Single-component epoxy adhesive for magnetic core bonding

Abstract

The application discloses a single-component epoxy adhesive for magnetic core bonding, which comprises A) a rigid ring structure containing epoxy resin prepolymer, accounting for 30-60% of the total weight percentage of A-D; B) an organic silicon modified anhydride curing agent, accounting for 15-40% of the total weight percentage of A-D; C) a liquid anhydride curing agent, accounting for 15-42% of the total weight percentage of A-D; D) a curing accelerator, accounting for 0.5-5% of the total weight percentage of A-D; and E) glass microbeads, accounting for 5-30% of the total weight percentage of A-D. The adhesive has the characteristics of high adhesion, good heat resistance, low linear thermal expansion coefficient, low curing volume shrinkage, excellent wet heat resistance and excellent heat shock resistance, and can form a bonding layer with high uniformity in thickness between the magnetic cores.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of adhesives, and particularly relates to a single-component epoxy adhesive for magnetic core bonding. BACKGROUND

[0002] A magnetic core refers to a sintered magnetic metal oxide composed of various iron oxide mixtures, and is a key part of electronic components and has a wide application in transformers, inductors and electromagnetic components. In order to facilitate assembly, in addition to ring-shaped products, the magnetic cores of transformers and inductors are generally composed of two parts, such as commonly known PQ type, EE type, EI type, ER type and EP type. During assembly, the two parts of the magnetic core are bonded and fixed together to form a reliable magnetic circuit structure, maintain the stability of inductance, and prevent the magnetic core from vibrating and generating noise under the action of a magnetic field.

[0003] The relative position, fitting gap and glue layer thickness of the upper and lower magnetic cores bonded by magnetic core bonding have precise requirements. Traditional production processes generally use non-Newtonian fluid single-component epoxy adhesives with high viscosity and slow flow rate. After glue application, the inductance is adjusted to the target value by means of longitudinal pressure regulation and reciprocating shear motion of the upper and lower magnetic cores in the transverse direction. In the field of electronics and electrical appliances, the demand for miniaturization and integration is increasingly high, and the accuracy and consistency of the bonding thickness of the adhesive are required to be higher. The traditional production process has poor control accuracy and consistency of the bonding thickness, and is difficult to realize automatic control, resulting in low production efficiency.

[0004] The magnetic core bonding adhesive also requires high bonding strength after curing, low linear thermal expansion coefficient, impact resistance, vibration resistance, low water absorption, moisture and water resistance, moisture resistance, and small shrinkage rate during curing. After curing, the original state can be maintained, and the inductance difference before and after curing is small. In addition, if the material linear thermal expansion coefficient (CTE) and elastic modulus between the bonding material and the magnetic core material do not match, a large internal stress will be generated under cold and hot impact conditions. When the internal stress is too large and exceeds the strength of the magnetic core material, cracks or even breakage of the magnetic core material will occur, resulting in unqualified electrical performance of the product and seriously affecting the reliability of the product. The traditional magnetic core bonding adhesive often reduces the thermal expansion coefficient of the adhesive by increasing the crosslinking degree of the adhesive (such as the magnetic core bonding nano single-component ductile epoxy composite and its preparation method disclosed in patent document CN201711014852.6), but the crosslinking degree of the adhesive increases, and the curing shrinkage rate also increases, resulting in a large inductance difference before and after curing of the transformer or inductor, which is not conducive to the accurate control of inductance. SUMMARY

[0005] The present application provides a kind of epoxy resin adhesive for magnetic core bonding with high adhesion, low linear thermal expansion coefficient, low curing volume shrinkage, excellent wet heat resistance, the viscosity of the epoxy adhesive is low, it also contains the spacer particle of control bonding gap, and the control accuracy and consistency of bonding thickness are both good, very beneficial to automation control.

[0006] The present application provides a kind of epoxy adhesive for magnetic core bonding with high adhesion, low linear thermal expansion coefficient, low curing volume shrinkage, excellent wet heat resistance, the viscosity of the epoxy adhesive is low, it also contains the spacer particle of control bonding gap, and the control accuracy and consistency of bonding thickness are both good, very beneficial to automation control.

