Resin composition for hue adjustment and optical laminate using the same

Abstract

To provide a resin composition for hue adjustment that can correct the color of polyimide films and has high overall light transmission and low haze, thereby having a minimal impact on visibility even when used in the front panel of an image display component, and to provide an optical laminate including the same.SOLUTION: The present invention provides a photocurable resin composition for use in hue adjustment of polyimide films, including a binder resin, a bluing agent, hollow nano silica, and a photopolymerization initiator, in which the amount of the hollow silica relative to 100 pts.wt. of the binder resin is 15-550 pts.wt.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a resin composition used for hue adjustment of polyimide films, and an optical laminate using the same. [Background technology]

[0002] Currently, image display devices such as LCDs and OLEDs are widely used in various fields, including televisions, personal computers, touch panels, and mobile phones. In recent years, these devices have been required to be thinner, lighter, and more flexible. In particular, with the advent of foldable displays, it is no longer enough to simply bend them; they must also be resistant to bending, preventing whitening or cracking even after repeated bending.

[0003] The demand for flexible displays can be met by replacing the image display component with a polymer material that has good bending properties. For example, polyimide-based substrates have been proposed as such polymer materials (Patent Document 1). Polyimide resin is a polymer that contains imide bonds in its repeating units, and because the imide bonds have strong intermolecular forces, it is a material that has the highest level of mechanical and chemical stability among many polymer materials and has good properties that can withstand repeated bending.

[0004] However, since polyimide resins are generally yellow or brown in color, when polyimide film is used as the front panel material for image display devices, even if it is a polyimide-based film with improved transparency, the color tone of the bezel and other parts may change, affecting visibility. Therefore, there was a need for an optical laminate with a polyimide-based substrate that would not significantly affect visibility when used as the front panel material for foldable displays. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2016-93992 [Overview of the project] [Problems that the invention aims to solve]

[0006] The object of the present invention is to provide a resin composition for hue adjustment that, when applied to a polyimide (hereinafter referred to as PI) film, can correct the color of the PI resin, has high total light transmittance and low haze, and therefore does not significantly affect visibility even when used as a front panel for an image display component, and an optical laminate using the same. [Means for solving the problem]

[0007] To solve the above problems, the invention of claim 1 is a resin composition used for hue adjustment of polyimide-based substrate films, comprising a binder resin (A), a bluing agent (B), hollow nanosilica (C), and a photopolymerization initiator (D), The above (A) includes urethane (meth)acrylate and / or trifunctional or more (meth)acrylate, (A) 100 parts by weight The amount of (B) is 2 to 5 parts by weight. The present invention provides a photocurable resin composition characterized by having an amount of (C) of 15 to 550 parts by weight.

[0008] Furthermore, the invention described in claim 2 provides a photocurable resin composition according to claim 1, characterized in that, in a laminate in which a cured layer of a photocurable resin composition with a thickness of 100 nm is formed on one side of a polyimide substrate film, the total light transmittance is greater than or equal to that of the polyimide substrate film alone, and the b* value is 0 or greater and less than or equal to the polyimide substrate film alone × 0.6.

[0009] Furthermore, the invention described in claim 3 is, An optical laminate characterized by having a cured layer of the photocurable resin composition according to claim 1 or 2 on a polyimide-based substrate film. To provide.

[0010] Furthermore, the invention described in claim 4 is, An optical laminate characterized by having a cured layer of the photocurable resin composition according to claim 1 or 2 on one side of a polyimide substrate film, and further having a hard coat layer on the cured layer and / or on the opposite side of the polyimide substrate. To provide. [Effects of the Invention]

[0012] The resin composition of the present invention has low haze and high total light transmittance, and when applied to a PI-based film, it can correct the yellowish color of the PI resin and improve visibility, making it useful as a resin composition for hue adjustment. [Best Mode for Carrying Out the Invention]

[0013] The composition of the present invention comprises a binder resin (A), a bluing agent (B), hollow nanosilica (C), and a photopolymerization initiator (D). In this specification, (meth)acrylate includes both acrylate and methacrylate.

