TWI776038B - Polyimide film and flexible display device cover substrate using the same - Google Patents

Abstract

A polyimide film and a flexible display device cover substrate using the same are provided, and the polyimide film includes a polyimide and an blue infrared absorbing agent. The blue infrared absorbing agent includes cerium tungsten oxide, tungsten oxide, Prussian blue or tin oxide. The blue infrared absorbing agent has infrared absorbing and photothermal conversion effects, and the surface temperature of the polyimide resin can be enhanced by infrared irradiation, so as to shorten the baking time.

Description

Polyimide film and flexible display device cover substrate using the same plate

The present invention relates to a polyimide film and a flexible display device covering substrate using the same, and particularly to a polyimide film containing a blue infrared absorbing agent and a flexible display device covering substrate using the same.

With the development of displays, thinning, light weight and even flexibility are the current development directions of displays. Therefore, how to reduce the thickness and weight of glass substrates or even replace glass substrates with plastic substrates is an important direction currently considered by the industry.

Polyimide polymer is a plastic material with thermal stability, high mechanical strength and chemical resistance. However, due to the molecular structure relationship, it is easy to cause charge transfer between molecules and between molecules, resulting in the yellow color of the polyimide film, which limits its application. In order to reduce the phenomenon of charge transfer, a linkage group can generally be introduced to make the main chain flexible, or some larger groups can be introduced to destroy its stacking, which can also achieve the effect. As described above, such as: (-O-), (-CO-), (-CH ₂ -), (-CF ₃ CCF ₃ -), etc., or introduce alicyclic structure into polyimide. Although these methods can make the polyimide transparent, when the thickness of the polyimide film increases, the yellowness index YI of the film also increases, resulting in a yellowish appearance visually.

Since polyimide needs to undergo an imidization step during the film forming process, whether it is thermal imidization or chemical imidization, it needs to be baked at a high temperature of 250°C to 400°C. In order to increase production efficiency and reduce baking Baking time, currently the industry will choose to use infrared heating. However, fluorine-containing functional groups and alicyclic structures are introduced for transparency, so that the polyimide does not absorb in the infrared region, so that the infrared heating process cannot be used.

Based on the above, a polyimide film has been developed, which can increase the surface temperature of the polyimide resin by irradiating infrared rays, thereby shortening the baking time, which is an important subject of current research.

The present invention provides a polyimide film and a flexible display device covering substrate using the same. The polyimide film contains a blue infrared absorbing agent with infrared absorption and photothermal conversion effects. Therefore, the polyimide film can be irradiated with infrared rays to enhance the polyimide The surface temperature of the imine resin is close to shorten the baking time.

The polyimide film of the present invention includes polyimide and a blue infrared absorbing agent, and the blue infrared absorbing agent includes cesium tungsten oxide, tungsten oxide, Prussian blue or tin antimony oxide.

In an embodiment of the present invention, the polyimide film has a wavelength of 800 nm to 4000nm has an absorption peak.

In an embodiment of the present invention, the thickness of the polyimide film is 10 μm to 100 μm, the total light transmittance is more than 85%, and the yellowness index YI is less than 2.

In an embodiment of the present invention, the absorption wavelength of the blue infrared absorbing agent is 500 nm to 4000 nm, and the thermal conversion efficiency of the blue infrared absorbing agent is greater than 50%.

In an embodiment of the present invention, the particle size of the blue infrared absorber is less than 100 nm.

In an embodiment of the present invention, based on the total weight of the polyimide film, the content of the blue infrared absorber is 0.05wt% to 0.5wt%.

In an embodiment of the present invention, the polyimide film further includes a hue adjustment material, and the hue adjustment material includes a blue dye, a blue pigment, and a fluorescent dye with an absorption wavelength of 360 nm to 430 nm and an emission wavelength of 430 nm to 530 nm. or fluorescent pigments.

In an embodiment of the present invention, based on the total weight of the polyimide film, the content of the blue dye or blue pigment is 0.001 wt % to 0.01 wt %.

