Conductive paste and method for manufacturing solid electrolytic capacitor element

Abstract

A conductive paste including a metal powder, a thermoplastic resin, and a solvent, said conductive paste having a shear viscosity of 0.4-35 Pa・s at a shear rate of 0.05-1 s-1 and a shear viscosity of 0.2-1.5 Pa・s at a shear rate of 20-200 s-1, and having a thixotropic value, which is the ratio between the shear viscosity at a shear rate of 0.05 s-1 and the shear viscosity at a shear rate of 1s-1, of 5-20.

Description

Conductive paste and method for manufacturing solid electrolytic capacitor element

[0001] The present invention relates to a conductive paste and a method for manufacturing a solid electrolytic capacitor element.

[0002] Patent Document 1 describes a powder with an average particle size of 4 to 10 μm and a specific surface area of ​​1.5 to 3.0 m ２ / g, aspect ratio 40 to 150, apparent density 0.4 to 1.0 g / cm ３ 30 to 60% by weight of silver particle aggregate A having an average particle diameter of 2 to 5 μm and a specific surface area of ​​1.0 to 1.5 m ２ / g, aspect ratio less than 50, apparent density 2.0 to 3.5 g / cm ３ The document describes a conductive paste that comprises an aggregate of flake silver particles, which becomes 100% by weight when mixed with silver particle aggregate B of the above-mentioned compound, a resin, and a solvent, and that has a solid content of 40 to 55% by weight, a viscosity of 2.0 to 6.0 dPa s, and a thixotropy value of 1.5 to 1.8.

[0003] Patent No. 6103404

[0004] Patent Document 1 describes that in a method of applying a conductive paste by a dipping method, by providing the paste with a moderate viscosity and high thixotropy, the paste at the ends of the element is less likely to flow, and a thin conductive coating can be formed with a consistent thickness at the ends and flat (side) parts, a coating strength, a low resistivity, and stable conductivity.

[0005] However, Patent Document 1 does not disclose any conductive paste suitable for the roller transfer method.

[0006] The present invention has been made to solve the above problems, and aims to provide a conductive paste suitable for the roller transfer method and a method for manufacturing a solid electrolytic capacitor element using this conductive paste.

[0007] The conductive paste of the present invention contains a metal powder, a thermoplastic resin, and a solvent, and is heated at a shear rate of 0.05 to 1 s －１ The shear viscosity is 0.4 to 35 Pa s and the shear rate is 20 to 200 s －１ The shear viscosity is 0.2 to 1.5 Pa·s, and the shear rate is 0.05 s－１ Shear viscosity at shear rate 1 s －１ The thixotropy value, which is the ratio of the shear viscosity to the shear viscosity at 1000 kJ / cm2, is 5 to 20.

[0008] The method for manufacturing a solid electrolytic capacitor element of the present invention comprises the steps of supplying the conductive paste of the present invention onto a pair of rollers, transporting an assembly of solid electrolytic capacitor elements having element portions between the pair of rollers onto which the conductive paste has been supplied, and transferring the conductive paste on the pair of rollers to the element portions.

[0009] According to the present invention, it is possible to provide a conductive paste suitable for the roller transfer method and a method for manufacturing a solid electrolytic capacitor element using the conductive paste.

[0010] FIG. 1 is a plan view schematically showing an example of an assembly of solid electrolytic capacitor elements (strip structure type) used in the method for manufacturing a solid electrolytic capacitor element according to an embodiment of the present invention. FIG. 2 is a plan view schematically showing an example of a process of performing a masking treatment for chemical conversion on element portions of an assembly of solid electrolytic capacitor elements. FIG. 3 is a plan view schematically showing an example of a process of performing a masking treatment for polarization (polarization treatment) on element portions of an assembly of solid electrolytic capacitor elements. FIG. 4 is a plan view schematically showing an example of a process of forming a solid electrolyte layer on element portions of an assembly of solid electrolytic capacitor elements. FIG. 5 is a cross-sectional view taken along line X-X of the element portion shown in FIG. 4. FIG. 6 is an enlarged cross-sectional view of the polarized portion of the element portion shown in FIG. 5. FIG. 7 is a plan view schematically showing another example of an assembly of solid electrolytic capacitor elements (double-door structure type) used in the method for manufacturing a solid electrolytic capacitor element according to an embodiment of the present invention. FIG. 8 is a plan view schematically showing yet another example of an assembly of solid electrolytic capacitor elements (strip structure type) used in the method for manufacturing a solid electrolytic capacitor element according to an embodiment of the present invention. FIG. 9 is a plan view schematically showing yet another example (double-door structure type) of an assembly of solid electrolytic capacitor elements used in the method for manufacturing a solid electrolytic capacitor element according to an embodiment of the present invention. FIG. 10 is a plan view schematically showing an example of a process for forming a carbon layer on the element portion of the assembly of solid electrolytic capacitor elements. FIG. 11 is a plan view schematically showing an example of a process for forming a conductive layer on the element portion of the assembly of solid electrolytic capacitor elements. FIG. 12 is a schematic diagram of an example of a roller transfer device used for roller transfer of conductive paste. FIG. 13 is a schematic diagram of another example of a roller transfer device used for roller transfer of conductive paste. FIG. 14 is a perspective view schematically showing the appearance of one side of the element portion of the assembly of solid electrolytic capacitor elements to which the conductive paste has been roller-transferred. FIG. 15 is a perspective view schematically showing the appearance of the other side of the element portion of the assembly of solid electrolytic capacitor elements to which the conductive paste has been roller-transferred. FIG. 16 is a cross-sectional view schematically showing an example of a solid electrolytic capacitor element produced by the method for manufacturing a solid electrolytic capacitor element according to an embodiment of the present invention, and corresponds to the cross-sectional view shown in FIG. 5. FIG. 17 is a cross-sectional view taken along line YY of the solid electrolytic capacitor element shown in FIG.Fig. 18 is a cross-sectional view schematically showing an example of a solid electrolytic capacitor. Fig. 19 is a graph showing the dependency of the shear viscosity of the conductive pastes of Example 2, Example 3, and Comparative Example 2 on the shear rate.

