JP7732072B2 - Sealant for organic EL display element, organic EL display device, and method for manufacturing organic EL display device - Google Patents

Description

The present invention relates to a sealing material for organic EL display elements, an organic EL display device, and a method for manufacturing an organic EL display device.

In recent years, organic electroluminescence (EL) displays have become known as image display devices equipped with optical elements. In such image display devices, the optical elements are sealed with a sealing layer to prevent deterioration of the optical elements due to moisture in the atmosphere.

The sealing layer is formed, for example, by embedding the optical element in a sealing composition and then curing the sealing composition by irradiating it with light.

As such a sealing composition, for example, a sealant for organic EL display elements containing a cationically polymerizable compound, a polymerization initiator, and a benzotriazole compound has been proposed (see, for example, Example 1 of Patent Document 1).

International Publication No. 2021/006070 Brochure

On the other hand, in the sealant for organic EL display elements disclosed in Patent Document 1, even weak light such as that from a fluorescent lamp generates acid from the polymerization initiator (photoacid generator). This acid then remains active, and the polymerization (hardening) of the sealant for organic EL display elements progresses, causing an increase in viscosity. In other words, the sealant for organic EL display elements disclosed in Patent Document 1 has the disadvantage of being poorly stable under white light.

In addition, the cured product of such sealing compositions must be reliable.

The present invention provides a sealing material for organic EL display elements that has excellent stability against white light and reliability after curing, an organic EL display device having a sealing layer made of a cured product of the sealing material for organic EL display elements, and a method for manufacturing an organic EL display device.

The present invention [1] is an encapsulant for organic EL display elements, which comprises a cationically polymerizable compound, a cationic polymerization initiator, an ultraviolet absorber, and a compound having a phenolic hydroxyl group, and the mass ratio of the compound having a phenolic hydroxyl group to the ultraviolet absorber (compound having a phenolic hydroxyl group/ultraviolet absorber) is 0.01 or more and less than 1.00.

The present invention [2] includes a sealing material for organic EL display elements described in [1] above, in which the cationically polymerizable compound is an epoxy compound and/or an oxetane compound.

The present invention [3] includes an encapsulant for organic EL display elements described in [1] or [2] above, in which the ultraviolet absorber is a benzotriazole compound or a benzophenone compound.

The present invention [4] includes an encapsulant for organic EL display elements described in any one of [1] to [3] above, in which the content of the ultraviolet absorber is 0.1% by mass or more and 2% by mass or less.

The present invention [5] includes a sealing material for organic EL display elements described in any one of [1] to [4] above, in which the content of the compound having a phenolic hydroxyl group is 0.01% by mass or more and 0.5% by mass or less.

The present invention [6] includes a sealing material for organic EL display elements described in any one of [1] to [5] above, which is liquid at 25°C and has a solvent content of 0.05% by mass or less.

The present invention [7] includes a sealing material for organic EL display elements described in any one of [1] to [6] above, which has a viscosity at 25°C of 5 mPa·s or more and 50 mPa·s or less.

The present invention [8] includes an organic EL display device comprising a substrate, an organic EL element mounted on one surface of the substrate in the thickness direction, and a sealing layer covering the organic EL element, wherein the sealing layer is made of a cured product of the sealing material for organic EL display elements described in any one of [1] to [7] above.

The present invention [9] includes a method for manufacturing an organic EL display device, comprising: a first step of preparing a substrate; a second step of mounting an organic EL element on one thickness-wise surface of the substrate; and a third step of forming a sealing layer that covers the organic EL element by an inkjet method, wherein the sealing layer is made of a cured product of the sealing material for organic EL display elements described in any one of [1] to [7] above.

In the encapsulant for organic EL display elements of the present invention, the mass ratio of the compound having a phenolic hydroxyl group to the ultraviolet absorber (compound having a phenolic hydroxyl group/ultraviolet absorber) is 0.01 or more and less than 1.00. Because this mass ratio is 0.01 or more, this encapsulant for organic EL display elements can improve stability against white light. Furthermore, because this mass ratio is less than 1.00, this encapsulant for organic EL display elements can improve reliability after curing.

The organic EL display device of the present invention has an organic EL element coated with a sealing layer made of the cured product of the sealing material for organic EL display elements of the present invention. Therefore, it has excellent reliability.

The method for manufacturing an organic EL display device of the present invention uses an inkjet method to coat an organic EL element and form a sealing layer made of a cured product of the sealing material for organic EL display elements of the present invention. This makes it possible to manufacture an organic EL display device with excellent reliability.

FIG. 1 is a cross-sectional view of an embodiment of an organic EL display device according to the present invention. 2A to 2C are schematic diagrams showing one embodiment of the method for manufacturing an organic EL display device of the present invention. Fig. 2A shows a first step of preparing a substrate. Fig. 2B shows a second step of mounting an organic EL element on one surface of the substrate in the thickness direction. Fig. 2C shows a third step of forming a sealing layer 3 that covers the organic EL element 2 by an inkjet method.

The sealing material for organic EL display elements contains a cationic polymerizable compound, a cationic polymerization initiator, an ultraviolet absorber, and a compound having a phenolic hydroxyl group.

<Cationically polymerizable compound>
Examples of the cationically polymerizable compound include an epoxy compound and an oxetane compound. That is, the cationically polymerizable compound is preferably an epoxy compound and/or an oxetane compound. More preferably, the cationically polymerizable compound is an epoxy compound or an oxetane compound.

