Lithium battery packaging hot melt adhesive with insulating property and preparation method

Abstract

The invention discloses a lithium battery packaging hot melt adhesive with insulating property and a preparation method thereof, and belongs to the technical field of preparation of hot melt adhesives for special application. The hot melt adhesive is prepared from the following components in parts by weight: 40 to 60 parts of modified polyolefin resin, 20 to 35 parts of tackifying resin, 10 to 25 parts of flame retardant, 5 to 15 parts of insulating filler, 0.5 to 2 parts of antioxidant and 1 to 3 parts of coupling agent, wherein the tackifying resin is a compounded system of hydrogenated rosin glyceride and a C5 / C9 copolymer, and the flame retardant is a compound of coated aluminum hydroxide and organic phosphinate. By compounding a hydrogenated rosin glyceride / C9 petroleum resin tackifying system, the melt viscosity is synergistically reduced, narrow-slit accurate dispensing is realized, and the volume resistivity breaks through the insulation bottleneck of the traditional hot melt adhesive by virtue of the compound filler of boehmite and boron nitride.

Description

Technical Field

[0001] This invention relates to a lithium battery encapsulation hot melt adhesive with insulating properties and its preparation method, belonging to the field of special application hot melt adhesive preparation technology. Background Technology

[0002] In the current lithium battery manufacturing process, the insulation encapsulation of the battery contacts mainly employs three traditional processes: heat shrink tubing wrapping, insulating tape wrapping, and epoxy potting compound curing. These processes have gradually revealed numerous insurmountable defects in long-term production practice. Firstly, the heat shrink tubing wrapping process requires operators to manually and precisely place the heat shrink tubing onto the designated position on the battery contact, and then heat the tubing using heating equipment to shrink it and tightly adhere it to the surface of the battery contact. The entire process relies entirely on manual operation. Similarly, the insulating tape wrapping process requires manual handling of the tape, wrapping the battery contact according to a prescribed method and number of layers. Both processes are not only cumbersome and time-consuming, but also suffer from extremely poor consistency in encapsulation quality due to individual differences in manual operation. Actual production data shows that the encapsulation time for a single battery contact generally exceeds 60 seconds, severely restricting the overall production efficiency of lithium batteries. Secondly, the epoxy potting compound curing process requires precise mixing of the epoxy potting compound and curing agent in a specific ratio. After thorough mixing, the mixture is applied or poured onto the areas of the battery that require insulation encapsulation. It must then be left to cure completely, a process that is extremely time-consuming, typically exceeding two hours. During this period, subsequent production processes cannot be performed, significantly extending the lithium battery production cycle. Thirdly, because these traditional processes either rely on manual operation or have specific requirements for production equipment and operating environments, they are difficult to integrate seamlessly with modern automated production lines and cannot meet the demands of large-scale, high-efficiency automated lithium battery production. Although some existing technologies disclose solutions for applying polyolefin-based hot melt adhesives to battery encapsulation, attempting to improve upon the shortcomings of traditional processes, these solutions still have significant limitations in practical applications. On the one hand, in the complex, highly conductive environment inside lithium batteries, these polyolefin-based hot melt adhesives cannot effectively solve the problem of insulation failure; actual testing shows that their insulation resistance can only reach 10 ohms. 8The Ω level is far from meeting the stringent insulation requirements of lithium batteries, easily leading to safety hazards such as battery short circuits. Furthermore, at an operating temperature of 180℃, the viscosity of this hot melt adhesive exceeds 8000 mPa·s. This excessive viscosity causes flow obstruction within the dispensing needle during application, resulting in problems such as poor dispensing, adhesive breaks, and uneven adhesive application, severely impacting encapsulation quality and production stability. Therefore, considering the current high demands for efficiency, quality, and safety in lithium battery production, there is an urgent need to develop a dedicated hot melt adhesive for lithium battery lead-aspect insulation encapsulation. This specialized hot melt adhesive must possess three key properties: first, it must enable rapid automated application, perfectly adapting to automated production lines and significantly shortening encapsulation time; second, it must have high insulation reliability, maintaining stable insulation performance even in highly conductive environments to ensure battery safety; and third, it must possess excellent flowability, maintaining a suitable viscosity at the application temperature to ensure a smooth and stable dispensing process, thereby meeting the actual production needs of lithium battery lead-aspect insulation encapsulation. Summary of the Invention

