WO2024095904A1 - Adhesive for optical image formation device, cured resin article, optical element, and optical image formation device - Google Patents

Abstract

This adhesive for an optical image formation device is for bonding two resin substrates of an optical image formation device in which two resin substrates each have a relief surface, each have a light-reflection section on a portion of the relief surface, and are bonded such that the relief surfaces face each other. The adhesive for an optical image formation device includes an alicyclic epoxy resin, an oxetane-ring-containing compound, an ether-group-containing epoxy resin, a tackifier resin, and a photopolymerization initiator.

Description

Adhesive for optical imaging device, cured resin, optical element, and optical imaging device

The present invention relates to an adhesive for optical imaging devices, a cured resin, an optical element, and an optical imaging device.

Optical imaging devices are known that form images in the air by transmitting light from an image display device (e.g., a liquid crystal display).

As such an optical imaging device, for example, an optical imaging device has been proposed that has a pair of light control panels (a first light control panel and a second light control panel) that have multiple grooves arranged in parallel on the surface and have a metal reflective film on some of the grooves (see, for example, Patent Document 1).

In such an optical imaging device, the first light control panel and the second light control panel are joined together via a transparent resin (adhesive).

In more detail, the first light control panel and the second light control panel are joined together via a transparent resin (adhesive) so that the grooves in the first light control panel and the grooves in the second light control panel face each other and the directions in which the two grooves extend are perpendicular to each other.

As such an adhesive, for example, an adhesive for optical imaging devices has been proposed that contains an alicyclic epoxy resin (3,4-epoxycyclohexylmethyl(3,4-epoxy)cyclohexanecarboxylate), an oxetane ring-containing compound (3-ethyl-3{[(3-ethyloxetane-3-yl)methoxy]methyl}oxetane), a tackifier resin, and a photopolymerization initiator (see, for example, Example 1 of Patent Document 2).

International Publication No. 2009/131128 JP 2019-178208 A

On the other hand, adhesives are required to have even better light transmittance after curing.

The present invention provides an adhesive for optical imaging devices that has excellent light transmission after curing, a cured resin, an optical element, and an optical imaging device.

The present invention [1] is an adhesive for optical imaging devices for bonding two resin substrates of an optical imaging device, the two resin substrates having uneven surfaces and light reflecting portions provided on parts of the uneven surfaces, the two resin substrates being bonded together so that the uneven surfaces face each other, the adhesive for optical imaging devices comprising an alicyclic epoxy resin, an oxetane ring-containing compound, an ether group-containing epoxy resin, a tackifier resin, and a photopolymerization initiator.

The present invention [2] includes the adhesive for optical imaging devices described in [1] above, in which the blending ratio of the oxetane ring-containing compound is 40 parts by mass or less per 100 parts by mass of the total amount of the alicyclic epoxy resin, the oxetane ring-containing compound, and the ether group-containing epoxy resin.

The present invention [3] includes the adhesive for optical imaging devices described in [1] or [2] above, in which the blending ratio of the photopolymerization initiator is 0.20 parts by mass or less per 100 parts by mass of the total amount of the alicyclic epoxy resin, the oxetane ring-containing compound, and the ether group-containing epoxy resin.

The present invention [4] includes a resin cured product, which is a cured product of the adhesive for optical imaging devices described in any one of [1] to [3] above.

The present invention [5] includes the cured resin described in [4] above, which has a haze of 7.0% or less.

The present invention [6] includes the cured resin described in [4] above, which has a haze of 3.0% or less.

The present invention [7] includes a cured resin material according to any one of the above [4] to [6], which has a refractive index of 1.550 or less.

The present invention [8] includes the resin cured product described in [4] to [7] above, which has an average parallel light transmittance of 90% or more for wavelengths of 380 nm to 780 nm.

The present invention [9] includes an optical element comprising one resin substrate, another resin substrate, and the resin cured product described in [4] to [8] above interposed between the one resin substrate and the other resin substrate.

The present invention [10] includes the optical element described in [9] above, in which the ratio of the refractive index of the cured resin to the refractive index of the one resin substrate is 0.996 or more and 1.005 or less.

The present invention [11] includes an optical imaging device having the optical element described in [9] or [10] above.

The adhesive for optical imaging devices of the present invention contains an ether group-containing epoxy resin. This improves light transmittance after curing.

The cured resin of the present invention is a cured product of the adhesive for optical imaging devices of the present invention. Therefore, it is possible to improve light transmittance.

The optical element of the present invention comprises the resin cured product of the present invention. Therefore, the light transmittance can be improved.

The optical imaging device of the present invention is equipped with the optical element of the present invention. Therefore, the light transmittance can be improved.

<Adhesive for optical imaging devices>
The adhesive for optical imaging devices of the present invention, which will be described in more detail below, is a curable resin composition for bonding two resin substrates provided in a known optical imaging device, and bonds the two resin substrates together by curing.

