TWI700709B - Method for forming conductive paste and conductive film - Google Patents

Abstract

The subject of the present invention is to provide a conductive paste for gravure printing capable of forming a continuous and thin conductor film suitable for internal electrodes of a small high-capacity MLCC, and a method for forming the conductor film. The solution of the present invention is to provide a conductive paste, because the viscosity x (Pa･s) and the contact angle y (∘) of the test surface with respect to the arithmetic mean roughness Ra of 0.010 (μm) or less satisfy y< 17.6x+19.1 (however, x≦3.0, y<40), so when gravure printing is performed on a ceramic green sheet using this conductive paste, the conductive paste can be quickly and uniformly transferred from the gravure printing plate. As a result, since the surface of the paste becomes smooth immediately after transfer, it is easy to reduce the film thickness while maintaining continuity, and thus it is possible to form a continuous and thin film suitable for internal electrodes of small high-capacity MLCCs Thick conductor film.

Description

Method for forming conductive paste and conductive film Invention field

The present invention relates to a conductive paste suitable for use in gravure printing and a method for forming a conductive film by gravure printing.

Background of the invention

For example, when manufacturing a multilayer ceramic capacitor (MLCC) 10 whose cross-sectional structure is schematically shown in FIG. 1, a conductive paste containing a heat-resistant metal as a conductive component is printed and applied to the dielectric layer 12. Unfired ceramic green sheet (ceramic green sheet) surface, and after laminating a large number of them and pressing and bonding, the calcination process is performed to generate the dielectric layer 12 from the green sheet, and at the same time, internal electrodes composed of conductive paste are generated The conductor layer 14. In addition, in Fig. 1, 16 is used to energize the outer electrode of the inner electrode (conductor layer 14). In the printing and formation of such internal electrodes, a gravure printing method, which is a type of gravure printing, can be applied (for example, refer to Patent Document 1). The gravure printing method is a continuous printing method in which the conductive paste is filled into the recesses provided in the plate making, and the conductive paste is transferred from the plate making by pressing it into contact with the printed surface, which has the advantage of faster printing speed.

In the past, the screen printing method is usually used to print the conductive paste used to form the internal electrodes of the MLCC. However, the screen printing method has a problem caused by the low dimensional accuracy of the plate extension. Especially in ultra-small MLCCs such as 0603 size (outer size 0.6mm×0.3mm×0.3mm) and 0402 size (outer size 0.4mm×0.2mm×0.2mm), it is further difficult to ensure the dimensional accuracy of the printed film. In contrast, when the aforementioned gravure printing method is used, since plate extension does not occur, it is suitable for MLCC applications that require such high-precision printing.

Prior art literature Patent literature

Patent Document 1: Japanese Patent 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 Laid-Open No. 06-142579

Summary of the invention

In small high-capacity MLCCs such as the aforementioned 0603 size, 0402 size, etc., it is required to set the thickness of the internal electrode to 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 with a smooth surface. In the gravure printing method where the printing speed is faster and the tact time of the printing and drying steps is short, the time from printing to drying becomes shorter, and the time for leveling the printed film is also shorter. Therefore, in order to obtain a printed film with excellent surface smoothness, it is preferable to uniformly transfer from the plate making by a conductive paste, and to form a printed film with a smooth surface immediately after the transfer.

In the past, various proposals have been made to improve conductive pastes used in gravure printing. For example, when the gravure printing method is applied to MLCC, it has been proposed to use petroleum solvents or alcohol solvents to suppress swelling and re-dissolution (sheet erosion) of ceramic green sheets due to solvents (for example, refer to the aforementioned Patent Document 1). In addition, when suppressing sheet erosion, there are proposals to disclose the use of solvents such as 1-p-menthene and p-menthane in consideration of the drying speed of the printed coating film (for example, refer to Patent Document 2 ).

In addition, when manufacturing laminated ceramic parts such as MLCC, after printing a conductive paste on a ceramic green sheet, a paste mainly composed of a ceramic raw material is printed on a portion other than the conductor pattern formation portion to make the ceramic green sheet When the surface is flattened, it has been proposed that the paste contains not only ethyl cellulose resin but also terpene resin with a number average molecular weight of 300 to 5,000 to form a printed film with excellent flexibility (for example, refer to Patent Document 3). In gravure printing, a conductive paste with low viscosity and suppressed thixotropy is used to make it easy to transfer from the printing plate to the to-be-printed body, but the print produced from this conductive paste Film brushing, when the ceramic paste is printed, the conductor pattern is easily damaged when the printing plate contacts. Fall off. Therefore, it is desired to improve the flexibility of the printed film to suppress the breakage and peeling.