[Epoxy compound]
Examples of epoxy compounds include alicyclic epoxy resins, aliphatic epoxy resins, and aromatic epoxy resins, and preferably alicyclic epoxy resins and aliphatic epoxy resins. More preferably, the epoxy compound includes an alicyclic epoxy resin and an aliphatic epoxy resin, and even more preferably, the epoxy compound consists of an alicyclic epoxy resin and an aliphatic epoxy resin.

(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.

Examples of alicyclic epoxy resins include glycidyl group-containing alicyclic epoxy resins, glycidyl ether group-containing alicyclic epoxy resins, and epoxycyclo structure-containing epoxy resins.

((Glycidyl group-containing alicyclic epoxy resin))
The glycidyl group-containing alicyclic epoxy resin has, for example, a glycidyl group bonded to an aliphatic ring. Such a glycidyl group-containing alicyclic epoxy resin is represented, for example, by the following general formula (1).

In formula (1), R represents a monovalent organic group, n represents the degree of polymerization, and a substituent such as an alkyl group may be bonded to a carbon atom constituting the cyclohexane ring.

Specific examples of glycidyl group-containing alicyclic epoxy resins represented by the above general formula (1) include 1,2-epoxy-4-(2-oxiranyl)cyclohexane adducts of 2,2-bis(hydroxymethyl)-1-butanol.

The glycidyl group-containing alicyclic epoxy resin represented by the general formula (1) above can also be a commercially available product. An example of a commercially available glycidyl group-containing alicyclic epoxy resin represented by the general formula (1) above is EHPE3150 (epoxy equivalent weight 170-190 g/eq., manufactured by Daicel Corporation).

((Glycidyl ether group-containing alicyclic epoxy resin))
The glycidyl ether group-containing alicyclic epoxy resin has glycidyl ether units bonded to an aliphatic ring, and is preferably a polyglycidyl ether-containing alicyclic epoxy resin having a plurality of glycidyl ether units bonded to an aliphatic ring.

Examples of glycidyl ether-containing alicyclic epoxy resins include difunctional glycidyl ether-containing alicyclic epoxy resins. Examples of difunctional glycidyl ether-containing alicyclic epoxy resins include hydrogenated bisphenol A diglycidyl ether, hydrogenated bisphenol F diglycidyl ether, and hexahydrophthalic acid diglycidyl ester.

((Epoxy cyclo structure-containing epoxy resin))
The epoxy cyclo structure-containing epoxy resin has an epoxy cyclo structure having an epoxy group composed of two adjacent carbon atoms forming an aliphatic ring and one oxygen atom bonded to those two carbon atoms.

Examples of epoxy resins containing an epoxycyclohexane structure include epoxy resins containing an epoxycyclohexane structure (hereinafter referred to as ECH structure-containing epoxy resins).

Examples of ECH structure-containing epoxy resins include 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 products thereof.

In formula (3), X represents a linking group (a divalent group having one or more atoms). m represents 0 or 1. R2 represents an atom or 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 R2s in formula (3) may be the same or different.

Epoxy resins containing two ECH structures represented by the above general formula (3) (hereinafter referred to as ECH structure-containing epoxy resins represented by general formula (3)) have ECH structures (epoxycyclohexyl groups) at both ends of the molecule, with the two epoxycyclohexyl groups bonded via a linking group (a carbon-carbon bond when m is 0). The epoxycyclohexyl group is a functional group containing a cyclohexane ring and an epoxy group composed of two adjacent carbon atoms forming the cyclohexane ring and one oxygen atom bonded to those two carbon atoms.

Examples of the alkyl group represented by R2 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, hexyl, etc.).

Examples of the fluoroalkyl group represented by R2 in the above general formula (3) include linear or branched fluoroalkyl groups having 1 to 6 carbon atoms (e.g., perfluoromethyl, perfluoroethyl, perfluoropropyl, etc.).

Examples of the aryl group represented by R2 in the above general formula (3) include aryl groups having 6 to 18 carbon atoms (e.g., phenyl groups, naphthyl groups, etc.).

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 polyoxyalkylene group, a carbonyl group, an ether group, a thioether group, an ester group, a carbonate group, an amide group, and groups formed by linking these. When m is 0, the two ECH structures are linked via a carbon-carbon bond.

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, butylene, etc.), and linear or branched unsaturated hydrocarbon groups having 1 to 20 carbon atoms (e.g., propenylene, methylpropenylene, butenylene, etc.).

Examples of polyoxyalkylene groups include linear or branched polyoxyalkylene groups having 1 to 120 carbon atoms (e.g., polyoxyethylene groups, polyoxypropylene groups, etc.).

Specific examples of ECH structure-containing epoxy resins represented by general formula (3) include (3,3',4,4'-diepoxy)bicyclohexyl, bis(3,4-epoxycyclohexylmethyl)ether, 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, with (3,3',4,4'-diepoxy)bicyclohexyl being preferred (in the above formula (3), m is 0 and R2 is a hydrogen atom).

In addition, commercially available ECH structure-containing epoxy resins represented by the general formula (3) above can also be used. Examples of commercially available ECH structure-containing epoxy resins represented by the general formula (3) above include Celloxide 8000, Celloxide 8010, Celloxide 2021P, and Celloxide 2081 (all manufactured by Daicel Corporation).

Preferably, the ECH structure-containing epoxy resin is an ECH structure-containing epoxy resin represented by the above general formula (3).

As an alicyclic epoxy resin, an epoxy resin containing an epoxycyclo structure is preferably used.

The weight-average molecular weight of the alicyclic epoxy resin is, for example, 200 or more, and, for example, 1,000 or less, 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 same applies below).

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 (the same applies below).