[0007] A) epoxy resin containing rigid annular structure;

[0008] B) organic silicon modified anhydride curing agent with the following structure (I):

[0009]

[0010] wherein R1 to R4 are each independently a monovalent hydrocarbon group having 1 to 10 carbon atoms, and n represents an integer of 10 to 200;

[0011] C) liquid anhydride curing agent, which is liquid at room temperature, and only contains one anhydride functional group in the molecular structure, and the room temperature refers to 25℃;

[0012] D) curing accelerator;

[0013] E) glass microbeads, the coefficient of variation of the average particle size of the glass microbeads should be less than 5%, and the addition amount of the glass microbeads is 5-30wt%, accounting for all weight percentages of A-D;

[0014] F) other additives, and the addition amount of any other additive is 0-0.2wt%, accounting for all weight percentages of A-D.

[0015] The components are described in detail as follows:

[0016] 1) Component A: epoxy resin containing rigid annular structure

[0017] The epoxy resin containing rigid annular structure is an epoxy resin prepolymer containing rigid annular structure with two epoxy functional groups at the end of molecular chain.

[0018] The epoxy resin containing rigid annular structure can be selected from one or a combination of naphthalene type epoxy resin, fluorene type epoxy resin, dicyclopentadiene phenol epoxy resin. These epoxy resins contain rigid annular aromatic hydrocarbon structure with high heat resistance, low water absorption, low linear thermal expansion coefficient, low shrinkage characteristics. These epoxy resins containing rigid annular structure have ultra-low water absorption, low linear thermal expansion coefficient and low curing volume shrinkage after curing.

[0019] The naphthalene type epoxy resin can be selected from any one or more of HP-4032, HP-4701, HP-4700, HP-4770 of Japan Ink Chemical Industry Co., Ltd., or any one or two of NC-7300L, NC-7000L of Japan Chemical.

[0020] The fluorene type epoxy resin can be selected from any one or more of EX-1010, EX-1020, EX-1030, EX-1040, EX-1050 of Nagase Chemicals Technology Co., Ltd.

[0021] The dicyclopentadiene phenol epoxy resin can be selected from any one or more of SQDN-301, SQDN-302, SQDN-303 of Jinan Shengquan Group.

[0022] The epoxy resin containing rigid ring structure preferably has a softening point lower than 80°C, more preferably a softening point lower than 60°C, and the viscosity of the one-component epoxy adhesive for magnetic core bonding prepared by using the epoxy resin with low softening point is lower, and the construction is easier.

[0023] The epoxy resin containing rigid ring structure is added in an amount of 30-60wt%, accounting for all the weight percentages of A-D.

[0024] 2) Component B: organosilicon modified anhydride curing agent with the following structure (I)

[0025]

[0026] wherein R1 to R4 are each independently a monovalent hydrocarbon group having 1 to 10 carbon atoms, and n represents an integer of 10 to 200.

[0027] In formula (I), R 1 to R 4 , which can be the same or different, are monovalent hydrocarbon groups of 1 to 10 carbon atoms, preferably monovalent hydrocarbon groups of 1 to 6 carbon atoms, such as straight-chain, branched-chain or cyclic alkyl groups, such as methyl, ethyl, propyl, isopropyl, n-butyl and the like, tertiary butyl and cyclohexyl, straight-chain, branched-chain or cyclic alkenyl groups, such as ethenyl, allyl, propenyl, butenyl, hexenyl and cyclohexenyl, aryl groups, such as phenyl and tolyl, and aralkyl groups, such as benzyl and phenethyl. These groups can be included in any desired proportions.

[0028] The subscript n in structure (I) represents the number of repeating units, and n is an integer of 10 to 200. If n is less than the minimum value of this range, the toughness is insufficient, and the shear strength after thermal shock aging is insufficient; if n is greater than the maximum value of this range, the viscosity of the organosilicon modified anhydride curing agent is too high, and it cannot be used, and it has a large influence on the linear thermal expansion coefficient of the cured epoxy resin.

[0029] The amount of the liquid anhydride curing agent added is 15-42 wt%, based on the total weight of A-D.

[0030] 3) Component C: Liquid anhydride curing agent

[0031] The liquid anhydride curing agent is an anhydride which is liquid at room temperature. The liquid anhydride can reduce the viscosity of the adhesive system.

[0032] The liquid anhydride curing agent can be selected from one or more of methyltetrahydrophthalic anhydride, methylhexahydrophthalic anhydride, methyl nadic anhydride, dodecenyl succinic anhydride. These liquid anhydride curing agents only contain one anhydride functional group in their molecular structure.

[0033] The anhydride curing agent contains one anhydride functional group in its molecular structure, and the crosslinking degree after curing is 2. The adhesive using this anhydride curing agent has a smaller curing shrinkage than the adhesive using an anhydride curing agent containing two or more anhydride functional groups.