[0011] The conductive paste and the method for manufacturing a solid electrolytic capacitor element of the present invention are described below. However, the present invention is not limited to the following configurations, and can be appropriately modified and applied within the scope of the present invention. Note that a combination of two or more of the individual desirable configurations described below also constitutes the present invention.

[0012] The drawings shown below are schematic diagrams, and the dimensions, aspect ratio, scale, etc. may differ from those of the actual product.

[0013] In this specification, terms indicating the relationship between elements (e.g., "parallel," "perpendicular," "orthogonal," etc.) and terms indicating the shapes of elements not only mean the literal strict form, but also mean a range that is substantially equivalent, for example, a range that includes a difference of about a few percent.

[0014] In this specification, a numerical range expressed by a lower limit and an upper limit, i.e., "lower limit to upper limit," includes the lower limit and the upper limit. For example, a range expressed by "1 to 2" means 1 or more and 2 or less, including 1 and 2. In this specification, the upper limit and the lower limit may be any combination of ranges.

[0015] (Conductive Paste) The conductive paste according to an embodiment of the present invention contains a metal powder, a thermoplastic resin, and a solvent, and is melt-melted at a shear rate of 0.05 to 1 s －１ The shear viscosity is 0.4 to 35 Pa s and the shear rate is 20 to 200 s －１ The shear viscosity is 0.2 to 1.5 Pa·s, and the shear rate is 0.05 s －１ Shear viscosity at shear rate 1 s －１ The thixotropy value, which is the ratio of the shear viscosity to the shear viscosity at 1000 kJ / cm2, is 5 to 20.

[0016] The metal powder for the conductive paste of the present invention may be a metal powder made of silver, copper, nickel, or an alloy of at least two of these metals, or a silver-coated powder obtained by coating the surface of a metal powder other than silver with silver by electroless silver plating or the like. Of these, silver powder is preferred.

[0017] The conductive paste according to this embodiment is suitable for the roller transfer method. The roller transfer method differs significantly from the dipping method in that the conductive paste is subjected to shear stress due to the shear rate of the roller, resulting in a low viscosity (shear viscosity) of the conductive paste. Furthermore, since the shear stress is almost eliminated after roller transfer, the viscosity (shear viscosity) of the conductive paste increases.

[0018] Therefore, the rheology of a conductive paste required for roller transfer is desirable to be high viscosity at low shear rates, such as before and after roller transfer, and low viscosity at high shear rates, such as during roller transfer. High viscosity at low shear rates improves the applicability on the roller before transfer and the coating properties on the side and end surfaces of the solid electrolytic capacitor element after transfer (the faster the viscosity returns, the better the shape retention of the conductive paste on the side and end surfaces of the solid electrolytic capacitor element). Furthermore, low viscosity at high shear rates improves the uniformity (ease of leveling) and applicability (ease of thinning) on ​​the main surfaces of the solid electrolytic capacitor element.

[0019] The conductive paste according to this embodiment is applied at a low shear rate (0.05 to 1 s －１ At high shear rates (20 to 200 s), the shear viscosity is as high as 0.4 to 35 Pa·s, so when roller transfer is performed, the coating properties on the peripheral surface of the roller before transfer are good. －１ At low shear rates (0.05 to 1 s), the shear viscosity is low at 0.2 to 1.5 Pa·s, so when roller transfer is performed, the coating is highly uniform and easy to level on the main surface of the solid electrolytic capacitor element, and the coating is easy to apply and form a thin layer. －１) has a high thixotropy with a thixotropy value of 5 to 20, and therefore when roller transfer is performed, the viscosity returns to high after roller transfer, so that the conductive paste transferred to the side surfaces and end surfaces of the solid electrolytic capacitor element is retained as is, improving the coverage of the side surfaces and end surfaces of the solid electrolytic capacitor element.

[0020] The shear rate is 0.05 to 1 s －１ If the shear viscosity is less than 0.4 Pa·s, the paste does not return to a high viscosity after roller transfer, and the conductive paste transferred to the side or end surface of the solid electrolytic capacitor element is not easily retained. －１ If the shear viscosity exceeds 35 Pa·s, the viscosity becomes too high after roller transfer, and the film thickness on the main surface of the solid electrolytic capacitor element becomes too thick, making it difficult to thin the film.

[0021] Also, the shear rate is 20 to 200 s －１ If the shear viscosity is less than 0.2 Pa·s, the viscosity will be too low when roller transfer is performed, resulting in poor application properties on the peripheral surface of the roller. －１ If the shear viscosity exceeds 1.5 Pa·s, the viscosity becomes too high when roller transfer is performed, causing problems such as variations in film thickness due to stringiness.

[0022] Furthermore, if the thixotropy value is less than 5, the viscosity does not return to a high level after roller transfer, making it difficult for the conductive paste transferred to the side or end surfaces of the solid electrolytic capacitor element to be retained.If the thixotropy value exceeds 20, the viscosity becomes too high after roller transfer, making it difficult for the main surfaces of the solid electrolytic capacitor element to be leveled, and the film thickness on the main surfaces varies greatly.

[0023] Shear rate: 0.05 to 1 s －１ In the above, the shear viscosity is preferably 1 to 30 Pa·s, and more preferably 2 to 30 Pa·s.

[0024] Shear rate: 20 to 200 s －１ In the above, the shear viscosity is preferably 0.2 to 0.8 Pa·s, and more preferably 0.2 to 0.4 Pa·s.

[0025] The thixotropy value is preferably 5 to 15, and more preferably 5 to 10.

[0026] In this specification, the shear viscosity at a certain shear rate can be measured at 25° C. using a modular compact rheometer MCR302 manufactured by Anton Paar GmbH. This device allows continuous measurement of the rheology curve within the above shear rate range.

