Flame-retardant hot melt adhesive for electronic devices and method for preparing the same

Abstract

The application relates to the technical field of hot melt adhesives, and particularly relates to a flame-retardant hot melt adhesive for electronic devices and a preparation method thereof.The flame-retardant hot melt adhesive for electronic devices comprises the following raw materials: an ethylene-vinyl acetate copolymer, a poly(styrene-b-acrylic acid) diblock copolymer, a flame retardant, a silane coupling agent and an antioxidant.The preparation method of the poly(styrene-b-acrylic acid) diblock copolymer comprises the following steps: under the condition of a synthetic solvent A and nitrogen protection, styrene, 2-bromoisobutyryl bromide, pentamethyldiethylene triamine and cuprous bromide are heated to 85-95 DEG C to obtain a PS segment; under the condition of a synthetic solvent B and nitrogen protection, acrylic acid, an activated PS segment, pentamethyldiethylene triamine and cuprous bromide are heated to 55-65 DEG C to obtain the poly(styrene-b-acrylic acid) diblock copolymer; and the hot melt adhesive for electronic devices provided by the application has high heat resistance, high bonding strength and excellent flame-retardant performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of hot melt adhesives, and particularly relates to a flame-retardant hot melt adhesive for electronic devices and a preparation method thereof. BACKGROUND

[0002] In the field of electronic devices, hot melt adhesives are widely used in bonding, sealing and fixing, etc. However, with the development of electronic products towards miniaturization and high performance, higher requirements are put forward for the performance of hot melt adhesives.

[0003] Firstly, heat is generated during the operation of electronic devices, so the hot melt adhesive needs to have excellent heat resistance to prevent softening, deformation and even failure. Traditional hot melt adhesives, such as EVA (ethylene-vinyl acetate copolymer) hot melt adhesives, have a low glass transition temperature and insufficient heat resistance, which are difficult to meet the use requirements in high-temperature environments. In order to improve the heat resistance, high-melting-point polymers are usually selected, but this often leads to processing difficulties and affects the bonding performance with substrates.

[0004] Secondly, there are a large number of high-surface-energy materials such as metals and glasses in electronic devices, and the bonding strength of traditional hot melt adhesives with them is low, which is prone to debonding.

[0005] In addition, electronic products have high requirements for flame-retardant performance, and traditional hot melt adhesives need to add flame retardants to meet the requirements. Commonly used additive flame retardants, such as halogen-based flame retardants and phosphorus-based flame retardants, have a large amount of addition, which affects the bonding strength, heat resistance and processing performance of the hot melt adhesive.

[0006] In order to improve the bonding strength of hot melt adhesives with materials such as metals, some methods use surface treatment or primer, but these methods are complex and high in cost. Therefore, it is an urgent problem for those skilled in the art to develop a hot melt adhesive for electronic devices with high heat resistance, high bonding strength and excellent flame-retardant performance. SUMMARY

[0007] In view of the deficiencies of the prior art, the purpose of the present application is to provide a flame-retardant hot melt adhesive for electronic devices and a preparation method thereof, aiming to prepare a hot melt adhesive for electronic devices with high heat resistance, high bonding strength and excellent flame-retardant performance.

[0008] The technical solution of the present application is as follows:

[0009] A flame-retardant hot melt adhesive for electronic devices comprises the following raw materials by mass:

[0010] 50-70 parts of ethylene-vinyl acetate copolymer, 20-30 parts of poly (styrene-b-acrylic acid) diblock copolymer, 5-15 parts of flame retardant, 0.5-2 parts of silane coupling agent, and 0.1-0.5 parts of antioxidant;

[0011] The method for preparing the poly(styrene-b-acrylic acid) diblock copolymer comprises the following steps:

[0012] PS segment synthesis: styrene, 2-bromoisobutyryl bromide, pentamethyldiethylene triamine, cuprous bromide are added in a molar ratio of 100: (0.95-1.05): (0.95-1.05): (0.95-1.05) under the condition of synthetic solvent A and nitrogen protection, heated to 85-95℃, and reacted for 12-24h to obtain the PS segment;

[0013] PAA segment synthesis: the PS segment and an activating agent are dissolved in an activating solvent, and activated for 1-2h to obtain an activated PS segment; acrylic acid, the activated PS segment, pentamethyldiethylene triamine, and cuprous bromide are added in a molar ratio of 50: (0.95-1.05): (0.95-1.05): (0.95-1.05) under the condition of synthetic solvent B and nitrogen protection, heated to 55-65℃, and reacted for 24-48h;

[0014] Post-processing: after the reaction is completed, the precipitate is washed with an alcohol solution, and the poly(styrene-b-acrylic acid) diblock copolymer is obtained after drying.

