distilled water in a <NUM> vial using a magnetic stirrer. Then, an aqueous sodium hydroxide solution was added as a catalyst, and the mixture was stirred at <NUM> RPM with a mechanical stirrer at <NUM> for <NUM> hours using a thermostat. Then, the resulting mixture was diluted with <NUM>-butanone to a solid content of <NUM> wt% and then filtered through a <NUM> Teflon filter to obtain a siloxane resin. The molecular weight of the resin was measured using GPC, and the result showed that the resin had a number average molecular weight of <NUM>,<NUM>, a weight average molecular weight of <NUM>,<NUM> and a polydispersity index (PDI, Mw/Mn) of <NUM>. Then, a resin composition for coating was prepared in the same manner as in Example <NUM>, and was coated on a polyimide film to prepare a <NUM> coating film.

KBM-<NUM> (Shin-Etsu Chemical Co. ), ethylene glycol (Sigma-Aldrich Corporation) and distilled water were mixed at a ratio of <NUM> : <NUM> : <NUM> (200mmol : 150mmol : 150mmol), the resulting mixture was injected into a <NUM>,<NUM> double-jacket reactor, and <NUM> of sodium hydroxide was dissolved in <NUM> of distilled water in a <NUM> vial using a magnetic stirrer. Then, an aqueous sodium hydroxide solution was added as a catalyst, and the mixture was stirred at <NUM> RPM with a mechanical stirrer at <NUM> for <NUM> hours using a thermostat. Then, the resulting mixture was diluted with <NUM>-butanone to a solid content of <NUM> wt% and then filtered through a <NUM> Teflon filter to obtain a siloxane resin. The molecular weight of the resin was measured using GPC, and the result showed that the resin had a number average molecular weight of <NUM>,<NUM>, a weight average molecular weight of <NUM>,<NUM>, and a polydispersity index (PDI, Mw/Mn) of <NUM>. Then, a resin composition for coating was prepared in the same manner as in Example <NUM>, and was coated on a polyimide film to prepare a <NUM> coating film.

KBM-<NUM> (Shin-Etsu Chemical Co. ), ethylene glycol (Sigma-Aldrich Corporation) and distilled water were mixed at a ratio of <NUM> : <NUM> : <NUM> (200mmol : 90mmol : 210mmol), the resulting mixture was injected into a <NUM>,<NUM> double-jacket reactor, and <NUM> of sodium hydroxide was dissolved in <NUM> of distilled water in a <NUM> vial using a magnetic stirrer. Then, an aqueous sodium hydroxide solution was added as a catalyst, and the mixture was stirred at <NUM> RPM with a mechanical stirrer at <NUM> for <NUM> hours using a thermostat. Then, the resulting mixture was diluted with <NUM>-butanone to a solid content of <NUM> wt% and then filtered through a <NUM> Teflon filter to obtain a siloxane resin. The molecular weight of the resin was measured using GPC, and the result showed that the resin had a number average molecular weight of <NUM>,<NUM>, a weight average molecular weight of <NUM>,<NUM> and a polydispersity index (PDI, Mw/Mn) of <NUM>. Then, a resin composition for coating was prepared in the same manner as in Example <NUM>, and was coated on a polyimide film to prepare a <NUM> coating film.

KBM-<NUM> (Shin-Etsu Chemical Co. ), ethylene glycol (Sigma-Aldrich Corporation) and distilled water were mixed at a ratio of <NUM> : <NUM> : <NUM> (200mmol : 30mmol : 270mmol), the resulting mixture was injected into a <NUM>,<NUM> double-jacket reactor, and <NUM> of sodium hydroxide was dissolved in <NUM> of distilled water in a <NUM> vial using a magnetic stirrer. Then, an aqueous sodium hydroxide solution was added as a catalyst, and the mixture was stirred at <NUM> RPM with a mechanical stirrer at <NUM> for <NUM> hours using a thermostat. Then, the resulting mixture was diluted with <NUM>-butanone to a solid content of <NUM> wt% and then filtered through a <NUM> Teflon filter to obtain a siloxane resin. The molecular weight of the resin was measured using GPC, and the result showed that the resin had a number average molecular weight of <NUM>,<NUM>, a weight average molecular weight of <NUM>,<NUM> and a polydispersity index (PDI, Mw/Mn) of <NUM>. Then, a resin composition for coating was prepared in the same manner as in Example <NUM>, and was coated on a polyimide film to prepare a <NUM> coating film.

