KR20180072268A - Composition For Hard Coating and Polyimide Substrate Including Cured Product Of The Same As A Hard Coating Layer - Google Patents

Abstract

The present invention relates to siloxane resins chemically bonded by compounds comprising an alkoxy silane and an alkoxy metal having an alicyclic epoxy group in a molecular structure; a resin composition for hard coating containing a dye having a maximum absorbance at 550 to 700 nm; and a polyimide substrate including cured products thereof as a hard coating layer on at least one surface of a polyimide film. According to the present invention, it is possible to provide the resin composition for hard coating which can significantly reduce yellowing properties while improving physical properties such as bending properties, surface hardness, scratch resistance and adhesion when applied to the polyimide substrate as the hard coating layer.

Description

Technical Field [0001] The present invention relates to a resin composition for hard coating and a polyimide substrate comprising the same as a hard coating layer,

The present invention relates to a resin composition for hard coating, and a polyimide substrate comprising the cured product as a hard coat layer.

Flexible electronic devices such as flexible OLEDs, lightweight displays, flexible encapsulants, color EPDs, plastic LCDs, TSPs, and OPVs have attracted attention as electronic devices that can bend or bend into one of the next generation displays have. Flexible type display capable of such bending or rolling is possible, and a new type of flexible cover substrate is required to replace the conventional glass cover substrate in order to protect the lower element. In addition, such a substrate needs to maintain high hardness, low moisture permeability, chemical resistance and light transmittance in order to protect the parts included in the display device.

As such flexible display cover substrate materials, various high-hardness plastic substrates have been studied as candidates, and a transparent polyimide film capable of realizing a thinner thickness and a higher hardness has been considered as a major candidate. However, since the transparent plastic substrate has a lower surface hardness than the glass, there is a limit in securing the abrasion resistance. For this purpose, high hardness coating, that is, hard coating technology, has been an important issue for improving the surface hardness of the polymer film.

As a prior art related to an optical or thermosetting coating agent applied to optical products, Korean Patent Laid-Open Publication No. 2010-0041992 discloses a thermosetting resin composition containing a high hardness hard coating containing an ultraviolet ray curable polyurethane acrylate oligomer for the purpose of improving the surface hardness of a plastic substrate To provide a film composition. This patent minimizes the curling phenomenon and prevents rainbow phenomenon due to optical interference, but fails to overcome the limit of low surface hardness as a hard coating film. In addition, International Publication No. WO2013-187699 proposes a high hardness siloxane resin composition containing an alicyclic epoxy group, a process for producing the same, and an optical film comprising the above cured product. However, the above- There is still a problem that curling can occur.

If the surface hardness of the hard coat layer is improved by forming a dense network between the molecules, the shrinkability increases and the flexibility becomes poor. In addition, the problem of curling and cracking occurs, and when the curl and crack are removed, It is difficult to overcome the problem. Accordingly, there is a continuing demand for development of a plastic substrate having excellent flexibility, no curling, and easy processing.

On the other hand, in order to apply a plastic substrate to a display cover substrate, it is necessary to have high transparency at a level of optical film and low yellowing degree. However, the conventional polyimide has a deep yellow color, which makes it difficult to use it as an optical film. Thus, the yellow color improves with the development of transparent polyimide film technology, but still shows a high yellow color for application to optical use. Therefore, further work to further improve the yellowness degree of the polyimide is also urgently required.

Accordingly, the present invention provides a resin composition for hard coating which can significantly reduce the yellowing degree when applied to a polyimide substrate, while improving physical properties such as bending properties, surface hardness, scratch resistance and adhesion, By including a cured product of the composition as a hard coat layer, it is possible to improve the physical properties such as bending properties, surface hardness, scratch resistance and adhesion, and in particular, to a transparent polyimide substrate .

A first preferred embodiment of the present invention for solving the above-mentioned problems is a siloxane resin chemically bonded by compounds comprising an alkoxysilane represented by Chemical Formula 1 and an alkoxy metal represented by Chemical Formula 2; And a dye having a maximum absorbance at 550 to 700 nm:

???????? R ¹ _n Si (OR ² ) _{4 -n} ????? (1)

M (OR < ³ _> ) _m

Wherein R ¹ is a C ₁ to C ₃ linear alkyl group containing an alicyclic epoxy group, R ² and R ³ are C ₁ to C ₄ linear or branched alkyl groups, M is aluminum, titanium and Zinc, and n is an integer of 1 to 3, and m is an integer of 2 to 4.

Also, a second preferred embodiment of the present invention relates to a polyimide film; And a cured product of the resin composition for hard coating of the first embodiment as a hard coat layer on at least one side of the polyimide film.

