JP7528022B2 - Encapsulating Sheet - Google Patents

Description

The present invention relates to a sealing sheet having a sealant layer that has excellent application properties at room temperature (23°C; the same applies below) and is resistant to deformation during the heat curing process.

In recent years, organic EL elements have been attracting attention as light-emitting elements capable of emitting high-luminance light when driven by a low-voltage direct current.
However, organic EL elements have a problem in that their light-emitting characteristics, such as light-emitting luminance, light-emitting efficiency, and light-emitting uniformity, tend to deteriorate over time.
The cause of the problem of the deterioration of the light-emitting characteristics was thought to be the infiltration of oxygen, moisture, etc. into the organic EL element, which deteriorates the electrodes and the organic layer, and therefore, the organic EL element has been sealed with a sealant to prevent the infiltration of oxygen and moisture.

For example, Patent Document 1 describes an image display device sealant that contains a resin component and a curing agent, and that is characterized in that the resin component contains a biphenyl skeleton-containing epoxy resin having a weight-average molecular weight within a specific range, an alicyclic skeleton-containing epoxy resin having a weight-average molecular weight within a specific range, and a styrene-based oligomer having a weight-average molecular weight within a specific range.

WO2018/235824

As described in Patent Document 1, a curable sheet-like adhesive has been suitably used as a material for forming a sealant (hereinafter, the "sheet-like adhesive for forming a sealant" may be referred to as a "sealant layer").
However, some of the curable sealant layers have poor application properties at room temperature, and require heating to soften the surface when they are applied to an object to be sealed.
Furthermore, when the sealant layer has thermosetting properties, in the initial stage of the thermosetting process, the sealant layer, whose fluidity has been increased by heating, may deform due to external influences such as vibration, and the sealant layer may not be able to exhibit its inherent sealing performance.

The present invention has been made in consideration of the above-mentioned circumstances, and aims to provide a sealing sheet having a sealant layer that has excellent application properties at room temperature and is not easily deformed during the thermal curing process.

In order to solve the above problems, the present inventors conducted extensive research into sealant layers containing epoxy compounds. As a result, they discovered that a sealant layer that satisfies the requirements regarding the storage modulus at 23°C and the requirements regarding the complex viscosity when heated under specified conditions has excellent adhesion at room temperature and is not easily deformed during the heat curing process, which led to the completion of the present invention.

Thus, according to the present invention, the following encapsulating sheets [1] to [9] are provided.

[1] An encapsulating sheet having a thermosetting encapsulant layer,
The present invention is characterized by satisfying the following requirements (I), (II), and (III) :
The sealant layer contains an epoxy compound, a binder resin, and a curing agent,
At least one of the epoxy compounds is a liquid epoxy compound at 25°C;
At least one of the curing agents is a thermal cationic polymerization initiator having an exothermic peak top temperature of 120° C. or lower when differential scanning calorimetry is performed under the following conditions:
(Differential Scanning Calorimetry)
A mixture of 0.1 part by mass of a thermal cationic polymerization initiator, 100 parts by mass of bisphenol A diglycidyl ether, and 0.1 part by mass of γ-butyrolactone is used as a measurement sample, and differential scanning calorimetry is performed at a temperature increase rate of 10° C./min from 30° C. to 300° C.
Requirement (I): The sealant layer contains one or more epoxy compounds.
Requirement (II): The storage modulus of the sealant layer at 23° C. is 1.3×10 ⁷ Pa or less.
Requirement (III): When the sealant layer is heated from 35° C. to 110° C. at a rate of 25° C./min and then maintained at 110° C., the complex viscosity of the sealant layer 250 seconds after the start of heating is 1×10 ⁴ Pa·s or more.
[2] The encapsulating sheet according to [1], wherein the sealant layer satisfies the following requirement (IV):
Requirement (IV): Prepare sealant layers of the same quality [sealant layer (A) and sealant layer (B)], and use sealant layer (A) as a test piece to perform differential scanning calorimetry at a temperature rise rate of 10°C/min from 0°C to 200°C to determine the area of the exothermic peak [area (α)]. Next, sealant layer (B) is stored for 7 days in an environment of 23°C and relative humidity of 50%, and then used as a measurement sample to perform differential scanning calorimetry at a temperature rise rate of 10°C/min from 0°C to 200°C to determine the area of the exothermic peak [area (β)]. Based on the obtained area value, X calculated from the following formula (1) is 95% or more.

[3] The encapsulating sheet according to [1] or [2], wherein at least one of the epoxy compounds is an epoxy compound having a glycidyl ether group.
[4] The encapsulating sheet according to any one of [1] to [3], wherein at least one of the epoxy compounds is an epoxy compound having an alicyclic skeleton.
[5] The encapsulating sheet according to any one of [1] to [4], further comprising, as at least one of the curing agents, a thermal cationic polymerization initiator having an exothermic peak top temperature of more than 120° C. when differential scanning calorimetry is performed under the following conditions:
(Differential Scanning Calorimetry)
A mixture of 0.1 part by mass of a thermal cationic polymerization initiator, 100 parts by mass of bisphenol A diglycidyl ether, and 0.1 part by mass of γ-butyrolactone is used as a measurement sample, and differential scanning calorimetry is performed at a temperature increase rate of 10° C./min from 30° C. to 300° C.
[6] The encapsulating sheet according to any one of [1] to [5], wherein all of the curing agents are thermal cationic polymerization initiators.
[7] The encapsulating sheet according to any one of [1] to [6], wherein at least one of the binder resins is a resin having a glass transition temperature (Tg) of 60° C. or higher.
[8] The encapsulating sheet according to any one of [1] to [7], wherein the binder resin is one or more resins selected from a phenoxy resin, a modified olefin resin, and an acetal resin.
[9] The encapsulating sheet according to any one of [1] to [8], which is used for encapsulating an optical device.

The present invention provides a sealing sheet having a sealant layer that has excellent application properties at room temperature and is not easily deformed during the thermal curing process.

The encapsulating sheet of the present invention is an encapsulating sheet having a thermosetting sealant layer, and is characterized in that it satisfies the following requirements (I), (II), and (III).
Requirement (I): The sealant layer contains one or more epoxy compounds.
Requirement (II): The storage modulus of the sealant layer at 23° C. is 1.3×10 ⁷ Pa or less.
Requirement (III): When the sealant layer is heated from 35° C. to 110° C. at a rate of 25° C./min and then maintained at 110° C., the complex viscosity of the sealant layer 250 seconds after the start of heating is 1×10 ⁴ Pa·s or more.

In the present invention, the term "sealant layer" means a "sheet-shaped adhesive for forming a sealant." The cured product of the sealant layer is used as a sealant.
The sealant layer may be in the form of a strip or a long sheet (strip).

[Requirement (I)]
The sealant layer contains one or more epoxy compounds.
When the sealant layer contains an epoxy compound, the sealant layer becomes thermosetting.

The epoxy compound refers to a compound having at least one, and preferably two or more, epoxy groups in the molecule. In the present invention, the phenoxy resin described below is not included in the epoxy compound.
The epoxy group includes groups containing an oxirane structure, such as a glycidyl group, a glycidyl ether group, and an epoxycyclohexyl group.