KBM-<NUM> (Shin-Etsu Chemical Co. ), TEOS (Sigma-Aldrich Corporation), ethylene glycol (Sigma-Aldrich Corporation) and distilled water were mixed at a ratio of <NUM> : <NUM> : <NUM> : <NUM> (100mmol : 100mmol : 245mmol : 105mmol), the resulting mixture was injected into a <NUM>,<NUM> double-jacket reactor, and <NUM> of sodium hydroxide was dissolved in <NUM> of distilled water in a <NUM> vial using a magnetic stirrer. Then, an aqueous sodium hydroxide solution was added as a catalyst, and the mixture was stirred at <NUM> RPM with a mechanical stirrer at <NUM> for <NUM> hours using a thermostat. Then, the resulting mixture was diluted with <NUM>-butanone to a solid content of <NUM> wt% and then filtered through a <NUM> Teflon filter to obtain a siloxane resin. The molecular weight of the resin was measured using GPC, and the result showed that the resin had a number average molecular weight of <NUM>,<NUM>, a weight average molecular weight of <NUM>,<NUM> and a polydispersity index (PDI, Mw/Mn) of <NUM>.

Then, a resin composition for coating was prepared in the same manner as in Example <NUM>, and was coated on a polyimide film to prepare a <NUM> coating film.

KBM-<NUM> (Shin-Etsu Chemical Co. ), TEOS (Sigma-Aldrich Corporation), ethylene glycol (Sigma-Aldrich Corporation) and distilled water were mixed at a ratio of <NUM> : <NUM> : <NUM> : <NUM> (140mmol : 60mmol : 231mmol : <NUM> mmol), the resulting mixture was injected into a <NUM>,<NUM> double-jacket reactor, and <NUM> of sodium hydroxide was dissolved in <NUM> of distilled water in a <NUM> vial using a magnetic stirrer. Then, an aqueous sodium hydroxide solution was added as a catalyst, and the mixture was stirred at <NUM> RPM with a mechanical stirrer at <NUM> for <NUM> hours using a thermostat. Then, the resulting mixture was diluted with <NUM>-butanone to a solid content of <NUM> wt% and then filtered through a <NUM> Teflon filter to obtain a siloxane resin. The molecular weight of the resin was measured using GPC, and the result showed that the resin had a number average molecular weight of <NUM>,<NUM>, a weight average molecular weight of <NUM>,<NUM> and a polydispersity index (PDI, Mw/Mn) of <NUM>. Then, a resin composition for coating was prepared in the same manner as in Example <NUM>, and was coated on a polyimide film to prepare a <NUM> coating film.

KBM-<NUM> (Shin-Etsu Chemical Co. ), TEOS (Sigma-Aldrich Corporation), ethylene glycol (Sigma-Aldrich Corporation) and distilled water were mixed at a ratio of <NUM> : <NUM> : <NUM> : <NUM> (180mmol : 20mmol : 217mmol : 93mmol), the resulting mixture was injected into a <NUM>,<NUM> double-jacket reactor, and <NUM> of sodium hydroxide was dissolved in <NUM> of distilled water in a <NUM> vial using a magnetic stirrer. Then, an aqueous sodium hydroxide solution was added as a catalyst, and the mixture was stirred at <NUM> RPM with a mechanical stirrer at <NUM> for <NUM> hours using a thermostat. Then, the resulting mixture was diluted with <NUM>-butanone to a solid content of <NUM> wt% and then filtered through a <NUM> Teflon filter to obtain a siloxane resin. The molecular weight of the resin was measured using GPC, and the result showed that the resin had a number average molecular weight of <NUM>,<NUM>, a weight average molecular weight of <NUM>,<NUM> and a polydispersity index (PDI, Mw/Mn) of <NUM>. Then, a resin composition for coating was prepared in the same manner as in Example <NUM> and was coated on a polyimide film to prepare a <NUM> coating film.

