LED sealant

Abstract

The purpose of the present invention is to provide an LED sealant which can be applied with high precision and a cured product of which can conform to expansion and contraction of an LED chip and bending of a substrate. The present invention is a LED sealant comprising a curable resin and a polymerization initiator, wherein viscosity at 25°C is not more than 100 mPa·s, and tensile breaking elongation of a cured product at 25°C is not less than 50%.

Description

LED encapsulant

[0001] The present invention relates to an encapsulant for an LED.

[0002] Light-emitting diodes (LEDs) are widely used in display devices and the like due to their low power consumption and long life. In recent years, display devices that enable high-quality image display by mounting LED chips using tiny LEDs called micro-LEDs have attracted attention (see, for example, Patent Document 1). LEDs deteriorate when exposed to moisture and gases in the atmosphere, resulting in a decrease in light extraction efficiency. Therefore, LEDs are typically encapsulated using an encapsulant (LED encapsulant). However, when using micro-LEDs, the LED chips are low in height and the spacing between them is narrow, so it is necessary to apply the LED encapsulant with high application accuracy using an inkjet method or the like. Furthermore, the LED encapsulant must be flexible enough that the cured product can adapt to the expansion and contraction of the LED chips and the bending of the substrate.

[0003] Japanese Patent Application Laid-Open No. 2019-212694

[0004] When a urethane acrylate or the like is used as a curable resin to improve the flexibility of the cured product of an LED encapsulant, there has been a problem in that it is difficult to apply with high application accuracy by an inkjet method, etc. The present invention aims to provide an LED encapsulant that can be applied with high application accuracy and whose cured product can follow the expansion and contraction of an LED chip, bending of a substrate, etc.

[0005] Disclosure 1 relates to an LED encapsulant containing a curable resin and a polymerization initiator, having a viscosity of 100 mPa·s or less at 25°C, and a tensile break elongation of the cured product at 25°C of 50% or more. Disclosure 2 relates to the LED encapsulant of Disclosure 1, wherein the curable resin contains a dithiol compound (A) having two thiol groups per molecule, a polythiol compound (B) having three or more thiol groups per molecule, and a polyene compound (C) having two or more aliphatic carbon-carbon double bonds per molecule. Disclosure 3 relates to an LED encapsulant containing a curable resin and a polymerization initiator, wherein the curable resin contains a dithiol compound (A) having two thiol groups per molecule, a polythiol compound (B) having three or more thiol groups per molecule, and a polyene compound (C) having two or more aliphatic carbon-carbon double bonds per molecule. Disclosure 4 relates to the LED encapsulant of Disclosure 2 or 3, wherein the polyene compound (C) is a (meth)allyl compound having two or three aliphatic carbon-carbon double bonds in one molecule. Disclosure 5 relates to the LED encapsulant of Disclosure 1, 2, 3, or 4, further containing a leveling agent. Disclosure 6 relates to the LED encapsulant of Disclosure 1, 2, 3, 4, or 5, which is used for application by an inkjet method. The present invention is described in detail below. The LED encapsulant of Disclosure 1 is also referred to as the "LED encapsulant of Invention 1," and the LED encapsulant of Disclosure 3 is also referred to as the "LED encapsulant of Invention 2." Furthermore, matters common to the LED encapsulant of Invention 1 and the LED encapsulant of Invention 2 are not particularly specified or are described as the "LED encapsulant of the present invention."

[0006] The present inventors have investigated how to make an LED encapsulant have a viscosity at 25°C of a specific value or less while producing a cured product with a tensile break elongation of a specific value or more, by using a combination of specific compounds as a curable resin, etc. As a result, they have found that an LED encapsulant can be obtained that can be applied with high application accuracy and that can produce a cured product that follows the expansion and contraction of an LED chip and the bending of a substrate, etc., and have completed the present invention.

