JP7529431B2 - Resin composition, substrate film, laminate and display cover window - Google Patents

Description

The present invention relates to a resin composition, a substrate film, a laminate, and a cover window for a display.

In order to further improve the portability of mobile information terminals such as smartphones and tablets, there is an increasing demand for foldable devices such as foldable displays and touch panels. In addition to the transparency required of general display materials, the displays of foldable devices must be bent 180° with a small bending radius (for example, a bending radius of about 2.5 mm) to improve portability, and therefore require extremely high flexibility. In addition, the displays of foldable devices are carried in a folded state, unfolded when used, and folded again after use for repeated use, so they are also required to have high bending durability, i.e., durability that does not cause cracks even when folded repeatedly.

On the other hand, in order to prevent pressure marks and scratches on the surface of the display caused by touch with a finger or a touch pen, and to prevent bending marks caused by folding, studies are being conducted on the display surface of foldable devices, such as providing a hard coat layer and improving the elastic modulus of the substrate film that serves as the base for the hard coat layer.

Patent Document 1 discloses a polyimide resin composition that combines polyimide having a specific molecular structure with silica particles, with the aim of providing a film for flexible displays that combines heat resistance, transparency, mechanical strength, surface hardness, and bending resistance.

International Publication No. 2016/060213

However, in the polyimide resin composition described in Patent Document 1, unless the silica fine particles are highly loaded, sufficient elastic modulus cannot be achieved. When the silica fine particles are highly loaded, the flexibility and transparency of the film decrease, which causes problems such as the film cracking during the film manufacturing process and the display manufacturing process, and the optical properties required for display materials cannot be satisfied.

Therefore, a main object of the present invention is to provide a resin composition which has high elasticity without impairing flex resistance and transparency, something which could not be achieved by conventional techniques.
Another object of the present invention is to provide a substrate film, a laminate, and a cover window for a display, each of which is made of the above resin composition.

The present inventors have conducted extensive research to achieve the above object. As a result, they have discovered that by using a resin composition containing alumina filler, (meth)acrylate having a molecular weight of 10,000 or less, or a blocked isocyanate having an isocyanuric ring, together with polyimide, it is possible to obtain a substrate film, a laminate, and a display cover window made of a resin composition having high elasticity without impairing bending resistance or transparency, something that could not be achieved by conventional techniques, and have thus completed the present invention.

That is, the resin composition of the present invention is characterized by containing (A) a polyimide, (B) an alumina filler, and (C1) a (meth)acrylate having a molecular weight of 10,000 or less, or (C2) a blocked isocyanate having an isocyanuric ring.
In the present invention, the term "molecular weight" refers to the weight average molecular weight in a mixture of two or more substances having different molecular weights, such as oligomers and polymers.

In the resin composition of the present invention, the alumina filler (B) has an average particle size of 10 nm or more and 100 nm or less, and is preferably spherical or amorphous, more preferably spherical, and is preferably contained in an amount of 5 parts by mass to 180 parts by mass relative to 100 parts by mass of the polyimide (A). The resin composition of the present invention preferably contains 1 part by mass to 50 parts by mass of the (C1) (meth)acrylate having a molecular weight of 10,000 or less or the (C2) blocked isocyanate having an isocyanuric ring, relative to 100 parts by mass of the polyimide (A).
In the present invention, the "average particle size" of the alumina filler (B) refers to the average particle size (D50) including not only the particle size of the primary particles but also the particle size of the secondary particles (aggregates), and refers to the D50 value measured by a laser diffraction method.

The substrate film of the present invention is characterized by being made of the above-mentioned resin composition.

The laminate of the present invention is characterized in that a hard coat layer is laminated on the substrate film.

The cover window of the display of the present invention is characterized by being the laminate.

According to the present invention, it is possible to obtain a resin composition which, when used for a base film, has high elasticity without impairing bending resistance or transparency, which could not be achieved by conventional techniques.
Furthermore, according to the present invention, it is possible to obtain a substrate film, a laminate, and a cover window for a display, each of which is made of the above-mentioned resin composition.

The resin composition of the present invention is characterized by containing (A) a polyimide, (B) an alumina filler, and (C1) a (meth)acrylate having a molecular weight of 10,000 or less, or (C2) a blocked isocyanate having an isocyanuric ring.

When alumina filler (B) is added to polyimide (A), a significant effect of increasing elasticity can be obtained. However, when alumina filler (B) is simply added to polyimide (A), stress is concentrated on alumina filler (B) dispersed in polyimide (A) when external stress such as bending or compression is applied, resulting in brittle fracture and a decrease in flexibility (elongation).
Therefore, in the resin composition of the present invention, (C1) a (meth)acrylate having a molecular weight of 10,000 or less, or (C2) a blocked isocyanate having an isocyanuric ring is further added, which results in the relaxation of stress concentration on the alumina filler (B) dispersed in the polyimide (A), and the resin composition of the present invention can maintain its flexibility while achieving the aforementioned remarkable effect of high elasticity.

The components that make up the resin composition of the present invention are described in detail below.

[(A) Polyimide]
The resin composition of the present invention contains (A) a polyimide.
Polyimide is obtained by reacting a tetracarboxylic acid component with a diamine component. It is preferable to obtain a polyamic acid by polymerization of the tetracarboxylic acid component and the diamine component, and then imidize the polyamic acid. The imidization may be performed by thermal imidization or chemical imidization. Polyimide can also be produced by a method that combines thermal imidization and chemical imidization.

