Optically activated energy ray polymerizable adhesives and optical laminates

Abstract

To provide an active energy ray curing adhesive and a laminate using the same, which can control high refractive index and Abbe number and form laminates with excellent transparency, adhesive strength, and heat resistance. [Solution] An optically active energy ray polymerizable adhesive comprising metal oxide particles (X), a monofunctional monomer (A) that does not have an aromatic ring, and a photopolymerization initiator, wherein the monofunctional monomer (A) includes a monofunctional monomer (A1) that has a hydroxyl group and does not have an aromatic ring, does not contain epoxy (meth)acrylate or polyester (meth)acrylate, and does not contain aromatic ring moieties in an amount of 5% by mass or more of the total amount of the adhesive.

Description

[Technical Field]

[0001] The present invention relates to an optically active energy ray polymerizable adhesive and an optical laminate. [Background technology]

[0002] Image display devices such as liquid crystal displays (LCDs) utilize layers on their surfaces that have various functions, such as anti-glare, viewing angle adjustment, and hard coating. When bonding these functional layers, such as anti-reflective films and conductive films (ITO films), to the LCD panel, adhesives using acrylic polymers were traditionally used. However, mobile information terminals such as smartphones have smaller screens and require greater portability compared to televisions, leading to a strong market demand for thinner LCD panels. To replace adhesives whose bonding strength decreases with thinner layers, thermosetting epoxy adhesives and UV-curing acrylic or epoxy adhesives, which offer relatively high bonding strength even at thinner layers, were being considered.

[0003] In addition, the market has demanded adhesives that combine adhesive and optical functions, and furthermore, due to the coating and bonding processes of adhesives, there is a demand for solvent-free adhesives (adhesives that do not contain solvents). Optical functions include, for example, refractive index control. Liquid crystal panels consist of layers with multiple optical functions, such as phase difference plates, laminated on a glass substrate and a polarizing plate. However, since the refractive index of the adhesive used for lamination is generally around 1.47, there is a large difference in refractive index between the adhesive and each component used for lamination (refractive index glass: around 1.52, acrylic resin: around 1.51, polycycloolefin: 1.53-1.54, polycarbonate: 1.58-1.60, polyethylene terephthalate: around 1.65). This has resulted in problems such as the screen becoming darker and the clarity decreasing as light emitted from the liquid crystal panel is attenuated as it passes through each layer. To solve this problem, adhesive coatings, adhesives, and the like containing metal oxide particles have been disclosed (Patent Documents 1-3).

[0004] However, adhesives containing these conventional metal oxide particles have a problem in that they contain aromatic compounds to adjust the refractive index, resulting in a low Abbe number and having an adverse effect on chromatic aberration. In addition, when polyester (meth)acrylate or epoxy (meth)acrylate is used as a component in the adhesive, there is a problem that the haze of the coating film deteriorates as the content of the metal oxide particles increases. Furthermore, when thermoforming a laminate bonded with an adhesive containing metal oxide particles, there is also a problem that peeling occurs at high temperatures.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0006] The problem to be solved by the present invention is to provide an active energy ray-curable adhesive capable of controlling a high refractive index and Abbe number and forming a laminate excellent in transparency, adhesive strength, and heat resistance, and a laminate using the same.

Means for Solving the Problems

[0007] In order to solve the above problems, the present inventors have conducted intensive studies and have completed the present invention. That is, the present invention is an active energy ray-curable adhesive for optical use containing metal oxide particles (X), a monofunctional monomer (A) having no aromatic ring, and a photopolymerization initiator, wherein the monofunctional monomer (A) contains a monofunctional monomer (A1) having a hydroxyl group and no aromatic ring, does not contain epoxy (meth) acrylate and polyester (meth) acrylate, and contains no more than 5% by mass of aromatic ring sites in 100% by mass of the total amount of the adhesive, and relates to an active energy ray-curable adhesive for optical use.

[0008] Further, the present invention relates to the above active energy ray-curable adhesive for optical use, wherein the monofunctional monomer (A) further contains one or more selected from the group consisting of a monofunctional monomer (A2) having an aliphatic cyclic hydrocarbon group and no aromatic ring, and a monofunctional monomer (A3) having two or more repeating structures of an alkyleneoxy group and no aromatic ring.

[0009] Further, the present invention relates to the above active energy ray-curable adhesive for optical use, wherein the metal oxide particles (X) are metal oxide particles (X) containing one or more elements selected from the group consisting of titanium, zinc, zirconium, antimony, indium, tin, and aluminum.

[0010] Further, the present invention relates to the above active energy ray-curable adhesive for optical use, which further contains a bifunctional monomer (B) having no aromatic ring.

[0011] Further, the present invention relates to the above active energy ray-curable adhesive for optical use, wherein the bifunctional monomer (B) further contains one or more selected from the group consisting of a bifunctional monomer (B1) having an aliphatic cyclic hydrocarbon group and no aromatic ring, and a bifunctional monomer (B2) having two or more repeating structures of an alkyleneoxy group and no aromatic ring.

[0012] Further, the present invention relates to the above active energy ray-curable adhesive for optical use, wherein the photopolymerization initiator has a molar absorption coefficient at 365 nm of 200 L·mol

[0012] , , , , -1 , <0·cm -1 The following is a photopolymerization initiator for the above-mentioned optically active energy ray polymerizable adhesive.