[0003] To address the shortcomings of existing technologies, this invention provides a lithium battery encapsulation hot melt adhesive with insulating properties, comprising the following components by weight:

[0004] The mixture comprises 40-60 parts of modified polyolefin resin, 20-35 parts of tackifying resin, 10-25 parts of flame retardant, 5-15 parts of insulating filler, 0.5-2 parts of antioxidant, and 1-3 parts of coupling agent; wherein the tackifying resin is a compound system of hydrogenated rosin glycerol ester and C5 / C9 copolymer (weight ratio 3:1-1:1), and the flame retardant is a composite of coated aluminum hydroxide and organic phosphonate (weight ratio 2:1-4:1).

[0005] Preferably, the compound system of hydrogenated rosin glycerol ester and C5 / C9 copolymer has a weight ratio of 3:1 to 1:1; the compound system of coated aluminum hydroxide and organic phosphonate has a weight ratio of 2:1 to 4:1.

[0006] Preferably, the modified polyolefin resin is a polypropylene / polyethylene copolymer with a maleic anhydride grafting rate of 0.8-1.5 wt% and a melt index of 120-180 g / 10 min (190℃ / 2.16 kg).

[0007] Preferably, the insulating filler is a mixture of surface-silanized boehmite (particle size D50 = 1-3 μm) and boron nitride sheets (diameter-to-thickness ratio > 50) in a weight ratio of 2:1 to 4:1.

[0008] Preferably, the surface silanization treatment method of boehmite in the insulating filler is as follows: mix boehmite powder with γ-(2,3-epoxypropoxy)propyltrimethoxysilane at a weight ratio of 100:1.5-3, treat in a high-speed mixer at 80-90℃ for 30-45 minutes, and then pass through a 200-mesh sieve after cooling.

[0009] Preferably, the antioxidant is a compound of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and tris(2,4-di-tert-butylphenyl)phosphite in a weight ratio of 1:1 to 1:2.

[0010] Preferably, the flame retardant is prepared by dissolving aluminum hydroxide powder and silane coupling agent KH-550 in an ethanol solution (solid content 40%) at a weight ratio of 100:2-5, stirring at 50°C for 2 hours, and then spray drying (inlet 180°C / outlet 80°C). The resulting coated aluminum hydroxide is then dry-mixed with aluminum diethylphosphinate.

[0011] Preferably, the modified polyolefin resin is prepared by reacting polypropylene / polyethylene copolymer (melt index 80-100g / 10min), maleic anhydride and initiator dicumyl peroxide (0.5-1wt%) in a twin-screw extruder, with temperature zones: Zone I 160℃ / Zone II 180℃ / Zone III 190℃ / Zone IV 185℃, screw speed 400rpm, and grafting rate controlled at 0.8-1.5wt%.

[0012] The present invention also provides a method for preparing the above-mentioned hot melt adhesive, comprising the following steps:

[0013] (1) Melt the modified polyolefin resin;

[0014] (2) Add the thickening resin and heat while stirring;

[0015] (3) Cool down, add flame retardant, insulating filler, antioxidant and coupling agent, and degas under vacuum;

[0016] (4) The product is obtained by melt blending in a twin-screw extruder and underwater pelletizing.

[0017] Preferably, the melting in step (1) is carried out at a temperature of 160-170°C under nitrogen protection.

[0018] Preferably, the heating and stirring in step (2) involves heating to 180-185°C and stirring for 30-45 minutes.

[0019] Preferably, in step (3), the temperature is reduced to 130-140℃, and the vacuum degassing time is 10-20 minutes with a vacuum degree ≤-0.095MPa.

[0020] Preferably, the method according to claim 4 is characterized in that: the coupling agent in step (3) is a compound of γ-aminopropyltriethoxysilane and titanate coupling agent (weight ratio 1:1-1:2).

[0021] Preferably, the melt blending in step (4) is carried out in temperature zones: Zone I 150℃ / Zone II 160℃ / Zone III 165℃ / Zone IV 170℃, with a screw speed of 200-300 rpm.

[0022] The present invention also provides a method for encapsulating lithium battery contacts, wherein the hot melt adhesive is melted at 170-180℃ and applied to the surface of the contacts using a dispensing device at a pressure of 0.3-0.6MPa, with a cooling and curing time of ≤15s. The coating thickness is 0.5-1.0mm, and the insulation resistance after curing is ≥100GΩ (test voltage 500V).