Specific examples of the tetracarboxylic acid component include tetracarboxylic dianhydrides, such as cyclohexane tetracarboxylic dianhydride, cyclopentane tetracarboxylic dianhydride, dicyclohexane-3,4,3',4'-tetracarboxylic dianhydride, pyromellitic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, 2,2',3,3'-benzophenone tetracarboxylic dianhydride, 3,3',4,4'-biphenyl tetracarboxylic dianhydride, 2,2',3,3'-biphenyl tetracarboxylic dianhydride, 2,2-bis(3,4-dicarboxyphenyl)propane dianhydride, 2,2-bis(2,3-dicarboxyphenyl)propane dianhydride, and bis(3,4-dicarboxyphenyl)ether dianhydride. , bis(3,4-dicarboxyphenyl)sulfone dianhydride, 1,1-bis(2,3-dicarboxyphenyl)ethane dianhydride, bis(2,3-dicarboxyphenyl)methane dianhydride, bis(3,4-dicarboxyphenyl)methane dianhydride, 2,2-bis(3,4-dicarboxyphenyl)-1,1,1,3,3,3-hexafluoropropane dianhydride, 2,2-bis(2,3-dicarboxyphenyl)-1,1,1,3,3,3-hexafluoropropane dianhydride, 1,3-bis[(3,4-dicarboxy)benzoyl]benzene dianhydride, 1,4-bis[(3,4-dicarboxy)benzoyl]benzene dianhydride, 2,2-bis{4-[4-(1,2-dicarboxy)phenoxy]phenyl}propane dianhydride, 2,2- Bis{4-[3-(1,2-dicarboxy)phenoxy]phenyl}propane dianhydride, bis{4-[4-(1,2-dicarboxy)phenoxy]phenyl}ketone dianhydride, bis{4-[3-(1,2-dicarboxy)phenoxy]phenyl}ketone dianhydride, 4,4'-bis[4-(1,2-dicarboxy)phenoxy]biphenyl dianhydride, 4,4'-bis[3-(1,2-dicarboxy)phenoxy]biphenyl dianhydride, bis{4-[4-(1,2-dicarboxy)phenoxy]phenyl}ketone dianhydride, bis{4-[3-(1,2-dicarboxy)phenoxy]phenyl}ketone dianhydride, bis{4-[4-(1,2-dicarboxy)phenoxy]phenyl}ketone dianhydride, bis{4-[4-(1,2-dicarboxy)phenoxy]phenyl}sulfone dianhydride, bis{4-[3-(1,2-dicarboxy)phenoxy]phenyl}sulfone dianhydride, bis{4-[4-(1,2-dicarboxy)phenoxy]phenyl}sulfone dianhydride, bis{4-[4-(1,2-dicarboxy)phenoxy]phenyl}sulfide dianhydride, bis{4-[3-(1,2-dicarboxy)phenoxy]phenyl}sulfide dianhydride, 4,4'-(hexafluoroisopropylidene)diphthalic anhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride, 1,4,5,8-naphthalenetetracarboxylic dianhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, 1,2,3,4-benzenetetracarboxylic dianhydride, 3,4,9,10-perylenetetracarboxylic dianhydride, 2,3,6,7-anthracenetetracarboxylic dianhydride, 1,2,7,8-phenanthrenetetracarboxylic dianhydride, and the like.
These tetracarboxylic dianhydrides may be used alone or in combination of two or more.

Specific examples of the diamine component include p-phenylenediamine, m-phenylenediamine, o-phenylenediamine, 3,3'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl ether, 3,3'-diaminodiphenyl sulfide, 3,4'-diaminodiphenyl sulfide, 4,4'-diaminodiphenyl sulfide, 3,3'-diaminodiphenyl sulfone, 3,4'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl sulfone, 3,3'-diaminobenzophenone, 4,4'-diaminobenzophenone, 3,4'-diaminobenzophenone, 4,4'-diaminobenzanilide, 3,3'-diaminodiphenylmethane, 4,4'-diaminodiphenylmethane, 3,4'-diaminodiphenylmethane, 2,2-di(3-aminophenyl)propane. Pan, 2,2-di(4-aminophenyl)propane, 2-(3-aminophenyl)-2-(4-aminophenyl)propane, 2,2-di(3-aminophenyl)-1,1,1,3,3,3-hexafluoropropane, 2,2-di(4-aminophenyl)-1,1,1,3,3,3-hexafluoropropane, 2-(3-aminophenyl)-2-(4-aminophenyl)-1,1,1,3,3,3-hexafluoropropane 1,1-di(3-aminophenyl)-1-phenylethane, 1,1-di(4-aminophenyl)-1-phenylethane, 1-(3-aminophenyl)-1-(4-aminophenyl)-1-phenylethane, 1,3-bis(3-aminophenoxy)benzene, 1,3-bis(4-aminophenoxy)benzene, 1,4-bis(3-aminophenoxy)benzene, 1,4-bis(4-aminophenoxy)benzene, 1,3-bis(3-aminobenzoyl)benzene, 1,3-bis(4-aminobenzoyl)benzene, 1,4-bis(3-aminobenzoyl)benzene, 1,4-bis(4-aminobenzoyl)benzene, 1,3-bis(3-amino-α,α-dimethylbenzyl)benzene, 1,3-bis(4-amino-α,α-dimethylbenzyl)benzene, 1,4-bis(3-amino-α,α-dimethylbenzyl)benzene, 1,4-bis(4-amino-α,α-dimethylbenzyl)benzene, 1,3-bis(3-amino-α,α-ditrifluoromethylbenzyl)benzene, 1,3-bis(4-amino-α,α-ditrifluoromethylbenzyl)benzene, 1,4-bis(3-amino-α,α-ditrifluoromethylbenzyl)benzene, 1,4-bis(4-amino-α,α-ditrifluoromethylbenzyl)benzene )benzene, 2,6-bis(3-aminophenoxy)benzonitrile, 2,6-bis(3-aminophenoxy)pyridine, N,N'-bis(4-aminophenyl)terephthalamide, 9,9-bis(4-aminophenyl)fluorene, 2,2'-dimethyl-4,4'-diaminobiphenyl, 2,2'-ditrifluoromethyl-4,4'-diaminobiphenyl (2,2-bis(trifluoromethyl)benzidine), 3,3'-dichloro-4,4'-diaminobiphenyl, 3,3'-dimethoxy-4,4'-diaminobiphenyl, 3,3'-dimethyl-4,4'-diaminobiphenyl, 4,4'-bis(3-aminophenoxy)biphenyl, 4,4'-bis(4-aminophenoxy)biphenyl, bis[4-(3-aminophenoxy)phenyl]ketone, bis[4-(4-aminophenoxy)phenyl]ketone, bis[ 4-(3-aminophenoxy)phenyl]sulfide, bis[4-(4-aminophenoxy)phenyl]sulfide, bis[4-(3-aminophenoxy)phenyl]sulfone, bis[4-(4-aminophenoxy)phenyl]sulfone, bis[4-(3-aminophenoxy)phenyl]ether, bis[4-(4-aminophenoxy)phenyl]ether, 2,2-bis[4-(3-aminophenoxy) phenyl]propane, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, 2,2-bis[3-(3-aminophenoxy)phenyl]-1,1,1,3,3,3-hexafluoropropane, 2,2-bis[4-(4-aminophenoxy)phenyl]-1,1,1,3,3,3-hexafluoropropane, 1,3-bis[4-(3-aminophenoxy)benzoyl]benzene, 1,3-bis[4 -(4-aminophenoxy)benzoyl]benzene, 1,4-bis[4-(3-aminophenoxy)benzoyl]benzene, 1,4-bis[4-(4-aminophenoxy)benzoyl]benzene, 1,3-bis[4-(3-aminophenoxy)-α,α-dimethylbenzyl]benzene, 1,3-bis[4-(4-aminophenoxy)-α,α-dimethylbenzyl]benzene, 1,4-bis[4-(3-aminophenoxy)-α,α-dimethylbenzyl]benzene, 1,4-bis[4-(4-aminophenoxy)-α,α-dimethylbenzyl]benzene, 4,4'-bis[4-(4-aminophenoxy)benzoyl]diphenyl ether, 4,4'-bis[4-(4-amino-α,α-dimethylbenzyl)phenoxy]benzophenone, 4,4'-bis[4-(4-amino-α,α-dimethylbenzyl)phenoxy] Diphenyl sulfone, 4,4'-bis[4-(4-aminophenoxy)phenoxy]diphenyl sulfone, 3,3'-diamino-4,4'-diphenoxybenzophenone, 3,3'-diamino-4,4'-dibiphenoxybenzophenone, 3,3'-diamino-4-phenoxybenzophenone, 3,3'-diamino-4-biphenoxybenzophenone, 6,6'-bis(3-aminophenoxy)-3,3,3 ',3'-tetramethyl-1,1'-spirobiindane, 6,6'-bis(4-aminophenoxy)-3,3,3',3'-tetramethyl-1,1'-spirobiindane, 1,3-bis(3-aminopropyl)tetramethyldisiloxane, 1,3-bis(4-aminobutyl)tetramethyldisiloxane, α,ω-bis(3-aminopropyl)polydimethylsiloxane, α,ω-bis(3-aminobutyl)poly Dimethylsiloxane, bis(aminomethyl)ether, bis(2-aminoethyl)ether, bis(3-aminopropyl)ether, bis(2-aminomethoxy)ethyl]ether, bis[2-(2-aminoethoxy)ethyl]ether, bis[2-(3-aminoprotoxy)ethyl]ether, 1,4-cyclohexanediamine, trans-1,4-bismethylenecyclohexanediamine (trans-1,4-bis(aminomethyl)cyclohexane), 2,6-bis(aminomethyl)bicyclo[2,2,1]heptane, 2,5-bis(aminomethyl)bicyclo[2,2,1]heptane, and diamines in which some or all of the hydrogen atoms on the aromatic ring of the above diamines are substituted with substituents selected from fluoro groups, methyl groups, methoxy groups, trifluoromethyl groups, and trifluoromethoxy groups can also be used.
These diamines may be used alone or in combination of two or more.

