JP6170339B2 - Low shear type concentric twin screw mixer and method for producing water-based negative electrode paste using the same - Google Patents

Description

The present invention provides an active material paste applied to a current collector of an electrode layer such as a lithium ion secondary battery,
In particular, the present invention relates to a low-shear type concentric twin-screw mixer that is suitably used for the production of an aqueous negative electrode paste and a method for producing an aqueous negative electrode paste using the same.

  The electrode layer of the lithium ion secondary battery includes a positive electrode layer in which a positive electrode active material paste is applied to the surface of a current collector made of metal foil, and a negative electrode layer in which the negative electrode active material paste is applied to the current collector. As the paste, for example, a negative electrode active material paste is manufactured by mixing a negative electrode active material with a binder, adding a solvent to form a negative electrode mixture, and kneading the mixture. Since this binder has a function of binding active materials and binding the active material to a current collector, if the binder is not homogeneously kneaded in the active material, the peel strength decreases, and the active material and The current collector cannot be firmly bound. As such binders, solvent-based binders containing organic solvents and water-soluble water-based binders are known, and water-based binders reduce material costs, simplify equipment, handle safely, and prevent environmental problems. It is preferable from the viewpoint. However, binders containing, for example, styrene butadiene rubber latex (SBR) and the like used as this aqueous binder are metastable to heat, so there is a risk of deterioration if heat is generated during the kneading process. It was.

  As described above, if the active material particles and the binder are sufficiently mixed and are not uniformly dispersed in the solvent, the peel strength with respect to the current collector is weakened, and the characteristics of the battery are deteriorated. Conventionally, in order to knead an active material and a binder, as described in Patent Document 1, for example, a mixer having an anchor type blade or a torsion type blade is used. However, in the mixer having such a configuration, the flow state of the fluid in the tank (stirring tank) is different between the upper part and the lower part of the tank, and it is difficult to obtain the entire flow. For this reason, it is difficult to uniformly knead the entire mixer in the conventional mixer, and it cannot be said that it is sufficiently satisfactory for the production of an active material paste.

  As a mixer that generates the entire flow in the tank, a high-speed blade is arranged in the center of the tank, and a concentric twin shaft provided with a frame-type low-speed blade that rotates at a low speed close to the inner surface of the tank. A mixer is known (see, for example, Patent Document 2). Such a concentric twin-screw mixer can generate an entire flow in a tank by means of a high-speed blade and a low-speed blade. A phenomenon accompanied by heat generation is seen. Therefore, as described above, the water-based binder composed of SBR or the like has a possibility that it is deteriorated when heat is generated because the elastomer fine particles are dispersed in water in a metastable state with respect to heat. Therefore, if a high shear mixer with a strong shearing action as described above is used, even if the entire flow is obtained in the tank, the large amount of heat generated at the same time causes the water-based binder to be denatured and its characteristics sufficiently While not being utilized, homogeneous stirring is insufficient, and the resulting active material paste is weakly bound to the current collector.

  In order to avoid such a situation, it is conceivable that the stirring blade such as the high-speed blade is agitated in a medium shear type without rotating at high speed, but in such rotation, between the vicinity of the stirring blade and the center of the tank. In addition, a so-called eddy tide is formed, which is a fixed point where no fluid flows, and the entire flow cannot be obtained, so that uniformization of the entire tank is prevented. For this reason, it is necessary to extend the working time of stirring, kneading, dispersion and the like, and it is necessary to increase the amount of aqueous binder added. However, when the amount of the binder is increased, the amount of the active material is relatively reduced, so that the storage capacity is reduced and sufficient electric characteristics as the lithium ion secondary battery cannot be exhibited.