[0034] The amount of the liquid anhydride curing agent added is 15-42 wt%, based on the total weight of A-D. If the amount of the liquid anhydride curing agent added is less than the minimum value of this range, the viscosity of the single-component epoxy adhesive for bonding magnetic cores will be too high, which is not conducive to construction. If the amount of the liquid anhydride curing agent added is greater than the maximum value of this range, the viscosity of the single-component epoxy adhesive for bonding magnetic cores will be too low, and the flowability will be too good, which is prone to sagging.

[0035] 4) Component D: Curing accelerator

[0036] The curing accelerator is selected from imidazole compounds, boron trifluoride-amine adducts, microencapsulated latent amine curing agents, and the like known in the art. Suitable imidazole compounds include, but are not limited to, 2-methyl-4-ethylimidazole (2E4MZ), 2-phenylimidazole (2PZ), 2-methylimidazole (2MZ), and 1-benzyl-2-phenylimidazole (1B2PZ). Suitable microencapsulated latent amine curing agents include HX-3722, HX-3742, HX-3921HP, HX-3922HP, and the like from Asahi Kasei.

[0037] The amount of the curing accelerator added is 0.5-5 wt%, based on the total weight of A-D.

[0038] 5) Component E: Glass microbeads

[0039] The glass microbeads are spacing particles for controlling the bonding gap. The glass microbeads can be in the shape of an ellipse, droplet, or sphere, and the glass microbeads preferably have a smooth surface. The glass microbeads are preferably solid glass beads, in particular solid glass spheres. The glass material used is not subject to any particular limitation, as long as it is compatible with the adhesive.

[0040] The average diameter of the glass microbeads is 10-150 μm, and the coefficient of variation of the average diameter should be less than 5%. The shape of the glass microbeads is preferably spherical, and for non-spherical microbeads, the diameter each refers to the largest measurable diameter of the glass microbeads.

[0041] The addition amount of the glass microbeads is 5-30 wt%, based on the total weight percentage of A-D. If the addition amount of the glass microbeads is too small, the spacing effect cannot be fully exerted, and the magnetic core bonding gap becomes uneven, and if the addition amount of the glass microbeads is too large, the contact area of the magnetic core bonding single-component epoxy adhesive with the magnetic core bonding surface becomes small, which will affect the bonding force.

[0042] If the coefficient of variation of the glass microbeads is greater than 5%, the magnetic core bonding gap will become uneven, which is not conducive to the automatic bonding of the magnetic core.

[0043] 6) Component F: Other additives

[0044] Optionally, the magnetic core bonding single-component epoxy adhesive can also include other additives, such as leveling agents, defoaming agents, wetting dispersants, etc. The addition amount of any additive is 0-0.2 wt%, based on the total weight percentage of A-D.

[0045] The leveling agent preferably uses one of BYK-333, BYK-307, BYK-378, BYK-310 or BYK-354 of BYK-Chemie.

[0046] The defoaming agent preferably uses one of BYK-066N, BYK-055, BYK-A535, BYK-054, BYK-088, BYK-1796 or BYK-1790 of BYK-Chemie.

[0047] The wetting dispersant preferably uses one of BYK-W094, BYK-111 or BYK2700 of BYK-Chemie.

[0048] The content of each component of the magnetic core bonding single-component epoxy adhesive of the present application can be selected within the range described above, and a selectable component content is as follows:

[0049] A magnetic core bonding single-component epoxy adhesive comprises the following components:

[0050] A) Epoxy resin prepolymer containing rigid linked ring structure, 40-50 wt%, based on the total weight percentage of A-D;

[0051] B) Silicone-modified anhydride curing agent having the above structure (I), 15-20 wt%, based on the total weight percentage of A-D;

[0052] C) liquid anhydride curing agent, 19-42 wt% of the total weight percentage of A-D;

[0053] D) curing accelerator, 1.5-2.0 wt% of the total weight percentage of A-D;

[0054] E) glass microbeads, 7-25 wt% of the total weight percentage of A-D.