(Aliphatic epoxy resin)
Examples of the aliphatic epoxy resin include difunctional aliphatic epoxy resins, such as ethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, and neopentyl glycol diglycidyl ether, and preferably neopentyl glycol diglycidyl ether.

The weight average molecular weight of the aliphatic epoxy resin is, for example, 150 or more and, for example, 400 or less.

Furthermore, the epoxy equivalent of the aliphatic epoxy resin is, for example, 60 g/eq. or more and, for example, 250 g/eq. or less.

When the epoxy compound contains an alicyclic epoxy resin and an aliphatic epoxy resin, the content of the alicyclic epoxy resin is, for example, 10 parts by mass or more, preferably 20 parts by mass or more, and for example, 50 parts by mass or less, preferably 40 parts by mass or less, per 100 parts by mass of the total amount of the alicyclic epoxy resin and the aliphatic epoxy resin. Furthermore, the content of the alicyclic epoxy resin is, for example, 5% by mass or more, preferably 10% by mass or more, and for example, 30% by mass or less, preferably 20% by mass or less, relative to the amount of the cationically polymerizable compound.

When the epoxy compound contains an alicyclic epoxy resin and an aliphatic epoxy resin, the content of the aliphatic epoxy resin is, for example, 40 parts by mass or more, preferably 50 parts by mass or more, more preferably 60 parts by mass or more, and for example, 90 parts by mass or less, preferably 80 parts by mass or less, per 100 parts by mass of the total amount of the alicyclic epoxy resin and the aliphatic epoxy resin. The content of the aliphatic epoxy resin is, for example, 20% by mass or more, preferably 30% by mass or more, and for example, 50% by mass or less, preferably 40% by mass or less, relative to the cationically polymerizable compound.

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

The content of the epoxy compound is, for example, 30% by mass or more, preferably 40% by mass or more, and, for example, 70% by mass or less, preferably 60% by mass or less, relative to the cationically polymerizable compound.

[Oxetane Compounds]
The oxetane compound contains, for example, 1 to 5 oxetane rings.

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

Examples of monofunctional oxetane compounds include 3-ethyl-3-hydroxymethyloxetane, 3-(meth)allyloxymethyl-3-ethyloxetane, (3-ethyl-3-oxetanylmethoxy)methylbenzene, 2-ethylhexyl (3-ethyl-3-oxetanylmethyl) ether, ethyl diethylene glycol (3-ethyl-3-oxetanylmethyl) ether, and 3-cyclohexylmethyl-3-ethyloxetane.

Examples of bifunctional oxetane compounds include 1,4-bis{[(3-ethyl-3-oxetanyl)methoxy]methyl}benzene, 3,3'-(oxybismethylene)bis(3-ethyloxetane), 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-oxetanylmeth 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, preferably 3,3'-(oxybismethylene)bis(3-ethyloxetane).

Examples of trifunctional or higher oxetane 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.

Commercially available oxetane compounds can also be used. Examples of commercially available oxetane compounds include Aron Oxetane OXT-221 (3,3'-(oxybismethylene)bis(3-ethyloxetane)) and Aron Oxetane OXT-121 (both manufactured by Toagosei Chemical Industry Co., Ltd.).

Preferably, the oxetane compound is a bifunctional oxetane compound.

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

The content of the oxetane compound is, for example, 30% by mass or more, preferably 40% by mass or more, and, for example, 70% by mass or less, preferably 60% by mass or less, relative to the cationically polymerizable compound.

Furthermore, the content of the cationic polymerizable compound in the sealing material for organic EL display elements is, for example, 80% by mass or more, preferably 90% by mass or more, and, for example, 98% by mass or less.

<Cationic Polymerization Initiator>
The cationic polymerization initiator is, for example, a photoacid generator that generates an acid upon irradiation with light.

The cationic polymerization initiator is not particularly limited, and any known cationic polymerization initiator can be used.

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

The content of the cationic polymerization initiator is, for example, 0.5 parts by mass or more, preferably 0.8 parts by mass or more, more preferably 1.3 parts by mass or more, and for example, 5 parts by mass or less, preferably 2.5 parts by mass or less, per 100 parts by mass of the cationic polymerizable compound.

The content of the cationic polymerization initiator in the sealing material for organic EL display elements is, for example, 0.5% by mass or more, preferably 1% by mass or more, and, for example, 10% by mass or less, preferably 5% by mass or less.

<Ultraviolet absorber>
The ultraviolet absorber is a component that absorbs white light and suppresses the generation of acid from the cationic polymerization initiator.

Examples of ultraviolet absorbers include benzotriazole compounds, benzophenone compounds, triazine compounds, and cyanoacrylate compounds.

Examples of benzotriazole compounds include 2-(5-methyl-2-hydroxyphenyl)benzotriazole, 2,2-hydroxy-3,5-bis(α,α-dimethylbenzyl)phenyl, 2-(2'-hydroxy-5'-methyl-phenyl)benzotriazole, 2-(2'-hydroxy-3',5'-di-t-butyl-phenyl)benzotriazole, 2-(2'-hydroxy-3'-t-butyl-5'-methyl-phenyl)-5-chlorobenzotriazole, 2-(2'-hydroxy-3',5'-di-t-butyl-phenyl)-5-chlorobenzotriazole, 2-(2H-benzotriazol-2-yl)-4,6-bis(1-methyl-1-phenylethyl)-phenol, 2-(2-hydroxy-5-methylphenyl)benzotriazole, and 2-(2'-hydroxy-4'-n-octoxyphenyl)benzotriazole. Preferred are 2-(2H-benzotriazol-2-yl)-4,6-bis(1-methyl-1-phenylethyl)-phenol, 2-(2-hydroxy-5-methylphenyl)benzotriazole, and 2-[2-hydroxy-5-[2-(methacryloyloxy)ethyl]phenyl]-2H-benzotriazole. More preferred are 2-(2H-benzotriazol-2-yl)-4,6-bis(1-methyl-1-phenylethyl)-phenol and 2-(2-hydroxy-5-methylphenyl)benzotriazole, and even more preferred are 2-(2-hydroxy-5-methylphenyl)benzotriazole.

