Liquid epoxy resin composition and electronic component

Abstract

The invention provides a liquid epoxy resin composition and an electronic component which have good glossiness when cured. A liquid epoxy resin composition containing (A) an epoxy resin, (B) a curing agent, and (C) a urea-based curing accelerator having a melting point of 230 DEG C or less.

Description

Technical Field

[0001] The present invention relates to a liquid epoxy resin composition and an electronic component, and particularly to a liquid epoxy resin composition for airtightly sealing electronic components such as relays and an electronic component using the liquid epoxy resin composition. Background Art

[0002] A control relay (hereafter referred to as a "relay") is a device that controls circuits by receiving external electrical signals to connect / disconnect them, switching them. Relays are widely used in household appliances, machine tools, industrial machinery, and transportation equipment, with their use particularly increasing in electronic components mounted on printed circuit boards.

[0003] Figure 1 A schematic diagram showing the airtight structure of a common relay is shown in FIG. Figure 1 This is a schematic diagram illustrating the airtight structure of the relay; components within the housing 11 are omitted. The relay 10 has input terminals 12 and output terminals 12. It receives external signals via the input terminals 12 and, through the electromagnetic action of a coil (not shown) within the housing 11, moves contacts (not shown) located at the output terminals 12, thereby connecting and disconnecting the circuit and switching it. Furthermore, in the relay 10, the housing 11 is covered by a resin base 13 that also serves as a fixing portion for the terminals 12.

[0004] Relay 10 is crucial for repeated on / off switching between contacts within housing 11. If flux, cleaning fluid, or contact-contaminating gases intrude through the gaps between terminals 12 and base 13, or between housing 11 and base 13, contact failure can occur, reducing contact reliability and potentially preventing relay functionality. Therefore, relay 10 is provided with an insulating sealant 14 to seal the gaps between terminals 12 and base 13, and between housing 11 and base 13. This sealant 14 ensures the airtight structure of relay 10.

[0005] Typically, the housing 11 used for electronic components such as relays is mainly made of resin materials such as polybutylene terephthalate (PBT) and polycarbonate (PC). Therefore, most housings have a heat-resistant temperature of about 120 to 130°C, and are required to be cured at a low temperature when curing the epoxy resin composition serving as the sealant.

[0006] Patent Document 1 discloses a single-liquid epoxy resin composition as a sealant for relays. The composition contains an epoxy resin, dicyandiamide, an epoxy resin adduct, and a non-latent imidazole compound. The patent states that this composition cures even at low temperatures and exhibits high heat resistance, enabling sufficient hermetic sealing of electronic components such as relays even when subjected to reflow or flow treatments using lead-free solder.

[0007] Furthermore, Patent Document 2 discloses a one-part liquid epoxy resin composition for hermetically or insulatively sealing small electronic or electrical components. The composition comprises (A) an epoxy resin, (B) dicyandiamide, (C) a latent curing agent other than dicyandiamide, (D) calcium carbonate treated with a resin acid, and (E) calcium carbonate treated with a fatty acid, wherein the amount of the fatty acid-treated calcium carbonate (E) is 0.5 to 20 parts by weight per 100 parts by weight of the epoxy resin (A). Furthermore, Patent Document 2 discloses that this composition provides a one-part liquid epoxy resin composition with improved flow into extremely narrow gaps of several micrometers or less.

[0008] The relay sealing process typically involves placing components such as coils and terminals on a resin base and inserting them into a housing to assemble the relay. Next, the sealant is applied to close the gap between the terminals and the base, and to close the gap between the housing and the base from above, followed by heat curing. After the sealant cures, visual inspection is sometimes performed to confirm that the gap between the housing and the base is tightly sealed.

[0009] However, sealants are often primarily composed of epoxy resin, resulting in a dull, cured product. Once cured on a resin base, the sealant is difficult to distinguish from the base, making it difficult to visually verify that the sealant has been applied where desired. Consequently, relay airtightness verification testing can be time-consuming, reducing manufacturing efficiency.

[0010] Prior art literature

[0011] Patent Literature

[0012] Patent Document 1: Japanese Patent Application Laid-Open No. 2009-215368

[0013] Patent Document 2: Japanese Patent Application Laid-Open No. 2015-098520 Summary of the Invention

[0014] The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide a liquid epoxy resin composition and an electronic component having good glossiness when cured.

[0015] In order to solve the above-mentioned technical problems, the present invention is defined as the following solutions 1 to 6.