[0027] In this specification, a shear rate of 0.05 s －１ Shear viscosity at shear rate 1 s －１ The thixotropy value, which is the ratio of the shear viscosity at a shear rate of 0.05 s －１ and shear viscosity at 25 ° C. and shear rate 1 s －１ and shear viscosity at 25°C were measured and substituted into the following formula 1 to calculate the value.

[0028] Thixotropy value = shear rate 0.05 s －１ Shear viscosity (Pa s) / shear rate 1 s －１ Shear viscosity (Pa s) at (Equation 1)

[0029] The metal powder is not particularly limited, and for example, those obtained by atomization, electrolysis, chemical reduction, or the like can be used.

[0030] The shape of the metal powder is not particularly limited, and examples thereof include spherical, flat, and thin (flake) shapes. Metal powders of different shapes may be mixed and used. For example, a spherical metal powder (e.g., spherical silver powder) and a flat metal powder (e.g., flat silver powder) may be used in combination.

[0031] The average particle size of the metal powder is not particularly limited, but is preferably 1 to 10 μm, and more preferably 1 to 5 μm.

[0032] The average particle size of the metal powder is the median equivalent circle diameter obtained by image analysis of an image of the metal powder observed with a scanning electron microscope. The median equivalent circle diameter is the particle size (D50) at which the cumulative percentage is 50% in a distribution curve of cumulative percentage against particle size.

[0033] The conductive paste according to this embodiment preferably contains substantially one type of metal powder as the conductive powder, and preferably does not substantially contain anything other than the metal powder.

[0034] The thermoplastic resin functions as a binder resin, and specific examples thereof are not particularly limited, and examples thereof include fluorine-based resins, acrylic resins, and polyester-based resins. Examples of fluorine-based resins that can be used include TFE-propylene copolymers. Examples of polyester-based resins that can be used include saturated copolymer polyester resins. These thermoplastic resins can be used alone or in combination of two or more.

[0035] The solvent dissolves the thermoplastic resin and adjusts the shear viscosity and thixotropy value, and may be an inorganic solvent, but is preferably an organic solvent.

[0036] Examples of organic solvents that can be used include butyl carbitol acetate (BCA), carbitol acetate (CA), isopentyl acetate, butyl carbitol, butyl cellosolve, propylene glycol monomethyl ether, propylene glycol monoethyl ether, 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate (Texanol), etc. These organic solvents can be used alone or in combination of two or more.

[0037] The proportion of the solid content in the total amount of the conductive paste according to this embodiment is not particularly limited, but is preferably 50 to 70% by weight, and more preferably 55 to 65% by weight.

[0038] The proportion of the metal powder in the solid content is not particularly limited, but is preferably 60 to 95% by weight, and more preferably 70 to 90% by weight.

[0039] The specific gravity of the conductive paste according to this embodiment is not particularly limited, but is preferably 1 to 4, and more preferably 1 to 2.

[0040] In this specification, the specific gravity of the conductive paste can be measured using a hydrometer.

[0041] As described above, the conductive paste according to this embodiment is suitable for the manufacture of solid electrolytic capacitor elements, and is preferably a conductive paste used to form the conductive layer of a solid electrolytic capacitor element by roller transfer. This improves the applicability of the conductive paste when it is applied to the peripheral surfaces of the rollers used in roller transfer. Furthermore, leveling of the conductive paste is facilitated on the main surfaces of the solid electrolytic capacitor element, and the conductive paste layer can be easily thinned. Furthermore, improved coverage of the conductive paste on the side and end surfaces of the solid electrolytic capacitor element enables a solid electrolytic capacitor including this solid electrolytic capacitor element to have a low ESR (equivalent series resistance). Here, the conductive layer is preferably a silver layer, the conductive paste is preferably a silver paste, and the conductive paste layer is preferably a silver paste layer.

[0042] (Method for Manufacturing Solid Electrolytic Capacitor Element) Next, a method for manufacturing a solid electrolytic capacitor element according to an embodiment of the present invention will be described.

[0043] A method for manufacturing a solid electrolytic capacitor element according to an embodiment of the present invention includes the steps of supplying the conductive paste according to the embodiment described above onto a pair of rollers, transporting an assembly of solid electrolytic capacitor elements having element portions between the pair of rollers onto which the conductive paste has been supplied, and transferring the conductive paste on the pair of rollers to the element portions.

[0044] According to the method for manufacturing a solid electrolytic capacitor element of this embodiment, the conductive paste of this embodiment is used, which results in good coating properties when the conductive paste is supplied onto the peripheral surface of each roller. Furthermore, leveling of the conductive paste is easy on the main surface of the element portion, and the conductive paste layer can be easily thinned. Furthermore, the coverage of the conductive paste on the side and end surfaces of the element portion is improved, making it possible to reduce the ESR of a solid electrolytic capacitor including this element portion. In the method for manufacturing a solid electrolytic capacitor element of this embodiment, the conductive paste is preferably a silver paste, and the conductive paste layer is preferably a silver paste layer.

[0045] The method for manufacturing a solid electrolytic capacitor element according to this embodiment will be described in more detail below with reference to the drawings.

[0046] FIG. 1 is a plan view schematically showing an example of an assembly of solid electrolytic capacitor elements (strip structure type) used in a manufacturing method of a solid electrolytic capacitor element according to an embodiment of the present invention. FIG. 2 is a plan view schematically showing an example of a process of performing a masking treatment for chemical conversion on element portions of an assembly of solid electrolytic capacitor elements. FIG. 3 is a plan view schematically showing an example of a process of performing a masking treatment for polarization (polarization treatment) on element portions of an assembly of solid electrolytic capacitor elements. FIG. 4 is a plan view schematically showing an example of a process of forming a solid electrolyte layer on element portions of an assembly of solid electrolytic capacitor elements. FIG. 5 is a cross-sectional view taken along line X-X of the element portion shown in FIG. 4. FIG. 6 is an enlarged cross-sectional view of the polarization portion of the element portion shown in FIG. 5.

