CN106653146B - Conductive paste and method for forming conductive film - Google Patents

Abstract

The present invention provides 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. For the conductive paste, since the viscosity x Pa·s and the contact angle y° relative to the test surface with the arithmetic mean roughness Ra of 0.010 μm or less satisfy y<17.6x+19.1, where x≤3.0 and y<40, when using When this conductive paste is subjected to gravure printing on a green ceramic tape, the conductive paste is quickly and uniformly transferred from the gravure printing plate. As a result, the surface of the conductive paste becomes a smooth surface immediately after transfer, so that it is easy to reduce the film thickness while maintaining continuity. Therefore, it is possible to form a conductive film having a continuous film thickness suitable for the internal electrodes of small-sized high-capacity MLCCs.

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 and a method for forming a conductive film by the gravure printing method.

Background technique

For example, when manufacturing a multilayer ceramic capacitor (MLCC) 10 whose cross-sectional structure is schematically shown in FIG. 1 , by printing on the surface of an unfired ceramic green sheet for constituting its dielectric layer 12 A conductive paste containing a heat-resistant metal as a conductive component is applied, and the surfaces of a plurality of green ceramic tapes are laminated and pressure-bonded, and then fired to form the dielectric layer 12 from the green ceramic tapes. The paste constitutes the conductor layer 14 of the internal electrodes. In addition, in FIG. 1, 16 is an external electrode for energizing this internal electrode (conductor layer 14). A gravure printing method, which is a type of gravure printing, is applied to the printing and formation of such internal electrodes (for example, refer to 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 to transfer the conductive paste from the printing plate, and has the advantage of high printing speed.

When printing a conductive paste used for forming internal electrodes of MLCCs, etc., a screen printing method has been generally used. However, there is a problem in the screen printing method that a reduction in dimensional accuracy due to elongation of a printing plate occurs. In particular, in ultra-small MLCCs such as 0603 size (outer dimensions 0.6mm x 0.3mm x 0.3mm) and 0402 size (outer dimensions 0.4mm x 0.2mm x 0.2mm), it is more difficult to ensure the dimensional accuracy of the printed film. On the other hand, according to the above-mentioned gravure printing method, the plate is not stretched, so it is suitable for such MLCCs that require high-precision printing.

prior art literature

Patent Literature

[Patent Document 1] Japanese Patent Application Laid-Open No. 10-199331

[Patent Document 2] Japanese Patent Laid-Open No. 2003-249121

[Patent Document 3] Japanese Patent Laid-Open No. 2005-126505

[Patent Document 4] Japanese Patent Application Laid-Open No. 06-142579

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

Conventionally, various proposals for improvement of the conductive paste used in the gravure printing method have been made. For example, in order to suppress swelling and re-dissolution (sheet-attack) of a green ceramic tape caused by a solvent when applying a gravure printing method to MLCC, it has been proposed to use a petroleum-based solvent or an alcohol-based solvent ( For example, refer to the aforementioned Patent Document 1). In addition, in consideration of the drying speed of the printed coating film when suppressing the belt impact, a proposal to use a solvent such as 1-P-montane and P-montane has been proposed (for example, refer to Patent Document 2).

In addition, when manufacturing laminated ceramic parts such as MLCCs, after printing a conductive paste on a green ceramic tape, a paste containing a ceramic raw material as a main component is printed on a portion other than the conductor pattern forming portion to make a green ceramic tape. In the case of flattening the surface of a thin film, a printed film having excellent flexibility is formed by including a terpene resin having an arithmetic average molecular weight of 300 to 5,000 in the paste in addition to the ethyl cellulose resin (for example, refer to Patent Reference 3). In gravure printing, the use of a low-viscosity and thixotropy-suppressed conductive paste makes it easy to transfer from a printing plate to a to-be-printed body. Plate contact is prone to breakage and drop of the conductor pattern. Therefore, the present invention aims to suppress the breakage and drop by improving the flexibility of the printed film.