[0016] 1. A liquid epoxy resin composition comprising: (A) an epoxy resin; (B) a curing agent; and (C) a urea-based curing accelerator having a melting point of 230° C. or less.

[0017] 2. The liquid epoxy resin composition according to item 1, further comprising: (D) calcium carbonate having a surface treated with a resin acid.

[0018] 3. The liquid epoxy resin composition according to 1 or 2, wherein the curing agent (B) is dicyandiamide and / or modified imidazole.

[0019] 4. The liquid epoxy resin composition according to any one of 1 to 3, wherein the liquid epoxy resin composition contains 0.5 to 20.0 parts by mass of the (C) urea curing accelerator relative to 100 parts by mass of the (A) epoxy resin.

[0020] 5. The liquid epoxy resin composition according to any one of 1 to 4 above, wherein the (C) urea-based curing accelerator has any of the following structural formulas (1) to (4).

[0021]

[0022]

[0023] 6. An electronic component comprising the liquid epoxy resin composition according to any one of 1 to 5 above as a sealant.

[0024] Effects of the Invention

[0025] According to the embodiments of the present invention, a liquid epoxy resin composition and an electronic component having good glossiness when cured can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a schematic diagram showing the airtight structure of a common relay.

[0027] Description of reference numerals:

[0028] 10: Relay; 11: Housing; 12: Terminal; 13: Base; 14: Sealant. DETAILED DESCRIPTION

[0029] The liquid epoxy resin composition and electronic component according to the embodiments of the present invention are described below. However, the present invention is not to be construed as being limited thereto, and various changes, modifications, and improvements can be made based on the knowledge of those skilled in the art without departing from the scope of the present invention.

[0030] It should be noted that, in this specification, " to " indicating a numerical range means a range including the numerical values ​​recorded as the upper limit and lower limit, respectively. In addition, when only the upper limit is recorded in a numerical range, it means that the lower limit is also in the same unit as the upper limit.

[0031] In the numerical ranges described in stages in this specification, the upper limit or lower limit described in a certain numerical range can be replaced with the upper limit or lower limit of another numerical range described in stages.

[0032] In addition, in the numerical range described in this specification, the upper limit value or the lower limit value described in a certain numerical range can be replaced with the value shown in the Examples.

[0033] (Liquid epoxy resin composition)

[0034] The liquid epoxy resin composition according to an embodiment of the present invention includes (A) an epoxy resin, (B) a curing agent, and (C) a urea-based curing accelerator having a melting point of 230° C. or less.

[0035] Hereinafter, each component contained in the liquid epoxy resin composition according to the embodiment of the present invention will be described.

[0036] <Components contained in the liquid epoxy resin composition>

[0037] <(A) Epoxy resin>

[0038] The epoxy resin (A) used in the embodiment of the present invention is not particularly limited, and examples thereof include bisphenol A epoxy resin, bisphenol F epoxy resin, bisphenol S epoxy resin, biphenyl epoxy resin, alicyclic epoxy resin, phenol novolac epoxy resin, cresol novolac epoxy resin, naphthol novolac epoxy resin, dicyclopentadiene epoxy resin, naphthalene epoxy resin, and epoxy resins obtained by various modifications thereof such as CTBN (carboxyl-terminated butadiene acrylonitrile rubber) modification and halogenation. These epoxy resins may be used alone or in combination of two or more.

[0039] As the epoxy resin (A), bisphenol A epoxy resin and bisphenol F epoxy resin are particularly preferred. The liquid epoxy resin composition containing the bisphenol A epoxy resin and bisphenol F epoxy resin has good mechanical properties, chemical resistance, electrical properties and corrosion resistance as a sealant formed by the cured product after sealing.

[0040] The bisphenol A epoxy resin preferably has an epoxy equivalent of 165 to 270 g / eq. The bisphenol F epoxy resin preferably has an epoxy equivalent of 155 to 270 g / eq. By setting the epoxy equivalent of the bisphenol A epoxy resin or the bisphenol F epoxy resin to 270 g / eq or less, the viscosity of the resin composition is low and the workability is good. Two or more bisphenol A epoxy resins with different epoxy equivalents can be used in combination in a manner such that the epoxy equivalent is in the range of 165 to 270 g / eq. In addition, two or more bisphenol F epoxy resins with different epoxy equivalents can be used in combination in a manner such that the epoxy equivalent is in the range of 155 to 270 g / eq.