[0013] Furthermore, the present invention relates to an optical laminate in which a first substrate, an adhesive layer made of the above-mentioned optically active energy ray polymerizable adhesive, and a second substrate are arranged in this order.

[0014] Furthermore, the present invention relates to the above-mentioned optical laminate, wherein the refractive index of the adhesive layer is 1.52 to 1.60. [Effects of the Invention]

[0015] This invention makes it possible to control high refractive index and Abbe number, and to provide an adhesive with excellent transparency, adhesive strength, and heat resistance. [Modes for carrying out the invention]

[0016] Preferred embodiments of the present invention are described below. In this specification, when "(meth)acrylic" is written, it refers to "acrylic or methacrylic" unless otherwise specified. Furthermore, "monomer" refers to "a monomer having an ethylenically unsaturated double bond group", "monofunctional monomer" refers to "a monomer having one ethylenically unsaturated double bond group", and "polyfunctional monomer" refers to "a monomer having two or more ethylenically unsaturated double bond groups".

[0017] Furthermore, "monofunctional monomer without an aromatic ring (A)" may be abbreviated as "compound (A)", "monofunctional monomer having a hydroxyl group and without an aromatic ring (A1)" as "compound (A1)", "monofunctional monomer having an aliphatic cyclic hydrocarbon group and without an aromatic ring (A2)" as "compound (A2)", "monofunctional monomer having two or more repeating alkylene oxy groups and without an aromatic ring (A3)" as "compound (A3)", "difunctional monomer without an aromatic ring (B)" as "compound (B)", "difunctional monomer having an aliphatic cyclic hydrocarbon group and without an aromatic ring (B1)" as "compound (B1)", "difunctional monomer having two or more repeating alkylene oxy groups and without an aromatic ring (B2)" as "compound (B2)", and "optical active energy ray curable adhesive" as "adhesive".

[0018] <Optical-grade active energy ray polymerizable adhesive> The optically active energy ray polymerizable adhesive of the present invention (hereinafter sometimes simply referred to as "adhesive") contains metal oxide particles (X), a monofunctional monomer (A) that does not have an aromatic ring, and a photopolymerization initiator. The monofunctional monomer (A) includes a monofunctional monomer (A1) that has a hydroxyl group and does not have an aromatic ring, and does not contain epoxy (meth)acrylate or polyester (meth)acrylate. The adhesive is characterized in that it does not contain 5% by mass or more of aromatic ring moieties in 100% by mass of the total amount of the adhesive. The materials constituting the adhesive will be described below.

[0019] <Metal oxide particles (X)> The metal oxide particles (X) have the function of adjusting the refractive index of the adhesive, and by controlling the type and amount of metal oxide particles (X) added, an adhesive layer with a high refractive index can be formed. Furthermore, when D50 is defined as the particle size at which the cumulative frequency from the small particle size side accounts for 50% in the volume-based cumulative particle size distribution, the D50 of the metal oxide particles (X) in the adhesive is preferably 10 to 200 nm, and more preferably 10 to 100 nm. By being 200 nm or less, the adhesive layer is less prone to light scattering and has excellent transparency.

[0020] The D50 of metal oxide particles (X) can be measured using a particle size distribution analyzer, particularly one using dynamic light scattering (such as the "NANOTRAC WAVE II EX150" manufactured by Microtrac-Bell). In this specification, methyl ethyl ketone was used as the solvent, and the average value of three 60-second measurements were taken at a concentration in the range of 1.0 ± 0.2.

[0021] The metal oxide particles (X) preferably contain one or more elements from titanium, zinc, zirconium, antimony, indium, tin, and aluminum. Therefore, specific examples of metal oxide particles (X) include antimony pentoxide, antimony-doped tin oxide (ATO), tin-doped indium oxide (ITO), fluorine-doped tin oxide (FTO), phosphorus-doped tin oxide (PTO), zinc antimonate (AZO), indium-doped zinc oxide (IZO), tin oxide, ATO-coated titanium oxide, aluminum-doped zinc oxide, titanium oxide, zinc oxide, zirconium oxide, aluminum oxide, etc. These can be used individually or in combination of two or more.

[0022] The shapes of metal oxide particles (X) include spherical, rectangular, needle-shaped, fibrous, spindle-shaped, and plate-shaped particles. Here, the average primary particle diameter of metal oxide particles other than spherical ones is calculated by averaging the shortest sides that make up the particle's shape. For example, if a particle has both a major axis length and a minor axis length, the average minor axis length is used for calculation.

[0023] The refractive index of the metal oxide particles (X) is preferably between 1.7 and 2.8. By using metal oxide particles (X) having a refractive index within this range, the refractive index of the adhesive can be adjusted to a high value. Examples of metal oxide particles (X) having a refractive index within this range include titanium oxide (refractive index 2.72), zinc oxide (refractive index 1.95), zirconium oxide (refractive index 2.22), and aluminum oxide (refractive index 1.77). Titanium oxide (refractive index 2.72) or zirconium oxide (refractive index 2.22) are preferred due to their high refractive index.

[0024] The metal oxide particles (X) are preferably present in an amount of 10 to 70% by mass, and more preferably 10 to 60% by mass, of the total adhesive mass. Including 10% by mass or more facilitates refractive index control, while keeping it at 70% by mass or less allows for good control of haze, adhesive strength, and heat resistance.