[0055] The present application uses epoxy resin containing rigid bi-cyclic structure and anhydride curing agent to form the main component of adhesive system. Compared with other curing agents, the anhydride curing agent has small curing volume shrinkage, high rigidity, high heat distortion temperature, good heat resistance, low linear thermal expansion coefficient, excellent mechanical and electrical properties; but due to the ester bond after anhydride curing, it is easy to be corroded by alkali and has water absorption, and it cannot be used as a curing agent for epoxy resin adhesive for magnetic core bonding in general sense, but the present application uses epoxy resin containing rigid bi-cyclic structure to solve this problem. Since the rigid bi-cyclic structure is arranged in a mesh chain, the free volume is reduced, the linear thermal expansion coefficient and water absorption are reduced, thereby protecting the ester bond after anhydride curing to a certain extent, and inhibiting the hydrolysis of ester group. At the same time, the rigidity of rigid bi-cyclic structure further reduces the curing volume shrinkage. In addition, the present application uses 2-functional rigid bi-cyclic structure epoxy resin and 2-functional anhydride curing agent. Compared with the conventional epoxy resin adhesive, the present application has low crosslinking degree after curing, and the curing volume shrinkage is smaller. This makes the one-component epoxy adhesive for magnetic core bonding of the present application have the advantages of good heat resistance, low linear thermal expansion coefficient and small curing volume shrinkage, overcoming the shortcomings of conventional epoxy adhesive that cannot simultaneously reduce the linear thermal expansion coefficient and improve the heat resistance by increasing the crosslinking degree.

[0056] The present application uses silicone-modified anhydride curing agent, which is effective in improving the heat resistance, mechanical strength and electrical properties of the cured epoxy resin composition due to the strong rigidity of the anhydride after curing in the molecule, and the siloxane chain contained in the molecule is effective in reducing the elasticity of the cured epoxy resin composition to form a flexible elastomer. The introduction of long-chain silicone segment reduces the elastic modulus and reduces the internal stress. Controlling and reducing the internal stress caused by the bonding material is of great significance to improve the reliability and long-term stability of the transformer and inductor.

[0057] At the same time, silicone belongs to hydrophobic structure, and the use of silicone segment to toughen epoxy resin is also beneficial to improve the hydrophobicity of epoxy resin, thereby having a certain protective effect on ester group and further inhibiting the hydrolysis of ester group.

[0058] The organic silicon modified anhydride curing agent connects two anhydride groups by a long-chain organic silicon segment, and the high flexibility of the long-chain organic silicon segment does not increase the effective crosslinking degree of the anhydride, so the organic silicon modified anhydride curing agent has little effect on the curing volume shrinkage rate.

[0059] The liquid anhydride curing agent and the organic silicon modified anhydride curing agent are combined in the present application, the viscosity of the system is reduced, glass microbeads with a fixed thickness are added as spacer particles, the longitudinal pressure and transverse shear force required in the upper and lower magnetic core bonding process are significantly reduced, the processing difficulty is significantly reduced, the inductance consistency is significantly improved, the adhesive between the spacer particles and the bonding surface can be fully removed during the magnetic core bonding process, the magnetic core bonding gap is more accurate and uniform, and the situation of one side being high and the other side being low is less likely to occur.

[0060] Compared with the prior art, the present application has at least the following beneficial effects:

[0061] 1. The single-component epoxy adhesive for magnetic core bonding has the characteristics of high adhesion, good heat resistance, low linear thermal expansion coefficient, low curing volume shrinkage rate, excellent wet heat resistance and excellent heat shock resistance. Through formula design, both low linear thermal expansion coefficient and low curing volume shrinkage rate are considered, so that the inductance difference of the transformer or inductor before and after curing is small, which is beneficial to accurate inductance control, and the inductance change with temperature change is small.

[0062] 2. The viscosity of the single-component epoxy adhesive for magnetic core bonding is low, which is convenient for construction. In addition, glass microbeads with a fixed thickness are added as spacer particles, the longitudinal pressure and transverse shear force required in the upper and lower magnetic core bonding process are significantly reduced, the processing difficulty is significantly reduced, the bonding layer thickness uniformity is high, the inductance consistency is significantly improved, the adhesive between the spacer particles and the bonding surface can be fully removed during the magnetic core bonding process, the magnetic core bonding gap is more accurate and uniform, and automatic control can be easily realized, thereby improving production efficiency. DETAILED DESCRIPTION

[0063] Preparation of the organic silicon modified anhydride curing agent:

[0064] Synthesis Example 1

[0065] Synthesis of trimellitic anhydride chloride: 288 g of trimellitic anhydride, 150 g of benzene, 232 g of sulfoxonium chloride were sequentially added to a flask equipped with a condensing device, a stirring device and a tail gas absorption device, the flask was placed in a water bath, the stirring device was turned on, 0.96 g of catalyst dimethylformamide was added dropwise to the flask at 10-15 °C, at the same time 119 g of pyridine was started to be added dropwise, about 30 min was needed for the dropwise addition, then the water bath was turned on for heating, the reaction liquid was allowed to react at reflux temperature for about 5 h, it was observed that the solid material gradually dissolved, the reaction liquid changed from turbid to clear, accompanied by smoke and bubbles, finally the precipitate in the bottle was completely dissolved to form a light yellow clear liquid, smoke and bubbles were no longer generated. The benzene and excess sulfoxonium chloride were distilled off at normal pressure, after distilling off a small amount of the front fraction at reduced pressure, the middle fraction was collected, the collected liquid was cooled to obtain white crystalline trimellitic anhydride chloride, which was sealed and stored.