According to the present invention, it is possible to provide a resin composition for hard coating which can significantly reduce yellowing while improving physical properties such as bending properties, surface hardness, scratch resistance and adhesion when applied to a polyimide substrate as a hard coating layer , Thereby providing a transparent polyimide substrate which can be applied to optical applications by significantly improving the yellowing degree while maintaining physical properties such as excellent bending property and high surface hardness by applying the resin composition to the polyimide substrate for hard coating can do.

In addition, the transparent polyimide substrate according to the present invention can be used effectively as a cover substrate of a flexible electronic device that can prevent breakage, which is a disadvantage of tempered glass, and can replace a product using tempered glass, have.

FIG. 1 is a graph showing transmittance of a dye solution of Production Example 4 by visible light wavelength band. FIG.

The present invention relates to siloxane resins chemically bonded by compounds comprising an alkoxy silane and an alkoxy metal having an alicyclic epoxy group in the molecular structure; And a dye having a maximum absorbance at 550 to 700 nm and a cured product thereof as a hard coating layer on at least one side of the polyimide film.

Hereinafter, the present invention will be described more specifically.

The resin composition for hard coating of the present invention comprises a siloxane resin chemically bonded by a compound including an alkoxysilane represented by the following formula (1) and an alkoxy metal represented by the following formula (2); And dyes having a maximum absorbance at 550 to 700 nm.

???????? R ¹ _n Si (OR ² ) _{4 -n} ????? (1)

M (OR < ³ _> ) _m

Wherein R ¹ is a C ₁ to C ₃ linear alkyl group containing an alicyclic epoxy group, R ² and R ³ are C ₁ to C ₄ linear or branched alkyl groups, M is aluminum, titanium and Zinc, and n is an integer of 1 to 3, and m is an integer of 2 to 4.

More specifically, the alicyclic epoxy group contained in R ¹ of Formula 1 preferably has an alicyclic structure formed by C ₃ to C ₈ alicyclic alkyl groups. However, the C ₃ to C ₅ When cycloaliphatic be of may curling phenomenon caused by reducing intermolecular spacing, C ₇ to in the epoxy curing reaction can take place later, if the cycloaliphatic be of, improve the curing speed and the local characteristic aspects of the C ₈ C ₆ It is preferably an alicyclic epoxy group, but the present invention is not necessarily limited thereto.

In the present invention, the epoxy-based monomer represented by the above formula (1) has a low curing shrinkage ratio, which is very significant from the standpoint of suppressing curling and ensuring excellent surface hardness. If the formula (1) is an acrylic monomer, it can exhibit a fast curing rate and a high hardness, but the contraction ratio is high and the curling probability can be increased. When the monomer of formula (1) is an isocyanate-based monomer, the flexibility is high due to its high modulus of elasticity, and thus the curling probability is low, but it can exhibit low surface hardness.

The present invention is characterized by having a high surface hardness relative to an isocyanate group and a curing shrinkage ratio lower than that of an acrylic group, since the epoxy group-containing monomer (1) is an epoxy-based monomer. In particular, since the compound of formula (1) of the present invention is an alicyclic epoxy-based monomer, securing the intermolecular space when cured is more advantageous than the linear epoxy-based monomer, the resin composition for hard coating of the present invention suppresses hardening shrinkage, .

As a result, the siloxane resin of the present invention can densely cross-link siloxane molecules having various molecular weights during photopolymerization or thermal polymerization, and as a result, it is possible to provide a hard-coated cured product having high hardness.

In the present invention, the alkoxysilane represented by the general formula (1) is preferably selected from the group consisting of 2- (3,4-epoxycyclohexyl) ethyltrimethoxysilane, 2- (3,4-epoxycyclohexyl) ethyltriethoxysilane and 2- , 4-epoxycyclohexyl) ethyltripropoxysilane may be more preferable.

In the present invention, the alkoxy metal represented by the formula (2) may be contained in an amount of 0.1 to 5.0 mol%, more preferably 0.2 to 3.0 mol%, based on 100 mol% of the alkoxysilane represented by the formula (1). When the content of the alkoxy metal is less than 0.1 mol%, the curl suppressing effect is insignificant, whereas when it exceeds 5.0 mol%, the viscosity of the resin increases rapidly as the gelation progresses rapidly, The workability may be significantly lowered and the reaction can not be sufficiently carried out, so that the improvement of the surface hardness may not be made to a final extent.

The siloxane resin of the present invention may further include an alkoxysilane represented by the following general formula (3) to form a chemical bond.

<Formula 3> Si (OR ^{₄₎ 4}

In Formula 3, R ⁴ is a C ₁ to C ₄ linear or branched alkyl group.