The adhesive for optical imaging devices contains an alicyclic epoxy resin, an oxetane ring-containing compound, an ether group-containing epoxy resin, a tackifier resin, and a photopolymerization initiator.

<Alicyclic epoxy resin>
The alicyclic epoxy resin is a curable resin (photocurable resin, preferably ultraviolet curable resin) that has an epoxy group and an aliphatic ring (alicyclic skeleton) but does not have an aromatic ring.

Also, alicyclic epoxy resins do not have ether groups and are distinguished from ether group-containing epoxy resins (described below) that do have ether groups.

If the adhesive for optical imaging devices contains an alicyclic epoxy resin, the optical transparency after curing can be improved.

Examples of alicyclic epoxy resins include epoxy resins containing an epoxycyclo structure.

Epoxy resins containing an epoxycyclo structure have an epoxycyclo structure with an epoxy group composed of two adjacent carbon atoms forming an aliphatic ring and one oxygen atom bonded to those two carbon atoms.

An example of an epoxy resin containing an epoxycyclo structure is an epoxy resin containing an epoxycyclohexane structure (hereinafter referred to as an ECH structure-containing epoxy resin).

Examples of ECH structure-containing epoxy resins include epoxy resins containing one ECH structure as shown in the following chemical formula (1), epoxy resins containing one ECH structure as shown in the following chemical formula (2), epoxy resins containing two ECH structures as shown in the following general formula (3), and modified versions of these.

In formula (3), X represents a linking group (a divalent group having one or more atoms). R1 represents one atom or a substituent selected from the group consisting of a hydrogen atom, a fluorine atom, an alkyl group, a fluoroalkyl group, an aryl group, a furyl group, and a thienyl group. The two R1s in formula (3) may be the same or different from each other.

The epoxy resin containing two ECH structures shown in the above general formula (3) (hereinafter referred to as the ECH structure-containing epoxy resin shown in general formula (3)) has an ECH structure (epoxycyclohexyl group) at both ends of the molecule, and the two epoxycyclohexyl groups are bonded via a linking group. The epoxycyclohexyl group is a functional group that contains a cyclohexane ring and an epoxy group composed of two adjacent carbon atoms forming the cyclohexane ring and one oxygen atom bonded to the two carbon atoms.

Examples of the alkyl group represented by R1 in the above general formula (3) include linear or branched alkyl groups having 1 to 6 carbon atoms (e.g., methyl, ethyl, propyl, butyl, pentyl, and hexyl groups).

Examples of the fluoroalkyl group represented by R1 in the above general formula (3) include linear or branched fluoroalkyl groups having 1 to 6 carbon atoms (e.g., perfluoromethyl, perfluoroethyl, and perfluoropropyl groups).

In the above general formula (3), examples of the aryl group represented by R1 include aryl groups having 6 to 18 carbon atoms (e.g., phenyl and naphthyl groups).

Examples of the linking group represented by X in the above general formula (3) include an oxygen atom, a sulfur atom, a divalent hydrocarbon group, a carbonyl group, an ester group, a carbonate group, an amide group, and groups formed by linking these groups.

Examples of divalent hydrocarbon groups include linear or branched alkylene groups having 1 to 20 carbon atoms (e.g., methylene, methylmethylene, dimethylmethylene, ethylene, propylene, trimethylene, and butylene), and linear or branched unsaturated hydrocarbon groups having 1 to 20 carbon atoms (e.g., propenylene, methylpropenylene, and butenylene).

Specific examples of the ECH structure-containing epoxy resin represented by the general formula (3) include (3,3',4,4'-diepoxy)bicyclohexyl, 1,2-bis(3,4-epoxycyclohexane-1-yl)ethane, 2,2-bis(3,4-epoxycyclohexane-1-yl)propane, 3',4'-epoxycyclohexylmethyl(3,4-epoxy)cyclohexanecarboxylate, and ε-caprolactone-modified 3',4'-epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate. A preferred example of the ECH structure-containing epoxy resin represented by the general formula (3) is 3',4'-epoxycyclohexylmethyl(3,4-epoxy)cyclohexanecarboxylate.

The ECH structure-containing epoxy resin represented by the above general formula (3) may be a commercially available product. An example of a commercially available ECH structure-containing epoxy resin represented by the above general formula (3) is Celloxide 2021P (3',4'-epoxycyclohexylmethyl(3,4-epoxy)cyclohexanecarboxylate) (both manufactured by Daicel Corporation).

As an example of an ECH structure-containing epoxy resin, the ECH structure-containing epoxy resin shown in the above general formula (3) can be preferably used.

