Photocurable adhesive composition having good aging stability, method for preparing same, and adhesive for bonding electronic components

Abstract

The present invention provides a photocurable adhesive composition having good aging stability, a method for preparing the same, and an adhesive for bonding electronic components. Specifically, in terms of 100 wt% of the weight of the photocuring adhesive composition, the photocuring adhesive composition comprises: 2-80 wt% of linear epoxy resin or cyclic epoxy resin containing a siloxane structure; 10 to 80% by weight of a cationically curable resin; and 0.1 to 5 wt% of a photoinitiator. The photocuring adhesive composition disclosed by the invention has good bonding stability, and has good bonding performance after being aged at high temperature and high humidity.

Description

Technical Field

[0001] This invention relates to the field of electronic component bonding technology, and more specifically, to a photocurable adhesive composition, a method for preparing the same, and an adhesive for bonding electronic components. Background Technology

[0002] In the current era of rapid development in the electronics and information industry, compared with thermosetting adhesives, photocurable adhesives have been widely used in electronic equipment assembly due to their advantages such as fast curing speed, short production cycle, and environmental friendliness. They not only need to meet the assembly requirements of efficient production of intelligent equipment, but also need to ensure the stable adhesion and bonding of commonly used substrates for electronic components.

[0003] Mainstream electronic equipment manufacturers have stringent requirements for the performance of adhesives: on the one hand, adhesives are required to have strong initial bonding strength to various substrates to ensure the structural stability of components after assembly; on the other hand, since electronic equipment may face complex environments such as high temperature and high humidity during service, adhesives must have excellent long-term aging stability and maintain sufficient bonding strength after long-term exposure to high temperature and high humidity environments to avoid abnormal equipment function due to bonding failure.

[0004] In existing technologies, photocurable epoxy adhesives are commonly used for bonding electronic components, but they have significant shortcomings in terms of aging stability. Especially under high temperature and humidity conditions, the bonding interface between traditional photocurable epoxy adhesives and the substrate is prone to hydrolysis and oxidation, leading to a significant decrease in bond strength and making it difficult to meet the requirements for long-term reliable operation of electronic devices. To improve the overall performance of adhesives, some technologies have attempted to introduce silicon-containing components into the formulation. However, silicon-containing components have poor compatibility with epoxy systems, often resulting in a decrease in the initial bonding performance of the adhesive, making it difficult to balance the contradiction between initial bond strength and aging stability.

[0005] Therefore, developing a photocurable adhesive composition that combines good initial bond strength with excellent high-temperature and high-humidity aging stability and is compatible with a variety of substrates and other commonly used materials for electronic components has become a pressing technical problem to be solved in this field. It is of great significance for promoting the upgrading of electronic equipment assembly processes and improving product reliability. Summary of the Invention

[0006] Based on the technical problems described above, the object of this invention is to provide a photocurable adhesive composition, a method for preparing the same, and an adhesive for bonding electronic components. The photocurable adhesive composition according to this invention exhibits good adhesion to metal substrates such as stainless steel, and particularly demonstrates good aging stability in terms of adhesion performance.

[0007] Specifically, according to one aspect of the present invention, a photocurable adhesive composition is provided, comprising, based on 100% by weight of the photocurable adhesive composition:

[0008] 2-80% by weight of linear or cyclic epoxy resins containing siloxane structures;

[0009] 10-80% by weight of cationic curable resin; and

[0010] 0.1-5% by weight of photoinitiator.

[0011] According to certain preferred embodiments of the present invention, the structure of the linear epoxy resin or cyclic epoxy resin containing the siloxane structure is represented by the following general formula (I):

[0012]

[0013] General Formula (I)

[0014] Wherein: R1, R2, R3 and R4 each independently represent C1-12 alkyl groups, and n is an integer from 1 to 10.

[0015] According to certain preferred embodiments of the invention, R1, R2, R3 and R4 each independently represent a C1-6 alkyl group.

[0016] According to certain preferred embodiments of the present invention, R1, R2, R3 and R4 are identical to each other.

[0017] According to certain preferred embodiments of the present invention, n is an integer from 1 to 4.

[0018] According to certain preferred embodiments of the present invention, the structure of the linear epoxy resin or cyclic epoxy resin containing the siloxane structure is represented by the following general formula (II):

[0019]

[0020] General Formula (II)

[0021] Where n is an integer between 3 and 10.

[0022] According to certain preferred embodiments of the present invention, n is an integer from 3 to 5.

[0023] According to certain preferred embodiments of the present invention, the photocurable adhesive composition comprises 3-60% by weight, preferably 5-50% by weight, of the linear epoxy resin or cyclic epoxy resin containing a siloxane structure.

[0024] According to certain preferred embodiments of the present invention, the cationic curable resin is a liquid alicyclic epoxy resin.

[0025] According to certain preferred embodiments of the present invention, the weight-average molecular weight of the cationic curable resin is in the range of 100-100,000.

[0026] According to certain preferred embodiments of the invention, the epoxy value of the cationic curable resin is in the range of 0.05-2 eq / 100g.

[0027] According to certain preferred embodiments of the invention, the photocurable adhesive composition comprises 18-75% by weight of the cationic curable resin.