[0066] Synthesis Example 2

[0067] Synthesis of hydroxyalkyl silicone oil 1: 800 g of dimethylsiloxane oligomer with two terminal Si-H groups (molecular formula as follows structure (II), number average molecular weight 800, corresponding to n = 10) was added to a 2L four-necked flask equipped with stirring and condensing devices, 0.01 g of chloroplatinic acid was preheated to 80 °C, deoxygenated by nitrogen for 15 min, then 265.5 g of ethylene glycol monomethallyl ether was added dropwise to the flask, after the dropwise addition, the mixture was aged at 100 °C for 2 hours, after removing the excess ethylene glycol monomethallyl ether under reduced pressure, hydroxyalkyl silicone oil 1 was obtained.

[0068] Synthesis Example 3

[0069] Synthesis of hydroxyalkyl silicone oil 2: 1170 g of dimethylsiloxane oligomer with two terminal Si-H groups (molecular formula as follows structure (II), number average molecular weight 1170, corresponding to n = 15) was added to a 2L four-necked flask equipped with stirring and condensing devices, 0.014 g of chloroplatinic acid was preheated to 80 °C, deoxygenated by nitrogen for 15 min, then 265.5 g of ethylene glycol monomethallyl ether was added dropwise to the flask, after the dropwise addition, the mixture was aged at 100 °C for 2 hours, after removing the excess ethylene glycol monomethallyl ether under reduced pressure, hydroxyalkyl silicone oil 2 was obtained.

[0070] Synthesis Example 4

[0071] Synthesis of hydroxyalkyl silicone oil 3: 1880 g of dimethylsiloxane oligomer with two terminal Si-H groups (molecular formula as follows structure (II), number average molecular weight 3760, corresponding to n = 50) was added to a 3L four-necked flask equipped with stirring and condensing devices, 0.02 g of chloroplatinic acid was preheated to 80 °C, deoxygenated by nitrogen for 15 min, then 132.8 g of ethylene glycol monomethallyl ether was added dropwise to the flask, after the dropwise addition, the mixture was aged at 100 °C for 2 hours, after removing the excess ethylene glycol monomethallyl ether under reduced pressure, hydroxyalkyl silicone oil 3 was obtained.

[0072] Synthesis Example 5

[0073] Synthesis of hydroxylalkyl silicone oil 4: In a 3L four-necked flask equipped with stirring and condensing device, 2232g of dimethylsiloxane oligomer with two end Si-H groups (molecular formula as structure (II) below, number average molecular weight 11160, corresponding to n = 150) was added, 0.023g of chloroplatinic acid was preheated to 80°C, deoxygenated by nitrogen for 15min, then 53.1g of ethylene glycol monomethallyl ether was added dropwise into the flask, after dropping, it was matured at 100°C for 2h, after removing the excess ethylene glycol monomethallyl ether under reduced pressure, hydroxylalkyl silicone oil 4 was obtained.

[0074] Synthesis Example 6

[0075] Synthesis of hydroxylalkyl silicone oil 5: In a 5L four-necked flask equipped with stirring and condensing device, 2972g of dimethylsiloxane oligomer with two end Si-H groups (molecular formula as structure (II) below, number average molecular weight 14860, corresponding to n = 200) was added, 0.03g of chloroplatinic acid was preheated to 80°C, deoxygenated by nitrogen for 15min, then 53.1g of ethylene glycol monomethallyl ether was added dropwise into the flask, after dropping, it was matured at 100°C for 2h, after removing the excess ethylene glycol monomethallyl ether under reduced pressure, hydroxylalkyl silicone oil 5 was obtained.

[0076]

[0077] Synthesis Example 7

[0078] Synthesis of silicone-modified trimellitic anhydride curing agent 1:

[0079] Into a flask equipped with condensing device, stirring device and tail gas absorption device, 210.57g of trimellitic anhydride acyl chloride, solvent benzene, was added, the flask was placed in a cold water bath, the stirring device was started, 79.1g of pyridine was added dropwise into the flask at 0-10°C, it was dropped for about 30min, after the dropping was completed, the reaction was continued for about 1h, at this time, a milky white precipitate was observed in the flask, and the mixture in the flask became turbid.

