Light-cured moisture-resistant and heat-resistant thiol epoxy resin adhesive

Abstract

The application discloses a light-cured moisture and heat resistant thiol epoxy resin adhesive, which comprises the following components in parts by weight: 100 parts of epoxy resin, 60-100 parts of multifunctional thiol (mercapto) silane coupling agent, 0.5-5 parts of light alkali generator and 0.5-5 parts of photosensitizer. The adhesive of the application cannot be cured immediately after UV light irradiation, and needs low-temperature heating to be completely cured, thus having the delayed curing characteristic. The thiol compound coupling agent used in the application does not contain an ester bond in the structure, the cured product is elastic, has excellent moisture and heat resistance, and still maintains good adhesive strength after high-temperature and high-humidity treatment.

Description

Technical Field

[0001] This invention relates to epoxy resin adhesives, and more particularly to a light-curable one-component epoxy resin, belonging to the field of adhesive technology. Background Technology

[0002] Photocurable epoxy resins are widely used in semiconductor packaging and bonding applications due to their low curing shrinkage, high bonding strength, good corrosion resistance, excellent electrical insulation properties, high production efficiency, energy saving, and environmental friendliness.

[0003] The photocuring mechanism of epoxy resins is generally based on cationic reactions caused by photoacid generators. Although it lacks the surface oxygen inhibition effect of free radical curing mechanisms such as acrylate monomers or oligomers, it is easily affected by environmental humidity and fails to cure. Furthermore, the superacids generated by photoinitiation can accelerate the corrosion of metal substrates, limiting its application in electronic packaging.

[0004] Photoalkali-generating agents are compounds that produce strongly alkaline substances when exposed to ultraviolet light. When used in conjunction with photosensitizers, they can be used to prepare high-performance one-component epoxy resin adhesives. Since the alkaline substances generated by photoinitiation generally do not cause corrosion of the substrate, and the curing process is not affected by environmental humidity or surface oxygen inhibition, they are ideal materials for semiconductor electronic component packaging.

[0005] Epoxy groups and thiols (mercapto groups) can undergo a click reaction in the presence of an alkaline catalyst, so photocurable thiol epoxy resin adhesives can be prepared using photoalkali-generating agents.

[0006] Li Zhiquan et al. published a paper titled "Synthesis and Performance Study of Reduced Amidine-Based LED Photoalkali Generators" (Imaging Science and Photochemistry, Vol 38, No. 1, 2020). The paper describes how the release of a strong base, DBN (amidine compounds), after ultraviolet irradiation can effectively initiate a thiol-epoxy group click reaction. However, the thiol structure used in the paper contains ester bonds and is prone to hydrolysis under high temperature and humidity conditions. This results in a significant decrease in the bonding strength or even failure of the epoxy resin cured product after exposure to high temperature and humidity (e.g., 85℃, 85% RH), making it unsuitable for applications requiring high temperature and humidity resistance, such as electronic and electrical components.

[0007] Patent CN113736403A discloses a one-component thermosetting thiol epoxy resin composition, comprising 20-30 parts of bisphenol A epoxy resin, 20-30 parts of epoxy resin containing rigid rings, 30-50 parts of isocyanurate-type polythiol compound (see molecular formula-1), 1-5 parts of latent curing agent, and 0.1-10 parts of additives. It can achieve rapid curing at low temperatures, and the cured product exhibits good resistance to damp heat and good adhesive strength under heat. Isocyanurate-type polythiol compounds, due to the absence of ester bonds, are not easily hydrolyzed and have good resistance to damp heat. However, these polythiol compounds are extremely expensive and difficult to obtain. Furthermore, the resulting cured product is very brittle and lacks toughness and elasticity, is not resistant to impact, and is prone to stress in thermal shock tests, leading to a decrease in adhesive strength. Therefore, using isocyanurate-type polythiol compounds to prepare photocurable thiol epoxy is not ideal.