In an embodiment of the present invention, based on the total weight of the polyimide film, the content of the fluorescent dye or fluorescent pigment is 0.001 wt % to 0.5 wt %.

In an embodiment of the present invention, the blue infrared absorbing agent has a hue adjustment function.

The present invention also provides a cover substrate for a flexible display device, which includes the above-mentioned polyimide film and a device protection layer. The device protective layer is formed of a hydrophobic hard coating and is disposed on at least one side of the polyimide film.

In an embodiment of the present invention, the total light transmittance of the cover substrate of the flexible display device is more than 85%, and the thickness is 50 μm to 200 μm.

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

In an embodiment of the present invention, the hydrophobic hard coating contains a blue infrared absorbing agent and a hue adjustment material, and the hue adjustment material includes a blue dye, a blue pigment, the absorption wavelength is 360nm to 430nm, and the emission wavelength is 430nm Fluorescent dyes or fluorescent pigments to 530nm.

In an embodiment of the present invention, based on the total weight of the hydrophobic hard coating, the content of the blue infrared absorber is 0.05wt% to 0.5wt%.

In an embodiment of the present invention, the content of the blue dye or blue pigment is 0.001 wt % to 0.01 wt % based on the total weight of the hydrophobic hard coat layer.

In an embodiment of the present invention, the content of the fluorescent dye or fluorescent pigment is 0.001 wt % to 0.5 wt % based on the total weight of the hydrophobic hard coating.

Based on the above, the polyimide film of the present invention contains a blue infrared absorber with infrared absorption and photothermal conversion effects, so the surface temperature of the polyimide resin can be increased by infrared irradiation, and the baking time can be shortened. Reducing energy consumption and increasing production rate can also reduce the yellowness index YI of polyimide, and improve the appearance and visual yellowish phenomenon.

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.

1 is a schematic diagram of transmittance and wavelength of Example 4, Example 6, Comparative Example 1 and Comparative Example 3.

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.

The present invention provides a polyimide film, which can be used as a cover substrate of a flexible display device. 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.

<Polyimide film>

The present invention provides a polyimide film, which includes polyimide and a blue infrared absorbing agent. The blue infrared absorbing agent has the effects of infrared absorption and photothermal conversion, and also has the effect of hue adjustment, and the thermal conversion efficiency is about 50%. , the surface temperature of the polyimide resin can be increased by infrared irradiation, and the surface temperature of the polyimide film after infrared irradiation can reach above 300 ℃, shortening the baking time. The polyimide film of the present invention has an absorption peak at a wavelength of about 800 nm to about 4000 nm, a thickness of, for example, 10 μm to 100 μm, a total light transmittance of, for example, more than 85%, and a yellow index. YI is less than 2, for example. The content of the infrared absorber is, for example, 0.05 wt % to 0.5 wt % based on the total weight of the polyimide film. Hereinafter, the above-mentioned various components will be described in detail.

<Blue infrared absorber>

The infrared absorber of the present invention is, for example, composed of inorganic nano-particles, preferably an infrared absorber whose powder is blue, and the particle size is less than 100 nm, which may include cesium tungsten oxide, tungsten oxide, Prussian blue or oxide Tin antimony. Nanoparticles can be synthesized by sol-gel method, hydrothermal method, solvothermal method, microwave synthesis method, etc., or sintered into micron powder by powder metallurgy, and then obtained by dry or wet grinding. The blue infrared absorber can also be used as a hue adjuster and an ultraviolet absorber, which can reduce the yellow index of transparent polyimide, and reduce the yellowing caused by UV irradiation for a long time, and has a hue adjustment effect.

