TWI768197B - Flexible display cover substrate - Google Patents

Abstract

A flexible display cover substrate is provided, includes transparent polyimide film and device protective layer. The device protective layer is formed by a hard coating layer, disposed on at least one side of the transparent polyimide film, and the hard coating layer is composed of three or more reactive functional compounds, an initiator, an elastic oligomer, a nano inorganic modified compound, and a fluorescent pigment. The flexible display cover substrate of the present invention, after being folded by a radius of curvature of 1 mm, does not cause cracks on the surface of the hard coat layer or break the substrate, and the yellow index YI of the flexible display cover substrate is less than 2.0.

Description

Flexible display cover substrate

The present invention relates to a flexible display cover substrate, and in particular, to a flexible display cover substrate with excellent bending performance.

In recent years, the development of displays has gradually developed from thin and light to flexible displays that can be bent and deformed. In this development process, the cover substrate used in the flexible display is no longer a traditional glass substrate, but a flexible substrate made of a bendable and flexible material such as plastic (ie, a flexible material). However, the flexible display is prone to wear and scratches on the cover substrate during the deformation process, thereby causing fogging or damage to the display area. In order to solve this problem, a layer of acrylic-based or epoxy-based organic hardened film is generally coated on the surface of the plastic material as a protective layer to improve the hardness of the material, but this organic hardened film is not flexible and exists in bending or impact resistance tests. Surface cracking problem.

In addition to the problem of scratch resistance and abrasion resistance, optical color shift is also a problem that needs to be overcome for the cover substrate. At present, the existing optical-grade plastic substrates include polyethylene terephthalate (PET) products, but the operating temperature is limited because the glass transition temperature is less than 200 °C, and due to the crystalline polymer, fog will occur after long-term folding Thermal and elastic fatigue, so that the display area light emission is affected.

Polyimide has the advantages of high temperature resistance, good chemical resistance and high mechanical strength. After molecular and structural design, the phenomenon of charge transfer between molecules and between molecules can be reduced, and a transparent colorless polyimide film can be obtained. After time folding, no fogging will occur, and it can be used for optical substrate applications such as flexible displays. However, when the thickness of the transparent polyimide film is greater than 50 μm, its yellow chromaticity (YI) will increase accordingly, which affects the appearance of the display.

In order to solve the increase of YI caused by the thickening of the polyimide-covered substrate, in the prior art, it is proposed to add blue pigments such as phthalocyanine, Yangdanone, indophenol, Allium quinone, etc., reduce the yellow index YI by the principle of color complementarity. However, the general absorption wavelength of blue pigment is 550nm to 600nm, which affects the optical transmittance of the cover substrate, and affects the appearance of the product because the cover substrate will produce a bluish light under visible light after being added.

Based on the above, a flexible display cover substrate has been developed, which has excellent bending performance and can reduce the yellow index YI, which is an important subject of current research.

The invention provides a flexible display cover substrate, which can suppress the yellow index YI which is increased due to the increase of the thickness of the transparent polyimide substrate, does not affect the total light transmittance, and has excellent bending performance.

The flexible display cover substrate of the present invention includes a transparent polyimide film and a device protection layer. The device protective layer is formed by a hard coat layer, which is arranged on at least one side of the transparent polyimide film, and the hard coat layer is composed of three or more reactive functional compounds, It is composed of initiator, elastic oligomer, nano inorganic modified particles and fluorescent pigment.

In an embodiment of the present invention, the yellow index YI of the flexible display cover substrate is less than 2.0.

In an embodiment of the present invention, the fluorescent colorant is composed of a photoluminescent material, and has an absorption wavelength of 360 nm to 430 nm and an emission wavelength of 430 nm to 520 nm.

In an embodiment of the present invention, the Stokes shift of the fluorescent colorant is less than 150 nm.

In an embodiment of the present invention, the fluorescent colorant is an organic fluorescent colorant such as Coumarin series, Fluorol 7GA(2-butyl-6-(butylamino)-1H-benz[de]isoquinoline-1 ,3(2H)-dione), Pyridine, 1(1-Ethyl-2-(4-(p-Dimethylaminophenyl)-1,3-butadienyl)-pyridinium Perchlorat), Carbazole, Inorganic Fluorescence Colorants such as phosphors and quantum dots.

In an embodiment of the present invention, based on the total weight of the hard coating, the content of the fluorescent colorant is 0.01 wt % to 1 wt %.

In an embodiment of the present invention, the thickness of the flexible display cover substrate is 50 μm to 130 μm, and the total light transmission rate is more than 90%.