The weight average molecular weight of the alicyclic epoxy resin is, for example, 200 or more, for example, 1000 or less, and preferably 500 or less. The weight average molecular weight (Mw) can be determined by gel permeation chromatography (GPC) using polystyrene as the standard substance.

The epoxy equivalent of the alicyclic epoxy resin is, for example, 90 g/eq. or more, preferably 100 g/eq. or more, and for example, 250 g/eq. or less, preferably 190 g/eq. or less. The epoxy equivalent can be measured in accordance with JIS K7236:2001.

Alicyclic epoxy resins can be used alone or in combination of two or more types.

The content of the alicyclic epoxy resin is, for example, 30 parts by mass or more, preferably 40 parts by mass or more, more preferably 45 parts by mass or more, and for example, 70 parts by mass or less, preferably 60 parts by mass or less, per 100 parts by mass of the total amount of the alicyclic epoxy resin, the oxetane ring-containing compound, and the ether group-containing epoxy resin.

The content of the alicyclic epoxy resin in the adhesive for optical imaging devices is, for example, 10% by mass or more, preferably 15% by mass or more, more preferably 20% by mass or more, even more preferably 25% by mass or more, and, for example, 40% by mass or less, preferably 30% by mass or less.

<Oxetane Ring-Containing Compound>
The oxetane ring-containing compound contains, for example, 1 to 5 oxetane rings.

Examples of oxetane ring-containing compounds include monofunctional oxetane ring-containing compounds having one oxetane ring, bifunctional oxetane ring-containing compounds having two oxetane rings, and trifunctional or higher oxetane ring-containing compounds having three or more oxetane rings.

Examples of monofunctional oxetane ring-containing compounds include 2-ethylhexyl oxetane, 3-ethyl-3-hydroxymethyl oxetane, 3-(meth)allyloxymethyl-3-ethyl oxetane, (3-ethyl-3-oxetanylmethoxy)methylbenzene, 2-ethylhexyl (3-ethyl-3-oxetanylmethyl) ether, ethyl diethylene glycol (3-ethyl-3-oxetanylmethyl) ether, and 3-cyclohexylmethyl-3-ethyl-oxetane. Preferably, 2-ethylhexyl oxetane is used as a monofunctional oxetane ring-containing compound.

Commercially available monofunctional oxetane ring-containing compounds can also be used. An example of a commercially available monofunctional oxetane ring-containing compound is Aron Oxetane OXT-212 (2-ethylhexyl oxetane, manufactured by Toa Gosei Chemical Industry Co., Ltd.).

Examples of bifunctional oxetane ring-containing compounds include 1,4-bis{[(3-ethyl-3-oxetanyl)methoxy]methyl}benzene, 3-ethyl-3{[(3-ethyloxetan-3-yl)methoxy]methyl}oxetane, 1,4-bis[(3-ethyl-3-oxetanyl)methoxy]benzene, 1,3-bis[(3-ethyl-3-oxetanyl)methoxy]benzene, 3,7-bis(3-oxetanyl)-5-oxa -nonane, 1,4-bis[(3-ethyl-3-oxetanylmethoxy)methyl]benzene, 1,2-bis[(3-ethyl-3-oxetanylmethoxy)methyl]ethane, 1,2-bis[(3-ethyl-3-oxetanylmethoxy)methyl]propane, ethylene glycol bis(3-ethyl-3-oxetanylmethyl)ether, and dicyclopentenyl bis(3-ethyl-3-oxetanylmethyl)ether. As a bifunctional oxetane ring-containing compound, 3-ethyl-3{[(3-ethyloxetan-3-yl)methoxy]methyl}oxetane is preferable.

The bifunctional oxetane ring-containing compound may be a commercially available product. An example of a commercially available bifunctional oxetane ring-containing compound is Aron Oxetane OXT-221 (3-ethyl-3{[(3-ethyloxetane-3-yl)methoxy]methyl}oxetane, manufactured by Toa Gosei Chemical Industry Co., Ltd.).

Examples of trifunctional or higher oxetane ring-containing compounds include trimethylolpropane tris(3-ethyl-3-oxetanylmethyl) ether, pentaerythritol tris(3-ethyl-3-oxetanylmethyl) ether, pentaerythritol tetrakis(3-ethyl-3-oxetanylmethyl) ether, and dipentaerythritol pentakis(3-ethyl-3-oxetanylmethyl) ether.

The oxetane ring-containing compound is preferably a bifunctional oxetane ring-containing compound.

Oxetane ring-containing compounds can be used alone or in combination of two or more types.

The content of the oxetane ring-containing compound is, for example, 55 parts by mass or less, preferably 45 parts by mass or less, and from the viewpoint of further improving the light transmittance after curing, more preferably 40 parts by mass or less, and even more preferably 35 parts by mass or less, and for example, 20 parts by mass or more, and for example, 30 parts by mass or more, relative to 100 parts by mass of the total amount of the alicyclic epoxy resin, the oxetane ring-containing compound, and the ether group-containing epoxy resin.