[0041] Examples of commercially available bisphenol A epoxy resins include jER (registered trademark) 828, jER 827, jER 825, and jER 834 (all manufactured by Mitsubishi Chemical Co., Ltd.), YD-127 and YD-128 (all manufactured by Nippon Steel Chemical & Material Co., Ltd.), GELR-128 (manufactured by Epoxy Base Electronic Material Corp., Ltd.), EPICLON (registered trademark) 840 and EPICLON 850 (manufactured by DIC Corporation), and ADEKA RESIN (registered trademark) EP-4100 (manufactured by ADEKA Corporation).

[0042] Examples of commercially available bisphenol F epoxy resins include jER805, jER805H, and jER807 (all manufactured by Mitsubishi Chemical Co., Ltd.), YDF-170 (manufactured by Nippon Steel Chemical & Material Co., Ltd.), EPICLON 830 (manufactured by DIC Corporation), and ADEKA RESINEP-4901 (manufactured by ADEKA Corporation).

[0043] The viscosity of the epoxy resin (A) used in the embodiment of the present invention at 25°C is preferably 0.1 to 100 Pa·s. If the viscosity of the epoxy resin (A) is 0.1 to 100 Pa·s, the workability is good. The viscosity of the epoxy resin (A) is more preferably 0.1 to 50 Pa·s, and even more preferably 0.1 to 20 Pa·s. When two or more epoxy resins (A) are mixed, even if the viscosity of any of the epoxy resins (A) exceeds the above-mentioned viscosity range, it can be used as long as the viscosity of the mixture of the two or more epoxy resins (A) is set to within the range of 0.1 to 100 Pa·s. The viscosity of the epoxy resin (A) can be measured at 25°C using a rotational viscometer (manufactured by Toki Sangyo Co., Ltd., trade name TVE-35 type viscometer, rotor diameter 28 mm, angle 3°).

[0044] (B) Curing agent

[0045] As the curing agent of (B), dicyandiamide, imidazole curing agent, amine curing agent, phenol curing agent, acid anhydride curing agent, etc. can be used alone or in combination. The amount of compounding can be appropriately adjusted according to the application. For example, in the case of dicyandiamide, relative to 100 parts by mass of the epoxy resin of (A), it is preferred that 0.1 to 20 parts by mass of dicyandiamide be included, further more preferably 1 to 12 parts by mass of dicyandiamide, further more preferably 2 to 8 parts by mass of dicyandiamide be included. In the case of an imidazole curing agent, relative to 100 parts by mass of the epoxy resin of (A), it is preferred that 1 to 40 parts by mass of an imidazole curing agent be included, further more preferably 3 to 30 parts by mass of an imidazole curing agent, further more preferably 5 to 20 parts by mass of an imidazole curing agent be included. In the case of an amine curing agent, the content is preferably 1 to 40 parts by mass, more preferably 3 to 30 parts by mass, and even more preferably 5 to 20 parts by mass, based on 100 parts by mass of the epoxy resin (A).

[0046] Imidazole curing agents may include, for example, modified imidazoles, 2-methylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 1,2-dimethylimidazole, 2-phenyl-4,5-dihydroxymethylimidazole, and triazine compounds having an imidazole ring. Examples of triazine compounds having an imidazole ring include 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine. Two or more imidazole curing agents may be used in combination. Among them, modified imidazoles are preferably used in consideration of single-liquid storage stability and the ability to cure at low temperatures. Examples of modified imidazoles include epoxy-modified imidazoles and urea-modified imidazoles. Epoxy-modified imidazoles are compounds formed by modifying alkyl imidazoles with epoxy compounds. Urea-modified imidazoles are compounds formed by modifying alkyl imidazoles with urea.

[0047] Examples of amine curing agents include aliphatic amines, alicyclic amines, aromatic amines, modified amines, and polyamidoamines. Two or more amine curing agents can be used in combination. Among them, modified amines are preferably used in view of single-liquid storage stability and the ability to cure at low temperatures. Examples of modified amines include epoxy-modified polyamines and urea-modified polyamines. Epoxy-modified polyamines are compounds obtained by mixing or reacting phenolic resins and / or polyphenol compounds with N,N-dialkylaminoalkylamines modified with epoxy compounds. Urea-modified polyamines are compounds obtained by modifying N,N-dialkylaminoalkylamines with urea, or compounds obtained by modifying N,N-dialkylaminoalkylamines with isocyanates.