[0025] <Monofunctional monomer (A) without an aromatic ring> Compound (A) refers to a compound that does not have an aromatic ring and has one ethylenically unsaturated double bond group. Compound (A) can be broadly classified into monofunctional monomers (A1) that have a hydroxyl group and do not have an aromatic ring, monofunctional monomers (A2) that have an aliphatic cyclic hydrocarbon group and do not have an aromatic ring, monofunctional monomers (A3) that have two or more repeating alkylene oxy groups and do not have an aromatic ring, and other monofunctional (meth)acrylates that do not have an aromatic ring.

[0026] The adhesive of the present invention, by containing compound (A), can have a low viscosity even without solvents, has good wettability to the substrate, and can have a low crosslink density after curing, resulting in good adhesive strength. Furthermore, since compound (A) does not have an aromatic ring, a high Abbe number can be easily obtained.

[0027] <A monofunctional monomer (A1) having a hydroxyl group and lacking an aromatic ring> Compound (A1) refers to a compound that has a hydroxyl group, lacks an aromatic ring, and has one ethylenically unsaturated double bond group. Including compound (A1) in the adhesive improves the dispersion of metal oxide particles (X), resulting in improved haze.

[0028] The content of compound (A1) is preferably 10 to 60% by mass, and more preferably 20 to 50% by mass, of the total 100% by mass of monomers contained in the adhesive. When it is 10 to 60% by mass, haze and adhesive strength are further improved.

[0029] Examples of compound (A1) include hydroxyl group-containing (meth)acrylic acid esters such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, and cyclohexanedimethanol mono(meth)acrylate;

[0030] (Meth)acrylic acid esters obtained by ring-opening addition of ε-caprolactone to the above-mentioned hydroxyl group-containing (meth)acrylic acid esters; Alkylene oxide-modified (meth)acrylic acid esters having the above-mentioned hydroxyl group-containing alkylene oxide; Hydroxyl group-containing vinyl ethers such as 2-hydroxyethyl vinyl ether, diethylene glycol monovinyl ether, and 4-hydroxybutyl vinyl ether; Examples include hydroxyethyl (meth)acrylamide and other hydroxyl group-containing (meth)acrylamides.

[0031] From the viewpoint of maintaining a good dispersion state of the metal oxide particles (X), the compound (A1) is preferably 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, or diethylene glycol mono(meth)acrylate, with 4-hydroxybutyl (meth)acrylate being more preferred.

[0032] <A monofunctional monomer (A2) having an aliphatic cyclic hydrocarbon group and lacking an aromatic ring> Compound (A2) is a compound having an aliphatic cyclic hydrocarbon group, lacking an aromatic ring, and possessing one ethylenically unsaturated double bond group. However, compounds having a hydroxyl group, such as compound (A1), are excluded. Including compound (A2) in the adhesive of the present invention is preferable because it reduces curing shrinkage, improves the cohesive strength of the adhesive coating, and enhances adhesive strength.

[0033] The content of compound (A2) is preferably 10 to 50% by mass, and more preferably 10 to 40% by mass, of the total 100% by mass of monomers contained in the adhesive. The adhesive strength is further improved when it is 10% to 50% by mass.

[0034] Examples of compound (A2) include cyclohexyl (meth)acrylate, 3,3,5-trimethylcyclohexyl (meth)acrylate, t-butylcyclohexyl (meth)acrylate, dicyclopentenyl (meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate, dicyclopentanyl (meth)acrylate, isobornyl (meth)acrylate, 2-methyl-2-adamantyl (meth)acrylate, 2-ethyl-2-adamantyl (meth)acrylate, and 2-propyl-2-adamantyl (meth)acrylate. Of these, dicyclopentenyl (meth)acrylate, dicyclopentanyl (meth)acrylate, and isobornyl (meth)acrylate are particularly preferred due to their excellent adhesive strength.

[0035] <A monofunctional monomer (A3) having two or more repeating alkylene oxy groups and lacking an aromatic ring> Compound (A3) is a compound having two or more repeating alkylene oxy groups, lacking an aromatic ring, and possessing one ethylenically unsaturated double bond group. However, compounds having hydroxyl groups and aliphatic cyclic hydrocarbon groups are excluded. Including compound (A3) in the adhesive of the present invention is preferable because it forms an interaction between the alkylene oxy group and the substrate, reducing curing shrinkage and improving the cohesive force of the adhesive coating, thereby improving adhesive strength.

[0036] The content of compound (A3) is preferably 10 to 50% by mass, and more preferably 10 to 40% by mass, of the total 100% by mass of monomers contained in the adhesive. Adhesion is further improved when it is 10% by mass or more, and adhesion is further improved on a wide range of substrates when it is 50% by mass or less.

[0037] Examples of compound (A3) include polyethylene glycol monoalkyl ether mono(meth)acrylates such as ethyl carbitol (meth)acrylate, methoxytriethylene glycol (meth)acrylate, and methoxypolyethylene glycol (meth)acrylate; Polypropylene glycol monoalkyl ether mono(meth)acrylates such as methoxydipropylene glycol (meth)acrylate; Examples include polyethylene glycol, polypropylene glycol, monoalkyl ether, and mono(meth)acrylate, with ethyl carbitol (meth)acrylate (also referred to as "carbitol (meth)acrylate") being particularly preferred due to its excellent adhesive strength.