[0047] 1 to 4, an assembly 10 of solid electrolytic capacitor elements is prepared, which includes a plurality of element portions 11. Each element portion 11 has a pair of main surfaces 11a and 11b, a pair of side surfaces 11c and 11d, and one end surface 11e.

[0048] 5 and 6 , each element unit 11 has a rectangular flat plate shape in a plan view, and includes an anode foil 31 having a porous surface made of a valve action metal substrate, a dielectric layer 33 (see FIG. 6 , not shown in FIG. 5 ) provided on the surface of the anode foil 31, two insulating mask materials 35 and 37 that are annular (extending in a strip-like shape) insulating members provided around the anode foil 31 with the dielectric layer 33 interposed therebetween, and a solid electrolyte layer 39 provided on the anode foil 31 with the dielectric layer 33 interposed therebetween, on the end face 11 e side of the insulating mask material 37. In each element unit 11, the solid electrolyte layer 39 faces the anode foil 31 with the dielectric layer 33 interposed therebetween.

[0049] As shown in FIG. 4, the solid electrolytic capacitor element assembly 10 includes a belt-shaped holding portion 13 in which a plurality of element portions 11 are connected at regular intervals.

[0050] Each step shown in FIGS. 1 to 4 will be described below.

[0051] First, as shown in FIG. 1 , an anode foil 31 is cut into the shape of a solid electrolytic capacitor element (preferably rectangular) by laser processing, punching, or the like, and then welded to a conveying substrate 15 serving as a holding portion 13, for example, to produce an assembly 10 of solid electrolytic capacitor elements.

[0052] In this way, the assembly 10 of solid electrolytic capacitor elements includes a conveying substrate 15 made of a metal or resin material that is provided parallel to the conveying direction in which the assembly 10 is conveyed in the conductive paste transfer process described below, and the element portion 11 is provided on only one side of the conveying substrate 15. Side surfaces 11c and 11d of the element portion 11 extend in a direction perpendicular to the conveying direction (holding portion 13), and an end surface 11e of the element portion 11 extends parallel to the conveying direction (holding portion 13).

[0053] A valve metal substrate having a porous portion on its surface is used as the anode foil 31 constituting the element portion 11. As shown in Fig. 6, the anode foil 31 is a thin film (foil) having a rectangular shape in a plan view, and including a metal substrate portion 31a and a porous portion 31b on the metal substrate portion 31a. A dielectric layer 33 is provided on the surface of the porous portion 31b.

[0054] In this specification, the term "plan view" means a view from the normal direction of the main surface of the anode foil.

[0055] The valve metal substrate is made of a valve metal such as an elemental metal such as aluminum, tantalum, niobium, titanium, or zirconium, or an alloy containing these metals.

[0056] The valve metal substrate may be formed of a core and a porous portion provided on at least one of the main surfaces of the core, and may be formed from a metal foil having an etched surface, a metal foil having a porous sintered powder body formed on the surface, or the like.

[0057] FIG. 7 is a plan view schematically showing another example (double-door structure type) of an assembly of solid electrolytic capacitor elements used in the method for manufacturing a solid electrolytic capacitor element according to an embodiment of the present invention.

[0058] The solid electrolytic capacitor element assembly 10 is not particularly limited to the strip structure type shown in Fig. 1, but may also have a double-open structure (fishbone structure) type as shown in Fig. 7. In this case, the element portions 11 are provided on both sides of the conveying substrate 15.

[0059] Examples of the metal material for the transport substrate 15 include aluminum and stainless steel. Examples of the resin material for the transport substrate 15 include fluororesin, phenolic resin, and glass-epoxy resin composites.

[0060] In any case, unlike the anode foil 31, the transport base material 15 is a highly rigid member, and can prevent the solid electrolytic capacitor element assembly 10 from pulsating even in the conductive paste transfer process described below.

[0061] Fig. 8 is a plan view schematically showing yet another example (strip structure type) of an assembly of solid electrolytic capacitor elements used in the method for manufacturing a solid electrolytic capacitor element according to an embodiment of the present invention. Fig. 9 is a plan view schematically showing yet another example (double-door structure type) of an assembly of solid electrolytic capacitor elements used in the method for manufacturing a solid electrolytic capacitor element according to an embodiment of the present invention.

[0062] The solid electrolytic capacitor element assembly 10 does not necessarily have to include the conveying substrate 15 shown in FIGS. 1 and 7 , but may instead include, as shown in FIGS. 8 and 9 , bones 17 as holding portions 13, which are arranged parallel to the conveying direction in which the assembly 10 is conveyed in the conductive paste transfer process described below. In this case, the element portions 11 contain the same material as the bone portions 17. Specifically, both are made of the same valve metal base and are formed by cutting the same anode foil. The element portions 11 may be provided on only one side of the bone portion 17 (strip structure type) as shown in FIG. 8 , or may be provided on both sides of the bone portion 17 (double-open structure (fishbone structure) type) as shown in FIG. 9 .

[0063] Next, as shown in FIG. 2, an insulating mask material 35 is applied to the element portion 11, and a masking process for chemical conversion is carried out.

[0064] The insulating mask material 35 is formed by applying a mask material such as a composition containing an insulating resin by screen printing, roller transfer, dispenser, inkjet printing, etc. Examples of insulating resins include polyphenylsulfone (PPS), polyethersulfone (PES), cyanate ester resin, fluororesin (tetrafluoroethylene, tetrafluoroethylene-perfluoroalkylvinylether copolymer, etc.), a composition consisting of soluble polyimidesiloxane and epoxy resin, polyimide resin, polyamideimide resin, and derivatives or precursors thereof.

[0065] When the bone portion 17 is used instead of the transport base material 15, this masking treatment for chemical conversion is not necessary.

[0066] Next, the solid electrolytic capacitor element assembly 10 is subjected to a chemical conversion treatment (anodic oxidation treatment). This forms an oxide film that serves as a dielectric layer on the surface of the valve metal substrate. For example, the dielectric layer is made of aluminum oxide. At this time, an oxide film is also formed on the pair of side faces 11c and 11d and one end face 11e of the element portion 11 that has been cut by laser processing, punching, or the like.