The alkoxysilane represented by the formula (3) has a silane Q structure in the molecular structure, that is, a chemical bonding structure such as the following formula 1 in which Si does not have an alkoxy functional group, thereby ensuring excellent hardness.

<Structure 1>

That is, as the Q structure found in the molecular structure of the glass is contained in the molecular structure, the resin composition of the present invention can achieve hardness similar to that of glass upon curing.

In the present invention, the alkoxysilane represented by the formula (1) and the alkoxysilane represented by the formula (3) are preferably in a molar ratio of 99: 1 to 20:80, more preferably 85:15 to 45:55 It is easy to prevent gelation during polymerization while maintaining high hardness.

In the present invention, the siloxane resin forming reaction is carried out by hydrolysis and condensation reaction between the compounds of the formulas 1 and 2 or the compounds of the formulas 1, 2 and 3 and may proceed at room temperature. However, in order to accelerate the reaction, The mixture may be stirred at 120 DEG C for 1 hour to 120 hours. As a catalyst for carrying out the hydrolysis and condensation reaction during the reaction, an acid catalyst such as hydrochloric acid, acetic acid, hydrogen fluoride, nitric acid, and sulfuric acid iodic acid, a base such as ammonia, potassium hydroxide, sodium hydroxide, barium hydroxide, imidazole A catalyst, and an amberite. These catalysts may be used alone or in combination. The amount of the catalyst is not particularly limited, but 0.0001 to about 10 parts by weight based on 100 parts by weight of the siloxane resin may be added.

Also, in the present invention, the resin composition for hard coating may include the siloxane resin as a first component, and may further include at least one of an epoxy resin and an acrylic resin as a second component. Here, the second component may be a monomer or an oligomer containing at least one functional group selected from the group consisting of an epoxy group, an oxetane group, an acrylate group, a methacrylate group, a urethane acrylate group and an ethylene oxide (EO) addition type acrylate group .

 In the present invention, the epoxy resin may be at least one selected from the group consisting of a glycidyl type epoxy resin, an alicyclic epoxy resin and an oxetane resin. The glycidyl type epoxy resin may be at least one selected from the group consisting of bisphenol A type epoxy resin, bisphenol F type epoxy Resins, bisphenol S type epoxy resins, naphthalene type epoxy resins or hydrogenated products thereof; An epoxy resin having a dicyclopentadiene skeleton; An epoxy resin having a triglycidyl isocyanurate skeleton; An epoxy resin having a cardo skeleton; And an epoxy resin having a polysiloxane structure.

 In addition, the alicyclic epoxy resin can be produced by reacting 3,4-epoxycyclohexylmethyl-3 ', 4'-epoxycyclohexanecarboxylate, 1,2,8,9-diepoxy limonene and? -Caprolactone oligomer at both ends Epoxycyclohexylmethane and 3,4-epoxycyclohexanecarboxylic acid, respectively, or an epoxy resin having a hydrogenated bisphenol A skeleton. The oxetane resin may be an oxetane resin having a hydroxy structure , An ether-based oxetane resin, or an oxetane resin having a methoxymethylbenzene structure.

 In the present invention, the acrylic resin is specifically exemplified by bisphenol-A ethylene oxide diacrylate, bisphenol-A ethylene oxide dimethacrylate, bisphenol-A ethoxylate diacrylate, bisphenol-A ethoxylate Diacrylate, bisphenol-A polyethoxylate diacrylate, bisphenol-A diacrylate, bisphenol-S diacrylate, dicyclopentadienyl diacrylate, pentaerythritol triacrylate, tris Hydroxyethyl isocyanurate triacrylate, pentaerythritol tetraacrylate, bisphenol-A dimethacrylate, bisphenol-S dimethacrylate, dicyclopentadienyl dimethacrylate, pentaerythritol trimethacrylate Tris (2-hydroxyethyl) isocyanurate trimethacrylate, and pentaerythritol And tetramethacrylate. A commercially available acrylic resin may also be used.

 In the present invention, the epoxy resin or the acrylic resin is preferably used alone or in combination of two or more. However, the compatibility between the resins used in combination may be lowered, resulting in lower uniformity of the coating film. Therefore, it may be more preferable to use them alone or in combination of three or less.

The first component and the second component are preferably mixed in a weight ratio of 10: 1 to 10: 4. With the use of the second component, the resin composition for hard coating according to the present invention has improved flexibility as well as hardness, abrasion resistance, and heat resistance, thereby preventing cracks and the like in a process such as cutting after hard coating, If the second component is used in an excess ratio, it may be difficult to secure the hardness, which is a necessary physical property of the hard coat layer.