[0048] Examples of commercially available modified imidazoles and / or modified amines include Ajicare (registered trademark) PN-23, Ajicare PN-H, Ajicare PN-40J, and Ajicare MY-24 (all manufactured by Ajinomoto Fine-Techno Co., Ltd.), Fujicare FXR-1121, Fujicare FXR-1020, and Fujicare FXR-1081 (manufactured by T&K Toka Co., Ltd.), and Adeka Hardener (registered trademark) EH4344S, Adeka Hardener EH4356S, Adeka Hardener EH4342S, Adeka Hardener EH4345S, and Adeka Hardener EH4354S (all manufactured by Adeka Co., Ltd.).

[0049] Examples of the phenolic curing agent include o-cresol novolac resins and the like.

[0050] Examples of the acid anhydride curing agent include tetrahydrophthalic anhydride, methyltetrahydrophthalic anhydride, methylnadic anhydride, hexahydrophthalic anhydride, methylhexahydrophthalic anhydride, hydrogenated methylnadic anhydride, and trialkyltetrahydrophthalic anhydride.

[0051] As the curing agent (B), it is particularly preferred to use dicyandiamide and modified imidazole in combination. If dicyandiamide is used, a glossy cured product of the epoxy resin composition can be obtained when thermally cured, and the adhesion (sealing) achieved by the epoxy resin composition is also excellent. However, it is difficult to cure the epoxy resin composition at a low temperature of about 120-130°C. On the other hand, modified imidazole cannot impart gloss like dicyandiamide and has poor adhesion, but it can cure the epoxy resin composition at a low temperature of about 120-130°C. By using dicyandiamide and modified imidazole having such characteristics in combination, and further containing the urea-based curing accelerator (C) described later, the reaction of dicyandiamide is accelerated during thermal curing. Therefore, even when cured at a low temperature of about 120-130°C, an epoxy resin composition with gloss and excellent adhesion can be obtained. Therefore, the combination of dicyandiamide and modified imidazole as (B) as a curing agent is particularly useful for obtaining an epoxy resin composition with excellent gloss and adhesion even when cured at a low temperature. From the viewpoints of gloss, adhesion, and low-temperature curing properties, the mixing ratio of dicyandiamide to modified imidazole is preferably in the range of 10:3 to 10:200 by mass, more preferably 10:5 to 10:100, and even more preferably 10:10 to 10:60.

[0052] <(C) Urea-based curing accelerator>

[0053] The urea-based curing accelerator (C) is a curing accelerator containing a dimethylurea group in its structural formula. The inclusion of a urea-based curing accelerator imparts gloss to the epoxy resin composition during thermal curing. From the perspective of gloss during thermal curing and storage stability of the epoxy resin composition, the urea-based curing accelerator (C) is preferably present in an amount of 0.5 to 20.0 parts by mass, and more preferably 1.0 to 16.0 parts by mass, per 100 parts by mass of the epoxy resin (A).

[0054] The melting point of the urea-based curing accelerator (C) is 230°C or lower. The lower the melting point of the urea-based curing accelerator (C), the higher the gloss of the epoxy resin composition during thermal curing. The melting point of the urea-based curing accelerator (C) is more preferably 190°C or lower, even more preferably 175°C or lower, and even more preferably 160°C or lower.

[0055] The urea curing accelerator (C) is not particularly limited as long as it contains a dimethylurea group in the structural formula as described above. Specific examples include urea curing accelerators having any of the following structural formulas (1) to (4).

[0056]

[0057]

[0058] <(D) Calcium carbonate with resin acid treatment on the surface>

[0059] The liquid epoxy resin composition according to an embodiment of the present invention preferably further comprises (D) calcium carbonate whose surface has been treated with a resin acid. The calcium carbonate (D) whose surface has been treated with a resin acid is calcium carbonate whose surface has been treated with a resin acid. The calcium carbonate whose surface has been treated with a resin acid has a structure in which all or part of the surface of the calcium carbonate particles is covered with a resin acid.

[0060] As the calcium carbonate used as the raw material of the calcium carbonate (D) whose surface has been treated with a resin acid, known heavy calcium carbonate, synthetic (precipitated) calcium carbonate, etc. can be used. As the resin acid, for example, abietic acid, dehydroabietic acid, dihydroabietic acid, or other abietic acid or polymers thereof, disproportionated rosin, hydrogenated rosin, polymerized rosin, or salts thereof (e.g., alkali metal salts, alkaline earth metal salts), or esters thereof can be used.