[0008]

[0009] Molecular formula -1 (isocyanurate type polythiol compound TSIC)

[0010] Patent CN115029092A discloses a moisture- and heat-resistant one-component epoxy resin adhesive, its preparation method, and its application. The one-component epoxy resin adhesive comprises an epoxy resin, a toughening resin, a thiol curing agent (molecular formula -2), a curing accelerator, and nano-calcium carbonate. By limiting the curing agent to a thiol curing agent without ester bonds, the adhesive's hydrolysis resistance and moisture- and heat-resistant aging performance are greatly enhanced. However, while polyfunctional thiols containing ether bonds exhibit excellent hydrolysis resistance, their small molecular weight, high volatility, and extremely unpleasant odor make them unacceptable for electronic and electrical applications in enclosed environments. Therefore, using polyfunctional thiol compounds containing ether bonds to prepare photocurable thiol epoxy is also unsuitable.

[0011]

[0012] Molecular formula -2

[0013] Patent CN115232585A discloses a single-component epoxy resin composition resistant to wet heat hydrolysis, its preparation method, and its application. The composition comprises: 40-60 parts epoxy resin, 20-60 parts non-esterified thiol compound (molecular formula -3), 0.5-10 parts curing accelerator, 0.1-5 parts stabilizer, 0.1-5 parts silane coupling agent, and 0.1-40 parts filler. Because the thiol compound structure does not contain ester bonds but has two benzene rings, it exhibits good resistance to wet heat after curing and maintains good adhesive strength even after wet heat treatment. However, the synthesis steps of the thiol compound used in this invention are extremely cumbersome, involving large amounts of solvent, extremely long reaction times, and complex processes such as alkaline washing, water washing, solvent extraction, distillation, and purification, generating large amounts of wastewater and waste solvent. The synthesis process is environmentally unfriendly, the yield of the target product is low, and the cost is very high, making it unsuitable for the encapsulation and sealing applications of ordinary electronic components. Therefore, using this non-esterified thiol compound to prepare photocurable thiol epoxy is also not ideal.

[0014]

[0015] Molecular formula -3. Summary of the Invention

[0016] The purpose of this invention is to provide a multifunctional thiol silane coupling agent with a simple synthesis process and low cost, and a light-curing, moisture-resistant thiol epoxy resin adhesive composition containing the coupling agent.

[0017] The technical solution to achieve the purpose of this invention is:

[0018] In a first aspect, the present invention provides a multifunctional thiol (mercapto) silane coupling agent having the following structure:

[0019]

[0020] Where R represents methyl or methoxy, and n is an integer from 0 to 100.

[0021] In a second aspect, the present invention provides a method for preparing the multifunctional thiol (mercapto) silane coupling agent described in the first aspect, wherein the agent is synthesized by hydrolysis of mercaptopropylmethyldimethoxysilane coupling agent and / or mercaptopropyltrimethoxysilane coupling agent in the presence of a catalyst.

[0022] Preferably, the catalyst is selected from any one or more of inorganic acids, organic acids, organotin compounds, cation exchange resins, titanate compounds, α-silane coupling agents, Lewis acids or Lewis bases, and more preferably from any one or more of inorganic acids, organic acids and organotin compounds. The weight ratio of mercaptopropylmethyldimethoxysilane coupling agent and / or mercaptopropyltrimethoxysilane coupling agent to the catalyst is 100:0.05 to 2.

[0023] Specifically, inorganic acids and organic acids include hydrochloric acid, sulfuric acid, phosphoric acid, methanesulfonic acid, trifluoromethanesulfonic acid, and methylbenzenesulfonic acid.

[0024] Specifically, organotin compounds include dibutyl ketone oxime dibutyltin, diacetylacetone dibutyltin, ethyl diacetate dibutyltin, dibutyl dilaurate dibutyltin, dibutyltin bis(triethoxy)silyltin, dioctyltin bis(triethoxy)silyltin, and tetravalent tin compounds, which are the reaction products of diketone oxime dioxide and silicate compounds.