[0067] Alternatively, a chemically-formed foil on which aluminum oxide has already been formed may be used as the valve metal substrate. In this case, too, a chemical conversion treatment is performed on the valve metal substrate after cutting, thereby forming an oxide film on the pair of side faces 11c and 11d and one end face 11e of the cut element portion 11.

[0068] Next, as shown in FIG. 3, an insulating mask material 37 is applied to the element portion 11, and a masking process (polarization process) for polarization of the anode portion and the cathode portion is performed.

[0069] The insulating mask material 37 is formed by applying a mask material such as a composition containing an insulating resin by screen printing, roller transfer, dispenser, inkjet printing, etc. Examples of insulating resins include polyphenylsulfone (PPS), polyethersulfone (PES), cyanate ester resin, fluororesin (tetrafluoroethylene, tetrafluoroethylene-perfluoroalkylvinylether copolymer, etc.), a composition consisting of soluble polyimidesiloxane and epoxy resin, polyimide resin, polyamideimide resin, and derivatives or precursors thereof.

[0070] Next, as shown in FIG. 4 , a solid electrolyte layer 39 is formed on the dielectric layer of the element portion 11. Specifically, the element portion 11 is immersed in a treatment liquid containing a solid electrolyte, thereby impregnating the porous portion of the valve metal substrate with the treatment liquid. After immersion for a predetermined time, the element portion 11 is removed from the treatment liquid and dried at a predetermined temperature for a predetermined time. The solid electrolyte layer 39 is formed by repeating the immersion in the treatment liquid, removal, and drying process a predetermined number of times. The solid electrolyte layer 39 may also be formed by repeating a predetermined number of times of immersion in a treatment liquid containing a solid electrolyte precursor (a monomer that becomes a solid electrolyte by oxidative polymerization) and further immersion in a treatment liquid containing an oxidizing agent that oxidatively polymerizes the solid electrolyte precursor.

[0071] The method for forming the solid electrolyte layer 39 (the method for applying the treatment liquid containing the solid electrolyte or the treatment liquid containing the precursor of the solid electrolyte) is not particularly limited to the immersion method described above, and may be, for example, application using a dispenser or roller transfer. Furthermore, these methods may be combined.

[0072] The solid electrolyte layer 39 is formed over the entire device portion 11 on the end face 11e side of the insulating mask material 37. The solid electrolyte layer 39 may be in contact with the insulating mask material 37, as shown in FIGS.

[0073] The solid electrolyte layer 39 is provided on the dielectric layer 33. As shown in Fig. 6 , the solid electrolyte layer 39 is preferably provided so as to fill a plurality of pores (recesses) in the porous portion 31b of the anode foil 31. However, it is sufficient that the solid electrolyte layer 39 covers part of the outer surface of the dielectric layer 33, and there may be pores (recesses) in the porous portion 31b of the anode foil 31 that are not filled with the solid electrolyte layer 39.

[0074] As a treatment liquid containing a solid electrolyte, for example, a dispersion of a conductive polymer such as polypyrroles, polythiophenes, or polyanilines is used. Among these, polythiophenes are preferred, and poly(3,4-ethylenedioxythiophene), also known as PEDOT, is particularly preferred. Furthermore, the conductive polymer may contain a dopant such as polystyrene sulfonic acid (PSS). A conductive polymer film can be formed by applying a dispersion of a conductive polymer to the outer surface of the dielectric layer and drying it. Alternatively, a liquid containing a polymerizable monomer, such as 3,4-ethylenedioxythiophene, may be used as a treatment liquid containing a solid electrolyte precursor. The polymerizable monomer may contain a dopant, such as polystyrene sulfonic acid. Furthermore, the treatment liquid containing a solid electrolyte precursor may contain an oxidizing agent. This treatment liquid can be applied to the outer surface of the dielectric layer to form a conductive polymer film by oxidative polymerization (chemical polymerization). This conductive polymer film becomes the solid electrolyte layer 39.

[0075] FIG. 10 is a plan view schematically showing an example of a process for forming a carbon layer on the element portion of an assembly of solid electrolytic capacitor elements.

[0076] Next, a carbon paste is transferred as a cathode paste to each element portion 11 of the solid electrolytic capacitor element assembly 10 by roller transfer, forming a carbon layer 41 on each element portion 11 as shown in FIG.

[0077] The carbon layer 41 is formed over the entire element portion 11, closer to the end face 11e than the insulating mask material 37. The carbon layer 41 may be formed so that a portion of the solid electrolyte layer 39 on the insulating mask material 37 side is exposed on the outer surface of the element portion 11, or may completely cover the solid electrolyte layer 39 or may be in contact with the insulating mask material 37, as shown in FIG.

[0078] The method for forming the carbon layer 41 (the method for applying the carbon paste) is not particularly limited to roller transfer, and may be, for example, immersion, but roller transfer is preferable. Also, the application of the carbon paste itself may be omitted.

[0079] FIG. 11 is a plan view schematically showing an example of a process for forming a conductive layer on the element portion of an assembly of solid electrolytic capacitor elements.

[0080] Next, the conductive paste according to this embodiment is transferred as a cathode paste to each element portion 11 of the solid electrolytic capacitor element assembly 10 by roller transfer, to form a conductive layer 43 on each element portion 11, as shown in Fig. 11. The conductive layer 43 is preferably a silver layer.

[0081] The conductive layer 43 is formed over the entire element portion 11 on the side of the end face 11 e closer to the insulating mask material 37 .

[0082] Furthermore, the conductive layer 43 is formed so that portions of the solid electrolyte layer 39 and the carbon layer 41 on the insulating mask material 37 side are exposed on the outer surface of the element portion 11, but as shown in FIG. 11 , it may completely cover the carbon layer 41 or may be in contact with the insulating mask material 37. If the carbon layer 41 is not formed, it is preferable that the conductive layer 43 completely covers the solid electrolyte layer 39. This can further improve the moisture resistance reliability of the solid electrolytic capacitor element. It is also preferable that the conductive layer 43 be in contact with the insulating mask material 37.