Commercially available benzotriazole compounds can also be used. Examples of commercially available benzotriazole compounds include Tinuvin 234 (2-(2H-benzotriazol-2-yl)-4,6-bis(1-methyl-1-phenylethyl)-phenol, manufactured by BASF Japan Ltd.), KEMISORB 71 (2-(2-hydroxy-5-methylphenyl)benzotriazole, manufactured by Chemipro Chemical Co., Ltd.), and RUVA-93 (2-[2-hydroxy-5-[2-(methacryloyloxy)ethyl]phenyl]-2H-benzotriazole, manufactured by Otsuka Chemical Co., Ltd.).

Examples of benzophenone compounds include [2-hydroxy-4-(octyloxy)phenyl](phenyl)methanone, 2-hydroxy-4-n-octyloxybenzophenone, 2,4-dihydroxybenzophenone, 2-hydroxy-4-methoxybenzophenone, 2,2'-dihydroxy-4-methoxybenzophenone, 2,2'-dihydroxy-4,4'-dimethoxybenzophenone, 2,2'-dihydroxy-4,4'-dimethoxy-5-sulfobenzophenone, 2- Examples of the hydroxybenzophenone include hydroxy-4-methoxy-2'-carboxy benzophenone, 2-hydroxy-4-methoxy-5-sulfobenzophenone trihydrate, 2-hydroxy-4-n-dodecyloxy benzophenone, 2-hydroxy-4-benzyloxybenzophenone, 2,2',4,4'-tetrahydroxy benzophenone, 2-hydroxy-4-dodecyloxy-benzophenone, and 2-hydroxy-4-(2-hydroxy-3-methacryloxy)propoxybenzophenone. Preferred examples include [2-hydroxy-4-(octyloxy)phenyl](phenyl)methanone and 2-hydroxy-4-n-octyloxybenzophenone. More preferred examples include 2-hydroxy-4-n-octyloxybenzophenone.

Commercially available benzophenone compounds can also be used. Examples of commercially available benzophenone compounds include KEMISORB12 (2-hydroxy-4-n-octyloxybenzophenone, manufactured by Chemipro Chemicals Co., Ltd.) and Adekastab 1413 ([2-hydroxy-4-(octyloxy)phenyl](phenyl)methanone, manufactured by ADEKA Corporation).

Examples of triazine compounds include 2-[4,6-di(2,4-xylyl)-1,3,5-triazin-2-yl]-5-octyloxyphenol and 2,4-diphenyl-6-(2-hydroxy-4-hexyloxyphenyl)-1,3,5-triazine, preferably 2,4-diphenyl-6-(2-hydroxy-4-hexyloxyphenyl)-1,3,5-triazine.

Commercially available triazine compounds can also be used. Examples of commercially available triazine compounds include KEMISORB102 (2,4-diphenyl-6-(2-hydroxy-4-hexyloxyphenyl)-1,3,5-triazine, manufactured by Chemipro Chemicals).

Examples of cyanoacrylate compounds include ethyl-2-cyano-3-(3',4'-methylenedioxyphenyl)-acrylate.

As ultraviolet absorbers, preferably, benzotriazole compounds, benzophenone compounds, and triazine compounds are selected, more preferably, benzotriazole compounds and benzophenone compounds, and even more preferably, benzotriazole compounds or benzophenone compounds are selected as ultraviolet absorbers.

If the UV absorber is a benzotriazole compound or a benzophenone compound, it will have even better stability against white light.

Particularly preferably, the ultraviolet absorber is a benzotriazole compound, from the viewpoint of further improving stability against white light.

UV absorbers can be used alone or in combination with two or more types.

The content of the ultraviolet absorber is, for example, 0.05 parts by mass or more, preferably 0.4 parts by mass or more, more preferably 0.8 parts by mass or more, and for example, 2 parts by mass or less, preferably 1.5 parts by mass or less, per 100 parts by mass of the cationic polymerizable compound.

The content of the ultraviolet absorber in the sealing material for organic EL display elements is, for example, 0.1% by mass or more, preferably 0.5% by mass or more, more preferably 0.8% by mass or more, and, for example, 2% by mass or less, preferably 1.5% by mass or less, and even more preferably 1.2% by mass or less, from the viewpoint of improving the reliability of the sealing material for organic EL display elements after curing.

If the content of ultraviolet absorber is above the above lower limit, stability against white light can be improved.

Furthermore, if the content of ultraviolet absorber is below the above upper limit, the curing properties are maintained when cured by irradiating ultraviolet light.

<Compounds having a phenolic hydroxyl group>
The compound having a phenolic hydroxyl group is a component that captures the acid generated from the cationic polymerization initiator upon irradiation with light.

A compound having a phenolic hydroxyl group is a compound that has one or more phenolic hydroxyl groups in its molecule. Furthermore, compounds having a phenolic hydroxyl group do not include the above-mentioned benzotriazole compounds, benzophenone compounds, triazine compounds, and cyanoacrylate compounds.

