Low-moisture high-heat-resistance solution type acrylic acid adhesive and preparation method thereof

Abstract

The invention relates to the technical field of lithium battery diaphragms, in particular to a low-moisture and high-heat-resistance solution type acrylic acid binder and a preparation method thereof. Through the synergistic effect of the protective colloid composite cross-linking monomer, the low moisture content is achieved in a breakthrough mode. Wherein the steric hindrance effect of the polyvinyl alcohol in the protective colloid mixture inhibits exposure of hydrophilic groups, the polyvinyl pyrrolidone improves the dispersion stability, and the polyether polyol enhances the film-forming flexibility; hydroxyethyl acrylamide and diacetone methacrylamide in the crosslinking monomer mixture construct a dual crosslinking network, so that the covalent bond density between molecular chains is remarkably enhanced, and cyano groups of acrylonitrile further reduce the moisture adsorption path and improve the interface anchoring force through strong polarity and hydrophobicity; the three components cooperate with each other to achieve a heat-resistant effect which can only be achieved by a high addition amount in the prior art under a low addition amount, and meanwhile, the problem of diaphragm deformation caused by high-temperature long-time reaction is avoided.

Description

Technical Field

[0001] This invention relates to the field of lithium battery separator technology, and more specifically, to a low-moisture, high-heat-resistant solution-type acrylic binder and its preparation method. Background Technology

[0002] Currently, lithium-ion and lithium-ion polymer batteries use polyolefin-based separators to prevent short circuits between the positive and negative electrodes. However, because polyolefin-based separators have a melting point of 130°C or lower, they can shrink or melt when the battery temperature rises due to internal or external factors, causing volume changes. This makes short circuits between the positive and negative electrodes caused by separator shrinkage or melting highly likely, potentially leading to accidents such as battery explosions caused by discharge. Therefore, it is necessary to provide a separator that does not cause thermal shrinkage at high temperatures.

[0003] In related technologies, emulsion-type acrylic acid and polyacrylic acid solution (high heat resistance type) are two types. Although the current polyacrylic acid solution can withstand temperatures up to 180℃, it has high hydrophilicity, which leads to disadvantages such as high moisture content and low peel strength when used in lithium battery separators. Summary of the Invention

[0004] The purpose of this invention is to provide a low-moisture, high-heat-resistant solution-type acrylic adhesive and its preparation method, in order to solve the technical problems of high moisture content and low peel strength in existing polyacrylic acid solution-type lithium battery separator adhesives.

[0005] To achieve the above objectives, the present invention is implemented through the following solutions;

[0006] A method for preparing a low-moisture, high-heat-resistant solution-type acrylic adhesive includes the following steps:

[0007] (1) Mix 30-40 parts water, 0.2-2 parts protective colloid, 15-25 parts basic monomer, 0.2-1 part crosslinking monomer, and 0.5-2 parts pH adjuster evenly under stirring to obtain a monomer mixture;

[0008] (2) Add 40-50 parts water, 0.5-2 parts pH adjuster, and 0.2-2 parts protective colloid to the reaction vessel, stir evenly, and heat to 60-90℃;

[0009] (3) Add part of the monomer mixture obtained in step (1) to the reactor, add 0.05-0.5 parts of initiator, maintain the stirring speed at 100-200 rpm, react for 20-30 min initially, and then add the remaining monomer mixture from step (1) dropwise over 1-4 h, while adding 0.1-0.5 parts of initiator dropwise, and control the temperature between 70-90℃.

[0010] (4) After the addition is complete, keep the temperature at 75-90℃ for 1-3 hours;

[0011] (5) Cool down to 65-80℃ and carry out the redox reaction, and keep warm for 0.5-1H;

[0012] (6) Cool down to below 45°C, add additives, stir, filter, and discharge to obtain a low-moisture, high-heat-resistant solution-type acrylic adhesive.

[0013] Preferably, the base monomers include 2-5 parts of acrylic monomers, 12-15 parts of acrylate monomers, and 1-5 parts of styrene.