[0028] According to certain preferred embodiments of the present invention, the cationic curable resin does not contain a siloxane structure.

[0029] According to certain preferred embodiments of the invention, the photocurable adhesive composition comprises 0.5-3% by weight of the photoinitiator.

[0030] According to certain preferred embodiments of the present invention, the photoinitiator is a cationic photoinitiator.

[0031] According to certain preferred embodiments of the present invention, the cationic photoinitiator is selected from one or more of diaryliodomonium salts, triarylthiomonium salts, alkylthiomonium salts, and iron aromatic salts.

[0032] According to certain preferred embodiments of the invention, the photocurable adhesive composition further comprises 4-30% by weight of a polyol.

[0033] According to certain preferred embodiments of the present invention, the polyol is selected from one or more of the group consisting of polyether polyols, polyester polyols, polycarbonate polyols and polyolefin polyols.

[0034] According to certain preferred embodiments of the present invention, the polyol is one or more selected from polycaprolactone polyol, polyether polyol, and polycarbonate polyol.

[0035] According to certain preferred embodiments of the present invention, the polyol is polycaprolactone diol, polycaprolactone triol, polycaprolactone tetraol, polyether diol, polyether triol, polyether tetraol, polycarbonate polyol, or a mixture thereof.

[0036] According to certain preferred embodiments of the present invention, the number average molecular weight of the polyol is 100-30000.

[0037] According to certain preferred embodiments of the invention, the photocurable adhesive composition further comprises a free radical photoinitiator.

[0038] According to certain preferred embodiments of the present invention, the free radical photoinitiator is selected from one or more of 1-hydroxycyclohexylphenyl ketone, benzophenone, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide and phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide.

[0039] According to certain preferred embodiments of the invention, the photocurable adhesive composition further comprises 0.1-18% by weight of an unsaturated acid.

[0040] According to certain preferred embodiments of the present invention, the unsaturated acid is an organic acid containing unsaturated double bonds and having a number-average molecular weight in the range of 70-1000.

[0041] According to certain preferred embodiments of the invention, the unsaturated acid is selected from one or more of the following groups: mono[2-(2-methyl-1-oxo-2-propenyl)oxy]ethyl ester of acrylic acid, methacrylic acid, crotonic acid and 1,2-phthalic acid, a dimer of acrylic acid / methacrylic acid and a trimer of acrylic acid / methacrylic acid.

[0042] According to certain preferred embodiments of the invention, the photocurable adhesive composition further comprises a toughening agent.

[0043] According to certain preferred embodiments of the present invention, the toughening agent is a core-shell rubber toughening agent.

[0044] According to certain preferred embodiments of the invention, the core-shell rubber toughening agent has a core formed of polybutadiene, styrene-butadiene rubber, polyacrylate or polysiloxane.

[0045] According to certain preferred embodiments of the invention, the photocurable adhesive composition comprises 9-25% by weight of the toughening agent.

[0046] According to certain preferred embodiments of the invention, the photocurable adhesive composition further comprises 0.1-18% by weight of a hydroxy acid.

[0047] According to certain preferred embodiments of the present invention, the hydroxy acid is an organic acid containing hydroxyl groups and having a number-average molecular weight in the range of 70-1000.

[0048] According to certain preferred embodiments of the present invention, the hydroxy acid is selected from one or more of the following groups: lactic acid, dimethylolpropionic acid, glycolic acid, hydroxypropionic acid, and dimethylolbutyric acid.

[0049] According to certain preferred embodiments of the invention, the photocurable adhesive composition further comprises a silane coupling agent.

[0050] According to certain preferred embodiments of the present invention, the silane coupling agent is selected from one or more of the group consisting of 3-glycidyl etheroxypropyltrimethoxysilane and 3-(methacryloyloxy)propyltrimethoxysilane.

[0051] According to certain preferred embodiments of the present invention, the photocurable adhesive composition further comprises one or more of aromatic epoxy resins, glycidyl ether epoxy resins, glycidyl ester epoxy resins, phenolic epoxy resins, and solid alicyclic epoxy resins.

[0052] According to certain preferred embodiments of the invention, the photocurable adhesive composition further comprises one or more of oxetane and vinyl ether.

[0053] According to another aspect of the present invention, a method for preparing a photocurable adhesive composition is provided, the method comprising uniformly mixing the components of the photocurable adhesive composition described above.

[0054] According to another aspect of the invention, an adhesive for bonding electronic components is provided, the adhesive comprising the photocurable adhesive composition described above.

[0055] Compared with existing photocurable adhesive compositions, the photocurable adhesive composition of the present invention has the advantage of achieving dual optimization of initial bond strength and aging stability: traditional photocurable epoxy adhesives struggle to balance initial bond strength and aging stability, either exhibiting high initial strength but severe degradation after aging, or good aging stability but insufficient initial strength. The present invention achieves a perfect balance between the two through the synergistic effect of the core components and the functional enhancement of the auxiliary components. Detailed Implementation

[0056] The present invention will now be described in further detail with reference to specific embodiments. It will be understood that other embodiments may be implemented without departing from the scope or spirit of the invention. Therefore, the following detailed description is non-limiting.