<Polyimide>

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'-isopropyl bis(phthalic anhydride) (BPADA) and 2,2-bis[4-(3,4-dicarboxyphenoxy)phenyl]hexafluoroisopropane dianhydride (HFBPADA), Ethylene glycol bis-anhydro trimellitate (TMEG), propylene glycol bis(trimellitic anhydride) (TMPG), bicyclo[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]octane-2,3,5,6-tetracarboxylic dianhydride A mixture of two or more of them, such as (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). To convert polyimide resin When making a film or an insulating layer, the polyamide resin (polyimide resin precursor) can be coated on the substrate first, and then the entire substrate is sent to an oven for heating for curing. The chemical method of ring closure can also be used, that is, under nitrogen or oxygen, an unlimited basic reagent such as pyridine, triethylamine or N,N-diisopropylethylamine and the dehydration reagent acetic anhydride are added to the polyamide In acid, after the reaction is completed, the colloid is washed and filtered to obtain polyimide powder, and then the powder is dissolved in a solvent; Not limited to toluene or xylene, the temperature is raised to 180°C to remove the water and the azeotropic reagent produced by the ring closure of the polyimide. After the reaction is completed, the polyimide solution can be obtained.

<Hue adjustment material>

In the present invention, in addition to adding an infrared absorber to reduce the yellow index YI of the film, the polyimide film may further include a hue adjustment material, and the hue adjustment material may include a blue dye, a blue pigment, and the absorption wavelength is 360nm to 430nm and Fluorescent dyes or fluorescent pigments that emit light at a wavelength of 430nm to 530nm.

In this embodiment, the blue dye and blue pigment may include Ultramarine; metal phthalocyanines such as Pigment 15, Pigment 15:1, Pigment 15:2, Pigment 15:3, Pigment 15: 4; Allium quinone pigments such as Pigment blue 60; Indigo pigments such as Indigo. The content of the blue dye or blue pigment is, for example, 0.001 wt % to 0.01 wt % based on the total weight of the polyimide film.

In this embodiment, the blue dye and the blue pigment are mechanically ground and dispersed, for example, by grinding media such as zirconia, alumina, silicon carbide, etc. Collision and shearing, so that the material can be suspended and dispersed in the organic solvent, and after grinding, the secondary particle size of the material can be less than 200 nanometers. Mechanical grinding and dispersing methods can be ball mill (Ball mill), attritor mill (Attritor mill), high-efficiency bead mill (Media mill), etc. The organic solvent can be ethyl acetate, n-butyl acetate, γ-butyl Solvents such as lactone, ethanol, isopropanol, propylene glycol, acetone, methyl ethyl ketone and cyclopentanone.

In this embodiment, the fluorescent dyes and fluorescent pigments may include Coumarin series, such as 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, Fragrance Pyridine 522, Coumarin 6H; Pilot 512, Fluorol 7GA, Pyridine 1, Carbazole, etc. The content of the fluorescent dye or fluorescent pigment is, for example, 0.001 wt % to 0.5 wt % based on the total weight of the polyimide film.

<UV Absorber>

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.

<Flexible Display Device Covering Substrate>

The present invention also provides a cover substrate for a flexible display device, comprising the above-mentioned poly Imide films and device protection layers. The device protective layer can be formed of a hydrophobic hard coating layer and is disposed on at least one side of the polyimide film. The total light transmittance of the cover substrate of the flexible display device of the present invention is more than 85%, and the thickness is, for example, 50 μm to 200 μm. The thickness of the hydrophobic hard coat layer is, for example, 5 μm to 30 μm, and the hardness is, for example, 7H to 9H.

In this embodiment, the hydrophobic hard layer can be coated on either side of the polyimide film and cured by ultraviolet light or heating. The hydrophobic hard 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 hydrophobic hard layer is composed of three or more reactive functional group compounds, initiators, elastic oligomers, and nano-inorganic modified particles, and blue can also be added to the hydrophobic hard layer. The infrared absorber and the hue modifier are used to adjust the yellow index YI of the covering substrate. The hue modifier can include blue dyes, blue pigments, and fluorescence with absorption wavelengths such as 360nm to 430nm and emission wavelengths such as 430nm to 530nm. Dyes or fluorescent pigments. In more detail, the content of the blue infrared absorbing agent is, for example, 0.05 wt % to 0.5 wt % based on the total weight of the hydrophobic hard coat layer. The content of the blue dye or blue pigment is, for example, 0.001 wt % to 0.01 wt % based on the total weight of the hydrophobic hard coat layer. The content of the fluorescent dye or fluorescent pigment is, for example, 0.001 wt % to 0.5 wt % based on the total weight of the hydrophobic hard coat layer.