The content of the oxetane ring-containing compound in the adhesive for optical imaging devices is, for example, 30% by mass or less, preferably 20% by mass or less, and, for example, 10% by mass or more, preferably 15% by mass or more.

If the content of the oxetane ring-containing compound is equal to or less than the above upper limit, the curing reaction speed of the adhesive for optical imaging devices can be prevented from becoming excessively fast. This can prevent unevenness from occurring in the cured product of the adhesive for optical imaging devices, and improve the light transmittance after curing.

In addition, if the content of the oxetane ring-containing compound is equal to or greater than the lower limit, the adhesive for optical imaging devices can be cured reliably.

<Ether group-containing epoxy resin>
The ether group-containing epoxy resin, which will be described in detail later, is a component that captures cations generated from a photopolymerization initiator and undergoes cationic polymerization with the alicyclic epoxy resin and the oxetane ring-containing compound.

Ether group-containing epoxy resins contain both epoxy groups and ether groups.

An example of an ether group-containing epoxy resin is a glycidyl ether group-containing epoxy resin.

Examples of glycidyl ether group-containing epoxy resins include glycidyl ether group-containing aromatic ring epoxy resins and glycidyl ether group-containing alicyclic epoxy resins.

Examples of aromatic ring epoxy resins containing glycidyl ether groups include bisphenol A diglycidyl ether, bisphenol F diglycidyl ether, and their alkylene oxide adducts (e.g., ethylene oxide adducts, propylene oxide adducts, the same below). A preferred example of aromatic ring epoxy resins containing glycidyl ether groups is a propylene oxide adduct of bisphenol A diglycidyl ether.

Examples of glycidyl ether group-containing alicyclic epoxy resins include hydrogenated bisphenol A diglycidyl ether, hydrogenated bisphenol F diglycidyl ether, and alkylene oxide adducts thereof.

As the ether group-containing epoxy resin, from the viewpoint of high refractive index and rigidity, a glycidyl ether group-containing aromatic ring epoxy resin is preferably used.

Ether group-containing epoxy resins can be used alone or in combination of two or more types.

The content of the ether group-containing epoxy resin is, for example, 10 parts by mass or more, preferably 15 parts by mass or more, and, for example, 40 parts by mass or less, preferably 30 parts by mass or less, and more preferably 20 parts by mass or less, per 100 parts by mass of the total amount of the alicyclic epoxy resin, the oxetane ring-containing compound, and the ether group-containing epoxy resin.

The content of the ether group-containing epoxy resin in the adhesive for optical imaging devices is, for example, 3% by mass or more, preferably 5% by mass or more, more preferably 7% by mass or more, and, for example, 20% by mass or less, preferably 10% by mass or less.

If the content of the ether group-containing epoxy resin is equal to or greater than the lower limit, the curing reaction speed of the adhesive for optical imaging devices can be prevented from becoming excessively fast. This can prevent unevenness from occurring in the cured product of the adhesive for optical imaging devices, and improve the light transmittance after curing.

In addition, if the content of the ether group-containing epoxy resin is equal to or less than the above upper limit, the adhesive for optical imaging devices can be cured reliably.

<Tackifying Resin>
The tackifier resin is a component for imparting tackiness.

The tackifier resin is a thermoplastic resin that does not react with alicyclic epoxy resins, oxetane ring-containing compounds, and ether group-containing epoxy resins.

Tackifying resins include, for example, aromatic hydrocarbon resins, unsaturated aliphatic hydrocarbon resins, and saturated aliphatic hydrocarbon resins.

Examples of aromatic hydrocarbon resins include C9 petroleum resins and terpene phenol resins.

Examples of unsaturated aliphatic hydrocarbon resins include rosin-based hydrocarbon resins, polyterpene resins, and C5-based petroleum resins.

Examples of the saturated aliphatic hydrocarbon resin include hydrogenated products of the aromatic hydrocarbon resins described above (specifically, hydrogenated C9 petroleum resins, hydrogenated terpene phenol resins, etc.), and hydrogenated products of the unsaturated aliphatic hydrocarbon resins described above (specifically, hydrogenated rosin hydrocarbon resins, hydrogenated polyterpene resins, hydrogenated C5 petroleum resins, etc.). Examples of the saturated aliphatic hydrocarbon resin include preferably hydrogenated products of the unsaturated aliphatic hydrocarbon resins described above.
More preferably, the saturated aliphatic hydrocarbon resin is a hydrogenated rosin hydrocarbon resin.

The tackifier resin is preferably a saturated aliphatic hydrocarbon resin.