Furthermore, for the purpose of improving the transferability of the paste by changing the plate-making side, there is a proposal to disclose a plate-making method in which the groove is covered with a film having a contact angle of 50° or more to water (for example, refer to Patent Document 4) . According to this platemaking, because the contact angle with water is increased to 50° or more by covering the grooves with perfluoroalkoxy resin or the like, it is believed that the wettability of the paste and the platemaking is reduced and the transferability is improved.

In this way, from the viewpoints of suppressing sheet erosion and increasing the strength of the printed film, various proposals have been made to improve the conductive paste used in the gravure printing method and to improve the plate making. However, these cannot be used to form a continuous film with a thin film thickness of 1 ( μm ) or less. In addition, even if the conductive paste is prepared so as to have the same contact angle, when the type of conductive powder, particle size, etc., and the composition of the vehicle are different, the transferability is different, and good results may not be obtained. Also tried again to clearly understand the above results.

The present invention is based on the above-mentioned circumstances, and its object is to provide an electro-paste for gravure printing capable of forming a continuous and thin conductor film suitable for internal electrodes of a small high-capacity MLCC, and a method for forming the conductor film.

In order to achieve such an objective, as the gist of the first invention, a conductive paste for gravure printing containing conductive powder, adhesive, and organic solvent, at a temperature of 25 (℃) and a shear rate of 40 (1/s) Set the viscosity as x (Pa.s), and the contact angle of the test surface with the arithmetic mean roughness Ra of 0.010 (μm) or less when dropping 10 (μL) at 25 (℃) as y (°), at this time x , Y satisfies the following formula (1).

y<17.6x+19.1 (however, x≦3.0, y<40). . . (1)

In addition, in order to achieve the foregoing object, as the gist of the second invention, a method for forming a conductive film includes the steps of: preparing a conductive paste containing conductive powder, an adhesive, and an organic solvent; and filling the conductive paste with The printing step of gravure printing the concave portion of the plate making and transferring to the printed surface; and the calcining step of forming a conductive film on the printed surface by calcining the formed printed film; wherein, the step of preparing the conductive paste , The preparation of the aforementioned conductive paste is carried out under the following conditions: at 25 (℃) and shear rate The viscosity x (Pa.s) of degree 40 (1/s), the contact angle y (°) when using the same material as the outermost peripheral surface of the gravure printing plate and the test surface arranged horizontally so as to become the same surface state, The x and y satisfy the aforementioned formula (1).

According to the aforementioned first invention, the viscosity x (Pa.s) of the conductive paste for gravure printing and the contact angle y (°) of the test surface with respect to the arithmetic mean roughness Ra of 0.010 (μm) or less satisfy the aforementioned (1) Therefore, when gravure printing is performed on the printed surface using the conductive paste, the conductive paste is quickly and uniformly transferred from the gravure printing plate to the printed surface. As a result, since the surface of the paste becomes smooth immediately after transfer, it is easy to reduce the film thickness while maintaining continuity. Therefore, when the conductive paste is used, it is possible to form an internal electrode suitable for small high-capacity MLCCs. Continuous and thin conductor film.

Furthermore, according to the aforementioned second invention, when the conductive film is formed by the gravure printing method, in the step of preparing the conductive paste, the preparation of the conductive paste is performed under the following conditions: the viscosity of 40 (1/s) x (Pa .S). The contact angle y(°) when the test surface, which is the same material as the outermost peripheral surface of the gravure printing plate and is arranged in the same surface state, drops 10 (μL), and the x and y satisfy the aforementioned ( 1) Type. Therefore, in the printing step, when gravure printing is performed using the conductive paste, the conductive paste is quickly and uniformly transferred to the printed surface. As a result, since the surface of the paste becomes smooth immediately after transfer, it is easy to reduce the film thickness while maintaining continuity. Therefore, it is possible to form a continuous and thin film suitable for internal electrodes of small high-capacity MLCCs. Thick conductor film. In addition, in this case, "the outermost peripheral surface of the plate making" means the surface on the cylindrical surface before the printing pattern is formed in the plate making.

Incidentally, in the past, for the purpose of uniformly transferring from the gravure printing plate to the printed surface, attempts have been made to optimize the organic composition of the conductive paste and the rheology. However, as mentioned above, these The attempt did not yield sufficient results. In contrast, the invention of the present application found that not only the wettability between the plate making and the conductive paste, that is, the size of the contact angle, but also the viscosity of the conductive paste is also related to the transferability. By adjusting the viscosity and contact angle to satisfy the aforementioned formula (1), that is, by setting the contact angle below a certain value in relation to the viscosity, the conductive paste can be uniformly transferred from the gravure printing plate to the Printed side The surface of the film becomes smooth after printing.