Examples of the above-mentioned three or more reactive functional compounds include but are not limited to dipentaerythritol hexaacrylate, pentaerythritol triacrylate (pentaerythritoltriacrylate), dipentaerythritol triacrylate (dipentaerythritoltriacrylate), dipentaerythritol acrylate (dipentaerythritolacrylate), pentaerythritol hexaacrylate (pentaerythritolhexaacrylate), trimethylolpropane triacrylate, trimethallyl isocyanurate, triallyl isocyanurate, tetramethyltetraethylene Cyclotetrasiloxane, Ethoxylated Trimethylolpropane Triacrylate (TMPEOTA), Propoxylated Glycerol Triacrylate (GPTA), Pentaerythritol Tetraacrylate (PETA), Pentaerythritol Tri(meth)acrylic Acid ester, pentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)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.

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 -Hydroxy-2-methyl-1-phenylpropane-1-one (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 acetophenone; benzoins, such as benzoin, benzoin methyl ether, benzyl dimethyl ketal, other suitable benzoins; diphenyl ketones, such as diphenyl ketone (benzophenone), 4-phenyl benzophenone (4-phenyl benzophenone), hydroxyl benzophenone, or other suitable benzophenone; thioxanthones, such as isopropyl thioxanthone (isopropyl thioxanthone), 2-chlorothioxanthone (2-chlorothioxanthone), or other suitable thioxanthone; anthraquinones, such as 2-ethylanthraquinone (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 yl)-azo]formamide (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 Alkane (1,1-bis(tert-butylperoxy)cyclohexane), 2,5-bis(tert-butylperoxy)-2,5-dimethylcyclohexane (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 peroxybenzoate, anisyl hydroperoxide ( cumene hydroperoxide), cyclohexanone peroxide, dicumyl peroxide, lauroyl peroxide, or other suitable peroxide. The above thermal initiators In addition to being used singly, two or more kinds can also be used in combination, depending on the needs.

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, trimethyl hexamethylene diisocyanate, 4-diphenylmethane diisocyanate, 1,5 naphthalene diisocyanate, etc. . 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 %.

The modified nano-inorganic 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. The modifier suitable for the present invention can be a silane coupling agent, which includes chlorosilane, alkoxysilane Or organosilicon compounds of 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-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, N-phenyl-3-aminopropyltrimethyl Oxysilane, 3-chloropropyltriethoxysilane, 3-mercaptopropyltrimethoxysilane, bis(triethoxysilylpropyl)tetrasulfide, 3-isocyanatopropyltriethoxysilane .

The mixing method of the modified nano-inorganic particles, the monomers 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 %.

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 polyimide film of the present invention has good performance, this experimental example is specially made below.

Preparation of polyimide solutions Synthesis Example 1

8.97g (0.028mole) of 2,2'-bis(trifluoromethyl)benzidine (TFMB), 2.40g (0.012mole) of 4,4'-diaminodiphenyl ether (ODA) and 100g The dimethylacetamide (DMAc) was placed in a three-necked flask. After stirring at 30°C until completely dissolved, 8.8g (0.02mole) of 2,2'-bis-(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) and 5.88g (0.02mole) of Biphenyltetracarboxylic dianhydride (BPDA), followed by continuous stirring and reacting at 25° C. for 24 hours, can obtain a polyamic acid solution. After that, 7.46 g (0.06 mole) of pyridine and 12.252 g (0.12 mole) of acetic anhydride were further added, followed by continuous stirring and reaction at room temperature for 24 hours. After the reaction, polyimide was precipitated with methanol/water (volume ratio 1:2) solution, and the powder was collected by filtration and dried to obtain polyimide powder. Finally, the powder was dissolved in dimethylacetamide solvent to form a 20wt% polyimide solution.