In an embodiment of the present invention, the thickness of the hard coating is 5 μm to 30 μm, and the hardness is 7H to 9H.

In an embodiment of the present invention, the thickness of the transparent polyimide film is 25 μm to 100 μm.

In an embodiment of the present invention, based on the total weight of the hard coat layer, the content of the three or more reactive functional group compounds and the initiator is 10 wt % to 60 wt %.

Based on the above, the flexible display cover substrate of the present invention has a thin hard coating, so it has excellent flexibility, and the hard coating will not crack even after 100,000 bending times with a radius of curvature of 1 mm. At the same time, the introduction of fluorescent colorants can adjust the yellow index of the flexible display cover substrate without affecting the visual color of the screen.

In order to make the above-mentioned features and advantages of the present invention more obvious and easy to understand, the following examples are given and described in detail as follows.

FIG. 1 is a schematic diagram of transmittance and wavelength of Example 5 and Comparative Example 5. FIG.

Figure 2 is a schematic diagram of intensity and wavelength.

As used herein, a range represented by "one value to another value" is a general representation that avoids listing all the values in the range in the specification. Therefore, the recitation of a specific numerical range includes any numerical value within the numerical range and a smaller numerical range defined by any numerical value within the numerical range, as if the arbitrary numerical value and the smaller numerical value were expressly written in the specification. same range. Hereinafter, the embodiment is given as an example in which the present invention can be actually implemented. However, these embodiments are exemplary, and the present disclosure is not limited thereto.

<Flexible display cover substrate>

The invention provides a flexible display cover substrate, which includes a transparent polyimide film and a device protection layer. The protective layer of the device is formed by a hard coating, which is arranged on at least one side of the transparent polyimide film. It is composed of particles and fluorescent pigments, and the hard surface has hydrophobicity with a water drop angle >105°. . After the flexible display cover substrate of the present invention is folded with a radius of curvature of, for example, 1 mm, it will not cause cracks on the surface of the hard coating or breakage of the substrate, and the yellow index YI of the flexible display cover substrate is less than 2.0.

<Transparent Polyimide Film>

The polyimide of the present invention can be composed of the unit represented by the following chemical formula (1):

In the above chemical formula (1), X represents a dianhydride, which may include but is not limited to: 2,2'-bis-(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA), 4 ,4'-diphenyl ether tetracarboxylic anhydride (ODPA), biphenyl tetracarboxylic dianhydride (BPDA), benzophenone tetracarboxylic dianhydride (BTDA), cyclobutane tetracarboxylic dianhydride (CBDA), cyclobutane tetracarboxylic dianhydride (CBDA), Pentanetetracarboxylic dianhydride (CPDA), 3,3',4,4'-diphenyltetracarboxylic anhydride (DSDA), 4,4'-(4,4'-isopropyldiphenoxy) Bis(phthalic anhydride) (BPADA) and 2,2-bis[4-(3,4-dicarboxyphenoxy)phenyl]hexafluoroisopropane dianhydride (HFBPADA), ethylene glycol double anhydride Trimellitic acid ester (TMEG), propylene glycol bis(trimellitic anhydride) (TMPG), bicyclic [2.2.1] Heptane-2,3,5,6-tetracarboxylic dianhydride (BHDA), bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride (BOTDA), bicyclo [2.2.2] A mixture of two or more of them, such as octane-2,3,5,6-tetracarboxylic dianhydride (BODA).

In the above chemical formula (1), Y represents a diamine, which may include, but is not limited to, bis[4-(4-aminophenoxy)phenyl]phenium (BAPS), 2,2'-bis[4 -(4-Aminophenoxy)phenyl]propane (BAPP), 2,2-bis[4-(4-aminophenoxy)phenyl]-1,1,1,3,3,3 - Hexafluoropropane (APHF), 2,2'-bis(trifluoromethyl)benzidine (TFMB), 4,4'-diaminodiphenyl ether (ODA), diaminodiphenylene (3DDS) , 4DDS) and 2,2-bis(4-aminophenyl)hexafluoropropane (BISAF), cyclohexanediamine (CHDA), 1,3-bis(3-aminophenoxy)benzene (TPE-M ), 1,3-bis(4-aminophenoxy)benzene (TPE-R), 1,4-bis(3-aminophenoxy)benzene, 1,4-bis(4-aminophenoxy) A mixture of two or more of them, such as benzene (TPE-Q).