KBM-<NUM> (Shin-Etsu Chemical Co. ), TEOS (Sigma-Aldrich Corporation), ethylene glycol (Sigma-Aldrich Corporation) and distilled water were mixed at a ratio of <NUM> : <NUM> : <NUM> : <NUM> (190mmol : 10mmol : 214mmol : 92mmol), the resulting mixture was injected into a <NUM>,<NUM> double-jacket reactor, and <NUM> of sodium hydroxide was dissolved in <NUM> of distilled water in a <NUM> vial using a magnetic stirrer. Then, an aqueous sodium hydroxide solution was added as a catalyst, and the mixture was stirred at <NUM> RPM with a mechanical stirrer at <NUM> for <NUM> hours using a thermostat. Then, the resulting mixture was diluted with <NUM>-butanone to a solid content of <NUM> wt% and then filtered through a <NUM> Teflon filter to obtain a siloxane resin. The molecular weight of the resin was measured using GPC, and the result showed that the resin had a number average molecular weight of <NUM>,<NUM>, a weight average molecular weight of <NUM>,<NUM> and a polydispersity index (PDI, Mw/Mn) of <NUM>. Then, a resin composition for coating was prepared in the same manner as in Example <NUM> and was coated on a polyimide film to prepare a <NUM> coating film.

KBM-<NUM> (Shin-Etsu Chemical Co. ), TEOS (Sigma-Aldrich Corporation), ethylene glycol (Sigma-Aldrich Corporation) and distilled water were mixed at a ratio of <NUM> : <NUM> : <NUM> : <NUM> (198mmol : 2mmol : 211mmol : 90mmol), the resulting mixture was injected into a <NUM>,<NUM> double-jacket reactor, and <NUM> of sodium hydroxide was dissolved in <NUM> of distilled water in a <NUM> vial using a magnetic stirrer. Then, an aqueous sodium hydroxide solution was added as a catalyst, and the mixture was stirred at <NUM> RPM with a mechanical stirrer at <NUM> for <NUM> hours using a thermostat. Then, the resulting mixture was diluted with <NUM>-butanone to a solid content of <NUM> wt% and then filtered through a <NUM> Teflon filter to obtain a siloxane resin. The molecular weight of the resin was measured using GPC, and the result showed that the resin had a number average molecular weight of <NUM>,<NUM>, a weight average molecular weight of <NUM>,<NUM> and a polydispersity index (PDI, Mw/Mn) of <NUM>. Then, a resin composition for coating was prepared in the same manner as in Example <NUM> and was coated on a polyimide film to prepare a <NUM> coating film.