The molecular weight of the epoxy compound is usually from 100 to 5,000, preferably from 200 to 3,000.
The epoxy equivalent of the epoxy compound is preferably 50 g/eq or more and 1000 g/eq or less, and more preferably 100 g/eq or more and 800 g/eq or less.
When the epoxy equivalent of the epoxy compound is within the above range, a sealing material (cured product) having high adhesive strength can be formed more efficiently.
In the present invention, the epoxy equivalent means a value obtained by dividing the molecular weight by the number of epoxy groups.

The content of the epoxy compound is preferably 55% by mass or more, and more preferably 57 to 75% by mass, based on the total mass of the sealant layer.
When the content of the epoxy compound is 55 mass % or more based on the entire sealant layer, a sealant having high adhesive strength can be formed more efficiently.

Examples of the epoxy compound include an aliphatic epoxy compound (excluding an alicyclic epoxy compound), an aromatic epoxy compound, and an alicyclic epoxy compound.
Examples of the aliphatic epoxy compounds include monofunctional epoxy compounds such as glycidyl ethers of aliphatic alcohols and glycidyl esters of alkyl carboxylic acids;
Polyfunctional epoxy compounds such as polyglycidyl ethers of aliphatic polyhydric alcohols or their alkylene oxide adducts, and polyglycidyl esters of aliphatic long-chain polybasic acids.

Representative compounds of these aliphatic epoxy compounds include alkenyl glycidyl ethers such as allyl glycidyl ether; alkyl glycidyl ethers such as butyl glycidyl ether, 2-ethylhexyl glycidyl ether, and C12-13 mixed alkyl glycidyl ether; 1,4-butanediol diglycidyl ether, neopentyl glycol diglycidyl ether, triglycidyl ether of glycerin, triglycidyl ether of trimethylolpropane, tetraglycidyl ether of sorbitol, hexaglycidyl ether of dipentaerythritol, and diglycidyl ether of polyethylene glycol. glycidyl ethers of polyhydric alcohols such as diglycidyl ether of polypropylene glycol; polyglycidyl ethers of polyether polyols obtained by adding one or more alkylene oxides to aliphatic polyhydric alcohols such as propylene glycol, trimethylolpropane, and glycerin; diglycidyl esters of aliphatic long-chain dibasic acids; monoglycidyl ethers of aliphatic higher alcohols, glycidyl esters of higher fatty acids, epoxidized soybean oil, epoxy octyl stearate, epoxy butyl stearate, and epoxidized polybutadiene; and the like.

Commercially available aliphatic epoxy compounds may also be used, including Denacol EX-121, Denacol EX-171, Denacol EX-192, Denacol EX-211, Denacol EX-212, Denacol EX-313, Denacol EX-314, Denacol EX-321, Denacol EX-411, Denacol EX-421, Denacol EX-512, Denacol EX-521, Denacol EX-611, Denacol EX-612, and Denacol EX-61. 4, Denacol EX-622, Denacol EX-810, Denacol EX-811, Denacol EX-850, Denacol EX-851, Denacol EX-821, Denacol EX-830, Denacol EX-832, Denacol EX-841, Denacol EX-861, Denacol EX-911, Denacol EX-941, Denacol EX-920, Denacol EX-931 (all manufactured by Nagase ChemteX Corporation);
Epolight M-1230, Epolight 40E, Epolight 100E, Epolight 200E, Epolight 400E, Epolight 70P, Epolight 200P, Epolight 400P, Epolight 1500NP, Epolight 1600, Epolight 80MF, Epolight 100MF (all manufactured by Kyoeisha Chemical Co., Ltd.);
Examples of the glycerol are ADEKA GLYCILOR ED-503, ADEKA GLYCILOR ED-503G, ADEKA GLYCILOR ED-506, and ADEKA GLYCILOR ED-523T (all manufactured by ADEKA Corporation).

Examples of aromatic epoxy compounds include phenols having at least one aromatic ring, such as phenol, cresol, and butylphenol, or mono- or polyglycidyl ethers of their alkylene oxide adducts; epoxy compounds having an aromatic heterocycle; and the like.

Representative examples of these aromatic epoxy compounds include glycidyl ethers of bisphenol A, bisphenol F, or compounds obtained by further adding alkylene oxide to these compounds, and epoxy novolac resins;
Mono/polyglycidyl ethers of aromatic compounds having two or more phenolic hydroxyl groups, such as resorcinol, hydroquinone, catechol, etc.;
Glycidyl ethers of aromatic compounds having two or more alcoholic hydroxyl groups, such as phenyldimethanol, phenyldiethanol, and phenyldibutanol;
Glycidyl esters of polybasic aromatic compounds having two or more carboxylic acids, such as phthalic acid, terephthalic acid, trimellitic acid, etc., glycidyl esters of benzoic acid, epoxidized products of styrene oxide or divinylbenzene;
Epoxy compounds having a triazine skeleton such as 2,4,6-tri(glycidyloxy)-1,3,5-triazine; and the like.

Commercially available aromatic epoxy compounds may also be used, such as Denacol EX-146, Denacol EX-147, Denacol EX-201, Denacol EX-203, Denacol EX-711, Denacol EX-721, Oncoat EX-1020, Oncoat EX-1030, Oncoat EX-1040, Oncoat EX-1050, Oncoat EX-1051, Oncoat EX-1010, Oncoat EX-1011, and Oncoat 1012 (all manufactured by Nagase ChemteX Corporation);
OGSOL PG-100, OGSOL EG-200, OGSOL EG-210, OGSOL EG-250 (all manufactured by Osaka Gas Chemicals Co., Ltd.);
HP4032, HP4032D, HP4700 (all manufactured by DIC Corporation);
ESN-475V (all manufactured by Nippon Steel Chemical & Material Co., Ltd.);
JER (formerly Epicoat) YX8800 (all manufactured by Mitsubishi Chemical Corporation);
MARPROOF G-0105SA, MARPROOF G-0130SP (both manufactured by NOF Corporation);
Epicron N-665, Epicron HP-7200 (both manufactured by DIC Corporation);
EOCN-1020, EOCN-102S, EOCN-103S, EOCN-104S, XD-1000, NC-3000, EPPN-501H, EPPN-501HY, EPPN-502H, NC-7000L (all manufactured by Nippon Kayaku Co., Ltd.);
ADEKA RESIN EP-4000, ADEKA RESIN EP-4005, ADEKA RESIN EP-4100, ADEKA RESIN EP-4901 (all manufactured by ADEKA Corporation);
TECHMORE VG-3101L (all manufactured by Printec):
TEPIC-FL, TEPIC-PAS, TEPIC-UC (all manufactured by Nissan Chemical Industries, Ltd.);

Examples of alicyclic epoxy compounds include polyglycidyl ethers of polyhydric alcohols having at least one alicyclic structure, and cyclohexene oxide- or cyclopentene oxide-containing compounds obtained by epoxidizing cyclohexene- or cyclopentene ring-containing compounds with an oxidizing agent.