Also, commercially available tackifier resins can be used. For example, Pine Crystal KE-100 (hydrogenated rosin-based hydrocarbon resin, manufactured by Arakawa Chemical Industries Co., Ltd.) is an example of a commercially available tackifier resin.

Tackifying resins can be used alone or in combination of two or more types.

The content of the tackifier resin is, for example, 30 parts by mass or more, preferably 50 parts by mass or more, more preferably 60 parts by mass or more, and for example, 250 parts by mass or less, preferably 100 parts by mass or less, more preferably 80 parts by mass or less, per 100 parts by mass of the total amount of the alicyclic epoxy resin, the oxetane ring-containing compound, and the ether group-containing epoxy resin.

The content of the tackifier resin in the adhesive for optical imaging devices is, for example, 20% by mass or more, preferably 30% by mass or more, and, for example, 70% by mass or less, preferably 50% by mass or less, more preferably 40% by mass or less.

<Photopolymerization initiator>
The photopolymerization initiator is, for example, a photoacid generator that generates an acid upon irradiation with light (preferably, ultraviolet light).

The photopolymerization initiator is not particularly limited, and any known cationic photopolymerization initiator can be used. Specific examples of cationic polymerization initiators include sulfonium salts, phosphonium salts, quaternary ammonium salts, diazonium salts, and iodonium salts. Preferred examples of cationic polymerization initiators include sulfonium salts.

Examples of sulfonium salts include triarylsulfonium salts.

In addition, in these cationic polymerization initiators, the counter anion that forms the salt consists of, for example, a central atom and a ligand coordinated to the central atom.

Examples of the central atom include P, As, and Sb. The central atom is preferably P.

Examples of the ligand include F ⁻ , Cl ⁻ , and (CF ₂ CF ₃ ) _n F _(6-n) ^— .

Specific examples of such counter anions include PF ₆ ⁻ , (CF ₂ CF ₃ ) _n PF _(6-n) ⁻ , AsF ₆ ⁻ , SbF ₆ ⁻ , BF ₄ ⁻ , and SbCl ₆ ⁻ .

As the cationic polymerization initiator, preferably, a sulfonium salt (preferably, a triarylsulfonium salt) having (CF ₂ CF ₃ ) _n PF _(6-n) ^- as a counter anion is used.

The cationic polymerization initiator may be a commercially available product, such as CPI-210S (a sulfonium salt having (CF ₂ CF ₃ ) _n PF _(6-n) ^- as a counter anion (specifically, a triarylsulfonium salt), manufactured by San-Apro Co., Ltd.).

Photopolymerization initiators can be used alone or in combination of two or more types.

The content of the photopolymerization initiator is, for example, 0.50 parts by mass or less, more preferably 0.20 parts by mass or less from the viewpoint of further improving the light transmittance after curing, and is, for example, 0.05 parts by mass or more, preferably 0.10 parts by mass or more, per 100 parts by mass of the total amount of the alicyclic epoxy resin, the oxetane ring-containing compound, and the ether group-containing epoxy resin.

The content of the photopolymerization initiator in the adhesive for optical imaging devices is, for example, 0.050% by mass or less, preferably 0.20% by mass or less, more preferably 0.15% by mass or less, and for example, 0.05% by mass or more.

If the content of the photopolymerization initiator is equal to or less than the above upper limit, the curing reaction speed of the adhesive for optical imaging devices can be prevented from becoming excessively fast. This can prevent unevenness from occurring in the cured product of the adhesive for optical imaging devices, and improve the light transmittance after curing.

In addition, if the content of the photopolymerization initiator is equal to or greater than the lower limit, the adhesive for the optical imaging device can be cured reliably.

<Additives>
The adhesive for optical imaging devices may contain additives in appropriate proportions as required.

Additives include, for example, silane coupling agents (e.g., 3-glycidoxypropyltrimethoxysilane), leveling agents (e.g., silicone-based polymers), and defoamers (e.g., polyethylene-based defoamers), stabilizers, polymerization initiators, antioxidants, wettability improvers, surfactants, plasticizers, UV absorbers, preservatives, and antibacterial agents.

Additives can be used alone or in combination of two or more types.

Preparation of Adhesive for Optical Imaging Devices
To prepare the optical imaging device adhesive, the alicyclic epoxy resin, the oxetane ring-containing compound, the ether group-containing epoxy resin, and the tackifier resin are first mixed, optionally with heating.

As heating conditions, the heating temperature is, for example, 80°C or higher, preferably 100°C or higher, for example, 150°C or lower, preferably 140°C or lower. The heating time is, for example, 30 minutes or higher, preferably 40 minutes or higher, and, for example, 120 minutes or lower, preferably 80 minutes or lower.

As a result, the alicyclic epoxy resin, the oxetane ring-containing compound, the ether group-containing epoxy resin, and the tackifier resin become compatible with each other, and a resin mixture is prepared.