In addition, from the viewpoint of improving light transmittance and impact resistance, it is preferable to contain a polyimide containing an aromatic ring and at least one selected from the group consisting of (i) a fluorine atom, (ii) an aliphatic ring, and (iii) a structure in which aromatic rings are linked together by an alkylene group which may be substituted with a sulfonyl group or a fluorine atom. When an aromatic ring is contained in a polyimide, the orientation is increased and the rigidity is improved, so that the impact resistance is improved, but the transmittance tends to decrease depending on the absorption wavelength of the aromatic ring.
When the polyimide contains (i) fluorine atoms, the electronic state in the polyimide skeleton is made difficult to transfer charges, and thus the light transmittance is improved.
When the polyimide contains (ii) an aliphatic ring, the conjugation of π electrons in the polyimide skeleton can be broken, thereby inhibiting the movement of charges in the skeleton, and thus improving the light transmittance.
When the polyimide contains (iii) a structure in which aromatic rings are linked together via an alkylene group which may be substituted with a sulfonyl group or a fluorine atom, the conjugation of π electrons in the polyimide skeleton can be broken, thereby inhibiting the movement of charges in the skeleton, and thus improving the light transmittance.

Among these, polyimides containing an aromatic ring and a fluorine atom are preferably used from the viewpoints of improving light transmittance and impact resistance.
The content of fluorine atoms in the polyimide is preferably such that the ratio (F/C) of the number of fluorine atoms (F) to the number of carbon atoms (C) measured on the surface of the polyimide by X-ray photoelectron spectroscopy is 0.01 or more, more preferably 0.05 or more. On the other hand, if the content of fluorine atoms is too high, there is a risk that the inherent heat resistance of the polyimide may decrease, so that the ratio (F/C) of the number of fluorine atoms (F) to the number of carbon atoms (C) is preferably 1 or less, more preferably 0.8 or less.
Here, the above ratio measured by X-ray photoelectron spectroscopy (XPS) can be found from the atomic % value of each atom measured using an X-ray photoelectron spectrometer (for example, Theta Probe manufactured by Thermo Scientific).

In addition, in terms of improving impact resistance, when the total of the tetracarboxylic acid residues and the diamine residues in the polyimide is taken as 100 mol %, the total of the tetracarboxylic acid residues having an aromatic ring and the diamine residues having an aromatic ring is preferably 50 mol % or more, more preferably 60 mol % or more, and even more preferably 75 mol % or more.

In the present invention, the content ratio of each repeating unit in the polyimide and the content ratio (mol %) of each tetracarboxylic acid residue and each diamine residue can be determined from the molecular weight of the charge during the production of the polyimide. The content ratio (mol %) of each tetracarboxylic acid residue and each diamine residue in the polyimide can be determined by using high performance liquid chromatography, gas chromatography mass spectrometry, NMR, elemental analysis, XPS/ESCA, TOF-SIMS, and pyrolysis CG-MS for the decomposition product of the polyimide obtained by decomposing the sample with an alkaline aqueous solution or supercritical methanol.