Representative compounds of these alicyclic epoxy compounds include hydrogenated bisphenol A diglycidyl ether, 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate, 3,4-epoxy-1-methylcyclohexyl-3,4-epoxy-1-methylhexane carboxylate, 6-methyl-3,4-epoxycyclohexylmethyl-6-methyl-3,4-epoxycyclohexane carboxylate, 3,4-epoxy-3-methylcyclohexylmethyl-3,4-epoxy-3-methylcyclohexane carboxylate, 3,4-epoxy-5-methylcyclohexylmethyl-3,4-epoxy-5-methylcyclohexane carboxylate, bis(3,4 -epoxycyclohexylmethyl)adipate, 3,4-epoxy-6-methylcyclohexanecarboxylate, methylene bis(3,4-epoxycyclohexane), propane-2,2-diyl-bis(3,4-epoxycyclohexane), 2,2-bis(3,4-epoxycyclohexyl)propane, dicyclopentadiene diepoxide, ethylene bis(3,4-epoxycyclohexanecarboxylate), dioctyl epoxyhexahydrophthalate, di-2-ethylhexyl epoxyhexahydrophthalate, 1-epoxyethyl-3,4-epoxycyclohexane, 1,2-epoxy-2-epoxyethylcyclohexane, α-pinene oxide, limonene dioxide, etc.

In addition, commercially available products can also be used as the alicyclic epoxy compound. Examples of commercially available products include Celoxide 2021P, Celoxide 2081, Celoxide 2000, and Celoxide 3000 (all manufactured by Daicel Corporation); Epolite 4000 (manufactured by Kyoeisha Chemical Co., Ltd.); YX8000 and YX8034 (all manufactured by Mitsubishi Chemical Corporation); ADEKA RESIN EP-4088S, ADEKA RESIN EP-4088L, and ADEKA RESIN EP-4080E (all manufactured by ADEKA Corporation); and the like.

These epoxy compounds can be used alone or in combination of two or more.

At least one of the epoxy compounds is preferably an epoxy compound that is liquid at 25°C.
"Liquid at 25° C." means that it has fluidity at 25° C. The epoxy compound preferably has a viscosity of 2 to 10,000 mPa·s as measured at 25° C. and 1.0 rpm using an E-type viscometer.
By using an epoxy compound that is liquid at 25° C., it becomes easier to form a sealant layer that satisfies the requirement (II).

When the sealant layer contains an epoxy compound that is liquid at 25°C, the content thereof is preferably 55 to 70 mass%, and more preferably 57 to 65 mass%, based on the entire sealant layer, from the viewpoint of preventing the sealant layer from adhering to unintended objects at its ends.
By controlling the content of the epoxy compound that is liquid at 25° C. to 55 mass % or more based on the entire sealant layer, it becomes easier to form a sealant layer that satisfies the requirement (II).

At least one of the epoxy compounds is preferably an epoxy compound having a glycidyl ether group.
Since a glycidyl ether group is not so highly reactive as compared with an epoxycyclohexyl group or the like, by using an epoxy compound having a glycidyl ether group, an encapsulating sheet having superior storage stability can be obtained.

When the sealant layer contains an epoxy compound having a glycidyl ether group, the content thereof is preferably 90% by mass or more, and more preferably 95 to 100% by mass, based on the total amount of the epoxy compounds.
By making the content of the epoxy compound having a glycidyl ether group 90 mass % or more based on the total amount of the epoxy compounds, an encapsulating sheet having more excellent storage stability can be obtained.

At least one of the epoxy compounds is preferably an epoxy compound having an alicyclic skeleton.
By using an epoxy compound having an alicyclic skeleton, the curing reaction by cationic polymerization is easily promoted, and a sealant layer having a low relative dielectric constant and excellent colorless transparency is easily formed.

When the sealant layer contains an epoxy compound having an alicyclic skeleton, the content thereof is preferably 80% by mass or more, and more preferably 90 to 100% by mass, based on the total amount of the epoxy compounds.
By making the content of the epoxy compound having an alicyclic skeleton 80% by mass or more based on the total amount of the epoxy compounds, the curing reaction by cationic polymerization is facilitated, and further, it becomes easy to form a sealant layer having a low relative dielectric constant and excellent colorless transparency.

[Requirement (II)]
The storage modulus of the sealant layer at 23° C. is 1.3×10 ⁷ Pa or less.
When the storage modulus of the sealant layer at 23° C. is 1.3×10 ⁷ Pa or less, the sealant layer has excellent application property at room temperature.
The storage modulus of the sealant layer at 23° C. is preferably 1.1×10 ⁷ Pa or less, and more preferably 1.0×10 ⁷ Pa or less.
As long as a certain shape can be maintained, there is no particular lower limit for the storage modulus of the sealant layer at 23° C., but the storage modulus of the sealant layer at 23° C. is usually equal to or greater than 5.0×10 ⁴ Pa. From the viewpoint of preventing the sealant layer from adhering to unintended objects at its ends, the storage modulus of the sealant layer at 23° C. is preferably equal to or greater than 3.0×10 ⁵ Pa, and more preferably equal to or greater than 9.5×10 ⁵ Pa.
The storage modulus at 23° C. of the sealant layer can be measured according to the method described in the examples.

As the amount of the liquid component in the sealant layer increases, the storage modulus of the sealant layer at 23° C. tends to decrease.
Therefore, the sealant layer satisfying the requirement (II) can be efficiently formed by adjusting the state (solid, liquid) of the epoxy compound used and the content thereof.

[Requirement (III)]
When the sealant layer is heated from 35°C to 110°C at a rate of 25°C/min and then maintained at 110°C, the complex viscosity of the sealant layer 250 seconds after the start of heating (hereinafter, the complex viscosity under these measurement conditions may be referred to as "complex viscosity (Y)") is 1 x ¹⁰⁴ Pa·s or more.
When the complex viscosity (Y) is 1×10 ⁴ Pa·s or more, the curing reaction starts at a relatively early stage in the thermal curing process. Therefore, the sealant layer of the encapsulating sheet of the present invention is cured without undergoing a state in which the fluidity is increased by a temperature rise, and is therefore less likely to deform in the thermal curing process.
The complex viscosity (Y) is preferably from 1×10 ⁴ to 1×10 ⁶ Pa·s, and more preferably from 1×10 ⁵ to 1×10 ⁶ Pa·s.
The complex viscosity (Y) can be measured according to the method described in the Examples.

The value of complex viscosity (Y) is greater as the epoxy compound reacts at a lower temperature.
Therefore, a sealant layer satisfying the requirement (III) can be efficiently formed by adjusting the type and amount of a curing agent according to the reactivity of the epoxy compound used.
For example, as described below, the value of the complex viscosity (Y) can be increased by using a low-temperature reactive thermal cationic polymerization initiator as a curing agent.