Then, at room temperature (25°C), add a photopolymerization initiator and any additives that may be added as needed to the resin mixture and mix.

This prepares the adhesive for the optical imaging device.

The viscosity of the adhesive for optical imaging devices is, for example, 300 mPa·s or more, and from the viewpoint of fluidity, 50,000 mPa·s or less.

The above viscosity can be measured using an E-type viscometer set at 25°C. Specifically, the above viscosity can be measured using an E-type viscometer (Toki Sangyo Co., Ltd., TV25 viscometer, rotor angle: 1°34', rotor radius: 2.4 cm).

Then, the adhesive for optical imaging devices can be cured by irradiating it with light (e.g., ultraviolet light) and, if necessary, by heating it. This makes it possible to produce a resin cured product, which is the cured product of the adhesive for optical imaging devices.

As heating conditions, the heating temperature is, for example, 40°C or higher, preferably 60°C or higher, for example, 110°C or lower, preferably 90°C or lower. The heating time is, for example, 10 minutes or longer, and, for example, 120 minutes or shorter.

The cured product (resin cured product) of the adhesive for optical imaging devices has excellent light transmittance. Light transmittance can be evaluated by measuring parallel light transmittance and haze.

In more detail, the average parallel light transmittance for wavelengths of 380 nm to 780 nm in a cured product (resin cured product) of the adhesive for optical imaging devices having a thickness of 100 μm is, for example, 90% or more, preferably 93% or more, and more preferably 95% or more, for example, 100% or less.

The haze of the cured product (resin cured product) of the adhesive for optical imaging devices having a thickness of 1 mm is, for example, 7.0% or less, preferably 6.0% or less, more preferably 5.0% or less, particularly preferably 3.0% or less, and for example, 0% or more.

If the average parallel light transmittance and the haze are within the above ranges, the cured product of the adhesive for optical imaging devices will have excellent light transmittance.

The method for measuring the parallel light transmittance and the method for measuring the haze will be described in detail in the examples below.

The refractive index at the D line of the cured product (resin cured product) of the adhesive for optical imaging devices is, for example, 1.300 or more, preferably 1.400 or more, and more preferably 1.500 or more, for example, 1.700 or less, preferably 1.600 or less, and from the viewpoint of improving the imaging performance of the optical imaging device (described later), more preferably 1.550 or less.

The method for measuring the refractive index will be described in detail in the examples below.

The ratio of the refractive index of the cured product (resin cured product) of the adhesive for optical imaging devices to the refractive index of the resin substrate (described below) used in the optical imaging device (described below) (the refractive index of the cured product of the adhesive/refractive index of the resin substrate used in the optical imaging device) is, for example, 0.996 or more, preferably 0.998 or more, for example, 1.005 or less, preferably 1.004 or less, and more preferably 1.000 or less.

If the above ratio is within the above range, the imaging performance of the optical imaging device (described below) can be improved.

Use of Adhesives for Optical Imaging Devices
Optical imaging device adhesives (adhesives) are used to bond two resin substrates of known optical imaging devices together.

Examples of optical imaging devices include the optical imaging device described in WO 2009/131128, the optical imaging device described in JP 2015-14777 A, the stereoscopic imaging device described in Japanese Patent No. 6203989, the stereoscopic imaging element described in JP 2018-13585 A, the optical imaging device described in JP 2011-90117 A, and the optical imaging means described in WO 2013/129063.

Such an optical imaging device has an optical element having two resin substrates with uneven surfaces, with light reflecting portions provided on parts of the uneven surfaces.

The uneven surface has, for example, a plurality of grooves extending in a predetermined direction arranged in parallel to each other in a direction intersecting the predetermined direction. The shape of the grooves is not particularly limited, and may be, for example, a rectangular or triangular cross section. The depth of the grooves is not particularly limited, and is, for example, about 0.5 mm. The material of the resin substrate is not particularly limited, and examples thereof include polyolefins (e.g., cycloolefin polymers).

The light reflecting portion is provided on a part of the uneven surface, specifically, on a part of the surface of each of the multiple grooves. The material of the light reflecting portion is, for example, a metal such as aluminum, and the light reflecting portion is, for example, a metal vapor deposition film.

Then, these two resin substrates are arranged so that their uneven surfaces face each other, and are bonded together using the optical imaging device adhesive described above.

Specifically, two resin substrates are stacked so that the uneven surfaces of the two resin substrates face each other and the multiple grooves contained in the uneven surfaces intersect with each other, and uncured adhesive is filled between the two resin substrates. The adhesive is then irradiated with light (specifically, ultraviolet light) to harden it, and then dried as necessary.

In this way, the two resin substrates are bonded together with the adhesive to produce an optical element. Such an optical element comprises one resin substrate, another resin substrate, and a cured product (resin cured product) of the adhesive for optical imaging devices interposed between the one resin substrate and the other resin substrate.