The siloxane resin thus produced preferably has a weight average molecular weight of 3,000 to 50,000 and a polydispersion index (PDI) of 1.5 to 7.0. The weight average molecular weight (Mw) and the number average molecular weight (Mn) of polystyrene were determined by gel permeation chromatography (GPC) (model name e2695, manufactured by Waters Co.) Value. More specifically, it is dissolved in tetrahydrofuran so as to have a concentration of 1% of the polymer to be measured, and 20 μl of the solution is injected into GPC at a flow rate of 1.0 mL / min, and analysis can be performed at 30 ° C. Here, two columns of Waters Styragel HR3 are connected in series, and the detector can be measured at 40 캜 using an RI detector (Waters, 2414).

On the other hand, since all the objects have their own absorption wavelengths and when the object receives sunlight, the light of the inherent light absorption region is absorbed, so that the object recognizes the object as a color having a complementary relationship with the absorbed light . By using this principle in reverse, however, it is possible to add light of a complementary color to a specific object so that it can absorb light in a wavelength range that the object can not absorb by itself, so that the object may have a completely different color.

The resin composition for hard coating of the present invention is intended to improve the yellowing degree of a polyimide film using the above-described principle, and includes a dye having a maximum absorbance at 550 to 700 nm as a dye for correcting yellowing. However, in general, the coloring matter substance can be classified into a pigmenting method using an inorganic particle and a dyeing method using an organic material. In the case of a pigment, since it is difficult to ensure transparency and surface uniformity of a substrate due to dispersion problems, Is preferably applied.

At this time, when the dye has a maximum absorbance of less than 550 nm, the yellowness of the polyimide substrate may be increased, and the color of the polyimide substrate may change to red when the dye has a maximum absorbance of 700 nm or more. On the other hand, since the blue dye having the maximum absorbance at 550 to 700 nm can effectively absorb the wavelength of the yellow region in the visible light spectrum, it is possible to compensate the absorption wavelength region of the polyimide film layer to improve the yellowing degree of the polyimide substrate So that it is possible to manufacture a transparent polyimide substrate.

The dye may be used singly or in combination of two or more species. As the dye having compatibility with the resin composition for hard coating, a dye group including a chromophore or a product having the following chemical structure can be applied. The commercially available dye is not particularly limited to the following structure.

&Lt; Formula 2 >

<Formula 3>

<Formula 4>

Further, the resin composition for hard coating of the present invention may further include an initiator for the polymerization of the siloxane resin. As the initiator, for example, a photopolymerization initiator such as an onium salt or an organic metal salt, a thermal polymerization initiator such as amine, , Or a cationic polymerization agent can be used. However, the addition amount of the initiator is preferably about 0.01 to 10 parts by weight based on 100 parts by weight of the resin composition in consideration of curing efficiency and transparency of the hard coat layer.

In addition, the resin composition for hard coating of the present invention may further contain an antioxidant or a leveling agent to suppress the oxidation reaction resulting from the polymerization reaction of the siloxane resin, and may further contain a surfactant or a coating aid May also be included. In particular, an organic solvent may be further added to control the viscosity of the siloxane resin to facilitate workability and to control the thickness of the coating film.

The amount of the organic solvent to be added is not particularly limited, but the use of a solvent capable of sufficiently dissolving the dye is required to be specially selected. Examples of the organic solvent usable in the present invention include ketones such as acetone, methyl ethyl ketone, methyl butyl ketone and cyclohexanone, cellosolves such as methyl cellosolve and butyl cellosolve, dichloromethane, chloroform, trichlorethylene , Or a solvent composed of hydrocarbons such as normal hexane, benzene, and toluene, and the like. When alcohols such as ethyl ether, dioxane and the like, isobutyl alcohol, isopropyl alcohol, butanol, and methanol are used, they do not have sufficient solubility to dyes, so that dye aggregation occurs and it is difficult to secure a transmittance suitable for the optical film .

The dye of the present invention preferably contains 0.01 to 0.5 parts by weight of the dye relative to 100 parts by weight of the siloxane resin. When the amount of the dye is less than 0.01 part by weight, the dye content of the polyimide film is low due to low dye content in the solid content. If the amount of the dye is more than 0.5 part by weight, the optical characteristics of the polyimide substrate are deteriorated .

The resin composition for hard coating of the present invention may be applied to any one selected from spraying, dip coating, spin coating, die coating, comma coating, screen coating, inkjet printing, pad printing, knife coating, kiss coating, bar coating and gravure coating Layered on at least one side of the polyimide film by a method such as coating, casting, molding, etc., and then can be produced as a hard-coated cured product by photopolymerization or thermal polymerization. For the photopolymerization it is possible to obtain a uniform surface over the light article pre-heat treatment, which can be carried out at a temperature below about 300 ℃ than 40 ℃, if the irradiation light amount performed under the conditions of 50mJ / cm ² or more 20000mJ / cm ² or less But is not limited thereto. Further, in the case of thermal polymerization, it may be carried out at a temperature of from 40 ° C to about 300 ° C, but is not limited thereto.