In addition, from the viewpoint of improving impact resistance and light transmittance, it is preferable that at least one of the tetracarboxylic acid residue and the diamine residue contains an aromatic ring and a fluorine atom, and it is further preferable that the polyimide has a tetracarboxylic acid residue containing an aromatic ring and a fluorine atom, and a diamine residue containing an aromatic ring and a fluorine atom.
In the polyimide, when the total of the tetracarboxylic acid residues and the diamine residues is taken as 100 mol %, the total of the tetracarboxylic acid residues having an aromatic ring and a fluorine atom and the diamine residues having an aromatic ring and a fluorine atom is preferably 50 mol % or more, more preferably 60 mol % or more, and even more preferably 75 mol % or more.

In addition, polyimides in which 50% or more of hydrogen atoms bonded to carbon atoms contained in the polyimide are hydrogen atoms directly bonded to aromatic rings are preferably used from the viewpoints of improving light transmittance and improving rigidity. The ratio of hydrogen atoms (number) directly bonded to aromatic rings among all hydrogen atoms (number) bonded to carbon atoms contained in the polyimide is further preferably 60% or more, and even more preferably 70% or more.
In the case where 50% or more of the hydrogen atoms bonded to the carbon atoms contained in the polyimide are hydrogen atoms bonded directly to the aromatic ring, even if the polyimide is heated in the atmosphere and stretched at, for example, 200°C or higher, the optical properties, particularly the total light transmittance and the yellowness index YI value, are less likely to change. In the case where 50% or more of the hydrogen atoms bonded to the carbon atoms contained in the polyimide are hydrogen atoms bonded directly to the aromatic ring, it is estimated that the chemical structure of the polyimide is less likely to change due to low reactivity with oxygen. Polyimide films are often used in devices that require processing steps involving heating, taking advantage of their high heat resistance, but in the case where 50% or more of the hydrogen atoms bonded to the carbon atoms contained in the polyimide are hydrogen atoms bonded directly to the aromatic ring, there is no need to carry out these subsequent steps under an inert atmosphere to maintain transparency, so there is an advantage in that the equipment costs and the costs for atmosphere control can be suppressed.
Here, the ratio of the hydrogen atoms (number) directly bonded to aromatic rings in the total hydrogen atoms (number) bonded to carbon atoms contained in polyimide can be obtained by using high performance liquid chromatography, gas chromatography mass spectrometer and NMR on the decomposition product of polyimide.For example, a sample is decomposed with an alkaline aqueous solution or supercritical methanol, the decomposition product of polyimide obtained is separated by high performance liquid chromatography, and each peak separated is qualitatively analyzed by using a gas chromatography mass spectrometer and NMR, etc., and quantified by high performance liquid chromatography, thereby the ratio of the hydrogen atoms (number) directly bonded to aromatic rings in the total hydrogen atoms (number) contained in polyimide can be obtained.

In addition, the polyimide used in the present invention may contain a polyamide structure in part, so long as the effect of the present invention is not impaired. Examples of the polyamide structure that may be contained include a polyamideimide structure containing a tricarboxylic acid residue such as trimellitic anhydride, and a polyamide structure containing a dicarboxylic acid residue such as terephthalic acid.

From the viewpoint of heat resistance, the polyimide used in the present invention preferably has a glass transition temperature of 200° C. or higher, more preferably 250° C. or higher, and further preferably 270° C. or higher.
The glass transition temperature of the polyimide used in the present invention is determined from the peak temperature of a temperature-tan δ (tan δ=loss modulus (E″)/storage modulus (E′)) curve obtained by dynamic viscoelasticity measurement. When there are multiple peaks in the tan δ curve, the glass transition temperature of the polyimide refers to the temperature of the peak with the largest local maximum value. The dynamic viscoelasticity measurement can be performed, for example, with a dynamic viscoelasticity measuring device RSA III (TA Instruments Japan Co., Ltd.) in the measurement range of −150° C. to 400° C., at a frequency of 1 Hz and a temperature rise rate of 5° C./min. The measurement can also be performed with a sample width of 5 mm and a chuck distance of 20 mm.
In the present invention, a peak of a tan δ curve refers to a curve that has an inflection point that is a maximum value and has a peak width between the valleys of the peak of 3° C. or more. Small fluctuations up and down due to measurement noise or the like are not interpreted as the peak.

[(B) Alumina filler]
The resin composition of the present invention contains (B) an alumina filler.

The (B) alumina filler is preferably contained in an amount of 5 to 180 parts by mass, more preferably 30 to 150 parts by mass, and even more preferably 50 to 120 parts by mass, per 100 parts by mass of (A) polyimide. If it is contained in an amount of 5 or more by mass per 100 parts by mass of (A) polyimide, the elastic modulus of the adjustment layer can be improved, and if it is contained in an amount of 180 or less by mass, the haze and YI value can be reduced, and excellent transparency can be obtained.

(B) The alumina filler preferably has an average particle size of 10 nm or more and 100 nm or less, more preferably 30 nm or more and 90 nm or less, and even more preferably 50 nm or more and 80 nm or less. If the average particle size is within the above range, good dispersibility can be obtained, and a laminate with reduced haze can be formed. In addition, from the viewpoint of dispersibility, the shape is preferably spherical or amorphous, and more preferably spherical.
Here, the "average particle size" of the (B) alumina filler is the average particle size (D50) including not only the particle size of the primary particles but also the particle size of the secondary particles (aggregates), and is the value of D50 measured by a laser diffraction method. An example of a measuring device using the laser diffraction method is Microtrac MT3300EXII manufactured by Nikkiso Co., Ltd. The maximum particle size (D100) and particle size (D10) can also be measured in the same manner using the above device.

The (B) alumina filler may be surface-treated. The surface treatment can increase dispersibility, and the use of surface-treated (B) alumina filler can also prevent aggregation.

The method for treating the surface of the (B) alumina filler is not particularly limited, and any known, commonly used method may be used. For example, it is preferable to treat the surface of the (B) alumina filler with a coupling agent or the like.