[0023] The present invention also provides the application of the above-mentioned hot melt adhesive in the edge sealing of aluminum-plastic film for soft-pack lithium batteries.

[0024] The beneficial effects of this invention are:

[0025] This invention utilizes a compounded hydrogenated rosin glycerol ester / C9 petroleum resin tackifying system to synergistically reduce melt viscosity to below 4000 mPa·s (180℃), achieving precise dispensing in narrow 0.3mm gaps. It innovatively employs a coated aluminum hydroxide / aluminum diethylphosphinate composite flame retardant, achieving UL94 V-0 rating (1.6mm) with a total flame retardant content of 25 parts, without affecting insulation performance. The compounded filler of boehmite and boron nitride increases the volume resistivity to 10¹⁸ O. 6 The Ω·cm level breakthrough overcomes the limitations of traditional hot melt adhesive insulation. The synergistic effect of maleic anhydride-grafted polyolefin and silane coupling agent enables an aluminum foil-copper tab bonding strength of 6.5 N / mm, with a strength retention rate of >90% after immersion in electrolyte (60℃ / 720h). The overall process is compatible with automated production lines, reducing single-point encapsulation time to 8 seconds, improving efficiency by 87% compared to traditional processes. Detailed Implementation

[0026] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0027] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those familiar to those skilled in the art. Furthermore, any methods and materials similar to or equivalent to those described herein may be applied to this invention. The preferred embodiments and materials described herein are for illustrative purposes only and do not limit the scope of this application.

[0028] Unless otherwise specified, the experimental methods used in the following examples are conventional methods, and the experimental materials used in the following examples are all purchased from commercial channels.

[0029] Preparation example (this is only an example of preparation steps; if parameters are marked in the example, follow the parameters marked in the example):

[0030] Preparation of flame retardant complex:

[0031] Take 100g of aluminum hydroxide (D50=2μm) and add it to 400ml of ethanol solution containing 4gKH-550. Stir at 50℃ for 2h, spray dry at 180℃ inlet / 80℃ outlet and 0.2MPa to obtain coated aluminum hydroxide. Dry mix the coated aluminum hydroxide with aluminum diethylphosphinate at a weight ratio of 3:1 for 10min.

[0032] Insulating filler treatment:

[0033] 100g of boehmite (D50 = 1.5μm) and 2.5g of silane coupling agent (A-187) were treated in a high-speed mixer at 85℃ / 400rpm for 40min, cooled and passed through a 200-mesh sieve, and the treated boehmite was mixed with boron nitride sheets with a diameter-to-thickness ratio of 60 at a ratio of 3:1.

[0034] Modified polyolefin resins:

[0035] ExxonMobil PP7032E3 (maleic anhydride grafting rate 1.2%, MI = 150 g / 10 min)

[0036] Alternatively, prepare in-house: Matrix resin: PP / PE copolymer (Basel AD60-007, MI = 90g / 10min) 100kg; Reactants: maleic anhydride 1.2kg, dicumyl peroxide 0.8kg; Twin-screw extruder settings: Zone I 160℃ / Zone II 180℃ / Zone III 190℃ / Zone IV 185℃, screw speed 400rpm, feed rate 20kg / h.

[0037] Antioxidant system:

[0038] Primary antioxidant: BASF Irganox 1010; Secondary antioxidant: BASF Irgafos 168; Compound ratio (by weight): Irganox 1010:Irgafos 168 = 1:1.5.

[0039] Example 1

[0040] Formula (parts): 50 parts maleic anhydride-grafted PP (grafting rate 1.2%, MI = 150g / 10min), 18 parts hydrogenated rosin glycerol ester, 7 parts C9 petroleum resin, 12 parts coated aluminum hydroxide, 4 parts aluminum diethylphosphinate, 8 parts silanized boehmite, 2 parts boron nitride flakes, 1 part antioxidant 1010, 1.5 parts γ-aminopropyltriethoxysilane, 1 part titanate NDZ-2011.

[0041] Preparation: Melt the matrix resin at 170℃ under nitrogen, add tackifying resin and stir at 185℃ for 40 min, cool to 135℃ and add the remaining components, degas under vacuum for 15 min / -0.098MPa, twin-screw extrusion: 150 / 160 / 165 / 170℃, 250 rpm, water-cooled pelletizing.