[0061] The surface treatment method of calcium carbonate using resin acid is not particularly limited, and it can be treated by a known treatment method. The amount of resin acid attached is not particularly limited, and is preferably 5 to 30 parts by mass, more preferably 10 to 20 parts by mass, relative to 100 parts by mass of calcium carbonate as a raw material. The particle size of the calcium carbonate (D) treated with resin acid on the surface is preferably an average particle size D50 = 0.05 to 50 μm, and more preferably an average particle size D50 = 0.1 to 20 μm. It should be noted that the average particle size (D50) of the calcium carbonate (D) treated with resin acid on the surface and the calcium carbonate (D') described later listed in this specification refers to the value measured by a particle size distribution measuring device based on the laser diffraction scattering method (product name: HELOS & RODOS, manufactured by Sympatec).

[0062] The liquid epoxy resin composition according to an embodiment of the present invention contains (D) calcium carbonate having a resin acid treatment on its surface. This allows for improved gloss during thermal curing of the liquid epoxy resin composition without excessive addition of (C) urea-based curing accelerator. Specifically, the inclusion of (D) calcium carbonate having a resin acid treatment on its surface allows for a reduction in the content of (C) urea-based curing accelerator required to achieve a desired gloss.

[0063] The calcium carbonate (D) whose surface has been treated with a resin acid is preferably contained in an amount of 1 to 100 parts by mass, more preferably 5 to 60 parts by mass, and even more preferably 7 to 50 parts by mass, relative to 100 parts by mass of the epoxy resin (A).

[0064] Examples of commercially available products of the calcium carbonate (D) whose surface has been treated with a resin acid include Homocal (registered trademark) D, Homocal DM, White IGV-IV, White Yanhua (registered trademark) T-DD, White Yanhua DD, White Yanhua O, Calmos, and Unifant-15 (all manufactured by Shiraishi Industries, Ltd.), NEOLIGHT SA-100, NEOLIGHT SA-200, NEOLIGHT SA-300, NEOLIGHT GP-20, NEOLIGHT EG-320, and NEOLIGHT R-700 (all manufactured by Takehara Chemical Industry Co., Ltd.).

[0065] The calcium carbonate (D) having been subjected to resin acid treatment on its surface may be in a state where resin acid is attached to the surface of the calcium carbonate. In addition, the calcium carbonate may be a surface-treated calcium carbonate that has been subjected to a combination of resin acid treatment and inorganic treatment, a surface-treated calcium carbonate that has been subjected to a combination of resin acid treatment and organic compound treatment (fatty acid treatment, cationic surfactant treatment, silane coupling agent treatment, etc.), or a surface-treated calcium carbonate that has been subjected to a combination of resin acid treatment and inorganic compound treatment (silicon dioxide treatment, zinc oxide treatment, hydroxyapatite treatment, etc.). In addition, it is preferred that the surface of the calcium carbonate is entirely surface-treated with resin acid, or a portion thereof may be surface-treated with resin acid.

[0066] <Other ingredients>

[0067] In addition to the above-mentioned components, conventional auxiliary components such as thermoplastic resins, curing accelerators, diluents, fillers, thixotropy-imparting agents, flame retardants, pigments, leveling agents, surface modifiers, anti-settling agents, coupling agents, defoaming agents, release agents, and dispersants may be appropriately blended into the liquid epoxy resin composition according to the embodiment of the present invention, within a range that does not impair the effects of the present embodiment.

[0068] Examples of the curing accelerator include phosphorus-based curing accelerators, amine-based curing accelerators, and imidazole-based curing accelerators. These curing accelerators may be used in combination of two or more.

[0069] Examples of the diluent include butyl glycidyl ether, phenyl glycidyl ether, alkylphenol glycidyl ether, allyl glycidyl ether, butanediol diglycidyl ether, hexanediol diglycidyl ether, neopentyl glycol diglycidyl ether, and benzyl alcohol.

[0070] Examples of fillers include calcium carbonate, silica, alumina, talc, mica, white carbon, zirconium oxide, titanium dioxide, red iron oxide (Bengara), silicon carbide, boron nitride, aluminum nitride, silicon nitride, magnesium oxide, and magnesium silicate, other than the above-mentioned component (D).

[0071] Examples of the thixotropy-imparting agent include ultrafine silicon dioxide, ultrafine aluminum oxide, and ultrafine calcium carbonate other than the above-mentioned component (D).

[0072] Examples of the flame retardant include phosphorus compounds, halogen compounds, antimony compounds such as antimony trioxide, and metal hydroxides.

[0073] Examples of the pigment include titanium dioxide, ferric oxide, carbon black, and phthalocyanine blue.