[0057] Unless otherwise specified, all figures used in this specification to represent characteristic dimensions, quantities, and physical properties should be understood to be modified by the term "about" in all cases. Therefore, unless otherwise stated, the numerical parameters listed in the foregoing specification are approximations, and those skilled in the art can appropriately modify these approximations to obtain the desired properties using the teachings disclosed herein.

[0058] As mentioned above, photocurable adhesives in the electronics field require strong initial adhesion and long-term stability. However, existing products show a sharp decrease in adhesion strength to metal substrates after high-temperature and high-humidity aging, and are difficult to adapt to various metal substrates. These contradictions urgently need to be resolved to meet equipment reliability requirements. This invention aims to solve the above technical problems.

[0059] Based on the above-mentioned technical problems, the object of the present invention is to provide a photocurable adhesive composition, a method for preparing the same, and an adhesive for bonding electronic components.

[0060] Specifically, according to one aspect of the present invention, a photocurable adhesive composition is provided, comprising, based on 100% by weight of the photocurable adhesive composition:

[0061] 2-80% by weight of linear or cyclic epoxy resins containing siloxane structures;

[0062] 10-80% by weight of cationic curable resin; and

[0063] 0.1-5% by weight of photoinitiator.

[0064] Specifically, the photocurable adhesive composition according to the present invention comprises a linear epoxy resin or a cyclic epoxy resin containing a siloxane structure as a mandatory component. From a molecular structure design perspective, the epoxy resin of the present invention can be selected from two general structures, corresponding to linear and cyclic siloxane-modified epoxy systems, respectively. By adjusting parameters such as the type of substituent and the degree of polymerization, synergistic effects with other components can be achieved.

[0065] Specifically, the structure of the linear epoxy resin or cyclic epoxy resin containing the siloxane structure is represented by the following general formula (I):

[0066]

[0067] General Formula (I)

[0068] Wherein: R1, R2, R3 and R4 each independently represent C1-12 alkyl groups, and n is an integer from 1 to 10.

[0069] For linear siloxane epoxy resins represented by general formula (I), the siloxane chain segment (-Si-O-) forms a linear backbone in its molecular structure, with epoxy functional groups connected to both ends or side chains, forming a composite structure of "siloxane flexible chain + epoxy reactive group". R1, R2, R3, and R4 are alkyl substituents, and their carbon chain length and structural symmetry significantly affect component compatibility and hydrolytic stability. Preferably, R1, R2, R3, and R4 are each independently C1-12 alkyl groups, more preferably C1-6 alkyl groups, and most preferably the same alkyl group (such as methyl, ethyl, or propyl). This is because C1-6 alkyl groups have moderate steric hindrance, which can protect the siloxane bond from hydrolytic attack through steric effects, improving aging stability, while avoiding decreased compatibility with cationic curable resins (such as alicyclic epoxy resins) due to excessively long carbon chains; the design of identical substituents ensures the symmetry of the molecular structure, further optimizing the system's dispersion uniformity and avoiding adhesion defects caused by local component aggregation.

[0070] In general formula (I), n represents the number of repeating units in the siloxane segment, which is an integer from 1 to 10, preferably an integer from 1 to 4. When n is too large (e.g., n>10), the hydrophobicity of the siloxane segment is too strong, which leads to a sharp decrease in compatibility with the epoxy system, resulting in phase separation. At the same time, the epoxy functional group density decreases, affecting the degree of curing crosslinking and initial bond strength. When n=1-4, the length of the siloxane segment is moderate. It can block moisture penetration to the bonding interface through its excellent resistance to humid heat, inhibiting hydrolysis, and can also relieve internal stress during the curing process with moderate flexibility, reducing bond failure caused by stress cracking during aging. At the same time, it ensures sufficient epoxy functional group density to ensure the efficiency of crosslinking reaction with cationic curable resin.

[0071] Commercially available examples of linear epoxy resins containing a siloxane structure represented by general formula (I) that can be used in this invention include X-40-2669 manufactured by Shin-Etsu Chemical Co., Ltd. of Japan, which has a structure represented by general formula (I), wherein: R1, R2, R3 and R4 are all methyl groups, and n is 1.

[0072] Alternatively, the structure of the linear epoxy resin or cyclic epoxy resin containing the siloxane structure is represented by the following general formula (II):

[0073]

[0074] General Formula (II)

[0075] Where n is an integer between 3 and 10.

[0076] For cyclic siloxane epoxy resins represented by general formula (II), their molecular structure is based on cyclic siloxanes (such as cyclotrisiloxanes and cyclotetrasiloxanes) as the core framework, with epoxy functional groups connected to silicon atoms by chemical bonds, forming a combination of a cyclic rigid framework and epoxy reactive groups. In general formula (II), n is limited to an integer from 3 to 10, preferably an integer from 3 to 5. Cyclic siloxane structures have higher structural stability than linear siloxanes. Their ring strain and molecular packing density can effectively improve the compactness of the cured coating, reduce the penetration channels of moisture and oxygen, and thus further enhance aging stability. The ring size of n=3-5 (such as cyclotrisiloxane n=3, cyclotetrasiloxane n=4) has the best reactivity and compatibility. If the ring size is too small (n<3), the ring strain is too large and the stability is insufficient. If the ring size is too large (n>5), the steric hindrance increases, the reactivity of the epoxy functional groups decreases, and the compatibility with other resins deteriorates.