[0014] Preferably, the acrylic monomers include at least two of acrylic acid, methacrylic acid, acrylamide, and methacrylamide.

[0015] Preferably, the acrylate monomers include methyl methacrylate and hydroxyethyl (meth)acrylate.

[0016] Preferably, the protective colloid includes at least one of polyvinyl alcohol, polyvinylpyrrolidone, and polyether polyol.

[0017] Preferably, the crosslinking monomer includes at least one of acrylonitrile, hydroxyethyl acrylamide, and diacetone methacrylamide.

[0018] Preferably, the initiator includes at least one of sodium persulfate, ammonium persulfate, and potassium persulfate.

[0019] Another object of the present invention is to provide a low-moisture, high-heat-resistant solution-type acrylic adhesive, which is prepared by the aforementioned preparation method.

[0020] This application has the following beneficial effects: Through the synergistic effect of the protective colloid composite crosslinking monomers, this application achieves a breakthrough in low moisture content (<1000ppm), high peel strength (>120N / m), and excellent heat resistance (shrinkage rate <5% at 180℃). Specifically, the steric hindrance effect of polyvinyl alcohol in the protective colloid mixture inhibits the exposure of hydrophilic groups, polyvinylpyrrolidone improves dispersion stability, and polyether polyol enhances film-forming flexibility. In the crosslinking monomer mixture, hydroxyethyl acrylamide and diacetone methacrylamide construct a dual crosslinking network, significantly enhancing the density of covalent bonds between molecular chains. Meanwhile, the cyano group (-CN) of acrylonitrile further reduces the moisture adsorption pathway and enhances interfacial anchoring force through its strong polarity and hydrophobicity. The synergistic effect of these three components achieves the heat resistance effect that requires high addition amounts in existing technologies with low addition amounts, while avoiding the membrane deformation problem caused by long-term high-temperature reactions. Detailed Implementation

[0021] The present invention will be further described below with reference to embodiments, but the scope of protection of the present invention is not limited to the scope described in the embodiments.

[0022] Example 1

[0023] A method for preparing a low-moisture, high-heat-resistant solution-type acrylic adhesive includes the following steps:

[0024] (1) Mix 35 parts of deionized water, 0.2 parts of protective colloid, 19.5 parts of base monomer, 0.7 parts of crosslinking monomer and 0.7 parts of pH adjuster evenly under stirring to obtain monomer mixture;

[0025] (2) Add 45 parts of deionized water, 0.8 parts of pH adjuster, and 1.3 parts of protective colloid to the reactor, stir evenly, and heat to 80±3℃;

[0026] (3) Add 15% by weight of the monomer mixture obtained in step (1) to the reactor, add 0.05 parts of initiator, maintain the stirring speed at 150±10 rpm, react for 30 min initially, and then add the remaining monomer mixture from step (1) dropwise over 3.5-4 h, while adding 0.25 parts of initiator dropwise, and control the temperature between 80±5℃.

[0027] (4) After the addition is complete, keep warm at 80±5℃ for 3 hours;

[0028] (5) Cool down to 65℃, add appropriate amounts of oxidant and reducing agent in sequence to carry out oxidation-reduction reaction, and then keep warm for 1 hour;

[0029] (6) Cool down to below 45°C, add an appropriate amount of additives, stir, filter, and discharge to obtain a low-moisture, high-heat-resistant solution-type acrylic adhesive.

[0030] Examples 2-5

[0031] According to the formulation shown in Table 1, a low-moisture, high-heat-resistant solution-type acrylic adhesive was prepared according to the preparation method of Example 1 (only the weight parts of each raw material were changed). In step (1), the amount of deionized water added was approximately 35-45% of the total weight, the amount of protective colloid added was approximately 15-20% of the total weight, and the amount of pH adjuster added was approximately 40-50% of the total weight. In step (2), the amount of deionized water, protective colloid, and pH adjuster added was the remaining weight of each. In step (3), the weight ratio of the initiator added before and after the two additions was approximately 1:(4-5).