As the coupling agent, silane-based, titanate-based, aluminate-based, zircoaluminate-based, and other coupling agents can be used. Among them, silane-based coupling agents are preferred. Examples of such silane-based coupling agents include vinyltrimethoxysilane, vinyltriethoxysilane, N-(2-aminomethyl)-3-aminopropylmethyldimethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-anilinopropyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-methacryloxypropyltrimethoxysilane, and 3-mercaptopropyltrimethoxysilane, which can be used alone or in combination. It is preferable that these silane-based coupling agents are immobilized in advance on the surface of the (B) alumina filler by adsorption or reaction. Here, the amount of coupling agent to be treated per 100 parts by mass of (B) alumina filler is preferably 0.5 to 10 parts by mass.

In addition, when the (B) alumina filler is surface-treated, the surface-treated (B) alumina filler may be contained in the resin composition in a surface-treated state. Although the surface-untreated (B) alumina filler and the surface treatment agent may be mixed separately to surface-treat the (B) alumina filler in the composition, it is preferable to mix the (B) alumina filler that has been surface-treated in advance. By mixing the (B) alumina filler that has been surface-treated in advance, it is possible to prevent a decrease in crack resistance, etc. due to the surface treatment agent that was not consumed in the surface treatment, which may remain when mixed separately. When the surface is treated in advance, it is preferable to mix a pre-dispersion in which the (B) alumina filler is pre-dispersed in a solvent or a curable component. It is more preferable to pre-disperse the surface-treated (B) alumina filler in a solvent and mix the pre-dispersion in the composition, or to pre-disperse the surface-untreated (B) alumina filler in a solvent and then sufficiently surface-treat it, and then mix the pre-dispersion in the composition.

In addition, (B) alumina filler may be blended with (A) polyimide etc. in a powder or solid state, or may be mixed with a solvent or dispersant to form a slurry and then blended with (A) polyimide etc.

[(C1) (meth)acrylate having a molecular weight of 10,000 or less, or (C2) blocked isocyanate]
The resin composition of the present invention contains (C1) a (meth)acrylate having a molecular weight of 10,000 or less, or (C2) a blocked isocyanate.

The (C1) (meth)acrylate with a molecular weight of 10,000 or less or the (C2) blocked isocyanate is preferably contained in an amount of 0.1 to 100 parts by weight, more preferably 1 to 50 parts by weight, and particularly preferably 2 to 20 parts by weight, per 100 parts by weight of the (A) polyimide. If it is contained in an amount of 0.1 part by weight or more, external stresses such as drying shrinkage, bending, and compression during the film manufacturing process are alleviated, thereby suppressing damage to the film, and if it is contained in an amount of 100 parts by weight or less, heat resistance is not impaired.

[(C1) (Meth)acrylate with Molecular Weight of 10,000 or Less]
The molecular weight of the (meth)acrylate (C1) of the present invention is not more than 10000. If the molecular weight is not more than 10000, transparency is not impaired, and it is more preferably not more than 6000, and particularly preferably not more than 500.

As the (meth)acrylate, a publicly known and commonly used (meth)acrylate oligomer or (meth)acrylate monomer can be used. The (meth)acrylate compound may be used alone or in combination of two or more kinds.

Examples of (meth)acrylate oligomers include epoxy (meth)acrylates such as phenol novolac epoxy (meth)acrylate, cresol novolac epoxy (meth)acrylate, and bisphenol-type epoxy (meth)acrylate, as well as urethane (meth)acrylate, epoxy urethane (meth)acrylate, polyester (meth)acrylate, polyether (meth)acrylate, and polybutadiene-modified (meth)acrylate.

(Meth)acrylate monomers include (meth)acrylamides such as acrylamide, methacrylamide, N-hydroxymethylacrylamide, N-hydroxymethylmethacrylamide, N-methoxymethylacrylamide, N-ethoxymethylacrylamide, and N-butoxymethylacrylamide; allyl compounds such as triallyl isocyanurate, diallyl phthalate, and diallyl isophthalate; 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, isopropyl alcohol, and the like. (meth)acrylic acid esters such as isobornyl (meth)acrylate, phenyl (meth)acrylate, and phenoxyethyl (meth)acrylate; hydroxyalkyl (meth)acrylates such as hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, and pentaerythritol tri(meth)acrylate; alkoxyalkylene glycol mono(meth)acrylates such as methoxyethyl (meth)acrylate and ethoxyethyl (meth)acrylate; ethylene glycol di(meth)acrylate, tri(meth)acrylate, and the like. alkylene polyol poly(meth)acrylates such as dipropylene glycol di(meth)acrylate, butanediol di(meth)acrylates, neopentyl glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, pentaerythritol tetra(meth)acrylate, and dipentaerythritol hexa(meth)acrylate; diethylene glycol di(meth)acrylate, triethylene Examples of such polyoxyalkylene glycol poly(meth)acrylates include glycol di(meth)acrylate, ethoxylated trimethylolpropane triacrylate, trimethylolpropane tri(meth)acrylate, and propoxylated trimethylolpropane tri(meth)acrylate; poly(meth)acrylates such as hydroxypivalic acid neopentyl glycol ester di(meth)acrylate; and isocyanurate-type poly(meth)acrylates such as tris[(meth)acryloxyethyl]isocyanurate.

[(C2) Blocked isocyanate having an isocyanuric ring]
The resin composition of the present invention may contain (C2) a blocked isocyanate having an isocyanuric ring, instead of (C1) a (meth)acrylate having a molecular weight of 10,000 or less. The blocked isocyanate group contained in the blocked isocyanate having an isocyanuric ring (C2) is a group in which the isocyanate group is protected and temporarily inactivated by a reaction with a blocking agent. When heated to a predetermined temperature, the blocking agent is cleaved to generate an isocyanate group. Therefore, even after application, the reaction via the isocyanate group of the blocked isocyanate having an isocyanuric ring (C2) does not proceed until the drying step.