[0077] Commercially available examples of cyclic epoxy resins containing a siloxane structure, represented by general formula (II), which can be used in this invention include KR-470 manufactured by Shin-Etsu Chemical Co., Ltd. of Japan, which has a structure represented by general formula (II), wherein: n is 4.

[0078] Regarding the content ratio, the content of the linear epoxy resin or cyclic epoxy resin containing the siloxane structure according to the present invention is 2-80% by weight, preferably 3-60% by weight, and more preferably 5-50% by weight. This content range is determined based on a synergistic consideration of multiple factors: when the content is less than 2% by weight, the introduction of the siloxane structure is insufficient, failing to form an effective moisture-resistant protective layer, making it difficult to improve aging stability, and the performance of the composition is essentially no different from that of traditional photocurable epoxy adhesives; when the content is greater than 80% by weight, the hydrophobicity and steric hindrance of the siloxane structure dominate, leading to a severe deterioration in compatibility with cationic curable resins, photoinitiators, and other components, resulting in problems such as layering and precipitation in the system. Simultaneously, the relative content of epoxy functional groups decreases, resulting in insufficient crosslinking density after curing, and a significant decrease in initial bond strength, failing to meet the basic requirements for adhesive strength of electronic components. In the preferred range of 3-60% by weight, especially 5-50% by weight, epoxy resin containing siloxane structure can form a uniform and stable mixture with other components. During the curing process, siloxane segments can migrate to the bonding interface to form a dense protective film, which blocks the erosion of the interface by the humid and hot environment. At the same time, epoxy functional groups fully participate in the crosslinking reaction, ensuring a balance between initial bonding strength and aging stability.

[0079] According to the technical solution of the present invention, the photocurable adhesive composition includes a cationic curable resin as an essential component. Preferably, the cationic curable resin of the present invention is a liquid alicyclic epoxy resin, and does not contain a siloxane structure. This selection is based on the unique performance advantages of alicyclic epoxy resins: compared with aromatic epoxy resins, alicyclic epoxy resins have lower viscosity, which is beneficial for coating and wetting of the composition, and is suitable for the process requirements of precision assembly of electronic components; their cationic curing reaction has higher activity and faster curing speed, which can meet the core requirement of "rapid prototyping" in photocuring processes; at the same time, the molecular structure of alicyclic epoxy resins does not contain easily oxidized groups such as benzene rings, resulting in better weather resistance and resistance to damp heat, and synergistic effect with epoxy resins containing siloxane structures can further improve aging stability.

[0080] According to the technical solution of the present invention, the weight-average molecular weight of the cationic curable resin is 100-100,000, preferably 1,000-50,000. When the weight-average molecular weight is too low (<100), the viscosity of the resin is too small, resulting in insufficient mechanical strength and poor adhesion of the cured coating; when the weight-average molecular weight is too high (>100,000), the viscosity of the resin increases significantly, leading to a decrease in the fluidity and coatability of the composition, making it difficult to uniformly wet the substrate surface, and worsening the compatibility with other components. Furthermore, internal stress is easily generated during the curing process, affecting the adhesion effect and aging stability.

[0081] According to the technical solution of the present invention, the epoxy value of the cationic curable resin is 0.05-2 eq / 100g, preferably 0.1-1.5 eq / 100g.

[0082] According to the technical solution of the present invention, the content of the cationic curable resin is 10-80% by weight, preferably 15-80% by weight. Determining this range requires a synergistic ratio with the epoxy resin containing a siloxane structure: when the content is less than 10% by weight, the proportion of the matrix resin is insufficient, making it impossible to form a continuous cross-linked network, and the mechanical strength and adhesion performance of the cured coating are difficult to meet the requirements; when the content is greater than 80% by weight, the relative content of the epoxy resin containing a siloxane structure is too low, its moisture and heat resistance modification effect is not obvious, and the aging stability of the composition cannot be effectively improved.

[0083] The mechanism of action of cationic curable resin is mainly reflected in the following aspects: As a matrix material, its epoxy functional groups undergo ring-opening polymerization under the action of cationic photoinitiators to form a three-dimensional cross-linked network, which firmly binds the components together and forms chemical bonds and physical adsorption with the substrate surface, providing basic adhesive strength; at the same time, the alicyclic groups in its molecular structure have good rigidity and stability, which can enhance the density of the cross-linked network and its resistance to environmental erosion, forming a "rigid matrix + flexible protection" composite system with epoxy resin containing siloxane structure, jointly improving the comprehensive performance of the composition.

[0084] According to the technical solution of the present invention, the photocurable adhesive composition includes a photoinitiator as an essential component. The content of the photoinitiator according to the present invention is 0.1-5% by weight, preferably 0.5-3% by weight, and preferably a cationic photoinitiator.