[0032] Table 1. Formulation of Examples (parts by weight)

[0033]

[0034] Comparative Example 1

[0035] The difference from Example 1 is that the crosslinking monomers were removed and replaced with an equal amount of deionized water.

[0036] Comparative Example 2

[0037] The difference from Example 1 is that the crosslinking monomer consists of only 0.7 parts of acrylonitrile.

[0038] Comparative Example 3

[0039] The difference from Example 1 is that the crosslinking monomer is composed of 0.4 parts of hydroxyethyl acrylamide and 0.3 parts of diacetone methacrylamide.

[0040] Comparative Example 4

[0041] The difference from Example 1 is that styrene was removed and replaced with an equal amount of deionized water.

[0042] Comparative Example 5

[0043] The difference from Example 1 is that the protective colloid was removed and replaced with an equal amount of deionized water.

[0044] Comparative Example 6

[0045] The difference from Example 1 is that the protective colloid consists of only 1.5 parts polyvinyl alcohol.

[0046] Comparative Example 7

[0047] The difference from Example 1 is that polyvinylpyrrolidone was removed and replaced with an equal amount of deionized water.

[0048] Comparative Example 8

[0049] The difference from Example 1 is that the polyether polyol is removed and replaced with an equal amount of deionized water.

[0050] Comparative Example 9

[0051] The difference from Example 1 is that the acrylate monomers are removed and replaced with an equal amount of deionized water.

[0052] Comparative Example 10

[0053] The difference from Example 1 is that acrylamide was removed and replaced with an equal amount of deionized water.

[0054] A basic ceramic slurry formulation was used: 33 parts ceramic powder, 5 parts membrane binder (from the examples or comparative examples), 0.5 parts carboxymethyl cellulose, 0.3 parts wetting agent, and 0.3 parts dispersant. This was prepared into a ceramic slurry with a solid content of 40%. A ceramic slurry coating of approximately 2 μm thickness was then applied to obtain a membrane with a ceramic coating. The basic properties of the ceramic membrane were then tested. The substrate selected was a conventional breathable membrane, a 9 μm porous PE membrane with an air permeability between 180-200S.

[0055] The performance of the ceramic diaphragms prepared in each embodiment and comparative example was tested. The thickness of the ceramic coating was measured using a film thickness gauge. Heat resistance at 150℃ and 180℃ was characterized by thermal tensile tests, with results expressed as transverse tensile shrinkage (TD) and longitudinal tensile shrinkage (MD). Peel force was measured using a peel tester. The moisture content of the ceramic diaphragm was determined using the Karl Fischer coulometric method. All test data were averaged from three measurements, and the results are summarized in Table 2.

[0056] Table 2 Performance test data of ceramic diaphragms

[0057]

[0058] As shown in Table 2, Examples 1-5 all exhibited excellent overall performance, with moisture content controlled at 750-810 ppm (far below the target value of 1000 ppm), peel strength reaching 122-130 N / m (significantly higher than the requirement of 120 N / m), and heat shrinkage at 180℃ maintained at 3.2-4.7% (fully meeting the technical indicator of <5%). These examples achieved a balance between low moisture, high adhesion, and excellent heat resistance by optimizing the synergistic effect of the protective colloid (polyvinyl alcohol / polyvinylpyrrolidone / polyether polyol blend) and the crosslinking monomers (acrylonitrile / hydroxyethyl acrylamide / diacetone methacrylamide combination). Among them, Example 4 exhibited the best overall performance (790 ppm moisture, 130 N / m peel strength, and 3.8% shrinkage at 180℃), which was attributed to its optimized monomer ratio and protective colloid proportion.

[0059] In contrast, the moisture content of Comparative Example 1 (without crosslinking monomers) surged to 1350 ppm, the peel strength plummeted to 72 N / m, and the shrinkage rate at 180°C reached as high as 8.3%, proving that the crosslinking network is indispensable for reducing moisture, improving adhesion and heat resistance.

[0060] Comparative Example 2 (acrylonitrile only) had a peel strength of only 96 N / m and a shrinkage rate of 6.9% at 180°C; Comparative Example 3 (without acrylonitrile) had a peel strength reduced to 118 N / m and a moisture content of 980 ppm, demonstrating the key role of the cyano group of acrylonitrile in interfacial anchoring force and hydrophobicity.