  In addition, a stirring blade having a flat blade and a lattice blade continuous to the flat blade is attached to a stirring shaft provided in the central portion of the stirring tank, and around the stirring blade along the inner surface of the side wall of the stirring tank. There is also known a stirrer provided with a baffle plate that can rotate (see, for example, Patent Document 3). According to such a stirrer, it is possible to stir the fluid with a low shearing force throughout the tank by rotating the stirring blade at a low speed, but the active material paste of the lithium ion secondary battery, particularly the aqueous negative electrode paste There are problems in the manufacture of That is, when manufacturing the aqueous negative electrode paste, first, the negative electrode active material (negative electrode base) is kneaded in the tank, and after the negative electrode active material is kneaded to some extent in the tank, the aqueous binder is put into the tank. However, when the stirring blade is rotating at a low speed, a large downward axial flow does not occur in the center of the tank, and the kneaded material of the negative electrode active material and the aqueous binder have a large specific gravity difference. The aqueous binder charged in the tank is merely floating on the surface of the kneaded material and is not easily caught in the kneaded material of the negative electrode active material. If the agitating blade is rotated at a high speed, even if a large whole flow can be generated, a large amount of heat is generated. Therefore, the metastable aqueous binder is denatured as described above. In addition, in the lattice-type wing, the upper part of the opening is blocked by the lattice frame forming the opening, so that the flow in the vertical direction is hindered by the upper frame piece and may stay below the upper frame, etc. It also becomes a cause of hindering uniform stirring throughout the tank. Therefore, in any case, it is difficult to uniformly mix the aqueous binder, and as a result, the binding property of the aqueous negative electrode paste to the current collector is inferior, and sufficient peel strength cannot be obtained.

JP 11-329416 A (paragraphs 0021 to 0023) Japanese Patent Laying-Open No. 2001-259397 (paragraph 0002, FIG. 4) Japanese Patent No. 3110781 (Claims, FIG. 1)

As described above, the problem to be solved by the present invention is that when an active material paste for an electrode such as a lithium ion secondary battery, particularly an aqueous negative electrode paste, is produced using an aqueous binder that is metastable to heat, the negative electrode active material A low-shearing concentric twin-screw mixer that can be mixed with a small amount of water-based binder and that can be stirred, kneaded and dispersed uniformly and softly with low shearing force without alteration. It is providing the manufacturing method of the water-system negative electrode paste using this .

  As described above, when stirring, kneading, and dispersing a heat-stable water-based binder, various methods and devices that do not generate heat have been researched. '' And slowly stirring with a large plate-shaped stirring blade, and if a flow that entrains an aqueous binder to be added later is generated, the aqueous binder with a specific gravity difference can be converted into a negative electrode active material without alteration. It was found that it can be mixed and stirred uniformly throughout the tank.

  The present invention is a low-shearing concentric twin-screw mixer suitably used for the production of a water-based negative electrode paste used for the electrode layer of a lithium ion secondary battery developed based on the above investigation results. A large flat blade with a slit at the center of the tank that rotates at a low speed in the center of the tank, and a frame-shaped blade that surrounds the large flat blade with a slit and rotates at a low speed along the inner wall of the tank side wall And an inclined paddle type wing that is concentrically provided above the cut flat plate large wing and generates a downward axial flow, and the tank is formed by the frame type wing, the cut flat plate wing, and the inclined paddle wing. A low-shear concentric twin-screw mixer is provided, which generates an overall flow in the tank and an axial flow from the top to the bottom in the tank, thereby solving the above problem.

In the present invention, the rotational speed of the frame-shaped wing is about 1.0 to 2.0 m / sec, and the rotational speed of the cut flat plate large wing is about 1.0 to 2.0 m / sec. Preferably, the inclined paddle type blade is an inclined paddle type blade having an inclination angle of about 30 ° to 60 °. The liquid level height of the processing material supplied into the tank is as follows: h is the liquid level height from the upper surface of the inclined paddle blade, d is the diameter of the circle formed when the inclined paddle blade is rotating , and X is the coefficient. In the formula of h = d / X, it is preferable that X = 4-6. In addition, the surface of the cut flat wing may be treated with a hydrophobic plastic such as Teflon (registered trademark).