[0015] The PS segment is compatible with EVA, the PAA segment has a high glass transition temperature, and can strongly interact with metal, glass and other substrates. During melt blending, the PS-b-PAA diblock copolymer self-assembles to form a core-shell structure, the PAA segment aggregates to form a core, and the PS segment is dispersed in the EVA matrix, thereby improving the heat resistance and bonding strength of the hot melt adhesive.

[0016] The application selects an amphiphilic block copolymer, the PS segment is compatible with EVA, the PAA segment has a high glass transition temperature, and can interact with metal, glass and other substrates. During melt blending, the incompatible blocks undergo microphase separation to form a nanoscale core-shell structure, thereby improving the heat resistance and bonding strength of the hot melt adhesive. This method does not require pre-synthesis of a core-shell structure polymer, simplifying the production process and reducing costs. Through the above in-situ self-assembly, a core-shell structure with smaller particle size and better dispersion can be obtained, thereby improving the comprehensive performance of the hot melt adhesive.

[0017] Further, nitrogen gas is bubbled into the synthetic solvent A for 30-60min.

[0018] It is intended to remove dissolved oxygen in the synthetic solvent A and reduce the influence on the subsequent reaction.

[0019] Further, the activating solvent comprises one or a mixture of two of toluene, DMF and DMSO;

[0020] The mass ratio of the PS segment to the activation solvent is 1:(10-20).

[0021] The aim is to activate the bromine atom at the end of the PS segment, transforming it back into a highly active free radical or transition state species, thereby initiating the polymerization of acrylic acid monomers.

[0022] In its unactivated state, the bromine atoms at the ends of PS may be in a relatively stable state, making it difficult for them to react directly with acrylic monomers. Through activation treatment, the bromine atoms can interact with the activator to generate active species that can initiate chain growth, thereby achieving the connection between the PS segment and the PAA segment and forming a specific diblock copolymer.

[0023] Furthermore, the flame retardant is an epoxy phosphate reactive flame retardant, and the preparation method includes the following steps:

[0024] Phosphorylation: Trimethylolpropane and triethyl phosphate are mixed in a molar ratio of 1:(1.15-1.25) under nitrogen protection and heated to 130-150℃ for 3-5 h to obtain the phosphorylated product TMP-P.

[0025] Epoxidation: The mass ratio of TMP-P, epichlorohydrin, and anhydrous sodium carbonate is 1:(0.65-0.7):(0.9-1). The reaction solvent, catalyst, TMP-P, and anhydrous sodium carbonate are mixed, and then epichlorohydrin is added dropwise below 20°C. After the addition is complete, the temperature is raised to 38-42°C, and the reaction is carried out for 5-7 hours.

[0026] After the reaction is complete, the mixture is filtered, extracted, and dried to obtain the epoxy phosphate reactive flame retardant.

[0027] In epoxy-based reactive flame retardants, the epoxy groups can undergo ring-opening reactions with the carboxyl or anhydride groups in EVA, chemically bonding the flame retardant to the EVA polymer chain. The phosphate groups decompose at high temperatures to produce phosphoric acid, which catalyzes the dehydration and carbonization of EVA, forming a flame-retardant layer. Compared to transesterification, epoxy ring-opening reactions have higher reaction rates and selectivity, and do not produce byproducts. This reduces the precipitation and migration of flame retardants, improving flame-retardant efficiency.

[0028] Furthermore, the epoxy phosphate reactive flame retardant, in combination with both EVA and PS-b-PAA, helps to form a dense cross-linked network. This structure can effectively improve the Tg and Td of the hot melt adhesive and restrict molecular chain movement to enhance cohesive strength, thereby improving the adhesion and high-temperature resistance of the hot melt adhesive.

[0029] Furthermore, before the reaction of the trimethylolpropane and the triethyl phosphate, the air in the reaction vessel is replaced with nitrogen gas multiple times.

[0030] Further, after the epoxidation reaction is completed, filtering is performed, and then the pH of the filtrate is adjusted to 5-6.

[0031] Further, the silane coupling agent is a non-hydrolytic silane coupling agent.

[0032] Further, the non-hydrolytic silane coupling agent is N-(2-aminoethyl)-3-aminopropyl trimethoxysilane.

[0033] N-(2-aminoethyl)-3-aminopropyl trimethoxysilane does not contain easily hydrolyzable ethoxyl groups, and thus the occurrence of a hydrolysis reaction is avoided. The amino groups can form hydrogen bonds or coordination bonds with the hydroxyl groups on the surface of metals and glass, thereby forming a stable connection between the hot melt adhesive and the substrate.