The optical imaging device includes the optical element.

<Action and effect>
The adhesive for optical imaging devices contains an ether group-containing epoxy resin, which can improve the light transmittance after curing.

In more detail, when this adhesive for optical imaging devices is irradiated with light (e.g., ultraviolet light), cations are generated from the photopolymerization initiator, and the alicyclic epoxy resin, the oxetane ring-containing compound, and the ether group-containing epoxy resin undergo cationic polymerization, thereby causing the curing reaction to proceed.

On the other hand, if the curing reaction is fast, the heat generated during curing cannot be suppressed, and unevenness occurs in the cured product of the adhesive for optical imaging devices. This reduces the light transmittance of the cured product of the adhesive for optical imaging devices.

In contrast, this adhesive for optical imaging devices contains an ether group-containing epoxy resin. The ether group in the ether group-containing epoxy resin can capture cations generated from the photopolymerization initiator, slowing down the rate of the curing reaction. This can suppress heat generation during curing and unevenness. As a result, the optical transmittance of the cured product of the adhesive for optical imaging devices can be improved.

The cured resin is a cured adhesive for optical imaging devices. This allows for improved light transmittance.

The optical element contains a cured resin, which allows for improved light transmittance.

The optical imaging device of the present invention is equipped with the optical element of the present invention. Therefore, the light transmittance can be improved.

The present invention is described in more detail below with examples, but is not limited thereto. Specific numerical values of the compounding ratio (content ratio), physical property values, parameters, etc. used in the following description can be replaced with the upper limit values (numerical values defined as "equal to or less than") or lower limit values (numerical values defined as "equal to or more than" or "exceeding") of the corresponding compounding ratio (content ratio), physical property values, parameters, etc. described in the above "Form for carrying out the invention." Note that "parts" and "%" are based on mass unless otherwise specified.

<Ingredient details>
The trade names and abbreviations of the components used in each Example and Comparative Example are described in detail below.
CEL2021P: 3',4'-epoxycyclohexylmethyl (3,4-epoxy)cyclohexanecarboxylate, an ECH structure-containing epoxy resin represented by the above general formula (3), trade name "Celloxide 2021P", molecular weight: 252.3, epoxy equivalent: 128 to 145 g/eq. OXT-221: (3-ethyl-3{[(3-ethyloxetan-3-yl)methoxy]methyl}oxetane, trade name "ARON OXETANE OXT-221" manufactured by Daicel Corporation; EP-4010S: propylene oxide adduct of bisphenol A diglycidyl ether, manufactured by Toa Gosei Chemical Industry Co., Ltd.; KE-100: hydrogenated rosin-based hydrocarbon resin, trade name "Pine Crystal KE-100" manufactured by Arakawa Chemical Industries Co., Ltd.; CPI-210S: sulfonium salt with (CF ₂ CF ₃ ) _n PF _(6-n) ^- as counter anion (specifically, triarylsulfonium salt); CPI-100P: PF Sulfonium salt with ₆ as a counter anion (specifically, triarylsulfonium salt), manufactured by San-Apro Co., Ltd. KBM-403: silane coupling agent, 3-glycidoxypropyltrimethoxysilane, manufactured by Shin-Etsu Chemical Co., Ltd. BYK-1790: antifoaming agent, manufactured by BYK Japan K.K.

Preparation of Adhesive for Optical Imaging Devices
Examples 1 to 8, Comparative Examples 1 and 2
An alicyclic epoxy resin, an oxetane ring-containing compound, an ether group-containing epoxy resin, and a tackifier resin were charged into a flask according to the formulation shown in Table 1, and heated at 120°C for 1 hour. After confirming that the tackifier resin had dissolved, a resin mixture was prepared.

Then, after cooling to room temperature (25°C), a photopolymerization initiator, a silane coupling agent, and an antifoaming agent were added to the resin mixture according to the formula shown in Table 1 and mixed. This produced an adhesive for optical imaging devices.

<Evaluation>
(Light transmittance after curing)
[Parallel light transmittance measurement]
The adhesive for optical imaging devices of each Example and Comparative Example was applied to a glass plate to a thickness of 100 μm, and then the adhesive was irradiated with 3000 mJ of UV light using a conveyor-type UV irradiation device.Then, the adhesive for optical imaging devices was cured using a hot air dryer at 80° C. for 30 minutes.

Then, the parallel light transmittance of the 100 μm-thick cured product at wavelengths of 380 to 780 nm and the average light transmittance of a glass plate used as a reference were measured using an ultraviolet-visible spectrophotometer (product name: UV-2550, manufactured by Shimadzu Corporation).