In the polymerization method, the dianhydride monomer and the diamine monomer can be dissolved in a solvent, and then the dissolved dianhydride monomer and the diamine monomer can be mixed and reacted to obtain a polyimide resin (polyimide resin precursor) . For example, the solvent can be aprotic solvent such as N,N-dimethylacetamide, N,N-diethylacetamide, N,N-dimethylformamide and N-methyl-2-pyrrolidone , but not limited to this, other suitable aprotic solvents can also be used.

The method of imidization can use high temperature curing, such as continuous or staged heating of the polyimide resin (polyimide resin precursor). When the polyimide resin is to be made into a film or an insulating layer, the polyimide resin (polyimide resin precursor) can be applied to the substrate first, and then the entire substrate is sent to an oven for heating. maturation. Chemical closed-loop methods can also be used, that is, under nitrogen or oxygen, an unrestricted alkaline test can be used. pyridine, triethylamine or N,N-diisopropylethylamine, etc. and dehydration reagent acetic anhydride are added to the polyimide, after the reaction, the colloid is washed and filtered to obtain polyimide powder, and then Dissolve this powder in a solvent; in addition, a heating ring-closure method can be used to add polyamic acid to an azeotrope reagent, not limited to toluene or xylene, and the temperature is raised to 180 ° C, and the water generated by polyamic acid ring-closure And the azeotropic reagent is removed, and after the reaction is completed, the polyimide solution can be prepared.

In this embodiment, the thickness of the transparent polyimide film is, for example, 25 μm to 100 μm, and the total light transmittance is more than 90%. The polyimide film of the present invention can also add one or two or more kinds of ultraviolet absorbers. The ultraviolet absorber can be selected from the materials commonly used as ultraviolet absorbers in general plastics, and can also be light compounds or inorganic nanomaterials containing absorption wavelengths below 400 nm. As the ultraviolet absorber, benzophenone compounds, salicylate compounds, benzotriazole compounds and triazine compounds can be used, and at least one compound is selected. By adding an ultraviolet absorber, the yellowing and deterioration of the material of the polyimide resin due to ultraviolet irradiation can be suppressed.

<Device Protection Layer>

The device protective layer of the present invention is formed of a hard coat layer, and is disposed on at least one side of the transparent polyimide film. In more detail, the hard coat layer of the present invention is coated on at least one side of the transparent polyimide film and cured by ultraviolet light or heating. The hard coat layer can be prepared by conventional coating methods, including, but not limited to, slot coating, spin coating or inkjet printing. In the present invention, the hard coating is modified by more than 3 reactive functional group compounds, initiators, elastic oligomers, and nano-inorganic compounds. Particles and fluorescent pigments. The content of the three or more reactive functional group compounds and the initiator is, for example, 10 wt % to 60 wt % based on the total weight of the hard coat layer. The content of the fluorescent colorant is, for example, 0.01 wt % to 1 wt % based on the total weight of the hard coat layer.

Curing by ultraviolet light, for example, irradiates the composition with ultraviolet light with a wavelength of 312 nm to 365 nm and an energy of 500 to 10,000 mJ/cm ² , so that the components in the composition undergo a cross-linking reaction and are cured. By heating the curing system, the composition is baked at 150°C to 200°C, and the components in the composition undergo a crosslinking reaction and are cured. In the present invention, the hard coat layer has excellent pencil hardness such as 7H to 9H when the thickness is, for example, 5 μm to 30 μm, and can be folded 100,000 times with a folding radius of 1 mm.

<Three or more reactive functional group compounds>

Examples of more than 3 reactive functional compounds include, but are not limited to, dipentaerythritol hexaacrylate, pentaerythritol triacrylate, dipentaerythritol triacrylate, dipentaerythritol triacrylate, dipentaerythritol acrylate, trimethylol Propane Triacrylate, Trimethylallyl Isocyanurate, Triallyl Isocyanurate, Tetramethyltetravinylcyclotetrasiloxane, Ethoxylated Trimethylolpropane Triacrylate (TMPEOTA), propoxylated glycerol triacrylate (GPTA), pentaerythritol tetraacrylate (PETA), pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate base) acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritol penta(meth)acrylate, tripentaerythritol hepta(meth)acrylate. Three or more reactive functional group compounds may be used alone or in combination of two or more, depending on needs.