KBM-<NUM> (Shin-Etsu Chemical Co. ; <NUM>-methacryloxypropyl trimethoxysilane), TEOS (Sigma-Aldrich Corporation), ethylene glycol (Sigma-Aldrich Corporation) and distilled water were mixed at a ratio of <NUM> : <NUM> : <NUM> : <NUM> (180mmol : 20mmol : 217mmol : 93mmol), the resulting mixture was injected into a <NUM>,<NUM> double-jacket reactor, and <NUM> of sodium hydroxide was dissolved in <NUM> of distilled water in a <NUM> vial using a magnetic stirrer. Then, an aqueous sodium hydroxide solution was added as a catalyst, and the mixture was stirred at <NUM> RPM with a mechanical stirrer at <NUM> for <NUM> hours using a thermostat. Then, the resulting mixture was diluted with <NUM>-butanone to a solid content of <NUM> wt% and then filtered through a <NUM> Teflon filter to obtain a siloxane resin. The molecular weight of the resin was measured using GPC, and the result showed that the resin had a number average molecular weight of <NUM>,<NUM>, a weight average molecular weight of <NUM>,<NUM> and a polydispersity index (PDI, Mw/Mn) of <NUM>. Then, a resin composition for coating was prepared in the same manner as in Example <NUM>, except that IRGACURE <NUM> (BASF Corporation) was used instead of IRGACURE <NUM> (BASF Corporation), and was coated on a polyimide film to prepare a <NUM> coating film.

A resin was obtained by polymerization in the same manner as in Example <NUM>, except that propylene glycol (Sigma-Aldrich Corporation) was used instead of ethylene glycol (Sigma-Aldrich Corporation), and the resin was found to have a number average molecular weight of <NUM>,<NUM>, a weight average molecular weight of <NUM>,<NUM> and a polydispersity index (PDI, Mw/Mn) of <NUM>. A resin composition for coating was prepared in the same manner as in Example <NUM> and was coated on a polyimide film to prepare a <NUM> coating film.

A resin was obtained by polymerization in the same manner as in Example <NUM>, except that butane diol (Sigma-Aldrich Corporation) was used instead of ethylene glycol (Sigma-Aldrich Corporation), and the resin was found to have a number average molecular weight of <NUM>,<NUM>, a weight average molecular weight of <NUM>,<NUM> and a polydispersity index (PDI, Mw/Mn) of <NUM>. A resin composition for coating was prepared in the same manner as in Example <NUM> and was coated on a polyimide film to prepare a <NUM> coating film.

A resin was obtained by polymerization in the same manner as in Example <NUM>, except that pentane diol (Sigma-Aldrich Corporation) was used instead of ethylene glycol (Sigma-Aldrich Corporation), and the resin was found to have a number average molecular weight of <NUM>,<NUM>, a weight average molecular weight of <NUM>,<NUM> and a polydispersity index (PDI, Mw/Mn) of <NUM>. A resin composition for coating was prepared in the same manner as in Example <NUM> and was coated on a polyimide film to prepare a <NUM> coating film.

A resin was obtained by polymerization in the same manner as in Example <NUM>, except that hexane diol (Sigma-Aldrich Corporation) was used instead of ethylene glycol (Sigma-Aldrich Corporation), and the resin was found to have a number average molecular weight of <NUM>, a weight average molecular weight of <NUM>,<NUM> and a polydispersity index (PDI, Mw/Mn) of <NUM>. A resin composition for coating was prepared in the same manner as in Example <NUM> and was coated on a polyimide film to prepare a <NUM> coating film.

KBM-<NUM> (Shin-Etsu Chemical Co. ) and distilled water were mixed at a ratio of <NUM> : <NUM> (200mmol : 300mmol), the resulting mixture was injected into a <NUM>,<NUM> double-jacket reactor, and <NUM> of sodium hydroxide was dissolved in <NUM> of distilled water in a <NUM> vial using a magnetic stirrer. Then, an aqueous sodium hydroxide solution was added as a catalyst, and the mixture was stirred at <NUM> RPM with a mechanical stirrer at <NUM> for <NUM> hour using a thermostat. Then, the resulting mixture was diluted with <NUM>-butanone to a solid content of <NUM> wt% and then filtered through a <NUM> Teflon filter to obtain a siloxane resin. The molecular weight of the resin was measured using GPC and the result showed that the resin had a number average molecular weight of <NUM>,<NUM>, a weight average molecular weight of <NUM>,<NUM> and a polydispersity index (PDI, Mw/Mn) of <NUM>.