[0007] The LED encapsulant of Invention 1 has an upper limit of viscosity at 25°C of 100 mPa·s. Since the viscosity at 25°C is 100 mPa·s or less, the LED encapsulant of Invention 1 exhibits excellent coating accuracy by an inkjet method or the like. The upper limit of the viscosity at 25°C is preferably 50 mPa·s, and more preferably 30 mPa·s. From the viewpoint of shape retention after coating, the lower limit of the viscosity at 25°C of the LED encapsulant of Invention 1 is preferably 10.0 mPa·s, and more preferably 15.0 mPa·s. Furthermore, the LED encapsulant of Invention 2 has an upper limit of viscosity at 25°C of 100 mPa·s. Since the viscosity at 25°C is 100 mPa·s or less, the LED encapsulant of Invention 2 exhibits excellent coating accuracy by an inkjet method or the like. The upper limit of the viscosity at 25° C. is more preferably 50 mPa·s, and even more preferably 30 mPa·s. From the viewpoint of shape retention after application, etc., the lower limit of the viscosity of the LED encapsulant of invention 2 at 25° C. is preferably 10.0 mPa·s, and more preferably 15.0 mPa·s. The viscosity can be measured, for example, using a VISCOMETER TV-22 (manufactured by Toki Sangyo Co., Ltd.) as an E-type viscometer with a No. 1 rotor at a rotation speed of 100 rpm.

[0008] The LED encapsulant of Invention 1 has a lower limit of the tensile break elongation at 25°C of the cured product of 50%. Since the tensile break elongation at 25°C of the cured product is 50% or more, the LED encapsulant of Invention 1 has excellent flexibility and can follow the expansion and contraction of the LED chip and the bending of the substrate. There is no particular preferred upper limit to the tensile break elongation at 25°C of the cured product of the LED encapsulant of Invention 1, but a substantial upper limit is 500%. The LED encapsulant of Invention 2 has a preferred lower limit of 50% of the tensile break elongation at 25°C of the cured product of 50% or more. Since the tensile break elongation at 25°C of the cured product of the LED encapsulant of Invention 2 has excellent flexibility and can follow the expansion and contraction of the LED chip and the bending of the substrate. There is no particular preferred upper limit to the tensile break elongation at 25°C of the cured product of the LED encapsulant of Invention 2, but a substantial upper limit is 500%. The tensile elongation at break of the cured product at 25°C can be measured for a cured product having a width of 5 mm, a length of 400 mm, and a thickness of 500 µm using a tensile tester (for example, "Autograph AG-Xplus" manufactured by Shimadzu Corporation) under conditions of a gripper distance of 25 mm and a pulling speed of 5 mm / s. In addition, when the LED encapsulant contains, for example, a dithiol compound (A), a polythiol compound (B), and a polyene compound (C) as well as a photoradical polymerization initiator, the cured product for which the tensile elongation at break is measured is measured using a tensile tester having a width of 5 mm, a length of 400 mm, and a thickness of 500 µm. In addition, in cases where the LED encapsulant contains, for example, a dithiol compound (A), a polythiol compound (B), and a polyene compound (C), as well as a photoradical polymerization initiator as described below, the cured product for which the tensile elongation at break is measured is measured using a tensile tester having a width of 5 mm, a length of 400 mm, and a thickness of 500 µm. In addition, in cases where the LED encapsulant contains, for example, a dithiol compound (A), a polythiol compound (B), a polyene compound (C), and a photoradical polymerization initiator as described below, the cured product for which the tensile elongation at break is measured is measured using a tensile tester having a width of 5 mm, a length of 500 mm, and a thickness of 500 µm. ２ The method can be achieved by irradiating the film with ultraviolet light.