<Initiator>

The initiator may be a photoinitiator or a thermal initiator, and may be used alone or in combination of two or more. There is no particular limitation on the preparation amount of the three or more reactive functional group compounds and the initiator. Generally speaking, the composition ratio of the three or more reactive functional group compounds and the initiator is 5:1 to 100:1, and The content of the three or more reactive functional group compounds and the initiator is, for example, 10 wt % to 60 wt % based on the total weight of the hard coating. If the amount of the initiator is above the lower limit, the degree of polymerization will be maintained to a certain extent, and the polymer formed by the monomers will retain the high-molecular properties. If the amount of the initiator is below the upper limit, the polymer formed by the monomer will not have the problem that the polymerization is too high and is brittle. If the amount of the monomer with unsaturated bond is too low, the degree of crosslinking of the polymer is insufficient and it cannot be cured. If the proportion of monomers with unsaturated bonds is too high, the polymer is brittle.

Photoinitiators suitable for use in the present invention include, but are not limited to, acetophenones, such as 2-methyl-1-(4-(methylthiol)phenyl-2-morpholinylpropyl ketone (2 -methyl-1-(4-(methylthio)phenyl)-2-morpholino-propane), 1-hydroxycyclohexyl phenyl ketone, diethoxyacetophenone, 2-hydroxyl -2-methyl-1-phenyl-1-propane (2-hydroxy-2-methyl-1-phenylpropane-1-one), 2-methylphenyl-2-(dimethylamino)-1-[ 4-(morpholinyl)phenyl]-1-butyl-1-one (2-benzyl-2-(dimethylamino)-1-[4-(morpholinyl)phenyl]-1-butanone), other suitable benzene ethyl ketone; benzoins, such as benzoin, benzoin methyl ether, benzyl dimethyl ketal, other suitable benzoins; diphenylketones, such as benzophenone ), 4- 4-phenyl benzophenone, hydroxyl benzophenone, or other suitable benzophenones; thioxanthones, such as isopropyl thioxanthone, 2 -2-chlorothioxanthone, or other suitable thioxanthone; anthraquinones, such as 2-ethylanthraquinone, or other suitable anthraquinone. The above-mentioned photoinitiators can be used alone or in combination of two or more, depending on the needs of users. For example: in order to obtain a faster photospeed, isopropyl thioxanthone can be combined with 2-tolyl-2-(dimethylamino)-1-[4-(morpholinyl)phenyl]-1- Butyl-1-one is mixed and used as a photoinitiator.

Thermal initiators suitable for use in the present invention include, but are not limited to: azos, such as 2,2'-azobis(2,4-dimethyl-n-valeronitrile) (2,2'-azobis(2, 4-dimethyl valeronitrile)), dimethyl-2,2'-azobis(2-methylpropionate) (dimethyl 2,2'-azobis(2-methylpropionate)), 2,2-azobisiso Butyronitrile (2,2-azobisiso butyronitrile, AIBN), 2,2-azobis(2-methylisobutyronitrile) (2,2-azobis(2-methylisobutyronitrile)), 1,1'-azobis (Cyclohexane-1-carbonitrile)(1,1'-azobis(cyclohexane-1-carbonitrile)), 2,2'-azobis[N-2-propyl-2-methylpropionamide]( 2,2'-azobis[N-(2-propenyl)-2-methyl propionamide]), 1-[(cyano-1-methylethyl)-azo]carboxamide (1-[(cyano -1-methylethyl)azo]formamide), 2,2'-azobis(N-butyl-2-methylpropionamide) (2,2'-azobis(N-butyl-2-methylpropionamide)), 2,2'-azobis(N-cyclohexyl-2-methylpropionamide) (2,2'-azobis(N-cyclohexyl-2-methylpropionamide), or other suitable azo initiators; Peroxides, such as benzoyl peroxide, 1,1-bis (tert-butylperoxy)cyclohexane (1,1-bis(tert-butylperoxy)cyclohexane), 2,5-bis(tert-butylperoxy)-2,5-dimethylcyclohexane Alkane (2,5-bis(tert-butylperoxy)-2,5-dimethylcyclohexane), 2,5-bis(tert-butylperoxy)-2,5-dimethyl-3-cyclohexyne (2 ,5-bis(tert-butylperoxy)-2,5-dimethyl-3-cyclohexyne), bis(1-(tert-butylperoxy)-1-methylethyl)benzene(bis(1-(tert -butylpeorxy)-1-methyethyl)benzene), tert-butyl hydroperoxide, tert-butyl peroxide, tert-butyl peroxybenzoic acid -butyl peroxybenzoate), cumene hydroperoxide, cyclohexanone peroxide, dicumyl peroxide, lauroyl peroxide, or others suitable peroxide. The above-mentioned thermal initiators may be used alone or in combination of two or more, depending on the needs.