Then, a resin composition for coating was prepared in the same manner as in Example <NUM> and was coated on a polyimide film to prepare a <NUM> coating film.

KBM-<NUM> (Shin-Etsu Chemical Co. ), TEOS (Sigma-Aldrich Corporation) and distilled water were mixed at a ratio of <NUM> : <NUM> : <NUM> (180mmol : 20mmol : 310mmol), the resulting mixture was injected into a <NUM>,<NUM> double-jacket reactor, and <NUM> of sodium hydroxide was dissolved in <NUM> of distilled water in a <NUM> vial using a magnetic stirrer. Then, an aqueous sodium hydroxide solution was added as a catalyst, and the mixture was stirred at <NUM> RPM with a mechanical stirrer at <NUM> for <NUM> hour using a thermostat. Then, the resulting mixture was diluted with <NUM>-butanone to a solid content of <NUM> wt% and then filtered through a <NUM> Teflon filter to obtain a siloxane resin. The molecular weight of the resin was measured using GPC, and the result showed that the resin had a number average molecular weight of <NUM>,<NUM>, a weight average molecular weight of <NUM>,<NUM> and a polydispersity index (PDI, Mw/Mn) of <NUM>. Then, a resin composition for coating was prepared in the same manner as in Example <NUM> and was coated on a polyimide film to prepare a <NUM> coating film.

KBM-<NUM> (Shin-Etsu Chemical Co. ) and distilled water were mixed at a ratio of <NUM> : <NUM> (200mmol : 300mmol), the resulting mixture was injected into a <NUM>,<NUM> double-jacket reactor, and <NUM> of sodium hydroxide was dissolved in <NUM> of distilled water in a <NUM> vial using a magnetic stirrer. Then, an aqueous sodium hydroxide solution was added as a catalyst, and the mixture was stirred at <NUM> RPM with a mechanical stirrer at <NUM> for <NUM> hour using a thermostat. Then, the resulting mixture was diluted with <NUM>-butanone to a solid content of <NUM> wt% and then filtered through a <NUM> Teflon filter to obtain a siloxane resin. The molecular weight of the resin was measured using GPC, and the result showed that the resin had a number average molecular weight of <NUM>,<NUM>, a weight average molecular weight of <NUM>,<NUM> and a polydispersity index (PDI, Mw/Mn) of <NUM>. Then, a resin composition for coating was prepared in the same manner as in Example <NUM> and was coated on a polyimide film to prepare a <NUM> coating film.

A resin was obtained by polymerization in the same manner as in Example <NUM>, except that hydroquinone (Sigma-Aldrich Corporation) was used instead of ethylene glycol (Sigma-Aldrich Corporation), and the resin was found to have a number average molecular weight of <NUM>,<NUM>, a weight average molecular weight of <NUM>,<NUM> and a polydispersity index (PDI, Mw/Mn) of <NUM>. A resin composition for coating was prepared in the same manner as in Example <NUM> and was coated on a polyimide film to prepare a <NUM> coating film.

A resin was obtained by polymerization in the same manner as in Example <NUM>, except that <NUM>,<NUM>-dodecanediol (Sigma-Aldrich Corporation) was used instead of ethylene glycol (Sigma-Aldrich Corporation), and the resin was found to have a number average molecular weight of <NUM>, a weight average molecular weight of <NUM> and a polydispersity index (PDI, Mw/Mn) of <NUM>. A resin composition for coating was prepared in the same manner as in Example <NUM> and was coated on a polyimide film to prepare a <NUM> coating film.

The physical properties of the prepared coating films of Examples and Comparative examples were evaluated in accordance with the following methods, and the results are shown in Table <NUM> below.

Note) *: "<<NUM>" means that the bending property is less than <NUM>, it being impossible to measure values below <NUM> due to the limitations of measurement equipment. **: Simultaneous indication of L and S means that a long scratch (> <NUM>) and a short scratch (≤ <NUM>) were both formed in the same trial during the scratch resistance test, and that a long scratch is formed due to poor scratch resistance, and a short scratch is also formed.

