Aluminum powder slurry for capacitor anode foil and method of preparing the same

Abstract

The application relates to the technical field of capacitor anode foil, and discloses an aluminum powder slurry for capacitor anode foil and a preparation method thereof. A dispersing agent, single-monomallyl pentaerythritol grafted natural rubber and a binder are added into a solvent and stirred and mixed uniformly; then spherical aluminum oxide powder is added, the slurry is placed in a ball mill tank after stirring, ball mill beads are added, and ball milling is carried out to obtain the aluminum powder slurry. The natural rubber is grafted with a large number of hydroxyl groups, forms a strong interaction with the surface of the aluminum oxide powder, has a better dispersion effect on the aluminum oxide powder, can improve the dispersibility of the aluminum powder slurry, the aluminum powder particles are uniformly distributed and are not prone to agglomeration, and the activation degree is high, which is beneficial to better coating of the slurry on the aluminum foil and high adhesion of the natural rubber to the aluminum foil substrate, avoids the aluminum oxide powder from falling off from the surface of the aluminum foil substrate, is beneficial to improving the capacity of the aluminum oxide active substance of the anode foil and enhancing the electrochemical performance of the capacitor anode foil.

Description

Technical Field

[0001] This invention relates to the field of capacitor anode foil technology, specifically to an aluminum powder paste for capacitor anode foil and its preparation method. Background Technology

[0002] Aluminum electrolytic capacitors have advantages such as large capacity, low cost, and easy processing, and are widely used in household appliances, computers, and automotive electronic systems. The aluminum powder paste coating and sintering method is one of the important methods for preparing the anode foil of capacitors. The aluminum powder paste is usually prepared by mixing alumina powder with binders, dispersants, etc., among which the dispersant has a significant impact on the dispersibility of the alumina powder and the performance of the aluminum powder paste.

[0003] Chinese patent CN113140351B discloses a slurry for preparing high porosity electrode foil and its preparation method. It uses diethylene glycol butyl ether, tributyl citrate, dimethyl phthalate, etc. as dispersants and acrylic resin as a binder. The resulting aluminum powder slurry can be used to prepare electrode foils with various porosities. Compared with this patent, the present invention effectively solves the problem of poor dispersibility of aluminum powder slurry and improves the problem of low adhesion between aluminum powder slurry and aluminum foil substrate. Summary of the Invention

[0004] (a) Technical problems solved: The problem of poor dispersibility of aluminum powder slurry for capacitor anode foil and low adhesion performance between aluminum powder slurry and aluminum foil substrate was solved.

[0005] (II) Technical Solution: A method for preparing aluminum powder slurry:

[0006] (1) The preparation method of monoallyl pentaerythritol grafted natural rubber includes the following steps: In a nitrogen atmosphere, adding the following structural formula to natural rubber latex. Monoallyl pentaerythritol was stirred and then an aqueous solution of potassium persulfate was added dropwise to carry out the grafting reaction. After cooling, the product was coagulated, filtered, washed with water, and then purified by Soxhlet extraction with acetone to obtain monoallyl pentaerythritol-grafted natural rubber.

[0007] (2) Add dispersant and binder to solvent and stir to mix well; then add spherical alumina powder, stir and place the slurry in a ball mill jar, add ball milling beads and ball mill to obtain aluminum powder slurry.

[0008] Furthermore, in (1), the ratio of natural rubber latex, monoallyl pentaerythritol, and potassium persulfate is 100g: (6-15)g: (0.08-0.22)g.

[0009] Furthermore, in (1), the grafting reaction is carried out at 75-85℃ for 5-8 hours.

[0010] Furthermore, in (2), the ratio of solvent, dispersant, binder and spherical alumina powder is (120-140) mL: (2-10) g: (2-8) g: 100 g.

[0011] Furthermore, in (2), the solvent is one or more of N,N-dimethylacetamide and N-methylpyrrolidone; the binder includes polyvinylidene fluoride.