[0038] The adhesive of the present invention may also contain monofunctional (meth)acrylates that do not have other aromatic rings. Examples of monofunctional (meth)acrylates that do not have other aromatic rings include butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, n-hexyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, isostearyl (meth)acrylate, cetyl (meth)acrylate, tridecyl (meth)acrylate, and other monofunctional (meth)acrylates that have alkyl groups and do not have aromatic rings;

[0039] Examples of monofunctional (meth)acrylates that have an oxygen-containing heterocycle in their ring structure and lack an aromatic ring include (2-methyl-2-ethyl-1,3-dioxolan-4-yl)methyl (meth)acrylate, 5-ethyl-1,3-dioxan-5-ylmethyl (meth)acrylate, (2-oxo-1,3-dioxolan-4-yl)methyl (meth)acrylate, and 1,3-dioxan-2-one-5-yl (meth)acrylate.

[0040] <Aromatic ring-less bifunctional monomer (B)> Compound (B) is a compound that does not have an aromatic ring and has two ethylenically unsaturated double bond groups. The inclusion of compound (B) improves the crosslinking density of the cured adhesive film and enhances its heat resistance.

[0041] Compound (B) is preferably present in an amount of 1 to 50% by mass, and more preferably 3 to 30% by mass, of the total mass of monomers. This range results in better heat resistance.

[0042] Compound (B) is broadly classified into compounds (B1) having an aliphatic cyclic hydrocarbon group and no aromatic ring, and having two ethylenically unsaturated double bond groups, compounds (B2) having two or more repeating alkylene oxy groups and no aromatic ring, and having two ethylenically unsaturated double bond groups, and other bifunctional monomers. It is preferable that it contains at least one selected from compound (B1) and compound (B2). However, among compound (B), compounds having an aliphatic cyclic hydrocarbon group and two or more repeating alkylene oxy groups shall belong to compound (B2). Compound (B2) is preferable to include in the adhesive because it is excellent in achieving both adhesive strength and heat resistance. It is more preferable that compound (B2) has a weight-average molecular weight of 400 to 2000.

[0043] Examples of compound (B1) include cyclohexanedimethanol di(meth)acrylate, tricyclodecanedimethanol di(meth)acrylate, hydrogenated bisphenol A di(meth)acrylate, hydrogenated bisphenol A di(meth)acrylate, and ethylene oxide (EO)-modified hydrogenated bisphenol A di(meth)acrylate.

[0044] Examples of compound (B2) include diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, dipropylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, and polypropylene glycol di(meth)acrylate, which have alkylene oxy groups and do not have aromatic rings.

[0045] Compound (B2) is preferably a bifunctional (meth)acrylate having an alkylene oxy group because it improves adhesive strength. A weight-average molecular weight of 500 to 2000 is even more preferable because it improves adhesive strength.

[0046] The compound may also contain other bifunctional monomers that do not fall under compounds (B1) and (B2). Examples of other bifunctional monomers include glycerin di(meth)acrylate, trimethylolpropane di(meth)acrylate, pentaerythritol di(meth)acrylate, sorbitol di(meth)acrylate, and isocyanuric acid ethoxy-modified diacrylate.

[0047] The adhesive of the present invention may contain trifunctional monomers without aromatic rings and tetrafunctional monomers without aromatic rings. Examples of trifunctional monomers without aromatic rings include glycerin tri(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, sorbitol tri(meth)acrylate, trifunctional (meth)acrylic acid esters such as 1,1,1-trishydroxymethylethane tri(meth)acrylic acid and tris(2-acryloyloxyethyl) isocyanurate.

[0048] Examples of tetrafunctional monomers include tetrafunctional (meth)acrylic acid esters such as pentaerythritol tetra(meth)acrylate, 2,2-bis(hydroxymethyl)1,3-propanediol tetra(meth)acrylate, sorbitol tetra(meth)acrylate, and ditrimethylolpropane tetra(meth)acrylate.

[0049] The adhesive of the present invention may contain a cationic polymerizable compound having a structure without an aromatic ring. Examples of the cationic polymerizable compound having a structure without an aromatic ring include 2-ethylhexyl glycidyl ether and hexanediol diglycidyl ether.

[0050] <Photoinitiator> A photoinitiator is a compound having the property of initiating radical polymerization by photoexcitation. Examples thereof include monocarbonyl compounds, dicarbonyl compounds, acetophenone compounds, benzoin ether compounds, acylphosphine oxide compounds, aminocarbonyl compounds and the like.

[0051] The photoinitiator preferably has a molar extinction coefficient at 365 nm of 200 L·mol -1 ·cm -1 or less. More preferably, the molar extinction coefficient is 50 L·mol -1 ·cm -1 or less. When the molar extinction coefficient of the photoinitiator is 200 L·mol -1 ·cm -1 or less, the Abbe number becomes better.

[0052] Examples of the photoinitiator having a molar extinction coefficient at 365 nm of 200 L·mol -1 ·cm -1 or less include 2,2-dimethoxy-2-phenylacetophenone (molar extinction coefficient at 365 nm: 100 L·mol -1 ·cm -1 ), 1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-methylpropanone (molar extinction coefficient at 365 nm: 100 L·mol -1 ·cm -1 ), 2-hydroxy-1-(4-(4-(2-hydroxy-2-methylpropionyl)benzyl)phenyl)-2-methylpropane-1-one (molar extinction coefficient at 365 nm: 51 L·mol -1 ·cm -1), 1-hydroxycyclohexyl-phenyl ketone (molar extinction coefficient at 365 nm: 0 L·mol) -1 ·cm -1 ), 2-hydroxy-2-methyl-1-phenylpropanone (molar extinction coefficient at 365 nm: 0 L·mol) -1 ·cm -1 ) are some examples.