[0085] The preferred cationic photoinitiators of this invention include one or more of diaryliodoium salts, triarylthioium salts, alkylthioium salts, and iron aromatic salts. These photoinitiators exhibit excellent photosensitivity and reactivity, rapidly decomposing to generate active cations under ultraviolet or visible light irradiation, and possess good thermal stability, resisting decomposition and degradation during composition storage. Specifically, diaryliodoium salts and triarylthioium salts exhibit high photodecomposition efficiency and generate long-lived active cationic species, effectively initiating crosslinking reactions and ensuring complete curing; alkylthioium salts offer better solubility and compatibility with resin systems; and iron aromatic salts possess a wider light absorption range, adaptable to different wavelengths of light sources, and improved process adaptability.

[0086] Furthermore, in some embodiments of the present invention, a free radical photoinitiator may be added, such as 1-hydroxycyclohexylphenyl ketone, benzophenone, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, and phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide. The free radical photoinitiator generates free radicals under light irradiation, initiating a free radical polymerization reaction of unsaturated bonds, forming a synergistic curing system with the cationic polymerization reaction, further increasing the crosslinking density and the compactness of the coating, thereby enhancing the adhesive strength and aging stability.

[0087] In addition to the components mentioned above, the photocurable adhesive composition of the present invention may also include auxiliary components such as polyols, unsaturated acids, toughening agents, hydroxy acids, and silane coupling agents according to actual needs. Each auxiliary component, through synergistic effect with the core component, further optimizes the overall performance of the composition and expands its application scenarios.

[0088] Specifically, the polyol is one of the auxiliary components in the composition of the present invention, and its content is 4-30% by weight, preferably 8-25% by weight. The polyol molecule contains multiple hydroxyl groups (-OH), which can undergo ring-opening reactions with the epoxy groups of the epoxy resin to form hydroxyl ether bonds. Simultaneously, the hydroxyl groups can also form hydrogen bonds with active groups (such as hydroxyl and carboxyl groups) on the surface of the substrate, thereby improving the performance of the composition in multiple aspects. Preferred polyols of the present invention include one or more of polyether polyols, polyester polyols, polycarbonate polyols, and polyolefin polyols; more preferably, one or more of polycaprolactone polyols, polyether polyols, and polycarbonate polyols; and even more preferably, one or more of polycaprolactone diol, polycaprolactone triol, polycaprolactone tetraol, polyether diol, polyether triol, polyether tetraol, and polycarbonate polyols. These polyols have good solubility and compatibility, and can form a uniform and stable system with the necessary components. At the same time, their molecular chain segments have moderate flexibility, which can effectively improve the toughness of the cured coating, relieve internal stress during curing, and reduce adhesion failure caused by stress cracking during aging.

[0089] According to the technical solution of the present invention, the number average molecular weight of the polyol is 100-30000.

[0090] According to the technical solution of the present invention, the photocurable adhesive composition further comprises an unsaturated acid. The content of the unsaturated acid is 0.1-18% by weight, preferably 0.5-12% by weight, and its molecular structure contains both unsaturated double bonds (such as carbon-carbon double bonds) and carboxyl groups (-COOH), making it a multifunctional auxiliary component. The unsaturated acid according to the present invention is an organic acid containing unsaturated double bonds and having a number average molecular weight in the range of 70-1000, preferably one or more of acrylic acid, methacrylic acid, crotonic acid, and 1,2-phthalic acid mono[2-(2-methyl-1-oxo-2-propenyl)oxy]ethyl ester, acrylic acid / methacrylic acid dimer, and acrylic acid / methacrylic acid trimer.

[0091] According to the technical solution of the present invention, the photocurable adhesive composition further comprises a toughening agent. The addition of the toughening agent aims to further improve the toughness of the cured coating and reduce brittleness, and its content is 3-25% by weight. Preferably, the toughening agent of the present invention is a core-shell rubber toughening agent, which has a unique structure of "rigid shell + flexible core". The core is usually formed of polybutadiene, styrene-butadiene rubber, polyacrylate or polysiloxane, and the shell is a polymer with good compatibility with epoxy resin (such as methyl methacrylate polymer).

[0092] According to the technical solution of the present invention, the photocurable adhesive composition further comprises a hydroxy acid. The content of the hydroxy acid is 0.1-18% by weight, preferably 1-12% by weight, and its molecular structure contains both hydroxyl and carboxyl groups, possessing some of the functional characteristics of polyols and unsaturated acids. Preferred hydroxy acids of the present invention include one or more of lactic acid, dimethylolpropionic acid, glycolic acid, hydroxypropionic acid, and dimethylolbutyric acid, which have good solubility and reactivity.

[0093] Preferably, the photocurable adhesive composition further comprises a silane coupling agent. The silane coupling agent is an auxiliary component that improves the interfacial adhesion between the composition and the substrate. In this invention, one or more of 3-glycidyl etheroxypropyltrimethoxysilane and 3-(methacryloyloxy)propyltrimethoxysilane are preferred. These silane coupling agents contain two functional groups with different properties: one end is a siloxane group (-Si(OR)3) that can react with hydroxyl groups on the surface of inorganic substrates (such as glass or metal), and the other end is an epoxy group or unsaturated double bond that can react with organic resins (such as epoxy resins). During the curing process, the siloxane group hydrolyzes to generate silanol groups (-SiOH), which undergo a dehydration condensation reaction with the hydroxyl groups on the substrate surface to form a strong chemical bond; simultaneously, the epoxy group or unsaturated double bond reacts with the epoxy group and unsaturated bond in the resin system, tightly connecting the organic resin and the inorganic substrate, significantly improving the interfacial adhesion, reducing the risk of interfacial peeling under humid and hot conditions, and thus further enhancing aging stability.