[0034] The application also provides a preparation method of the flame-retardant hot melt adhesive for electronic devices, which comprises the following steps:

[0035] The raw materials are mixed at high speed, and then melt blended and screw extruded at 120-150°C to obtain the flame-retardant hot melt adhesive for electronic devices.

[0036] Further, the raw materials are dried in an oven at 60-80°C for 2-4h in advance, and then mixed at high speed.

[0037] Compared with the prior art, the application has the following beneficial effects:

[0038] 1. The PS segment is compatible with EVA, the PAA segment has a high glass transition temperature, and can strongly interact with the substrate such as metal and glass through hydrogen bonds. During melt blending, the poly(styrene-b-acrylic acid) diblock copolymer self-assembles to form a core-shell structure, the PAA segment aggregates to form a core, and the PS segment is dispersed in the EVA matrix, thereby improving the heat resistance and bonding strength of the hot melt adhesive.

[0039] 2. The epoxy groups in the epoxy phosphate reactive flame retardant can react with the carboxyl groups or anhydride groups in EVA to chemically bond the flame retardant to the EVA polymer chain, thereby reducing the precipitation and migration of the flame retardant and improving the flame-retardant efficiency. The phosphate groups can decompose to produce phosphoric acid at high temperatures, and the phosphoric acid can catalyze the dehydration and carbonization of EVA to form a flame-retardant layer.

[0040] 3. N-(2-aminoethyl)-3-aminopropyl trimethoxysilane does not contain easily hydrolyzable ethoxyl groups, and thus the occurrence of a hydrolysis reaction is avoided. The amino groups can form hydrogen bonds or coordination bonds with the hydroxyl groups on the surface of metals and glass, thereby forming a stable connection between the hot melt adhesive and the substrate.

[0041] 4. EVA provides basic adhesive properties, amphiphilic block copolymer improves heat resistance and adhesive strength, epoxy phosphate reactive flame retardant provides flame retardant properties, amino vinyl silane coupling agent enhances adhesion to metal and glass, and antioxidant improves long-term stability. Through the synergistic effect of each component, the final realization of high heat resistance, high adhesion, flame retardant and low migration of hot melt adhesive for electronic devices. DETAILED DESCRIPTION

[0042] In order to facilitate the understanding of the present application, the present application is listed as follows. It should be understood by those skilled in the art that the examples are only to help understand the present application, and should not be regarded as specific limitations of the present application.

[0043] The present application provides a flame-retardant hot melt adhesive for electronic devices, comprising the following mass parts of raw materials:

[0044] 50-70 parts of ethylene-vinyl acetate copolymer, 20-30 parts of poly(styrene-b-acrylic acid) diblock copolymer, 5-15 parts of flame retardant, 0.5-2 parts of silane coupling agent, 0.1-0.5 parts of antioxidant.

[0045] The silane coupling agent is a non-hydrolytic silane coupling agent, and is further preferably N-(2-aminoethyl)-3-aminopropyl trimethoxysilane.

[0046] The antioxidant has no special requirements and can be antioxidant 1010 or antioxidant 1076.

[0047] The poly(styrene-b-acrylic acid) diblock copolymer is self-made, and the preparation method comprises the following steps:

[0048] Step 1: PS segment synthesis:

[0049] Step 1a: Oxygen removal treatment is performed on the synthesis solvent A:

[0050] Specifically, the synthesis solvent A is added to the reaction bottle, and nitrogen is bubbled for 30-60 min to remove the oxygen dissolved in the synthesis solvent A.

[0051] The synthesis solvent A is toluene.

[0052] Step 1b: styrene, 2-bromoisobutyryl bromide, pentamethyldiethylene triamine, and cuprous bromide are added to the reaction bottle equipped with a stirring device, a thermometer, and a reflux condenser in a molar ratio of 100: (0.95-1.05): (0.95-1.05): (0.95-1.05), with the synthesis solvent A as the solvent.

[0053] The mass of the synthesis solvent A is 5-10 times the total mass of styrene, 2-bromoisobutyryl bromide, pentamethyldiethylene triamine, and cuprous bromide.

[0054] Step 1c: The material in the reaction bottle is heated to 85-95°C under nitrogen protection for 12-24h to obtain the PS segment.

[0055] Step 2: PAA segment synthesis:

[0056] Step 2a: Activation treatment of the PS segment:

[0057] Specifically, the PS segment and the activation agent are dissolved in the activation solvent, and the activation reaction is carried out at room temperature for 1-2h to obtain the activated PS segment.

[0058] The activation solvent includes one or a mixture of two of toluene, DMF and DMSO.

[0059] The mass ratio of the PS segment to the activation solvent is 1: (10-20).

[0060] The amount of the activation agent is 0.1-0.5% of the mass of the PS segment.

[0061] The activation agent is tris (2-aminoethyl) amine (TREN).