[0080] After 1h of reaction, 502g of hydroxylalkyl silicone oil 1 was added dropwise, then heating was started, and the reaction was carried out under reflux for 3h, then the reaction was stopped, and hot filtration was carried out, then the liquid was left, then the solvent benzene was removed by rotary evaporation, and the remaining white viscous material was vacuum dried to obtain silicone-modified trimellitic anhydride curing agent 1.

[0081] Synthesis Examples 8-11

[0082] Synthesis of silicone-modified trimellitic anhydride curing agents 2-5:

[0083] According to the same method as in synthesis example 7, the hydroxylalkyl silicone oil was replaced by 687g of hydroxylalkyl silicone oil 2 to obtain trimellitic anhydride curing agent 2;

[0084] According to the same method of synthesis example 7, replace the hydroxyl alkyl silicone oil with 1982g hydroxyl alkyl silicone oil 3, to obtain trimellitic anhydride curing agent 3;

[0085] According to the same method of synthesis example 7, replace the hydroxyl alkyl silicone oil with 5682g hydroxyl alkyl silicone oil 4, to obtain trimellitic anhydride curing agent 4;

[0086] According to the same method of synthesis example 7, replace the hydroxyl alkyl silicone oil with 7532g hydroxyl alkyl silicone oil 5, to obtain trimellitic anhydride curing agent 5.

[0087] Examples and comparative examples of one-component epoxy adhesive for magnetic core bonding

[0088] Prepare raw materials according to the raw materials and amounts in Table 1, and prepare one-component epoxy adhesive for magnetic core bonding according to the following method:

[0089] Add epoxy resin prepolymer containing rigid annular structure, silicone modified anhydride curing agent, and liquid anhydride curing agent into a batching tank, stir and mix uniformly with a high-speed disperser, then transfer to a planetary stirred tank, add glass beads and other additives, stir and mix uniformly, cool to room temperature, then add curing accelerator, stir and mix for about 30min, vacuum degassing, package, and obtain one-component epoxy adhesive for magnetic core bonding. The preparation method of the comparative examples is similar, only the corresponding raw materials are used to replace the raw materials in the examples.

[0090] Table 1 Raw material types and amounts (mass, parts) of examples and comparative examples

[0091]

[0092]

[0093] (Continued) Table 1 Raw material types and amounts (mass, parts) of examples and comparative examples

[0094]

[0095]

[0096] Test the adhesives obtained from each example and comparative example, and the test method is:

[0097] 1) Curing conditions: 120-180℃, heating for 30-120min for curing.

[0098] 2) Water absorption test: Determine the 24h water absorption at 23℃ according to GB / T 1034.

[0099] 3) Shear strength test: Take appropriate amount of sample, cure according to the curing condition above, make Al-Al shear piece. According to GB / T 7124, test the shear strength at 25℃ and 125℃ respectively.

[0100] 4) Glass transition temperature (Tg) test: Take appropriate amount of sample, cure according to the curing condition above, make 3mm*25mm*10mm adhesive strip. Use dynamic mechanical analysis test (DMA), according to 5℃ / min to 200℃, to determine.

[0101] 5) Linear thermal expansion coefficient test: Take appropriate amount of sample, cure according to the curing condition above, make 3mm*5mm*5mm adhesive block. Use thermal mechanical analysis method (TMA) test, according to 5℃ / min to 200℃, to determine.

[0102] 7) Curing volume shrinkage test: Take appropriate amount of sample, cure according to the curing condition above. According to ISO 3521, to determine.

[0103] 8) Humidity resistance evaluation:

[0104] According to GB / T 7124, prepare 5 Al-Al shear pieces, age in 85℃, 85% humidity oven for 1000h, take out and restore at room temperature for 24h, test the average shear strength, and compare with the shear strength of the shear pieces placed at 25℃, the evaluation standard is as follows:

[0105] Excellent: the ratio of the shear strength after aging to the shear strength of the shear pieces placed at 25℃ is 0.8 or above;

[0106] Good: the ratio of the shear strength after aging to the shear strength of the shear pieces placed at 25℃ is 0.7-0.8 (not including 0.8);

[0107] Medium: the ratio of the shear strength after aging to the shear strength of the shear pieces placed at 25℃ is 0.6-0.7 (not including 0.7);