  The present invention is configured as described above, and is provided with a slit blade that opens upward in a flat blade body and rotates at a low speed in the center of the tank, and surrounds the large slit blade and surrounds the side wall of the tank. Since the frame-type wing that rotates at a low speed along the inner surface and the inclined paddle-type wing are provided concentrically above the large cut flat blade, the processing material is put into the tank and the large cut flat blade is rotated slowly. The material on the front side of the flat plate-like cut flat large blade is compressed, and the material on the rear side is drawn into the blade surface side of the cut flat large blade by negative pressure and flows in the circumferential direction. In addition, the material discharged by the inclined paddle wing rotating with the large flat blade of the cut plate is a radial flow (radial flow) toward the radial direction of the inclined paddle wing and a swirl flow (circumferential flow) in the circumferential direction. In the treatment material that is mixed with the axial flow toward the lower part of the combined flow, scraped down while flowing in the radial direction, and directed toward the large blades of the cut plate, and stirred by the large blades of the cut plate Easily caught in. Furthermore, the frame-type wing rotating along the inner surface of the tank also exhibits a baffle plate effect and contributes to the vertical flow. Further, since the upper part of the cut is open, there is no possibility that the material stays in the upper part of the cut large plate blade. In this way, each of these blades cooperates and rotates slowly, so that an overall flow that uniformly flows in the entire tank with low shearing force can be obtained. Even if it is metastable to heat, it can be kneaded without alteration. In addition, even if there is a large specific gravity difference between the negative electrode active material and the water-based binder, it is scraped down by the inclined paddle type blades that rotate slowly and heads toward the cut large plate blades, so it is smoothly mixed into the negative electrode active material, It can knead | mix uniformly by the whole flow. At this time, since the frame type blades rotate along the inner wall surface of the tank, the material adhering to the inner wall surface of the tank can be scraped off, and the thermal efficiency of the cooling jacket usually provided along the tank side surface is increased, and the temperature is reduced. Can also contribute. In addition, as described above, an overall flow that reliably flows in the tank with a low shearing force can be obtained, so that a low-shear type concentric twin-screw mixer with high safety and improved productivity that does not require manual labor is obtained. It is done.

  Since the entire flow can be generated and kneaded without generating a large amount of heat as described above, the low shear type concentric twin-screw mixer of the present invention is used when the aqueous negative electrode paste is produced by kneading the aqueous binder with the negative electrode active material. By using this, it is possible to prevent the water-based binder from being altered and to knead uniformly over the upper and lower portions of the tank with a small addition amount. Therefore, the obtained water-based negative electrode paste is obtained by uniformly kneading a water-based binder in the negative electrode active material, and as a result, a lithium ion battery or the like having an excellent power storage effect can be obtained.

  When the rotation speed of the frame type blade is about 1.0 to 2.0 m / sec, the upstream and downstream of the processing material can be surely generated, and the shear rate between the inner surface of the tank side wall is not so high. Therefore, there is little heat generation and the alteration of the aqueous binder can be suppressed. In addition, when the rotational speed of the above-mentioned large cut flat blade is about 1.0 to 2.0 m / sec, when the aqueous binder is added later, the upstream and downstream can be surely generated and mixed into the negative electrode active material. In addition, there is no possibility that bubbles are involved due to excessive flow, and there is no possibility of uneven mixing in the upper and lower parts of the tank. Further, when an inclined paddle type blade having an inclination angle of about 30 ° to 60 ° is used as the inclined paddle type blade, the axial flow is surely generated, and the aqueous binder is accurately entrained in the negative electrode active material. The upper part and the lower part of can be uniformly kneaded. Furthermore, if the surface of the cut flat plate large wing is treated with hydrophobicity, there is almost no sticking of material to the wing, and the material can be agitated by generating a whole flow without much difference in the upper and lower parts of the tank, The binding property of the aqueous negative electrode paste to the current collector can be improved, and the peel strength can be improved.

Sectional drawing which shows one Example of this invention. Sectional drawing which shows the other Example of this invention.

  The present invention is suitably used for the production of an aqueous negative electrode paste for a lithium ion secondary battery as described above, but is required to be stirred, kneaded, dispersed, etc. with a low shearing action. It can also be used to process food, feed and other processing materials. FIG. 1 shows an embodiment of the present invention. A bearing case 1 and a tank (stirring tank) 2 are provided such that either one of them can be moved up and down so that an opening above the tank 2 can be opened and closed. The state shown in FIG. 2 shows a state in which the opening of the tank 2 is closed by the hood 3, and a cooling jacket is provided around the tank.