[0012] Furthermore, in (2), the ball milling speed is 250-400 r / min and the ball milling time is 4-8 h.

[0013] Furthermore, the aluminum powder paste is applied to the anode foil of capacitors. The aluminum powder paste is uniformly coated on both sides of the aluminum foil substrate with a coating thickness of 100-140μm to form a paste layer. Then, it is placed in a vacuum chamber and vacuum dried at 80-100℃ for 10-18h to obtain aluminum powder coated aluminum foil.

[0014] (III) Beneficial technical effects: This invention utilizes monoallyl pentaerythritol to perform emulsion grafting on natural rubber to obtain grafted natural rubber. Natural rubber itself has good adhesion properties, and at the same time, it is grafted with a large number of hydroxyl groups, which is beneficial to improve the adhesion performance between natural rubber and aluminum foil substrate, prevent alumina powder from falling off the surface of aluminum foil substrate, and facilitate the subsequent aluminum powder coating and aluminum foil sintering process to produce high-performance capacitor anode foil.

[0015] The natural rubber of this invention is grafted with a large number of hydroxyl groups, which form a strong interaction with the surface of alumina powder, resulting in better dispersion of alumina powder. This improves the dispersibility of the aluminum powder slurry, makes the aluminum powder particles uniformly distributed, prevents agglomeration, and has high activation. It also exhibits excellent dispersibility in solvents such as N,N-dimethylformamide and N-methylpyrrolidone, which facilitates better coating of the slurry onto the aluminum foil, increases the capacity of the alumina active material in the anode foil, and enhances the electrochemical performance of the capacitor anode foil. Attached Figure Description

[0016] Figure 1 This is a scanning electron microscope image of the aluminum powder slurry prepared in Example 1. Detailed Implementation

[0017] The following natural rubber latex has a solid content of approximately 60% and is sourced from Shandong Xufuyuan Chemical Co., Ltd. Example 1:

[0018] (1) In a nitrogen atmosphere, 5g of monoallyl pentaerythritol was added to 50g of natural rubber latex. After stirring, 30mL of an aqueous solution containing 0.08g of potassium persulfate was added dropwise. The mixture was heated to 85℃ and stirred for 5h. After cooling, the mixture was coagulated, filtered, and the product was washed with water. Then, it was purified by Soxhlet extraction with acetone to obtain monoallyl pentaerythritol-grafted natural rubber.

[0019] (2) Add 10g of dispersant (monallylyl pentaerythritol-grafted natural rubber) and 40g of binder (polyvinylidene fluoride) to 600mL of N,N-dimethylacetamide, and stir until well mixed; then add 500g of spherical alumina powder, stir, place the slurry in a ball mill jar, add milling beads, and ball mill for 8 hours at a speed of 250r / min to obtain an aluminum powder slurry. Figure 1 As can be seen from the scanning electron microscope images, the spherical alumina powder has excellent dispersibility, small particle size, and is not prone to agglomeration into large particles.

[0020] (3) The aluminum powder slurry is uniformly coated on both sides of the aluminum foil substrate (the pure aluminum foil substrate is weighed and recorded as m0), with a coating thickness of 120μm, forming a slurry layer. Then it is placed in a vacuum chamber and vacuum dried at 80℃ for 12h to obtain aluminum powder coated aluminum foil (weighed and recorded as m1). Example 2:

[0021] (1) In a nitrogen atmosphere, 3g of monoallyl pentaerythritol was added to 50g of natural rubber latex. After stirring, 20mL of an aqueous solution containing 0.04g of potassium persulfate was added dropwise. The mixture was heated to 75°C and stirred for 6h. After cooling, the mixture was coagulated. The product was filtered and washed with water. Then, it was purified by Soxhlet extraction with acetone to obtain monoallyl pentaerythritol-grafted natural rubber.