[0062] Step 2b: The activated PS segment, acrylic acid, pentamethyl diethylene triamine and cuprous bromide are added to a reaction bottle equipped with a stirrer, a thermometer and a reflux condenser in a molar ratio of 50: (0.95-1.05): (0.95-1.05): (0.95-1.05) to synthesize solvent B.

[0063] The synthesis solvent B is DMF.

[0064] The amount of the synthesis solvent B is 5-10 times the total mass of the acrylic acid, the activated PS segment, the pentamethyl diethylene triamine and the cuprous bromide.

[0065] Step 2c: The material in the reaction bottle is heated to 55-65°C under nitrogen protection for 24-48h.

[0066] Step 3: Post-treatment:

[0067] Step 3a: After the reaction is completed, the reaction solution obtained in step 2 is poured into a large amount of ethanol, and the polymer is fully precipitated by stirring.

[0068] Step 3b: Filtration to collect the precipitate.

[0069] Step 3c: The precipitate is washed with an appropriate amount of ethanol for 2-3 times.

[0070] Step 3d: The washed precipitate is vacuum dried at a temperature of 40-60℃ for 12-24 hours to obtain the poly(styrene-b-acrylic acid) diblock copolymer.

[0071] The flame retardant can be commercially available or self-made.

[0072] When the flame retardant is self-made, the flame retardant is an epoxy phosphate reactive flame retardant, and the preparation method comprises the following steps:

[0073] Step 1: Phosphorylation:

[0074] Step 1a: Trimethylolpropane and triethyl phosphate are added to a reaction bottle equipped with a stirrer, a thermometer, and a reflux condenser in a molar ratio of 1:(1.15-1.25).

[0075] Step 1b: The air in the reaction bottle is replaced with nitrogen three times, and then heated to 130-150℃ under nitrogen protection for 3-5h.

[0076] Step 1c: After the reaction is completed, the generated ethanol is removed by vacuum distillation to obtain the phosphorylated product TMP-P.

[0077] Step 2: Epoxidation:

[0078] Step 2a: The mass ratio of TMP-P, epichlorohydrin, and anhydrous sodium carbonate is 1:(0.65-0.7):(0.9-1), and TMP-P and anhydrous sodium carbonate are added to a reaction bottle equipped with a stirrer, a thermometer, and a dropping funnel, using a reaction solvent as a solvent, and adding TBAB as a catalyst.

[0079] The amount of reaction solvent is 5-10 times the total mass of TMP-P, epichlorohydrin, and anhydrous sodium carbonate.

[0080] The reaction solvent is dichloromethane.

[0081] The amount of catalyst is 0.1-0.5% of the total mass of TMP-P, epichlorohydrin, and anhydrous sodium carbonate.

[0082] Step 2b: Slowly add epichlorohydrin to the reaction bottle under ice water bath cooling, and control the reaction temperature below 20℃.

[0083] Step 2c: After the addition of epichlorohydrin is completed, the temperature is raised to 38-42℃, and the reaction is carried out for 6 hours.

[0084] Step 3: After the reaction is completed, the sodium carbonate is removed by filtration, and dilute hydrochloric acid is slowly added to the filtrate to adjust the pH of the solution to 5-6.

[0085] Step 4: The filtrate of Step 3 is extracted with dichloromethane, washed with water until neutral, and dried over anhydrous sodium sulfate (5%-10% of the volume of the solution).

[0086] Step 5: The dichloromethane in the material of Step 4 is removed by vacuum distillation to obtain an epoxy phosphate reactive flame retardant.

[0087] In the scheme, a preparation method of the flame-retardant hot melt adhesive for electronic devices is also provided, which comprises the following steps.

[0088] Step 1: Drying of raw materials:

[0089] The raw materials are placed in an oven and dried at 60-80°C for 2-4h.

[0090] Step 2: Pre-mixing:

[0091] The dried raw materials are weighed according to the formula ratio, added to a high-speed mixer, and mixed for 3-5 minutes to preliminarily disperse and uniformly distribute the components.

[0092] Step 3: Melt blending:

[0093] The material pre-mixed in Step 2 is added to a twin-screw extruder, the screw speed is set to 80-120 rpm, the heating temperature is set to 120-150°C, and melt blending is performed for 10-20 min.

[0094] Step 4: Extrusion granulation:

[0095] The material melt blended in Step 3 is extruded from the extruder die, cooled through a cooling water tank, and then cut into granules by a granulator to obtain the flame-retardant hot melt adhesive for electronic devices.

[0096] The present application is further illustrated by specific examples.