In addition, in the first invention, the arithmetic mean roughness Ra of the surface roughness of the test surface must be 0.010 ( μm ) or less. Because the surface roughness of the outermost peripheral surface of the gravure printing plate is usually Ra of 0.010 ( μm ) or less, the evaluation using the above-mentioned test surface can be regarded as the evaluation of the outermost peripheral surface using the normal gravure printing plate.

Moreover, in this case, the viscosity x (Pa.s) is a static viscosity at 25 (℃) and a shear rate of 40 (1/s). This condition is determined by considering the room temperature during gravure printing and the stress that acts on the conductive paste when the conductive paste is transferred to the printed surface during gravure printing. Therefore, by using this value, the viscosity of the conductive paste And the correlation between contact angle and transferability can be stably obtained. In addition, the viscosity measurement system can be performed using a commercially available viscometer.

Also, in this case, the contact angle y (°) is a value measured by dropping 10 (μL) droplets to the horizontal at 25 (°C). Because this condition is determined by considering the room temperature during the gravure printing and the amount of conductive paste transferred during the formation of the internal electrodes of the MLCC, by using this value, the viscosity and contact angle of the conductive paste are related to the transfer The correlation between sexes can be stably obtained. In addition, the dripping system of the conductive paste can be performed using, for example, a micropipette, and the measurement system of the contact angle can be used using a commercially available contact angle meter.

Furthermore, the aforementioned formula (1) holds true in the range of x≦3.0 and y<40. When the viscosity and contact angle are larger than these ranges, even if y<17.6x+19.1 is satisfied, good transferability cannot be obtained.

According to the invention of the present application, by measuring the viscosity and contact angle by using the method specified above, and preparing the conductive paste so that the value satisfies the aforementioned formula (1), the conductive paste can be uniformly produced from the gravure printing plate as described above. It is transferred to the printed surface and the film surface becomes smooth after transfer. That is, only when the wettability has a contact angle above a certain value, good transferability cannot always be obtained. The smaller the viscosity, the smaller the contact angle must be, that is, it must be easy to wet.

In addition, regarding the relationship between the contact angle and the transferability, the aforementioned Patent Document 4 discloses that the larger contact angle has good transferability and must be 50° or more, but when it is too large, the paste will not easily enter the grooves. situation. However, according to the research results of the inventors, it is In order to obtain good transferability, the contact angle is preferably smaller, and as shown in the above formula (1), it must be 40° or less when measured between the conductive paste and the plate making. Although the description in Patent Document 4 mentioned above is that "50° or more and not too large" is preferable, but according to the inventors of the present invention, the opposite result was obtained. In addition, although in Patent Document 4 mentioned above, the contact angle is limited by the value of water, this is the surface condition of the groove indirectly limited by the value of the contact angle with water, and the actual system is not considered. The appropriate contact angle is different depending on the physical properties of the paste used.

Here, it is preferable that either the test surface of the aforementioned first invention or the outermost peripheral surface of the aforementioned gravure printing plate and the aforementioned test surface of the aforementioned second invention is plated with Cr or Ni. In order to improve the wettability with the conductive paste, the gravure printing plate-making system should preferably be plated with Cr or Ni. Therefore, it is better to imitate it on the test surface and use a Cr-plated or Ni-plated one. In addition, in order to improve the wettability and reduce the contact angle, it is better to perform plating, and the plating type of the test surface is preferably the same as the plating type of the gravure printing plate. However, since the same contact angle can be obtained even if there are differences in the types of plating, it is not necessary to match the types of plating.

Furthermore, it is preferable that the range of the viscosity x (Pa·s) is 0.1≦x≦3.0 in the aforementioned formula (1). As shown in the aforementioned formula (1), because the lower the viscosity, the lower the upper limit of the allowable contact angle y, so it becomes difficult to prepare a conductive paste system that can satisfy the formula (1). Therefore, the viscosity should be set to 0.1 (Pa.s) or more.

Furthermore, it is preferable that in the aforementioned formula (1), 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.

Moreover, it is preferable that the viscosity x and the contact angle y satisfy y>8.8x+12.4. . . (2) Person. Although the smaller the contact angle y, the higher the wettability and the worse the handleability, but the lower the viscosity x, the lower the value of y can be allowed, so it is preferable to satisfy the above formula (2).