[0025] Thirdly, the present invention provides a photocurable, moisture- and heat-resistant thiol epoxy resin adhesive, comprising, by weight: 100 parts epoxy resin, 60-100 parts polyfunctional thiol (mercapto) silane coupling agent, 0.5-5 parts photoalkali-generating agent, and 0.5-5 parts photosensitizer.

[0026] Preferably, the epoxy resin is selected from one or a mixture of several of bisphenol A epoxy resin, bisphenol F epoxy resin, phenolic epoxy resin, glycidyl ester type epoxy resin, alicyclic epoxy resin, oxetane, etc., and more preferably one or two of bisphenol A epoxy resin and bisphenol F epoxy resin.

[0027] Preferably, the photobase generator (PBG) is selected from one or more of the following: cobalt ammonium complex, carbamate, ketooxime ester, formamide, quaternary ammonium salt, triphenylmethanol, and tetraphenylborates of organic amines and their derivatives, such as triethylamine, tributylamine, 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), and 1,5,7-triazidobicyclo[4.4.0]dec-5-ene (TBD), with a preference for tetraphenylborates of organic amines.

[0028] Preferably, the photosensitizer is selected from any one or more of benzoin and its derivatives, benzoyl derivatives, dialkoxyacetophenone, α-hydroxyalkylphenyl ketone, α-aminealkylphenyl ketone, acylphosphine oxide, benzophenone and its derivatives, thioxanthones, anthraquinones, fluorenones, etc., with thioxanthones being preferred. Considering ease of use and economy, isopropylthioxanthonone (ITX) is more preferred.

[0029] Preferably, the adhesive may further comprise a silane coupling agent, including but not limited to: one or more of γ-methacryloxypropyltrimethoxysilane, vinyltris(β-methoxyethoxy)silane, vinyltrimethoxysilane, vinyltriethoxysilane, anilinemethyltriethoxysilane, γ-(2,3-epoxypropoxy)propyltrimethoxysilane, β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, and γ-ureapropyltriethoxysilane.

[0030] Preferably, the adhesive may also contain various fillers, including but not limited to one or more of fused silica, glass fiber powder, and glass microspheres.

[0031] Preferably, the adhesive may also contain antioxidants, flame retardants, diluents, adhesion promoters, dyes, pigments, defoamers, leveling agents, etc., which are known to those skilled in the art and will not be elaborated here.

[0032] Fourthly, the present invention provides a method for using the light-curing, moisture-resistant, heat-resistant thiol epoxy resin adhesive described in the third aspect. After dispensing the adhesive, the adhesive is first irradiated with ultraviolet light, then the bonded specimens are aligned and bonded together, and then cured.

[0033] Ideally, depending on the production process requirements, it can be further cured by short-time heating or by being left to cure at room temperature.

[0034] Compared with the prior art, the advantages of the present invention are:

[0035] (1) The photocurable, moisture-resistant, heat-resistant thiol epoxy resin adhesive of the present invention cannot be cured immediately after being exposed to light, and has delayed curing characteristics. It can also be used for photocurable bonding of opaque materials.

[0036] (2) The photocurable moisture-resistant thiol epoxy resin adhesive of the present invention has excellent moisture resistance and maintains its original bonding strength without decreasing after high temperature and high humidity test. Detailed Implementation

[0037] The epoxy resin described in this invention is selected from one or more of the following: bisphenol A epoxy resin, bisphenol F epoxy resin, phenolic epoxy resin, glycidyl ester type epoxy resin, alicyclic epoxy resin, oxetane, etc., in order to achieve the required viscosity, hardness, or reaction rate.