[0074] <Characteristics of Liquid Epoxy Resin Composition>

[0075] <Visual confirmation (gloss)>

[0076] The liquid epoxy resin composition of the embodiment of the present invention has good gloss when heat-cured. Here, "good gloss" means that the liquid epoxy resin composition can be visually distinguished from the matte or matte resin material ( Figure 1 The liquid epoxy resin composition according to the embodiment of the present invention is glossy to the extent that it can be distinguished from the base 13 of the relay 10 shown in the figure). The stronger the gloss, the better. The evaluation and evaluation criteria of the visual recognition (gloss) of the liquid epoxy resin composition according to the embodiment of the present invention are as described in the description of the visual recognition (gloss) evaluation described below.

[0077] Viscosity (Pa·s)

[0078] The viscosity of the liquid epoxy resin composition at 25°C is preferably 150 Pa·s or less. The viscosity of the liquid epoxy resin composition at 25°C is more preferably 100 Pa·s or less, and even more preferably 50 Pa·s or less. A viscosity of 150 Pa·s or less improves the workability of the liquid epoxy resin composition. The method for measuring the viscosity of the liquid epoxy resin composition according to an embodiment of the present invention is described below in the section on viscosity evaluation.

[0079] <Gelation time(s)>

[0080] The gelation time of the liquid epoxy resin composition is preferably 1000 s or less at 120°C. The gelation time of the liquid epoxy resin composition is even more preferably 600 s or less, and even more preferably 300 s or less. A gelation time of 1000 s or less improves the low-temperature curability of the resin composition. The method for measuring the gelation time of the liquid epoxy resin composition according to an embodiment of the present invention is described below in the description of the gelation time evaluation.

[0081] <Glass transition temperature: Tg (°C)>

[0082] The glass transition temperature of the liquid epoxy resin composition is preferably 50°C or higher. The glass transition temperature of the liquid epoxy resin composition is more preferably 100°C or higher, and even more preferably 120°C or higher. By setting the glass transition temperature to 50°C or higher, the resin composition exhibits excellent heat resistance. The method for measuring the glass transition temperature of the liquid epoxy resin composition according to an embodiment of the present invention is described below in the description of the glass transition temperature for evaluation.

[0083] Tensile shear bond strength (MPa)

[0084] The tensile shear bond strength of the liquid epoxy resin composition is preferably 10 MPa or greater at room temperature. The tensile shear bond strength of the liquid epoxy resin composition is more preferably 13 MPa or greater. By setting the tensile shear bond strength to 10 MPa or greater, the adhesion between the resin composition and the metal terminal is good. The method for measuring the tensile shear bond strength of the liquid epoxy resin composition according to an embodiment of the present invention is described in the description of the tensile shear bond strength evaluated below.

[0085] (Method for producing liquid epoxy resin composition)

[0086] The method for producing the liquid epoxy resin composition of the present embodiment is not particularly limited. For example, a method can be used in which predetermined amounts of (A) epoxy resin, (B) curing agent, (C) urea curing accelerator, and other components as desired are mixed using a processor capable of applying high shear force, such as a rotary mixer, planetary mixer, dissolver, or butterfly mixer.

[0087] (Electronic components)

[0088] The liquid epoxy resin composition according to an embodiment of the present invention can be used as a sealant for electronic components requiring airtightness and insulation. Specifically, the electronic component has a housing with terminal contacts located within it. When it is desired to prevent the intrusion of specified liquids, gases, etc. through gaps in the housing, the sealant can be used to seal the gaps. While the electronic component is not particularly limited, the sealant is particularly useful for relays mounted on printed circuit boards.

[0089] The sealing method of the relay using the liquid epoxy resin composition of the embodiment of the present invention can implement the same method as the sealing method of the ordinary relay. That is, first, the components such as the coil and the terminal are arranged on a resin base and inserted into the housing to assemble the relay. Then, the liquid epoxy resin composition (sealant) of the embodiment of the present invention is sealed and heat-cured in a manner of blocking the gap between the terminal and the base and blocking the gap between the housing and the base from above the base. After the sealant is cured, it is visually confirmed whether the gap between the housing and the base is tightly sealed. At this time, the liquid epoxy resin composition of the embodiment of the present invention has good glossiness when cured, and its difference is obvious when it is arranged on a resin base that lacks glossiness, and visual confirmation is good. Therefore, it is easy to visually confirm whether the gap between the housing and the base is tightly sealed, and manufacturing efficiency is good.

