Protective slurry for chip resistor and preparation method thereof

Abstract

The invention discloses protective paste for a chip resistor and a preparation method of the protective paste, and relates to the technical field of electronic paste. The protective slurry for the chip resistor is prepared from modified epoxy resin, modified polyurethane, modified silicon dioxide, black pigment, a diluent, a wetting dispersant, a flatting agent, a defoaming agent, a thixotropic agent, a latent curing agent and a photoinitiator. The epoxy resin is prepared from ethyl 2, 5-dihydroxy cinnamate and epoxy chloropropane through a reaction; the modified polyurethane is obtained by polymerizing toluene diisocynate, polytetrahydrofuran ether glycol and hydroxypropyl-terminated polysiloxane, then reacting with carbon tetrachloride, and then hydrolyzing; the modified silicon dioxide is obtained by reacting pretreated silicon dioxide with methyl pyruvate, reducing and initiating ring opening polymerization of cyclic phosphate. The protective slurry for the chip resistor prepared by the invention has good flame retardance, aging resistance and self-repairing performance.

Description

Technical Field

[0001] The present invention relates to the technical field of electronic pastes, and particularly to a protective paste for chip resistors and a preparation method thereof. Background Art

[0002] Chip resistors, which are high-precision and miniaturized electronic components, are widely used in fields such as electronic devices and automotive electronics.

[0003] The preparation process of chip resistors is relatively complex, but can generally be summarized into the following key steps: First, materials for the resistor body need to be prepared, which are usually metals or semiconductor materials. Next, in order to protect the resistor body from damage, a protective layer needs to be coated on its surface. The protective layer is usually made of materials such as glass or resin, which can prevent the resistor layer from being damaged by mechanical or chemical factors. Currently, in the manufacturing process of chip resistors, a screen printing process is often used to print an epoxy resin-based insulating protective paste on the surface of the resistor layer as the outermost protective layer. However, this epoxy-based protective paste still has some problems.

[0004] Among them, poor toughness is a significant problem. The epoxy protective layer with poor toughness is prone to cracking or peeling off, which not only leads to poor protection effect, but also may pose a potential threat to the performance and safety of the resistor; improving the self-healing ability of the epoxy protective layer can repair the protective layer when it is damaged and scratched, thereby increasing the service life of the chip resistor; in addition, insufficient anti-aging ability is also an important problem; in harsh environments such as high temperature and high humidity, the epoxy protective layer is prone to aging and deterioration, thus losing its protective effect on the resistor; finally, non-flammability is also a defect of the epoxy-based protective paste; in extreme situations such as fire, the non-flammable protective layer will burn rapidly, thus exacerbating the spread of the fire and posing a serious threat to the safety of equipment and personnel.

[0005] Therefore, in view of these problems, developers are actively looking for alternative materials or improving processes to improve the reliability and safety of chip resistors. Summary of the Invention

[0006] The purpose of the present invention is to provide a protective paste for chip resistors and a preparation method thereof to solve the problems existing in the prior art.

[0007] To solve the above technical problems, the present invention provides the following technical solutions:

[0008] A protective paste for chip resistors, wherein the protective paste for chip resistors comprises a modified epoxy resin, a modified polyurethane, a modified silica, a black pigment, a diluent, a wetting dispersant, a leveling agent, an antifoaming agent, a thixotropic agent, a latent curing agent, and a photoinitiator.

[0009] As an optimization, the modified epoxy resin is prepared by reacting ethyl 2,5-dihydroxycinnamate, tetrabutylammonium bromide, and epichlorohydrin.

[0010] As an optimization, the modified polyurethane is obtained by reacting the pre-modified polyurethane obtained by polymerizing toluene diisocyanate, polytetrahydrofuran ether glycol, and hydroxypropyl-terminated polysiloxane with carbon tetrachloride and then hydrolyzing; the hydroxypropyl-terminated polysiloxane is obtained by polymerizing octamethylcyclotetrasiloxane, terminal-silicon-hydroxyl polysiloxane, and 1,3-bis(3-hydroxypropyl)-1,1,3,3-tetramethyldisiloxane; the terminal-silicon-hydroxyl polysiloxane is obtained by reacting diphenylsilanediol and 1-[(chlorodimethylsilyl)methyl]-4-vinylbenzene.

[0011] As an optimization, the modified silica is obtained by reacting silica modified with 3-(3-aminophenoxy)propyltrimethoxysilane with methyl pyruvate, reducing with lithium aluminum hydride, and then initiating ring-opening polymerization of 2-ethoxy-1,3,2-dioxaphospholane 2-oxide.

[0012] A preparation method of a protective paste for chip resistors, the following preparation steps:

[0013] (1) Mix ethyl 2,5-dihydroxycinnamate, tetrabutylammonium bromide, and epichlorohydrin, and add sodium hydroxide to react to obtain a modified epoxy resin;

[0014] (2) Hydrolyze methylphenyldimethoxysilane to obtain diphenylsilanediol, and react diphenylsilanediol with 1-[(chlorodimethylsilyl)methyl]-4-vinylbenzene to obtain terminal-silicon-hydroxyl polysiloxane; react terminal-silicon-hydroxyl polysiloxane, octamethylcyclotetrasiloxane, potassium hydroxide, and 1,3-bis(3-hydroxypropyl)-1,1,3,3-tetramethyldisiloxane to obtain hydroxypropyl-terminated polysiloxane;

[0015] (3) React toluene diisocyanate, polytetrahydrofuran ether glycol, hydroxypropyl-terminated polysiloxane, and dibutyltin dilaurate to obtain a pre-modified polyurethane; react the pre-modified polyurethane, copper oxide, diethylamine, and carbon tetrachloride to obtain a modified polyurethane precursor; hydrolyze the modified polyurethane precursor under the catalysis of an acidic catalyst to obtain a modified polyurethane;

[0016] (4) React pretreated silica with methyl pyruvate to obtain quinolinyl silica; reduce quinolinyl silica under a catalyst to obtain pre-modified silica; react the pre-modified silica with 2-ethoxy-1,3,2-dioxaphospholane 2-oxide to obtain modified silica;

[0017] (5) Weigh the following components: modified epoxy resin, modified polyurethane, modified silica, black pigment, diluent, wetting dispersant, leveling agent, defoaming agent, thixotropic agent, latent curing agent, photoinitiator; add the modified epoxy resin to the diluent, heat and stir at 60 - 90 °C for 20 - 30 min, and filter with a 500 - mesh gauze; then successively add the black pigment, wetting dispersant, leveling agent, defoaming agent, thixotropic agent, photoinitiator and mix, then add the modified polyurethane, modified silica, latent curing agent and mix thoroughly, disperse and defoam, and grind on a three - roll mill to make its fineness reach 7 μm to obtain the protective paste for chip resistors.

[0018] As an optimization, the preparation method of the modified epoxy resin described in step (1) is: mix ethyl 2,5 - dihydroxycinnamate, tetrabutylammonium bromide, and epichlorohydrin according to a mass ratio of 1:(0.08 - 0.1):(1.5 - 1.6), heat up to 60 °C and mix for 30 min, add sodium hydroxide in three portions, the addition amount of sodium hydroxide each time is 0.13 - 0.15 times the mass of ethyl 2,5 - dihydroxycinnamate, the addition interval is 30 min, continue to react for 1.5 h after adding the three portions of sodium hydroxide, after the reaction is completed, add absolute ethanol 3 times the mass of epichlorohydrin, filter and retain the filtrate, perform rotary evaporation at 100 °C and - 0.09 MPa, and then vacuum - dry at room temperature to obtain the modified epoxy resin.