The average parallel light transmittance for wavelengths of 380 to 780 nm was calculated for a cured product having a thickness of 100 μm. The average parallel light transmittance for wavelengths of 380 to 780 nm was determined as the average parallel light transmittance for every 1 nm of wavelength when the wavelength was scanned from 380 nm to 780 nm. The parallel light transmittance measurement was evaluated according to the following criteria. The results are shown in Table 1.
{standard}
A: The average parallel light transmittance was 90% or more.
×: The average parallel light transmittance was less than 90%.

[Haze measurement]
The adhesive for optical imaging devices of each Example and Comparative Example was applied to a glass plate to a thickness of 1 mm, and then the adhesive for optical imaging devices was irradiated with 3000 mJ of UV light using a conveyor-type UV irradiation device.Then, the adhesive for optical imaging devices was cured using a hot air dryer at 80°C for 30 minutes.

The haze of the cured product having a thickness of 1 mm was then measured using a haze meter (product name: NDH2000, manufactured by Nippon Denshoku Industries Co., Ltd.). The results are shown in Table 1.
{standard}
A: The haze value was 3.0% or less.
Δ: The haze value was more than 3.0% and 7.0% or less.
×: The haze value exceeded 7.0%.

[Peeling of light reflecting portion]
Two 100 mm×150 mm PP plates (polypropylene plates, thickness: 0.5 mm) were prepared, each having an aluminum vapor deposition film (thickness: 100 nm) on one surface as a light reflecting portion.

Then, a rectangular frame-shaped dam with a width of 10 mm was created on the periphery of the aluminum-deposited surface of one of the PP plates using a Teflon (registered trademark) sheet (thickness: 1 mm).

Next, the optical imaging device adhesive of each example and each comparative example was measured out to have the same volume as the inside of the dam, and each adhesive was poured into the inside of the dam.

Then, the other PP plate was placed on top of the adhesive inside the weir so that the aluminum-coated surface was in contact with the optical imaging device adhesive, and the optical imaging device adhesive was sandwiched between the two PP plates.

Then, a conveyor-type UV irradiation device was used to irradiate the optical imaging device adhesive with 3000 mJ of UV light. After that, a hot air dryer was used to harden the adhesive at 80°C for 30 minutes.

After the adhesive for the optical imaging device hardened, the resulting sample (the hardened adhesive sandwiched between two PP plates) was visually inspected for peeling of the aluminum vapor deposition film.

The peelability of the light reflecting portion was evaluated according to the following criteria. The results are shown in Table 1.
{standard}
◯: No peeling of the aluminum vapor deposition film occurred.
Δ: The peeled area of the aluminum vapor-deposited film was more than 0% and 20% or less.
x: The peeled area of the aluminum vapor-deposited film exceeded 20% by area.

The above invention is provided as an exemplary embodiment of the present invention, but this is merely an example and should not be interpreted as limiting. Modifications of the present invention that are obvious to those skilled in the art are intended to be included in the scope of the claims below.

The adhesive for optical imaging devices, the cured resin, and the optical element of the present invention can be suitably used in the manufacture of optical imaging devices. The optical imaging devices of the present invention can be suitably used in the manufacture of aerial displays.

Claims (11)

An adhesive for an optical imaging device for bonding two resin substrates of an optical imaging device, the two resin substrates having uneven surfaces and a light reflecting portion provided on a part of the uneven surfaces, the two resin substrates being bonded together such that the uneven surfaces face each other,
An alicyclic epoxy resin, an oxetane ring-containing compound, and an ether group-containing epoxy resin,
An adhesive for an optical imaging device comprising a tackifying resin and a photoinitiator. The adhesive for optical imaging devices according to claim 1, wherein the blending ratio of the oxetane ring-containing compound is 40 parts by mass or less per 100 parts by mass of the total amount of the alicyclic epoxy resin, the oxetane ring-containing compound, and the ether group-containing epoxy resin. The adhesive for optical imaging devices according to claim 1 or 2, wherein the mixing ratio of the photopolymerization initiator is 0.20 parts by mass or less per 100 parts by mass of the total amount of the alicyclic epoxy resin, the oxetane ring-containing compound, and the ether group-containing epoxy resin. A resin cured product that is a cured product of the adhesive for optical imaging devices described in claim 1. The cured resin according to claim 4, having a haze of 7.0% or less. The cured resin according to claim 4, having a haze of 3.0% or less. The cured resin according to claim 4, having a refractive index of 1.550 or less. The cured resin according to claim 4, in which the average parallel light transmittance for wavelengths between 380 nm and 780 nm is 90% or more. An optical element comprising one resin substrate, another resin substrate, and the cured resin material according to claim 4 interposed between the one resin substrate and the other resin substrate. The optical element according to claim 9, wherein the ratio of the refractive index of the cured resin to the refractive index of the first resin substrate is 0.996 or more and 1.005 or less. An optical imaging device comprising the optical element according to claim 9.