[0038] The initiation efficiency of photo-alkali-generating agents is generally lower than that of free radical and cationic photoinitiators, thus requiring the use of photosensitizers to achieve sufficiently high initiation efficiency. Unlike the rapid curing mechanism of acrylate free radical polymerization after light exposure, photo-alkali-generating agents produce strongly basic groups after UV (ultraviolet) light exposure, promoting the click reaction of thiol-epoxy groups and initiating anionic polymerization. However, they do not cure immediately and generally require short-term heating or placement at room temperature for a period of time to fully cure, exhibiting a delayed curing effect. Therefore, the thiol epoxy adhesive of this invention can also be used for bonding opaque materials. Unlike traditional free radical curing or cationic curing adhesives, which require bonding before light exposure, the photocurable thiol epoxy adhesive of this invention is used by first applying UV light after dispensing, then aligning and bonding the samples to be bonded. Depending on the production process requirements, further short-term heat curing or room temperature curing can be performed. The UV irradiation dose affects the subsequent heat curing speed; a higher irradiation dose requires a lower temperature or a shorter heating time for the same temperature.

[0039] Below are the synthesis methods of polyfunctional thiol silane coupling agents and formulation examples of light-cured, moisture-resistant, heat-resistant thiol epoxy resin adhesives.

[0040]

Thiol Silane Coupling Agent-1

[0041]

Thiol Silane Coupling Agent-2

[0042]

Thiol Silane Coupling Agent-3

Thiol Silane Coupling Agent-4

[0043] [Example-1]-[Example-4] The formulations are shown in Table 1, and the preparation process is the same. Epoxy resin, thiol silane coupling agent, photoalkali-generating agent, photosensitizer, etc., are added separately to a planetary mixer and vacuum-stirred until uniformly mixed.

[0044] The formulations for Comparative Examples 1-3 are shown in Table 1, and the preparation processes are the same.

[0045] The test results for each embodiment and comparative example are shown in Table 1.

[0046] Table 1

[0047] Example 1 Example 2 Example 3 Example 4 Comparative Example-1 Comparative Example-2 Comparative Example-3 850S 100 100 100 100 830S 100 100 100 Thiol silane coupling agent-1 90 Thiol silane coupling agent-2 90 Thiol silane coupling agent-3 90 Thiol silane coupling agent-4 90 PEMP 70 70 TSIC 70 Photo-alkali-producing agent WPBG-300 2.5 3.0 2.5 3.0 Photo-alkali-producing agent WPBG-345 3.0 2.0 2.0 ITX 2.0 2.0 2.0 2.0 2.0 2.0 2.0 Fe / Fe shear strength (MPa) <![CDATA[Irradiation dose 1000 mJ / cm 2 + 60 °C * 20 min]]> 5.5 6.1 6.8 7.1 18.1 25.1 18.3 After 85℃ and 85% RH for 500 hours 5.5 6.2 6.9 7.4 3.6 14.3 1.5 <![CDATA[Irradiation dose: 1000 mJ / cm 2 + 25 °C × 24 h]]> 5.2 5.8 6.2 6.4 15.4 21.2 16.5 After 85℃ and 85% RH for 500 hours 5.8 5.7 6.6 6.9 2.8 13.4 2.3

[0048] Note: 850S is a bisphenol A type epoxy resin from Zhonglan International Chemical Co., Ltd., 830S is a bisphenol F type epoxy resin from Zhonglan International Chemical Co., Ltd., PEMP is pentaerythritol tetrakis(3-mercaptopropionic acid) ester, TsIC is an isocyanurate type polythiol compound with molecular formula -1, and the photoalkalizing agents WPBG-300 and 345 are commercially available products from Wako Pure Chemical Industries, Ltd. of Japan. They belong to the organic guanidine class of tetrakis(3-fluorophenyl borate) and generate strong base biguanides when exposed to light. ITX is a commercially available isopropylthioxanthrone.