Furthermore, it is preferable that the aforementioned conductive paste is used for printing and coating the ceramic green sheet to form a conductive film for the user. The conductive paste of the present invention is not limited by use, but can be suitably used when a conductive film is formed on an insulator made of ceramics. Especially in green In the case of printing and coating on the sheet, when the firing process is performed to produce an insulator, a conductor film can also be produced by firing at the same time, which is advantageous in terms of manufacturing cost.

Moreover, it is preferable that the aforementioned conductive paste is used to form the internal electrodes of the MLCC for users. As described above, when the conductive paste of the present invention is used, since the film thickness can be easily reduced while maintaining continuity, it is suitable for internal electrodes of small high-capacity MLCCs.

Furthermore, it is preferable that the aforementioned conductive powder is nickel powder. For example, in the use of internal electrodes of MLCC, by laminating ceramic green sheets printed with conductive paste and subjecting them to firing treatment, the internal electrodes are generated at the same time as the dielectric layer is generated from the ceramic green sheets, so the conductive powder is It is required to have heat resistance. Therefore, as the conductive powder of the conductive paste of the present invention, a heat-resistant metal, such as Pt, Pd, Ag-Pd, Ag, Ni, Cu, etc., is preferred, but in terms of manufacturing cost, it is inexpensive In terms of heat resistance, conductivity, and price, nickel is especially preferred. The average particle size of the conductive powder can be appropriately determined within the range that can obtain the characteristics required for the conductive paste, for example, 1.0 (μm) or less, preferably 0.01 to 0.50 ( μm ), and 0.05 to 0.30 ( The range of μ m) is more preferable.

Furthermore, it is preferable that the aforementioned adhesive is polyvinyl butyral, polyvinyl alcohol, acrylic resin, epoxy resin, phenol resin, alkyd resin, cellulose polymer, rosin resin or the like. As the adhesive of the conductive paste of the present invention, it can be appropriately selected in the range that can achieve the required viscosity and contact angle. It is usually used by users. However, it is based on the coating film forming ability (that is, the adhesion to the substrate) and during firing. In terms of decomposability, the above substances are better.

In addition, the aforementioned organic solvent is preferred, and it is not particularly limited as long as it is suitable for dissolving or dispersing the conductive powder and the binder resin component. As an example, the system may include alcohol-based solvents such as terpineol, terpene-based solvents such as isobornyl acetate, glycol-based solvents such as ethylene glycol, and diethylene glycol monobutyl Glycol ether solvents such as ether (butyl carbitol), ester solvents, hydrocarbon solvents such as toluene and xylene, and organic solvents with high boiling points such as other mineral spirits. Because these organic solvents are not easy to The adhesive of the acetal resin and the acrylic resin dissolves and does not easily cause so-called flake erosion, which is preferable.

Furthermore, it is preferable that the aforementioned conductive paste system contains the constituent components (common material) of the ceramic green sheet to which it is applied, as is usually done. For example, when the dielectric layer of the MLCC is composed of barium titanate, it is preferable to contain barium titanate powder. Because the conductive paste of the present invention can easily form thinner internal electrodes, it is better that the average particle size of the common material is smaller, such as 0.5 ( μ m) or less, with 0.005 to 0.2 ( μ m) The range is preferable, and the range of 0.01 to 0.1 ( μ m) is more preferable.

In addition, the composition ratio of the conductive paste is not particularly limited, and can be appropriately determined to satisfy the aforementioned formulas (1) and (2). For example, in terms of mass ratio, it may contain 30-60 (%) of the aforementioned The composition of conductive powder, 1~5 (%) of the aforementioned adhesive, 35~65 (%) of the aforementioned organic solvent, and 0-20 (%) of the common material is preferable. In addition, when a common material is contained, the range of 1-20 (%) is preferable.

10: MLCC

12: Dielectric layer

14: Conductor layer

16: External electrode

FIG. 1 is a cross-sectional view of an MLCC in which a conductive paste is applied to internal electrodes according to an embodiment of the present invention.

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

Detailed description of the preferred embodiment

Hereinafter, an embodiment of the present invention will be described in detail. In addition, in the embodiment described below, unless otherwise notified in advance, a structure generally used in the past can be suitably used.

The conductive paste of the present embodiment is manufactured as shown in FIG. 1. When manufacturing the MLCC 10, it is used to form the conductor layer 14 serving as the internal electrode by the gravure printing method. In this embodiment, the thickness of one layer of the dielectric layer 12 is, for example, less than 10 ( μ m), for example, in the range of 0.1 to 3 ( μ m), for example, about 1 ( μ m). The thickness dimension is, for example, 10 ( μm ) or less, for example, within a range of 0.1 to 3 ( μm ), for example, about 0.5 ( μm ).