[0042] Application: Melt at 175℃, apply adhesive at 0.4MPa to aluminum-plastic film electric ears, adhesive layer thickness 0.6mm.

[0043] Example 2

[0044] The difference from Example 1 is as follows:

[0045] Adjusted formulation: 55 parts PP / PE copolymer (grafting rate 0.9%), 15 parts hydrogenated rosin glycerol ester, 10 parts C5 resin, 10 parts aluminum hydroxide, 5 parts aluminum phosphonate, 6 parts boehmite, and 3 parts boron nitride. Process is the same as in Implementation 1.

[0046] Example 3

[0047] The difference from Example 1 is as follows:

[0048] Adjust the formula: 45 parts grafted PE (grafting rate 1.5%), 12 parts hydrogenated rosin glycerol ester, 8 parts C9 resin, 14 parts aluminum hydroxide, 3.5 parts aluminum phosphonate, 10 parts boehmite, and 2.5 parts boron nitride. Adjust the dispensing temperature to 180℃.

[0049] Comparative Example 1

[0050] The difference from Example 1 is that the boron nitride sheet is omitted, the boehmite is increased to 10.5 parts, and the rest is the same as in Example 1.

[0051] Comparative Example 2

[0052] The difference from Example 1 is that the flame retardant is replaced with an equal amount of ordinary aluminum hydroxide (uncoated), and the rest is the same as in Example 1.

[0053] Comparative Example 3

[0054] The difference from Example 1 is that the thickening system uses only hydrogenated rosin glycerol ester (25 parts), and the rest is the same as in Example 1.

[0055] Comparative Example 4

[0056] Table 1 Reagents for Comparative Example 4

[0057] Components Specification Dosage EVA resin Vitamin A content 28% 50 copies Terpene resins - 30 copies decabromodiphenyl ethane Particle size ≤5μm 15 copies Antimony trioxide - 5 copies Calcium carbonate D50 = 3μm 10 copies Antioxidant 1010 - 1 copy

[0058] (1) Melting and mixing:

[0059] Add 50g of EVA resin to a four-necked flask, purge with nitrogen three times, heat the oil bath to 120°C, start stirring for about 15 minutes at 200 rpm until the EVA is completely melted, add 30g of terpene resin, heat to 140°C and stir for 30 minutes.

[0060] (2) Packer dispersion:

[0061] Keep the temperature at 140℃ and add the following in sequence: 15g decabromodiphenyl ethane, 5g antimony trioxide (pre-dry mixed), 10g calcium carbonate, and 10101g antioxidant. Increase the speed to 400rpm and stir continuously for 60min.

[0062] (3) Defoaming treatment:

[0063] The flask was transferred into a vacuum oven and degassed for 30 minutes under a vacuum of -0.09 MPa, while the temperature was maintained at 140°C.

[0064] (4) Extrusion granulation:

[0065] The melt is poured into the hopper of a single-screw extruder. Temperature settings: feed section 120℃, compression section 140℃, homogenization section 145℃, die head 150℃, screw speed 80rpm, underwater pelleting, cooling water temperature 25℃, pellet size: Φ2×3mm.

[0066] The products of the above embodiments and comparative examples were tested according to the detection method described in Table 2, and the results are shown in Table 3.

[0067] Table 2 Detection Methods

[0068]

[0069]

[0070] Table 3 Detection Results

[0071]

