CN106653146B

CN106653146B - Conductive paste and method for forming conductive film

Info

Publication number: CN106653146B
Application number: CN201610959190.9A
Authority: CN
Inventors: 大桥和久; 高田重治
Original assignee: Zhuzuwu Communication
Current assignee: Zhuzuwu Communication
Priority date: 2015-11-04
Filing date: 2016-10-27
Publication date: 2020-01-10
Anticipated expiration: 2036-10-27
Also published as: TW201729221A; CN106653146A; KR102600208B1; JP7023042B2; KR20170052498A; JP2017088668A; TWI700709B

Abstract

The invention provides a conductive paste for gravure printing and a method for forming the conductive film, wherein the conductive paste can form a continuous thin conductive film suitable for an internal electrode of a small-sized high-capacity MLCC. Since the viscosity x Pa · s and the contact angle y ° with respect to a test surface having an arithmetic mean roughness Ra of 0.010 μm or less satisfy y < 17.6x +19.1, where x is 3.0 or less and y < 40, when gravure printing is performed on a green tape using the conductive paste, the conductive paste is quickly and uniformly transferred from a gravure printing plate. Accordingly, since the surface of the conductive paste becomes smooth from immediately after the transfer, the thickness of the conductive paste can be easily reduced while maintaining continuity, and a continuous thin-film-thick conductive film suitable for the internal electrode of the small-sized high-capacity MLCC can be formed.

Description

Conductive paste and method for forming conductive film

Technical Field

The present invention relates to a conductive paste that can be suitably used for gravure printing (gravure printing) and a method for forming a conductor film by the gravure printing method.

Background

For example, in the manufacture of a multilayer ceramic capacitor (MLCC)10 having a cross-sectional structure schematically shown in fig. 1, a conductive paste containing a heat-resistant metal as a conductive component is applied by printing on the surface of an unfired green tape (ceramic green sheet) constituting a dielectric layer 12 thereof, and the surfaces of a plurality of green tapes are laminated and pressure-welded, followed by firing treatment, thereby forming the dielectric layer 12 from the green tape and the conductor layer 14 constituting the internal electrode from the conductive paste. In fig. 1, reference numeral 16 denotes an external electrode for energizing the internal electrode (conductor layer 14). A gravure printing method, which is a type of gravure printing, is applied to the printing formation of the internal electrodes (see, for example, patent document 1). The gravure printing method is a continuous printing method in which a concave portion provided in a printing plate is filled with a conductive paste and the printing plate is pressed against a surface to be printed, thereby transferring the conductive paste from the printing plate, and has an advantage of high printing speed.

In printing of a conductive paste used for forming an internal electrode of an MLCC or the like, a screen printing method has been generally used, but there is a problem in that dimensional accuracy is lowered due to plate elongation in the screen printing method. In particular, in a very small MLCC of 0603 size (outer dimension 0.6mm × 0.3mm × 0.3mm), 0402 size (outer dimension 0.4mm × 0.2mm × 0.2mm), etc., it is more difficult to ensure the dimensional accuracy of the printed film. On the other hand, the gravure printing method is suitable for MLCCs requiring high-precision printing because plate elongation does not occur.

Documents of the prior art

Patent document

[ patent document 1 ] Japanese patent application laid-open No. H10-199331

[ patent document 2 ] Japanese patent laid-open No. 2003-249121

[ patent document 3 ] Japanese patent application laid-open No. 2005-126505

[ patent document 4 ] Japanese patent application laid-open No. H06-142579

However, in the aforementioned small-sized high-capacity MLCCs such as 0603 size and 0402 size, the thickness of the internal electrodes is required to be 1 μm or less. In order to obtain a continuous film with such a thin film thickness, it is necessary to form a printed film having a smooth surface. In the gravure printing method in which the printing speed is high and the time required for the printing and drying steps to be executed is short, the time required from the printing to the drying step is short, and therefore the time required for leveling the printed film is also short. Therefore, in order to obtain a print film having excellent surface smoothness, it is preferable to form a print film having a smooth surface immediately after transfer by uniformly transferring the conductive paste from the printing plate.