In the present invention, the hard coat layer preferably has a thickness of 5 탆 or more in order to improve physical properties such as bending property and surface hardness, It is preferable to set the dry thickness to 50 탆 or less.

On the other hand, in the present invention, the polyimide film may be a conventional polyimide film obtained by polymerizing a diamine and an acid dianhydride (dianhydride) followed by imidization. The polyimide film of the present invention can be applied to any colorless transparent polyimide film which has inherent heat resistance of the polyimide resin and does not stand yellow, A polyimide film having an average transmittance at 350 to 700 nm of not less than 85%, a yellowness of not more than 5 and an average linear expansion coefficient (CTE) measured at 50 to 250 according to the TMA-Method of 50.0 ppm / May be more preferable.

If the average transmittance of the polyimide film is less than 85% based on the thickness of the polyimide film of 10 to 100 占 퐉 or the yellowness exceeds 5, the transparency becomes poor and it can not be applied to displays or optical elements. (CTE) is more than 50.0 ppm /, the thermal expansion coefficient difference with the plastic substrate becomes large, so that the device may be overheated or short-circuited if the temperature is high.

The dianhydrides which can be used in the present invention include 2,2-bis (3,4-dicarboxyphenyl) hexafluoropropanediamine hydrate (6FDA), biphenyltetracarboxylic dianhydride (BPDA), 4- (2,5-dioxotetrahydrofuran-3-yl) -1,2,3,4-tetrahydronaphthalene-1,2-dicarboxylic anhydride (TDA), pyromellitic acid dianhydride ), Benzophenone tetracarboxylic dianhydride (BTDA), oxydiphthalic dianhydride (ODPA), biscarboxyphenyldimethylsilanediamine hydride (SiDA), bisdicarboxyphenoxy diphenylsulfide dianhydride (BDSDA ), Sulfonyldiphthalic anhydride (SO2DPA), isopropylidene is phenoxybisphthalic anhydride (6HBDA), and the kind mentioned is not limited thereto. The dianhydride may be used singly or in combination of two or more, but is not limited thereto.

Examples of the diamine used in the present invention include oxydianiline (ODA), p-phenylenediamine (pPDA), m-phenylenediamine (mPDA), p-methylenediamine (pMDA), m- The reaction was carried out in the same manner as in Example 1 except that phenoxybenzene (133APB), bisaminophenoxybenzene (134APB), bisaminophenoxyphenylhexafluoropropane (4BDAF), bisaminophenylhexafluoropropane (33-6F), bisaminophenylhexafluoropropane (14CHD), cyclohexanediamine (14CHD), bisaminophenoxyphenyl (44CF), bis-aminophenylsulfone (4DDS), bisaminophenylsulfone (3DDS), bistrifluoromethylbenzidine (TFDB), cyclohexanediamine Propane (6HMDA), bisaminohydroxyphenylhexafluoropropane (DBOH), bisaminophenoxy diphenylsulfone (DBSDA), bis (4-aminophenyl) fluorene (FDA), bis Phenyl) fluorene (F-FDA), and the like, or two or more kinds thereof may be used , It does not limit a kind referred to this.

Examples of the aromatic dicarbonyl compounds usable in the present invention include terephthaloyl chloride (TPC), terephthalic acid (TPA), isophthaloyl dichloride (IPC), 4,4'-benzoyl chloride Raw materials may be mentioned but not limited thereto.

As described above, the polyimide substrate of the present invention comprising the cured product formed from the resin composition for hard coating as a hard coat layer has improved yellowing property and has a yellowness of 2 or less and a glass transition temperature of 450 to 450 nm as measured by CM- And the optical transmittance at 750 nm is 85 to 93%. In addition, the hard coating layer ensures the chemical resistance and impact resistance of the polyimide substrate, and can exhibit surface hardness of 5H to 9H according to JIS K56000 measurement standard.

The hard coating layer may be formed only on one side of the polyimide film, but may be formed on both sides to further increase the surface hardness and impact resistance. At this time, at least one of the two surfaces should contain a pigment, and the other surface may or may not include a pigment.

The polyimide substrate of the present invention satisfying the above optical transmittance, yellowing degree and heat resistance can be used as a protective film or a diffusion plate and a coating film for a TFT-LCD, for example, a TFT-LCD which has been limited in use due to the yellow of a conventional polyimide film Interlayer, gate insulator and liquid crystal alignment film can be used in areas where transparency is required. It can also be used as a flexible display substrate and a hard coating film that replace glass in existing displays.