[0022] (2) Add 20g of dispersant monoallyl pentaerythritol grafted natural rubber and 30g of binder polyvinylidene fluoride to 700mL of N,N-dimethylacetamide and stir until well mixed; then add 500g of spherical alumina powder, stir and place the slurry in a ball mill jar, add ball milling beads, and ball mill for 8h at a speed of 250r / min to obtain aluminum powder slurry.

[0023] (3) The aluminum powder slurry is uniformly coated on both sides of the aluminum foil substrate (the pure aluminum foil substrate is weighed and recorded as m0), with a coating thickness of 100μm, forming a slurry layer. Then it is placed in a vacuum chamber and vacuum dried at 80℃ for 18h to obtain aluminum powder coated aluminum foil (weighed and recorded as m1). Example 3:

[0024] (1) In a nitrogen atmosphere, 7.5g of monoallyl pentaerythritol was added to 50g of natural rubber latex. After stirring, 30mL of an aqueous solution containing 0.11g of potassium persulfate was added dropwise. The mixture was heated to 80℃ and stirred for 8h. After cooling, the mixture was coagulated, filtered, and the product was washed with water. Then, it was purified by Soxhlet extraction with acetone to obtain monoallyl pentaerythritol-grafted natural rubber.

[0025] (2) Add 35g of dispersant monoallyl pentaerythritol grafted natural rubber and 20g of binder polyvinylidene fluoride to 700mL of N-methylpyrrolidone and stir until well mixed; then add 500g of spherical alumina powder, stir and place the slurry in a ball mill jar, add ball milling beads, and ball mill for 4h at a speed of 400r / min to obtain aluminum powder slurry.

[0026] (3) The aluminum powder slurry is uniformly coated on both sides of the aluminum foil substrate (the pure aluminum foil substrate is weighed and recorded as m0), with a coating thickness of 140μm, forming a slurry layer. Then it is placed in a vacuum chamber and vacuum dried at 100℃ for 10h to obtain aluminum powder coated aluminum foil (weighed and recorded as m1). Example 4:

[0027] (1) In a nitrogen atmosphere, 6g of monoallyl pentaerythritol was added to 50g of natural rubber latex. After stirring, 30mL of an aqueous solution containing 0.11g of potassium persulfate was added dropwise. The mixture was heated to 80℃ and stirred for 6h. After cooling, the mixture was coagulated. The product was filtered and washed with water. Then, it was purified by Soxhlet extraction with acetone to obtain monoallyl pentaerythritol-grafted natural rubber.

[0028] (2) Add 50g of dispersant monoallyl pentaerythritol grafted natural rubber and 10g of binder polyvinylidene fluoride to 600mL of N,N-dimethylacetamide and stir until well mixed; then add 500g of spherical alumina powder, stir and place the slurry in a ball mill jar, add ball milling beads, and ball mill for 6h at a speed of 300r / min to obtain aluminum powder slurry.

[0029] (3) The aluminum powder slurry is uniformly coated on both sides of the aluminum foil substrate (the pure aluminum foil substrate is weighed and recorded as m0), with a coating thickness of 140μm, forming a slurry layer. Then it is placed in a vacuum chamber and vacuum dried at 100℃ for 10h to obtain aluminum powder coated aluminum foil (weighed and recorded as m1).

[0030] Comparative Example 1:

[0031] (1) Add 10g of monoallyl pentaerythritol and 40g of binder polyvinylidene fluoride to 600mL of N,N-dimethylacetamide and stir until well mixed; then add 500g of spherical alumina powder, stir and place the slurry in a ball mill jar, add ball milling beads, and ball mill for 8h at a speed of 250r / min to obtain aluminum powder slurry.

[0032] (2) The aluminum powder slurry is evenly coated on both sides of the aluminum foil substrate (the pure aluminum foil substrate is weighed and recorded as m0), with a coating thickness of 120μm to form a slurry layer. Then it is placed in a vacuum chamber and vacuum dried at 80℃ for 12h to obtain aluminum powder coated aluminum foil (weighed and recorded as m1).