Various improvements of conductive pastes for gravure printing have been proposed. For example, in order to suppress swelling and re-dissolution (sheet-attack) of a green ceramic tape caused by a solvent when a gravure printing method is applied to MLCC, it has been proposed to use a petroleum-based solvent or an alcohol-based solvent (see, for example, patent document 1). In addition, it has been proposed to use a solvent such as 1-P-menthane or P-menthane in consideration of the drying rate of the printed coating film when suppressing the belt impact (for example, see patent document 2).

In addition, the following solutions are proposed: in the case of producing a laminated ceramic part such as an MLCC, when a conductive paste is printed on a green tape and then a paste containing a ceramic material as a main component is printed on a portion other than a conductor pattern forming portion to flatten the surface of the green tape, a printed film having excellent flexibility is formed by including a terpene (terpene) resin having an arithmetic mean molecular weight of 300 to 5,000 in addition to an ethyl cellulose resin in the paste (for example, see patent document 3). In gravure printing, a conductive paste having a low viscosity and suppressed thixotropy is used so that transfer from a printing plate to a printing object is easy, but a printed film formed from such a conductive paste is likely to cause breakage and dropping of a conductor pattern when it comes into contact with the printing plate at the time of printing of a ceramic paste. Therefore, the present invention is intended to suppress such breakage and falling by improving the flexibility of the printed film.

Further, for the purpose of improving paste transferability by changing the plate side, a plate in a cell tank is proposed to be covered with a cover film having a contact angle with water of 50 ° or more (for example, see patent document 4). According to this printing plate, the cell grooves are covered with a perfluoroalkane (per fluoroakoxy) resin or the like, whereby the contact angle with water is increased to 50 ° or more, so that the wettability between the paste and the printing plate is decreased, and the transferability is improved.

In this way, various improvements of conductive paste and improvements of printing plate used in gravure printing have been proposed from the viewpoints of suppressing belt impact and improving the strength of printed film. However, they cannot be used for forming a continuous film with a thin film thickness of 1 μm or less. From the additional test results, it was found that: even if the conductive paste is prepared so as to have the same contact angle, good results cannot necessarily be obtained if the transferability varies depending on the kind and particle size of the conductive powder, the composition of the vehicle (vehicle), and the like.

Disclosure of Invention

The present invention has been made in view of the above circumstances, and an object thereof is to provide a conductive paste for gravure printing capable of forming a continuous thin conductive film suitable for an internal electrode of a small-sized high-capacity MLCC and a method for forming the conductive film.

To achieve the object, the invention of claim 1 is an electroconductive paste for gravure printing containing an electroconductive powder, a binder and an organic solvent, wherein: x and y satisfy the following formula (1) when the viscosity at a shear rate of 401/s at 25 ℃ is x Pa · s and the contact angle at which 10 μ L of the solution is dropped on a test surface having an arithmetic mean roughness Ra of 0.010 μm or less at 25 ℃ is y °.

y is less than 17.6x +19.1, wherein x is less than or equal to 3.0, y is less than 40 · (1)

In addition, the gist of the 2 nd invention for achieving the object is a method for forming a conductor film, including: preparing a conductive paste containing a conductive powder, a binder and an organic solvent; a printing step of filling the conductive paste in a recess of a gravure printing plate and transferring the conductive paste to a surface to be printed; and a firing step of performing firing treatment on the formed printed film to form a conductor film on the printed surface; in the step of preparing the conductive paste, the conductive paste is prepared so that a viscosity x Pa · s at a shear rate of 401/s at 25 ℃ and a contact angle y ° at which 10 μ L is dropped onto a test surface horizontally arranged with the same material as the outermost peripheral surface of the gravure printing plate on the same surface as the outermost peripheral surface satisfy the expression (1).

According to the invention described in claim 1, since the electroconductive paste for gravure printing has a viscosity x Pa · s and a contact angle y ° with respect to a test surface having an arithmetic mean roughness Ra of 0.010 μm or less, which satisfy the expression (1), when gravure printing is performed on a surface to be printed using the electroconductive paste, the electroconductive paste can be quickly and uniformly transferred from a gravure printing plate to the surface to be printed. Accordingly, since the paste surface is smooth from immediately after transfer, the film thickness can be easily reduced while maintaining continuity, and thus if this conductive paste is used, a continuous thin-film conductor film suitable for the internal electrode of a small-sized high-capacity MLCC can be formed.