As can be seen from Table <NUM>, in Comparative Examples <NUM> and <NUM>, in which ethylene glycol was not added, the radius of curvature was <NUM> or more, indicating that flexibility was remarkably deteriorated and the curl characteristics were also poor.

In addition, it can be seen from Examples <NUM> to <NUM> that additional incorporation of an alkoxysilane having a silane Q structure can improve hardness and scratch resistance. It can be seen from Examples <NUM> to <NUM> that the effect of improvement of the bending property depending on the chain length was determined using diol, having a longer chain, instead of ethylene glycol. However, the bending property of diol was found to be similar to that of ethylene glycol.

Meanwhile, as can be seen from Example <NUM> and Comparative Example <NUM>, alkoxysilane, having an acrylic functional group, was found to be more greatly affected by curl characteristics and bending property depending on the addition or absence of diol, and that when the diol was not added, the curling property, which is affected by the acrylic functional group, is poorer than that of epoxy.

Also, in Comparative Example <NUM>, the resin composition for coating was prepared using hydroquinone instead of the diol compound represented by Formula <NUM>, having a linear structure, and it was found that the bending property of Comparative Example <NUM> was remarkably lowered compared to Examples <NUM> to <NUM>. In Comparative Example <NUM>, the resin composition for coating was prepared using <NUM>,<NUM>-dodecanediol, wherein n was more than <NUM> in the diol compound represented by Formula <NUM>, and the scratch resistance of Comparative Example <NUM> was remarkably lowered compared to Examples <NUM> to <NUM>.

As can be seen from the Examples as described above, the resin composition for coating of the present disclosure has improved curl characteristics and remarkably excellent flexibility without causing deterioration in surface hardness or scratch resistance through incorporation of the dense cross-linking of silane network as well as the linear molecular chain of diol in the molecular structure thereof. In addition, the resin composition for coating can be imparted with further improved scratch resistance and hardness through addition of an alkoxysilane having a Q structure. Accordingly, the resin composition for coating of the present disclosure is suitable as a polymer film, especially a flexible display protective film.

Claim 1:
A coating film comprising:
a base film; and
a coating layer laminated on at least one surface of the base film and comprising a cured product of a resin composition for coating as a coating layer,
wherein the coating film has a radius of curvature, measured using a radius mode of a bending tester JIRBT-<NUM>-<NUM>, of <NUM> or less, based on a coating thickness of <NUM>,
wherein the resin composition for coating comprises a siloxane resin chemically bonded by a silane compound represented by the following Formula <NUM> and a diol compound represented by the following Formula <NUM>:

        <Formula <NUM>>     R<NUM>nSi(OR<NUM>)<NUM>-n

wherein R<NUM> is a C1-C3 linear, branched or cyclic alkylene group substituted with epoxy or acryl, R<NUM> is a C1-C8 linear, branched or cyclic alkyl group, and n is an integer of <NUM> to <NUM>,

        <Formula <NUM>>     HO(CH<NUM>)nOH

wherein n is an integer of <NUM> to <NUM>,
wherein the diol compound represented by Formula <NUM> is contained in a molar ratio of <NUM>:<NUM> to <NUM>:<NUM> relative to the silane compound represented by Formula <NUM>,
wherein the siloxane resin has a weight average molecular weight of <NUM>,<NUM> to <NUM>,<NUM> and a molecular weight distribution of <NUM> to <NUM>, and
wherein the weight average molecular weight (Mw) and the molecular weight distribution (PDI) correspond to the weight average molecular weight (Mw) and the number average molecular weight (Mn) determined for polystyrene through gel permeation chromatography (GPC, Waters Alliance, Model: e2695), and the molecular weight distribution (PDI) is calculated by dividing the measured weight average molecular weight by the number average molecular weight.