[Requirement (IV)]
The sealant layer preferably satisfies the following requirement (IV).
Requirement (IV): Prepare sealant layers of the same quality [sealant layer (A) and sealant layer (B)], and use sealant layer (A) as a test piece to perform differential scanning calorimetry at a temperature rise rate of 10°C/min from 0°C to 200°C to determine the area of the exothermic peak [area (α)]. Next, sealant layer (B) is stored for 7 days in an environment of 23°C and relative humidity of 50%, and then used as a measurement sample to perform differential scanning calorimetry at a temperature rise rate of 10°C/min from 0°C to 200°C to determine the area of the exothermic peak [area (β)]. Based on the obtained area value, X calculated from the following formula (1) is 95% or more.

Here, "sealant layers of the same quality" refers to a plurality of sealant layers having substantially the same composition and physical properties. For example, two sealant layers obtained by cutting one sealant layer into two are equivalent to sealant layers of the same quality [sealant layer (A) and sealant layer (B)]. In addition, two sealant layers taken from different sealant layers, rather than two sealant layers taken from one sealant layer, but even if they are taken from sealant layers sold as products with the same manufacturing number, are also equivalent to sealant layers of the same quality [sealant layer (A) and sealant layer (B)].
The "area of the exothermic peak" means the area of the region surrounded by the baseline and the DSC curve, which is determined from the portion of the DSC curve other than the exothermic peak.

The sealant layer (A) and the sealant layer (B) are preferably in a state similar to that of the sealant layer immediately after the production of the encapsulating sheet.
Therefore, after the production of the encapsulating sheet, the sealant layer (A) and the sealant layer (B) are preferably stored under conditions of −30 to +10° C., and more preferably stored under conditions of −15 to +5° C., until the above-mentioned measurement is performed.

As described above, the sealant layer of the encapsulating sheet of the present invention satisfies the requirement (III).
However, a sealant layer satisfying the requirement (III) may have poor storage stability because the curing reaction may proceed at a relatively low temperature.

In this regard, a sealant layer that satisfies requirement (IV) shows little curing reaction even when stored for 7 days in an environment of 23°C and 50% relative humidity, and has excellent storage stability.

A sealant layer that satisfies requirement (IV) can be efficiently formed by using an epoxy compound having a glycidyl ether group as the epoxy compound and adjusting the amount of the epoxy compound according to the reactivity of the curing agent.

[Hardening agent]
The sealant layer may contain a curing agent. When the sealant layer contains a curing agent, the curing property of the sealant layer is further enhanced.
The curing agent is not particularly limited as long as it initiates a curing reaction, but it is preferable to use a curing agent that initiates a curing reaction by heating.
The curing agent may be a thermal cationic polymerization initiator or other curing agents.
Examples of curing agents other than the thermal cationic polymerization initiator include tertiary amines such as benzylmethylamine and 2,4,6-trisdimethylaminomethylphenol; imidazole compounds such as 2-methylimidazole, 3-ethyl-4-methylimidazole, and 2-heptadecylimidazole; Lewis acids such as boron trifluoride-monoethylamine complex and boron trifluoride-piperazine complex; and the like.

The curing agent may be used alone or in combination of two or more kinds.
The content of the curing agent is not particularly limited, but is preferably 0.1 to 15 parts by mass, more preferably 1 to 10 parts by mass, and even more preferably 1 to 5 parts by mass, based on 100 parts by mass of the epoxy compound.

The sealant layer preferably contains a thermal cationic polymerization initiator as at least one type of curing agent.
By using the thermal cationic polymerization initiator, it becomes easier to control the curing property of the sealant layer at around room temperature, and the sealant layer satisfying the requirement (III) can be formed more efficiently.

A thermal cationic polymerization initiator is a compound that can generate cationic species that initiate polymerization upon heating.
Examples of the thermal cationic polymerization initiator include sulfonium salts, quaternary ammonium salts, phosphonium salts, diazonium salts, and iodonium salts.

Examples of sulfonium salts include triphenylsulfonium tetrafluoroborate, triphenylsulfonium hexafluoroantimonate, triphenylsulfonium hexafluoroarsinate, tris(4-methoxyphenyl)sulfonium hexafluoroarsinate, diphenyl(4-phenylthiophenyl)sulfonium hexafluoroarsinate, (4-acetoxyphenyl)methyl(2-methylbenzyl)sulfonium tetrakis(pentafluorophenyl)borate, (4-hydroxyphenyl)methyl(4-methylbenzyl)sulfonium tetrakis(pentafluorophenyl)borate, (4-acetoxyphenyl)benzyl(methyl)sulfonium tetrakis(pentafluorophenyl)borate, and benzyl(4-hydroxyphenyl)(methyl)sulfonium tetrakis(pentafluorophenyl)borate.

Commercially available sulfonium salts can also be used. Commercially available products include ADEKAOPTON SP-150, ADEKAOPTON SP-170, ADEKAOPTON CP-66, ADEKAOPTON CP-77 (all manufactured by Asahi Denka Co., Ltd.), SAN-AID SI-60L, SAN-AID SI-80L, SAN-AID SI-100L, SAN-AID SI-B2A, SAN-AID SI-B3, SAN-AID SI-B3A, SAN-AID SI-B7 (all manufactured by Sanshin Chemical Co., Ltd.), CYRACURE UVI-6974, CYRACURE Examples include UVI-6990 (all manufactured by Union Carbide), UVI-508, UVI-509 (all manufactured by General Electric), FC-508, FC-509 (all manufactured by Minnesota Mining and Manufacturing), CD-1010, CD-1011 (all manufactured by Thirstomer), and CI series products (manufactured by Nippon Soda Co., Ltd.).

Examples of quaternary ammonium salts include tetrabutylammonium tetrafluoroborate, tetrabutylammonium hexafluorophosphate, tetrabutylammonium hydrogen sulfate, tetraethylammonium tetrafluoroborate, tetraethylammonium p-toluenesulfonate, N,N-dimethyl-N-benzylanilinium hexafluoroantimonate, N,N-dimethyl-N-benzylanilinium tetrafluoroborate, N,N-dimethyl-N-benzylpyridinium hexafluoroantimonate, N,N-diethyl-N-benzyltrifluoromethanesulfonate, N,N-dimethyl-N-(4-methoxybenzyl)pyridinium hexafluoroantimonate, and N,N-diethyl-N-(4-methoxybenzyl)toluidinium hexafluoroantimonate.

Examples of phosphonium salts include ethyltriphenylphosphonium hexafluoroantimonate and tetrabutylphosphonium hexafluoroantimonate.

Examples of diazonium salts include AMERICURE (manufactured by American Can Co., Ltd.) and ULTRASET (manufactured by Asahi Denka Co., Ltd.).

Examples of iodonium salts include diphenyliodonium hexafluoroarsinate, bis(4-chlorophenyl)iodonium hexafluoroarsinate, bis(4-bromophenyl)iodonium hexafluoroarsinate, and phenyl(4-methoxyphenyl)iodonium hexafluoroarsinate. Commercially available products that can be used include UV-9310C (manufactured by Toshiba Silicone Co., Ltd.), Photoinitiator 2074 (manufactured by Rhone-Poulenc), UVE series products (manufactured by General Electric Co.), and FC series products (manufactured by Minnesota Mining and Manufacturing Co., Ltd.).