[0094] The compositions of the present invention may also incorporate one or more of aromatic epoxy resins, glycidyl ether epoxy resins, glycidyl ester epoxy resins, phenolic epoxy resins, and solid alicyclic epoxy resins, as needed. These resins can serve as auxiliary matrix resins, adjusting the viscosity, curing speed, and crosslinking density of the composition to further optimize adhesive properties. Furthermore, one or more of oxetane and vinyl ethers may be added as reactive diluents. These compounds have low viscosity, effectively reducing the overall viscosity of the composition and improving coatability and wettability; simultaneously, they possess high cationic polymerization reactivity, participating in the curing and crosslinking reaction to increase crosslinking density.

[0095] According to another aspect of the present invention, a method for preparing a photocurable adhesive composition is provided, the method comprising uniformly mixing the components of the photocurable adhesive composition described above. There are no particular limitations on the specific steps and conditions of the preparation method according to the present invention, which can be implemented according to conventional processes in the prior art.

[0096] According to another aspect of the present invention, an adhesive for bonding electronic components is provided. This adhesive comprises the aforementioned photocurable adhesive composition and can be directly used for bonding smart devices (such as mobile phones, tablets, and smartwatches), bonding screens to housings, and encapsulating electronic components (such as chips and sensors). The photocurable adhesive of the present invention has a fast curing speed, which improves production efficiency. The cured coating has high density, protecting electronic components from external environmental corrosion. It also has high initial bond strength, capable of withstanding impacts and vibrations during daily use. Furthermore, its performance remains stable after high-temperature and high-humidity aging, ensuring that electronic components are protected from external environmental corrosion and guaranteeing long-term reliable operation.

[0097] The present invention will now be described in more detail with reference to embodiments. It should be noted that these descriptions and embodiments are intended to facilitate understanding of the present invention and are not intended to limit the invention.

[0098] Example

[0099] In this invention, unless otherwise specified, all reagents used are commercially available products and are used directly without further purification. Furthermore, "%" refers to "weight %" and "parts" refers to "parts by weight".

[0100] Table 1 below lists specific information about the raw materials used in the embodiments and comparative examples of the present invention.

[0101] Table 1 List of Experimental Materials

[0102]

[0103] Example 1 (E1):

[0104] As shown in Table 2 below, 29.9 g of X-40-2669, 45.8 g of cationic curable resin 2021P, 2.1 g of photoinitiator 1176 and 0.4 g of photoinitiator 184, 18.9 g of polyol P425 and 2.9 g of unsaturated acid PA-HEMA were uniformly mixed to obtain photocurable adhesive composition 1.

[0105] Examples 2-14 (E2-E14) and Comparative Examples (CE1-CE6):

[0106] Examples 2-14 (E2-E14) and Comparative Examples (CE1-CE6) were carried out in a manner similar to that of Example 1, except that the types and proportions of the various components in the various examples and comparative examples were changed as shown in Table 2 below, in order to prepare photocurable adhesive compositions 2-14 and comparative photocurable adhesive compositions 1-6.

[0107] Table 2. Raw material ratios for Examples 1-14 (E1-E14) and Comparative Examples 1-6 (CE1-CE6)

[0108]

[0109] Performance testing

[0110] Aging stability test

[0111] The aging stability tests were performed on the curing adhesive compositions 1-14 and comparative light-curing adhesive compositions 1-6 prepared in Examples 1-14 and Comparative Examples 1-6 according to the methods described in detail below, and the measurement results are shown in Table 3 below.

[0112] Specifically, a stainless steel substrate (50mm × 50mm) was prepared. It was cleaned with isopropanol to ensure the substrate surface was clean and free of impurities. Each sample of the curable adhesive compositions 1-14 and comparative examples 1-6 prepared in Examples 1-14 and 1-6 was coated onto the stainless steel substrate, controlling the coating area to be 3 mm × 3 mm and the coating thickness to be maintained at 1 mm. Subsequently, an LED 365 UV lamp (power density 500 mW / cm²) was used. 2 The coated adhesive was then cured by irradiation for 60 seconds. The coated stainless steel substrate was fixed on the thrust test fixture of an Instron universal testing machine, and a thrust was applied at a speed of 10 mm / min until the adhesive was completely peeled off from the surface of the stainless steel substrate. The strength value at the time of peeling was recorded as the bond strength value on the stainless steel before hygrothermal aging (unit: MPa).