[0053] The molar extinction coefficient at 365 nm is 200 L·mol. -1 ·cm -1 Among photopolymerization initiators exceeding a certain level, preferred photopolymerization initiators include 2,4,6-trimethylbenzoyldiphenylphosphine oxide (molar extinction coefficient at 365 nm: 1397 L·mol). -1 ·cm -1 ) are some examples.

[0054] The content of the photopolymerization initiator is preferably 0.1 to 5% by mass, and more preferably 0.5 to 3% by mass, based on 100% by mass of the adhesive. If the content is 0.1% by mass or more, the curing of the adhesive is good, and if it is 5% by mass or less, the content of aromatic moieties is suppressed, resulting in a better Abbe number.

[0055] The adhesive of the present invention does not contain epoxy (meth)acrylate or polyester (meth)acrylate. The absence of epoxy (meth)acrylate and polyester (meth)acrylate tends to result in lower coating film haze when the metal oxide particle content in the adhesive is 20% by mass or more.

[0056] The adhesive of the present invention preferably contains no more than 5% by mass of aromatic ring moieties, and preferably no more than 2% by mass, and may contain 0% by mass, of the total amount of adhesive. The content of aromatic ring moieties referred to here means the content of aromatic ring moieties in all components, including not only compounds (A) and (B) but also other components such as photopolymerization initiators contained in the adhesive. If the content of aromatic ring moieties is less than 5% by mass, the Abbe number tends to be high. In this specification, the content of aromatic ring moieties in 100% by mass of the total amount of adhesive shall be the value calculated based on the following formula. (Content of aromatic ring moiety in adhesive) = (Mass %) of compounds containing aromatic rings in the adhesive × (Mass ratio of aromatic ring moiety in compounds containing aromatic rings)

[0057] Furthermore, the mass ratio of the aromatic ring portion of compounds containing an aromatic ring shall be the value calculated based on the following formula. (Mass ratio of aromatic ring portion in a compound containing an aromatic ring) = (Formula weight of aromatic ring portion in a compound containing an aromatic ring) ÷ (Molecular weight of compound containing an aromatic ring)

[0058] The adhesive of the present invention is preferably solvent-free, but may contain solvents necessary for dissolution, such as photopolymerization initiators.

[0059] The refractive index of a substance changes depending on the wavelength, but in the case of the adhesive of the present invention, the refractive index increases as the wavelength decreases. This wavelength dependence of the refractive index can be estimated by the Abbe number, and the relationship between the refractive index and the Abbe number is explained, for example, in "Ando et al., Molding and Processing, Vol. 20, No. 3, pp. 170-176 (2008)," but the Abbe number (ν) in this specification shall be calculated based on equation (1). Abbe number (ν) = (n 588 -1) / (n 486 -n 656 ) Formula (1) n 486 :Refractive index at 486nm n 588 :Refractive index at 588nm n 656 :Refractive index at 656nm

[0060] The Abbe number (ν) of the adhesive layer made of the adhesive of the present invention preferably satisfies formula (2), and more preferably satisfies formula (3). Being within the range of formula (2) results in good chromatic aberration when the adhesive is used as an optical component. -200 × n 594 +355≦ν<-200×n 594 +360 formula (2) -200 × n 594 +360≦ν Equation (3) n 594 :Refractive index at 594nm

[0061] One method for calculating the Abbe number is to use a prism coupler (METRICON Model 2010 / M) to measure the refractive index of laser light at wavelengths of 473 nm, 594 nm, and 657 nm. Then, using the functions of the Model 2010 / M, approximate refractive indices at 486 nm, 588 nm, and 656 nm can be obtained using Cauchy's dispersion formula, and the Abbe number can be calculated from equation (1).

[0062] <Optical laminate> The optical laminate of the present invention has a configuration in which a first substrate, an adhesive layer made of the active energy ray curable adhesive of the present invention, and a second substrate are arranged in this order. It may also be a configuration in which three or more substrates are stacked, such as first substrate / adhesive layer / second substrate / adhesive / third substrate.

[0063] <Base material> The substrate can take the form of a film, sheet, plate, lens, disc, or fiber. The base material can be metal, ceramics, glass, plastic, wood, slate, etc., and is not particularly limited. Examples of plastics include polyester, polyolefin, polycarbonate, polystyrene, polymethyl methacrylate, triacetylcellulose resin, ABS resin, AS resin, polyamide, epoxy resin, and melamine resin.

[0064] It is preferable to use optical films, optical sheets, or optical lenses as substrates. Optical films refer to films that have optical functions such as phase difference, light diffusion, light focusing, refraction, scattering, and haze. Examples of optical films include hard coat films, antistatic coating films, anti-glare coating films, polarizing films, phase difference films, elliptical polarizing films, anti-reflective films, light diffusion films, and brightness-enhancing films. Examples of optical sheets include prism sheets and light guide plates. Examples of optical lenses include light source diffusion lenses. These can be used individually or in combination of two or more types depending on the application.