  The bearing case 1 is provided with an outer drive shaft 4 and an inner drive shaft 5 in a concentric state, and the respective drive shafts are individually rotated by a drive source such as a motor (not shown) in the same direction. It can be rotated in different directions, rotated in a different direction, changed in rotational speed, or driven in various ways. The outer drive shaft 4 is provided with a low shear frame type blade 6 that rotates at a low speed along the inner surface of the side wall of the tank 2. The frame type wing 6 includes a skew member 7, a vertical member 8 extending downward from the lower end thereof in proximity to the inner surface of the tank side wall, and a bottom member 9 connecting the lower end of the vertical member 8 and extending along the bottom surface of the tank. It is configured. The vertical member 8 is formed in a substantially triangular cross section so that the processing material adhering to the inner surface of the tank can be scraped off. However, the vertical member 8 is formed in a plate shape to emphasize the baffle plate effect or in an appropriate cross sectional shape. can do. When the aqueous binder is kneaded, the rotational speed of the frame type blade 6 is preferably about 1.0 to 2.0 m / sec so as not to generate a high shearing force. If it is less than 1.0 m / sec, upstream or downstream of the processing material does not occur, and therefore it becomes impossible to contribute to the generation of the entire flow throughout the tank. In addition, if it exceeds 2.0 m / sec, the clearance between the inner wall of the tank and the tip of the frame-type blade is narrow, so the shear rate at this part is slightly increased, and the aqueous binder in a metastable state with respect to heat is altered, There is a possibility of deteriorating the characteristics of the battery.

  The inward drive shaft 5 extends downward at the center of the tank 2, and a cut plate large blade 10 that rotates at a low speed so as to generate a circumferential flow in the tank is provided at the lower end. ing. The cut flat plate large wing 10 has a large flat blade main body 11 that is surrounded by the frame-shaped blade 6 and has a cut slit 12 that opens at an upper portion with a gap therebetween. Yes. In the embodiment shown in the figure, the cut flat plate large wing 10 is provided with an opening 13 through which the inner drive shaft 5 is inserted at the center, and is connected to the wing body 11 by a connecting member 14. A plurality of slits 12 are formed by forming longitudinal groove-like openings at intervals toward the direction, but the shape and number of these slits can be appropriately formed (not shown). The rotational speed of the cut flat large blade is preferably about 1.0 to 2.0 m / sec. This is because if the rotational speed is less than 1.0 m / sec, a stationary part is seen in the aqueous binder added to the negative electrode active material later, and the upstream and downstream are insufficient. On the other hand, if it exceeds 2.0 m / sec, the flow in the circumferential direction becomes excessive, and the amount of entrainment of bubbles increases. As a result, the kneading of the upper part and the lower part in the tank becomes non-uniform, the homogenization is insufficient, and the peel strength when the aqueous negative electrode paste is applied to the current collector is deteriorated, which is not preferable.

  The frame type blade 6 and the cut flat plate large blade 10 rotate in the same direction, but can be rotated in the opposite direction. When rotating in the reverse direction, when vacuum defoaming is required during stirring, the liquid level can be renewed by stirring, so that the defoaming effect can be enhanced.

  The inward drive shaft 5 above the cut flat large blade 10 is provided with an inclined paddle blade 15 that generates a downward axial flow. The inclined paddle type blade 15 is an axial flow type inclined paddle type blade with the plate surface inclined at an appropriate angle so that fluid can be sucked from the upper part of the blade and discharged in the axial direction. According to this inclined paddle type blade, it becomes an axial oblique flow in which the radial radial flow (radial flow) and the circumferential swirl flow (circumferential flow) are combined without being completely axial flow, It changes with this inclination angle. This inclination angle is required to surely generate an axial flow when rotated at the same speed as the above-described large cut flat blade, and is preferably about 30 to 60 °. An inclined paddle type blade with an inclination angle of 30 ° has an axial flow of 2.0 with respect to a radial flow of 1.0 in the rotational direction. The paddle width is narrower than that of a flat paddle having an inclination angle of 90 ° with respect to the flow direction, and the power is reduced but the axial flow is weakened. For this reason, the inclined paddle type blade of less than 30 ° requires time for uniformly stirring the upper and lower portions in the tank, which is not preferable in terms of work efficiency. On the other hand, the inclined paddle type blade inclined at 60 ° has an axial flow of 1.0 with respect to the radial flow of 2.0, has a large resistance, and the power required for driving becomes close to a flat paddle and it takes time to equalize. . Therefore, it is not preferable to incline beyond 60 °. In the case of 45 °, the radial flow and the axial flow are theoretically divided into 1: 1 and become a diagonal flow, which is convenient.