Example

Hereinafter, the present invention will be described in more detail with reference to Examples. These examples are for the purpose of illustrating the present invention more specifically, and the present invention is not limited thereto.

< Manufacturing example  1. Production of polyimide film>

1-1: Preparation of polyimide powder

832 g of N, N-dimethylacetamide (DMAc) was charged into a 1 L reactor equipped with a stirrer, a nitrogen injector, a dropping funnel, a temperature controller and a condenser while nitrogen was passed through the reactor. 64.046 g (0.2 mol) of bistrifluoromethylbenzidine (TFDB) was dissolved and the solution was maintained at 25 占 폚. Thereto were added 31.09 g (0.07 mol) of 2,2-bis (3,4-dicarboxyphenyl) hexafluoropropanedioanhydride (6FDA) and 8.83 g (0.03 mol) of biphenyltetracarboxylic dianhydride (BPDA) ) Was added and stirred for a certain period of time to dissolve and react. The temperature of the solution was maintained at 25 占 폚. Then, 20.302 g (0.1 mol) of terephthaloyl chloride (TPC) was added to obtain a polyamic acid solution having a solid content of 13 wt%.

25.6 g of pyridine and 33.1 g of acetic anhydride were added to the polyamic acid solution, stirred for 30 minutes, and further stirred at 70 ° C for 1 hour. The mixture was cooled to room temperature and precipitated with 20 L of methanol. The precipitated solid was filtered and pulverized And then dried at 100 DEG C under vacuum for 6 hours to obtain 111 g of a solid powdery polyimide.

1-2: Production of polyimide film

0.03 g (0.03 wt%) of OH group-bonded amorphous silica particles was added to N, N-dimethylacetamide (DMAc) at a dispersion concentration of 0.1% and ultrasonic treatment was performed until the solvent became transparent. 100 g of the obtained polyimide powder as a solid powder was dissolved in 670 g of N, N-dimethylacetamide (DMAc) to obtain a 13 wt% solution. The solution thus obtained was applied to a stainless steel plate, cast to 340 占 퐉 and dried with hot air at 130 占 폚 for 30 minutes, and then the film was peeled off from the stainless plate and fixed to the frame with a pin.

The frame with the film fixed therein was placed in a vacuum oven, slowly heated from 100 ° C to 300 ° C for 2 hours, cooled gradually and separated from the frame to obtain a polyimide film. Thereafter, the substrate was subjected to heat treatment at 300 ° C for 30 minutes as a final heat treatment process. The prepared polyimide film had a thickness of 80 μm, an average light transmittance of 87%, a haze of 4.5, and an average coefficient of linear thermal expansion (CTE) measured at 50 to 250 ° C. according to the TMA-Method was 20 ppm / ° C. .

< Manufacturing example  2. Siloxane  Resin Manufacturing>

The mixture was mixed with KBM-303 (Shinetsu), Titanium isopropoxide (Sigma-Aldrich) and distilled water at a ratio of 365.87 g: 4.26 g: 40.66 mL and put into a 500 mL flask. Then, 0.06 g of sodium hydroxide was added as a catalyst, Stir for 10 hours. Thereafter, the solution was filtered using a 0.45-μm Teflon filter to obtain a siloxane resin (weight average molecular weight: 5000, polydispersity index: 2.6).

< Manufacturing example  3. Siloxane  Resin Manufacturing>

The mixture was mixed with KBM-303 (Shinetsu), TEOS (Sigma-Aldrich) and H ₂ O at a ratio of 295.66 g: 59.37 g: 43.22 mL and put into a 500 mL flask. Then, 0.06 g of sodium hydroxide was added as a catalyst, (Sigma-Aldrich), and the mixture was stirred at 60 ° C for 10 hours. Thereafter, the solution was filtered using a 0.45-μm Teflon filter to obtain a siloxane resin (weight average molecular weight 15,000, polydispersity index 3.0).

< Manufacturing example  4. Preparation of dye solution>

To 100 parts by weight of methyl ethyl ketone was added 0.1 part by weight of a blue dye Blue N (manufactured by Nippon Kayaku Co., Ltd.) having the maximum absorbance at 645 nm, followed by stirring and dissolution to prepare a dye solution. The transmittance of the prepared dye solution was found to be equal to 1, and it was found that the dye solution prepared by this method absorbed a wavelength of about 500 to 650 nm.