In addition, for the purpose of improving paste transferability by changing the printing plate side, it has been proposed to cover the printing plate in the cell tank with a cover film having a contact angle with respect to water of 50° or more (for example, see Patent Document 4). According to this printing plate, by covering the unit cells with perfluoroalkoxy resin or the like, the contact angle with water is increased to 50° or more, so that the wettability between the paste and the printing plate is reduced, and the transfer is performed. Sexual improvement.

In this way, from the viewpoints of suppressing tape impact and increasing the strength of the printed film, and the like, various improvements of the conductive paste used in the gravure printing method and improvements of the printing plate have been proposed. However, they cannot be used to form continuous films with film thicknesses below 1 μm. In addition, according to the results of additional tests, it was found that even if the conductive paste was prepared so as to have the same contact angle, the transferability was different when the type and particle size of the conductive powder and the composition of the vehicle were different. Not necessarily good results.

SUMMARY OF THE INVENTION

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

In order to achieve this object, the first invention is a conductive paste for gravure printing containing a conductive powder, a binder and an organic solvent, wherein the viscosity at a shear rate of 40 1/s at 25°C is x Pa ·s. When the contact angle when 10 μL is dropped on a test surface having an arithmetic mean roughness Ra of 0.010 μm or less at 25° C. is y°, x and y satisfy the following formula (1).

y<17.6x+19.1, where x≤3.0, y<40...(1)

In addition, the gist of the second invention for achieving the above-mentioned object resides in a method for forming a conductor film, including the steps of: preparing a conductive paste containing a conductive powder, a binder and an organic solvent; and filling the conductive paste in a A printing process of transferring the recesses of a gravure printing plate to the surface to be printed; and a baking process of generating a conductive film on the surface to be printed by subjecting the formed printed film to a firing process; preparing the conductive film In the paste process, the conductive paste was prepared so that the viscosity x Pa·s at a shear rate of 40 1/s at 25°C and the same material as the outermost peripheral surface of the gravure printing plate were set to The contact angle y° at the time of dropping 10 μL of the horizontally arranged test surface in a state where the outermost peripheral surface is the same surface satisfies the above-mentioned formula (1).

According to the first invention, in the conductive paste for gravure printing, 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 formula (1), so when When gravure printing is performed on the to-be-printed surface using this conductive paste, the conductive paste can be quickly and uniformly transferred from the gravure printing plate to the to-be-printed surface. As a result, since the paste surface is smooth immediately after transfer, it is easy to reduce the film thickness while maintaining continuity. Therefore, if this conductive paste is used, it is possible to form a continuous thin film suitable for the internal electrodes of small-sized high-capacity MLCCs. thick conductor film.

In addition, according to the second invention, when the conductive film is formed by the gravure printing method, 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 40 1/s and the The contact angle y° when 10 μL of the same material as the outermost peripheral surface of the gravure printing plate was placed on the same surface as the outermost peripheral surface and the contact angle y° when 10 μL was dropped on the horizontally arranged test surface satisfies the formula (1). Therefore, in the printing process, when gravure printing is performed using this conductive paste, the conductive paste can be quickly and uniformly transferred to the surface to be printed. As a result, the paste surface becomes a smooth surface immediately after transfer, so that it is easy to reduce the film thickness while maintaining continuity. Therefore, it is possible to form a conductor film having a continuous film thickness suitable for the internal electrode of a small-sized high-capacity MLCC. In addition, in this application, "the outermost peripheral surface of a printing plate" means the surface located on the cylindrical surface before a printing pattern is formed on a printing plate.

Therefore, conventionally, for the purpose of uniform transfer from the gravure printing plate to the printed surface, attempts have been made to optimize the organic components and/or the rheology of the conductive paste, but as described above, , these attempts have not yielded sufficient results. On the other hand, the present invention is an invention made by discovering that not only the wettability of the printing plate and the conductive paste, that is, the size of the contact angle, but also the viscosity of the conductive paste are related to the transferability. The conductive paste can be uniformly transferred from the gravure printing plate to the gravure printing plate by adjusting the viscosity and the contact angle so that the above formula (1) is satisfied, that is, by setting the contact angle to a certain value or less in relation to the viscosity. The surface to be printed, and the film surface becomes smooth from immediately after transfer.