<Elastomeric oligomer>

The elastic oligomer can be an oligomer of urethane (meth)acrylic acid, which can be formed by the reaction of hydroxy (meth)acrylate and diisocyanate. Among them, hydroxy (meth)acrylate can be synthesized from (meth)acrylate or acryl and polyol, and (meth)acrylate can be methyl (meth)acrylate, ethyl (meth)acrylate, ( isopropyl meth)acrylate, butyl (meth)acrylate, cyclohexyl (meth)acrylate). The polyol can be ethylene glycol, 1,3 propylene glycol, diethylene glycol, neopentyl glycol, 1,4-butanediol, 1,6-hexanediol, 1,5-pentanediol, trihydroxy Methyl propane, glycerol, 1,3,5-triol, pentaerythritol, dipentaerythritol, etc. The diisocyanate can be hexamethylene diisocyanate, 2,4-toluene diisocyanate, xylene diisocyanate, trimethylhexamethylene diisocyanate, 4-diphenylmethane diisocyanate, 1,5 naphthalene diisocyanate and the like. Urethane (meth)acrylic oligomer products such as U-2PPA, U10-HA, U10-PA, UA-1100H, UA-15HA, UA-33H, U-200PA produced by Shin-Nakamura Chemical can also be used , UA-290TM, UA-160TM, UA-122P, etc. Risheng Chemical produces UO22-081, UO26-001, UO22-162, UO52-002, UO26-012, UO22-312, etc. The added elastic oligomer has a molecular weight of 500 g/mol to 5000 g/mol, and based on the total weight of the hard coating, the content is, for example, 0.1 wt % to 10 wt %.

<Nano-inorganic modified particles>

The nano-inorganic modified particles can be obtained by reacting a reaction component comprising unmodified nano-inorganic particles with a modifying agent. In the reaction components, the content of the inorganic nano particles is preferably 90-98% by weight; the content of the modifier is preferably 2-10% by weight. Nano-inorganic particles suitable for the present invention include, but are not limited to, nano-inorganic metal oxide particles such as titanium dioxide, silicon dioxide, zirconium oxide, zinc oxide, and aluminum oxide. Modifiers suitable for use in the present invention may be silane coupling agents, which are organosilicon compounds containing chlorosilanes, alkoxysilanes, or silazanes. The functional groups contained in the silane coupling agent may include vinyl, methacryloyloxy, acryloxy, amine, urea, chloropropyl, mercapto, polysulfide or isocyanate, but are not limited thereto . Examples of silane coupling agents may include, but are not limited to: vinyltrichlorosilane, vinyltrimethoxysilane, vinyltriethoxysilane, 3-methacryloyloxypropyl-methyldimethoxysilane , 3-methacryloyloxypropyl-trimethoxysilane, 3-methacryloyloxypropyl-methyldiethoxysilane, 3-methacryloyloxypropyl-triethoxysilane, 3-Propenyloxypropyltrimethoxysilane, N-2-aminoethyl-3-aminopropylmethyldimethoxysilane, N-2-aminoethyl-3-aminopropyltrimethoxysilane, N-2-aminoethyl-3-aminopropyl Triethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, N-phenyl-3-aminopropyltrimethoxysilane, 3-chloropropyltriethoxysilane Silane, 3-mercaptopropyltrimethoxysilane, bis(triethoxysilylpropyl)tetrasulfide, 3-isocyanatopropyltriethoxysilane.

The mixing method of the nano-inorganic modified particles, the monomer with unsaturated bonds and the initiator is not particularly limited, and generally can be uniformly mixed by ball milling, screw, planetary mixing or stirring. Based on the total weight of the hard coating, the content of the modified nano-inorganic particles is, for example, 40 wt % to 80 wt %.