[0049] Comparing the results of Examples 1 to 4 in Table 1, it can be found that the hydrolyzed polyfunctional thiol silane coupling agent combined with the photoalkalizing agent and photosensitizer ITX, under high-pressure mercury lamp irradiation at 1000 mJ / cm², [the following results are observed]. 2Afterwards, it can be cured at room temperature (25°C) or rapidly cured by heating at 60°C for 20 minutes. Regardless of whether it is cured at room temperature or by heating, the shear strength does not decrease after high temperature and humidity; in some formulations, the shear strength even increases, possibly due to further cross-linking reactions at high temperatures. The excellent moisture and heat resistance of the polyfunctional thiol silane coupling agent formulation described in this invention may be partly due to its alkoxysilane structure, which produces a strong chemical anchoring effect with the bonded substrate. While Comparative Examples 1 and 3 showed relatively high initial shear strength, their shear strength decreased sharply after high temperature and humidity, indicating that thiol compounds containing ester bonds undergo severe hydrolysis under high temperature and humidity conditions, leading to molecular chain breakage, making them unsuitable for applications requiring stringent moisture resistance, such as bonding or sealing of electronic and electrical components. The thiol compound in Comparative Example 2 does not contain ester bonds, and its shear strength decreases much less after high temperature and humidity than Comparative Examples 1 and 3, which contain ester bonds, but still shows a significant decrease. Furthermore, the cured product is very hard and brittle, which is unfavorable for drop tests.

Claims

1. A light-curing, moisture- and heat-resistant thiol epoxy resin adhesive, characterized in that, By weight, it includes: 100 parts epoxy resin, 60-100 parts multifunctional thiol (mercapto) silane coupling agent, 0.5-5 parts photoalkali-generating agent, and 0.5-5 parts photosensitizer; Among them, the multifunctional thiol (mercapto) silane coupling agent has the following structure: ； Where R represents methyl or methoxy, and n is an integer from 0 to 100; The epoxy resin is selected from one or a mixture of several of the following: bisphenol A epoxy resin, bisphenol F epoxy resin, phenolic epoxy resin, glycidyl ester type epoxy resin, and alicyclic epoxy resin.

2. The adhesive as described in claim 1, characterized in that, Multifunctional thiol (mercapto) silane coupling agents are synthesized by hydrolysis of mercaptopropylmethyldimethoxysilane coupling agent and / or mercaptopropyltrimethoxysilane coupling agent in the presence of a catalyst.

3. The adhesive as described in claim 2, characterized in that, The catalyst is selected from any one or more of the following: inorganic acids, organic acids, organotin compounds, cation exchange resins, titanate compounds, α-silane coupling agents, Lewis acids, or Lewis bases.

4. The adhesive as described in claim 2, characterized in that, The catalyst is selected from any one or more of inorganic acids, organic acids, and organotin compounds.

5. The adhesive as described in claim 2, characterized in that, The weight ratio of mercaptopropylmethyldimethoxysilane coupling agent and / or mercaptopropyltrimethoxysilane coupling agent to catalyst is 100:0.05~2.

6. The adhesive as described in claim 1, characterized in that, The epoxy resin is selected from one or both of bisphenol A epoxy resin and bisphenol F epoxy resin.

7. The adhesive as described in claim 1, characterized in that, The photoalkali-producing agent is selected from one or more of the following: cobalt ammonium complex, carbamate, ketoxime ester, formamide, quaternary ammonium salt, triphenylmethanol, triethylamine, tributylamine, 1,8-diazabicyclo[5.4.0]undec-7-ene DBU, TBD, WPBG-300, and WPBG-345.

8. The adhesive as described in claim 1, characterized in that, The photosensitizer is selected from any one or more of benzoin and its derivatives, benzoyl derivatives, dialkoxyacetophenone, α-hydroxyalkylphenyl ketone, α-aminealkylphenyl ketone, acylphosphine oxide, benzophenone and its derivatives, thioxanthone compounds, anthraquinone compounds, and fluorenone compounds.

9. The adhesive as claimed in claim 1, characterized in that, The photosensitizer is a thioxanthone compound.

10. The adhesive as claimed in claim 1, characterized in that, The photosensitizer is isopropylthioxanthone (ITX).

11. A method of using the adhesive as described in any one of claims 1-10, characterized in that, After applying the adhesive, the sample is first irradiated with ultraviolet light, then the specimens to be bonded are aligned and bonded together, and then cured.

12. The method of use as described in claim 11, characterized in that, The curing process refers to curing by heating or curing at room temperature.

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