[0083] Here, the roller transfer device used for roller transfer of the conductive paste and the roller transfer process of the conductive paste will be further described with reference to FIG.

[0084] 12 is a schematic diagram of an example of a roller transfer device used for roller transfer of conductive paste. This roller transfer device can also be used for applying carbon paste.

[0085] 12 includes an unwinding section 210, a vertical conveying type roller transfer section 220A, a preliminary drying section 230, a drying section 240, and a winding section 250, and the assembly 10 of solid electrolytic capacitor elements unwound from the unwinding section 210 is transported through the roller transfer section 220A, the preliminary drying section 230, and the drying section 240 in this order, and then wound up by the winding section 250. The assembly 10 is transported through each section at a predetermined transport speed.

[0086] The unwinding unit 210 unwinds the assembly 10 of solid electrolytic capacitor elements wound in a roll on a unwinding reel. The roller transfer unit 220A transfers the conductive paste to the element portions 11 of the assembly 10 while transporting the assembly 10 supplied from the unwinding unit 210. The pre-drying unit 230 pre-dries the transferred conductive paste by transporting the assembly 10 to which the conductive paste has been transferred to the element portions 11. The drying unit 240 heats and dries the pre-dried conductive paste while transporting the assembly 10. The winding unit 250 winds the assembly 10, on which the conductive paste has been dried, in a roll on a winding reel.

[0087] The roller transfer unit 220A has a plurality of transport rollers 221 that transport the assembly 10 of solid electrolytic capacitor elements on a transport path formed by the assembly 10, a pair of rollers (transfer rollers) 222 between which the element parts 11 of the assembly 10 are transported, and a dispenser 223 and a squeegee 224 provided on each roller 222.

[0088] The pair of rollers 222 are provided on both sides of the assembly 10 of solid electrolytic capacitor elements transported by the transport roller 221. Each roller 222 has a circumferential surface made of metal or rubber, and grooves are formed on the circumferential surface into which the conductive paste is supplied. The depth of the grooves can be appropriately set taking into account the desired coating thickness of the conductive paste. The circumferential surface of each roller 222 does not need to have grooves, and may have a smooth circumferential surface. The circumferential surface may also be roughened by sandblasting or other methods. The circumferential surfaces of the pair of rollers 222 are spaced apart from each other by a predetermined distance from the two main surfaces 11a and 11b of the element portion 11 of the assembly 10, and the conductive paste contacts the element portion 11, transferring the conductive paste on the circumferential surfaces of the pair of rollers 222 to the two main surfaces 11a and 11b of the element portion 11 of the electronic component 40.

[0089] Each dispenser 223 supplies an appropriate amount of conductive paste to the corresponding roller 222, and the conductive paste does not drip from the circumferential surface of the roller 222. This makes it possible to minimize the consumption of conductive paste. The supply of conductive paste to the roller 222 may be continuous or intermittent.

[0090] Each squeegee 224 is disposed a predetermined distance from the circumferential surface of the corresponding roller 222, and adjusts the amount of conductive paste to an appropriate amount by scraping off the conductive paste adhering to the circumferential surface of the corresponding roller 222. Note that, for example, if the conductive paste has low viscosity, scraping by the squeegee 224 may not be necessary.

[0091] Using the roller transfer device 200 shown in FIG. 12, first, carbon paste is transferred to the solid electrolyte layer 39 of the element portion 11 of the assembly 10 shown in FIG. 4, and then the carbon paste is dried to form a carbon layer 41 (see FIG. 10).

[0092] Similarly, using the roller transfer device 200 shown in Figure 12, the conductive paste according to this embodiment is transferred to the carbon layer 41 of the element portion 11 of the assembly 10 shown in Figure 10, and then the conductive paste is dried to form a conductive layer 43 (see Figure 11).

[0093] More specifically, first, conductive paste is supplied onto a pair of rollers 222 of the roller transfer device 200. At this time, while each roller 222 is rotated along the transport direction of the assembly 10 of solid electrolytic capacitor elements, conductive paste is supplied onto each roller 222 from each dispenser 223, and the amount of conductive paste is adjusted by each squeegee 224.

[0094] The conductive paste according to this embodiment is applied at a low shear rate (0.05 to 1 s －１ ) has a high shear viscosity of 0.4 to 35 Pa·s, and therefore has good applicability when supplying the conductive paste onto the circumferential surface of each roller 222.

[0095] The carbon paste contains carbon particles as a conductive component and a resin component such as an epoxy resin or a phenolic resin, and exhibits electrical conductivity.

[0096] The viscosity and thixotropy of the carbon paste are set taking into consideration the shear rate of roller transfer, etc. Furthermore, since it is used in roller transfer, it is preferable to use a high-boiling point solvent as the organic solvent. By using a high-boiling point solvent, it is possible to impart slow drying properties and prevent drying on the circumferential surface of the roller.

[0097] The viscosity and thixotropy of the conductive paste according to this embodiment are as described above. Furthermore, since the paste is used in roller transfer, it is preferable to use a high-boiling-point solvent as the organic solvent. By using a high-boiling-point solvent, the paste can be slow-drying and prevent drying on the circumferential surface of the roller.

[0098] Next, the assembly 10 of solid electrolytic capacitor elements including the element portions 11 on which the solid electrolyte layer 39 is formed is transported between a pair of rollers 222 to which the conductive paste according to this embodiment has been supplied. At this time, the assembly 10 is transported in the extension direction of the holding portion 13 so that only the element portions 11 pass between the pair of adjacent rollers 222, thereby continuously transferring the conductive paste to the plurality of element portions 11. Only the region of the element portion 11 on the side of the end face 11e from the insulating mask material 37, on which the carbon layer 41 (or the solid electrolyte layer 39 if no carbon layer 41 is formed) is formed, is transported between the pair of rollers 222.