  The frame blade 6 for low-speed shearing is provided with a gap with the inner wall of the tank 2 of about 2 to 10 mm, and the rotation speed is determined by the blade diameter. The gap S between the inner surface of the frame-type blade 6 and the outer surface of the cut flat large blade 10 is preferably about 20 to 50 mm. Since both the stirring blades have a low rotational speed as described above, if the gap S is less than 20 mm, a phenomenon occurs in which the material rotates together and uniform processing cannot be performed. When the gap S exceeds 50 mm, it becomes impossible to repeatedly generate a circulating flow in which the circumferential flow generated by the cut flat plate large blade 10 is changed into an axial flow and a radial flow by the frame blade 6. This is because the generation of the entire flow in the tank is hindered.

In order to effectively entrain the water-based binder into the kneaded material of the negative electrode active material by the above-mentioned large cut flat blade 10 and the inclined paddle blade 15, the liquid level in the tank has the following relationship as a result of investigation. Was confirmed. That is, when the height from the upper surface of the inclined paddle blade 15 to the liquid surface is h, the diameter of the circle formed when the inclined paddle blade 15 is rotated is d, and the coefficient is X, the equation h = d / X In this case, a relationship of X = 4 to 6 is preferable, and X = 5 is particularly preferable. When the coefficient X is less than 4, the liquid level on the inclined paddle type blade 15 becomes deep, and in order to add an aqueous binder having a low specific gravity later to improve the stirring and mixing, the rotational speed of the blade 15 is increased. Needs to be 2 m / sec or more. If it does so, there exists a possibility that the shear rate of the notch flat plate large wing | blade 10 may become large, may generate | occur | produce heat | fever, and a metastable aqueous | water-based binder may change in quality. Further, when the coefficient X is 6 or more, the liquid level is located immediately above the upper surface of the inclined paddle blade 15, and even if the inclined paddle blade 15 is rotated at a low speed, bubbles are mixed in more. As a result, a large number of bubbles are present in the obtained aqueous negative electrode paste, so that the binding property between the current collector and the electrode layer is hindered, and the characteristics as a battery are affected.

  In the case of a large-scale facility with a large capacity of the tank 2, if the peripheral speed of the inclined paddle type blade 15 is made constant, the difference between the speed of the central axis of the inclined paddle type blade and the speed of the tip of the blade increases. The discharge flow rate on the side is insufficient, and stagnation is likely to occur near the inner drive shaft 5. In such a case, as shown in FIG. 2, the auxiliary inclined paddle type wing 16 can be provided from the longitudinal member 8 of the frame type wing 6 toward the axial center side. By this auxiliary inclined paddle type blade 16, flow deformation toward the scraping axis direction can be generated, and a flow without stagnation can be secured and the stirring effect can be improved. A plurality of the inclined paddle type blades 15 and the auxiliary inclined paddle type blades 16 can be provided. At this time, the optimum height h of the liquid level is a height from the upper surface of the uppermost auxiliary inclined paddle blade 16. It was confirmed by visual surface flow that the effect of the auxiliary inclined paddle type blade 16 is effective in a facility having a tank diameter of φ1000 mm or more and a total capacity of 1000 L or more.

  Even with the auxiliary inclined paddle type blade 16, the peripheral speed is 0 m / sec near the center of the drive shaft, resulting in poor flow. It is preferable to extend from the inside of the frame type blade 6 to the vicinity of the drive shaft 5 of the cut flat plate large blade 10. The gap between the outer peripheral surface of the drive shaft 5 and the inner tip of the auxiliary inclined paddle blade 16 is preferably about 5 to 10 mm and does not contact.

  Furthermore, it is preferable to coat the above-described large cut flat blade 10 with a hydrophobic treatment, for example, a hydrophobic plastic such as Teflon (registered trademark) or silicone. Since the surface of the blade is treated with hydrophobicity, it becomes hydrophobic, the coefficient of friction is low, and the treated material hardly sticks, so there is no great difference in the composition of the kneaded material flowing in the upper and lower parts of the tank. Contributes and can be stirred uniformly. As a result, the obtained aqueous negative electrode paste and the current collector are well bound, and the peel strength can be improved. In other words, when the peel strength of the same level as before can be used, the amount of the aqueous binder can be reduced, so that the amount of the negative electrode active material can be relatively increased, and the storage effect is enhanced. Excellent battery characteristics can be obtained. Moreover, it is excellent in washing | cleaning property and can improve work efficiency. The surface of the frame type blade 6 and the inclined paddle type blades 15 and 16 can also be subjected to a hydrophobic treatment.