<Fluorescent Pigment>

The fluorescent colorant is composed of photoluminescent materials, and has an absorption wavelength of 360nm to 430nm and an emission wavelength of 430nm to 520nm. The Stokes shift of the fluorescent pigment is less than 150 nm, and the Stokes shift refers to the difference between the strongest wavelengths in the absorption spectrum and the emission spectrum of the same electronic transition. Fluorescent pigments are organic fluorescent pigments such as Coumarin series such as Coumarin 1, Coumarin 2, Coumarin 4, Coumarin 7, Coumarin 30, Coumarin 47, Fragrance Coumarin 102, Coumarin 151, Coumarin 152, Coumarin 152A, Coumarin 153, Coumarin 307, Coumarin 314, Coumarin 500, Coumarin 510, Coumarin 522, Coumarin Soybean 6H, etc. or other organic fluorescent pigments such as Fluorol 7GA(2-butyl-6-(butylamino)-1H-benz[de]isoquinoline-1,3(2H)-dione), Pyridine 1( 1-Ethyl-2-(4-(p-Dimethylaminophenyl)-1,3-butadienyl)-pyridiniu m Perchlorat), carbazole (Carbazole) and the like. The fluorescent colorant can also be an inorganic fluorescent colorant such as fluorescent powder and quantum dots, the particle size of which is less than 100 nm. The content of the fluorescent colorant is, for example, 0.01 wt % to 1 wt % based on the total weight of the hard coat layer. The fluorescent pigment can be dissolved or dispersed in an organic solvent, and the organic solvent can be ethyl acetate, n-butyl acetate, γ-butyrolactone, ethanol, isopropanol, propylene glycol, acetone, methyl ethyl ketone or cyclopentanone and other solvents.

Hereinafter, the polyimide films of the above-mentioned embodiments will be described in detail by means of experimental examples. However, the following experimental examples are not intended to limit the present invention.

Experimental example

In order to prove that the flexible display cover substrate of the present invention has good performance, this experimental example is specially made below.

Preparation example

The composition for preparing the hard coating can be hardened by heat or light to form a coating with high hardness. The modified nano-inorganic particles in the hard coat were obtained by mixing 1 part by weight of the nano-silica particle solution with 0.01 part by weight of 3-methacryloyloxypropyl-trimethoxysilane, and adding it to Heating at 50°C under nitrogen and reacting for 4 hours to carry out modification synthesis. After the reaction was completed, the temperature was lowered to room temperature, and 1 part by weight of the modified nanoparticle solution was added to 0.133 parts by weight of dipentaerythritol hexaacrylate and 0.133 parts by weight of elastic oligomer UA160-TM and stirred for 30 minutes. Perform solution phase inversion. Finally, a solution of 1.5 parts by weight of the modified nano-inorganic particles and a monomer with unsaturated bonds is mixed with 0.03 parts by weight of 2-methyl-1-(4-(methylthiol) Phenyl-2-morpholinyl propyl ketone, and 0.01 part by weight of a leveling agent were mixed, and the final solid content was adjusted to 55% with solvent ethyl acetate. Add appropriate concentration of fluorescent pigments to obtain the compositions required by the subsequent examples and comparative examples.

Example 1

Take 20 g of the above hard coating composition, add 0.11 g of Coumarin 1 (1% dissolved in ethyl acetate), and after stirring and mixing for 30 minutes, spin-coat at 250 rpm for 10 seconds on a transparent polyimide (CPI) substrate. The surface was soft baked at 80°C for 5 minutes, then exposed at 500mJ/cm ² , and finally hard baked at 180°C for 30 minutes.

Example 2

Take 20 g of the above-mentioned hard coating composition, add 3 g of Coumarin 1 (1% dissolved in ethyl acetate), and after stirring and mixing for 30 minutes, spin-coat at 250 rpm for 10 seconds on the surface of a transparent polyimide (CPI) substrate , bake at 80°C for 5 minutes, then expose at 500mJ/cm ² , and finally bake at 180°C for 30 minutes.

Example 3

Take 20 g of the above-mentioned hard coating composition, add 1.1 g of Coumarin 1 (5% dissolved in ethyl acetate), and after stirring and mixing for 30 minutes, spin-coat at 250 rpm for 10 seconds on a transparent polyimide (CPI) substrate. The surface was soft baked at 80°C for 5 minutes, then exposed at 500mJ/cm ² , and finally hard baked at 180°C for 30 minutes.

Example 4

Take 20 g of the above hard coating composition, add 2.2 g of Coumarin 1 (5% dissolved in ethyl acetate), and after stirring and mixing for 30 minutes, spin-coat at 250 rpm for 10 seconds on a transparent polyimide (CPI) substrate. The surface was soft baked at 80°C for 5 minutes, then exposed at 500mJ/cm ² , and finally hard baked at 180°C for 30 minutes.

Example 5

Take 20 g of the above-mentioned hard coating composition, add 3 g of Coumarin 7 (1% dissolved in ethyl acetate), and after stirring and mixing for 30 minutes, spin-coat at 250 rpm for 10 seconds on the surface of a transparent polyimide (CPI) substrate , bake at 80°C for 5 minutes, then expose at 500mJ/cm ² , and finally bake at 180°C for 30 minutes.