Example  One

3 parts by weight of IRGACURE 250 (BASF) as a photoinitiator and 100 parts by weight of the dye solution prepared in Preparation Example 4 were added to 100 parts by weight of the siloxane resin prepared in Preparation Example 2, and mixed to prepare a hard coating composition.

Subsequently, the hard coating composition was coated on the upper surface of the polyimide film prepared in Preparation Example 1, dried in an oven at 80 ° C for 10 minutes, photocured at a wavelength of 315 nm at a rate of 1,000 mJ / cm 2 in the direction of coating the hard coating composition with an ultraviolet irradiation device , And then heat-treated in an oven at 85 캜 for 5 hours to prepare a polyimide substrate having a hard coat layer having a thickness of 10 탆.

Example  2

3 parts by weight of IRGACURE 250 (BASF) as a photoinitiator to 100 parts by weight of the siloxane resin prepared in Preparation Example 2, cycloaliphatic epoxide (manufactured by Toagosei Co., Ltd., UVR-6110) as an epoxy resin or acrylic resin, And 100 parts by weight of the dye solution prepared in Preparation Example 4 were added and mixed to prepare a hard coating composition.

Subsequently, a polyimide substrate was prepared in the same manner as in Example 1 above.

Example  3

3 parts by weight of IRGACURE 250 (BASF) as a photoinitiator to 100 parts by weight of the siloxane resin prepared in Preparation Example 2, cycloaliphatic epoxide (manufactured by Toagosei Co., Ltd., UVR-6110) as an epoxy resin or acrylic resin, And 100 parts by weight of methyl ethyl ketone as a solvent were added and mixed to prepare a hard coating composition for an upper surface. The hard coating composition prepared in the same manner as in Example 1 was prepared as a hard coating composition for a bottom.

Subsequently, a hard coating layer was formed on the upper surface of the polyimide film in the same manner as in Example 1, and a hard coating layer was formed on the lower surface of the polyimide film using the hard coating composition for upper surface, To prepare a polyimide substrate.

Example  4

3 parts by weight of IRGACURE 250 (BASF) as a photoinitiator and 100 parts by weight of cycloaliphatic epoxide (manufactured by Toagosei Co., Ltd., UVR-6110) as an acrylic resin were added to 100 parts by weight of the siloxane resin prepared in Preparation Example 3, And 100 parts by weight of methyl ethyl ketone as a solvent were added and mixed to prepare a hard coating composition for an upper surface. The hard coating composition prepared in the same manner as in Example 1 was prepared as a hard coating composition for a bottom.

Subsequently, a hard coating layer was formed on the upper surface of the polyimide film in the same manner as in Example 1, and a hard coating layer was formed on the lower surface of the polyimide film using the hard coating composition for upper surface, To prepare a polyimide substrate.

Comparative Example  One

The polyimide film prepared in Production Example 1 was prepared as it was and was designated as Comparative Example 1. [

Comparative Example  2

3 parts by weight of IRGACURE 250 (BASF) as a photoinitiator and 100 parts by weight of methyl ethyl ketone as a solvent were added to 100 parts by weight of the siloxane resin prepared in Preparation Example 2 to prepare a hardcoat composition. To prepare a polyimide substrate.

Comparative Example  3

A polyimide substrate was prepared in the same manner as in Example 1 except that 1 part by weight of IRGACURE 184 (BASF) was added as an initiator to acrylic resin (DPHA, manufactured by Nippon Kayaku Co., Ltd.) instead of the siloxane resin of Production Example 2.

Comparative Example  4

100 parts by weight of a pigment dispersion (manufactured by Shepherd Company, Cobalt violet, 563 (nm) absorption wavelength band) 0.03 g of particles were put into 30 g of N, N-dimethylacetamide (DMAc) 0.1 weight%) was used in place of the dye solution of Production Example 4 to prepare a polyimide substrate.

< Measurement example >

Next, the polyimide substrates of Examples 1 to 4 and Comparative Examples 1 to 3 were evaluated for pencil hardness, bending property and curl characteristics by the following methods. The results are shown in Table 1 below.

(1) Pencil hardness: The pencil hardness was measured at a rate of 180 mm / min under a load of 750 gf according to ASTM D3363 using a pencil hardness tester manufactured by IMOTO, Japan.

(2) Flexibility: The hard coating film prepared in Examples 1 to 2 and Comparative Examples 1 and 2 was wound on a rod whose radius was determined to face the coated surface in the outward direction so that the coating surface had a minimum crack- Diameter.

(3) Yellowness: Yellowness was measured using a spectrophotometer (CM-3700D, KONICA MINOLTA) according to ASTM E313.