[0097] Example 1

[0098] A flame-retardant hot melt adhesive for electronic devices comprises the following raw materials:

[0099] 60kg of ethylene-vinyl acetate copolymer (Elvax 250, DuPont), 23kg of poly(styrene-b-acrylic acid) diblock copolymer (self-made), 10kg of epoxy phosphate reactive flame retardant (self-made), 1.2kg of N-(2-aminoethyl)-3-aminopropyl trimethoxysilane, and 0.2kg of antioxidant 1076 (BASF).

[0100] The preparation method of the poly(styrene-b-acrylic acid) diblock copolymer comprises the following steps:

[0101] Step 1: Synthesis of PS segment:

[0102] Step 1a: Oxygen removal treatment of toluene:

[0103] Specifically, toluene was added to a reaction bottle, and nitrogen was bubbled for 45 min to remove oxygen dissolved in toluene.

[0104] Step 1b: Styrene, 2-bromoisobutyryl bromide, pentamethyldiethylenetriamine, and cuprous bromide were added to a reaction bottle equipped with a stirring device, a thermometer, and a reflux condenser in a molar ratio of 100:1:1:1, with toluene as the solvent.

[0105] The mass of toluene was 10 times the total mass of styrene, 2-bromoisobutyryl bromide, pentamethyldiethylenetriamine, and cuprous bromide.

[0106] Step 1c: The contents of the reaction bottle were heated to 90°C under nitrogen protection and reacted for 18 h to obtain the PS segment.

[0107] Step 2: PAA segment synthesis:

[0108] Step 2a: Activation treatment of the PS segment:

[0109] Specifically, the PS segment and the activator were dissolved in DMF, and the activation reaction was carried out at room temperature for 1.5 h to obtain the activated PS segment.

[0110] The amount of tris(2-aminoethyl)amine was 0.2% of the total mass of the PS segment.

[0111] The mass ratio of the PS segment to DMF was 1:15.

[0112] Step 2b: Acrylic acid, activated PS segment, pentamethyldiethylenetriamine, and cuprous bromide were added to a reaction bottle equipped with a stirrer, a thermometer, and a reflux condenser in a molar ratio of 50:1:1:1, with DMF as the solvent.

[0113] The activated PS segment, acrylic acid, pentamethyldiethylenetriamine, and cuprous bromide were added to a reaction bottle equipped with a stirrer, a thermometer, and a reflux condenser, with DMF as the solvent.

[0114] The amount of DMF was 8 times the total mass of acrylic acid, activated PS segment, pentamethyldiethylenetriamine, and cuprous bromide.

[0115] Step 2c: The contents of the reaction bottle were heated to 60°C under nitrogen protection and reacted for 36 h.

[0116] Step 3: Post-treatment:

[0117] Step 3a: After the reaction was completed, the reaction solution obtained in step 2 was poured into a large amount of ethanol, and the polymer was fully precipitated by stirring.

[0118] Step 3b: Filtration and collection of the precipitate.

[0119] Step 3c: The precipitate was washed with ethanol for 3 times.

[0120] Step 3d: The washed precipitate was vacuum dried at 50℃ for 18 hours to obtain the poly(styrene-b-acrylic acid) diblock copolymer.

[0121] The flame retardant is self-made, and the flame retardant is an epoxy phosphate reactive flame retardant. The preparation method comprises the following steps:

[0122] Step 1: Phosphorylation:

[0123] Step 1a: Trimethylolpropane and triethyl phosphate were added to a reaction bottle provided with a stirrer, a thermometer and a reflux condenser in a molar ratio of 1:1.2.

[0124] Step 1b: The air in the reaction bottle was replaced with nitrogen three times, and then heated to 140℃ under nitrogen protection for 4h.

[0125] Step 1c: After the reaction was completed, the generated ethanol was removed by vacuum distillation to obtain the phosphorylated product TMP-P.

[0126] Step 2: Epoxidation:

[0127] Step 2a: The mass ratio of TMP-P, epichlorohydrin and anhydrous sodium carbonate was 1:0.65:0.93, TMP-P and anhydrous sodium carbonate were added to a reaction bottle provided with a stirrer, a thermometer and a dropping funnel, dichloromethane was used as a solvent, and TBAB was added as a catalyst.

[0128] The amount of dichloromethane is 8 times the total mass of TMP-P, epichlorohydrin and anhydrous sodium carbonate.

[0129] The amount of catalyst is 0.2% of the total mass of TMP-P, epichlorohydrin and anhydrous sodium carbonate.

[0130] Step 2b: Under ice water bath cooling, epichlorohydrin was slowly added to the reaction bottle, and the reaction temperature was controlled below 20℃.

[0131] Step 2c: After the addition of epichlorohydrin was completed, the temperature was increased to 40℃, and the reaction was carried out for 6 hours.