(C2) As the blocked isocyanate having an isocyanuric ring, an addition reaction product of an isocyanate compound and an isocyanate blocking agent is used. As an isocyanuric ring-containing isocyanate compound that can react with a blocking agent, for example, 1,3,5-tris[(5-isocyanato-1,3,3-trimethylcyclohexyl)methyl]-1,3,5-triazine-2,4,6(1H,3H,5H)-trione, 2,4,6-trioxohexahydro-1,3,5-triazine-1,3,5-triyltris(6,1-hexanediyl)trisisocyanate, 1,3,5-tris[3-(isocyanatomethyl)phenyl]-1,3,5-triazine-2,4,6(1H,3H,5H)-trione, etc. are used.

Examples of isocyanate blocking agents include phenol-based blocking agents such as phenol, cresol, xylenol, chlorophenol, and ethylphenol; lactam-based blocking agents such as ε-caprolactam, δ-valerolactam, γ-butyrolactam, and β-propiolactam; active methylene-based blocking agents such as ethyl acetoacetate and acetylacetone; alcohol-based blocking agents such as methanol, ethanol, propanol, butanol, amyl alcohol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, propylene glycol monomethyl ether, benzyl ether, methyl glycolate, butyl glycolate, diacetone alcohol, methyl lactate, and ethyl lactate; formaldehyde Examples of suitable blocking agents include oxime-based blocking agents such as dehydroxime, acetaldoxime, acetoxime, methyl ethyl ketoxime, diacetyl monoxime, and cyclohexane oxime; mercaptan-based blocking agents such as butyl mercaptan, hexyl mercaptan, t-butyl mercaptan, thiophenol, methylthiophenol, and ethylthiophenol; acid amide-based blocking agents such as acetate amide and benzamide; imide-based blocking agents such as succinimide and maleimide; amine-based blocking agents such as xylidine, aniline, butylamine, and dibutylamine; imidazole-based blocking agents such as imidazole and 2-ethylimidazole; imine-based blocking agents such as methyleneimine and propyleneimine; pyrazole-based blocking agents such as dimethylpyrazole; and maleate ester-based blocking agents such as diethylmaleate.

(C2) The cleavage temperature of the blocked isocyanate having an isocyanuric ring is preferably 100°C or higher. If the temperature is 100°C or higher, the viscosity increase is suppressed and the coatability is maintained until the drying process for film formation.

As the blocked isocyanate having an isocyanuric ring (C2) of the present invention, commercially available products can be used, for example, BI7951 and BI7982 manufactured by TRIXENE. In addition, such blocked isocyanate having an isocyanuric ring (C2) can be used alone or in combination of two or more kinds.

[Other ingredients]
The resin composition of the present invention may contain other components within the range not impairing the effects of the present invention.

(1) Additives The resin composition according to the present invention may further contain additives in addition to the polyimide, if necessary. Examples of the additives include surfactants that improve film-forming properties and defoaming properties.

(2) Other Resins The resin composition according to the present invention may contain other resins other than polyimide, as long as the effects of the present invention are not impaired. Examples of other resins include polyester resins such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN), polyamide resins, polyamideimide resins, polyphenylene sulfide resins, polyether ether ketone resins, polyether sulfone resins, polycarbonate resins, polyetherimide resins, epoxy resins, phenolic resins, glass-epoxy resins, polyphenylene ether resins, acrylic resins, polyolefin resins such as polyethylene and polypropylene, and polycycloolefins such as polynorbornene.

[Base film]
The substrate film of the present invention is made of the above-mentioned resin composition and has high elasticity without impairing bending resistance or transparency, which could not be achieved by conventional techniques.

The base film of the present invention preferably has a thickness of 5 μm or more and 100 μm or less, and more preferably 10 μm or more and 50 μm or less. By setting the thickness within the above range, it is possible to achieve excellent flexibility and excellent transparency even as a laminate described later.

[Method of manufacturing base film]
The method for producing the substrate film of the present invention includes a method in which a solution for coating the substrate film, which is prepared by dissolving the resin composition of the present invention in a solvent, is applied onto a support by a known coating means, and then, after drying as necessary, the substrate is peeled off from the support. The coating means is not particularly limited as long as it is a method capable of coating the substrate with a desired film thickness.
The amount of the coating solution applied to the base film is preferably adjusted appropriately so that the thickness of the base film after drying falls within a predetermined range.

As described above, the coating solution for the substrate film, in which the resin composition of the present invention is dissolved in a solvent, is dried as necessary to remove the solvent. Examples of drying methods include drying under reduced pressure, drying by heating, and a combination of these. When drying is performed under normal pressure, it is preferable to dry at a temperature of 30°C or higher and 300°C or lower.

[Laminate]
The laminate of the present invention comprises a hard coat layer on the substrate film of the present invention.
In the laminate of the present invention, since the above-mentioned base film has a high elastic modulus without impairing bending resistance or transparency, warping during formation of a hard coat layer is suppressed, and the laminate has excellent flatness and high surface hardness, and the occurrence of bending marks and compression marks can be reduced.

The laminate of the present invention preferably has a total thickness of 10 μm or more and 150 μm or less, and more preferably 25 μm or more and 100 μm or less. If the total thickness of the laminate is within the above range, a display panel that is flexible and has excellent optical properties can be manufactured.

[Hard coat layer]
The hard coat layer can be made of a known coating solution (hard coat material) for hard coats, and can be made of either a photocurable or thermosetting hard coat material. Commercially available products include X-48-500 manufactured by Shin-Etsu Chemical Co., Ltd., which has excellent flexibility, and Luxidia V-6841 manufactured by DIC Corporation.

The hard coat layer preferably has a YI value of 4 or less at a film thickness of 50 μm, and more preferably 1 or less. If the YI value is 4 or less, a laminate with reduced yellowness (YI value) can be formed.

The hard coat layer preferably has a pencil hardness (surface hardness) of 2H or more, more preferably 4H or more. If the pencil hardness is 2H or more, a laminate having excellent scratch resistance can be formed.
The pencil hardness can be measured in accordance with JIS K 5600-5-4.

Furthermore, the hard coat layer preferably has a thickness of 1 μm or more and 50 μm or less, and more preferably 5 μm or more and 20 μm or less. If the thickness is 50 μm or less, a laminate with excellent flexibility can be formed.