Further, according to the above-mentioned invention 2, in the step of preparing the electroconductive paste, when the conductor film is formed by the gravure printing method, the electroconductive paste is prepared so that the viscosity x Pa · s at the shear rate of 401/s and the contact angle y ° at which 10 μ L is dropped onto a test surface horizontally arranged in a state in which the same material as the outermost peripheral surface of the gravure printing plate is made to be the same surface as the outermost peripheral surface satisfy the above-mentioned expression (1). Therefore, in the printing process, when gravure printing is performed using the conductive paste, the conductive paste can be quickly and uniformly transferred to the surface to be printed. Accordingly, since the paste surface becomes smooth from immediately after transfer, the film thickness can be easily reduced continuously, and a continuous thin-film-thick conductor film suitable for the internal electrode of a small-sized high-capacity MLCC can be formed. In the present application, the "outermost peripheral surface of the printing plate" means a surface located on the cylindrical surface of the printing plate before the printing pattern is formed thereon.

Therefore, conventionally, for the purpose of uniform transfer from a gravure printing plate to a printing surface, attempts have been made to optimize the organic component of the conductive paste and/or optimize the rheological property, but as described above, these attempts have not yet achieved sufficient results. In contrast, the present invention is an invention that has been made by finding that not only the wettability of the printing plate and the conductive paste, i.e., the size of the contact angle, but also the viscosity of the conductive paste has a relationship with transferability. By adjusting the viscosity and the contact angle so as to satisfy the above expression (1), that is, by setting the contact angle to a certain value or less in relation to the viscosity, the conductive paste can be uniformly transferred from the gravure printing plate to the surface to be printed, and the surface of the film just after the transfer can be made smooth.

In the invention 1, the arithmetic mean roughness Ra of the surface roughness of the test surface needs to be 0.010 μm or less. Since the surface roughness of the outermost peripheral surface of the gravure printing plate generally has an Ra of 0.010 μm or less, the evaluation using the above test surface can be regarded as an evaluation using the outermost peripheral surface of a general gravure printing plate.

In the present application, the viscosity x Pa · s is the static viscosity at a shear rate of 401/s at 25 ℃. The conditions are determined in consideration of the room temperature at the time of gravure printing and/or the stress acting on the conductive paste at the time of transfer of the conductive paste to the surface to be printed in gravure printing, and therefore, by using the values, the correlation between the viscosity and contact angle of the conductive paste and the transferability can be stably obtained. The viscosity measurement can be performed using a commercially available viscometer.

In the present application, the contact angle y ° is a value measured by dropping 10 μ L of a droplet on a horizontal surface at 25 ℃. This condition is determined in consideration of the room temperature at the time of gravure printing, the amount of conductive paste transferred at the time of formation of the internal electrode of the MLCC, and the like, and therefore by using this value, the correlation between the viscosity and contact angle of the conductive paste and transferability can be stably obtained. The dropping of the conductive paste can be performed using, for example, a micropipette, and the contact angle can be measured using a commercially available contact angle meter.

The expression (1) is satisfied in the ranges of x ≦ 3.0 and y < 40. In the range of the viscosity and the contact angle exceeding these ranges, good transferability cannot be obtained even if y < 17.6x +19.1 is satisfied.

According to the present invention, the following effects can be obtained by measuring the viscosity and the contact angle by the above-described methods, and preparing the conductive paste so that the values thereof satisfy the above formula (1): the conductive paste can be uniformly transferred from the gravure printing plate to the surface to be printed, and the film surface becomes smooth from immediately after the transfer. That is, if only the wettability is set to a certain value or more, good transferability cannot be always obtained, and as the viscosity becomes smaller, it becomes necessary to decrease the contact angle, that is, to facilitate wetting.