Example 6

Take 20 g of the above hard coating composition, add 3 g of Fluorol 7GA (1% dissolved in ethyl acetate), after 30 minutes of stirring and mixing, spin-coat on the surface of a transparent polyimide (CPI) substrate at 250 rpm for 10 seconds , bake at 80°C for 5 minutes, then expose at 500mJ/cm ² , and finally bake at 180°C for 30 minutes.

Comparative Example 1

Take 20 g of the above hard coating composition, spin-coat at 250 rpm for 10 seconds on the surface of a transparent polyimide (CPI) substrate, soft bake at 80 ° C for 5 minutes, then expose at 500 mJ/cm ² , and finally use 180 ° C hard bake 30 minutes.

Comparative Example 2

Take 20 g of the above hard coating composition, add 0.09 g of Coumarin 1 (1% dissolved in ethyl acetate), and after stirring and mixing for 30 minutes, spin-coat at 250 rpm for 10 seconds on a transparent polyimide (CPI) substrate. The surface was soft baked at 80°C for 5 minutes, then exposed at 500mJ/cm ² , and finally hard baked at 180°C for 30 minutes.

Comparative Example 3

Take 20 g of the above-mentioned hard coating composition, and add 2.4 g of Coumarin 1 (5% dissolved in ethyl acetate). The surface was soft baked at 80°C for 5 minutes, then exposed at 500mJ/cm ² , and finally hard baked at 180°C for 30 minutes.

Comparative Example 4

Take 20 g of the above hard coating composition, add 1 g of CuPc (Copper (II) phthalocyanine, copper phthalocyanine, 0.25% mixed in n-butyl acetate), after 30 minutes of stirring and mixing, spin coating at 250 rpm for 10 seconds on transparent The surface of the polyimide (CPI) substrate was soft baked at 80°C for 5 minutes, then exposed at 500mJ/cm ² , and finally hard baked at 180°C for 30 minutes.

Comparative Example 5

Take 20 g of the above hard coating composition, add 1.5 g of CuPc (2% mixed in n-butyl acetate), after 30 minutes of stirring and mixing, spin-coat at 250 rpm for 10 seconds on the transparent polyimide (CPI) substrate. The surface was soft baked at 80°C for 5 minutes, then exposed at 500mJ/cm ² , and finally hard baked at 180°C for 30 minutes.

Comparative Example 6

Take 50g of the above hard coating composition, and add 1g of pigment Blue 60 (0.25% mixed in n-butyl acetate), after 30 minutes of stirring and mixing, spin-coat at 250rpm for 10 seconds on a transparent polyimide (CPI) substrate On the surface, soft bake at 80°C for 5 minutes, then expose at 500mJ/cm ² , and finally bake at 180°C for 30 minutes.

performance evaluation Thickness measurement

Use a thickness gauge to measure the thickness of each plastic substrate, and then use the Alpha Step to measure the thickness of the hard coat on the plastic substrate.

Determination of Pencil Hardness

Using an electronic pencil hardness tester, use a Mitsubishi test pencil at a speed of 30mm/min under a load of 750g to draw a line of 10mm length on each cover substrate five times, and then observe the surface scratches to compare the pencil hardness.

Total light transmittance (%) and haze

The total light transmittance and haze of the cover substrate were measured using a Nippon Denshoku DOH 5500 according to ASTM D1007.

Determination of yellow index YI

The yellowness index YI value of the cover substrate was measured using Nippon Denshoku DOH 5500 according to ASTM E313.

The yellow index YI is a tristimulus value (x, y, z) measured by measuring the transmittance of light of 400-700 nm with a spectrophotometer, and YI is calculated by the following formula.

YI=100×(1.2769x-1.0592z)/y

Bending performance

The cover substrate was attached to a folding tester (YUASA System U-shape Folding) and folded 100,000 times at R=1mm. First, the cover substrate was observed for cracks, and then the hard coat was observed with the naked eye and a microscope for cracks. Any cracks in the cover substrate or cracks in the hard coat were marked as unacceptable (X), and those without cracks and cracks were marked as acceptable (O).

The test results of the aforementioned performance evaluation are recorded in Table 1.