[0019] As an optimization, the preparation method of the hydroxypropyl-terminated polysiloxane described in step (2) is as follows: Heat methylphenyldimethoxysilane to 80 °C, add pure water twice the mass of methylphenyldimethoxysilane, and after reacting for 3 h, carry out vacuum filtration to obtain diphenylsilanediol; Weigh phenylsilanediol, 1-[(chlorodimethylsilyl)methyl]-4-vinylbenzene, and pyridine according to a molar ratio of 4:3:8; Mix 1-[(chlorodimethylsilyl)methyl]-4-vinylbenzene and tetrahydrofuran in a mass ratio of 1:5 to obtain a 1-[(chlorodimethylsilyl)methyl]-4-vinylbenzene solution; Mix diphenylsilanediol and tetrahydrofuran in a mass ratio of 1:5, add pyridine and heat to 40 °C, add the 1-[(chlorodimethylsilyl)methyl]-4-vinylbenzene solution and continue to react for 6 h. After the reaction is completed, remove the low-boiling substances under reduced pressure, add ethyl acetate 10 times the mass of diphenylsilanediol; Centrifuge to take the supernatant, and the supernatant is washed with water, dried over anhydrous sodium sulfate, and rotary evaporated under reduced pressure at 60 °C to obtain a polysiloxane with terminal silicon hydroxyl groups; Weigh the polysiloxane with terminal silicon hydroxyl groups, octamethylcyclotetrasiloxane, tetrahydrofuran, potassium hydroxide, and 1,3-bis(3-hydroxypropyl)-1,1,3,3-tetramethyldisiloxane according to a mass ratio of 1:(0.3 - 0.5):(20 - 30):0.05:(0.2 - 0.3); Mix potassium hydroxide and ethanol in a mass ratio of 1:100 to obtain a potassium hydroxide-ethanol solution; Mix octamethylcyclotetrasiloxane, the polysiloxane with terminal silicon hydroxyl groups, and tetrahydrofuran and heat to 60 °C and stir for 6 h, then add the potassium hydroxide-ethanol solution and continue to stir for 3.5 h. After the stirring is completed, add pure water and 1,3-bis(3-hydroxypropyl)-1,1,3,3-tetramethyldisiloxane, and continue to react for 2.5 h. After the reaction is completed, evacuate under reduced pressure to remove the low-boiling substances, heat to 90 °C, and continue to evacuate to obtain the hydroxypropyl-terminated polysiloxane;

[0020] As an optimization, the preparation method of the modified polyurethane in step (3) is as follows: Mix toluene diisocyanate, polytetrahydrofuran ether glycol, hydroxypropyl-terminated polysiloxane, dibutyltin dilaurate, and toluene in a mass ratio of 1:(2 - 3):(0.3 - 0.5):(0.02 - 0.03):(20 - 30), heat up to 80 °C and react for 3 - 4 h, then add ethylene glycol which is 0.5 times the mass of the polytetrahydrofuran ether glycol and stir for 1 - 2 h. After stirring, add n-hexane which is 3 - 4 times the volume of toluene, filter and dry at 50 °C for 22 - 24 h to obtain pre-modified polyurethane; Mix the pre-modified polyurethane, copper oxide, diethylamine, carbon tetrachloride, and tetrahydrofuran in a mass ratio of 1:0.01:0.03:(5 - 6):(10 - 12), reflux at 70 - 75 °C for 5 h, then filter and retain the filtrate, and obtain the modified polyurethane precursor by rotary evaporation under reduced pressure. Mix the modified polyurethane precursor, acidic catalyst, and N,N-dimethylformamide in a mass ratio of 1:0.02:(3 - 4), heat up to 116 - 122 °C and react for 10 h. After the reaction, obtain the modified polyurethane by rotary evaporation under reduced pressure; The acidic catalyst is prepared by mixing 98 wt% concentrated sulfuric acid, p-toluenesulfonic acid, pure water, and glacial acetic acid in a molar ratio of 0.15:0.05:1:2.5; The molecular weight of the polytetrahydrofuran ether glycol is 2000.

[0021] As an optimization, the preparation method of the modified silica in step (4) is as follows: Mix pretreated silica, methyl pyruvate, acetonitrile, and iodine in a mass ratio of 1:(0.5 - 0.7):(20 - 30):0.001, reflux and stir at 50 °C for 12 h. After the reaction, filter and wash with pure water 3 - 4 times, and vacuum dry at room temperature to obtain quinoline-based silica; At 0 °C, mix lithium aluminum hydride and tetrahydrofuran in a mass ratio of 1:40 to obtain a catalyst solution. Under nitrogen protection, mix quinoline-based silica and tetrahydrofuran in a mass ratio of 1:(5 - 6) for 3 - 5 min, add the catalyst solution which is 20 - 30 times the mass of the quinoline-based silica and react for 8 h. After the reaction, cool down to 0 °C and stir for 20 min, then add ether which is 40 times the mass of the quinoline-based silica, pure water which is 2 times the mass of the quinoline-based silica, and 15 wt% sodium hydroxide solution which is 2 times the mass of the quinoline-based silica in sequence, filter and wash with pure water 3 - 4 times, and vacuum dry at room temperature to obtain pre-modified silica; At 0 °C, mix the pre-modified silica, 2-ethoxy-1,3,2-dioxaphospholane 2-oxide, 1,8-diazabicyclo[5.4.0]undec-7-ene, and toluene in a mass ratio of 1:(0.3 - 0.5):1:(10 - 12) for 3 - 5 min, heat up to 40 °C and react for 5 - 6 h. After the reaction, add acetic acid which is 3 - 4 times the mass of the pre-modified silica, filter and wash with pure water 3 - 4 times, and vacuum dry at room temperature to obtain modified silica.

[0022] As an optimization, the dosages of the components in step (5) are as follows: by mass parts, 60 - 80 parts of modified epoxy resin, 20 - 30 parts of modified polyurethane, 20 - 30 parts of modified silica, 7 - 9 parts of black pigment, 20 - 30 parts of diluent, 2 - 3 parts of wetting dispersant, 2 - 3 parts of leveling agent, 2 - 3 parts of defoaming agent, 1 - 2 parts of thixotropic agent, 3 - 5 parts of latent curing agent, and 0.5 - 1 part of photoinitiator; the black pigment is insulating carbon black; the diluent is diethylene glycol monobutyl ether; the latent curing agent is dicyandiamide.

[0023] As an optimization, the preparation method of the pretreated silica is as follows: Mix 3-(3-aminophenoxy)propyltrimethoxysilane, absolute ethanol, and pure water in a mass ratio of 1:5:10, heat to 40 °C and stir for 3 - 5 min, add silica which is 3 - 4 times the mass of 3-(3-aminophenoxy)propyltrimethoxysilane, heat to 70 °C and reflux for 3 - 4 h. After the reaction is completed, filter and wash with absolute ethanol 3 - 4 times, and vacuum dry at 70 °C to obtain pretreated silica; the particle size of the silica is 200 - 300 nm.