[0065] <Adhesive layer> The adhesive layer in the optical laminate of the present invention consists of the adhesive of the present invention and includes both cured and uncured layers. A cured adhesive layer can be obtained by curing the uncured adhesive layer, which is formed by applying the adhesive of the present invention to a substrate, by irradiation with active energy rays. In the optical laminate of the present invention, the adhesive may be applied to a first substrate, cured by irradiation with active energy rays, and then the second substrate may be provided, or the adhesive may be applied to the first substrate, the second substrate may be provided, and then the adhesive layer may be cured by irradiation with active energy rays. The thickness of the adhesive layer may be varied according to the desired optical laminate, but is usually preferably 0.1 to 300 μm, and more preferably 0.5 to 200 μm.

[0066] Methods for applying the adhesive to the substrate can be known. Specifically, these include methods such as rod, wire, microgravure, gravure, die, curtain, lip, slot, spin, and inkjet.

[0067] The active energy beam is an electromagnetic wave or particle beam, but ultraviolet light, visible light with a wavelength of 400-500 nm, or electron beams are preferred, with ultraviolet light or visible light with a wavelength of 400-500 nm being more preferred. Examples of irradiation sources for the active energy beam include high-pressure mercury lamps, ultra-high-pressure mercury lamps, metal halide lamps, gallium lamps, xenon lamps, and carbon arc lamps in the case of ultraviolet light or visible light with a wavelength of 400-500 nm, and in the case of electron beams, examples include thermionic emission guns and electrolytic emission guns.

[0068] The energy of the active energy rays used to cure adhesives is 5-2000 mJ / cm². 2 Preferably, 50-1000 mJ / cm² 2 This is more preferable. In addition to irradiation with active energy rays, heating by irradiation with hot air, infrared rays, far-infrared rays, high-frequency waves, etc., can be used in combination.

[0069] The adhesive and laminate of the present invention can be used in various display devices such as cathode ray tubes, flat display panels (liquid crystal displays, plasma displays, electrochromic displays, light-emitting diode displays, etc.), VR goggles, AR glasses, and smart glasses. [Examples]

[0070] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the examples shown below, and may be modified as desired without departing from the gist of the present invention and its equivalents. In the following description, "parts" and "%" indicating quantities refer to mass unless otherwise specified. The weight-average molecular weight is a value measured using the gel permeation chromatography "HLC-8220GPC" manufactured by Tosoh Corporation. Separation columns: Four columns of "TSK-GEL SUPER H5000", "TSK-GEL SUPER H4000", "TSK-GEL SUPER H3000", and "TSK-GEL SUPER H2000" manufactured by Tosoh Corporation were connected in series, and tetrahydrofuran at a temperature of 40°C was used as the mobile phase. The weight-average molecular weight is the weight-average molecular weight in terms of polystyrene with known molecular weight.

[0071] Furthermore, the acid value in this specification was measured as follows: Approximately 1 g of the sample was accurately weighed into a stoppered Erlenmeyer flask, and dissolved in 100 ml of a toluene / ethanol mixture (volume ratio: toluene / ethanol = 2 / 1). Phenolphthalein reagent was added as an indicator, and after holding for 30 seconds, the solution was titrated with 0.1 N alcoholic potassium hydroxide solution until it turned pale pink. The acid value (mgKOH / g) of the resin in its dry state was calculated using the following formula.

[0072] Acid value (mgKOH / g) = {(5.611 × a × F) / S} / (non-volatile content concentration / 100) However, S: Amount of sample taken (g) a: Amount of 0.1N alcoholic potassium hydroxide solution consumed (ml) F: Titer of 0.1N alcoholic potassium hydroxide solution

[0073] Furthermore, the hydroxyl value in this specification was measured as follows: Approximately 1 g of the sample was accurately weighed into a stoppered Erlenmeyer flask, and dissolved in 100 ml of a toluene / ethanol mixture (volume ratio: toluene / ethanol = 2 / 1). Then, exactly 5 ml of an acetylating agent (a solution of 25 g of acetic anhydride dissolved in pyridine, to a volume of 100 ml) was added, and the mixture was stirred for approximately 1 hour. Phenolphthalein reagent was added as an indicator and allowed to stand for 30 seconds. After that, the solution was titrated with 0.1 N alcoholic potassium hydroxide solution until it turned pale pink. The hydroxyl value (mgKOH / g) of the resin in its dry state was calculated using the following formula.

[0074] Hydroxyl value (mgKOH / g) = [{(ba) × F × 28.25} / S] / (non-volatile content concentration / 100) + D However, S: Amount of sample taken (g) a: Amount of 0.1N alcoholic potassium hydroxide solution consumed (ml) b: Amount of 0.1N alcoholic potassium hydroxide solution consumed in the blank experiment (ml) F: Titer of 0.1N alcoholic potassium hydroxide solution D: Acid value (mgKOH / g)

[0075] The materials used in the examples and comparative examples are as follows: <Metal oxide particles (X)> ZrO2: "PCS-60" manufactured by Nippon Denko Corporation (average primary particle diameter: 20 nm) TiO2: Ishihara Sangyo Co., Ltd. "TTO-51(A)" (Average primary particle size: 20nm)

[0076] <Monofunctional monomer (A)> • Monofunctional monomer (A1) having a hydroxyl group and lacking an aromatic ring. 4HBA: 4-hydroxybutyl acrylate • Monofunctional monomers (A2) having an aliphatic cyclic hydrocarbon group and lacking an aromatic ring. IBXA: Isoboronyl acrylate • Monofunctional monomers having two or more repeating alkylene oxy groups and lacking aromatic rings (A3) CBA: Carbitol Acrylate