Preparation of Polyimide Films Example 1

Take 100 grams of the polyimide solution of Synthesis Example 1 and add 0.86 grams of cesium tungsten oxide CsWO ₃ (particle size 50nm is dispersed in dimethylacetamide, the concentration is 5wt%), after 30 minutes of stirring and mixing, scraper coating Surface-drying is performed on the glass substrate and in the oven, and the surface-drying temperature is 100°C. Then, the polyimide film can be obtained by heating and baking with an infrared wavelength of 800 nm to 3000 nm for 10 minutes in a nitrogen environment.

Example 2

Take 100 grams of the polyimide solution of Synthesis Example 1, add 0.9 grams of Prussian blue (particle size 20nm is dispersed in dimethylacetamide, the concentration is 5wt%), after 30 minutes of stirring and mixing, the scraper is coated on the glass substrate And as for the drying oven, the surface drying temperature is 100°C. Then, the polyimide film can be obtained by heating and baking with an infrared wavelength of 800 nm to 3000 nm for 10 minutes in a nitrogen environment.

Example 3

Take 100 grams of the polyimide solution of Synthesis Example 1 and add 0.9 grams of tungsten oxide WO ₃ (particle size 20nm is dispersed in dimethylacetamide, the concentration is 5wt%), after 30 minutes of stirring and mixing, the scraper is coated on The glass substrate was surface-dried in an oven, and the surface-drying temperature was 100°C. Then, the polyimide film can be obtained by heating and baking with an infrared wavelength of 800 nm to 3000 nm for 10 minutes in a nitrogen environment.

Example 4

Get 100 grams of polyimide solution of synthesis example 1 and add 1.68 grams of cesium tungsten oxide CsWO ₃ (particle size 50nm is dispersed in dimethylacetamide, concentration is 5wt%), after 30 minutes of stirring and mixing, scraper coating Surface-drying is performed on the glass substrate and in the oven, and the surface-drying temperature is 100°C. Then, the polyimide film can be obtained by heating and baking with an infrared wavelength of 800 nm to 3000 nm for 10 minutes in a nitrogen environment.

Example 5

Take 100 grams of the polyimide solution of Synthesis Example 1 and add 0.2 grams of cesium tungsten oxide CsWO ₃ (particle size 50nm is dispersed in dimethylacetamide, the concentration is 5wt%), after 30 minutes of stirring and mixing, scraper coating Surface-drying is performed on the glass substrate and in the oven, and the surface-drying temperature is 100°C. Then, the polyimide film can be obtained by heating and baking with an infrared wavelength of 800 nm to 3000 nm for 10 minutes in a nitrogen environment.

Example 6

Take 100 g of the polyimide solution of Synthesis Example 1, add 0.9 g of Prussian blue (particle size 20nm dispersed in dimethylacetamide, concentration is 5wt%) and 0.2g Pigment blue 15 (particle size 100nm dispersed in dimethylacetamide) Acetamide, with a concentration of 0.1 wt %), after stirring and mixing for 30 minutes, a doctor blade was applied to the glass substrate, and the surface drying temperature was 100° C. in an oven. Then, the polyimide film can be obtained by heating and baking with an infrared wavelength of 800 nm to 3000 nm for 10 minutes in a nitrogen environment.

Example 7

Take 100 g of the polyimide solution of Synthesis Example 1, add 0.9 g of Prussian blue (particle size 20nm dispersed in dimethylacetamide, concentration is 5wt%) and 0.2g Coumarin 7 (dissolved in methylacetamide) , the concentration is 0.1wt%), after 30 minutes of stirring and mixing, the doctor blade is coated on the glass substrate and dried in an oven, and the surface drying temperature is 100 ° C. Then, the polyimide film can be obtained by heating and baking with an infrared wavelength of 800 nm to 3000 nm for 10 minutes in a nitrogen environment.