[0033] Comparative Example 2:

[0034] (1) Add 10g of natural rubber (dried solids of natural rubber latex) and 40g of binder polyvinylidene fluoride to 600mL of N,N-dimethylacetamide and stir until well mixed; then add 500g of spherical alumina powder, stir and place the slurry in a ball mill jar, add ball milling beads, and ball mill for 8h at a speed of 250r / min to obtain aluminum powder slurry.

[0035] (2) The aluminum powder slurry is evenly coated on both sides of the aluminum foil substrate (the pure aluminum foil substrate is weighed and recorded as m0), with a coating thickness of 120μm to form a slurry layer. Then it is placed in a vacuum chamber and vacuum dried at 80℃ for 12h to obtain aluminum powder coated aluminum foil (weighed and recorded as m1).

[0036] Comparative Example 3

[0037] (1) In a nitrogen atmosphere, 50g of natural rubber latex and 5g of monoallyl pentaerythritol were stirred and mixed, and dried to obtain a monoallyl pentaerythritol-natural rubber blend.

[0038] (2) Add 10g of monoallyl pentaerythritol-natural rubber blend and 40g of binder polyvinylidene fluoride to 600mL of N,N-dimethylacetamide and stir until well mixed; then add 500g of spherical alumina powder, stir and place the slurry in a ball mill jar, add ball milling beads, and ball mill for 8h at a speed of 250r / min to obtain aluminum powder slurry.

[0039] (3) The aluminum powder slurry is uniformly coated on both sides of the aluminum foil substrate (the pure aluminum foil substrate is weighed and recorded as m0), with a coating thickness of 120μm, forming a slurry layer. Then it is placed in a vacuum chamber and vacuum dried at 80℃ for 12h to obtain aluminum powder coated aluminum foil (weighed and recorded as m1).

[0040] Comparative Example 4:

[0041] (1) In a nitrogen atmosphere, 5g of hydroxyethyl acrylate was added to 50g of natural rubber latex. After stirring, 30mL of an aqueous solution containing 0.08g of potassium persulfate was added dropwise. The mixture was heated to 85℃ and stirred for 5h. After cooling, the mixture was coagulated, filtered, and the product was washed with water. Then, it was purified by Soxhlet extraction with acetone to obtain hydroxyethyl acrylate-grafted natural rubber.

[0042] (2) Add 10g of hydroxyethyl acrylate-grafted natural rubber and 40g of polyvinylidene fluoride binder to 600mL of N,N-dimethylacetamide and stir until well mixed; then add 500g of spherical alumina powder, stir and place the slurry in a ball mill jar, add ball milling beads, and ball mill for 8h at a speed of 250r / min to obtain aluminum powder slurry.

[0043] (3) The aluminum powder slurry is uniformly coated on both sides of the aluminum foil substrate (the pure aluminum foil substrate is weighed and recorded as m0), with a coating thickness of 120μm, forming a slurry layer. Then it is placed in a vacuum chamber and vacuum dried at 80℃ for 12h to obtain aluminum powder coated aluminum foil (weighed and recorded as m1).

[0044] The coated aluminum foil is bent into a continuous wavy shape, straightened after bending, and then bent again along the crease, which constitutes one bending process. This bending process is repeated 500 times. The coated aluminum foil is then weighed (recorded as m2), and the aluminum powder retention rate W is calculated. W = (m2 - m0) / (m1 - m0) × 100%. The higher the aluminum powder retention rate, the better the adhesion between the aluminum powder slurry and the aluminum foil substrate.