[0113] Prepare a stainless steel substrate (50mm × 50mm). Clean it with isopropanol to ensure the substrate surface is clean and free of impurities. Apply each sample of the cured adhesive compositions 1-14 and comparative adhesive compositions 1-6 prepared in Examples 1-14 and Comparative Examples 1-6 to the stainless steel substrate, controlling the coating area to be 3 mm × 3 mm and the coating thickness to be maintained at 1 mm. Subsequently, use an LED 365 UV lamp (power density 500 mW / cm²). 2 The coated adhesive was then cured by irradiation for 60 seconds. The stainless steel substrate coated with the adhesive was then placed at a temperature of 85°C. oC. The stainless steel substrate was placed in a high-temperature and high-humidity aging chamber with a humidity of 85% for 3 days, and then allowed to stand at room temperature for 2 hours. Afterwards, the stainless steel substrate was fixed on the thrust test fixture of an Instron universal testing machine, and a thrust was applied at a speed of 10 mm / min until the adhesive was completely peeled off from the surface of the stainless steel substrate. The strength value at the time of peeling was recorded as the adhesive strength value after damp heat aging on the stainless steel (unit: MPa).

[0114] Among them, the evaluation criteria for the bond strength of adhesives used for bonding electronic components to stainless steel substrates before damp heat aging are as follows:

[0115] Excellent: Greater than or equal to 11 MPa;

[0116] Good: Greater than or equal to 5 MPa and less than 11 MPa; and

[0117] Difference: less than 5 MPa.

[0118] In addition, the evaluation criteria for the bond strength of adhesives used for bonding electronic components to stainless steel substrates after damp heat aging are as follows:

[0119] Excellent: Greater than or equal to 10 MPa;

[0120] Good: Greater than or equal to 5 MPa and less than 10 MPa; and

[0121] Difference: less than 5 MPa.

[0122] Table 3 Performance test results of Examples 1-14 (E1-E14) and Comparative Examples 1-6 (CE1-CE6)

[0123]

[0124] As can be seen from the results in Table 3 above, in Examples 1-14, the adhesive strength of all compositions before hygrothermal aging reached a good or better grade (≥5 MPa), with most examples reaching an excellent grade (≥11 MPa); after hygrothermal aging, the adhesive strength of all compositions reached an excellent grade (≥10 MPa), and the strength of some examples (such as E14) after aging was even higher than the initial strength (17.4 MPa vs 14.8 MPa). This indicates that the present invention, through the synergistic ratio of 2-80 wt% of epoxy resin containing siloxane structure and 10-80 wt% of cationic curable resin, not only ensures the initial bonding strength, but also effectively blocks the erosion of the bonding interface by moisture and oxygen through the hygrothermal resistance of the siloxane structure and the dense cross-linked network of the alicyclic epoxy resin, inhibiting the occurrence of aging reactions such as hydrolysis and oxidation, thus achieving the dual goal of "high initial strength and excellent aging stability".

[0125] In Comparative Example 1 (CE1), because no epoxy resin containing a siloxane structure was added, although the initial bond strength reached 16.2 MPa (excellent), the strength dropped sharply to 1.6 MPa (poor) after hygrothermal aging, highlighting the irreplaceable role of the siloxane structure in improving aging stability. Comparative Example 2 (CE2), because no cationic curable resin was added, had an initial bond strength of only 4.9 MPa (poor). Although the strength remained at 14.5 MPa (excellent) after aging, it could not meet the stringent requirements for initial bond strength in electronic components, demonstrating the crucial supporting role of cationic curable resin as a matrix resin in basic bond performance. In Comparative Examples 3-6 (CE3-CE6), the contents of epoxy resin containing a siloxane structure were 1 wt%, 0.6 wt%, 0.1 wt%, and 0.3 wt%, respectively, all below the 2 wt% lower limit specified in this invention. Test results showed that although the initial bond strength of these comparative examples reached the excellent level (14.6-17.0 MPa), the strength after damp heat aging was all below 5 MPa (poor), with CE5 showing a strength of only 1.9 MPa after aging. This indicates that when the content of epoxy resin containing siloxane structure is insufficient, an effective damp heat resistant protective layer cannot be formed, and aging stability cannot be improved.

[0126] Obviously, those skilled in the art can make various modifications and variations to this disclosure without departing from the spirit and scope of this disclosure. Therefore, if such modifications and variations fall within the scope of this invention, this disclosure is also intended to include such modifications and variations.

Claims

1. A photocurable adhesive composition, comprising, based on 100 parts by weight of the photocurable adhesive composition: 2 to 80 parts by weight of a linear or cyclic epoxy resin containing a siloxane structure; 10 to 80 parts by weight of a cationically curable resin; and 0.1 to 5 parts by weight of a photoinitiator.

2. The photocurable adhesive composition according to claim 1, wherein the structure of the linear or cyclic epoxy resin containing a siloxane structure is represented by the following general formula (I): General Formula (I) R1 R2 R3 R4 n wherein: R1, R2, R3, and R4 each independently represent a C1-12 alkyl group, and n is an integer of 1 to 10.

3. The photocurable adhesive composition according to claim 2, wherein R1, R2, R3, and R4 each independently represent a C1-6 alkyl group.

4. The photocurable adhesive composition according to claim 2, wherein R1, R2, R3, and R4 are the same as each other.

5. The photocurable adhesive composition according to claim 2, wherein n is an integer of 1 to 4.

6. The photocurable adhesive composition according to claim 1, wherein the structure of the linear or cyclic epoxy resin containing a siloxane structure is represented by the following general formula (II): General Formula (II) n wherein: n is an integer of 3 to 10.