[0024] Compared with the prior art, the beneficial effects achieved by the present invention are:

[0025] When preparing the protective paste for chip resistors, first, react ethyl 2,5-dihydroxycinnamate, tetrabutylammonium bromide, and epichlorohydrin to obtain modified epoxy resin; polymerize the terminal silicon hydroxyl polyorganosiloxane obtained by reacting diphenylsilanediol and 1-[(chlorodimethylsilyl)methyl]-4-vinylbenzene with octamethylcyclotetrasiloxane and 1,3-bis(3-hydroxypropyl)-1,1,3,3-tetramethyldisiloxane to obtain hydroxypropyl-terminated polyorganosiloxane; polymerize toluene diisocyanate, polytetrahydrofuran ether diol, and hydroxypropyl-terminated polyorganosiloxane, then react with carbon tetrachloride and hydrolyze to obtain modified polyurethane; secondly, react the silica modified by 3-(3-aminophenoxy)propyltrimethoxysilane with methyl pyruvate, reduce it with lithium aluminum hydride, and then initiate the ring-opening polymerization of 2-ethoxy-1,3,2-dioxaphospholane 2-oxide to obtain modified silica; finally, mix the modified epoxy resin, modified polyurethane, modified silica, black pigment, diluent, wetting dispersant, leveling agent, defoaming agent, thixotropic agent, latent curing agent, and photoinitiator to obtain the protective paste for chip resistors.

[0026] First, ethyl 2,5-dihydroxycinnamate, tetrabutylammonium bromide, and epichlorohydrin are reacted to prepare a modified epoxy resin with a cinnamoyl group in the side chain; a polysiloxane with terminal silanol groups is obtained by reacting diphenylsilanediol and 1-[(chlorodimethylsilyl)methyl]-4-vinylbenzene; the side chain of the polysiloxane with terminal silanol groups is a styrene group; then it is polymerized with octamethylcyclotetrasiloxane and 1,3-bis(3-hydroxypropyl)-1,1,3,3-tetramethyldisiloxane to obtain a hydroxypropyl-terminated polysiloxane; toluene diisocyanate, polytetrahydrofuran ether diol, and hydroxypropyl-terminated polysiloxane are polymerized to form a pre-modified polyurethane with a styrene group in the side chain, and the pre-modified polyurethane undergoes an addition reaction with carbon tetrachloride under a catalytic system composed of copper oxide and diethylamine to generate 1,1,1,3,3,3-hexachloropropane, and then it is hydrolyzed in an acidic catalytic system to obtain a cinnamic acid group containing a cinnamoyl group; the cinnamoyl group can promote crosslinking under 368 nm irradiation and can be de-crosslinked under 254 nm irradiation, and the epoxy resin material containing the cinnamoyl group has a photo-responsive self-healing effect;

[0027] Secondly, silica modified with 3-(3-aminophenoxy)propyltrimethoxysilane is reacted with methyl pyruvate to generate a dihydroquinoline structure containing a methyl ester. The dihydroquinoline structure is a type of functional group with anti-aging effects and can endow the material with good anti-aging performance. After the ester group is reduced by lithium aluminum hydride, the generated alcohol hydroxyl group can be used as an initiator to initiate the ring-opening polymerization of 2-ethoxy-1,3,2-dioxaphospholane 2-oxide on the silica surface to generate a polyphosphate structure with good flame retardancy and a hydroxyl group at the end.

[0028] Finally, the modified epoxy resin, modified polyurethane, modified silica, black pigment, diluent, wetting dispersant, leveling agent, defoamer, thixotropic agent, and latent curing agent are mixed to obtain a protective paste for chip resistors; the polyurethane containing polysiloxane segments can well improve the hydrophobicity and toughness of the epoxy resin; the modified epoxy resin containing a cinnamoyl group and the polyurethane containing a cinnamoyl group can undergo controllable crosslinking under ultraviolet irradiation and have good photo-responsive self-healing ability. During the curing process of the protective paste, the hydroxyl groups on the surface of the modified silica and the carboxyl groups in the side chain of the polyurethane can further crosslink with the epoxy groups to generate a more complex and dense network structure, thereby improving the mechanical properties of the material. Specific Embodiments

[0029] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

[0030] In the following examples and comparative examples, the molecular weight of polytetrahydrofuran ether diol is 2000; the particle size of the silica is 200 nm; the black pigment is insulating carbon black; the diluent is diethylene glycol monobutyl ether; the latent curing agent is dicyandiamide; the wetting and dispersing agent model is BYK-110; the leveling agent model is BYK-306; the defoaming agent model is BYK-088; the thixotropic agent model is BYK-410; the photoinitiator model is 1173.

[0031] Example 1:

[0032] A preparation method of a protective paste for chip resistors, the preparation method of the protective paste for chip resistors includes the following preparation steps:

[0033] (1) Mix ethyl 2,5-dihydroxycinnamate, tetrabutylammonium bromide, and epichlorohydrin in a mass ratio of 1:0.08:1.5, heat up to 60 °C and mix for 30 min, add sodium hydroxide in three portions, with the addition amount of sodium hydroxide each time being 0.13 times the mass of ethyl 2,5-dihydroxycinnamate, and the addition interval being 30 min. After adding the three portions of sodium hydroxide, continue the reaction for 1.5 h. After the reaction is completed, add anhydrous ethanol three times the mass of epichlorohydrin, filter and retain the filtrate, perform rotary evaporation at 100 °C and -0.09 MPa, and then perform vacuum drying at room temperature to obtain a modified epoxy resin;

[0034] (2) Heat methylphenyldimethoxysilane to 80 °C, add pure water twice the mass of methylphenyldimethoxysilane, and after reacting for 3 h, carry out vacuum filtration to obtain diphenylsilanediol; weigh phenylsilanediol, 1-[(chlorodimethylsilyl)methyl]-4-vinylbenzene, and pyridine according to a molar ratio of 4:3:8; mix 1-[(chlorodimethylsilyl)methyl]-4-vinylbenzene and tetrahydrofuran in a mass ratio of 1:5 to obtain a 1-[(chlorodimethylsilyl)methyl]-4-vinylbenzene solution; mix diphenylsilanediol and tetrahydrofuran in a mass ratio of 1:5, add pyridine and heat to 40 °C, add the 1-[(chlorodimethylsilyl)methyl]-4-vinylbenzene solution and continue to react for 6 h. After the reaction is completed, remove the low-boiling substances under reduced pressure, add ethyl acetate ten times the mass of diphenylsilanediol; centrifuge and take the upper clear liquid, and the upper clear liquid is washed with water, dried over anhydrous sodium sulfate, and rotary evaporated under reduced pressure at 60 °C to obtain a polysiloxane with terminal silanol groups; weigh the polysiloxane with terminal silanol groups, octamethylcyclotetrasiloxane, tetrahydrofuran, potassium hydroxide, and 1,3-bis(3-hydroxypropyl)-1,1,3,3-tetramethyldisiloxane according to a mass ratio of 1:0.3:20:0.05:0.2; mix potassium hydroxide and ethanol in a mass ratio of 1:100 to obtain a potassium hydroxide-ethanol solution; mix octamethylcyclotetrasiloxane, the polysiloxane with terminal silanol groups, and tetrahydrofuran and heat to 60 °C and stir for 6 h, then add the potassium hydroxide-ethanol solution and continue to stir for 3.5 h. After stirring is completed, add pure water and 1,3-bis(3-hydroxypropyl)-1,1,3,3-tetramethyldisiloxane and continue to react for 2.5 h. After the reaction is completed, evacuate under reduced pressure to remove the low-boiling substances, heat to 90 °C, and continue to evacuate to obtain a hydroxypropyl-terminated polysiloxane;