[0009] The LED encapsulant of the present invention has a storage modulus at 25°C of a cured product of 0.01 MPa as a lower limit and 500 MPa as a upper limit. When the storage modulus at 25°C of the cured product is within this range, the LED encapsulant of the present invention exhibits excellent reliability and is more effective in following the expansion and contraction of the LED chip and the bending of the substrate. The storage modulus at 25°C of the cured product is more preferably 0.1 MPa as a lower limit and 300 MPa as an upper limit. The storage modulus at 25°C of the cured product having a width of 5 mm, a length of 400 mm, and a thickness of 500 μm can be measured using a dynamic viscoelasticity measuring device (e.g., "DVA-200" manufactured by IT Measurement Control Co., Ltd.) under the conditions of a tension mode, a gripping width of 25 mm, and a frequency of 1.0 Hz. Furthermore, the cured product for measuring the storage modulus may be, for example, a cured product containing a dithiol compound (A), a polythiol compound (B), and a polyene compound (C), as well as a photoradical polymerization initiator, which will be described later. In this case, the cured product is a product containing a dithiol compound (A), a polythiol compound (B), a polyene compound (C), and ... ２ The method can be achieved by irradiating the film with ultraviolet light.

[0010] The LED encapsulant of the present invention contains a curable resin. In the LED encapsulant of Invention 2, the curable resin includes a dithiol compound (A) having two thiol groups per molecule, a polythiol compound (B) having three or more thiol groups per molecule, and a polyene compound (C) having two or more aliphatic carbon-carbon double bonds per molecule. Furthermore, in the LED encapsulant of Invention 1, the curable resin preferably includes a dithiol compound (A) having two thiol groups per molecule, a polythiol compound (B) having three or more thiol groups per molecule, and a polyene compound (C) having two or more aliphatic carbon-carbon double bonds per molecule. By including these components as the curable resin, the resulting LED encapsulant has low viscosity and excellent coatability, and the cured product has excellent flexibility. Furthermore, by including the dithiol compound (A), the polythiol compound (B), and the polyene compound (C), the cured product of the resulting LED encapsulant also has excellent heat resistance.

[0011] The thiol group of the dithiol compound (A) is preferably a secondary thiol group. When the thiol group of the dithiol compound (A) is a secondary thiol group, the resulting LED encapsulant has excellent storage stability.

[0012] Examples of the dithiol compound (A) include 1,4-bis(3-mercaptobutyryloxy)butane, butanediol bisthiopropionate, ethylene bis(3-mercaptopropionate), 1,2-bis(2-mercaptoethoxy)ethane, ethylene bis(thioglycolate), etc. These dithiol compounds (A) may be used alone or in combination of two or more.

[0013] The content of the dithiol compound (A) in 100 parts by mass of the curable resin is preferably 20 parts by mass at its lower limit and 70 parts by mass at its upper limit. By having the content of the dithiol compound (A) in this range, the resulting LED encapsulant has better flexibility. The content of the dithiol compound (A) is more preferably 30 parts by mass at its lower limit and 60 parts by mass at its upper limit.

[0014] The thiol group of the polythiol compound (B) is preferably a secondary thiol group. When the thiol group of the polythiol compound (B) is a secondary thiol group, the resulting LED encapsulant has excellent storage stability.

[0015] From the viewpoint of improving the storage modulus, the polythiol compound (B) preferably has 3 to 6 thiol groups, and more preferably 3 to 4 thiol groups, in one molecule.

[0016] Examples of the polythiol compound (B) include 1,3,5-tris(2-(3-sulfanylbutanoyloxy)ethyl)-1,3,5-triazinane-2,4,6-trione, pentaerythritol tetrakis(3-mercaptobutyrate), pentaerythritol tetrakis(3-mercaptopropionate), dipentaerythritol hexakis(3-mercaptopropionate), etc. These polythiol compounds (B) may be used alone or in combination of two or more.

[0017] The content of the polythiol compound (B) in 100 parts by mass of the curable resin is preferably 2.0 parts by mass at its lower limit and 70 parts by mass at its upper limit. By having the content of the polythiol compound (B) in this range, the resulting LED encapsulant has better flexibility and low viscosity. The content of the polythiol compound (B) is more preferably 3.0 parts by mass at its lower limit and 30 parts by mass at its upper limit.