[0099] The conveying speed of the assembly 10 is, for example, 20 to 150 mm / s. The rotation speed (rpm) of each roller 222 is calculated from the conveying speed and the roller diameter. The gap (mm) between the pair of rollers 222 is set in consideration of the thickness of the element portion 11 (thickness after the solid electrolyte layer is formed) and the thickness of the conductive paste, but is set to be at least larger than the thickness of the anode foil.

[0100] The thickness of the anode foil may be 100 to 150 μm, but is preferably 110 to 130 μm.

[0101] The thickness of the element portion 11 (thickness after the solid electrolyte layer is formed) may be 110 to 180 μm, but is preferably 120 to 160 μm.

[0102] 12, the solid electrolytic capacitor element assembly 10 may be transported between a pair of rollers 222 while being transported in a direction perpendicular to the horizontal direction. This makes it easier to uniform the thickness of the conductive paste on both main surfaces 11a and 11b of the element portion 11. This is because it makes it easier to uniform the amount of conductive paste supplied to the pair of rollers 222.

[0103] 13 is a schematic diagram of another example of a roller transfer device used for roller transfer of conductive paste. This roller transfer device can also be used for applying carbon paste.

[0104] 13, the roller transfer device 200 may include a horizontally conveying roller transfer unit 220B instead of the vertically conveying roller transfer unit 220A. Similar to the vertically conveying roller transfer unit 220A, the horizontally conveying roller transfer unit 220B includes, on a conveyance path formed by the aggregate 10 of solid electrolytic capacitor elements, a plurality of conveyance rollers 221 for conveying the aggregate 10, a pair of rollers (transfer rollers) 222 between which the element portions 11 of the aggregate 10 are conveyed, and a dispenser 223 and a squeegee 224 provided on each roller 222.

[0105] However, in the horizontal conveyance type roller transfer unit 220B, the assembly 10 of solid electrolytic capacitor elements is conveyed between a pair of rollers 222 while being conveyed in the horizontal direction. This mode is suitable when a conveyance substrate 15 is used as the holding unit 13. This is because the conveyance substrate 15 is hard and therefore difficult to bend in the vertical direction in the conveyance direction. Furthermore, in the case of horizontal conveyance, if the rigidity of the holding unit 13 is low, the assembly 10 may pulsate, but if the conveyance substrate 15 has high rigidity, the assembly 10 can be prevented from pulsating even when conveyed horizontally.

[0106] Fig. 14 is a perspective view schematically showing the appearance of one side of an element portion of an assembly of solid electrolytic capacitor elements to which a conductive paste has been roller-transferred, and Fig. 15 is a perspective view schematically showing the appearance of the other side of an element portion of an assembly of solid electrolytic capacitor elements to which a conductive paste has been roller-transferred.

[0107] The conductive paste on the pair of rollers 222 is then transferred to the pair of principal surfaces 11a and 11b of the element portion 11, and the conductive paste transferred to the pair of principal surfaces 11a and 11b is connected to the pair of side surfaces 11c and 11d and one end surface 11e. More specifically, the conductive paste that overflows between each roller 222 and each principal surface 11a and 11b flows from both principal surfaces 11a and 11b to contact the side surfaces 11c and 11d and the end surface 11e, thereby connecting the conductive paste to the side surfaces 11c and 11d and the end surface 11e. Therefore, as shown in FIGS. 14 and 15 , the conductive paste layers 50 on both principal surfaces 11a and 11b, both side surfaces 11c and 11d, and the end surface 11e are seamlessly connected without creating interfaces at their boundaries.

[0108] The conductive paste used here is subjected to high shear rate (20 to 200 s －１ ), the shear viscosity is low at 0.2 to 1.5 Pa·s, so when the conductive paste is transferred to the element portion 11 by the pair of rollers 222, the conductive paste can be easily leveled on the main surface of the element portion 11, and the conductive paste layer can be easily thinned. In addition, this conductive paste can be easily transferred to the element portion 11 at a low shear rate (0.05 to 1 s －１ ) has a high thixotropy of 5 to 20, so that the coating properties of the conductive paste on both side surfaces 11c and 11d and the end surface 11e of the element portion 11 are improved.

[0109] Fig. 16 is a cross-sectional view schematically showing an example of a solid electrolytic capacitor element produced by a method for producing a solid electrolytic capacitor element according to an embodiment of the present invention, and corresponds to the cross-sectional view shown in Fig. 5. Fig. 17 is a cross-sectional view taken along line YY of the solid electrolytic capacitor element shown in Fig. 16.

[0110] 16 and 17, a solid electrolytic capacitor element 30 is formed in each element portion 11. Furthermore, the conductive layers 43 on each surface of the solid electrolytic capacitor element 30 are connected seamlessly (without interruption) without creating an interface at the boundary between them.

[0111] In each element portion 11, the solid electrolyte layer 39, the carbon layer 41, and the conductive layer 43 (if the carbon layer 41 is not formed, the solid electrolyte layer 39 and the conductive layer 43) located closer to the end face 11e than the insulating mask material 37 function as a cathode, and the anode foil 31 on the opposite side functions as an anode. Therefore, by using each element portion 11, a two-terminal solid electrolytic capacitor can be fabricated.

[0112] For example, a plurality of element portions 11 are stacked, and the anode and cathode are connected to lead frames to form a stacked body.

[0113] Adjacent stacked element portions 11 may be bonded together with a conductive adhesive, but it is preferable to integrate them by remelting the thermoplastic resin contained in the conductive layer 43 of each element portion 11.

[0114] The laminate is then sealed, and the lead frames are formed and cut to form external terminals, resulting in a two-terminal solid electrolytic capacitor with low ESR.

[0115] FIG. 18 is a cross-sectional view schematically showing an example of a solid electrolytic capacitor.

[0116] The solid electrolytic capacitor 100 shown in FIG. 18 is a two-terminal solid electrolytic capacitor, and has a structure in which a lead frame 101 is located at the bottom and solid electrolytic capacitor elements 30 are stacked in order on the lead frame 101 .