Such compounds having a phenolic hydroxyl group preferably include monofunctional phenolic hydroxyl compounds having one benzene ring with one phenolic hydroxyl group on the benzene ring, difunctional phenolic hydroxyl compounds having one benzene ring with two phenolic hydroxyl groups on the benzene ring, and trifunctional or higher phenolic hydroxyl compounds having one benzene ring with three or more phenolic hydroxyl groups on the benzene ring. In other words, compounds having a phenolic hydroxyl group preferably have one benzene ring. This provides excellent stability.

Examples of the compound having a monofunctional phenolic hydroxyl group include the compound represented by the following formula (4).

In the above formula (4), R3 represents a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, or an alkyl ester group.

This refers to an alkyl group having 1 to 10 carbon atoms. Examples of alkyl groups having 1 to 10 carbon atoms include methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, and decyl groups.

The alkyl ester group is represented by the following formula (5):
-R ⁴ -C(=O)-O-R ⁵ (5)

In the above formula (5), R4 represents an alkylene group having 1 to 6 carbon atoms. Examples of alkylene groups having 1 to 6 carbon atoms include methylene, methylmethylene, dimethylmethylene, ethylene, propylene, trimethylene, and butylene.

In the above formula (5), R5 represents an alkyl group having 1 to 10 carbon atoms. Examples of alkyl groups having 1 to 10 carbon atoms include methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, and decyl groups.

Preferably, examples of such compounds having a monofunctional phenolic hydroxyl group include 2,6-di-tert-butyl-p-cresol (a compound in which R3 represents a methyl group in the above formula (4)) and benzenepropanoic acid 3,5-bis(1,1-dimethylethyl)-4-hydroxy-C7-C9 side chain alkyl ester (a mixture of a compound in which R3 represents an alkyl ester group in the above formula (4), and in which R4 represents an ethylene group and R5 represents a heptyl group in the above formula (5), a compound in which R4 represents an ethylene group and R5 represents an octyl group, and a compound in which R4 represents an ethylene group and R5 represents a nonyl group), and preferably 2,6-di-tert-butyl-p-cresol.

In other words, the compound represented by formula (4) above preferably does not contain an alkyl ester group. Therefore, the amount added contributes significantly to white light stability, making it even more superior in terms of achieving both white light stability and curability.

Examples of compounds having a bifunctional phenolic hydroxyl group include hydroquinone, resorcinol, tert-butylcatechol, and tert-butylhydroquinone.

An example of a compound having a trifunctional or higher phenolic hydroxyl group is pyrogallol.

Preferably, compounds having a phenolic hydroxyl group are compounds having a monofunctional phenolic hydroxyl group and compounds having a bifunctional phenolic hydroxyl group, and more preferably, compounds having a monofunctional phenolic hydroxyl group from the viewpoint of achieving both stability under white light and curability.

The molecular weight of the compound having a phenolic hydroxyl group is, for example, 94 or more, preferably 100 or more, more preferably 200 or more, and for example, 1000 or less, preferably 500 or less, and from the viewpoint of achieving both white light stability and curability, more preferably 300 or less. A lower molecular weight makes a greater contribution to white light stability than a lower molecular weight compound, resulting in even better compatibility between white light stability and curability.

Compounds having a phenolic hydroxyl group can be used alone or in combination of two or more types.

The content of the compound having a phenolic hydroxyl group is, per 100 parts by mass of the cationically polymerizable compound, for example, 0.01 parts by mass or more, preferably 0.05 parts by mass or more, more preferably 0.08 parts by mass or more, even more preferably 0.1 parts by mass or more, and for example, 0.5 parts by mass or less, preferably 0.3 parts by mass or less, more preferably 0.15 parts by mass or less.

The content of the compound having a phenolic hydroxyl group in the sealing material for organic EL display elements is, for example, 0.01% by mass or more, preferably 0.05% by mass or more, more preferably 0.08% by mass or more, and even more preferably 0.1% by mass or more, and is, for example, 0.5% by mass or less, preferably 0.3% by mass or less, and more preferably 0.15% by mass or less.

If the content of compounds having phenolic hydroxyl groups is above the above lower limit, stability against white light can be improved.

Furthermore, if the content of compounds having phenolic hydroxyl groups is below the above upper limit, the curing properties are excellent.

The mass ratio of the compound having a phenolic hydroxyl group to the UV absorber (compound having a phenolic hydroxyl group/UV absorber) is 0.01 or more, preferably 0.03 or more, more preferably 0.07 or more, even more preferably 0.09 or more, particularly preferably 0.1 or more, and is less than 1.00, preferably 0.5 or less, more preferably 0.3 or less, even more preferably 0.2 or less.

If the above mass ratio is greater than or equal to the above lower limit, stability to white light can be improved.

On the other hand, if the mass ratio is below the lower limit, stability to white light decreases.

Furthermore, if the above mass ratio is below the above upper limit, the reliability of the sealing material for organic EL display elements will be excellent.

On the other hand, if the above mass ratio exceeds the above upper limit, the reliability of the sealing material for organic EL display elements will decrease.

<Preparation of sealing material for organic EL display element>
To prepare the sealant for an organic EL display element, first, a cationically polymerizable compound, an ultraviolet absorber, and a compound having a phenolic hydroxyl group are mixed to prepare a mixture. Next, a cationic polymerization initiator is added to the mixture and mixed. This produces a sealant for an organic EL display element.

In the above preparation, additives can be blended as needed. In other words, the sealing material for organic EL display elements can also contain additives.

Additives include, for example, sensitizers, tackifiers, antioxidants, polymerization initiators, antioxidants, wettability improvers, surfactants, plasticizers, UV absorbers, preservatives, and antibacterial agents.

The proportion of additives to be added is set appropriately depending on the application and purpose.