[0108] Poor: the ratio of the shear strength after aging to the shear strength of the shear pieces placed at 25℃ is less than 0.6;

[0109] 9) Heat shock resistance evaluation:

[0110] According to GB / T 7124, prepare 5 Al-Al shear pieces, age in 85℃, 85% humidity oven for 1000h, take out and restore at room temperature for 24h, test the average shear strength, and compare with the shear strength of the shear pieces placed at 25℃, the evaluation standard is as follows:

[0111] Excellent: the ratio of the shear strength after aging to the shear strength of the shear pieces placed at 25℃ is 0.8 or above;

[0112] Good: the ratio of the shear strength after aging to the shear strength of the shear piece stored at 25°C is 0.7 to 0.8 (excluding 0.8);

[0113] Fair: the ratio of the shear strength after aging to the shear strength of the shear piece stored at 25°C is 0.6 to 0.7 (excluding 0.7);

[0114] Poor: the ratio of the shear strength after aging to the shear strength of the shear piece stored at 25°C is less than 0.6;

[0115] 10) Test of thickness uniformity of the adhesive layer:

[0116] Ten shear pieces were prepared from a smooth aluminum sheet, and cross sections were polished. From the images of the cross sections, the average thickness of the adhesive layer was determined. The uniformity of the thickness of the adhesive layer was determined based on the following criteria. Criteria for determining the uniformity of the thickness of the adhesive layer:

[0117] Good: the ratio of the minimum value of the thickness of the adhesive layer to the maximum value of the thickness of the adhesive layer (minimum value of the thickness of the adhesive layer / maximum value of the thickness of the adhesive layer) is 0.9 or more;

[0118] Fair: the ratio of the minimum value of the thickness of the adhesive layer to the maximum value of the thickness of the adhesive layer (minimum value of the thickness of the adhesive layer / maximum value of the thickness of the adhesive layer) is 0.7 or more and less than 0.9;

[0119] Poor: the ratio of the minimum value of the thickness of the adhesive layer to the maximum value of the thickness of the adhesive layer (minimum value of the thickness of the adhesive layer / maximum value of the thickness of the adhesive layer) is less than 0.7.

[0120] Table 2 Test results of Examples and Comparative Examples

[0121]

[0122] (Continued) Table 2 Test results of Examples and Comparative Examples

[0123]

[0124] 1. Examples 1-5 are single-component epoxy adhesives for bonding magnetic cores with different numbers of repeating units (n) of the silicone-modified anhydride curing agent. As can be seen from the test data in Table 2, with the increase of the number of repeating units (n), the viscosity of the epoxy adhesive increases, and the linear coefficient of thermal expansion increases. This is because with the increase of the number of repeating units (n), the molecular weight of the silicone-modified anhydride curing agent increases, and the length of the flexible silicone chain segments increases, resulting in a corresponding increase in viscosity. Furthermore, the closer the number of repeating units (n) is to the aforementioned lower limit of 10, the lower the shear strength after thermal shock aging. This is because the length of the flexible silicone chain segments decreases, reducing the toughness of the epoxy adhesive. Within a certain range, Example 6 reduced the amount of glass microspheres, while Example 7 increased the amount of glass microspheres; both examples achieved good performance.

[0125] 2. In Comparative Example 1 and Comparative Example 3, the epoxy resin containing a rigid ring structure was replaced with a bisphenol A epoxy resin without a rigid ring structure. The result was a significant increase in water absorption and a significant decrease in resistance to damp heat. Furthermore, the bisphenol A epoxy resin had lower rigidity, thus lowering its glass transition temperature and heat resistance (shear strength at 125°C decreased). Comparative Example 1 had too low a viscosity and too high fluidity, making it unsuitable for sizing.

[0126] 3. Comparative Example 2, unlike Example 3, did not contain the silicone-modified anhydride curing agent. As a result, the adhesive toughness decreased, manifested as a reduction in thermal shock resistance and shear strength. Comparative Example 2 had too low a viscosity and too high fluidity, making it unsuitable for application.

[0127] 4. In Comparative Example 3, the amount of liquid anhydride (methyltetrahydrophthalic anhydride) was reduced compared to Example 3, below the specified minimum value. As a result, the viscosity increased significantly and the thickness uniformity of the adhesive layer was poor.

[0128] 5. Comparative Example 4 increased the amount of liquid anhydride (methyltetrahydrophthalic anhydride) compared to Example 3, exceeding the specified maximum value. As a result, the viscosity was too low and the fluidity was too high, which was not conducive to sizing. The water absorption rate also increased.