[0035] (3) Mix toluene diisocyanate, polytetrahydrofuran ether glycol, hydroxypropyl-terminated polysiloxane, dibutyltin dilaurate, and toluene in a mass ratio of 1:2:0.3:0.02:20, heat to 80 °C and react for 4 h, then add ethylene glycol half the mass of polytetrahydrofuran ether glycol and stir for 2 h. After stirring is completed, add n-hexane three times the volume of toluene, filter and dry at 50 °C for 24 h to obtain a pre-modified polyurethane; mix the pre-modified polyurethane, copper oxide, diethylamine, carbon tetrachloride, and tetrahydrofuran in a mass ratio of 1:0.01:0.03:5:10, reflux at 75 °C for 5 h, filter and retain the filtrate, and obtain a modified polyurethane precursor by rotary evaporation under reduced pressure. Mix the modified polyurethane precursor, acidic catalyst, and N,N-dimethylformamide in a mass ratio of 1:0.02:3, heat to 122 °C and react for 10 h. After the reaction is completed, obtain the modified polyurethane by rotary evaporation under reduced pressure; the acidic catalyst is prepared by mixing 98 wt% concentrated sulfuric acid, p-toluenesulfonic acid, pure water, and glacial acetic acid in a molar ratio of 0.15:0.05:1:2.5;

[0036] (4) Mix 3-(3-aminophenoxy)propyltrimethoxysilane, absolute ethanol, and pure water in a mass ratio of 1:5:10. Heat the mixture to 40 °C and stir for 5 min. Add silica that is 3 times the mass of 3-(3-aminophenoxy)propyltrimethoxysilane. Heat the mixture to 70 °C and reflux for 4 h. After the reaction, filter and wash 4 times with absolute ethanol. Dry under vacuum at 70 °C to obtain pretreated silica. Mix the pretreated silica, methyl pyruvate, acetonitrile, and iodine in a mass ratio of 1:0.5:20:0.001. Reflux and stir at 50 °C for 12 h. After the reaction, filter and wash 3 times with pure water. Dry under vacuum at room temperature to obtain quinolinyl silica. At 0 °C, mix lithium aluminum hydride and tetrahydrofuran in a mass ratio of 1:40 to obtain a catalyst solution. Under nitrogen protection, mix quinolinyl silica and tetrahydrofuran in a mass ratio of 1:5 for 5 min. Add a catalyst solution that is 20 times the mass of quinolinyl silica and react for 8 h. After the reaction, cool to 0 °C and stir for 20 min. Sequentially add diethyl ether that is 40 times the mass of quinolinyl silica, pure water that is 2 times the mass of quinolinyl silica, and a 15 wt% sodium hydroxide solution that is 2 times the mass of quinolinyl silica. Filter and wash 3 times with pure water. Dry under vacuum at room temperature to obtain pre-modified silica. At 0 °C, mix pre-modified silica, 2-ethoxy-1,3,2-dioxaphospholane 2-oxide, 1,8-diazabicyclo[5.4.0]undec-7-ene, and toluene in a mass ratio of 1:0.3:1:10 for 5 min. Heat to 40 °C and react for 6 h. After the reaction, add acetic acid that is 3 times the mass of pre-modified silica. Filter and wash 4 times with pure water. Dry under vacuum at room temperature to obtain modified silica;

[0037] (5) Weigh the following components: by mass parts, 60 parts of modified epoxy resin, 20 parts of modified polyurethane, 20 parts of modified silica, 7 parts of black pigment, 20 parts of diluent, 2 parts of wetting dispersant, 2 parts of leveling agent, 2 parts of defoamer, 1 part of thixotropic agent, 3 parts of latent curing agent, and 0.5 part of photoinitiator. Add the modified epoxy resin to the diluent, heat and stir at 90 °C for 30 min, and filter with a 500-mesh gauze. Then sequentially add the black pigment, wetting dispersant, leveling agent, defoamer, and thixotropic agent and mix. Then add the modified polyurethane, modified silica, and latent curing agent and mix thoroughly, disperse, and defoam. Grind on a three-roll mill until the fineness reaches 7 μm to obtain a protective paste for chip resistors.

[0038] Example 2:

[0039] A preparation method of a protective paste for chip resistors, the preparation method of the protective paste for chip resistors comprising the following preparation steps:

[0040] (1) Ethyl 2,5-dihydroxycinnamate, tetrabutylammonium bromide, and epichlorohydrin were mixed at a mass ratio of 1:0.09:1.55, heated to 60 °C and mixed for 30 min. Sodium hydroxide was added in three portions, with each addition amount being 0.14 times the mass of ethyl 2,5-dihydroxycinnamate, and the addition interval was 30 min. After the three additions of sodium hydroxide were completed, the reaction continued for 1.5 h. After the reaction ended, anhydrous ethanol three times the mass of epichlorohydrin was added, filtered, and the filtrate was retained. Rotary evaporation was carried out at 100 °C and -0.09 MPa, and then vacuum drying was carried out at room temperature to obtain the modified epoxy resin;

[0041] (2) Methylphenyldimethoxysilane was heated to 80 °C, and pure water twice the mass of methylphenyldimethoxysilane was added. After reacting for 3 h, vacuum filtration was carried out to obtain diphenylsilanediol; Phenylsilanediol, 1-[(chlorodimethylsilyl)methyl]-4-vinylbenzene, and pyridine were weighed according to a molar ratio of 4:3:8; 1-[(chlorodimethylsilyl)methyl]-4-vinylbenzene and tetrahydrofuran were mixed at a mass ratio of 1:5 to obtain a 1-[(chlorodimethylsilyl)methyl]-4-vinylbenzene solution; Diphenylsilanediol and tetrahydrofuran were mixed at a mass ratio of 1:5, pyridine was added, and the temperature was raised to 40 °C. The 1-[(chlorodimethylsilyl)methyl]-4-vinylbenzene solution was added and the reaction continued for 6 h. After the reaction ended, low-boiling substances were removed under reduced pressure. After adding ethyl acetate ten times the mass of diphenylsilanediol; The upper layer clear liquid was taken by centrifugation, and the upper layer clear liquid was washed with water, dried over anhydrous sodium sulfate, and rotary evaporated under reduced pressure at 60 °C to obtain a polysiloxane with terminal silicon hydroxyl groups; A polysiloxane with terminal silicon hydroxyl groups, octamethylcyclotetrasiloxane, tetrahydrofuran, potassium hydroxide, and 1,3-bis(3-hydroxypropyl)-1,1,3,3-tetramethyldisiloxane were weighed according to a mass ratio of 1:0.4:25:0.05:0.25; Potassium hydroxide and ethanol were mixed at a mass ratio of 1:100 to obtain a potassium hydroxide-ethanol solution; Octamethylcyclotetrasiloxane, a polysiloxane with terminal silicon hydroxyl groups, and tetrahydrofuran were mixed and heated to 60 °C and stirred for 6 h, then the potassium hydroxide-ethanol solution was added, and stirring continued for 3.5 h. After stirring ended, pure water and 1,3-bis(3-hydroxypropyl)-1,1,3,3-tetramethyldisiloxane were added, and the reaction continued for 2.5 h. After the reaction ended, low-boiling substances were removed by vacuum pumping, the temperature was raised to 90 °C, and vacuum pumping continued to obtain a hydroxypropyl-terminated polysiloxane;

[0042] (3) Mix toluene diisocyanate, polytetrahydrofuran ether glycol, hydroxypropyl-terminated polysiloxane, dibutyltin dilaurate, and toluene in a mass ratio of 1:2.5:0.4:0.025:25. After heating to 80 °C and reacting for 3.5 h, add ethylene glycol with a mass 0.5 times that of polytetrahydrofuran ether glycol and stir for 1.5 h. After stirring, add n-hexane with a volume 3.5 times that of toluene, filter, and dry at 50 °C for 23 h to obtain pre-modified polyurethane; mix the pre-modified polyurethane, copper oxide, diethylamine, carbon tetrachloride, and tetrahydrofuran in a mass ratio of 1:0.01:0.03:5.5:11, reflux at 72 °C for 5 h, filter to retain the filtrate, and obtain a modified polyurethane precursor by rotary evaporation under reduced pressure. Mix the modified polyurethane precursor, acidic catalyst, and N,N-dimethylformamide in a mass ratio of 1:0.02:3.5, heat to 120 °C and react for 10 h. After the reaction, obtain the modified polyurethane by rotary evaporation under reduced pressure; the acidic catalyst is prepared by mixing 98 wt% concentrated sulfuric acid, p-toluenesulfonic acid, pure water, and glacial acetic acid in a molar ratio of 0.15:0.05:1:2.5;