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

The sealant for organic EL display elements may also contain a solvent, but preferably the sealant for organic EL display elements is substantially solvent-free. Specifically, the solvent content is, for example, 0.05% by mass or less, preferably 0.01% by mass or less, and more preferably 0.001% by mass or less.

<Physical properties of encapsulant for organic EL display elements>
The sealing material for organic EL display elements is preferably liquid at 25° C. Being liquid at 25° C. is defined as a property in which the viscosity at 25° C. is 5 mPa·s or more and 50 mPa·s or less. When the sealing material for organic EL display elements is liquid at 25° C., it has excellent inkjet ejection properties.

Furthermore, the viscosity at 25°C (initial viscosity described below) is, for example, 1 mPa·s or more, preferably 5 mPa·s or more, more preferably 10 mPa·s or more, and for example, 50 mPa·s or less, preferably 30 mPa·s or less, more preferably 25 mPa·s or less.

The method for measuring the above viscosity is described in detail in the examples below.

The cured product of the encapsulant for organic EL display elements preferably has transparency. Specifically, the total light transmittance (in accordance with JIS K 7361-1) of the cured product of the encapsulant for organic EL display elements is, for example, 80% or more, preferably 85% or more, more preferably 90% or more, and, for example, 100% or less.

<Action and effect>
In this sealing material for organic EL display elements, the mass ratio of the compound having a phenolic hydroxyl group to the ultraviolet absorber (compound having a phenolic hydroxyl group/ultraviolet absorber) is 0.01 or more and less than 1.00. In this sealing material for organic EL display elements, since the mass ratio is 0.01 or more, stability against white light can be improved. Furthermore, in this sealing material for organic EL display elements, since the mass ratio is less than 1.00, reliability of the organic EL element after curing can be improved from the viewpoint of curability.

This type of encapsulant for organic EL display elements has excellent stability against white light and reliability after curing, making it suitable for use as an encapsulant for organic EL display elements. In particular, because this encapsulant for organic EL display elements is stable against white light, thickening is suppressed. Therefore, it can be used effectively in inkjet printing.

<Modification>
In the above explanation, to prepare the sealing material for organic EL display elements, first, a cationically polymerizable compound, an ultraviolet absorber, and a compound having a phenolic hydroxyl group are mixed to prepare a mixture, and then a cationic polymerization initiator is added to this mixture. However, it is also possible to add the cationic polymerization initiator all at once together with the cationically polymerizable compound, the ultraviolet absorber, and the compound having a phenolic hydroxyl group.

<Organic EL display device>
An embodiment of the organic EL display device of the present invention will be described with reference to FIG.

The organic EL display device 10 comprises a substrate 1, an organic EL element 2 mounted on one thickness-wise surface of the substrate 1, and a sealing layer 3 covering the organic EL element 2.

[substrate]
The substrate 1 supports the organic EL element 2 .

Examples of substrate 1 include glass substrates and plastic substrates, and preferably glass substrates.

The thickness of substrate 1 is, for example, 0.1 mm or more and, for example, 20 mm or less.

[Organic EL element]
The organic EL element 2 is a known organic EL element and is mounted on the substrate 1. Although not shown, the organic EL element 2 includes a cathode reflective electrode, an organic EL layer, and an anode transparent electrode.

The sealing layer 3 is a layer that prevents the organic EL element 2 from deteriorating due to moisture in the atmosphere.

The sealing layer 3 consists of the cured product of the above-mentioned sealing material for organic EL display elements.

The thickness of the sealing layer 3 is, for example, 1 μm or more and, for example, 100 μm or less.

<Method of manufacturing an organic EL display device>
An embodiment of the method for manufacturing an organic EL display device according to the present invention will be described with reference to FIGS. 2A to 2C.

The manufacturing method for an organic EL display device comprises a first step of preparing a substrate 1, a second step of mounting an organic EL element 2 on one thickness-wise surface of the substrate 1, and a third step of forming a sealing layer 3 that covers the organic EL element 2 using an inkjet method.

[First step]
In the first step, a substrate 1 is prepared as shown in FIG. 2A.

[Second step]
In the second step, as shown in FIG. 2B, the organic EL element 2 is mounted on one surface of the substrate 1 in the thickness direction by, for example, a known method (for example, vacuum deposition).

[Third step]
2C, in the third step, the sealing layer 3 is formed by an inkjet method to cover the organic EL element 2. By using the inkjet method, the organic EL element 2 can be reliably sealed.

Specifically, first, an organic EL display element sealant is placed by inkjet printing so as to cover the organic EL element 2. Then, the organic EL display element sealant is irradiated with light to harden it. This completes the production of the organic EL display device 10.

The organic EL display device 10 has an organic EL element 2 covered with a sealing layer 3 made of a highly reliable cured sealant for organic EL display elements. This provides excellent reliability.

In addition, the manufacturing method for an organic EL display device uses an inkjet method to form a sealing layer 3 made of a cured product of a highly reliable sealant for organic EL display elements, which covers the organic EL element 2. As a result, an organic EL display device 10 with excellent reliability can be manufactured.

Furthermore, although not shown, the organic EL display device 10 may also be provided with another sealing layer (e.g., an inorganic sealing layer) on one surface in the thickness direction and/or the other surface in the thickness direction.

Next, the present invention will be described based on examples and comparative examples, but the present invention is not limited to these examples. Note that "parts" and "%" are by mass unless otherwise specified. Furthermore, specific numerical values for blending ratios (content ratios), physical properties, parameters, etc. used in the following description can be substituted with the corresponding upper limit (a numerical value defined as "equal to or less than") or lower limit (a numerical value defined as "equal to or greater than") of the blending ratios (content ratios), physical properties, parameters, etc. described in the "Description of the Invention" above.