[0018] Examples of the polyene compound (C) include diallyl isophthalate, diallyl maleate, diallyl diphenate, triallyl isocyanurate, pentaerythritol tetraallyl ether, and 1,3,4,6-tetraallyltetrahydroimidazo[4,5-d]imidazole-2,5(1H,3H)-dione. Among these, the polyene compound (C) is preferably a (meth)allyl compound having two or three aliphatic carbon-carbon double bonds per molecule. These polyene compounds (C) may be used alone or in combination of two or more. In this specification, the term "(meth)allyl" refers to allyl or methallyl.

[0019] The polyene compound (C) content in 100 parts by mass of the curable resin is preferably 20 parts by mass at its lower limit and 60 parts by mass at its upper limit. By ensuring that the polyene compound (C) content is within this range, the resulting LED encapsulant has superior flexibility and low viscosity. The polyene compound (C) content is more preferably 30 parts by mass at its lower limit and 50 parts by mass at its upper limit.

[0020] The content ratio of the dithiol compound (A), the polythiol compound (B), and the polyene compound (C) is preferably such that the ratio of the thiol groups in the dithiol compound (A) and the polythiol compound (B) to the aliphatic carbon-carbon double bonds in the polyene compound (C) is, in molar ratio, thiol groups:aliphatic carbon-carbon double bonds=1.5:1.0 to 1.0:1.5, and more preferably thiol groups:aliphatic carbon-carbon double bonds=1.2:1.0 to 1.0:1.2.

[0021] The LED encapsulant of the present invention contains a polymerization initiator. Examples of the polymerization initiator include a photoradical polymerization initiator and a thermal radical polymerization initiator, and a photoradical polymerization initiator is preferably used.

[0022] Examples of the photoradical polymerization initiator include benzophenone compounds, acetophenone compounds, acylphosphine oxide compounds, titanocene compounds, oxime ester compounds, benzoin ether compounds, and thioxanthone compounds. Specific examples of the photoradical polymerization initiator include 1-hydroxycyclohexyl phenyl ketone, 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-1-butanone, 2-(dimethylamino)-2-((4-methylphenyl)methyl)-1-(4-(4-morpholinyl)phenyl)-1-butanone, 2,2-dimethoxy-1,2-diphenylethan-1-one, bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, 2-methyl-1-(4-methylthiophenyl)-2-morpholinopropan-1-one, 1-(4-(2-hydroxyethoxy)-phenyl)-2-hydroxy-2-methyl-1-propan-1-one, 1-(4-(phenylthio)phenyl)-1,2-octanedione 2-(O-benzoyloxime), and 2,4,6-trimethylbenzoyldiphenylphosphine oxide. The photoradical polymerization initiators may be used alone or in combination of two or more.

[0023] Examples of the thermal radical polymerization initiator include those composed of azo compounds and organic peroxides. Examples of the azo compounds include those having a structure in which multiple units such as polyalkylene oxides or polydimethylsiloxanes are bonded via azo groups. Polymeric azo compounds having a structure in which multiple units such as polyalkylene oxides are bonded via azo groups are preferably those having a polyethylene oxide structure. Specific examples of the azo compounds include polycondensates of 4,4'-azobis(4-cyanopentanoic acid) and polyalkylene glycols, and polycondensates of 4,4'-azobis(4-cyanopentanoic acid) and polydimethylsiloxanes having terminal amino groups. Examples of the organic peroxides include ketone peroxides, peroxyketals, hydroperoxides, dialkyl peroxides, peroxyesters, diacyl peroxides, and peroxydicarbonates.

[0024] The content of the polymerization initiator is preferably 0.1 parts by mass or less and 5.0 parts by mass or less per 100 parts by mass of the curable resin. By using the polymerization initiator in this range, the resulting LED encapsulant has better storage stability and curability. The content of the polymerization initiator is more preferably 0.5 parts by mass or less and 2.0 parts by mass or less.

[0025] From the viewpoint of the flatness of the coating film, the LED encapsulant of the present invention preferably further contains a leveling agent.