Comparative Example 1

Take the polyimide solution of Synthesis Example 1 and apply it to a glass substrate with a doctor blade, and then perform surface drying in an oven, and the surface drying temperature is 100°C. Then, the polyimide film can be obtained by heating and baking with an infrared wavelength of 800 nm to 3000 nm for 10 minutes in a nitrogen environment.

Comparative Example 2

Take 100 grams of the polyimide solution of Synthesis Example 1 and add 2 grams of cesium tungsten oxide CsWO ₃ (particle size 300nm is dispersed in dimethylacetamide, the concentration is 5wt%), after 30 minutes of stirring and mixing, scraper coating Surface-drying is performed on the glass substrate and in the oven, and the surface-drying temperature is 100°C. Then, the polyimide film can be obtained by heating and baking with an infrared wavelength of 800 nm to 3000 nm for 10 minutes in a nitrogen environment.

Comparative Example 3

Take 100 grams of the polyimide solution of Synthesis Example 1 and add 1 gram of Pigment Blue 15 (particle size 100nm is dispersed in dimethylacetamide, the concentration is 0.1wt%), after 30 minutes of stirring and mixing, the scraper is coated on The glass substrate was surface-dried in an oven, and the surface-drying temperature was 100°C. Then, the polyimide film can be obtained by heating and baking with an infrared wavelength of 800 nm to 3000 nm for 10 minutes in a nitrogen environment.

Comparative Example 4

Take 100 grams of the polyimide solution of Synthesis Example 1 and add 2 grams of cesium tungsten oxide CsWO ₃ (particle size 50nm is dispersed in dimethylacetamide, the concentration is 5wt%), after 30 minutes of stirring and mixing, scraper coating Surface-drying is performed on the glass substrate and in the oven, and the surface-drying temperature is 100°C. Then, the polyimide film can be obtained by heating and baking with an infrared wavelength of 800 nm to 3000 nm for 10 minutes in a nitrogen environment.

Comparative Example 5

Take 100 grams of the polyimide solution of Synthesis Example 1 and add 0.11 grams of cesium tungsten oxide CsWO ₃ (particle size 50nm is dispersed in dimethylacetamide, the concentration is 5wt%), after 30 minutes of stirring and mixing, scraper coating Surface-drying is performed on the glass substrate and in the oven, and the surface-drying temperature is 100°C. Then, the polyimide film can be obtained by heating and baking with an infrared wavelength of 800 nm to 3000 nm for 10 minutes in a nitrogen environment.

Comparative Example 6

Take the polyimide solution of Synthesis Example 1 and apply it to a glass substrate with a doctor blade, and then perform surface drying in an oven, and the surface drying temperature is 100°C. Then, it was heated to 280° C. by hot air baking in a nitrogen atmosphere, and the baking time was 60 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.

Total light transmittance (%) determination

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 color

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

IR irradiated surface temperature measurement

The surface of the polyimide film was irradiated with infrared light with a wavelength of 800nm to 3000nm to measure the surface temperature change.

Chemical resistance evaluation

The polyimide film was soaked in methyl ethyl ketone at room temperature, and after 1 minute, it was confirmed whether there was white fog on the film surface.

The test results of the aforementioned performance evaluations are reported in Table 1.

The results from Example 1 to Example 5 and Comparative Example 1 show that when a blue infrared absorber is added to the polyimide film, the blue infrared absorber can be absorbed between 500-700 to produce blue Therefore, adding different blue infrared absorbers can reduce the yellow index of the polyimide film to below 2. And after adding blue infrared absorber, it can improve the light absorption ability in infrared, as shown in Figure 1, and then improve the heating efficiency of infrared irradiation, so the surface temperature can reach above 280 ℃ under infrared irradiation, with the increase of the addition amount. The temperature has an upward trend.