7. The photocurable adhesive composition according to claim 6, wherein n is an integer of 3 to 5.

8. The photocurable adhesive composition according to claim 1, wherein the photocurable adhesive composition comprises 3 to 60 parts by weight of the linear or cyclic epoxy resin containing a siloxane structure.

9. The photocurable adhesive composition according to claim 1, wherein the cationically curable resin is a liquid alicyclic epoxy resin.

10. The photocurable adhesive composition according to claim 1, wherein the weight average molecular weight of the cationically curable resin is in the range of 100 to 100000.

11. The photocurable adhesive composition according to claim 1, wherein the epoxy value of the cationically curable resin is in the range of 0.05 to 2 eq / 100 g.

12. The photocurable adhesive composition according to claim 1, wherein the photocurable adhesive composition comprises 18 to 75 parts by weight of the cationically curable resin.

13. The photocurable adhesive composition according to claim 1, wherein the cationically curable resin does not contain a siloxane structure.

14. The photocurable adhesive composition according to claim 1, comprising 0.5 to 3 parts by weight of the photoinitiator.

15. The photocurable adhesive composition according to claim 1, wherein the photoinitiator is a cationic photoinitiator.

16. The photocurable adhesive composition according to claim 15, wherein the cationic photoinitiator is selected from one or more of diaryliodonium salts, triarylsulfonium salts, alkylsulfonium salts, and iron arene salts.

17. The photocurable adhesive composition according to claim 1, further comprising 4 to 30 parts by weight of a polyol.

18. The photocurable adhesive composition according to claim 1, wherein the polyol is one or more selected from the group consisting of polyether polyol, polyester polyol, polycarbonate polyol, and polyolefin polyol.

19. The photocurable adhesive composition according to claim 1, wherein the polyol is one or more of polycaprolactone polyol, polyether polyol, and polycarbonate polyol.

20. The photocurable adhesive composition according to claim 1, wherein the polyol is one or more of polycaprolactone diol, polycaprolactone triol, polycaprolactone tetraol, polyether diol, polyether triol, polyether tetraol, polycarbonate polyol.

21. The photocurable adhesive composition according to claim 1, wherein the number average molecular weight of the polyol is 100 to 30,000.

22. The photocurable adhesive composition according to claim 1, further comprising a radical photoinitiator.

23. The photocurable adhesive composition according to claim 22, wherein the radical photoinitiator is one or more selected from the group consisting of 1-hydroxycyclohexyl phenyl ketone, benzophenone, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, and phenyl bis(2,4,6-trimethylbenzoyl)phosphine oxide.

24. The photocurable adhesive composition according to claim 1, further comprising 0.1 to 18% by weight of an unsaturated acid.

25. The photocurable adhesive composition according to claim 24, wherein the unsaturated acid is an organic acid containing an unsaturated double bond and having a number average molecular weight in the range of 70 to 1,000.

26. The photocurable adhesive composition according to claim 24, wherein the unsaturated acid is one or more selected from the group consisting of acrylic acid, methacrylic acid, crotonic acid, mono[2-(2-methyl-l-oxo-2-propenyl)oxy]ethyl ester of 1,2-benzenedicarboxylic acid, dimer of acrylic acid / methacrylic acid, and trimer of acrylic acid / methacrylic acid.

27. The photocurable adhesive composition according to claim 1, further comprising a toughener.

28. The photocurable adhesive composition according to claim 27, wherein the toughener is a core-shell rubber-based toughener.

29. The photocurable adhesive composition according to claim 28, wherein the core-shell rubber-based toughener has a core formed of polybutadiene, styrene-butadiene rubber, polyacrylate, or polysiloxane.

30. The photocurable adhesive composition according to claim 27, comprising 9 to 25% by weight of the toughener.

31. The photocurable adhesive composition according to claim 1, further comprising 0.1 to 18% by weight of a hydroxy acid.

32. The photocurable adhesive composition according to claim 31, wherein the hydroxy acid is an organic acid containing a hydroxyl group and having a number average molecular weight in the range of 70 to 1,000.

33. The photocurable adhesive composition of claim 31, wherein the hydroxy acid is selected from one or more of the group consisting of lactic acid, dimethylolpropionic acid, glycolic acid, hydroxypropionic acid, and dimethylolbutyric acid.

34. The photocurable adhesive composition of claim 1, further comprising a silane coupling agent.

35. The photocurable adhesive composition of claim 34, wherein the silane coupling agent is selected from one or more of the group consisting of 3-glycidyloxypropyltrimethoxysilane and 3-(methacryloyloxy)propyltrimethoxysilane.

36. The photocurable adhesive composition of claim 1, further comprising one or more of an aromatic epoxy resin, a glycidyl ether epoxy resin, a glycidyl ester epoxy resin, a phenolic epoxy resin, and a solid alicyclic epoxy resin.

37. The photocurable adhesive composition of claim 1, further comprising one or more of an oxetane and a vinyl ether.

38. A method of making a photocurable adhesive composition, the method comprising uniformly mixing the components of the photocurable adhesive composition of any one of claims 1-37.

39. An adhesive for bonding electronic components, the adhesive comprising the photocurable adhesive composition of any one of claims 1-37.

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