[0026] Examples of the leveling agent include silicone-based leveling agents, fluorine-based leveling agents, and acrylic-based leveling agents.

[0027] The content of the leveling agent is preferably 0.01 parts by mass at the lower limit and 10 parts by mass at the upper limit relative to 100 parts by mass of the curable resin. By using the leveling agent in this range, the resulting LED encapsulant has better coatability and coating film flatness. The more preferred lower limit of the content of the leveling agent is 0.1 parts by mass, and the more preferred upper limit is 1.0 parts by mass.

[0028] The LED encapsulant of the present invention may further contain additives such as a filler, a plasticizer, a surfactant, a flame retardant, an antistatic agent, an antifoaming agent, and an ultraviolet absorber, as long as the object of the present invention is not impaired.

[0029] Examples of a method for producing the LED encapsulant of the present invention include a method in which the dithiol compound (A), the polythiol compound (B), the polyene compound (C), a polymerization initiator, and a leveling agent added as needed are uniformly mixed using a stirrer.

[0030] The LED encapsulant of the present invention is preferably one that can be cured by at least one of light irradiation and heat, and more preferably one that can be cured by light irradiation.

[0031] The LED encapsulant of the present invention can be cured by light irradiation, for example, at a wavelength of 300 to 400 nm and at a rate of 300 to 3,000 mJ / cm. ２ and a method of irradiating the object with light having an integrated amount of light of 1000 times or more.

[0032] Examples of light sources for irradiating the LED encapsulant of the present invention with light include low-pressure mercury lamps, medium-pressure mercury lamps, high-pressure mercury lamps, ultra-high-pressure mercury lamps, excimer lasers, chemical lamps, black light lamps, microwave-excited mercury lamps, metal halide lamps, sodium lamps, halogen lamps, xenon lamps, LED lamps, fluorescent lamps, sunlight, electron beam irradiation devices, etc. These light sources may be used alone or in combination of two or more.

[0033] Examples of means for irradiating the LED encapsulant of the present invention with light include simultaneous irradiation from various light sources, sequential irradiation with a time lag, and a combination of simultaneous irradiation and sequential irradiation, and any of these irradiation means may be used.

[0034] The LED encapsulant of the present invention can be applied with high application accuracy, and is therefore particularly preferably used for application by an inkjet method.

[0035] According to the present invention, it is possible to provide an LED encapsulant that can be applied with high application accuracy and whose cured product can follow the expansion and contraction of an LED chip, bending of a substrate, etc.

[0036] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0037] (Examples 1 to 14, Comparative Examples 1 and 2) LED encapsulants of Examples 1 to 14 and Comparative Examples 1 and 2 were prepared by stirring and mixing each material using a stirring mixer according to the blending ratios shown in Tables 1 and 2. The stirring mixer used was an Awatori Rentaro ARE-310 (manufactured by Thinky Corporation). The viscosity of each LED encapsulant obtained in the Examples and Comparative Examples was measured using an E-type viscometer (manufactured by Toki Sangyo Co., Ltd., "VISCOMETER TV-22") and a No. 1 rotor at 25°C and a rotation speed of 100 rpm. The results are shown in Tables 1 and 2. Each LED encapsulant obtained in the Examples and Comparative Examples was applied to a slide glass to a thickness of 500 μm, and then irradiated with 100 mW / cm using a metal halide lamp. ２ The LED encapsulant was cured by irradiating it with ultraviolet light (wavelength 365 nm) for 30 seconds. The obtained cured product was cut into a width of 5 mm, length of 400 mm, and thickness of 500 μm to obtain a test piece. The tensile elongation at break of the obtained test piece was measured using a tensile tester (Shimadzu Corporation, "Autograph AG-XPlus") under conditions of 25°C, a gripping distance of 25 mm, and a tensile speed of 5 mm / s. The results are shown in Tables 1 and 2. Note that the cured product of the LED encapsulant obtained in Comparative Example 1 was too soft to prepare a test piece.