[0014] The binder resin (A) used in the present invention disperses the bluing agent (B) and hollow nanosilica (C), and is the main component that constitutes the film. Examples of oligomers include urethane (meth)acrylate (hereinafter referred to as urea), epoxy (meth)acrylate, polyester (meth)acrylate, polycarbonate (meth)acrylate, acrylic (meth)acrylate, diene (meth)acrylate, etc., which can be used alone or in combination of two or more types. Among these, urea is preferred because it has excellent adhesion to the PI substrate and, when used as a primer, also provides stable adhesion to the resin that forms the upper layer.

[0015] The aforementioned urea is not particularly limited and can be obtained, for example, by reacting a urethane prepolymer obtained by reacting a polyol with an excess of polyisocyanate with a (meth)acrylate having a hydroxyl group, or by reacting a polyisocyanate with a (meth)acrylate having a hydroxyl group.

[0016] There are no particular restrictions on the method of synthesizing the ureaac, and known methods can be used. The reaction may be carried out without a solvent, but as the molecular weight increases, the viscosity becomes high and stirring may become difficult, so ketones such as butanone, aromatic inert solvents such as xylene, etc. may be used. Furthermore, it is preferable to use a catalyst for the reaction between the hydroxyl group of (meth)acrylate and the isocyanate group. Examples of catalysts in this case include tin-based catalysts such as dibutyltin dilaurate and metal alkoxide-based catalysts such as cobalt naphthenate. The reaction temperature can be set as appropriate, but 40 to 120°C is preferred, and 60 to 100°C is more preferred.

[0017] Polyisocyanates used in the synthesis of ureac include hexamethylene diisocyanate (hereinafter referred to as HDI), isophorone diisocyanate (hereinafter referred to as IPDI), diphenylmethane diisocyanate, tolylene diisocyanate, dicyclohexylmethane-4,4'-diisocyanate, hydrogenated xylylene diisocyanate, methylcyclohexylene diisocyanate, HDI isocyanurate, and IPDI isocyanurate. These may be used individually or in combination of two or more. Among these, aliphatic and alicyclic diisocyanates with high weather resistance and low yellowing are preferred, and among them, HDI with high stretchability and IPDI with high rigidity are preferred.

[0018] Examples of the (meth)acrylate having a hydroxyl group used in the synthesis of ureak include monofunctional (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, difunctional (meth)acrylates such as glycerin di(meth)acrylate, trifunctional (meth)acrylates such as pentaerythritol tri(meth)acrylate, tetrafunctional (meth)acrylates such as dipentaerythritol tetra(meth)acrylate, pentafunctional (meth)acrylates such as dipentaerythritol penta(meth)acrylate, etc. They can be used alone or in combination of two types. Among these, trifunctional to pentafunctional ones are preferred in terms of high reactivity. Particularly, pentaerythritol triacrylate and dipentaerythritol hexaacrylate are preferred because even when a bluing agent is present, a film with good reactivity and high hardness can be obtained.

[0019] A low molecular weight binder may be used as a component other than the oligomer. For example, (meth)acrylates having functional groups such as aliphatic, alicyclic, polyether skeletons, hydroxyl groups and amino groups, and acrylamide compounds can be mentioned, and they can be used alone or in combination of two or more types. From the viewpoint of reactivity, the number of functional groups is preferably 3 or more, and more preferably 4 or more. Examples include pentaerythritol triacrylate (hereinafter referred to as PET3A), pentaerythritol tetraacrylate (hereinafter referred to as PETA4A), dipentaerythritol tetraacrylate, dipentaerythritol pentaacrylate, dipentaerythritol hexaacrylate, etc.

[0020] The blending amount of the above (A) is preferably 10 to 85% by weight, more preferably 15 to 80% by weight, and particularly preferably 25 to 70% by weight based on the total solid content. By setting it at 10% by weight or more, sufficient curability and film strength can be ensured, and by setting it at 85% by weight or less, sufficient total light transmittance can be ensured.

[0021] The bluing agent (B) used in the present invention is an additive that mainly absorbs light in the orange to yellow wavelength region of the visible light region and is blended for the purpose of adjusting the hue of the PI film. Examples thereof include inorganic dyes and pigments such as ultramarine and cobalt blue, and condensed polycyclic bluing agents such as anthraquinone-based and phthalocyanine-based ones, and they can be used alone or in combination of two or more. Among these, condensed polycyclic bluing agents are preferred from the viewpoints of heat resistance, light resistance, and solubility, and anthraquinone-based ones are particularly preferred in terms of excellent stability.