[0132] Step 3: After the reaction was completed, the sodium carbonate was removed by filtration, and dilute hydrochloric acid was slowly added to the filtrate to adjust the pH to 5-6.

[0133] Step 4: The filtrate of step 3 was extracted with dichloromethane, washed with water until neutral, and dried by adding anhydrous sodium sulfate (the amount is 8% of the solution volume).

[0134] Step 5: Remove the dichloromethane in the material of step 4 by vacuum distillation to obtain the epoxy phosphate ester reactive flame retardant.

[0135] The embodiment also discloses a preparation method of the flame-retardant hot melt adhesive for electronic devices, comprising the following steps:

[0136] Step 1: drying of raw materials

[0137] The raw materials are placed in an oven and dried at 70°C for 3h.

[0138] Step 2: premixing

[0139] The dried raw materials are weighed according to the formula proportion, added into a high-speed mixer, and mixed for 4 minutes to preliminarily disperse and uniformly distribute the components.

[0140] Step 3: melt blending

[0141] The material after the premixing of step 2 is added into a double-screw extruder, the screw rotation speed is set to 110 rpm, the heating temperature is 140°C, and melt blending is performed for 15 min.

[0142] Step 4: extrusion granulation

[0143] The material after the melt blending of step 3 is extruded from the extruder die, cooled through a cooling water tank, and then cut into granules through a granulator to obtain the flame-retardant hot melt adhesive for electronic devices.

[0144] Performance test

[0145] 1. Heat resistance test: The glass transition temperature (Tg) of the hot melt adhesive is tested by differential scanning calorimetry (DSC), according to the standard GB / T 19466.2-2004. The heating rate is 10°C / min, and the test range is 25-200°C.

[0146] 2. Adhesion strength test: The adhesion strength of the hot melt adhesive and the aluminum plate is tested by tensile shear method, according to the standard GB / T 7124-2008. The aluminum plate size is 100mm×25mm×1.6mm, the lap area is 25mm×12.5mm, and the tensile rate is 5mm / min.

[0147] 3. Flame retardant performance test: The flame retardant performance of the hot melt adhesive is tested by vertical combustion method, according to the standard UL 94. The sample size is 127mm×12.7mm×3.2mm.

[0148] 4. Migration: The flame-retardant hot melt adhesive for electronic devices is stored at 50°C and 90% humidity for 90d, and then the flame retardant performance test is performed again according to test 3.

[0149] Test results

[0150] 1. Glass transition temperature (Tg): 102°C.

[0151] 2. Bonding strength (aluminum-aluminum): 13.2 MPa.

[0152] 3. Flame retardant rating: V-0.

[0153] 4. Migration: the flame retardant rating is V-0.

[0154] Example 2

[0155] A flame-retardant hot melt adhesive for electronic devices includes the following raw materials:

[0156] 50 kg of ethylene-vinyl acetate copolymer, 30 kg of poly(styrene-b-acrylic acid) diblock copolymer, 5 kg of epoxy phosphate reactive flame retardant, 2 kg of N-(2-aminoethyl)-3-aminopropyl trimethoxysilane, and 0.5 kg of antioxidant 1076.

[0157] The sources and preparation methods of the above raw materials are the same as those of Example 1.

[0158] The preparation method of the flame-retardant hot melt adhesive for electronic devices is the same as that of Example 1.

[0159] The performance detection method is the same as that of Example 1.

[0160] Detection results:

[0161] 1. Glass transition temperature (Tg): 100°C.

[0162] 2. Bonding strength (aluminum-aluminum): 12.9 MPa.

[0163] 3. Flame retardant rating: V-0.

[0164] 4. Migration: the flame retardant rating is V-0.

[0165] Example 3

[0166] A flame-retardant hot melt adhesive for electronic devices includes the following raw materials:

[0167] 70 kg of ethylene-vinyl acetate copolymer, 20 kg of poly(styrene-b-acrylic acid) diblock copolymer, 15 kg of epoxy phosphate reactive flame retardant, 0.5 kg of N-(2-aminoethyl)-3-aminopropyl trimethoxysilane, and 0.1 kg of antioxidant 1076.

[0168] The sources and preparation methods of the above raw materials are the same as those of Example 1.

[0169] The preparation method of the flame-retardant hot melt adhesive for electronic devices is the same as that of Example 1.

[0170] The performance detection method is the same as that of Example 1.

[0171] Test results:

[0172] 1. Glass transition temperature (Tg): 98℃.

[0173] 2. Bonding strength (aluminum-aluminum): 12.5 MPa.

[0174] 3. Flame retardant grade: V-0.

[0175] 4. Migration: the flame retardant grade is V-0.