<Ingredient details>
The trade names and abbreviations of the components used in each example and each comparative example are described in detail below. CEL8010: (3,3',4,4'-diepoxy)bicyclohexyl, trade name "Celloxide 8010", manufactured by Daicel Corporation NPG(G): neopentyl glycol diglycidyl ether, manufactured by Sakamoto Pharmaceutical Co., Ltd. OXT221: 3,3'-(oxybismethylene)bis(3-ethyloxetane), trade name "Aronoxetane", manufactured by Sakamoto Pharmaceutical Co., Ltd. OXT-221, Tinuvin 234: 2-(2H-benzotriazol-2-yl)-4,6-bis(1-methyl-1-phenylethyl)-phenol manufactured by Toagosei Chemical Co., Ltd., KEMISORB 71: 2-(2-hydroxy-5-methylphenyl)benzotriazole manufactured by BASF Japan Ltd., RUVA-93: 2-[2-hydroxy-5-[2-(methacryloyloxy)ethyl]phenyl]-2H-benzotriazole manufactured by Chemipro Chemical Co., Ltd., and Otsuka KEMISORB12 manufactured by ADEKA: 2-hydroxy-4-n-octyloxybenzophenone, Adekastab 1413 manufactured by Chemipro Chemicals: [2-hydroxy-4-(octyloxy)phenyl](phenyl)methanone, KEMISORB102 manufactured by ADEKA: 2,4-diphenyl-6-(2-hydroxy-4-hexyloxyphenyl)-1,3,5-triazine, BHT manufactured by Chemipro Chemicals: 2,6-di-tert-butyl-p-cresol, molecular weight 220
Irganox 1135: Benzenepropanoic acid 3,5-bis(1,1-dimethylethyl)-4-hydroxy-C7-C9 side chain alkyl ester, molecular weight 390

<Preparation of sealing material for organic EL display element>
Examples 1 to 7 and Comparative Examples 1 to 10
First, a cationically polymerizable compound, an ultraviolet absorber, and a compound having a phenolic hydroxyl group were mixed together to prepare a mixture based on the formulation shown in Table 1. Next, a cationic polymerization initiator was added to the mixture and mixed. This resulted in the preparation of an encapsulant for an organic EL display element.

<Evaluation>
[Stability to white light]
The viscosity of the encapsulant for organic EL display elements of each example and each comparative example was measured. Specifically, an E-type viscometer (LV-DV-II+ Pro, manufactured by BROOKFIELD, rotor angle: 1°, rotor radius: 24 mm) was used in accordance with the cone-plate viscometer method of JIS K5600-2-3 (2014). The viscosity (initial viscosity) was measured at 25°C immediately after preparation (within 60 minutes after preparation). The rotation speed of the cone-plate during measurement was 20 rpm.

10 ml of this encapsulant for organic EL displays was then weighed into a colorless, transparent 20 ml vial and rotated for 6 hours on a mixer rotor placed in a location where fluorescent lighting was at 600 lux. The viscosity (viscosity after 6 hours) was measured using an E-type viscometer under the same conditions as above.

The viscosity increase rate was calculated based on the following formula (6). The results are shown in Table 1.
Viscosity increase rate = (viscosity after 6 hours / initial viscosity) - 1 (6)

The stability to white light was evaluated based on the following criteria, and the results are shown in Table 1.
Good: The viscosity increase rate was less than 20%.
△: The viscosity increase rate was 20% or more and less than 50%.
×: The viscosity increase rate was 50% or more.

[Coating stability]
The organic EL display element encapsulant of each Example and Comparative Example was introduced into an inkjet cartridge DMC-11610 (manufactured by Fujifilm Dimatix Corporation). The inkjet cartridge was set in an inkjet device DMP-2831 (manufactured by Fujifilm Dimatix Corporation) installed under a fluorescent lamp, and after adjusting the coating condition, 1000 droplets were applied at 500 μm intervals onto a 50 mm x 50 mm alkali-free glass. Thereafter, this organic EL display element encapsulant was left under a fluorescent lamp for 3 hours, and then 1000 droplets were applied at 500 μm intervals onto alkali-free glass using the inkjet cartridge again, and the number of droplets that could not be coated was confirmed. Coating stability was evaluated based on the following criteria. The results are shown in Table 1.
◯: After being left for 3 hours, the number of droplets that could not be applied was 98% or more of the number before being left.
Δ: After being left for 3 hours, the number of droplets that could not be applied was 90% or more but less than 98% of that before being left.
x: After being left for 3 hours, the number of droplets that could not be applied was less than 90% of that before being left.

[Curing rate]
(Preparation of evaluation substrate)
The organic EL display element encapsulant of each example and comparative example was loaded into an inkjet cartridge DMC-11610 (manufactured by Fujifilm Dimatix Corporation). The inkjet cartridge was set into an inkjet device DMP-2831 (manufactured by Fujifilm Dimatix Corporation). After adjusting the coating conditions, the coating was applied to a 50 mm x 50 mm alkali-free glass substrate in a size of 40 mm x 40 mm so that the thickness after curing would be 10 μm. This resulted in a coating film. Next, the coating film was left for 1 minute in an environment of 25°C temperature and 50% humidity, and then irradiated with light from a UV-LED with a wavelength of 395 nm at an illuminance of 100 mW/cm ² and 1500 mJ/cm ² to cure the coating. This resulted in the production of an evaluation substrate.

(Measurement of cure rate)
FT-IR measurements were carried out on the sealing materials for organic EL display elements of each example and each comparative example, and the evaluation substrate.