[0043] (4) Mix 3-(3-aminophenoxy)propyltrimethoxysilane, absolute ethanol, and pure water in a mass ratio of 1:5:10. After heating to 40 °C, stir for 4 min, add silica with a mass 3.5 times that of 3-(3-aminophenoxy)propyltrimethoxysilane, heat to 70 °C and reflux for 3.5 h. After the reaction, filter and wash 3 times with absolute ethanol, and vacuum dry at 70 °C to obtain pretreated silica; mix the pretreated silica, methyl pyruvate, acetonitrile, and iodine in a mass ratio of 1:0.6:25:0.001, reflux and stir at 50 °C for 12 h. After the reaction, filter and wash 3 times with pure water, and vacuum dry at room temperature to obtain quinolinyl silica; at 0 °C, mix lithium aluminum hydride and tetrahydrofuran in a mass ratio of 1:40 to obtain a catalyst solution. Under nitrogen protection, mix quinolinyl silica and tetrahydrofuran in a mass ratio of 1:5.5 for 4 min, add a catalyst solution with a mass 25 times that of quinolinyl silica and react for 8 h. After the reaction, cool to 0 °C and stir for 20 min, successively add ether with a mass 40 times that of quinolinyl silica, pure water with a mass 2 times that of quinolinyl silica, and a 15 wt% sodium hydroxide solution with a mass 2 times that of quinolinyl silica, filter and wash 3 times with pure water, and vacuum dry at room temperature to obtain pre-modified silica; at 0 °C, mix the pre-modified silica, 2-ethoxy-1,3,2-dioxaphospholane 2-oxide, 1,8-diazabicyclo[5.4.0]undec-7-ene, and toluene in a mass ratio of 1:0.4:1:11 for 4 min, heat to 40 °C and react for 5.5 h. After the reaction, add acetic acid with a mass 3.5 times that of pre-modified silica, filter and wash 3 times with pure water, and vacuum dry at room temperature to obtain modified silica;

[0044] (5) Weigh the following components: 70 parts by mass of modified epoxy resin, 25 parts by mass of modified polyurethane, 25 parts by mass of modified silica, 8 parts by mass of black pigment, 25 parts by mass of diluent, 3 parts by mass of wetting dispersant, 3 parts by mass of leveling agent, 2 parts by mass of defoamer, 1 part by mass of thixotropic agent, 3 parts by mass of latent curing agent, and 0.7 parts by mass of photoinitiator; add the modified epoxy resin to the diluent, heat and stir at 70°C for 25 minutes, and filter with 500-mesh gauze; then add black pigment, wetting dispersant, leveling agent, defoamer, and thixotropic agent in sequence and mix, then add modified polyurethane, modified silica, and latent curing agent and mix thoroughly, disperse and degas, and grind on a three-roll mill to a fineness of 7 μm to obtain a protective slurry for chip resistors.

[0045] Embodiment 3:

[0046] A method for preparing a protective paste for a chip resistor, the method comprising the following steps:

[0047] (1) ethyl 2,5-dihydroxycinnamate, tetrabutylammonium bromide, and epichlorohydrin are mixed in a mass ratio of 1:0.1:1.6, heated to 60° C. and mixed for 30 minutes, and sodium hydroxide is added three times, the amount of sodium hydroxide added each time is 0.15 times the mass of ethyl 2,5-dihydroxycinnamate, the addition interval is 30 minutes, and the reaction is continued for 1.5 hours after the three additions of sodium hydroxide are completed. After the reaction is completed, anhydrous ethanol 3 times the mass of epichlorohydrin is added, and the filtrate is filtered and retained, and rotary evaporated at 100° C. and -0.09 MPa, and then vacuum dried at room temperature to obtain a modified epoxy resin;

[0048] (2) Heat methylphenyldimethoxysilane to 80 °C, add pure water twice the mass of methylphenyldimethoxysilane, and after reacting for 3 h, carry out vacuum filtration to obtain diphenylsilanediol; weigh phenylsilanediol, 1-[(chlorodimethylsilyl)methyl]-4-vinylbenzene, and pyridine according to a molar ratio of 4:3:8; mix 1-[(chlorodimethylsilyl)methyl]-4-vinylbenzene and tetrahydrofuran in a mass ratio of 1:5 to obtain a 1-[(chlorodimethylsilyl)methyl]-4-vinylbenzene solution; mix diphenylsilanediol and tetrahydrofuran in a mass ratio of 1:5, add pyridine and heat to 40 °C, add the 1-[(chlorodimethylsilyl)methyl]-4-vinylbenzene solution and continue to react for 6 h. After the reaction is completed, remove the low-boiling substances under reduced pressure, add ethyl acetate ten times the mass of diphenylsilanediol; centrifuge and take the supernatant. The supernatant is washed with water, dried over anhydrous sodium sulfate, and rotary evaporated under reduced pressure at 60 °C to obtain a polysiloxane with terminal silicon hydroxyl groups; weigh the polysiloxane with terminal silicon hydroxyl groups, octamethylcyclotetrasiloxane, tetrahydrofuran, potassium hydroxide, and 1,3-bis(3-hydroxypropyl)-1,1,3,3-tetramethyldisiloxane according to a mass ratio of 1:0.5:30:0.05:0.3; mix potassium hydroxide and ethanol in a mass ratio of 1:100 to obtain a potassium hydroxide-ethanol solution; mix octamethylcyclotetrasiloxane, the polysiloxane with terminal silicon hydroxyl groups, and tetrahydrofuran and heat to 60 °C and stir for 6 h, then add the potassium hydroxide-ethanol solution and continue to stir for 3.5 h. After the stirring is completed, add pure water and 1,3-bis(3-hydroxypropyl)-1,1,3,3-tetramethyldisiloxane and continue to react for 2.5 h. After the reaction is completed, remove the low-boiling substances by vacuum pumping under reduced pressure, heat to 90 °C, and continue vacuum pumping to obtain a hydroxypropyl-terminated polysiloxane;

[0049] (3) Mix toluene diisocyanate, polytetrahydrofuran ether glycol, hydroxypropyl-terminated polysiloxane, dibutyltin dilaurate, and toluene in a mass ratio of 1:3:0.5:0.03:30, heat to 80 °C and react for 3 h, then add ethylene glycol half the mass of polytetrahydrofuran ether glycol and stir for 1 h. After the stirring is completed, add n-hexane four times the volume of toluene, filter and dry at 50 °C for 22 h to obtain a pre-modified polyurethane; mix the pre-modified polyurethane, copper oxide, diethylamine, carbon tetrachloride, and tetrahydrofuran in a mass ratio of 1:0.01:0.03:6:12, reflux at 70 °C for 5 h, filter and retain the filtrate, and obtain a modified polyurethane precursor by rotary evaporation under reduced pressure. Mix the modified polyurethane precursor, acidic catalyst, and N,N-dimethylformamide in a mass ratio of 1:0.02:4, heat to 116 °C and react for 10 h. After the reaction is completed, obtain the modified polyurethane by rotary evaporation under reduced pressure; the acidic catalyst is prepared by mixing 98 wt% concentrated sulfuric acid, p-toluenesulfonic acid, pure water, and glacial acetic acid in a molar ratio of 0.15:0.05:1:2.5;