Further, patent document 4 discloses a relationship between a contact angle and transferability: when the contact angle is large, transferability is good, and the contact angle needs to be 50 ° or more, but if it is too large, the conductive paste becomes difficult to enter the cell. However, according to the results of the studies by the present inventors, it is preferable that the contact angle is small in order to obtain good transferability, and it is necessary to set 40 ° or less when measuring between the conductive paste and the printing plate as shown in the above formula (1). The above-mentioned patent document 4 describes that "50 ° or more and not too large" is preferable, but the present inventors have obtained results contrary to this. In patent document 4, the contact angle is defined by a value corresponding to water, but the surface state of the cell well is indirectly defined by a value of the contact angle with respect to water, and it is not considered that an appropriate contact angle differs depending on the physical properties of the conductive paste actually used.

Here, it is preferable that the test surface in the 1 st invention or the outermost peripheral surface and the test surface of the gravure printing plate in the 2 nd invention are both surfaces plated with Cr or Ni. In order to improve the wettability with the conductive paste, the gravure printing plate is preferably a Cr-plated or Ni-plated printing plate. Therefore, it is preferable to use a test surface which is plated with Cr or Ni in a manner similar to the printing plate as the test surface. In addition, plating is preferably performed to improve wettability and reduce a contact angle, and the type of plating on the test surface is preferably the same as that of plating on a gravure printing plate. However, since the same contact angle can be obtained even when the plating type is different, it is not always necessary to make the contact angle uniform.

In the formula (1), the viscosity x Pa · s is preferably in the range of 0.1. ltoreq. x.ltoreq.3.0. As shown in the above formula (1), the lower the viscosity, the lower the upper limit value of the contact angle y is allowed to be, and therefore it is difficult to prepare the electroconductive paste so as to satisfy the formula (1). Therefore, the viscosity is preferably 0.1 pas or more.

In addition, in the above formula (1), the contact angle y ° is preferably in the range of 10 < y < 40. When the contact angle y is 10 ° or less, the wettability becomes too high, and thus a good transferability cannot be obtained on the contrary.

In addition, it is preferred that the viscosity x and the contact angle y satisfy y > 8.8x +12.4 · (2). The smaller the contact angle y becomes, the higher the wettability becomes, and the worse the handleability becomes, but the lower the viscosity x becomes, the smaller the contact angle y can be allowed, and therefore, the above formula (2) is preferably satisfied.

Preferably, the conductive paste is applied by printing to a green tape to form a conductive film. The conductive paste of the present invention is not limited to the application, but is suitably used for forming a conductive film on a ceramic insulator. In particular, if the green tape is printed and coated, the conductor film can be formed by firing at the same time as the insulator is formed by firing treatment, which is advantageous in terms of production cost.

In addition, it is preferable that the conductive paste is used to form an internal electrode of the MLCC. As described above, the conductive paste according to the present invention is suitable for an internal electrode of a small-sized high-capacity MLCC because it can easily achieve a continuous reduction in film thickness.

Preferably, the conductive powder is nickel powder. For example, in the application of an internal electrode to an MLCC, a green tape printed with a conductive paste is laminated and subjected to firing treatment, whereby the internal electrode is produced simultaneously with the production of a dielectric layer from the green tape, and therefore the conductive powder is required to have heat resistance. Therefore, as the conductive powder of the conductive paste of the present invention, metals having heat resistance such as Pt, Pd, Ag — Pd, Ag, Ni, Cu and the like are suitable, but inexpensive base metal materials are preferable in terms of production cost, and nickel is particularly preferable in terms of heat resistance, conductivity and price. The average particle diameter of the conductive powder may be suitably determined within a range in which the desired characteristics of the conductive paste can be obtained, but is preferably, for example, 1.0 μm or less and 0.01 to 0.50 μm, and more preferably 0.05 to 0.30 μm.

Further, the binder is preferably polyvinyl butyral, polyvinyl carbazole, an acrylic resin, an epoxy resin, a phenolic resin, an alkyd resin, a cellulose polymer, a rosin resin, or the like. The binder of the conductive paste of the present invention may be suitably selected from binders generally used in a range that can achieve a desired viscosity and contact angle, but the above binders are preferable in terms of coating film forming ability (i.e., adhesion to a substrate) and/or degradability during firing.