[0022] The blending amount of the (B) is preferably adjusted according to the total light transmittance and b * value of the PI substrate. For example, when coated on one side of the PI substrate with a thickness of 100 nm, it is preferable to blend (B) so that the total light transmittance including the PI substrate is not less than that of the PI substrate alone, and the b * value is not less than 0 and not more than 0.6 times that of the polyimide-based substrate film alone.

[0023] Taking an example of an embodiment of the present invention, the total light transmittance of the PI substrate (thickness: 50 μm) itself is 90.0%, haze is 0.23%, b * value is 1.28, and refractive index is 1.5814. In this case, as the blending amount of the (B), it is preferable to set so that the total light transmittance including the PI substrate is not less than 90% and the b * value is 0 to 0.77 (= 1.28 × 0.6). Specifically, 2 to 5 parts are preferable, and 3 to 4 parts are more preferable with respect to 100 parts by weight of (A). Also, with respect to the total amount of solids, 0.45 to 2.5% by weight is preferable, and 0.5 to 2.3% by weight is more preferable.

[0024] The hollow nanosilica (C) used in this invention is silica particle having a cavity containing air with a refractive index of 1, and is blended for the purpose of lowering the refractive index of the cured layer and improving the overall light transmittance including the PI substrate. The primary particle diameter of (C) is preferably 5 to 150 nm, more preferably 10 to 100 nm, and particularly preferably 40 to 80 nm. By setting it within this range, good dispersibility can be obtained without impairing the transparency of the cured layer. In particular, if it is 40 to 80 nm, the refractive index can be lowered by increasing the cavity occupancy rate while ensuring an outer shell thickness that does not result in insufficient strength. A commercially available product is Thru-Ria 4320 (product name: manufactured by JGC Catalysts & Chemicals, primary average particle diameter 60 nm).

[0025] The amount of (C) is 15 to 550 parts by weight per 100 parts by weight of (A), preferably 20 to 500 parts, and more preferably 30 to 100 parts. If it is less than 15 parts by weight, sufficient total light transmittance may not be ensured, and if it is more than 550 parts by weight, b * The value may become too large. Furthermore, the amount blended relative to the total solid content is preferably 10-90% by weight, more preferably 15-85% by weight, and even more preferably 20-40% by weight.

[0026] The photopolymerization initiator (D) used in this invention generates radicals upon irradiation with ultraviolet light or electron beams, and these radicals trigger the polymerization reaction. General-purpose photopolymerization initiators such as benzyl ketal, acetophenone, and phosphine oxide can be used. By arbitrarily selecting the light absorption wavelength of the polymerization initiator, curability can be imparted over a wide wavelength range from the ultraviolet region to the visible light region. Specifically, examples include 2,2-dimethoxy-1,2-diphenylethane-1-one as a benzyl ketal, 1-hydroxycyclohexyl-phenyl-ketone and 1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propane-1-one as α-hydroxyacetophenones, 2-methyl-1-(4-methylthiophenyl)-2-morpholinopropane-1-one as an α-aminoacetophenone, and 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide and bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide as acylphosphine oxides, which can be used individually or in combination of two or more.

[0027] The aforementioned (C) preferably contains an α-hydroxyacetophenone-based material that is less prone to yellowing, and commercially available examples include Omnirad2959, Omnirad127D, and Omnirad184 (product name: manufactured by IGM Resins). Among these, Omnirad2959 is particularly preferred because it exhibits less yellowing and excellent scratch resistance.

[0028] The resin composition of the present invention (hereinafter referred to as "this resin composition") may further contain, as necessary, leveling agents, ultraviolet absorbers, antioxidants, adhesion promoters, defoaming agents, thickeners, precipitate inhibitors, antistatic agents, antifogging agents, antibacterial agents, organic fine particles, etc., to the extent that it does not impair performance.

[0029] When applying this resin composition, it may be diluted with solvents such as toluene, isobutanol, ethyl acetate, butyl acetate, hexane, cyclohexane, cyclohexanone, methylcyclohexanone, acetone, methyl ethyl ketone, methyl isobutyl ketone, or propylene glycol monomethyl ether (hereinafter referred to as PGM) to improve coating properties. While a solid content of 1-10% is exemplified when diluting, there is no specific requirement, and it can be appropriately set to achieve a viscosity that facilitates coating.