[0176] Example 4

[0177] A flame-retardant hot melt adhesive for electronic devices comprises the following raw materials:

[0178] 60 kg of ethylene-vinyl acetate copolymer (Elvax 250, DuPont, USA), 23 kg of poly (styrene-b-acrylic acid) diblock copolymer (the same as in Example 1), 10 kg of flame retardant, 1.2 kg of N-(2-aminoethyl)-3-aminopropyl trimethoxysilane, and 0.2 kg of antioxidant 1076 (BASF).

[0179] The flame retardant is flame retardant TXP, which is purchased from Hubei Xiyu Hong Biological Medicine Technology Co., Ltd.

[0180] The preparation method of the flame-retardant hot melt adhesive for electronic devices is the same as that of Example 1.

[0181] The performance detection method is the same as that of Example 1.

[0182] Test results:

[0183] 1. Glass transition temperature (Tg): 95℃.

[0184] 2. Bonding strength (aluminum-aluminum): 11.2 MPa.

[0185] 3. Flame retardant grade: V-0.

[0186] 4. Migration: the flame retardant grade is V-1.

[0187] Comparative Example 1

[0188] A common flame-retardant hot melt adhesive A for electronic devices on the market is selected as a control group, and performance tests are performed, and the test method is the same as that of Example 1.

[0189] Performance data:

[0190] 1. Glass transition temperature (Tg): 75℃.

[0191] 2. Adhesion strength (aluminum-aluminum): 7.0 MPa.

[0192] 3. Flame retardant rating: V-0.

[0193] 4. Migration: the flame retardant rating is V-1.

[0194] Comparative Example 2

[0195] A common flame-retardant hot melt adhesive for electronic devices on the market was selected as the control group, and performance tests were conducted. The test method was the same as in Example 1.

[0196] Performance data:

[0197] 1. Glass transition temperature (Tg): 80℃.

[0198] 2. Adhesion strength (aluminum-aluminum): 7.5 MPa.

[0199] 3. Flame retardant rating: V-1.

[0200] 4. Migration: the flame retardant rating is V-1.

[0201] Comparative Example 3

[0202] A flame-retardant hot melt adhesive for electronic devices, different from Example 1, is that the source of the poly(styrene-b-acrylic acid) diblock copolymer is commercially available, purchased from Hangzhou Xinqiao Biotechnology Co., Ltd.

[0203] The test method is the same as in Example 1.

[0204] Performance data:

[0205] 1. Glass transition temperature (Tg): 92℃.

[0206] 2. Adhesion strength (aluminum-aluminum): 10.6 MPa.

[0207] 3. Flame retardant rating: V-0.

[0208] 4. Migration: the flame retardant rating is V-0.

[0209] Comparative Example 4

[0210] A flame-retardant hot melt adhesive for electronic devices, different from Example 4, is that the source of the poly(styrene-b-acrylic acid) diblock copolymer is commercially available, purchased from Hangzhou Xinqiao Biotechnology Co., Ltd.

[0211] The test method is the same as in Example 1.

[0212] Performance data:

[0213] 1. Glass transition temperature (Tg): 88℃.

[0214] 2. Bonding strength (Aluminum-Aluminum): 10.0 MPa.

[0215] 3. Flame retardant rating: V-0.

[0216] 4. Migration: the flame retardant rating is V-1.

[0217] Regarding the poly(styrene-b-acrylic acid) diblock copolymer, it can be seen from the test data of Comparative Example 1 and Comparative Example 3 that the performance of Comparative Example 3 is not as good as that of Example 1 in terms of heat resistance and bonding. It is indicated that the preparation conditions of the poly(styrene-b-acrylic acid) diblock copolymer need to be further limited in order to better improve the performance of the flame-retardant hot melt adhesive for electronic devices.

[0218] Comparative Example 4 is based on Example 4, and a commercially available poly(styrene-b-acrylic acid) diblock copolymer is selected. Comparative Example 4 has a decrease in glass transition temperature and bonding strength compared to Example 4. It also indicates that the poly(styrene-b-acrylic acid) diblock copolymer prepared in the present application can improve the heat resistance and bonding strength of the hot melt adhesive to a certain extent.

[0219] Regarding the selection of the flame retardant, Example 1 uses the epoxy phosphate reactive flame retardant prepared in the present application, and Example 4 uses a commonly used flame retardant on the market. It can be seen from the comparison of Comparative Example 1 and Example 4 that the flame-retardant effect of Example 4 is not as good as that of Example 1. Due to the lack of cooperation of the epoxy phosphate reactive flame retardant with the poly(styrene-b-acrylic acid) diblock copolymer and EVA, the glass transition temperature and bonding strength decrease. Moreover, under the storage condition of high temperature and high humidity, the flame retardant of Example 4 has a migration phenomenon, resulting in a significant decrease in flame-retardant performance. On the contrary, Example 1 performs well in terms of heat resistance, bonding, flame retardation, and migration resistance.