Thermal cationic polymerization initiators can be used alone or in combination of two or more.

The sealant layer preferably contains a thermal cationic polymerization initiator (hereinafter sometimes referred to as "thermal cationic polymerization initiator (P)") that produces an exothermic peak top temperature of 120°C or less when differential scanning calorimetry is performed under the following conditions.

(Differential scanning calorimetry conditions)
A mixture of 0.1 part by mass of a thermal cationic polymerization initiator, 100 parts by mass of bisphenol A diglycidyl ether, and 0.1 part by mass of γ-butyrolactone is used as a measurement sample, and differential scanning calorimetry is performed at a temperature increase rate of 10° C./min from 30° C. to 300° C.

The thermal cationic polymerization initiator (P) is a low-temperature reactive thermal cationic polymerization initiator. Therefore, a sealant layer containing the thermal cationic polymerization initiator (P) is more likely to satisfy requirement (III). Examples of the thermal cationic polymerization initiator (P) include (4-acetoxyphenyl)methyl(2-methylbenzyl)sulfonium tetrakis(pentafluorophenyl)borate, (4-hydroxyphenyl)methyl(4-methylbenzyl)sulfonium tetrakis(pentafluorophenyl)borate, and (4-acetoxyphenyl)benzyl(methyl)sulfonium tetrakis(pentafluorophenyl)borate. Examples of commercially available thermal cationic polymerization initiators (P) include San-Aid SI-B2A, San-Aid SI-B3A, and San-Aid SI-B7 (all manufactured by Sanshin Chemical Industry Co., Ltd.).

When the sealant layer contains a thermal cationic polymerization initiator (P), it is preferable that the sealant layer further contains a thermal cationic polymerization initiator (hereinafter sometimes referred to as "thermal cationic polymerization initiator (Q)") that has an exothermic peak top temperature of more than 120°C when differential scanning calorimetry is performed under the above conditions.

The thermal cationic polymerization initiator (Q) is a thermal cationic polymerization initiator that is highly reactive at high temperatures. Therefore, a sealant layer containing the thermal cationic polymerization initiator (Q) is likely to satisfy requirement (IV). The peak top temperature of the above-mentioned exothermic peak of the thermal cationic polymerization initiator (Q) is preferably 170°C or less, from the viewpoint of preventing the temperature during curing of the sealant layer from becoming too high. An example of the thermal cationic polymerization initiator (Q) is benzyl(4-hydroxyphenyl)(methyl)sulfonium tetrakis(pentafluorophenyl)borate. An example of a commercially available product of the thermal cationic polymerization initiator (Q) is San-Aid SI-B3 (manufactured by Sanshin Chemical Industry Co., Ltd.).

When the sealant layer contains the thermal cationic polymerization initiator (P) and the thermal cationic polymerization initiator (Q), the weight ratio thereof [thermal cationic polymerization initiator (P):thermal cationic polymerization initiator (Q)] is preferably 20:80 to 80:20, more preferably 35:65 to 65:35.
When the weight ratio of the thermal cationic polymerization initiator (P) to the thermal cationic polymerization initiator (Q) is within the above range, an encapsulating sheet having a sealant layer in which a curing reaction starts at a relatively early stage in the thermal curing process and excellent storage stability can be efficiently obtained.

In the sealing sheet of the present invention, all of the curing agents contained in the sealant layer are preferably thermal cationic polymerization initiators.
If a curing agent other than the thermal cationic polymerization initiator is used, the sealant layer may be colored or the transparency of the sealant layer may be reduced.
On the other hand, when a thermal cationic polymerization initiator is used, such problems are unlikely to occur. Therefore, when all of the curing agents contained in the sealant layer are thermal cationic polymerization initiators, a sealant layer having excellent colorless transparency can be efficiently formed.

[Binder resin]
The sealant layer may contain a binder resin. A sealant layer containing a binder resin has excellent shape retention and handleability.
The weight average molecular weight (Mw) of the binder resin is not particularly limited, but is preferably 10,000 or more, more preferably 10,000 to 1,000,000, and even more preferably 10,000 to 800,000, in order to provide excellent compatibility with the epoxy compound and excellent shape retention.
The weight average molecular weight (Mw) of the binder resin can be determined as a value converted into standard polystyrene by gel permeation chromatography (GPC) using tetrahydrofuran (THF) as a solvent.

When the sealant layer contains a binder resin, the content of the binder resin (when two or more kinds of binder resins are contained, the total amount of these) is preferably 20 to 43 mass %, more preferably 23 to 40 mass %, based on the entire sealant layer.
When the content of the binder resin is within the above range, a sealant layer having excellent shape retention and sufficient adhesive strength can be easily obtained.

The glass transition temperature (Tg) of the binder resin is not particularly limited, but is preferably 60° C. or higher, more preferably 90° C. or higher, and even more preferably 110° C. or higher.
When the glass transition temperature (Tg) of the binder resin is 60° C. or higher, it is easy to increase the storage modulus of the cured product of the adhesive layer. Also, when the glass transition temperature (Tg) of the binder resin is 90° C. or higher, it is possible to efficiently form a sealant layer having excellent shape retention.

Examples of the binder resin include a phenoxy resin, a modified olefin resin, and an acetal resin.
Among these, the phenoxy resin is preferred as the binder resin because it is easy to obtain a sealant layer having excellent shape retention.

Phenoxy resins generally fall under the category of high molecular weight epoxy resins, and refer to those having a degree of polymerization of about 100 or more.
The epoxy equivalent of the phenoxy resin is preferably at least 5,000, and more preferably at least 7,000. The epoxy equivalent value can be measured in accordance with JIS K7236.

Examples of the phenoxy resin include bisphenol A type, bisphenol F type, bisphenol S type phenoxy resin, copolymer type phenoxy resin of bisphenol A type and bisphenol F type, distilled products thereof, naphthalene type phenoxy resin, novolac type phenoxy resin, biphenyl type phenoxy resin, cyclopentadiene type phenoxy resin, and the like.
These phenoxy resins can be used alone or in combination of two or more.

The phenoxy resin can be obtained by reacting a difunctional phenol with an epihalohydrin to a high molecular weight, or by subjecting a difunctional epoxy resin to a polyaddition reaction with a difunctional phenol.
For example, it can be obtained by reacting a bifunctional phenol with an epihalohydrin in the presence of an alkali metal hydroxide in an inert solvent at a temperature of 40 to 120° C. Alternatively, it can be obtained by subjecting a bifunctional epoxy resin and a bifunctional phenol to a polyaddition reaction in the presence of a catalyst such as an alkali metal compound, an organophosphorus compound, a cyclic amine compound, or the like in an organic solvent having a boiling point of 120° C. or higher, such as an amide solvent, an ether solvent, a ketone solvent, a lactone solvent, or an alcohol solvent, by heating to 50 to 200° C. at a reaction solids concentration of 50% by weight or less.