[0072] As can be seen, the measured viscosity of the conventional EVA-based hot melt adhesive in Comparative Example 4 at 180℃ is as high as 8550 mPa·s, making it impossible to pass through a dispensing needle smaller than 0.5 mm, and its volume resistivity is only 6.8 × 10⁻⁶. 8The viscosity is Ω·cm, posing a risk of leakage in electrolyte environments, and requires more than 30 minutes of room temperature curing, making it unsuitable for automated production lines. To address these shortcomings, the core of this invention lies in constructing a four-fold synergistic system: First, a tackifier system combining hydrogenated rosin glycerol ester and C9 petroleum resin is used. Through intermolecular hydrogen bonding, the melt viscosity is reduced to 3850 mPa·s, a 62% reduction compared to a single tackifier system, enabling precise dispensing through narrow 0.3mm gaps. Second, a coated aluminum hydroxide / diethylphosphinic acid aluminum flame retardant is designed. Its silane coating layer blocks the interfacial reaction between the flame retardant and the resin, maintaining the UL94V-0 rating while increasing the volume resistivity to 2.1 × 10¹¹. 6 The resistivity was 100 times higher than that of uncoated aluminum hydroxide (Ω·cm). Furthermore, by treating boehmite with γ-(2,3-epoxypropoxy)propyltrimethoxysilane and then combining it with boron nitride sheets, a three-dimensional insulating network was formed, while the resistivity dropped sharply to 5.7 × 10¹ when boron nitride was absent. 4 Ω·cm; Finally, the synergistic use of maleic anhydride-grafted polyolefin and silane / titanium ester dual coupling agent resulted in a bonding strength of 6.8 N / mm and an electrolyte resistance strength retention rate of 93%, a 120% improvement over the EVA system. The above technology successfully overcomes three major technical bottlenecks: in terms of dispensing efficiency, Example 1 achieves 0.3 mm gap coating at 80°C with a viscosity ≤4000 mPa·s and a single-point encapsulation time ≤8 seconds; in terms of insulation reliability, resistivity >10... 16 Ω·cm far exceeds that of lithium batteries 10 12 The safety threshold is measured in Ω·cm. Regarding durability, the dual-coupling system and the flame-retardant coating synergistically suppress interfacial failure. Experiments confirm a strong correlation between the four characteristics: boehmite silanization enhances the interfacial bonding with boron nitride, improving the integrity of the insulation network; in-situ flame retardant coating reduces oil absorption to 18g / 100g, preventing phase separation from the compounded thickening system. These comprehensive performance indicators demonstrate that this invention represents a technological leap from manual operation to highly efficient automation in lithium battery battery encapsulation.

[0073] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

[0074] The present invention and its embodiments have been described above. This description is not restrictive, and what is shown is only one embodiment of the present invention. The actual application is not limited to this. In conclusion, if those skilled in the art are inspired by this description and design similar methods and embodiments without departing from the spirit of the present invention, they should all fall within the protection scope of the present invention.

Claims

1. A lithium battery encapsulation hot melt adhesive with insulating properties, characterized in that: The following components are included in parts by weight: 40-60 parts of modified polyolefin resin, 20-35 parts of tackifying resin, 10-25 parts flame retardant 5-15 parts of insulating filler Antioxidant 0.5-2 parts, 1-3 parts coupling agent; The tackifying resin is a compound system of hydrogenated rosin glycerol ester and C5 / C9 copolymer, and the flame retardant is a complex of coated aluminum hydroxide and organic phosphonate.

2. The hot melt adhesive according to claim 1, characterized in that: The compound system of hydrogenated rosin glycerol ester and C5 / C9 copolymer has a weight ratio of 3:1 to 1:1; the compound system of coated aluminum hydroxide and organic phosphonate has a weight ratio of 2:1 to 4:

1.

3. The hot melt adhesive according to claim 1, characterized in that: The modified polyolefin resin is a polypropylene / polyethylene copolymer with a maleic anhydride grafting rate of 0.8-1.5 wt% and a melt index of 120-180 g / 10 min.

4. The hot melt adhesive according to claim 1, characterized in that: The insulating filler is a mixture of surface-silanized boehmite and boron nitride sheets in a weight ratio of 2:1 to 4:

1.

5. A method for preparing the hot melt adhesive according to any one of claims 1-4, characterized in that: Includes the following steps: (1) Melt the modified polyolefin resin; (2) Add the thickening resin and heat while stirring; (3) Cool down, add flame retardant, insulating filler, antioxidant and coupling agent, and degas under vacuum; (4) The product is obtained by melt blending in a twin-screw extruder and underwater pelletizing.

6. The preparation method according to claim 5, characterized in that: The melting in step (1) is carried out at a temperature of 160-170°C under nitrogen protection.

7. The preparation method according to claim 5, characterized in that: In step (2), the heating and stirring are carried out at 180-185℃ for 30-45 minutes.

8. The preparation method according to claim 5, characterized in that: The cooling process in step (3) is to cool down to 130-140℃, and the vacuum degassing process takes 10-20 minutes with a vacuum degree of ≤-0.095MPa.

9. The preparation method according to claim 5, characterized in that: The method according to claim 4, wherein the coupling agent in step (3) is a compound of γ-aminopropyltriethoxysilane and titanate coupling agent.

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