[0090] [Example]

[0091] Examples of the present invention are shown below. However, these examples are provided for better understanding of the present invention and its advantages and are not intended to limit the present invention.

[0092] 1. Preparation of liquid epoxy resin composition

[0093] <Examples 1 to 13, Comparative Examples 1 to 6>

[0094] Compositions were prepared by mixing all the materials for each experimental example in the mixing ratios shown in Tables 1 and 2. The raw materials for the components shown in Tables 1 and 2 are shown below. In this specification, "mixing ratio" refers to a mass ratio unless otherwise specified. Viscosity refers to viscosity at 25°C.

[0095] (A) Epoxy resin

[0096] (a1) Bisphenol A type epoxy resin (viscosity: 12 to 15 Pa·s, epoxy equivalent: 184 to 194 g / eq).

[0097] (a2) Bisphenol A type epoxy resin (viscosity: 3.9 to 5.3 Pa·s, epoxy equivalent: 168 to 178 g / eq).

[0098] (a3) Bisphenol F-type epoxy resin (viscosity: 3 to 4.5 Pa·s, epoxy equivalent: 160 to 175 g / eq).

[0099] (a4) Bisphenol F-type epoxy resin (viscosity: 1.0 to 1.5 Pa·s, epoxy equivalent: 155 to 165 g / eq).

[0100] (B) Curing agent

[0101] (b1) Dicyandiamide.

[0102] (b2) Epoxy-modified imidazole.

[0103] (C) Urea curing accelerator

[0104] (c1) Urea-based curing accelerator of the above formula (1) (melting point: 221 to 225°C).

[0105] (c2) Urea-based curing accelerator of the above formula (2) (melting point: 185 to 189°C).

[0106] (c3) Urea-based curing accelerator of the above formula (3) (melting point: 173-175°C).

[0107] (c4) Urea-based curing accelerator of the above formula (4) (melting point: 159°C).

[0108] (D) Calcium carbonate with resin acid treatment on the surface

[0109] (d1) Calcium carbonate whose surface was treated with resin acid (resin acid-treated light calcium carbonate, average particle size D50 = 2.0 μm measured by laser diffraction method).

[0110] (d2) Calcium carbonate whose surface was treated with resin acid (resin acid-treated light calcium carbonate, average particle size D50 = 2.4 μm measured by laser diffraction method).

[0111] (d3) Calcium carbonate whose surface was treated with resin acid (resin acid-treated light calcium carbonate, average particle size D50 = 2.2 μm measured by laser diffraction method).

[0112] (D') Calcium carbonate

[0113] (d′1) Calcium carbonate (average particle size D50 measured by laser diffraction method = 1.7 μm).

[0114] (d'2) Calcium carbonate (average particle size D50 measured by laser diffraction method = 2.6 μm).

[0115] (E) Pigment

[0116] (e1) Carbon black.

[0117] (F) Leveling agent

[0118] (f1) Acrylic polymer leveling agent.

[0119] (G) Thixotropy Imparting Agent

[0120] (g1) Ultrafine silicon dioxide (BET specific surface area: 300 m 2 / g).

[0121] Next, the compositions were mixed using a rotary mixer to prepare liquid epoxy resin compositions of Examples and Comparative Examples.

[0122] 2. Evaluation

[0123] <Visual confirmation (gloss)>

[0124] 0.2 mL of the liquid epoxy resin composition obtained in the Examples and Comparative Examples was dripped onto the inclined surface of a galvanized steel sheet (Bonde-steel) SPCC-SD (cold-rolled steel sheet) tilted at 45°, and heat-cured at 120°C for 10 minutes. The appearance of the tilted flowed sample was then visually evaluated according to the following evaluation criteria. Criteria A to D were considered acceptable. The evaluation results are shown in Tables 1 and 2.

[0125] A: Black having stronger gloss than B is displayed.

[0126] B: Black with stronger gloss than C is displayed.

[0127] C: Black with stronger gloss than D is displayed.

[0128] D: Displays glossy black.

[0129] E: It is matte and has a gray hue.

[0130] Viscosity (Pa·s)

[0131] The viscosity (Pa·s) of the liquid epoxy resin compositions obtained in the Examples and Comparative Examples was measured at 25°C using a rotational viscometer (Toki Sangyo Co., Ltd., trade name TVE-35 type viscometer, rotor diameter 28 mm, angle 3°). The evaluation results are shown in Tables 1 and 2.