[0220] Meanwhile, it can be seen from the comparison of the test results of Examples 1-4 and Comparative Examples 1-2 that the flame-retardant hot melt adhesive for electronic devices prepared using the poly(styrene-b-acrylic acid) diblock copolymer and the epoxy phosphate reactive flame retardant prepared in the present application has a high glass transition temperature, i.e., can withstand a higher temperature during use and has better heat resistance; and has a high bonding strength on the surface of metal, while also having good flame retardation and migration resistance. The performance of the flame-retardant hot melt adhesive for electronic devices is excellent in all aspects, and it is suitable for popularization and use in the industry.

[0221] It should be understood that the application of the present application is not limited to the above examples, and those skilled in the art can make improvements or changes according to the above description, and all such improvements and changes shall fall within the scope of protection of the present application.

Claims

1. A flame-retardant hot melt adhesive for electronic devices, characterized by comprising: Comprise the following raw materials: 50-70 parts of ethylene-vinyl acetate copolymer, 20-30 parts of poly(styrene-b-acrylic acid) diblock copolymer, 5-15 parts of flame retardant, 0.5-2 parts of silane coupling agent, 0.1-0.5 parts of antioxidant; The preparation method of the poly(styrene-b-acrylic acid) diblock copolymer Comprise the following steps: PS segment synthesis: styrene, 2-bromoisobutyryl bromide, pentamethyldiethylene triamine, cuprous bromide are in a molar ratio of 100: (0.95-1.05): (0.95-1.05): (0.95-1.05), under the condition of synthetic solvent A, nitrogen protection, heated to 85-95℃, reaction for 12-24h, to obtain the PS segment; PAA segment synthesis: the PS segment, activator is dissolved in the activation solvent, and the activation reaction is 1-2h, to obtain the activated PS segment; acrylic acid, the activated PS segment, pentamethyldiethylene triamine, cuprous bromide are in a molar ratio of 50: (0.95-1.05): (0.95-1.05): (0.95-1.05), under the condition of synthetic solvent B, nitrogen protection, heated to 55-65℃, reaction for 24-48h; The activation solvent includes one or a mixture of two of toluene, DMF, DMSO; The activator is tris (2-aminoethyl) amine (TREN); Post-processing: after the reaction is completed, the precipitate is washed with an alcohol solution, and the poly (styrene-b-acrylic acid) diblock copolymer is obtained after drying; The flame retardant is an epoxy phosphate reactive flame retardant, and the preparation method comprises the following steps: Phosphorylation: trimethylolpropane, triethyl phosphate are in a molar ratio of 1: (1.15-1.25), heated to 130-150℃ under nitrogen protection, reaction for 3-5h, to obtain the phosphorylation product TMP-P; Epoxidation: the mass ratio of TMP-P, epichlorohydrin, anhydrous sodium carbonate is 1: (0.65-0.7): (0.9-1), the reaction solvent, catalyst, TMP-P, and anhydrous sodium carbonate are mixed, and then the epichlorohydrin is added dropwise below 20℃; after the dropwise addition is completed, it is warmed to 38-42℃ and reacted for 5-7h; After the reaction is completed, filter, extract, and dry to obtain the epoxy phosphate reactive flame retardant; The silane coupling agent is N-(2-aminoethyl)-3-aminopropyl trimethoxysilane.

2. The flame-retardant hot melt adhesive for electronic devices according to claim 1, wherein Nitrogen is bubbled into the synthetic solvent A for 30-60min.

3. The flame-retardant hot melt adhesive for electronic devices according to claim 1, wherein The mass ratio of the PS segment to the activation solvent is 1: (10-20).

4. The flame-retardant hot melt adhesive for electronic devices according to claim 1, wherein The trimethylolpropane and the triethyl phosphate are replaced with nitrogen several times before reaction.

5. The flame-retardant hot melt adhesive for electronic devices according to claim 1, wherein After the epoxidation reaction is completed, filter, and then adjust the pH of the filtrate to 5-6.

6. A process for the preparation of a flame-retardant hot-melt adhesive for electronic devices according to any one of claims 1-5, characterized by, Comprise the following steps: High-speed mix the raw materials, then melt blend under the condition of 120-150℃, and screw extrude to obtain the flame retardant hot melt adhesive for electronic devices.

7. The method of claim 6, wherein the flame-retardant hot melt adhesive for electronic devices is prepared by adding 0.1 to 5 parts by weight of the flame retardant to 100 parts by weight of the base resin. Dry the raw materials in an oven at 60-80℃ for 2-4h in advance, and then high-speed mix.