[0038] <Evaluation> Each of the LED encapsulants obtained in the examples and comparative examples was evaluated by the following methods. The results are shown in Tables 1 and 2.

[0039] (Ejectability and Coating Accuracy) Each LED sealant obtained in the examples and comparative examples was applied to a slide glass using an inkjet ejection device (Microjet Corporation, "NanoPrinter 500") so that one dot was a 10 pL droplet. The ejectability was evaluated as "○" if the dot was ejectable and "×" if it was not ejectable. Furthermore, the coating accuracy was evaluated by randomly selecting three ejected dots, and assigning a "◎" if the maximum error from the average diameter of the dots was within 5%, a "○" if it was more than 5% but less than 10%, and an "×" if it was more than 10% or the dot was not applicable.

[0040] (Flexibility) Each of the LED encapsulants obtained in Examples and Comparative Examples was applied to a slide glass to a thickness of 500 μm, and then irradiated with 100 mW / cm 2 using a metal halide lamp. ２ The LED encapsulant was cured by irradiating it with ultraviolet light (wavelength 365 nm) for 30 seconds. The obtained cured product was cut into a width of 5 mm, length of 400 mm, and thickness of 500 μm to obtain a test piece. The storage modulus of the obtained test piece was measured using a dynamic viscoelasticity measuring device (e.g., "DVA-200" manufactured by IT Measurement and Control Co., Ltd.) under conditions of 25 ° C, tensile mode, grip width 25 mm, and frequency 1.0 Hz. Flexibility was evaluated as follows: a storage modulus of 0.1 MPa or more and less than 10 MPa was marked "◎", a storage modulus of 10 MPa or more and less than 300 MPa was marked "○", and a storage modulus of less than 0.1 MPa or more and 300 MPa was marked "×". Note that for the LED encapsulant obtained in Comparative Example 1, the cured product was too soft to prepare a test piece.

[0041] (Storage Stability) For each of the LED encapsulants obtained in the Examples and Comparative Examples, the initial viscosity immediately after production and the viscosity after storage at 25°C for one week after production were measured. The viscosity increase ratio was calculated by dividing the viscosity after storage by the initial viscosity. Storage stability was evaluated by assigning a "good" to a viscosity increase ratio of less than 1.4, a "good" to a viscosity increase ratio of 1.4 or more but less than 2.0, and an "unclear" to a viscosity increase ratio of 2.0 or more or gelation. The viscosity of the LED encapsulants was measured using an E-type viscometer (manufactured by Toki Sangyo Co., Ltd., "VISCOMETER TV-22") and a No. 1 rotor at 25°C and a rotation speed of 100 rpm.

[0042]

[0043]

[0044] According to the present invention, it is possible to provide an LED encapsulant that can be applied with high application accuracy and whose cured product can follow the expansion and contraction of an LED chip, bending of a substrate, etc.

Claims

1. Contains a curable resin and a polymerization initiator, The viscosity at 25°C is 100 mPa·s or less, and the tensile elongation at break of the cured product at 25°C is 50% or more.

1. An LED encapsulant comprising:

2. The LED sealant according to claim 1, wherein the curable resin comprises a dithiol compound (A) having two thiol groups in one molecule, a polythiol compound (B) having three or more thiol groups in one molecule, and a polyene compound (C) having two or more aliphatic carbon-carbon double bonds in one molecule.

3. Contains a curable resin and a polymerization initiator, The curable resin includes a dithiol compound (A) having two thiol groups in one molecule, a polythiol compound (B) having three or more thiol groups in one molecule, and a polyene compound (C) having two or more aliphatic carbon-carbon double bonds in one molecule.

1. An LED encapsulant comprising:

4. 4. The LED sealant according to claim 2, wherein the polyene compound (C) is a (meth)allyl compound having two or three aliphatic carbon-carbon double bonds in one molecule.

5. The LED encapsulant according to claim 1 , further comprising a leveling agent.

6. The LED sealant according to claim 1, 2 or 3, which is applied by an ink-jet method.