[0050] (4) Mix 3-(3-aminophenoxy)propyltrimethoxysilane, absolute ethanol, and pure water in a mass ratio of 1:5:10. Heat to 40 °C and stir for 3 min. Add silica with a mass 4 times that of 3-(3-aminophenoxy)propyltrimethoxysilane. Heat to 70 °C and reflux for 3 h. After the reaction, filter and wash 3 times with absolute ethanol, and then vacuum dry at 70 °C to obtain pretreated silica. Mix the pretreated silica, methyl pyruvate, acetonitrile, and iodine in a mass ratio of 1:0.7:30:0.001. Reflux and stir at 50 °C for 12 h. After the reaction, filter and wash 3 times with pure water, and then vacuum dry at room temperature to obtain quinolinyl silica. At 0 °C, mix lithium aluminum hydride and tetrahydrofuran in a mass ratio of 1:40 to obtain a catalyst solution. Under nitrogen protection, mix quinolinyl silica and tetrahydrofuran in a mass ratio of 1:5 for 3 min. Add a catalyst solution with a mass 30 times that of quinolinyl silica and react for 8 h. After the reaction, cool to 0 °C and stir for 20 min. Then, add ether with a mass 40 times that of quinolinyl silica, pure water with a mass 2 times that of quinolinyl silica, and a 15 wt% sodium hydroxide solution with a mass 2 times that of quinolinyl silica in sequence. Filter and wash 3 times with pure water, and then vacuum dry at room temperature to obtain pre-modified silica. At 0 °C, mix pre-modified silica, 2-ethoxy-1,3,2-dioxaphospholane 2-oxide, 1,8-diazabicyclo[5.4.0]undec-7-ene, and toluene in a mass ratio of 1:0.5:1:12 for 3 min. Heat to 40 °C and react for 5 h. After the reaction, add acetic acid with a mass 4 times that of pre-modified silica. Filter and wash 3 times with pure water, and then vacuum dry at room temperature to obtain modified silica.

[0051] (5) Weigh the following components: 80 parts of modified epoxy resin, 30 parts of modified polyurethane, 30 parts of modified silica, 9 parts of black pigment, 30 parts of diluent, 3 parts of wetting dispersant, 3 parts of leveling agent, 3 parts of defoamer, 2 parts of thixotropic agent, 5 parts of latent curing agent, and 1 part of photoinitiator by mass. Add the modified epoxy resin to the diluent, heat and stir at 60 °C for 20 min, and filter with a 500-mesh gauze. Then, add the black pigment, wetting dispersant, leveling agent, defoamer, and thixotropic agent in sequence and mix. Then, add the modified polyurethane, modified silica, and latent curing agent and mix well, and disperse and defoam. Grind on a three-roll mill to make the fineness reach 7 μm to obtain the protective paste for chip resistors.

[0052] Comparative Example 1:

[0053] The difference between the preparation method of the protective paste for chip resistors in Comparative Example 1 and Example 2 is that step (4) is modified as follows: 3-(3-aminophenoxy)propyltrimethoxysilane, anhydrous ethanol, and pure water are mixed in a mass ratio of 1:5:10, heated to 40°C and stirred for 4 minutes, 3.5 times the mass of 3-(3-aminophenoxy)propyltrimethoxysilane is added, the temperature is raised to 70°C and refluxed for 3.5 hours, after the reaction is completed, the reaction is filtered and washed with anhydrous ethanol for 3 times, and vacuum dried at 70°C to obtain pretreated silica; the pretreated silica, methyl pyruvate, acetonitrile, and iodine are mixed in a mass ratio of 1:0.6:25:0.001, refluxed at 50°C and stirred for 12 hours, and the reaction is carried out. After completion, filter and wash with pure water for 3 times, and vacuum dry at room temperature to obtain quinolyl silica; at 0°C, mix lithium aluminum tetrahydride and tetrahydrofuran in a mass ratio of 1:40 to obtain a catalyst solution, under nitrogen protection, mix quinolyl silica and tetrahydrofuran in a mass ratio of 1:5.5 for 4 minutes, add 25 times the mass of quinolyl silica catalyst solution to react for 8 hours, after the reaction is completed, cool to 0°C and stir for 20 minutes, add 40 times the mass of quinolyl silica ether, 2 times the mass of quinolyl silica pure water, 2 times the mass of quinolyl silica 15wt% sodium hydroxide solution in sequence, filter and wash with pure water for 3 times, and vacuum dry at room temperature to obtain modified silica.

[0054] Comparative Example 2:

[0055] The preparation method of the protective paste for chip resistors in Comparative Example 2 differs from that in Example 2 in that step (4) is not included, and step (5) is modified as follows: the following components are weighed: 70 parts of modified epoxy resin, 25 parts of modified polyurethane, 25 parts of silica, 8 parts of black pigment, 25 parts of diluent, 3 parts of wetting dispersant, 3 parts of leveling agent, 2 parts of defoaming agent, 1 part of thixotropic agent, 3 parts of latent curing agent, and 0.7 parts of photoinitiator, by mass; the modified epoxy resin is added to the diluent, heated and stirred at 70° C. for 25 minutes, and filtered through a 500-mesh gauze; black pigment, wetting dispersant, leveling agent, defoaming agent, and thixotropic agent are added in sequence and mixed, and then modified polyurethane, modified silica, and latent curing agent are added and mixed thoroughly, and dispersed and degassed, and ground on a three-roll mill to a fineness of 7 μm to obtain a protective paste for chip resistors.

[0056] Comparative Example 3:

[0057] The preparation method of the protective paste for chip resistors in Comparative Example 3 is different from that in Example 2 in that step (3) is modified as follows: Toluene diisocyanate, polytetrahydrofuran ether glycol, hydroxypropyl-terminated polysiloxane, dibutyltin dilaurate, and toluene are mixed in a mass ratio of 1:2.5:0.4:0.025:25, heated to 80 °C and reacted for 3.5 h, then ethylene glycol with a mass 0.5 times that of the polytetrahydrofuran ether glycol is added and stirred for 1.5 h. After stirring, n-hexane with a volume 3.5 times that of the toluene is added, filtered, and dried at 50 °C for 23 h to obtain the modified polyurethane.

[0058] Test Example 1:

[0059] Test of flame retardancy performance:

[0060] Test method: The protective pastes prepared in the examples and comparative examples were cured at 180 °C for 10 min, and the limiting oxygen index was measured using a JF-3 type instrument. The results are shown in Table 1.

[0061] Table 1

[0062] Limiting oxygen index (%) Limiting oxygen index (%) Example 1 32.1 Comparative Example 1 25.7 Example 2 32.2 Comparative Example 2 24.5 Example 3 32.4 Comparative Example 3 31.8

[0063] From the comparison of the experimental data of Examples 1-3 and Comparative Examples 1-3 in Table 1, it can be found that the protective paste for chip resistors prepared by the present invention has good flame retardancy performance.

[0064] By comparison, the limiting oxygen index of Examples 1-3 is greater than that of Comparative Examples 1-2, indicating that after the reaction of silica modified with 3-(3-aminophenoxy)propyltrimethoxysilane and methyl pyruvate, a dihydroquinoline structure containing a methyl ester is formed. After the ester group is reduced by lithium aluminum tetrahydride, the generated alcohol hydroxyl group can act as an initiator to initiate the ring-opening polymerization of 2-ethoxy-1,3,2-dioxaphospholane 2-oxide on the silica surface to form a polyphosphate structure with good flame retardancy performance; thus endowing the material with good flame retardancy performance.