[0061] The peel strength of Comparative Example 4 (without styrene) decreased to 88 N / m, and the shrinkage rate at 180℃ was 6.6%, demonstrating the contribution of styrene as a rigid monomer to adhesion and heat resistance.

[0062] The performance of Comparative Example 5 (without protective colloid) completely collapsed (moisture content 1550 ppm, peel strength 60 N / m, shrinkage rate at 180℃ 14.8%), highlighting the core role of the protective colloid in stability and film formation.

[0063] Comparative Example 6 (polyvinyl alcohol only) showed a peel strength of 93 N / m and a shrinkage rate of 7.1% at 180°C, demonstrating that a single colloid cannot achieve the synergistic effect of the compound system.

[0064] The moisture content of Comparative Example 7 (without polyvinylpyrrolidone) increased to 1100 ppm, and the peel strength decreased to 85 N / m, demonstrating its important role in the dispersion and stability of the system.

[0065] The peel strength of Comparative Example 8 (without polyether polyol) decreased to 90 N / m, and the shrinkage rate at 180℃ was 7.3%, indicating that its flexibility enhancement effect is irreplaceable.

[0066] Comparative Example 9 (without acrylate monomers) showed a peel strength reduced to 89 N / m and a shrinkage rate of 7.5% at 180°C, verifying its key impact on the mechanical strength of the coating.

[0067] The moisture content of Comparative Example 10 (without acrylamide) increased to 920 ppm, and the shrinkage rate at 180°C was 7.6%, confirming the effect of amide groups in reducing hydrophilicity and improving heat resistance.

[0068] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a low-moisture, high-heat-resistant solution-type acrylic adhesive, characterized in that, Includes the following steps: (1) Mix 30-40 parts water, 0.2-2 parts protective colloid, 15-25 parts basic monomer, 0.2-1 part crosslinking monomer, and 0.5-2 parts pH adjuster evenly under stirring to obtain a monomer mixture; (2) Add 40-50 parts water, 0.5-2 parts pH adjuster, and 0.2-2 parts protective colloid to the reaction vessel, stir evenly, and heat to 60-90℃; (3) Add part of the monomer mixture obtained in step (1) to the reactor, add 0.05-0.5 parts of initiator, maintain the stirring speed at 100-200 rpm, react for 20-30 min initially, and then add the remaining monomer mixture from step (1) dropwise over 1-4 h, while adding 0.1-0.5 parts of initiator dropwise, and control the temperature between 70-90℃. (4) After the addition is complete, keep the temperature at 75-90℃ for 1-3 hours; (5) Cool down to 65-80℃ and carry out the redox reaction, and keep warm for 0.5-1H; (6) Cool down to below 45°C, add additives, stir, filter, and discharge to obtain a low-moisture, high-heat-resistant solution-type acrylic adhesive.

2. The preparation method according to claim 1, characterized in that, The basic monomers include 2-5 parts acrylic monomers, 12-15 parts acrylate monomers, and 1-5 parts styrene.

3. The preparation method according to claim 2, characterized in that, Acrylic monomers include at least two of acrylic acid, methacrylic acid, acrylamide, and methacrylamide.

4. The preparation method according to claim 3, characterized in that, Acrylic monomers include methyl methacrylate and hydroxyethyl (meth)acrylate.

5. The preparation method according to claim 1, characterized in that, The protective colloid includes at least one of polyvinyl alcohol, polyvinylpyrrolidone, and polyether polyol.

6. The preparation method according to claim 1, characterized in that, The crosslinking monomers include at least one of acrylonitrile, hydroxyethyl acrylamide, and diacetone methacrylamide.

7. The preparation method according to claim 1, characterized in that, The initiator includes at least one of sodium persulfate, ammonium persulfate, and potassium persulfate.

8. A low-moisture, high-heat-resistant solution-type acrylic adhesive, characterized in that, It is prepared by any one of claims 1-7.

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