[0045] To calculate the activation degree of alumina, taking Example 1 as an example, 10g of dispersant (monallylyl pentaerythritol-grafted natural rubber) and 40g of binder (polyvinylidene fluoride) were added to 600mL of N,N-dimethylacetamide and stirred until homogeneous. Then, 500g of spherical alumina powder was added, and the mixture was stirred. The slurry was then placed in a ball mill jar, milling beads were added, and the mixture was ball-milled for 8 hours at a speed of 250r / min to obtain an aluminum powder slurry. N,N-dimethylacetamide was then added to maintain the concentration of spherical alumina powder in the solution at 100g / L. 100mL of the solution (the total mass of spherical alumina powder in the solution is M) was added to a separatory funnel, ultrasonically dispersed for 30min, and shaken thoroughly. The mixture was allowed to stand for 12h, and the supernatant was collected, dried to constant weight, weighed, and recorded as m. The activation degree W was calculated as W = m / M × 100%.

[0046] Table 1. Aluminum powder retention rate test

[0047] Aluminum powder retention rate (%) Activation degree (%) Example 1 99.12 84.6 Example 2 99.66 93.8 Example 3 98.84 87.2 Example 4 99.45 96.1 Comparative Example 1 97.49 72.1 Comparative Example 2 98.16 11.8 Comparative Example 3 96.05 15.4 Comparative Example 4 98.54 47.3

[0048] Compared to the comparative examples, this embodiment incorporates monoallyl pentaerythritol-grafted natural rubber. Natural rubber itself possesses excellent adhesive properties, and the grafted hydroxyl groups further enhance the adhesion between the natural rubber and the aluminum foil substrate, preventing alumina powder from detaching from the substrate surface. This facilitates the subsequent aluminum powder coating and sintering process, resulting in a high-performance capacitor anode foil. Simultaneously, the grafted hydroxyl groups in the natural rubber create a strong interaction with the alumina powder surface, leading to better dispersion of the alumina powder. This improves the dispersibility of the aluminum powder slurry, resulting in uniform particle distribution, high activation, and excellent dispersibility in solvents such as N,N-dimethylformamide and N-methylpyrrolidone.

Claims

1. A method for preparing an aluminum powder slurry, characterized in that, The preparation method includes the following steps: adding a dispersant and a binder to a solvent and stirring to mix them; then adding spherical alumina powder, stirring, placing the slurry in a ball milling jar, adding milling beads, and ball milling to obtain an aluminum powder slurry; The dispersant is monoallyl pentaerythritol-grafted natural rubber. The structural formula of the monoallyl pentaerythritol is: ; The preparation method of monoallyl pentaerythritol-grafted natural rubber includes the following steps: In a nitrogen atmosphere, monoallyl pentaerythritol is added to natural rubber latex, stirred, and then an aqueous solution of potassium persulfate is added dropwise to carry out the grafting reaction. After cooling, the product is coagulated, filtered, washed with water, and then purified by Soxhlet extraction with acetone to obtain monoallyl pentaerythritol-grafted natural rubber.

2. The method for preparing aluminum powder slurry according to claim 1, characterized in that, The ratio of natural rubber latex, monoallyl pentaerythritol, and potassium persulfate is 100g:(6-15)g:(0.08-0.22)g.

3. The method for preparing aluminum powder slurry according to claim 1, characterized in that, The grafting reaction was carried out at 75-85℃ for 5-8 hours.

4. The method for preparing aluminum powder slurry according to claim 1, characterized in that, The ball mill speed is 250-400 r / min, and the ball milling time is 4-8 h.

5. The method for preparing aluminum powder slurry according to claim 1, characterized in that, The ratio of solvent, dispersant, binder and spherical alumina powder is (120-140) mL: (2-10) g: (2-8) g: 100 g.

6. An aluminum powder slurry obtained by the preparation method according to any one of claims 1-5.

7. The application of the aluminum powder paste according to claim 6 in the anode foil of a capacitor, characterized in that, Aluminum powder slurry is uniformly coated on both sides of the aluminum foil substrate, with a coating thickness of 100-140μm, to form a slurry layer. Then, it is placed in a vacuum chamber and vacuum dried at 80-100℃ for 10-18h to obtain aluminum powder coated aluminum foil.

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