In addition, the organic solvent is not particularly limited as long as the organic solvent can suitably dissolve or disperse the conductive powder and the binder resin. Examples thereof include alcohol solvents such as terpineol, terpene solvents such as isobornyl acetate, glycol solvents such as glycol esters, glycol ether solvents such as diethylene glycol monobutyl ether (diethylene glycol butyl ether), ester solvents, hydrocarbon solvents such as toluene and xylene, and organic solvents having a high boiling point such as other mineral spirits. These organic solvents are preferable because the binder of the butyral resin and the acrylic resin in the green tape is hardly dissolved, and so-called tape impact is hardly generated.

Further, it is preferable that the conductive paste contains a constituent component (co-material) of a green tape to which the conductive paste is applied, as is generally performed. For example, when the dielectric layer of the MLCC is made of barium titanate, barium titanate powder is preferable. The conductive paste of the present invention can easily form a thin internal electrode, and therefore, the average particle size of the co-material is preferably small, for example, 0.5 μm or less, preferably in the range of 0.005 to 0.2 μm, and more preferably in the range of 0.01 to 0.1 μm.

The ratio of the components of the conductive paste is not particularly limited, and is suitably determined so as to satisfy the formulas (1) and (2), but is preferably a component containing, for example, 30 to 60% by mass of the conductive powder, 1 to 5% by mass of the binder, 35 to 65% by mass of the organic solvent, and 0 to 20% by mass of other co-materials. When the co-material is contained, the content is preferably in the range of 1 to 20%.

Drawings

Fig. 1 is a view showing a cross section of an MLCC in which a conductive paste of one embodiment of the present invention is applied to an internal electrode.

Fig. 2 is a graph showing a relationship between the viscosity and the contact angle of the conductive paste according to one embodiment of the present invention.

Description of the symbols

10: MLCC 12: dielectric layer 14: conductor layer 16: external electrode

Detailed Description

Hereinafter, one embodiment of the present invention will be described in detail. In the embodiments described below, a conventionally generally employed configuration can be suitably used unless otherwise specified.

The conductive paste of this example was used to form the conductor layer 14 serving as the internal electrode thereof by gravure printing when manufacturing the MLCC10 as shown in fig. 1. In the present embodiment, the thickness of the dielectric layer 12 is, for example, 10 μm or less, for example, in the range of 0.1 to 3 μm, for example, about 1 μm, and the thickness of the conductive layer 14 is, for example, 10 μm or less, for example, in the range of 0.1 to 3 μm, for example, about 0.5 μm.

The conductor layer 14 is made of, for example, nickel, and the dielectric layer 12 is made of, for example, barium titanate. In manufacturing such MLCC10, a conductive paste is prepared by mixing a conductive powder, a ceramic powder, a binder, and an organic solvent according to a predetermined formulation specification, and the conductive paste is applied by gravure printing to one surface of a green tape that is separately prepared and constitutes the dielectric layer 12. The MLCC10 shown in fig. 1 is obtained by laminating and soldering a green tape layer coated with a conductive paste, then performing a firing process to form the conductive layer 14 from the conductive paste simultaneously with the formation of the dielectric layer 12 from the green tape, and then forming the external electrode 16 by a method such as dipping (dipping).

The conductive powder is, for example, nickel powder having an average particle diameter of 1 μm or less, for example, 0.13 to 0.18 μm, and is mixed with the conductive paste in a proportion of, for example, about 30 to 60 wt%. The ceramic powder is, for example, barium titanate powder having an average particle diameter of 0.1 μm or less, for example, in the range of 10 to 20nm, that is, a co-material (co-material) of barium titanate constituting the dielectric layer 12, and is mixed in the conductive paste at a ratio of, for example, about 10 to 15 wt%. The binder is, for example, ethyl cellulose (ethocel) or polyvinyl butyral (polyvinylbutyral), and the organic solvent is dihydroterpineol (dihydroterpineol), isobornyl acetate (isobornyl acetate), or methyl propionate (methylproprionate) as a main solvent. They are used in a proportion of about 1 to 5% and 30 to 65%, respectively.