[0117] Note that FIG. 18 shows only the characteristic parts of the configuration of the solid electrolytic capacitor, and omits details such as the joining of the anode to the outside and resin sealing, but these can be configured in the same way as in a normal solid electrolytic capacitor.

[0118] Furthermore, the lead frame 101 does not have to be arranged in the bottom layer, and may be sandwiched between the cathodes of two solid electrolytic capacitor elements 30. Therefore, the cathodes of a plurality of solid electrolytic capacitor elements 30 may be stacked to form a laminate of a plurality of solid electrolytic capacitor elements 30, the lead frame 101 may be placed on the laminate, and the cathode of another solid electrolytic capacitor element 30 may be stacked on the lead frame 101 to form another laminate of a plurality of solid electrolytic capacitor elements 30, and a laminate in which the lead frame 101 is sandwiched between the cathode portions may be produced, and then heated and pressed.

[0119] EXAMPLES The following examples more specifically disclose the conductive paste and the method for manufacturing a solid electrolytic capacitor element according to the present invention, but the present invention is not limited to these examples.

[0120] Silver powder, a thermoplastic resin, and an organic solvent were mixed in the proportions shown in Table 1 below to obtain conductive pastes of the examples and comparative examples.

[0121]

[0122] The silver powder used was spherical silver powder with an average particle size of 2 μm and flat silver powder with an average particle size of 10 μm. The thermoplastic resin used was saturated copolymer polyester resin or tetrafluoroethylene (TFE) propylene copolymer. The organic solvent used was butyl carbitol acetate (BCA) or isopentyl acetate.

[0123] Table 1 also shows the percentage (wt %) of the solid content in the total amount of each conductive paste.

[0124] (Specific Gravity) The specific gravity of each conductive paste was measured using a hydrometer.

[0125] (Shear Viscosity and Thixotropy Value) The shear viscosity (Pa·s) of each conductive paste was measured at a shear rate of 0.01 to 1000 s using a modular compact rheometer MCR302 manufactured by Anton Paar. －１ The measurement was carried out at 25°C in the range of 100°C.

[0126] The thixotropy value of each conductive paste was measured at a shear rate of 0.05 s －１and shear viscosity (Pa s) at 25 ° C. and shear rate 1 s －１ and shear viscosity (Pa·s) at 25°C were measured and calculated using the above formula 1.

[0127] The measurement results are shown in Table 2 below and Fig. 19. Fig. 19 is a graph showing the dependency of the shear viscosity of the conductive pastes of Example 2, Example 3 and Comparative Example 2 on the shear rate.

[0128]

[0129] As a result, the conductive paste of the present invention exhibited good applicability on the peripheral surface of the roller when roller transfer was performed, and when roller transfer was performed, the paste was highly uniform and easy to level on the main surface of the solid electrolytic capacitor element, and had good applicability and was easy to form a thin layer, and had good coverage of the side and end surfaces of the solid electrolytic capacitor element.

[0130] The present specification discloses the following:

[0131] <1> A mixture containing a metal powder, a thermoplastic resin, and a solvent, and having a shear rate of 0.05 to 1 s －１ The shear viscosity is 0.4 to 35 Pa s, and the shear rate is 20 to 200 s －１ The shear viscosity is 0.2 to 1.5 Pa s, and the shear rate is 0.05 s －１ Shear viscosity at shear rate 1 s －１ The conductive paste has a thixotropy value, which is the ratio of the shear viscosity at 1000 kJ / cm2 to the shear viscosity at 1000 kJ / cm2, of 5 to 20.

[0132] <2> The conductive paste according to <1>, which is a conductive paste used for forming a conductive layer of a solid electrolytic capacitor element by roller transfer.

[0133] <3> A method for manufacturing a solid electrolytic capacitor element, comprising: a step of supplying the conductive paste according to <1> or <2> onto a pair of rollers; a step of transporting an assembly of solid electrolytic capacitor elements having element portions between the pair of rollers onto which the conductive paste has been supplied; and a step of transferring the conductive paste on the pair of rollers to the element portions.

[0134] 10 Assembly of solid electrolytic capacitor elements 11 Element portion 11a, 11b Main surface of element portion 11c, 11d Side surface of element portion 11e End surface of element portion 13 Holding portion 15 Transport substrate 17 Rib portion 30 Solid electrolytic capacitor element 31 Anode foil 31a Metal base portion 31b Porous portion 33 Dielectric layer 35, 37 Insulating mask material 39 Solid electrolyte layer 41 Carbon layer 43 Conductive layer 50 Conductive paste layer 100 Solid electrolytic capacitor 101 Lead frame 200 Roller transfer device 210 Unwinding portion 220A Vertical conveying type roller transfer portion 220B Horizontal conveying type roller transfer portion 221 Conveying roller 222 Roller (transfer roller) 223 Dispenser 224 Squeegee 230 Pre-drying portion 240 Drying portion 250 Winding section

Claims

1. Contains metal powder, thermoplastic resin, and solvent, and has a shear rate of 0.05 to 1 s －１ The shear viscosity is 0.4 to 35 Pa s, and the shear rate is 20 to 200 s －１ The shear viscosity is 0.2 to 1.5 Pa s, and the shear rate is 0.05 s －１ Shear viscosity at shear rate 1 s －１ The conductive paste has a thixotropy value, which is the ratio of the shear viscosity at 1000 kJ / cm2 to the shear viscosity at 1000 kJ / cm2, of 5 to 20.

2. The conductive paste according to claim 1, which is a conductive paste used to form a conductive layer of a solid electrolytic capacitor element by roller transfer.

3. A method for manufacturing a solid electrolytic capacitor element, comprising: a step of supplying the conductive paste according to claim 1 or 2 onto a pair of rollers; a step of transporting an assembly of solid electrolytic capacitor elements having element portions between the pair of rollers onto which the conductive paste has been supplied; and a step of transferring the conductive paste on the pair of rollers to the element portions.

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