The results from Example 1 and Comparative Example 2 show that when the particle size of the blue infrared absorbing agent is too large, the ability to absorb infrared rays will decrease, resulting in a decrease in the photothermal conversion efficiency, resulting in no significant increase in temperature under the same infrared irradiation. , so that the degree of solvent resistance of the polyimide film is insufficient.

From the results of Examples 4, 5 and Comparative Examples 4 and 5, when the concentration of the infrared absorber is lower than 0.05%, the yellow index of the polyimide film is greater than 2, and the surface temperature of the film cannot be effectively increased under infrared irradiation. , there is little difference with the temperature of Comparative Example 1 without adding infrared absorber. When the addition amount of the infrared absorber is more than 0.5%, although the yellow index of the polyimide can be reduced to below 1, the transmittance of the polyimide film is less than 85 due to the visible light absorption of the infrared absorber. %.

From the results of Comparative Example 1 and Comparative Example 6, it is shown that when there is no addition of infrared absorption The prepared polyimide film is heated to 280°C for 60 minutes in a hot air circulation oven, and the polyimide film at this time can also withstand the erosion of methyl ethyl ketone. From the point of view of imidization, when the polyimide is ring-closed by thermal imidization, the lowest ring-closure temperature is 250°C. If the temperature is too low, the ring-closure will be incomplete and the chemical resistance will be deteriorated. If the chemical ring closure method is used, although it has been completely imidized, an isoimide structure will be formed due to the catalysis of chemical catalysts, which will make the chemical resistance of the polyimide worse. Generally, a heat setting step is required to make The isoimide is converted into an imide structure to improve chemical resistance. Therefore, under infrared heating, if the surface temperature cannot exceed 250°C, the chemical resistance of polyimide will be affected.

In addition, a hue modifier can also be added to adjust the yellow index YI of the polyimide film. From Example 6 and Example 7, it is shown that the addition of PB15 and Coumarin fluorescent materials can effectively reduce the yellow index of the polyimide film. . However, if only the hue modifier is added, the material only has yellow to orange absorption, which is not helpful for infrared absorption, so the photothermal effect will not be generated under infrared irradiation, as shown in Figure 1, so the surface temperature of the film is different from that of the unadded one. The results of Comparative Example 1 were the same.

Preparation Example 1

The hard coating composition can be prepared by heat curing or light curing to form a coating with high hardness. The modified nano-inorganic particles in the hard coat layer 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 heated at 50 °C for 4 hours under nitrogen for modification and synthesis. The reaction was completed and lowered to room temperature, and 1 part by weight of the modified nanoparticle solution was added to 0.133 part by weight of pentaerythritol hexaacrylate and 0.133 part by weight of pentaerythritol hexaacrylate. After stirring for 30 minutes, the elastic oligomer UA160-TM was inverted according to the required solvent. Finally, 1.5 parts by weight of modified nano-inorganic particles and monomers with unsaturated bonds are mixed with 0.03 parts by weight of 2-methyl-1-(4-(methylthiol) Phenyl-2-morpholinyl propyl ketone, and 0.01 parts by weight of leveling agent are mixed, and the final solid part is adjusted to 55% with solvent ethyl acetate. Add appropriate concentration of hue-adjusting material to obtain subsequent examples and comparisons the desired composition.

Example 8

Take 20 g of the above-mentioned hard coating composition, spin-coat at 250 rpm for 10 seconds on the surface of the polyimide film produced in Example 1, bake softly at 80 ° C for 5 minutes, and then expose at 500 mJ/cm ² , and finally use 180 Bake hard for 30 minutes.

Example 9

Get above-mentioned hard coating composition 20g, and add 1g PB15 (0.25% is mixed in n-butyl acetate, particle diameter is 100nm), after 30 minutes of stirring and mixing, spin coating at 250rpm for 10 seconds in Example 1 The surface of the polyimide film 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 10

Get the above-mentioned hard coating composition 20g, 0.11g Coumarin 1 (1% dissolved in ethyl acetate), after 30 minutes of stirring and mixing, spin-coat the polyimide film produced in Example 1 at 250rpm for 10 seconds 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.