[0132] <Gelation time(s)>

[0133] The gelation time of the liquid epoxy resin compositions obtained in Examples and Comparative Examples was measured using an apparatus in accordance with JIS C 2161. The time required for 0.4 ml of the liquid epoxy resin composition to gel on a hot plate at 120° C. The evaluation results are shown in Tables 1 and 2.

[0134] <Glass transition temperature: Tg (°C)>

[0135] The liquid epoxy resin compositions obtained in the Examples and Comparative Examples were heated at 120°C for 30 minutes to form cured products. Differential scanning calorimetry (DSC) was performed to measure the glass transition temperature (Tg) (°C) under the following conditions and evaluated according to the following criteria. The measuring apparatus used was a DSC6220 manufactured by SII NanoTechnology Co., Ltd., sample weight: 10 mg, measurement atmosphere: nitrogen atmosphere, heating rate: 20°C / min, and measurement temperature: 25°C to 200°C. The evaluation results are shown in Tables 1 and 2.

[0136] Tensile shear bond strength (MPa)

[0137] The liquid epoxy resin compositions obtained in the Examples and Comparative Examples were applied to two copper plates (trade name "C1020P-1 / 2H," dimensions 1 mm × 15 mm × 100 mm, manufactured by Standard-Testpiece Co., Ltd.) in accordance with JIS K 6850. The plates were then bonded together and cured by heating at 120°C for 30 minutes. The bonded plates were then left at room temperature and the tensile shear bond strength was measured. The evaluation results are shown in Tables 1 and 2.

[0138] [Table 1]

[0139]

[0140] [Table 2]

[0141]

[0142] 3. Investigation

[0143] The liquid epoxy resin compositions of Examples 1 to 13 all contain (A) an epoxy resin, (B) a curing agent, and (C) a urea-based curing accelerator with a melting point of 230°C or less. Consequently, the cured products exhibit excellent gloss. Furthermore, a comparison of Examples 9 and 10 demonstrates that (D) the calcium carbonate with a surface resin acid treatment further imparts gloss to the cured products. Furthermore, Examples 6 and 10 demonstrate that the combined use of (C) a urea-based curing accelerator with a melting point of 230°C or less and (D) the calcium carbonate with a surface resin acid treatment achieves a gloss that exceeds that achieved when (C) a urea-based curing accelerator with a melting point of 230°C or less is added in large quantities.

[0144] Furthermore, Example 8, which is compared with Comparative Examples 1 to 3, shows that by using dicyandiamide and modified imidazole in combination as the curing agent (B), and further containing a urea-based curing accelerator (C), the reaction of dicyandiamide is accelerated during thermal curing, and an epoxy resin composition having gloss and excellent adhesiveness can be obtained even when cured at a low temperature of 120°C.

[0145] The liquid epoxy resin compositions of Comparative Examples 1 to 6 did not contain (C) a urea-based curing accelerator having a melting point of 230° C. or less, and the appearance of the cured products was matte.

[0146] The liquid epoxy resin composition of Comparative Example 4 contained a leveling agent, but the appearance of the cured product was matte. This indicates that the use of a leveling agent alone does not produce good gloss during curing.

[0147] The liquid epoxy resin composition of Comparative Example 5 contains a large amount of black pigment, but the appearance of the cured product is matte. This shows that the use of only black pigment does not produce good gloss during curing.

[0148] Comparative Examples 3 to 5 contain untreated calcium carbonate. Furthermore, the liquid epoxy resin composition of Comparative Example 6 does not contain calcium carbonate and is matte. Therefore, it is clear that the gloss loss in Comparative Examples 3 to 5 is not due to calcium carbonate.

Claims

1. A liquid epoxy resin composition, wherein Include: Epoxy resin A; Curing agent B; and Urea-based curing accelerator C with a melting point of 230°C or less.

2. The liquid epoxy resin composition according to claim 1, wherein Also includes: Calcium carbonate D with resin acid treatment on the surface.

3. The liquid epoxy resin composition according to claim 1, wherein The curing agent B is dicyandiamide and / or modified imidazole.

4. The liquid epoxy resin composition according to claim 1, wherein The liquid epoxy resin composition includes 0.5 to 20.0 parts by mass of the urea-based curing accelerator C relative to 100 parts by mass of the epoxy resin A.

5. The liquid epoxy resin composition according to claim 1, wherein The urea curing accelerator C has any of the following structural formulas (1) to (4):

6. An electronic component, wherein: have: The liquid epoxy resin composition according to any one of claims 1 to 5 as a sealant.

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