Then, the height (P2) of the peak at a wave number of 831 cm ⁻¹ (a peak attributable to epoxy groups) was calculated using the height (P1) of the peak at a wave number of 1371 cm ⁻¹ (a peak attributable to CH- stretching vibration) as a reference, and the cure rate was calculated based on the following formula (7).
The results are shown in Table 1.
{(P2b/P1b)-(P2a/P1a)}/(P2b/P1b)×100 (7)

In the above formula (7), P1a represents the peak height at a wave number of 1371 ^cm after curing, P1b represents the peak height at a wave number of 1371 ^cm before curing, P2a represents the peak height at a wave number of 831 ^cm after curing, and P2b represents the peak height at a wave number of 831 ^cm before curing.

[Reliability of organic EL elements]
The organic EL display element sealing material of each example and each comparative example was introduced into an inkjet cartridge DMC-11610 (manufactured by Fujifilm Dimatix Corp.). The inkjet cartridge was set in an inkjet device DMP-2831 (manufactured by Fujifilm Dimatix Corp.), and after adjusting the discharge state, the composition was applied to a glass substrate in a size of 15 mm x 15 mm so that the thickness after curing would be 10 μm, thereby obtaining a coating film.

The coating film was then left for 1 minute in an environment at a temperature of 25°C and a humidity of 50%, and then irradiated with light from a UV-LED with a wavelength of 395 nm at an illuminance of 100 mW/cm ² and an illuminance of 1500 mJ/cm ² to cure the coating film, thereby obtaining a cured film.

The cured film was then plasma treated for 1 minute under the following conditions: 2500 W (ICP power supply), 300 W (RF power supply), DC bias 200 V, argon (Ar) flow rate 50 sccm, and pressure 10 mtorr.

Then, a 100 nm-thick inorganic sealing layer (SiNx film) was formed on the cured film side by RF sputtering using a SiNx target. This produced the first evaluation substrate.

Separately, an organic EL element was mounted on another glass substrate to produce a second evaluation substrate. The first evaluation substrate and the second evaluation substrate were then bonded together. This produced an organic EL display device for evaluation.

Next, a reliability test was performed on the evaluation organic EL display devices at 85° C. Specifically, the light-emitting area ratio (%) of each evaluation organic EL display device after storage at 85° C. for 100 hours was determined by the following method. That is, using Motic Images Plus software (manufactured by Shimadzu Rika Corporation), the light-emitting area in the initial state and the light-emitting area after storage for 100 hours were calculated, and the light-emitting area ratio was calculated based on the following formula (8).
Luminescent area ratio (%) = luminescent area after 100 hours storage / luminescent area in initial state × 100 (8)

The reliability of the organic EL device was evaluated based on the following criteria. The results are shown in Table 1.
Good: The light-emitting area ratio was 80% or more.
Δ: The light-emitting area ratio was 50% or more and less than 80%.
×: The light-emitting area ratio was less than 50%.

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 within the scope of the following claims.

The sealing material for organic EL display elements, organic EL display devices, and methods for manufacturing organic EL display devices of the present invention are suitable for use in the manufacture of image display devices.

1 Substrate 2 Organic EL element 3 Sealing layer 10 Organic EL display device

Claims (9)

a cationically polymerizable compound;
a cationic polymerization initiator;
an ultraviolet absorber;
a compound having a phenolic hydroxyl group,
a mass ratio of the compound having a phenolic hydroxyl group to the ultraviolet absorber (compound having a phenolic hydroxyl group/ultraviolet absorber) is 0.01 or more and less than 1.00,
the ultraviolet absorber comprises a benzotriazole compound,
the benzotriazole compound comprises 2-(2H-benzotriazol-2-yl)-4,6-bis(1-methyl-1-phenylethyl)-phenol or 2-(2-hydroxy-5-methylphenyl)benzotriazole;
The sealing material for an organic EL display element, wherein the compound having a phenolic hydroxyl group contains 2,6-di-tert-butyl-p-cresol. The sealant for organic EL display elements according to claim 1, wherein the cationic polymerizable compound is an epoxy compound and/or an oxetane compound. 2. The sealing material for organic EL display elements according to claim 1, wherein the ultraviolet absorber is a benzotriazole compound containing 2-(2H-benzotriazol-2-yl)-4,6-bis(1-methyl-1-phenylethyl)-phenol or 2-(2-hydroxy-5-methylphenyl)benzotriazole . The encapsulant for organic EL display elements according to claim 1, wherein the content of the ultraviolet absorber is 0.1% by mass or more and 2% by mass or less. The encapsulant for organic EL display elements according to claim 1, wherein the content of the compound having a phenolic hydroxyl group is 0.01% by mass or more and 0.5% by mass or less. It is liquid at 25°C,
The sealing material for an organic EL display element according to claim 1 , wherein the solvent content is 0.05% by mass or less. The encapsulant for organic EL display elements according to claim 1, having a viscosity at 25°C of 5 mPa·s or more and 50 mPa·s or less. A substrate;
an organic EL element mounted on one surface of the substrate in the thickness direction;
a sealing layer that covers the organic EL element,
An organic EL display device, wherein the sealing layer is made of a cured product of the sealing material for an organic EL display element according to claim 1 . A first step of preparing a substrate;
a second step of mounting an organic EL element on one surface of the substrate in the thickness direction;
and a third step of forming a sealing layer that covers the organic EL element by an inkjet method.
The method for manufacturing an organic EL display device, wherein the sealing layer is made of a cured product of the sealing material for an organic EL display element according to claim 1 .