[Method of manufacturing laminate]
An example of a method for producing the laminate of the present invention includes a production method including a step of forming a substrate film by the above-described method for producing a substrate film, and a step of forming a hard coat layer thereon.

The method for producing the base film is as described above, and therefore the description thereof will be omitted here.
The process of forming a coating film of a hard coat layer on a substrate film includes a method of coating a coating solution (hard coat material) of a hard coat layer on one side of the substrate film formed by the above-mentioned method for producing a substrate film by a known coating means, and drying and curing as necessary. The coating means is not particularly limited as long as it is a method that can coat the substrate with a desired film thickness.
The amount of the coating solution for the hard coat layer to be applied varies depending on the performance required for the resulting laminate, but it is preferable to appropriately adjust the coating amount so that the film thickness after drying falls within a predetermined range.

As described above, the coating film made of the coating solution for the hard coat layer is dried as necessary to remove the solvent. Examples of drying methods include drying under reduced pressure, drying by heating, and a combination of these. When drying is performed under normal pressure, it is preferable to dry at 30°C or higher and 150°C or lower.

Furthermore, as a method for curing the hard coat layer, it is preferable to cure the coating film by at least one of light irradiation and heating depending on the components of the coating solution (hard coat material).

[Display cover window]
The cover window of the display of the present invention is the laminate of the present invention described above, and is used by being disposed so as to be positioned on the surface of various displays.

The display cover window of the present invention can be used for various known displays, and the applications are not particularly limited, and it can be used as a replacement for the cover window of a display in which glass products such as thin plate glass have been used in the past. The laminate of the present invention described above can be suitably used as a component such as a base material or cover window for a display that can accommodate curved surfaces, and can be particularly suitably used as a cover window for a display mounted on a foldable device.

The laminate of the present invention can be suitably used, for example, in thin, bendable foldable organic EL displays, mobile terminals such as smartphones and wristwatch-type terminals, display devices inside automobiles, flexible panels used in wristwatches, etc. It can also be used in components for image display devices such as liquid crystal displays and organic EL displays, components for touch panels, flexible printed circuit boards, solar cell panel components such as surface protection films and substrate materials, components for optical waveguides, and other semiconductor-related components.

The cover window of the display of the present invention may further have a fingerprint prevention layer on the surface on the hard coat layer side.

The method for placing the cover window of the display of the present invention on the surface of the display is not particularly limited, but may be, for example, a method using an adhesive layer. As the adhesive layer, a conventionally known adhesive layer that can be used for adhering a display surface material can be used.

The present invention will be described in more detail below using examples, but the present invention is not limited to the following examples. In the following, "parts" and "%" are all based on mass unless otherwise specified. In the examples, the film thickness was measured using a micrometer manufactured by Mitutoyo Corporation.

(Example of Polyimide Synthesis)
A 2L glass separable flask equipped with a stirring device and a stirring blade was charged with 460 g of solvent N,N-dimethylacetamide (DMAC) and 64.048 g (0.200 mol) of 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (TFMB), an aromatic diamine compound having a fluoro group, and stirred to dissolve TFMB in DMAC. Next, while stirring the contents of the separable flask, 89.294 g (0.201 mol) of 4,4'-(1,1,1,3,3,3-hexafluoropropane-2,2-diyl)diphthalic dianhydride (6FDA), a tetracarboxylic dianhydride, was added over a period of about 10 minutes under a nitrogen stream, and the temperature was adjusted to be in the range of 20 to 40 ° C. while stirring for 6 hours to carry out a polymerization reaction, resulting in a viscous polyamic acid solution. The molar ratio of the tetracarboxylic dianhydride to the aromatic diamine compound used was 1.005, and the concentration of the polyamic acid solution was 25% by weight.
Next, 409 g of DMAC was added to the obtained polyamic acid solution to dilute it to a concentration of 15% by weight, and then 25.83 g of isoquinoline was added as an imidization accelerator. The polyamic acid solution was kept at a temperature of 30 to 40°C while being stirred, and 122.5 g (1.20 moles) of acetic anhydride was slowly added dropwise thereto as an imidization agent over a period of about 10 minutes. Thereafter, the liquid temperature was further kept at 30 to 40°C and stirring was continued for 12 hours to carry out a chemical imidization reaction, thereby obtaining a polyimide solution.
Next, 1000 g of the resulting polyimide solution containing the imidization agent and the imidization accelerator was transferred to a 5 L separable flask equipped with a stirrer and a stirring blade, and the temperature was kept at 15 to 25°C while stirring at a speed of 120 rpm, and 1500 g of methanol was dropped therein at a rate of 10 g/min. When about 800 g of methanol was added, the polyimide solution became cloudy, and precipitation of powdery polyimide was confirmed. Subsequently, the entire amount of methanol (1500 g) was added to complete the precipitation of polyimide.
Next, the content of the separable flask was filtered using a suction filtration device, and further washed and filtered with 1,000 g of methanol.
Thereafter, 50 g of the polyimide powder containing the filtered volatile residue was dried at 50° C. for 24 hours using a dryer equipped with a local exhaust device, the weight was measured, and the powder was further dried at 260° C. for 2 hours to remove the remaining volatile components, thereby obtaining the desired polyimide powder. The weight after drying at 50° C. for 24 hours was 43.8 g, and the weight after drying at 260° C. for 2 hours was 43.3 g, and it was confirmed that the amount of volatile components after 24 hours at 50° C. was 1.1%.
The polyimide powder thus obtained had an average particle size of 0.10 mm, and 100% by volume of the particle size distribution was in the range of 0.01 to 2 mm. The reduced viscosity was 2.1 dL/g, the weight average molecular weight (Mw) measured by size exclusion chromatography was 210,000, and the polydispersity index expressed as weight average molecular weight (Mw)/number average molecular weight (Mn) was 2.1. The weight loss rate measured by a differential thermal/thermogravimetric analyzer in the range of 200 to 300°C was 0.03%, and the imidization rate was 95% or more.