[0077] <Bifunctional monomer (B)> • A difunctional monomer (B1) having an aliphatic cyclic hydrocarbon structure and lacking an aromatic ring. DCPA: Tricyclodecanedimethanol diacrylate • A difunctional monomer (B2) having two or more repeating alkylene oxy groups and lacking an aromatic ring. PEGDA: Polyethylene glycol diacrylate DPGDA: Dipropylene glycol diacrylate

[0078] <Monofunctional monomers containing aromatic rings> PPEA: Phenylphenoxyethyl acrylate (Mass ratio of aromatic ring portion in compounds containing aromatic rings = 153 ÷ 268 = 0.57)

[0079] <Photopolymerization initiator> Omnirad184: 1-Hydroxycyclohexyl phenyl ketone (molar extinction coefficient at 365 nm: 0 L·mol) -1 ·cm -1 (The mass ratio of the aromatic ring portion in a compound containing an aromatic ring = 77 ÷ 204 = 0.38) TPO:2,4,6-trimethylbenzoyldiphenylphosphine oxide (molar extinction coefficient at 365 nm: 1397 L·mol) -1 ·cm -1 (The mass ratio of the aromatic ring portion in a compound containing an aromatic ring = 273 ÷ 348 = 0.78)

[0080] <Examples of epoxy acrylate oligomer synthesis> In a five-neck separable flask equipped with a stirrer, reflux condenser, gas inlet tube, and thermometer, 67.8 parts of 1,6-hexanediol diglycidyl ether (manufactured by Sakamoto Pharmaceutical Co., Ltd.: SR-16HL, epoxy equivalent 125), 30.9 parts of succinic acid, 1.3 parts of acrylic acid, and 0.1 parts of hydroquinone monomethyl ether were charged. The mixture was heated to 60°C while introducing dry air and mixed until a homogeneous solution was obtained. Next, 0.5 parts of tetrabutylammonium borate was added, and the mixture was heated to 100°C and reacted for 8 hours to obtain an epoxy acrylate oligomer. The weight-average molecular weight of the obtained epoxy acrylate oligomer was 13000.

[0081] <Examples of polyester acrylate oligomer synthesis> In a five-neck separable flask equipped with a stirrer, distillation tube, gas inlet tube, and thermometer, 502 parts succinic anhydride, 498 parts 1,4-butanediol, and 0.04 parts zinc oxide were esterified under atmospheric pressure at approximately 210°C while passing nitrogen gas through the flask and distilling off water. When the acid value of the polyester fell below 0.3, a vacuum pump was connected, and the vacuum was gradually increased to complete the reaction, yielding a polyester polyol with a hydroxyl value of 14 mg KOH / g. To 100 parts of this polyester polyol, 1.8 parts acrylic acid and 0.1 parts hydroquinone monomethyl ether were added, and esterification was carried out at 100°C to obtain a polyester acrylate oligomer. The weight-average molecular weight of the obtained polyester acrylate oligomer was 16000.

[0082] <Example 1> Fifteen parts of zirconium dioxide (PCS-60, manufactured by Nippon Denko Co., Ltd.), forty-five parts of 4-hydroxybutyl acrylate, three parts of IBXA, and three parts of PEGDA were charged into a bead mill disperser, and dispersed using zirconia beads as the media to obtain a metal oxide dispersion paste. The D50 of the metal oxide dispersion paste was measured using a NANOTRAC WAVE II EX150 manufactured by Microtrac-Bell and found to be 50 nm. Two parts of the photopolymerization initiator Omnirad 184 were dissolved in the obtained metal oxide dispersion paste to obtain an adhesive.

[0083] <Examples 2-27, Comparative Examples 1-5> Adhesives for Examples 2-27 and Comparative Examples 1-5 were obtained by following the same procedure as in Example 1, except that the type and amount of raw materials were changed according to the formulations in Table 1.

[0084] [Table 1]

[0085] [Table 1]

[0086] <Preparation of samples for optical property evaluation> A 50 μm thick polyethylene terephthalate (PET) film (Toray Industries: Lumirror U403) was coated with the adhesive obtained in Example 1 using a bar coater so that the thickness after drying was 4 μm, and a release film (Lintec Corporation: SP-PET38GS) was laminated to the coated surface. Next, ultraviolet light at 1200 mJ / cm² was applied using a metal halide lamp. 2 An adhesive layer was formed by irradiation and curing, and an evaluation sample was obtained.

[0087] <Preparation of samples for adhesive strength evaluation> The adhesive obtained in Example 1 was applied to a 100 μm thick polycycloolefin (COP) film (Zeonor ZF14, manufactured by Zeon Corporation) using a bar coater to a dry thickness of 4 μm, and a 100 μm COP film was bonded to the coated surface. Next, ultraviolet light at 1200 mJ / cm² was applied using a metal halide lamp. 2 Laminate X was obtained by irradiation and curing. Laminate Y was obtained using the same method with a polycarbonate film (Teijin: Panlite PC-1151) as the substrate. The obtained evaluation samples were evaluated by the following method.

[0088] <Refractive Index Measurement> The peelable film was peeled from the optical property evaluation sample, and the refractive index of the adhesive layer was measured using a prism coupler (METRICON: Model 2010 / M) (control software: METRICON 2010 / M v1.81.106 MCU) with a 594nm laser beam to determine the refractive index n. 594 We measured it.