Moreover, in 1st invention, the arithmetic mean roughness Ra of the surface roughness of a test surface needs to be 0.010 micrometer or less. The surface roughness of the outermost peripheral surface of a gravure printing plate is generally 0.010 μm or less, so 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 addition, in the present application, the viscosity x Pa·s uses the static viscosity at a shear rate of 40 1/s at 25°C. This condition is determined in consideration of the room temperature during gravure printing and/or the stress applied to the conductive paste when the conductive paste is transferred to the printed surface during gravure printing. Therefore, by using this value, stable performance can be achieved. The viscosity of the conductive paste and the correlation between the contact angle and transferability were obtained. In addition, the viscosity measurement can be performed using a commercially available viscometer.

In addition, in this application, the contact angle y degree used the value which measured the droplet of 10 microliters on a horizontal surface at 25 degreeC. This condition is determined in consideration of the room temperature during gravure printing and/or the amount of the conductive paste transferred during the formation of the internal electrodes of the MLCC. Therefore, by using this value, the viscosity of the conductive paste can be stably obtained. and the correlation between contact angle and transferability. In addition, the dripping of the conductive paste can be performed using, for example, a micropipette, and the measurement of the contact angle can be performed using a commercially available contact angle meter.

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

According to the present invention, the viscosity and the contact angle are measured by the method determined as described above, and the conductive paste is prepared so that their values satisfy the formula (1), as described above, the following effects can be obtained: The gravure printing plate is uniformly transferred to the to-be-printed surface, and the film surface becomes smooth from immediately after the transfer. That is, if it has only the wettability whose contact angle is a certain value or more, good transferability cannot always be obtained, and as the viscosity becomes smaller, it is necessary to reduce the contact angle, even if wetting becomes easy.

In addition, regarding the relationship between the contact angle and the transferability, the above-mentioned Patent Document 4 shows that when the contact angle is large, the transferability is good, and the contact angle needs to be 50° or more, but if the contact angle is too large, it becomes difficult for the conductive paste to enter unit slot. However, according to the research results of the present inventors, in order to obtain good transferability, it is preferable that the contact angle is small, and as shown in the above-mentioned formula (1), it is necessary to set the measurement between the conductive paste and the printing plate. is 40° or less. The above-mentioned Patent Document 4 describes that "it is preferably 50° or more and not too large", but the inventors of the present invention have obtained the opposite result. In addition, in the above-mentioned Patent Document 4, the contact angle is defined by the value corresponding to water, but this is to indirectly define the surface state of the unit cell by the value of the contact angle relative to water, and the appropriate contact angle is not considered according to the actual situation. The physical properties of the conductive paste used vary.

Here, it is preferable that both the test surface in the first invention or the outermost peripheral surface and the test surface of the gravure printing plate in the second invention are Cr-plated or Ni-plated surface. In order to improve the wettability with the conductive paste, it is preferable that the gravure printing plate is Cr-plated or Ni-plated. Therefore, it is preferable to use a test surface which is Cr-plated or Ni-plated as well as the printing plate. In addition, in order to improve wettability and reduce the contact angle, it is preferable to perform plating, and the type of plating on the test surface is preferably the same as that of gravure plate plating. However, since the same contact angle can be obtained even if the types of plating are different, it is not necessary to make them match.

In addition, in the above formula (1), it is preferable that the range of the viscosity x Pa·s is 0.1≦x≦3.0. As shown in the above-mentioned formula (1), the lower the viscosity becomes, the lower the upper limit of the contact angle y is, so it is difficult to prepare the conductive paste so as to satisfy the formula (1). Therefore, the viscosity is preferably 0.1 Pa·s or more.