In this example, the components of the conductive paste were prepared so that the viscosity and the contact angle when dropped on a test surface prepared from the same material as the outermost peripheral surface of the gravure plate in the same surface state as the outermost peripheral surface satisfy the following expression (1). The viscosity is a value measured by using, for example, a rheometer (Rheodesss 6000, manufactured by HAAKE), and the static viscosity after 1 minute under the conditions of 25 ℃ and a shear rate of 401/s is used. The contact angle used was a contact angle measured by, for example, a FACE contact angle meter (CA-DT, Co., Ltd.) by dropping 10. mu.L of the solution onto a horizontally arranged test surface at 5 ℃ using a micropipette. The contact angle is an average value of, for example, 5 measurements.

y is less than 17.6x +19.1, wherein x is less than or equal to 3.0, y is less than 40 ┅ (1)

In the case where the gravure printing plate is a Cr-plated printing plate, for example, the test surface is a Cr plate, and the surface thereof is finished to have extremely high smoothness with an arithmetic mean roughness Ra of 0.010 μm or less. Instead of the Cr plate, a plate plated with Cr as in the printing plate may be used. In this embodiment, a material is used, for example, of a gravure printing plate whose surface material is peeled off from a portion where no pattern is formed. The size of the flat substrate for testing is, for example, 5cm × 3 cm.

The conductive paste thus prepared was applied by gravure printing to a green tape, and as a result, the formed printed film had a smooth surface with a dry film thickness of about 0.5 μm and a surface roughness Ra of 0.020 μm or less, and a smooth continuous film could be obtained by firing the same. This level of smoothness is obtained, and thus can contribute to further improvement in the characteristics and reliability of the capacitor.

Table 1 below summarizes the results of evaluating printability at various combinations of viscosity and contact angle by variously changing the composition of the conductive paste in the printing and coating step of the conductor layer 14. In table 1, "Ni particle diameter" and "BT particle diameter" are the average particle diameter of the nickel powder and the average particle diameter of the barium titanate powder, respectively. The "BT amount" is a mass ratio of barium titanate powder to Ni. Further, "MC" is a mass ratio of the nickel powder to the entire conductive paste. "401/s viscosity" is the static viscosity as measured by a rheometer as described above. The "contact angle with Cr plate" and "Cr-plated printing plate print Ra" are evaluation data for gravure printing using a Cr-plated printing plate, the former being a measured value of the contact angle between the conductive paste and the Cr plate, and the latter being the surface roughness of a printed film obtained by printing and coating the Cr-plated printing plate with the conductive paste after drying, respectively. The surface roughness was measured by using an interference microscope (Nikon LV150 ECLIPSE) under conditions of a magnification of 10 times, a measurement range of 50 μm × 1000 μm, and a measurement number of 12 to calculate the arithmetic mean roughness Ra. The "contact angle with the Ni plate" and the "Ni-plated printing plate print Ra" are evaluation data when gravure printing was performed using a Ni-plated printing plate.

TABLE 1

In table 1, the example in which the surface roughness Ra of the printed matter is 0.020 μm or less is an example which is good in printability, fig. 2 is a graph showing the evaluation results, fig. 2 shows a graph in which "◆" is an example, and "□" is a comparative example, examples 1 to 11 are conductive pastes satisfying the formula (1) on the lower side of the formula (1) shown in fig. 2, and comparative examples 1 to 8 are conductive pastes of comparative examples outside the scope of the present invention which do not satisfy the formula (1) on the upper side of the formula (1) or on the right side of the viscosity of 3.0Pa · s.

As shown in the above evaluation results, when the viscosity is in the range of 0.1 to 3.0 pas and the contact angle is in the range of 14 to 39 DEG, the combination of the viscosity and the contact angle satisfying the above expression (1) can provide an excellent result that the surface roughness of the printed matter is 0.003 to 0.016. mu.m. Therefore, when the internal electrode (conductor layer 14) of the MLCC10 is formed using such a conductive paste, good transferability from the gravure printing plate to the printing surface can be obtained, and as a result, a thin and smooth continuous film can be easily obtained, so that the small-sized high-capacity MLCC10 can be obtained with a high manufacturing yield. In addition, example 11 also evaluated the Ni-plated printing plate, and it was possible to obtain good results to the same extent as in the case of the Cr-plated printing plate. If the conductive paste is formulated so as to satisfy the formula (1), any of the Cr-plated printing plate and the Ni-plated printing plate can also obtain a thin continuous film having a smooth surface.