(Evaluation sample (base film))
The polyimide powder obtained by the synthesis was dissolved in dimethylacetamide in the amounts shown in Table 1, and then alumina or silica, and acrylate or blocked isocyanate were mixed, dispersed, and homogenized to prepare a coating solution for the substrate film. Next, this coating solution was applied onto a glass plate using a table coater (AFA-standard, manufactured by Coatec Co., Ltd.), dried in an inert gas oven (INL-45N1, manufactured by Yamato Scientific Co., Ltd.) at 250°C for 1 hour, and peeled off from the glass plate to form a substrate film having a thickness of 50 μm. Thereafter, each substrate film was peeled off from the glass plate to obtain evaluation samples of Examples 1 to 10 and Comparative Examples 1 to 4. The amounts in Table 1 are based on the mass of non-volatile solids.

The following evaluations were carried out on the evaluation samples of Examples 1 to 10 and Comparative Examples 1 to 4 obtained in this manner. The results are shown in Table 1.

(Evaluation of elasticity and elongation)
Both the elastic modulus and the elongation were measured under the following conditions using an EZ-SX manufactured by Shimadzu Corporation. The elastic modulus was determined from the slope of the obtained stress-strain curve at a stress range of 5 MPa to 10 MPa, and the elongation was determined from the elongation at the time of breakage of the evaluation sample.
[Test condition]
Sample size: 50mm x 5mm
Distance between grippers: 30 mm
Speed: 1 mm/min Number of measurements: 5 times The evaluation criteria for elastic modulus were as follows.
⊚: The elastic modulus was more than 7.5 GPa.
⊚: The elastic modulus was more than 7.1 GPa and 7.5 GPa or less.
Good: The elastic modulus was greater than 6.0 GPa and not greater than 7.1 GPa.
Δ: The elastic modulus was more than 3.0 GPa and not more than 6.0 GPa.
×: The elastic modulus was 3.0 GPa or less.
(2) The evaluation criteria for elongation were as follows:
⊚: The elongation rate was more than 5.0%.
Good: The elongation rate was more than 3.5% and 5.0% or less.
Δ: The elongation rate was more than 3.0% and 3.5% or less.
×: The elongation rate was 3.0% or less.

(Haze rating)
Each evaluation sample was cut to a size of 30 mm x 30 mm, and the haze (%) was measured using a haze meter (NDH 7000 II, manufactured by Nippon Denshoku Industries Co., Ltd.) in accordance with JIS K 7136: 2000. The evaluation criteria were as follows:
A: Haze was 1.5% or less.
×: Haze was more than 1.5%.

(YI Value (Yellow Index) Evaluation)
Each evaluation sample was cut to a size of 30 mm x 30 mm, and the YI was measured using a spectrophotometer (CM-5, manufactured by Konica Minolta, Inc.) in accordance with ASTM E313. The evaluation criteria were as follows.
A: The YI value was 4 or less.
×: YI value was more than 4.

(Flexibility evaluation)
A bending test was performed 200,000 times at R=2 mm using a bending tester (DMLHP-CS, manufactured by Yuasa System Co., Ltd.), and the change in appearance after the test was visually evaluated. The evaluation criteria were as follows:
◯: No physical damage such as cracks, peeling, deformation, etc., and no change in optical properties was observed.
x: Physical damage such as cracks, peeling, deformation, etc., and any change in optical properties were observed.

The components used in the examples and comparative examples shown in Table 1 are as follows.
(*1): Polyimide powder obtained in the Polyimide Synthesis Example (*2): Alumina filler manufactured by Toyo Color Co., Ltd. (average particle size 70 nm, added in a slurry dispersed in N,N-dimethylacetamide at a concentration of 20%, the values in the table exclude the solvent)
(*3): Silica filler manufactured by Nissan Chemical Co., Ltd. (average particle size 12 nm, added as a slurry dispersed in N,N-dimethylacetamide at a concentration of 20%, the values in the table exclude the solvent)
(*4): Aronix M220 manufactured by Toagosei Co., Ltd. (molecular weight 242, functional group equivalent 121 g/mol)
(*5): Aronix M309 manufactured by Toagosei Co., Ltd. (molecular weight 296, functional group equivalent 99 g/mol)
(*6): Aronix M408 manufactured by Toagosei Co., Ltd. (molecular weight 466, functional group equivalent 117 g/mol)
(*7): ARUFON UP1080 manufactured by Toagosei Co., Ltd. (weight average molecular weight 6000)
(*8): ARUFON UC3080 manufactured by Toagosei Co., Ltd. (weight average molecular weight 14000)
(*9): LANESS TRIXENE BI7951 (1,3,5-tris[(5-isocyanato-1,3,3-trimethylcyclohexyl)methyl]-1,3,5-triazine-2,4,6(1H,3H,5H)-trione, functional group equivalent: 539 g/mol)
(*10): LANESS TRIXENE BI7961 (1,3,5-tris(6-isocyanatohexyl) biuret, functional group equivalent: 410 g/mol)

The results shown in the table above show that the present invention makes it possible to obtain a resin composition that combines high elasticity without compromising flex resistance or transparency as a base film and laminate.

Claims (8)

(A) a polyimide;
(B) an alumina filler;
(C1) a (meth)acrylate having a molecular weight of 10,000 or less, or
(C2) a blocked isocyanate having an isocyanuric ring;
A solvent;
A resin composition comprising:
The resin composition (A) in which the polyimide is dissolved in the solvent (excluding a photosensitive adhesive composition containing a photopolymerization initiator and an alkali-soluble polyimide) . The resin composition according to claim 1, characterized in that the alumina filler (B) has an average particle size of 10 nm or more and 100 nm or less, and is spherical or amorphous. The laminate according to claim 1 or 2, characterized in that the alumina filler (B) is spherical. The resin composition according to any one of claims 1 to 3, characterized in that the alumina filler (B) is contained in an amount of 5 to 180 parts by mass per 100 parts by mass of the polyimide (A). The resin composition according to any one of claims 1 to 4, characterized in that the (C1) (meth)acrylate having a molecular weight of 10,000 or less or the (C2) blocked isocyanate having an isocyanuric ring is contained in an amount of 1 to 50 parts by mass per 100 parts by mass of the (A) polyimide. A substrate film obtained by applying and drying the resin composition according to any one of claims 1 to 5. A laminate comprising a hard coat layer laminated on the substrate film according to claim 6. A cover window for a display, comprising the laminate according to claim 7.