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

In addition, it is preferable that the viscosity x and the contact angle y satisfy y>8.8x+12.4·(2). The smaller the contact angle y and the higher the wettability, the worse the handleability, but the lower the viscosity x is, the smaller the contact angle y can be, so it is preferable to satisfy the above formula (2).

In addition, it is preferable that the conductive paste is applied to a green ceramic tape by printing to form a conductive film. The conductive paste of the present invention is not limited in use, but is suitably used when a conductor film is formed on an insulator made of ceramics. In particular, when the green ceramic tape is applied by printing, a conductor film can be produced by firing at the same time as firing treatment is performed to produce an insulator, which is advantageous in terms of production cost.

In addition, it is preferable that the conductive paste is used to form the internal electrodes of the MLCC. As described above, according to the conductive paste of the present invention, since it is easy to reduce the film thickness while maintaining continuity, it is suitable for the internal electrodes of small-sized high-capacity MLCCs.

Moreover, it is preferable that the said electroconductive powder is nickel powder. For example, in the internal electrode application of MLCC, by laminating green ceramic tapes printed with conductive paste and performing a firing process, the internal electrodes are formed simultaneously with the formation of the dielectric layer using the green ceramic tapes, so 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, etc. are suitable, but from the viewpoint of production cost, inexpensive base metal materials are preferred, In view of heat resistance, electrical conductivity, and price, nickel is particularly preferred. The average particle diameter of the conductive powder can be appropriately determined within a range in which the desired properties of the conductive paste can be obtained.

In addition, preferably, the binder is polyvinyl butyral, polyvinyl carbazole, acrylic resin, epoxy resin, phenolic resin, alkyd resin, cellulose-based polymer, rosin-based resin resin, etc. The binder of the conductive paste of the present invention can be appropriately selected from binders generally used within a range in which a desired viscosity and contact angle can be achieved, but the above-mentioned binders are limited by the coating film forming ability (ie, relative It is preferable from the viewpoint of substrate adhesion) and/or decomposability during firing.

In addition, it is preferable that the organic solvent is not particularly limited as long as it can appropriately dissolve or disperse the components of the conductive powder and the binder resin. Examples include alcohol-based solvents such as terpineol, terpene-based solvents such as isoborneol acetate, glycol-based solvents such as ethylene glycol esters, and diethylene glycol monobutyl ether (diethylene glycol butyl ether). Such as glycol ether-based solvents, ester-based solvents, hydrocarbon-based solvents such as toluene and xylene, and other organic solvents with high boiling points such as mineral spirits. These organic solvents are difficult to dissolve the binder of the butyral-based resin and the acrylic-based resin in the green ceramic tape, so that so-called tape shock is difficult to generate, so they are preferable.

In addition, it is preferable that the constituent components (common materials) of the green ceramic tape to which the conductive paste is applied are contained in the conductive paste, as is generally performed. For example, when the dielectric layer of the MLCC is made of barium titanate, it is preferable to contain barium titanate powder. Since the conductive paste of the present invention can easily form thin internal electrodes, the average particle diameter of the common 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.

In addition, the component ratio of the conductive paste is not particularly limited, and is appropriately determined to satisfy the above-mentioned formulas (1) and (2), but preferably contains, for example, 30 to 60% by mass of the conductive powder, 1 to 5% of the binder, 35-65% of the organic solvent and 0-20% of other co-material components. In addition, when a common material is included, the range of 1 to 20% is preferable.

Description of drawings

FIG. 1 is a diagram showing a cross-section of an MLCC to which a conductive paste according to an embodiment of the present invention is applied to internal electrodes.

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

Symbol Description

10: MLCC 12: Dielectric layer 14: Conductor layer 16: External electrode

Detailed ways

Hereinafter, an embodiment of the present invention will be described in detail. In addition, in the Example to be described below, the conventionally generally used structure can be used suitably, unless there is a specific objection.