On the other hand, in comparative examples 1 to 6, even though the viscosity is in the range of 0.2 to 3.0Pa · s, the contact angle is as large as 22 to 72 °, and the combination of the viscosity and the contact angle does not satisfy the above formula (1), so that the transferability of the gravure printing plate to transfer is poor, and the surface roughness Ra of the printed matter becomes as large as 0.021 to 0.194 μm. The size of the surface roughness Ra indicates the size of the irregularities on the surface of the printed film, but since the thickness of the conductor layer 14 is about 0.5 μm and is extremely thin, such large irregularities mean that continuity of the printed film cannot be obtained. That is, in the conductive paste of the comparative example, it was difficult to obtain a thin continuous film having a smooth surface.

In comparative examples 7 and 8, the viscosity was 5.3 to 6.9 pas and the contact angle was 51 to 61 ° although the viscosity was extremely high, and the contact angle was located below the formula (1). However, when gravure printing was performed using these, the surface roughness Ra of the printed film was as large as 0.036 to 0.095 μm, and a continuous film was not obtained as in comparative examples 1 to 6. Because even if it is located below the formula (1), the transferability is poor if the viscosity exceeds 3.0 pas.

As described above, according to the present embodiment, with respect to the conductive paste, since the viscosity x Pa · s and the contact angle y ° with respect to the test surface having the arithmetic mean roughness Ra of 0.010 μm or less satisfy the above expression (1), the conductive paste is quickly and uniformly transferred from the gravure printing plate when the gravure printing is performed on the green tape using the conductive paste. Since the surface of the conductive paste is smooth immediately after the transfer, the thickness of the conductive paste can be easily reduced continuously, and thus a continuous thin-film-thick conductive film 14 suitable for the internal electrode of the small-sized high-capacity MLCC10 can be formed.

The viscosity and contact angle of the conductive paste can be adjusted as appropriate by changing the Ni particle diameter, BT particle diameter, Ni amount, and BT amount, or by changing the type and amount of the binder and the organic solvent.

Further, from table 1 and fig. 2, the lower limit of the viscosity is preferably 0.1Pa · s. It is difficult to set the viscosity of the conductive paste to be lower than this. The lower limit of the contact angle is 10 °. When the contact angle is 10 ° or less, the wettability becomes too high, and a good transferability cannot be obtained.

The viscosity x and the contact angle y are preferably higher than those of the formula (2) in FIG. 2, that is, y > 8.8x + 12.4. The smaller the contact angle y becomes, the higher the wettability becomes and the inferior handling property becomes, but the lower the viscosity x becomes, the smaller the contact angle y can be allowed to be.

The present invention has been described in detail with reference to the drawings, but the present invention may be implemented by other embodiments and various changes may be made without departing from the spirit and scope thereof.

Claims

1. A conductive paste for gravure printing containing a conductive powder, a binder and an organic solvent, characterized in that:

when the viscosity at a shear rate of 401/s at 25 ℃ is x Pa · s, and the contact angle at 10 μ L by dropping 10 μ L of the solution onto a horizontal test surface having a cut amount of 80 μm and an evaluation length of 1.0mm Ra is y °, x and y satisfy the following formula:

y＜17.6x+19.1，

wherein x is less than or equal to 3.0 and y is less than 40.

2. The electroconductive paste according to claim 1, wherein:

the test surface is a test surface plated with Cr or Ni.

3. A method of forming a conductor film, comprising:

preparing a conductive paste containing a conductive powder, a binder and an organic solvent;

a printing step of filling the conductive paste in a recess of a gravure printing plate and transferring the conductive paste to a surface to be printed; and

a firing step of subjecting the formed printed film to firing treatment to form a conductor film on the surface to be printed,

the method for forming a conductor film is characterized in that:

in the step of preparing the conductive paste,

the conductive paste is prepared so that the viscosity x Pa · s at a shear rate of 401/s at 25 ℃ and the contact angle y DEG when 10 [ mu ] L of the conductive paste is dropped onto a test surface horizontally arranged with the same material as the outermost peripheral surface of the gravure printing plate on the same surface as the outermost peripheral surface satisfy y < 17.6x +19.1, where x is 3.0 or less and y is < 40.

4. The conductor film forming method according to claim 3, wherein:

the outermost peripheral surface and the test surface of the gravure printing plate are surfaces plated with Cr or Ni.