(4) Haze: The haze value was measured according to ASTM D1003 using a haze meter (Model: HM-150) equipment of MURAKAMI.

division Pencil hardness Flexibility Yellowness Hayes Example 1 6H Good 2mm radius
(Crack of radius 2.5mm occurred) 1.5 0.5 Example 2 6H Good 2mm radius
(Crack of radius 2.5mm occurred) 1.5 0.5 Example 3 7H Good radius 2.5mm
(3mm radius crack) 1.5 0.5 Example 4 7H Good radius 2.5mm
(3mm radius crack) 1.5 0.5 Comparative Example 1 2H Good 1mm radius 4.5 0.6 Comparative Example 2 6H Good 2mm radius
(Crack of radius 2.5mm occurred) 4.5 0.5 Comparative Example 3 4H Good 26mm radius
(25mm radius) 1.5 0.8 Comparative Example 4 6H Good 11mm radius
(10mm radius crack) 1.8 2.5

As can be seen from the results shown in Table 1, the polyimide substrates of Examples 1 to 4 exhibited excellent results in terms of pencil hardness, flexibility and yellowness. However, in Comparative Example 2, in which no dye was added, the pencil hardness was significantly lowered in Comparative Example 3 using an acrylic resin rather than a siloxane resin. When a pigment was used in place of the dye, the haze was lowered as in Comparative Example 4 and the use of the pigment as an optical substrate was limited. From these results, it was found that the polyimide substrate according to the present invention is excellent in surface hardness, chemical resistance, and warpage properties as well as optical characteristics, and thus can be usefully used as a material of a flexible electronic device.

Claims (13)

A siloxane resin chemically bonded by compounds comprising an alkoxysilane represented by the following formula (1) and an alkoxy metal represented by the following formula (2); And
A resin composition for hard coating comprising a dye having a maximum absorbance at 550 to 700 nm:
???????? R ¹ _n Si (OR ² ) _{4 -n} ????? (1)
M (OR < ³ _> ) _m
Wherein R ¹ is a C ₁ to C ₃ linear alkyl group containing an alicyclic epoxy group, R ² to R ³ are C ₁ to C ₄ linear or branched alkyl groups, M is aluminum, titanium and Zinc, and n is an integer of 1 to 3, and m is an integer of 2 to 4.
The method of claim 1, wherein the alkoxysilane represented by Formula 1 is selected from the group consisting of 2- (3,4-epoxycyclohexyl) ethyltrimethoxysilane, 2- (3,4-epoxycyclohexyl) ethyltriethoxysilane, and 2 - (3,4-epoxycyclohexyl) ethyltripropoxysilane. &Lt; / RTI &gt;
The resin composition for hard coating according to claim 1, wherein the alkoxy metal is contained in an amount of 0.1 to 5.0 mol% based on the total moles of the alkoxysilane.
The resin composition for hard coating according to claim 1, wherein the dye comprises 0.01 to 0.5 parts by weight of the dye relative to 100 parts by weight of the siloxane resin.
The resin composition for hard coating according to claim 1, wherein the siloxane resin further comprises an alkoxysilane represented by the following formula (3)
<Formula 3> Si (OR ^{₄₎ 4}
In Formula 3, R ⁴ is a C ₁ to C ₄ linear or branched alkyl group.
The resin composition for hard coating according to claim 1, wherein the resin composition for hard coating comprises the siloxane resin as a first component and further comprises at least one of an epoxy resin and an acrylic resin as a second component.
The resin composition for hard coating according to claim 6, wherein the first component and the second component are mixed in a weight ratio of 10: 1 to 10: 4.
The method according to claim 6, wherein the second component is a monomer or a copolymer comprising at least one functional group selected from the group consisting of an epoxy group, an oxetane group, an acrylate group, a methacrylate group, a urethane acrylate group and an ethylene oxide (EO) Wherein the resin composition is an oligomer.
The hard coating resin composition according to claim 1, wherein the resin composition for hard coating further comprises at least one additive selected from the group consisting of an organic solvent, a photoinitiator, a thermal initiator, an antioxidant, a leveling agent, Composition.
Polyimide films; And
A polyimide substrate comprising the cured product of the resin composition for hard coating according to any one of claims 1 to 9 as a hard coat layer on at least one side of the polyimide film.
The polyimide substrate according to claim 10, wherein the hard coating layer has a thickness of 5 to 50 탆.
11. The polyimide substrate according to claim 10, wherein the polyimide substrate has a surface hardness of 5H to 9H measured with an upper surface of a direction in which the hard coating layer is formed, measured according to JIS K56000 standard.
The polyimide substrate according to claim 10, wherein the polyimide substrate has a yellowness of 2 or less and a light transmittance at 450 to 750 nm of 85 to 93% as measured using CM-3700D of KONICA MINOLTA Co. .

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