The conductive paste of the present example is used to form the conductor layer 14 serving as its internal electrode by a gravure printing method when manufacturing the MLCC 10 shown in FIG. 1 . In this embodiment, the thickness dimension of one dielectric layer 12 is, for example, 10 μm or less, for example, in the range of 0.1 to 3 μm, such as about 1 μm, and the thickness of one conductor layer 14 is, for example, 10 μm or less, for example, in the range of 0.1 to 3 μm. within, 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 the manufacture of such MLCC10, conductive powder, ceramic powder, binder, and organic solvent are mixed according to predetermined specifications to prepare a conductive paste, and the conductive paste is applied by gravure printing on a separately prepared One side of the green ceramic tape for forming the dielectric layer 12 . The conductor layer 14 is formed with the conductive paste simultaneously with the formation of the dielectric layer 12 with the green ceramic tape by laminating and pressure-bonding the green ceramic tapes coated with the conductive paste, and then performing dipping or the like. The method forms the external electrodes 16 , thereby obtaining the MLCC 10 shown in FIG. 1 .

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

In this example, the components of the conductive paste described above were prepared so that the viscosity was the same as the contact angle when dropped on a test surface prepared with the same material as the outermost peripheral surface of the gravure printing plate to have the same surface state as the outermost peripheral surface. The following formula (1) is satisfied. The viscosity is a value measured using, for example, a rheometer (Rheostress 6000 manufactured by HAAKE), and the static viscosity after 1 minute is used under the conditions of 25° C. and a shear rate of 40 1/s. In addition, the contact angle measured with a FACE contact angle meter (CA-DT manufactured by Kyowa Interface Chemical Co., Ltd.) is used at 5°C by dropping 10 μL on a horizontally arranged test surface using a micropipette. The contact angle is, for example, an average value of five measurements.

y＜17.6x+19.1, where x≤3.0, y＜40┅(1)

When the gravure printing plate is, for example, a Cr-plated plate, the test surface is, for example, a Cr plate, and the surface is finished to a very smooth state with an arithmetic mean roughness Ra of 0.010 μm or less. In addition, instead of the Cr plate, a plate plated with Cr in the same manner as the printing plate may be used. In this embodiment, a material such as a gravure printing plate whose surface material is peeled off from a portion where no pattern is formed is used. The size of the flat substrate for the test is, for example, 5 cm×3 cm.

The conductive paste prepared in this way was printed and applied to a green ceramic tape by a gravure printing method. As a result, the resulting 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. By firing this, a smooth continuous film can be obtained. Since smoothness of this level is obtained, it can contribute to the improvement of the characteristic and reliability of a capacitor|condenser more.

The following Table 1 is a table summarizing the results of evaluating the printability under various combinations of viscosity and contact angle while changing the conductive paste composition in various ways in the printing and applying process 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. In addition, "BT amount" is the mass ratio of barium titanate powder with respect to Ni. In addition, "MC" is the mass ratio of nickel powder with respect to the whole electrically conductive paste. The "viscosity at 40 1/s" is the static viscosity measured with a rheometer as described above. In addition, "contact angle with Cr plate" and "Cr-plated printing plate printed body Ra" are the evaluation data when gravure printing is performed using Cr-plated printing plate, respectively, and the former is the measured value of the contact angle between the conductive paste and the Cr plate, The latter is the surface roughness after drying of the printed film obtained by printing and coating on the Cr-plated printing plate using the conductive paste. Regarding the surface roughness, the arithmetic mean roughness Ra was measured using an interference microscope (Nikon LV150 ECLIPSE) under the conditions of a magnification of 10 times, a measurement range of 50 μm×1000 μm, and a measurement number of 12. In addition, "contact angle with Ni plate" and "Ni-plated printing plate printed body Ra" are evaluation data when performing gravure printing using Ni-plated printing plate, respectively.