[0030] The method of applying the resin composition of this invention is not particularly limited, and it can be formed by known coating methods such as spray coating, roll coating, die coating, air knife coating, blade coating, spin coating, reverse coating, gravure coating, and wire bar coating, or by printing methods such as gravure printing, screen printing, offset printing, and inkjet printing.

[0031] The film thickness of this resin composition is preferably 50 to 200 nm when dry, and more preferably 80 to 150 nm. By setting it within this range, sufficient color correction can be achieved by the effect of (B), and at the same time, a sufficiently high total light transmittance can be achieved by the effect of (C).

[0032] The light source used for ultraviolet irradiation when curing the resin composition of this invention may be a low-pressure mercury lamp, a high-pressure mercury lamp, an ultra-high-pressure mercury lamp, a carbon arc lamp, a xenon lamp, a metal halide lamp, an LED lamp, or an electrodeless ultraviolet lamp, and is not particularly specified. Ultraviolet irradiation may be performed in air, but in the case of thin films, it is preferable to perform the irradiation in an inert gas atmosphere such as nitrogen or argon to avoid inhibition of curing by oxygen in the air. Furthermore, curing performance can be improved by heating the back roll or the coating film with an IR heater during ultraviolet irradiation.

[0033] The ultraviolet irradiation conditions for curing the resin composition of this invention are an irradiation intensity of 500 mW / cm². 2 ~3000mW / cm 2 Exposure dose: 50-400 mJ / cm² 2Examples are given, but the work is not limited to these.

[0034] The total light transmittance of a laminate having a 100 nm thick cured layer of this resin composition on one side of a PI-based substrate is preferably greater than or equal to that of the polyimide-based substrate film alone, and the b* value is preferably 0 or greater and 0.6 times or less of that of the polyimide-based substrate film alone. By keeping it within this range, a sufficient color correction effect can be confirmed. Furthermore, the absolute value of the b* value is more preferably between 0 and 0.5. Within this range, the color tone change of the bezel and other parts becomes very small, and the impact on visibility becomes very small.

[0035] This resin composition is used by coating at least one side of a PI-based substrate. Direct coating of the PI-based substrate is preferred, but it may also be coated via another resin curing layer. Furthermore, when a laminate having a cured layer of this resin composition is used as the front panel of an image processing device, it is preferable to further provide a hard coat layer. The hard coat layer may be placed on the cured layer of this resin composition, or it may be placed directly on the opposite side of the PI-based substrate.

[0036] The present invention will be described in detail below with reference to examples and comparative examples, but these are merely examples and the invention is not limited to them. Unless otherwise specified, measurements were taken under conditions of 25°C and 65% relative humidity, and the units in the formulation table are parts by weight.

[0037] Example 1 As (A), DPHA (product name: manufactured by Nippon Kayaku Co., Ltd., a mixture of dipentaerythritol pentaacrylate and dipentaerythritol hexaacrylate, solid content 100%), as (B), Kayaset Blue A-2R (product name: manufactured by Nippon Kayaku Co., Ltd., anthraquinone-based dye, solid content 100%), as (C), Thru-ria 4320 (product name: manufactured by JGC Catalysts & Chemicals Co., Ltd., average particle size 60 nm, solid content 20.5%), and as (D), Omnirad 2959 (product name: manufactured by IGM Resins, α-hydroxyacetophenone-based) were mixed and stirred until uniformly dissolved and dispersed according to the formulations shown in Table 1. Further dilution and stirring were performed by adding PGM to bring the solid content to 5%, thereby obtaining the resin composition of Example 1.

[0038] Examples 2-11 In addition to the materials used in Example 1, PET-30 (product name: manufactured by Nippon Kayaku Co., Ltd., a mixture of PET3A and PET4A), MT-3553 (product name: manufactured by Toagosei Co., Ltd., a polyfunctional acrylate), Ureac 1 (reaction product of HDI and PET3A, 90% solids, hexafunctional), Ureac 2 (reaction product of HDI and DPHA, 100% solids, decafunctional), and Ureac 3 (reaction product of IPDI isocyanurate and PET3A, 80% solids, 9afunctional) were mixed as (A) in the proportions shown in Table 1 until uniformly dissolved and dispersed. Further dilution and mixing were performed by adding PGM to bring the solids content to 5%, thereby obtaining the resin compositions of Examples 2 to 11.