It can be known from Comparative Example 1 that the YI value is significantly larger (>2) without any hue adjustment material, which is mainly due to the increase in the yellowness index caused by the increase in the thickness of the transparent polyimide film. The results of Examples 1 to 4 and Comparative Example 2 and Comparative Example 3 show that the addition of fluorescent colorant can obviously improve the yellow index YI of the covered substrate, but when the amount of fluorescent colorant added is less than 0.01%, the concentration is too high. Low makes the blue light intensity excited by the fluorescent color material insufficient, and cannot effectively reduce the yellow index YI. The results also show that with the increase of the concentration of fluorescent pigments, the yellow index can gradually decrease, but when the concentration is too high, the fluorescence intensity will be weakened due to the quantum confinement effect, and the yellow index YI cannot be effectively reduced. Comparative example 4 to comparative example 6 is to add blue pigment, The blue pigment can effectively balance the color, so that the yellow index can be significantly reduced, and the more you add, the lower the yellow index or even the negative value. However, the light transmittance of the cover substrate also decreases with the addition of blue pigment, and the appearance of the cover substrate also changes from colorless and transparent to light blue, which affects the appearance of the product. From the visible light spectra of Example 5 and Comparative Example 5 (Fig. 1), it can be clearly shown that the addition of blue pigment will have absorption at the wavelength of 550-600nm, which will affect the penetration of visible light; 420nm has absorption, which only affects the penetration of violet light and near-ultraviolet light, so the penetration ability of visible light is better than adding blue colorant. Figure 2 shows that after adding the fluorescent colorant, blue fluorescence will be generated under excitation at 400nm and 410nm, the maximum emission wavelength is 450nm, and the maximum emission intensity is at 410nm excitation. And the blue pigment is directly added to the hard coat, because the blue pigment cannot be dissolved in the solvent, and can only be mixed into the hard coat by means of suspension. Since the blue pigment does not have a photocrosslinking reaction with the hard coat paint, if the blue pigment particles are too large, it is very likely to cause defects in the hard coat, making the hard coat easy to produce during folding. Cracks affect the folding of the cover substrate.

To sum up, the flexible display cover substrate of the present invention has a thin hard coating, so it has excellent performance in flexibility, and the hard coating will not crack after 100,000 times of bending with a radius of curvature of 1 mm. . At the same time, the introduction of the fluorescent colorant can adjust the yellow index of the flexible display cover substrate without affecting the visual color of the screen, effectively solving the disadvantage that the appearance of the display is affected in the prior art.

Although the present invention has been disclosed above through the embodiments, it is not intended to limit the present invention, and any person with ordinary knowledge in the technical field does not depart from the present invention. Within the spirit and scope, some changes and modifications can be made, so the protection scope of the present invention should be determined by the scope of the appended patent application.

Claims (9)

A flexible display cover substrate, comprising: a transparent polyimide film; and a device protection layer, formed by a hard coating, disposed on at least one side of the transparent polyimide film, the hard coating is composed of three The above reactive functional group compounds, initiators, elastic oligomers, nano-inorganic modified particles and fluorescent colorants are composed, wherein based on the total weight of the hard coating, the three or more reaction The content of the functional group compound and the initiator is 10 wt % to 60 wt %, and the fluorescent colorant has an absorption wavelength of 360 nm to 430 nm. The flexible display cover substrate according to claim 1, wherein the yellow index YI of the flexible display cover substrate is less than 2.0. The flexible display cover substrate according to claim 1, wherein the fluorescent colorant is composed of a photoluminescent material and has an emission wavelength of 430 nm to 520 nm. The flexible display cover substrate according to claim 1, wherein the Stokes shift of the fluorescent colorant is less than 150 nm. The flexible display cover substrate according to claim 1, wherein the fluorescent pigments are Coumarin 1, Coumarin 2, Coumarin 4, Coumarin 7, Coumarin 30, Coumarin Coumarin 47, Coumarin 102, Coumarin 151, Coumarin 152, Coumarin 152A, Coumarin 153, Coumarin 307, Coumarin 314, Coumarin 500, Coumarin 510, Coumarin Fluorine 522, Coumarin 6H, Fluorol 7GA(2-butyl-6-(butylamino)-1H-benz[de]isoquinoline-1,3(2H)-dione), Pyridine (1-Ethyl-2-(4-(p-Dimethylaminophenyl)-1,3-butadienyl)-pyridinium Perchlorat), Carbazole, phosphor or quantum dots. The flexible display cover substrate according to claim 1, wherein the content of the fluorescent colorant is 0.01 wt % to 1 wt % based on the total weight of the hard coat layer. The flexible display cover substrate according to claim 1, wherein the flexible display cover substrate has a thickness of 50 μm to 130 μm, and a total light transmittance of more than 90%. The flexible display cover substrate according to claim 1, wherein the hard coating has a thickness of 5 μm to 30 μm and a hardness of 7H to 9H. The flexible display cover substrate according to claim 1, wherein the transparent polyimide film has a thickness of 25 μm to 100 μm.

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