Table 1

In Table 1 above, the examples in which the surface roughness Ra of the printed body is 0.020 μm or less are examples with good printability, that is, Examples. A graph of the above evaluation results is shown in FIG. 2 . In FIG. 2, "◆" is an example, and "□" is a comparative example. Examples 1 to 11 are on the lower side than the formula (1) shown in FIG. 2 , and are conductive pastes that satisfy the formula (1). Comparative Examples 1 to 8 are on the upper side of the formula (1) or on the right side of the viscosity of 3.0 Pa·s, do not satisfy the formula (1), and are conductive pastes of comparative examples outside the scope of the present invention.

As shown in the above evaluation results, within the range of the viscosity of 0.1 to 3.0 Pa·s and the contact angle of 14 to 39°, a printed body can be obtained by setting the combination of the viscosity and the contact angle that satisfies the above formula (1) Excellent results were obtained with a surface roughness of 0.003 to 0.016 μm. Therefore, when the internal electrodes (conductor layer 14 ) of the MLCC 10 are formed using such a conductive paste, good transferability from the gravure printing plate to the printed surface can be obtained, and as a result, a thin and smooth surface can be easily obtained Therefore, a small and high-capacity MLCC10 can be obtained with a high manufacturing yield. In addition, in Example 11, the Ni-plated printing plate was also evaluated, and good results were obtained to the same extent as in the case of the Cr-plated printing plate. If the conductive paste is prepared so as to satisfy the formula (1), either of the Cr-plated printing plate and the Ni-plated printing plate can similarly obtain a thin continuous film with a smooth surface.

On the other hand, in Comparative Examples 1 to 6, even if the viscosity was in the range of 0.2 to 3.0 Pa·s, the contact angle was as large as 22 to 72°, and thus the viscosity and the contact angle of the formula (1) were not satisfied. In combination, the transferability from the gravure printing plate is poor, and the surface roughness Ra of the printed body becomes a large value such as 0.021 to 0.194 μm. The size of the surface roughness Ra indicates the size of the unevenness on the surface of the printed film, but the thickness of the conductor layer 14 is extremely thin at about 0.5 μm, so the large unevenness as described above means that the 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 with a smooth surface.

In addition, in Comparative Examples 7 and 8, the viscosity is 5.3 to 6.9 Pa·s, which is extremely high, but the contact angle is 51 to 61°, which is on the lower side of the above-mentioned formula (1). However, when these were used for gravure printing, the surface roughness Ra of the printed film was a large value as large as 0.036 to 0.095 μm, and a continuous film was not obtained as in Comparative Examples 1 to 6. This is because transferability is poor if the viscosity exceeds 3.0 Pa·s even if it is on the lower side of the formula (1).

As described above, according to the present embodiment, with regard 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 formula (1), when When performing gravure printing on a green ceramic belt using this conductive paste, the conductive paste is quickly and uniformly transferred from a gravure printing plate. As a result, the surface of the conductive paste becomes a smooth surface immediately after the transfer, so that it is easy to reduce the film thickness while maintaining continuity.

In addition, the viscosity and contact angle of the conductive paste can be appropriately adjusted by changing the Ni particle diameter, the BT particle diameter, the amount of Ni, and the amount of BT, or by changing the types and amounts of binders and organic solvents.

Moreover, according to the said Table 1 and FIG. 2, the lower limit of a preferable viscosity is 0.1 Pa*s. It is difficult to set the viscosity of the conductive paste to be lower than this. In addition, the lower limit of the contact angle is 10°. When the contact angle is 10° or less, the wettability becomes too high, and on the contrary, good transferability cannot be obtained.

In addition, the viscosity x and the contact angle y are preferably higher than the formula (2) in FIG. 2 , that is, y>8.8x+12.4 is satisfied. The smaller the contact angle y becomes, the higher the wettability becomes and the worse the handleability, but the lower the viscosity x becomes, the smaller the value of the contact angle y can be.

As mentioned above, although this invention was demonstrated in detail with reference to drawings, this invention can also be implemented by other forms, and various changes can be added in the range which does not deviate from the summary.

Claims (4)

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.

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