[0039] Comparative Examples 1-5 In addition to the materials used in the examples, PGM-AC-4130Y (product name: manufactured by Nissan Chemical Corporation, average particle size 45 nm, acrylic surface-treated solid silica, solid content 32.1%) was mixed with the ingredients shown in Table 2 until it was uniformly dissolved and dispersed. Further dilution and mixing were performed by adding PGM until the solid content reached 5%, to obtain the resin compositions of Comparative Examples 1 to 5.

[0040] Table 1 JPEG0007887282000001.jpg74134

[0041] Table 2 JPEG0007887282000002.jpg143152

[0042] The evaluation method was as follows.

[0043] Preparation of evaluation film On one side of a PI substrate (thickness: 50 μm), the present resin composition was applied to a dry film thickness of 100 nm, dried at 80°C for 60 seconds, and then cured under a nitrogen atmosphere using an H-valve of an electrodeless lamp manufactured by Heraeus at an output of 1000 mW / cm 2 , 200 mJ / cm 2 to prepare an evaluation film. Photochemical properties of the PI substrate alone: total light transmittance 90.0%, haze 0.23%, b* value 1.28, YI value 2.18, refractive index 1.5814

[0044] Total light transmittance: Measured using a haze meter Haze-GARD2 manufactured by Toyo Seiki Seisaku-sho, Ltd. in accordance with JIS K7361-1. ○ was used for 90% or more, and × was used for less than 90%. The evaluation criteria were based on the total light transmittance of the PI film alone.

[0045] Haze: Measured using a haze meter Haze-GARD2 manufactured by Toyo Seiki Seisaku-sho, Ltd. in accordance with JIS K7361-1. ○ was used for 0.30% or less, and × was used for more than 0.30%.

[0046] b* value: The above evaluation film was measured using a color difference meter SD-6000 manufactured by Nippon Denshoku Industries Co., Ltd. in accordance with JIS K 0062. The evaluation was ◎ for less than 0.5, ○ for 0.5 to 0.77, and × for more than 0.77. The 0.77 in the evaluation criteria was the value obtained by multiplying the b* value 1.28 of the PI film alone by 0.6.

[0047] Evaluation results Table 3 JPEG0007887282000003.jpg49154

[0048] Table 4 JPEG0007887282000004.jpg98170

[0049] The example showed no problems and performed well in all evaluations, including total light transmittance, haze, and b* value.

[0050] On the other hand, Comparative Example 1, which did not contain (B), had a high b* value, while Comparative Example 2, which did not contain (C), and Comparative Example 3, which contained a small amount of (C), had low total light transmittance. Furthermore, Comparative Example 4, which contained a large amount of (C), had a high b* value, and Comparative Example 5, which used solid silica, had low total light transmittance; all of these were unsuitable for the present invention.

Claims

1. A photocurable resin composition for hue adjustment of polyimide-based substrate films, comprising a binder resin (A), a bluing agent (B), hollow nanosilica (C), and a photopolymerization initiator (D), wherein (A) comprises urethane (meth)acrylate and / or trifunctional or more (meth)acrylate, and the amount of (B) is 2 to 5 parts by weight and the amount of (C) is 15 to 550 parts by weight per 100 parts by weight of (A).

2. The photocurable resin composition according to claim 1, characterized in that, in a laminate in which a cured layer of a photocurable resin composition with a thickness of 100 nm is formed on one side of a polyimide substrate film, the total light transmittance is greater than or equal to that of the polyimide substrate film alone, and the b* value is 0 or greater and less than or equal to the polyimide substrate film alone × 0.

6.

3. An optical laminate characterized by having a cured layer of the photocurable resin composition according to claim 1 or 2 on a polyimide-based substrate film.

4. An optical laminate characterized by having a cured layer of the photocurable resin composition according to claim 1 or 2 on one side of a polyimide substrate film, and further having a hard coat layer on the cured layer and / or on the opposite side of the polyimide substrate.

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