The bifunctional phenols are not particularly limited as long as they are compounds having two phenolic hydroxyl groups. Examples include monocyclic bifunctional phenols such as hydroquinone, 2-bromohydroquinone, resorcinol, and catechol; bisphenols such as bisphenol A, bisphenol F, bisphenol AD, and bisphenol S; dihydroxybiphenyls such as 4,4'-dihydroxybiphenyl; and dihydroxyphenyl ethers such as bis(4-hydroxyphenyl)ether; and those in which a linear alkyl group, a branched alkyl group, an aryl group, a methylol group, an allyl group, a cyclic aliphatic group, a halogen (such as tetrabromobisphenol A), or a nitro group has been introduced into the aromatic ring of the phenol skeleton; and polycyclic bifunctional phenols in which a linear alkyl group, a branched alkyl group, an allyl group, an allyl group with a substituent, a cyclic aliphatic group, or an alkoxycarbonyl group has been introduced into the carbon atom in the center of the bisphenol skeleton; and the like.

Epihalohydrins include epichlorohydrin, epibromohydrin, epiiodohydrin, etc.

In addition, in the present invention, commercially available products can be used as the phenoxy resin. For example, Mitsubishi Chemical Corporation's product names: YX7200, YL7553, YL6794, YL7213, YL7290, YL7482, Mitsubishi Chemical Corporation's product name: YX8100 (phenoxy resin containing bisphenol S skeleton), Tohto Kasei Corporation's product names: FX280, FX293, FX293S (phenoxy resin containing fluorene skeleton), Mitsubishi Chemical Corporation's product names: jER1256, jER4250, Nippon Steel Chemical & Material Corporation's product names: YP-50, YP-50S (both phenoxy resin containing bisphenol A skeleton), Mitsubishi Chemical Corporation's product name: YX6954 (phenoxy resin containing bisphenol acetophenone skeleton), Nippon Steel Chemical & Material Corporation's product name: ZX-1356-2, etc. can be mentioned.

〔Silane coupling agent〕
The sealant layer may contain a silane coupling agent. By containing a silane coupling agent, a sealant layer having superior wet heat durability can be more easily obtained.

As the silane coupling agent, known silane coupling agents can be used, among which, an organosilicon compound having at least one alkoxysilyl group in the molecule is preferred.
Examples of the silane coupling agent include silane coupling agents having a (meth)acryloyl group, such as 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldiethoxysilane, 3-methacryloxypropyltriethoxysilane, and 3-acryloxypropyltrimethoxysilane; silane coupling agents having a vinyl group, such as vinyltrimethoxysilane, vinyltriethoxysilane, dimethoxymethylvinylsilane, diethoxymethylvinylsilane, trichlorovinylsilane, and vinyltris(2-methoxyethoxy)silane;
Silane coupling agents having an epoxy group, such as 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-glycidoxypropyltriethoxysilane, and 8-glycidoxyoctyltrimethoxysilane;
Silane coupling agents having a styryl group, such as p-styryltrimethoxysilane and p-styryltriethoxysilane;

Silane coupling agents having an amino group, such as N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-triethoxysilyl-N-(1,3-dimethylbutylidene)propylamine, N-phenyl-3-aminopropyltrimethoxysilane, and N-(vinylbenzyl)-2-aminoethyl-3-aminopropyltrimethoxysilane hydrochloride;
Silane coupling agents having a ureido group, such as 3-ureidopropyltrimethoxysilane and 3-ureidopropyltriethoxysilane;
Silane coupling agents having a halogen atom, such as 3-chloropropyltrimethoxysilane and 3-chloropropyltriethoxysilane;
silane coupling agents having a mercapto group, such as 3-mercaptopropylmethyldimethoxysilane and 3-mercaptopropyltrimethoxysilane;
Silane coupling agents having a sulfide group, such as bis(trimethoxysilylpropyl)tetrasulfide and bis(triethoxysilylpropyl)tetrasulfide;
Silane coupling agents having an isocyanate group, such as 3-isocyanatepropyltrimethoxysilane and 3-isocyanatepropyltriethoxysilane;
silane coupling agents having an allyl group, such as allyltrichlorosilane, allyltriethoxysilane, and allyltrimethoxysilane;
Silane coupling agents having a hydroxyl group, such as 3-hydroxypropyltrimethoxysilane and 3-hydroxypropyltriethoxysilane; and the like.
These silane coupling agents can be used alone or in combination of two or more.

When the sealant layer contains a silane coupling agent, the content of the silane coupling agent in the entire sealant layer is preferably 0.01 to 5 mass %, more preferably 0.05 to 1 mass %.

[Other ingredients]
The sealant layer may contain other components as long as the effects of the present invention are not impaired.
Examples of other components include additives such as ultraviolet absorbers, antistatic agents, light stabilizers, antioxidants, resin stabilizers, fillers, pigments, extenders, and softeners.
These may be used alone or in combination of two or more.
When the sealant layer contains these additives, the content thereof can be appropriately determined depending on the purpose.

[Sealant Layer]
The thickness of the sealant layer is usually 1 to 50 μm, preferably 1 to 25 μm, and more preferably 5 to 25 μm. A sealant layer having a thickness within the above range is suitably used as a material for forming a sealant.
The thickness of the sealant layer can be measured using a known thickness meter in accordance with JIS K 7130 (1999).

The method for forming the sealant layer is not particularly limited. For example, the sealant layer can be formed by a casting method.
When the sealant layer is produced by a casting method, a sealant composition containing components constituting the sealant layer is prepared, and the obtained sealant composition is applied to a release-treated release layer surface of a substrate or a release film using a known method, and the obtained coating film is dried to form the sealant layer.

The sealant composition may contain a solvent.
Examples of the solvent include aromatic hydrocarbon solvents such as benzene and toluene; ester solvents such as ethyl acetate and butyl acetate; ketone solvents such as acetone, methyl ethyl ketone and methyl isobutyl ketone; aliphatic hydrocarbon solvents such as n-pentane, n-hexane and n-heptane; and alicyclic hydrocarbon solvents such as cyclopentane, cyclohexane and methylcyclohexane.
These solvents may be used alone or in combination of two or more.
The content of the solvent can be appropriately determined taking into consideration the coatability and the like.

Methods for applying the sealant composition include, for example, spin coating, spray coating, bar coating, knife coating, roll coating, blade coating, die coating, and gravure coating.

Methods for drying the coating film include conventionally known drying methods such as hot air drying, heated roll drying, and infrared irradiation.
The coating film is dried, for example, at 80 to 150° C. for 30 seconds to 5 minutes.

The sealant layer is thermosetting. That is, by heating the sealant layer, at least the epoxy groups of the epoxy compound react, and the sealant layer hardens.

The conditions for thermally curing the sealant layer are not particularly limited.
The heating temperature is usually from 80 to 200°C, preferably from 90 to 150°C.
The heating time is usually from 30 minutes to 12 hours, preferably from 1 to 6 hours.