Comparative Example 7

Get above-mentioned hard coating composition 20g, and add 1g PB15 (0.25% is mixed in n-butyl acetate, particle size is 400nm), after 30 minutes of stirring and mixing, spin coating at 250rpm for 10 seconds in Example 1 The surface of the polyimide film 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.

Pencil Hardness Determination

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.

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 above performance test results are shown in Table 2 below.

From Example 9 and Example 10, it is shown that infrared absorbing material and hue adjustment material can be added to the hard coat layer to reduce the yellow index YI of the covered laminate. When the particle size of the adjustment material is larger than 200nm, because the particle size is too large, defects in the HC will occur due to agglomeration, which will affect the overall strength and surface smoothness of the HC, resulting in the covering of the base plate during folding.

To sum up, the polyimide film of the present invention contains an infrared absorber with infrared absorption and photothermal conversion effects. Therefore, the surface temperature of the polyimide resin can be increased through infrared irradiation, thereby shortening the baking time and reducing the Energy consumption and increased production rate. In addition, infrared absorbers can also be used as hue modifiers and ultraviolet absorbers, which can reduce the yellowness index of transparent polyimide, reduce the yellowing caused by UV irradiation for a long time, and improve the appearance and visual yellowing phenomenon.

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 (13)

A polyimide film for a flexible display device, comprising: polyimide; and a blue infrared absorbing agent, including cesium tungsten oxide, tungsten oxide, Prussian blue or antimony tin oxide, wherein the polyimide is used Based on the total weight of the amine film, the content of the blue infrared absorber is 0.05wt% to 0.5wt%. The polyimide film according to claim 1, wherein the polyimide film has an absorption peak at a wavelength of 800 nm to 4000 nm. The polyimide film according to item 1 of the claimed scope, wherein the thickness of the polyimide film is 10 μm to 100 μm, the total light transmittance is above 85%, and the yellowness index YI is less than 2. The polyimide film of claim 1, wherein the absorption wavelength of the blue infrared absorbing agent is 500 nm to 4000 nm, and the thermal conversion efficiency of the blue infrared absorbing agent is greater than 50%. The polyimide film according to item 1 of the patent application scope, wherein the particle size of the blue infrared absorbing agent is less than 100 nm. The polyimide film according to item 1 of the patent application scope, further comprising a hue adjustment material, the hue adjustment material comprising a blue dye, a blue pigment, an absorption wavelength of 360 nm to 430 nm and an emission wavelength of 430 nm to 530 nm fluorescent dyes or fluorescent pigments. The polyimide film according to item 6 of the claimed scope, wherein based on the total weight of the polyimide film, the content of the blue dye or the blue pigment is 0.001wt% to 0.01wt% %. The polyimide film according to item 6 of the claimed scope, wherein based on the total weight of the polyimide film, the content of the fluorescent dye or the fluorescent pigment is 0.001wt% to 0.5wt% %. The polyimide film according to claim 1, wherein the blue infrared absorbing agent has a hue-adjusting effect. A flexible display device covering substrate, comprising: the polyimide film according to any one of the first to ninth claims in the scope of the application; and a device protection layer, formed of a hydrophobic hard coating, disposed on the on at least one side of the polyimide film. The flexible display device cover substrate according to claim 10, wherein the flexible display device cover substrate has a total light transmittance of more than 85% and a thickness of 50 μm to 200 μm. The flexible display device covering substrate according to claim 10, wherein the hydrophobic hard coating has a thickness of 5 μm to 30 μm and a hardness of 7H to 9H. The flexible display device covering substrate according to claim 10, wherein the hydrophobic hard coating contains a blue infrared absorbing agent and a hue adjustment material, and the hue adjustment material includes a blue dye, a blue pigment, Absorption wavelength Fluorescent dyes or fluorescent pigments that are 360nm to 430nm and emit light at a wavelength of 430nm to 530nm.

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