[0065] Test Example 2:

[0066] Test of mechanical properties:

[0067] Test method: The protective pastes prepared in the examples and comparative examples were cured at 180 °C for 10 min; according to the standard GB / T1040.2-2006, the tensile properties of the protective pastes for chip resistors prepared in the examples and comparative examples were tested on a tensile testing machine, with a gauge length of 20 mm and a tensile speed of 5 mm / min, and the tensile strength was recorded. The results are shown in Table 2.

[0068] Test of anti-aging performance:

[0069] Testing method: Cure the protective slurries prepared in the examples and comparative examples at 180 °C for 10 min; conduct an aging test in accordance with Standard GB / T 7141-2008, and then test the tensile strength according to the mechanical property testing method and calculate the tensile strength retention rate before and after aging. The results are shown in Table 2.

[0070] Testing for self-healing performance:

[0071] Testing method: Cure the protective slurries prepared in the examples and comparative examples at 180 °C for 10 min; cut them into splines with dimensions of 5 mm × 10 mm × 100 mm, cut them off in the middle, splice the cross-sections together, and irradiate the joint with light of 365 nm extracted by a 250 W high-pressure mercury lamp with a filter for 4 h to repair it; then test the tensile strength according to the mechanical property testing method and calculate the tensile strength retention rate before and after repair. The results are shown in Table 2.

[0072] Table 2

[0073]

[0074] From the comparison of the experimental data of Examples 1 to 3 and Comparative Examples 1 to 3 in Table 2, it can be found that the protective slurry for chip resistors prepared by the present invention has good mechanical properties, anti-aging properties and self-healing properties.

[0075] The tensile strength of Examples 1 to 3 is greater than that of Comparative Examples 1 to 3. In the test of anti-aging performance, the tensile strength retention rate of Examples 1 to 3 is greater than that of Comparative Example 2. In the test of self-healing performance, after ultraviolet irradiation, the broken parts of Examples 1 to 3 and Comparative Examples 1 to 3 are reconnected, indicating that the reaction of 3-(3-aminophenoxy)propyltrimethoxysilane-modified silica and methyl pyruvate generates a dihydroquinoline structure containing a methyl ester, and the dihydroquinoline structure is a type of functional group with anti-aging effects, which can endow the material with good anti-aging properties; mix modified epoxy resin, modified polyurethane, modified silica, black pigment, diluent, wetting dispersant, leveling agent, defoaming agent, thixotropic agent, latent curing agent to obtain a protective slurry for chip resistors; the modified epoxy resin containing a cinnamoyl group and the polyurethane containing a cinnamoyl group can undergo controllable cross-linking under ultraviolet irradiation and have good photo-responsive self-healing ability. During the curing process of the protective slurry, the hydroxyl groups on the surface of the modified silica and the carboxyl groups on the side chain of the polyurethane can further cross-link with the epoxy groups to form a more complex and dense network structure, thereby improving the mechanical properties of the material.

[0076] It is obvious to those skilled in the art that the present invention is not limited to the details of the above-described exemplary embodiments, and that the present invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the present invention. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-restrictive. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be embraced within the present invention. Any reference signs in the claims should not be construed as limiting the claims involved.

Claims

1. A protective paste for a chip resistor, characterized in that: The protective paste for the chip resistor comprises modified epoxy resin, modified polyurethane, modified silicon dioxide, black pigment, diluent, wetting dispersant, leveling agent, defoamer, thixotropic agent, latent curing agent and photoinitiator; The modified epoxy resin is prepared by reacting ethyl 2,5-dihydroxycinnamate, tetrabutylammonium bromide and epichlorohydrin; The modified polyurethane is obtained by reacting a pre-modified polyurethane obtained by polymerizing toluene diisocyanate, polytetramethylene glycol, and hydroxypropyl-terminated polysiloxane with carbon tetrachloride and then hydrolyzing the pre-modified polyurethane; the hydroxypropyl-terminated polysiloxane is obtained by polymerizing octamethylcyclotetrasiloxane, terminal silanol polysiloxane, and 1,3-bis(3-hydroxypropyl)-1,1,3,3-tetramethyldisiloxane; the terminal silanol polysiloxane is obtained by reacting diphenylsilanediol with 1-[(chlorodimethylsilyl)methyl]-4-vinylbenzene; The modified silicon dioxide is obtained by reacting silicon dioxide modified with 3-(3-aminophenoxy)propyltrimethoxysilane with methyl pyruvate, reducing it with lithium aluminum hydroxide, and then initiating ring-opening polymerization of 2-ethoxy-1,3,2-dioxaphospholane 2-oxide.

2. A method for preparing a protective paste for a chip resistor, characterized in that: The method comprises the following preparation steps: (1) mixing ethyl 2,5-dihydroxycinnamate, tetrabutylammonium bromide and epichlorohydrin, and adding sodium hydroxide to react to obtain a modified epoxy resin; (2) hydrolyzing methylphenyldimethoxysilane to obtain diphenylsilanediol, reacting diphenylsilanediol with 1-[(chlorodimethylsilyl)methyl]-4-vinylbenzene to obtain terminal silanol polysiloxane; reacting terminal silanol polysiloxane, octamethylcyclotetrasiloxane, potassium hydroxide, and 1,3-di(3-hydroxypropyl)-1,1,3,3-tetramethyldisiloxane to obtain hydroxypropyl-terminated polysiloxane; (3) reacting toluene diisocyanate, polytetramethylene glycol, hydroxypropyl-terminated polysiloxane, and dibutyltin dilaurate to obtain a pre-modified polyurethane; reacting the pre-modified polyurethane, copper oxide, diethylamine, and carbon tetrachloride to obtain a modified polyurethane precursor; and hydrolyzing the modified polyurethane precursor under the catalysis of an acidic catalyst to obtain a modified polyurethane; (4) reacting pretreated silica and methyl pyruvate to obtain quinolyl silica; reducing quinolyl silica in the presence of a catalyst to obtain premodified silica; reacting premodified silica and 2-ethoxy-1,3,2-dioxaphospholane 2-oxide to obtain modified silica; (5) Weigh the following components: modified epoxy resin, modified polyurethane, modified silica, black pigment, diluent, wetting dispersant, leveling agent, defoaming agent, thixotropic agent, latent curing agent, and photoinitiator; add the modified epoxy resin to the diluent, heat and stir at 60-90° C. for 20-30 min, and filter with 500-mesh gauze; then add black pigment, wetting dispersant, leveling agent, defoaming agent, thixotropic agent, and photoinitiator in sequence and mix; then add modified polyurethane, modified silica, and latent curing agent and mix thoroughly, disperse and degas, and grind on a three-roll mill to a fineness of 7 μm to obtain a protective slurry for chip resistors.

3. The method for preparing a protective paste for a chip resistor according to claim 2, characterized in that: The preparation method of the modified epoxy resin in step (1) is as follows: 2,5-dihydroxycinnamic acid ethyl ester, tetrabutylammonium bromide and epichlorohydrin are mixed in a mass ratio of 1: (0.08-0.1): (1.5-1.6), the mixture is heated to 60° C. and mixed for 30 minutes, sodium hydroxide is added three times, the amount of sodium hydroxide added each time is 0.13-0.15 times the mass of 2,5-dihydroxycinnamic acid ethyl ester, the addition interval is 30 minutes, and the reaction is continued for 1.5 hours after the three additions of sodium hydroxide are completed. After the reaction is completed, anhydrous ethanol with a mass of 3 times that of epichlorohydrin is added, the filtrate is filtered and retained, and rotary evaporated at 100° C. and -0.09 MPa, and then vacuum dried at room temperature to obtain the modified epoxy resin.