The storage modulus at 90° C. of the cured sealant layer obtained by curing the sealant layer is preferably 1×10 ⁸ Pa or more, and more preferably 1×10 ⁹ to 1×10 ¹¹ Pa. A cured sealant layer having a storage modulus at 90° C. of 1×10 ⁸ Pa or more is excellent in sealing properties and is therefore more suitable as a sealant. In addition, in a process carried out for producing a device encapsulated body after the formation of the cured sealant layer, the cured sealant layer is more likely to be prevented from being broken or peeled off.

[Sealing sheet]
The encapsulating sheet of the present invention has the above-mentioned sealant layer.
The encapsulating sheet of the present invention may have a substrate, a release film, a functional film, etc. in addition to the sealant layer.

As the substrate, a resin film can usually be used.
Examples of the resin component of the resin film include polyimide, polyamide, polyamideimide, polyphenylene ether, polyether ketone, polyether ether ketone, polyolefin, polyester, polycarbonate, polysulfone, polyether sulfone, polyphenylene sulfide, polyarylate, acrylic resin, cycloolefin polymer, aromatic polymer, and polyurethane polymer.
The thickness of the substrate is not particularly limited, but is preferably 10 to 500 μm, more preferably 10 to 300 μm, and further preferably 15 to 200 μm.

The release film functions as a support in the manufacturing process of the encapsulating sheet, and also functions as a protective sheet for the sealant layer until the encapsulating sheet is used.
When the encapsulating sheet of the present invention is used, the release film is usually peeled off and removed.

As the release film, a conventionally known film can be used, for example, a film having a release layer that has been subjected to a release treatment with a release agent on a substrate for the release film.
Examples of substrates for release films include paper substrates such as glassine paper, coated paper, and fine paper; laminated paper obtained by laminating a thermoplastic resin such as polyethylene to these paper substrates; and plastic films such as polyethylene terephthalate resin, polybutylene terephthalate resin, polyethylene naphthalate resin, polypropylene resin, and polyethylene resin.

Examples of the release agent include rubber-based elastomers such as silicone-based resins, olefin-based resins, isoprene-based resins, and butadiene-based resins, long-chain alkyl-based resins, alkyd-based resins, and fluorine-based resins.
The thickness of the release film is not particularly limited, but is usually about 20 to 250 μm.

When the sealing sheet of the present invention has a release film, it may have two release films in total, one on each side of the sealant layer, or it may have a release film only on one side of the sealant layer.

Examples of the functional film include a conductive film, a gas barrier film, an anti-reflection film, a retardation film, a viewing angle improving film, a brightness improving film, etc. Among these, examples of the gas barrier film include a film having a metal or inorganic compound film, etc.
The thickness of the functional film is not particularly limited, but is usually 5 to 200 μm, preferably 10 to 100 μm.

The sealant layer of the encapsulating sheet of the present invention is suitably used as a material for forming an encapsulant for electronic devices, and among the electronic devices, light-related devices such as light-emitting devices, light-receiving devices, and display devices are preferred.
Examples of light-related devices include organic EL elements such as organic EL displays and organic EL lighting; liquid crystal elements such as liquid crystal displays; electronic paper elements; solar cell elements; and light-emitting diodes.

The method for sealing an electronic device using the sealing sheet of the present invention is not particularly limited. For example, the electronic device can be sealed by attaching the sealant layer of the sealing sheet of the present invention to the target electronic device and then curing the sealant layer by the above-mentioned method.

The present invention will be described in more detail below with reference to examples. However, the present invention is not limited to the following examples.

[Compounds used in the Examples and Comparative Examples]
Epoxy compound (A1): hydrogenated bisphenol A type epoxy resin (manufactured by Mitsubishi Chemical Corporation, product name: YX8000, epoxy equivalent: 205 g/eq)
Epoxy compound (A2): 3',4'-epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate (manufactured by Daicel Corporation, product name: Celloxide 2021P, epoxy equivalent: 128 to 145 g/eq)
Phenoxy resin (B1): (manufactured by Mitsubishi Chemical Corporation, product name: YX7200B35, glass transition temperature (Tg): 150° C.)
Thermal cationic polymerization initiator (C1): (4-hydroxyphenyl)methyl(4-methylbenzyl)sulfonium tetrakis(pentafluorophenyl)borate (manufactured by Sanshin Chemical Industry Co., Ltd., product name: San-Aid SI-B7)
Thermal cationic polymerization initiator (C2): benzyl(4-hydroxyphenyl)(methyl)sulfonium tetrakis(pentafluorophenyl)borate (manufactured by Sanshin Chemical Industry Co., Ltd., product name: San-Aid SI-B3)
Silane coupling agent (D1): 8-glycidoxyoctyltrimethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd., product name: KBM4803)

[Evaluation of the reactivity of thermal cationic polymerization initiators]
When a mixture of 0.1 parts by mass of a thermal cationic polymerization initiator (C1), 100 parts by mass of bisphenol A diglycidyl ether (manufactured by Mitsubishi Chemical Corporation, jER828), and 0.1 parts by mass of γ-butyrolactone was used as a measurement sample and differential scanning calorimetry was performed at a temperature increase rate of 10° C./min from 30 to 300° C., the peak top temperature of the exothermic peak was 105° C.
On the other hand, when the thermal cationic polymerization initiator (C2) was used instead of the thermal cationic polymerization initiator (C1), the peak top temperature of the exothermic peak was 140°C.

Example 1
A coating liquid was prepared by dissolving 170 parts by mass of the epoxy compound (A1), 100 parts by mass of the phenoxy resin (B1), 1.5 parts by mass of the thermal cationic polymerization initiator (C1), 1.5 parts by mass of the thermal cationic polymerization initiator (C2), and 0.2 parts by mass of the silane coupling agent (D1) in methyl ethyl ketone.
This coating liquid was applied onto the release-treated surface of a release film (first release film, manufactured by Lintec Corporation, product name: SP-PET752150), and the resulting coating film was dried at 100° C. for 2 minutes to form a sealant layer having a thickness of 15 μm. The release-treated surface of another release film (second release film, manufactured by Lintec Corporation, product name: SP-PET381130) was attached onto this sealant layer to obtain an encapsulating sheet.

[Examples 2 to 3, Comparative Examples 1 and 2]
An encapsulating sheet was obtained in the same manner as in Example 1, except that the types and amounts of the components constituting the encapsulant layer were changed to those shown in Table 1.

The following tests were conducted on the encapsulating sheets obtained in Examples 1 to 3 and Comparative Examples 1 and 2. The results are shown in Table 1.

[Measurement of storage modulus of sealant layer at 23° C.]
The sealant layers of the sealing sheets obtained in the Examples and Comparative Examples were laminated at 23° C. using a laminator to obtain test pieces with a thickness of about 1 mm.
The storage modulus of the obtained test piece was measured in the range of −20 to 150° C. using a dynamic viscoelasticity measuring device (manufactured by Anton Paar, product name: Physica MCR301) under conditions of a frequency of 1 Hz, a strain of 1%, and a heating rate of 3° C./min. The measurement results at 23° C. are shown in Table 1.