  As shown in FIG. 1, separately manufactured using a 70-L low-shearing concentric twin-screw mixer having a tilted paddle blade 15 and a large cut flat blade 10 in the center and a frame-shaped blade 6 around it. The aqueous negative electrode base of the lithium ion secondary battery (a mixture of aqueous negative electrode active materials) was added with a heat-stable aqueous binder, stirred for 15 minutes to produce an aqueous negative electrode paste, and evaluation of battery characteristics Went.

Test 1
When the rotational speeds of the frame type blade 6 and the cut flat large blade 10 were both set to 1.5 m / sec and stirred, the viscosity of the obtained paste was within the range of the rotational speed of the viscometer from 0.3 to 100 r / min. Yes, there was no difference in behavior between the upper and lower samples in the tank (stirring tank) compared to the ideal product.
When the inclined paddle type blade 15 was tested while changing the inclination angle, the peel strength index L and the viscosity stability index M with respect to the ideal peel strength value of 1.0 were as shown in Table 1.
here,
Peel strength index L = (Peel strength when using the upper sample of the tank) / (Peel strength using the lower sample of the tank)
Viscosity stability index M = (Viscosity ratio N1 of upper sample of tank) / (Viscosity ratio N2 of lower sample of tank)
Also,
Viscosity ratio N1 of the upper sample of the tank = viscosity immediately after the slurry at the top of the tank O / viscosity P one day after the slurry at the top of the tank
Viscosity ratio N2 of the lower sample of the tank = viscosity immediately after the slurry under the tank O / viscosity P 1 day after the slurry under the tank
It is.
The inclination angle of the inclined paddle type blade 15 is 30 degrees in the first embodiment, 45 degrees in the second embodiment, 60 degrees in the third embodiment, 0 degrees in the first comparative example, 15 degrees in the second comparative example, and 15 degrees in the third comparative example. Tested at 90 degrees.

  In Table 1 above, it can be seen that the peel strength index L is close to the ideal value in Examples 1-3. When the value of the peel strength index L is greater than 1, the peel strength when using the lower sample <the peel strength when using the upper sample, and when less than 1, the peel strength when using the lower sample Strength> Peel strength when using the upper sample. When the viscosity stability index M is greater than 1, N2 <N1 and the viscosity of the upper sample of the tank is higher than that of the lower sample of the tank, and when the viscosity stability index M is less than 1, N2> N1 and The viscosity of the lower sample is higher than the viscosity of the upper sample of the tank, and there is a possibility that the viscosity changes with time, so it cannot be said that the mixing is good.

Regarding the angle of the inclined paddle type blade 15, when there is no inclined paddle type blade, the binder concentration in the sample at the upper part of the tank is higher than that at the lower part of the tank and the peel strength is higher. Becomes thinner and the peel strength becomes lower. In the case of blades with an inclination angle of 90 degrees (90 degrees with respect to the flow direction), the same tendency as in the case without paddle type blades was shown. Inclination angle of 30 degrees, with 60 degrees inclination paddle wing, also Re not have a binder concentration in the upper sample of the tank slightly darker, peel strength slightly higher, the binder concentration of the lower sample of the tank is thin, the peel strength even slightly The result was low, and the inclined paddle type blade with an inclination angle of 45 degrees was equal to the ideal value.

Test 2
Next, using the inclined paddle type blade 15 with an inclination angle of 45 degrees in the apparatus shown in FIG. 1, the peel strength due to the difference in rotational speed between the cut flat plate large blade 10 and the frame type blade 6 under the same conditions as in Test 1 is obtained. When the influence was tested and an index with respect to the ideal value of 1.0 was obtained, the results shown in Table 2 were obtained.

As shown in Table 2 above, as shown in Examples 4 and 5, when the slit flat plate blade 10 and the frame blade 6 were rotated at the same rotational speed at a low speed, a peel strength index L close to the ideal value was obtained, and As shown in Example 6, almost good peel strength was obtained up to a rotational speed of about 2.0 m / sec. However, as shown in Comparative Example 4-8, the peel strength index as or to stop the cut flat large wing 10 and the frame-type blades 6 Neu not Re or the other rotating or raising the rotational speed, the ideal L was not obtained.