[0089] <Abbe's Rating> Similar to the refractive index measurements described above, the refractive index at each wavelength was measured using laser light at 473 nm and 657 nm. By inputting the refractive index at 473 nm, 594 nm, and 657 nm into the METRICON 2010 / M Cauchy Fit Calculation software tool mentioned above, a simulation curve of the refractive index in the range of 469.5 nm to 657.5 nm was obtained. From this simulation curve, the refractive index at 486 nm, 588 nm, and 656 nm was obtained, and the Abbe number was calculated based on equation (1). Abbe number (ν) = (n 588 -1) / (n 486 -n 656 ) Formula (1) The calculated Abbe number was evaluated in three stages based on the aforementioned equations (2) and (3), taking into account its correlation with the refractive index. ○: -200 × n 594 +360≦ν △:-200×n 594 +355≦ν<-200×n 594 +360 ×:ν<-200×n 594 +355

[0090] <Hayes> A peelable film was removed from the optical property evaluation sample, and the haze value was measured using a haze meter NDH-2000 (manufactured by Tokyo Denshoku Co., Ltd.). The measured values ​​were evaluated on a four-point scale. ◎: Less than 0.5, excellent ○: 0.5 or higher, less than 1, excellent △: 1 or more, less than 2, usable. ×: 2 or more, impractical.

[0091] <Adhesive strength> The obtained laminates X and Y were cut to a size of 25 mm x 150 mm using a cutter to prepare measurement samples. Double-sided adhesive tape (DF8712S, manufactured by Toyo Chem Co., Ltd.) was attached to the film side of the sample that had been irradiated with ultraviolet light, and the laminates were bonded to a metal plate using a laminator to create a laminate for adhesive strength measurement. A small section was peeled off between the two films bonded together by the adhesive of this laminate to serve as a starting point, and the laminate was peeled off from the starting point at a speed of 300 mm / min at a 90° angle under conditions of 23°C and 50% RH to measure the adhesive strength. The adhesive strength between laminate X1 and laminate X2 was evaluated on a four-point scale. [Evaluation Criteria] ◎: Adhesion strength of 2.0 (N / 25mm) or higher, excellent. ○: Adhesion strength of 1.5 (N / 25mm) or more, less than 2.0 (N / 25mm), excellent. △: Adhesive strength of 1.0 (N / 25mm) or more, but less than 1.5 (N / 25mm), usable. ×: Adhesion strength less than 1.0 (N / 25mm), unsuitable for practical use.

[0092] <Heat resistance> Laminates X and Y were placed in an oven at 140°C, and the degree of delamination was checked after 3 minutes, 10 minutes, and 30 minutes, and the heat resistance was evaluated on a four-point scale. [Evaluation Criteria] ◎: No peeling after 30 minutes, excellent. ○: No peeling after 10 minutes, peeling occurs after 30 minutes, excellent performance. △: No peeling after 3 minutes, peeling occurs after 10 minutes, usable. ×: Peeling occurs in 3 minutes, unusable.

[0093] The results in Table 1 show that the examples maintain a high refractive index while exhibiting good Abbe number and haze, as well as good adhesive strength and heat resistance. Therefore, they are suitable for optical applications. On the other hand, Comparative Examples 1 and 2, which used epoxy acrylate oligomer and polyester acrylate oligomer, exhibited poor haze. Furthermore, Comparative Examples 3 and 4, which used monomers containing aromatic rings, exhibited poor Abbe number.

Claims

1. An optically active energy ray polymerizable adhesive comprising metal oxide particles (X), a monofunctional monomer (A) that does not have an aromatic ring, and a photopolymerization initiator, wherein the monofunctional monomer (A) includes a monofunctional monomer (A1) that has a hydroxyl group and does not have an aromatic ring, does not contain epoxy (meth)acrylate or polyester (meth)acrylate, and does not contain aromatic ring moieties in an amount of 5% by mass or more of the total amount of the adhesive.

2. The optically active energy ray polymerizable adhesive according to claim 1, wherein the monofunctional monomer (A) further contains one or more selected from the group consisting of a monofunctional monomer (A2) having an aliphatic cyclic hydrocarbon group and not having an aromatic ring, and a monofunctional monomer (A3) having two or more repeating alkylene oxy groups and not having an aromatic ring.

3. The optically active energy ray polymerizable adhesive according to claim 1, wherein the metal oxide particles (X) are metal oxide particles (X) containing one or more elements selected from the group consisting of titanium, zinc, zirconium, antimony, indium, tin, and aluminum.

4. Furthermore, the optically active energy ray polymerizable adhesive according to claim 1, further containing a difunctional monomer (B) that does not have an aromatic ring.

5. The optically active energy ray polymerizable adhesive according to claim 4, wherein the difunctional monomer (B) further contains one or more selected from the group consisting of a difunctional monomer (B1) having an aliphatic cyclic hydrocarbon group and no aromatic ring, and a difunctional monomer (B2) having two or more repeating alkylene oxy groups and no aromatic ring.

6. The aforementioned photopolymerization initiator has a molar extinction coefficient of 200 L·mol at 365 nm. -1 ・cm -1 The optically active energy ray polymerizable adhesive according to claim 1, wherein the photopolymerization initiator is as follows.

7. An optical laminate comprising a first substrate, an adhesive layer made of an optically active energy ray polymerizable adhesive according to any one of claims 1 to 6, and a second substrate arranged in this order.

8. The optical laminate according to claim 7, wherein the refractive index of the adhesive layer is 1.52 to 1.60.

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