[Evaluation of suitability of sealant layer for application to object to be sealed]
The sealing sheets obtained in the examples and comparative examples were cut to obtain test pieces with a width of 50 mm and a length of 150 mm. The sealant layer exposed by peeling off the second release film of the obtained test piece was placed on an alkali-free glass plate under conditions of a temperature of 23° C. and a relative humidity of 50%, and a pressure of 0.5 MPa was applied using a pressure roller. The state of the sealant layer lifting from the alkali-free glass plate was observed, and those without lifting were evaluated as A, and those with lifting were evaluated as B.

[Complex Viscosity of Sealant Layer during Temperature Increase Process]
The sealant layers of the encapsulating sheets obtained in the Examples and Comparative Examples were laminated under conditions of 23° C. and a relative humidity of 50% to obtain test pieces having a thickness of about 1 mm.
The complex viscosity of the obtained test piece was measured in the range of 35 to 110° C. using a dynamic viscoelasticity measuring device (manufactured by TA Instruments, product name: ARES) under the conditions of a frequency of 1 Hz, a strain of 0.1%, and a heating rate of 25° C./min (maintaining 110° C. after reaching 110° C.).
The complex viscosity of the test piece 250 seconds after the start of the temperature rise is shown in Table 1.

[Evaluation of shape retention of sealant layer during heat curing process]
The second release film of the sealing sheet obtained in each of the Examples and Comparative Examples was peeled off to expose the sealant layer, which was then attached to an alkali-free glass plate, and then cut to a size of 50 mm wide x 50 mm long to obtain a test piece.
The first release film was peeled off from the test piece to expose the sealant layer, which was then placed on a non-alkali glass plate under conditions of a temperature of 23°C and a relative humidity of 50%, and a pressure of 0.5 MPa was applied using a pressure roll to obtain a laminate.
Then, the laminate was subjected to a heat press under conditions of 0.5 MPa and 110° C. The case where no deformation was observed in the sealant layer of the laminate after the heat press was evaluated as A, and the case where the area of the sealant layer was enlarged and deformation was observed was evaluated as B.

[Evaluation of storage stability of sealant layer]
Two encapsulating sheets were prepared for each of the examples and comparative examples.
The sealant layer of one of the encapsulating sheets was used as a test piece A, and differential scanning calorimetry (apparatus used: DSC Q2000, manufactured by TA Instruments) was performed at a temperature increase rate of 10° C./min from 0° C. to 200° C., and the peak area [area (α)] of the exothermic peak was determined.
The other encapsulating sheet was stored under an environment of 23° C. and a relative humidity of 50% for 7 days, and the encapsulant layer of the encapsulating sheet was similarly used as a test piece B to perform differential scanning calorimetry, and the peak area [area (β)] of the exothermic peak was obtained.
The ratio of the area (β) to the area (α) was 95% or more and was evaluated as A, and the ratio of the area (β) to the area (α) was less than 95%, respectively.

The following can be seen from Table 1.
The sealant layers of the encapsulating sheets obtained in Examples 1 to 3 have excellent adhesion at 23° C. and are not easily deformed during the thermal curing process.
On the other hand, the sealant layer of the encapsulating sheet obtained in Comparative Example 1 does not contain a thermal cationic polymerization initiator having low-temperature reactivity, and therefore does not satisfy the requirement (III) of the present invention. Therefore, the sealant layer is easily fluidized during the thermal curing process, and has poor shape retention.
In addition, the sealant layer of the encapsulating sheet obtained in Comparative Example 2 does not satisfy the requirement (II) of the present invention. Therefore, the application property at 23° C. is poor.
Furthermore, the sealant layer of the encapsulating sheet obtained in Comparative Example 2 contains a thermal cationic polymerization initiator having low temperature reactivity, but does not contain an epoxy compound having a glycidyl ether group, so that the encapsulating sheet has poor storage stability.

Claims (9)

An encapsulating sheet having a thermosetting encapsulant layer,
The present invention is characterized by satisfying the following requirements (I), (II), and (III) :
The sealant layer contains an epoxy compound, a binder resin, and a curing agent,
At least one of the epoxy compounds is a liquid epoxy compound at 25°C;
At least one of the curing agents is a thermal cationic polymerization initiator having an exothermic peak top temperature of 120° C. or lower when differential scanning calorimetry is performed under the following conditions:
(Differential Scanning Calorimetry)
A mixture of 0.1 part by mass of a thermal cationic polymerization initiator, 100 parts by mass of bisphenol A diglycidyl ether, and 0.1 part by mass of γ-butyrolactone is used as a measurement sample, and differential scanning calorimetry is performed at a temperature increase rate of 10° C./min from 30° C. to 300° C.
Requirement (I): The sealant layer contains one or more epoxy compounds.
Requirement (II): The storage modulus of the sealant layer at 23° C. is 1.3×10 ⁷ Pa or less.
Requirement (III): When the sealant layer is heated from 35° C. to 110° C. at a rate of 25° C./min and then maintained at 110° C., the complex viscosity of the sealant layer 250 seconds after the start of heating is 1×10 ⁴ Pa·s or more. The encapsulating sheet according to claim 1 , wherein the sealant layer satisfies the following requirement (IV):
Requirement (IV): Prepare sealant layers of the same quality [sealant layer (A) and sealant layer (B)], and use sealant layer (A) as a test piece to perform differential scanning calorimetry at a temperature rise rate of 10°C/min from 0°C to 200°C to determine the area of the exothermic peak [area (α)]. Next, sealant layer (B) is stored for 7 days in an environment of 23°C and relative humidity of 50%, and then used as a measurement sample to perform differential scanning calorimetry at a temperature rise rate of 10°C/min from 0°C to 200°C to determine the area of the exothermic peak [area (β)]. Based on the obtained area value, X calculated from the following formula (1) is 95% or more.

The encapsulating sheet according to claim 1 or 2, wherein at least one of the epoxy compounds is an epoxy compound having a glycidyl ether group. The encapsulating sheet according to any one of claims 1 to 3, wherein at least one of the epoxy compounds is an epoxy compound having an alicyclic skeleton. The encapsulating sheet according to any one of claims 1 to 4, further comprising, as at least one of the curing agents, a thermal cationic polymerization initiator having an exothermic peak top temperature of more than 120°C when differential scanning calorimetry is performed under the following conditions.
(Differential Scanning Calorimetry)
A mixture of 0.1 part by mass of a thermal cationic polymerization initiator, 100 parts by mass of bisphenol A diglycidyl ether, and 0.1 part by mass of γ-butyrolactone is used as a measurement sample, and differential scanning calorimetry is performed at a temperature increase rate of 10° C./min from 30° C. to 300° C. The encapsulating sheet according to any one of claims 1 to 5, wherein all of the curing agents are thermal cationic polymerization initiators. The encapsulating sheet according to any one of claims 1 to 6, wherein at least one of the binder resins is a resin having a glass transition temperature (Tg) of 60°C or higher. The encapsulating sheet according to any one of claims 1 to 7, wherein the binder resin is one or more resins selected from a phenoxy-based resin, a modified olefin-based resin, and an acetal-based resin. The encapsulating sheet according to any one of claims 1 to 8 , which is used for encapsulating an optical device.