[0129] 6. Compared with Example 3, Comparative Example 5 showed an increase in the average diameter difference coefficient of the glass microspheres, exceeding the specified maximum value, resulting in a decrease in the uniformity of the adhesive layer thickness.

[0130] 7. In Comparative Example 6 compared to Example 3, the amount of glass microspheres added was increased, exceeding the specified maximum value, resulting in a decrease in the uniformity of the adhesive layer thickness.

[0131] 8. In Comparative Example 7, compared to Example 3, the amount of glass microspheres added was reduced, falling below the specified minimum value, resulting in a decrease in the uniformity of the adhesive layer thickness.

[0132] 9、Comparative Example 8, relative to Example 3, added a multi-functional epoxy resin NPPN-638S (average functionality 3.6), the result is that the curing volume shrinkage increases greatly, and the shear strength also decreases. The present application does not use a multi-functional epoxy resin, and the cross-linking degree of the multi-functional epoxy resin is too high, which will result in high curing shrinkage.

[0133] 10、Comparative Example 9, relative to Example 3, added a multi-functional anhydride curing agent, pyromellitic dianhydride, the result is that the curing shrinkage increases, and the shear strength also decreases. The thickness uniformity of the adhesive layer also decreases.

Claims

1. A one-part epoxy adhesive for magnetic core bonding, characterized by comprising: a liquid epoxy resin; a curing agent; a curing accelerator; a filler; and a silane coupling agent. made of the following materials: A) an epoxy resin containing a rigid bi-cyclic structure, 30-60 wt% of the total weight of A-D; the epoxy resin containing a rigid bi-cyclic structure is an epoxy resin prepolymer containing a rigid bi-cyclic structure with 2 epoxy functional groups at the end of the molecular chain; B) a silicone-modified anhydride curing agent having the following structure (I), 15-40 wt% of the total weight of A-D: (I)， wherein R1 to R4 are each independently a monovalent hydrocarbon group having 1 to 10 carbon atoms, and n represents an integer of 10 to 200; C) a liquid anhydride curing agent, 15-42 wt% of the total weight of A-D; the liquid anhydride curing agent is selected from one or more of methyltetrahydrophthalic anhydride, methylhexahydrophthalic anhydride, methyl nadic anhydride, dodecenyl succinic anhydride; D) a curing accelerator, 0.5-5 wt% of the total weight of A-D; E) glass microbeads, 5-30 wt% of the total weight of A-D; the glass microbeads have an average diameter of 10-150 μm and a coefficient of variation of the average diameter less than 5%.

2. The one-part epoxy adhesive for magnetic core bonding according to claim 1, characterized by, The n is an integer of 10 to 50.

3. The one-part epoxy adhesive for magnetic core bonding according to claim 1, characterized by, The n is an integer of 50 to 200.

4. The one-part epoxy adhesive for magnetic core bonding according to claim 1, characterized by The epoxy resin containing a rigid bi-cyclic structure is selected from a combination of one or more of a naphthalene-type epoxy resin, a fluorene-type epoxy resin, a dicyclopentadiene phenol epoxy resin; the softening point of the epoxy resin containing a rigid bi-cyclic structure is less than 80°C, but greater than or equal to 50°C.

5. The one-part epoxy adhesive for magnetic core bonding according to claim 1, wherein In the formula (I), R 1 to R 4 are identical or different, R 1 to R 4 are selected from the group consisting of methyl, ethyl, propyl, n-butyl, cyclic alkyl, t-butyl, ethenyl, allyl, propenyl, butenyl, hexenyl, cyclohexenyl, phenyl, tolyl, benzyl, phenethyl.

6. The one-part epoxy adhesive for magnetic core bonding according to claim 1, wherein The curing accelerator is selected from an imidazole compound, a boron trifluoride-amine adduct, and a microencapsulated latent amine curing agent; the imidazole compound is selected from any one of 2-methyl-4-ethylimidazole, 2-phenylimidazole, 2-methylimidazole, 1-benzyl-2-phenylimidazole; the microencapsulated latent amine curing agent is selected from any one of HX-3722, HX-3742, HX-3921HP.

7. The one-part epoxy adhesive for magnetic core bonding according to claim 1, wherein The one-component epoxy adhesive for bonding a magnetic core further comprises a leveling agent, a defoaming agent, or a wetting dispersant, and the respective addition amount of the leveling agent, the defoaming agent, or the wetting dispersant is 0-0.2 wt% of the total weight of A-D.

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