Test 3
Further, the influence of the liquid level height h on the inclined paddle blade 15 on the battery characteristics was tested.
Here, the diameter of the circle formed during the rotation of the inclined paddle type blade 15 is d, the coefficient is X, the height of the liquid surface from the upper surface of the inclined paddle type blade h = the diameter d of the inclined paddle type blade / the coefficient X When the test was performed by changing the value of the coefficient X in the formula, the results shown in Table 3 were obtained.

  As shown in Examples 7 to 9, sufficient peel strength was obtained when the coefficient X was 4 to 6. However, as shown in Comparative Example 9, when X = 1.0, the diameter d of the inclined paddle blade and the liquid level height h are the same (h = d), resulting in poor mixing due to insufficient flow and insufficient peel strength. It was observed. Further, as shown in Comparative Example 10, when X = 10.0, the liquid level was low, and much foaming occurred and sufficient peel strength was not obtained. As shown in Table 3, when the liquid surface height was determined so that the coefficient X was 5, the highest peel strength was obtained.

  In each of the above embodiments, the low-shear type frame-shaped wing 6 functions as a baffle and also has an effect of scraping and moving the material adhering to the inner wall surface of the tank. Room temperature treatment was possible only by passing water.

Test 4
When tested without using the inclined paddle type blade 15 in the same manner as in each of the above examples, the peel strength when using the upper sample in the tank was similar to the standard product as shown in the examples. When the lower sample of the tank was used, the peel strength was about 5 to 10% lower than that of the standard product, and the stirring time had to be extended.

2 Tank 4 Outer drive shaft 5 Inner drive shaft 6 Frame type blade 10 Cutting flat plate large blade 11 Blade body 12 Cutting slit 15 Inclined paddle blade 16 Auxiliary inclined paddle blade

Claims (9)

An outer drive shaft and an inner drive shaft provided in a concentric state, an opening through which the inner drive shaft is inserted at the center, and a flat blade body connected to the inner drive shaft, the opening A large notched flat blade that is provided at the center of the tank and that is provided at the center of the tank at a low speed, and a large notched flat blade that is provided on the outer drive shaft . A frame-type wing that surrounds the periphery and rotates at a low speed along the inner wall of the side wall of the tank, and an inclined paddle-type wing that is provided concentrically above the cut flat plate large wing and generates a downward axial flow. The gap between the outer surface of the cut plate large blade and the inner surface of the frame blade is 20 to 50 mm. The frame blade, the cut plate large blade and the inclined paddle blade generate a whole flow in the tank and Produces an axial flow from top to bottom Low shear concentric biaxial mixer is characterized in that so as to. The mixer low shear concentric biaxial mixer according to claim 1 are those that are used in the production of water-based negative electrode paste used in the electrode layer of the lithium ion secondary battery.   The low shear type concentric twin-screw mixer according to claim 1, wherein a rotation speed of the frame type blade is 1.0 to 2.0 m / sec.   The low shear type concentric twin-screw mixer according to any one of claims 1 to 3, wherein a rotational speed of the cut flat large blade is 1.0 to 2.0 m / sec.   5. The low shear concentric twin-screw mixer according to claim 1, wherein an inclination angle of the inclined paddle type blade is 30 ° to 60 °. The low shear type concentric twin screw mixer according to any one of claims 1 to 5, wherein the frame type wing is provided with an auxiliary inclined paddle type wing toward the inside. The low-speed shear type concentric twin-screw mixer according to claim 6, wherein a gap between an inner tip of the auxiliary inclined paddle type blade and an outer peripheral surface of a drive shaft of a large cut flat blade is 5 to 10 mm. The low shear type concentric twin screw mixer according to any one of claims 1 to 7, wherein the surface of the cut flat plate large blade is subjected to a hydrophobic treatment with a hydrophobic plastic. The low-shear type according to any one of claims 1 to 8 , wherein the aqueous negative electrode paste is produced by stirring a treatment material obtained by adding an aqueous binder to an aqueous negative electrode base of a lithium ion secondary battery. Using a concentric twin-shaft mixer, the liquid level of the processing material supplied into the tank is set to h, the liquid level height from the upper surface of the inclined paddle type blade, and the circle formed when the inclined paddle type blade rotates. A method for producing a water-based negative electrode paste, characterized in that when the diameter is d and the coefficient is X, X = 4 to 6 in the formula h = d / X.

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