4. The method for preparing a protective paste for a chip resistor according to claim 2, characterized in that: The preparation method of the hydroxypropyl-terminated polysiloxane in step (2) is as follows: heating methylphenyldimethoxysilane to 80° C., adding pure water in an amount twice the mass of methylphenyldimethoxysilane, reacting for 3 hours, and filtering under reduced pressure to obtain diphenylsilanediol; weighing phenylsilanediol, 1-[(chlorodimethylsilyl)methyl]-4-vinylbenzene, and pyridine in a molar ratio of 4:3:8; mixing 1-[(chlorodimethylsilyl)methyl]-4-vinylbenzene and tetrahydrofuran in a mass ratio of 1:5 to obtain a 1-[(chlorodimethylsilyl)methyl]-4-vinylbenzene solution; mixing diphenylsilanediol and tetrahydrofuran in a mass ratio of 1:5, adding pyridine and heating the mixture to 40° C., adding 1-[(chlorodimethylsilyl)methyl]-4-vinylbenzene solution and continuing the reaction for 6 hours. After the reaction is completed, removing low-boiling substances under reduced pressure, adding ethyl acetate in an amount 10 times the mass of diphenylsilanediol, and centrifuging to obtain a supernatant, washing the supernatant with water, and rinsing with anhydrous sulfuric acid. The mixture was dried with sodium, and rotary evaporated under reduced pressure at 60°C to obtain terminal silanol polysiloxane; terminal silanol polysiloxane, octamethylcyclotetrasiloxane, tetrahydrofuran, potassium hydroxide, and 1,3-bis(3-hydroxypropyl)-1,1,3,3-tetramethyldisiloxane were weighed in a mass ratio of 1:(0.3-0.5):(20-30):0.05:(0.2-0.3); potassium hydroxide and ethanol were mixed in a mass ratio of 1:100 to obtain a potassium hydroxide-ethanol solution. ; Octamethylcyclotetrasiloxane, terminal silanol polysiloxane and tetrahydrofuran were mixed and heated to 60°C and stirred for 6 hours, then potassium hydroxide-ethanol solution was added and stirring was continued for 3.5 hours. After stirring, pure water and 1,3-bis(3-hydroxypropyl)-1,1,3,3-tetramethyldisiloxane were added and the reaction was continued for 2.5 hours. After the reaction was completed, the low-boiling substances were removed by vacuuming under reduced pressure, the temperature was raised to 90°C, and vacuuming was continued to obtain hydroxypropyl-terminated polysiloxane.

5. The method for preparing a protective paste for a chip resistor according to claim 2, characterized in that: The preparation method of the modified polyurethane in step (3) is as follows: toluene diisocyanate, polytetramethylene glycol, hydroxypropyl terminated polysiloxane, dibutyltin dilaurate, and toluene are mixed in a mass ratio of 1:(2-3):(0.3-0.5):(0.02-0.03):(20-30) mixed, heated to 80 ° C for 3-4 hours, added ethylene glycol with a mass of 0.5 times that of polytetrahydrofuran ether glycol and stirred for 1-2 hours, after the stirring was completed, added n-hexane with a volume of 3-4 times that of toluene, filtered and dried at 50 ° C for 22-24 hours to obtain pre-modified polyurethane; pre-modified polyurethane, copper oxide, diethylamine, carbon tetrachloride, tetrahydrofuran were mixed in a mass ratio of 1:0.01:0.03:(5-6):(10-12), After refluxing at 70-75° C. for 5 hours, the filtrate is filtered and retained, and a modified polyurethane precursor is obtained by vacuum rotary evaporation. The modified polyurethane precursor, the acid catalyst, and N,N-dimethylformamide are mixed in a mass ratio of 1:0.02:(3-4), and the temperature is raised to 116-122° C. for reaction for 10 hours. After the reaction is completed, the modified polyurethane is obtained by vacuum rotary evaporation; the acid catalyst is prepared by mixing 98wt% concentrated sulfuric acid, p-toluenesulfonic acid, pure water, and glacial acetic acid in a molar ratio of 0.15:0.05:1:2.5; the molecular weight of the polytetrahydrofuran ether diol is 2000.

6. The method for preparing a protective paste for a chip resistor according to claim 2, characterized in that: The preparation method of the modified silicon dioxide in step (4) is as follows: pretreated silicon dioxide, methyl pyruvate, acetonitrile and iodine are mixed in a mass ratio of 1: (0.5-0.7): (20-30): 0.001, refluxed and stirred at 50° C. for 12 h, filtered and washed with pure water for 3-4 times after the reaction is completed, and vacuum dried at room temperature to obtain quinolyl silicon dioxide; at 0° C., lithium aluminum hydroxide and tetrahydrofuran are mixed in a mass ratio of 1: 40 to obtain a catalyst solution; under nitrogen protection, quinolyl silicon dioxide and tetrahydrofuran are mixed in a mass ratio of 1: (5-6) for 3-5 min, a catalyst solution with a mass ratio of 20-30 times that of quinolyl silicon dioxide is added to react for 8 h, and after the reaction is completed, the temperature is lowered to 0° C. and stirred for 20 min, and quinolyl silicon dioxide is added in sequence. 40 times the mass of ethyl ether of quinolyl silica, 2 times the mass of pure water of quinolyl silica, and 2 times the mass of 15wt% sodium hydroxide solution of quinolyl silica, filtered and washed with pure water 3-4 times, and vacuum dried at room temperature to obtain pre-modified silica; at 0°C, pre-modified silica, 2-ethoxy-1,3,2-dioxaphospholane 2-oxide, 1,8-diazabicyclo[5.4.0]undec-7-ene, and toluene were mixed in a mass ratio of 1:(0.3-0.5):1:(10-12) for 3-5 minutes, heated to 40°C for reaction for 5-6 hours, and after the reaction was completed, 3-4 times the mass of pre-modified silica was added with acetic acid, filtered, washed with pure water 3-4 times, and vacuum dried at room temperature to obtain modified silica.

7. The method for preparing a protective paste for a chip resistor according to claim 2, characterized in that: The amounts of the components in step (5) are as follows: by mass, 60-80 parts of modified epoxy resin, 20-30 parts of modified polyurethane, 20-30 parts of modified silica, 7-9 parts of black pigment, 20-30 parts of diluent, 2-3 parts of wetting dispersant, 2-3 parts of leveling agent, 2-3 parts of defoaming agent, 1-2 parts of thixotropic agent, 3-5 parts of latent curing agent, and 0.5-1 part of photoinitiator; the black pigment is insulating carbon black; the diluent is diethylene glycol monobutyl ether; and the latent curing agent is dicyandiamide.

8. The method for preparing a protective paste for a chip resistor according to claim 6, characterized in that: The preparation method of the pretreated silicon dioxide is as follows: 3-(3-aminophenoxy)propyltrimethoxysilane, anhydrous ethanol and pure water are mixed in a mass ratio of 1:5:10, the mixture is heated to 40°C and stirred for 3-5 minutes, silicon dioxide of 3-4 times the mass of 3-(3-aminophenoxy)propyltrimethoxysilane is added, the mixture is heated to 70°C and refluxed for reaction for 3-4 hours, after the reaction is completed, the mixture is filtered and washed with anhydrous ethanol for 3-4 times, and vacuum dried at 70°C to obtain the pretreated silicon dioxide; the silicon dioxide particle size is 200-300nm.

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