The aforementioned conductor layer 14 is formed of, for example, nickel, and the aforementioned dielectric layer 12 is formed of, for example, barium titanate. When manufacturing this type of MLCC10, the conductive powder, ceramic powder, adhesive, and organic solvent are mixed to prepare a conductive paste according to a predetermined mixing method, and the conductive paste is printed and applied by gravure printing to a separately prepared composition medium. One side of the ceramic green sheet of the electric body layer 12. After the ceramic green sheet layer coated with the conductor paste is pressed and bonded, the calcination process is performed to produce the dielectric layer 12 produced from the ceramic green sheet, and the conductor layer 14 is produced from the conductor paste. The external electrodes 16 are formed by using methods such as dipping, and the MLCC 10 shown in FIG. 1 is obtained.

The above-mentioned conductive powder is, for example, an average particle diameter of 1 (μm) or less, for example, nickel powder in the range of 0.13 to 0.18 (μm), for example, is mixed in the conductive paste at a ratio of 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, in the range of 10-20 (nm), that is, a common material for the barium titanate constituting the dielectric layer 12, For example, the nickel ratio is mixed in the conductive paste at a ratio of about 10-15 (wt%). In addition, the above-mentioned adhesive system is, for example, ethyl cellulose and polyvinyl butyral, and the above-mentioned organic solvent system uses dihydroterpineol, isobornyl acetate, and menthano propionate as the main solvent. These systems use a ratio of 1 to 5 (%) and 30 to 65 (%) respectively.

In this embodiment, the composition of the above-mentioned conductive paste is based on its viscosity and the contact angle when it is dropped to the test surface with the same material as the outermost peripheral surface of the intaglio printing plate and prepared into the same surface state to satisfy the aforementioned (1) Formula (re-disclosure). The viscosity is a value measured by a rheometer (Rheostress 6000 manufactured by HAAKE) and the static viscosity after 1 minute under the conditions of 25 (°C) and a shear rate of 40 (1/s) is used. In addition, the contact angle is measured by dropping 10 (μL) with a micropipette at 25 (°C) onto the test surface that is arranged horizontally, and for example, using a FACE contact angle meter (CA-DT manufactured by Kyodo Interface Chemical Co., Ltd.) Contact angle. The contact angle is, for example, an average value measured 5 times.

y<17.6x+19.1 (however, x≦3.0, y<40). . . (1)

In addition, the above-mentioned test surface is, for example, a case where the gravure printing plate is a Cr-plated plate. For example, the surface of a Cr plate is finished to a very high smoothness state with an arithmetic average roughness Ra of 0.010 ( μm ) or less. In addition, it is possible to use a plate subjected to Cr plating in the same manner as the plate making instead of the Cr plate. In this embodiment, for example, the surface material is peeled off from the unpatterned portion of the gravure printing plate. The size of the test flat substrate is, for example, 5 (cm)×3 (cm).

As a result of printing and coating the conductive paste prepared in this way on the ceramic green sheet using the gravure printing method, the dry film thickness of the formed printed film is about 0.5 (μm) and the surface roughness Ra is 0.020 (μm) or less The smooth surface is calcined to obtain a smooth continuous film. By obtaining this level of smoothness, it can further contribute to the improvement of capacitor characteristics and reliability.

The following Table 1 summarizes the results of evaluating the printability with various combinations of viscosity and contact angle by changing the composition of the conductive paste in the printing and coating step of the conductor layer 14 described above. In Table 1, "Ni particle size" and "BT particle size" are the average particle size of nickel powder and the average particle size of barium titanate powder, respectively. In addition, the "BT amount" is the mass ratio of barium titanate powder to Ni. Also, "MC" is the mass ratio of nickel powder to the entire paste. "40(1/s) viscosity" is the static viscosity measured using a rheometer as described above. In addition, "contact angle with Cr plate" and "Cr plated plate-making printed matter Ra" are evaluation data when gravure printing is performed using Cr plated plate making respectively. The former is the measured value of the contact angle between conductive paste and Cr plate, and the latter is The surface roughness after drying of the printed film formed by printing and coating the conductive paste on a Cr-plated plate. The surface roughness is the arithmetic average roughness Ra measured using an interference microscope (Nikon LV150 ECLIPSE) at 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 plate-making printed matter Ra" are evaluation data when gravure printing is performed using Ni plate-making, respectively.

[Table 1]

In Table 1 above, those with a surface roughness Ra of 0.020 (μm) or less of the printed matter are those with good printability, that is, examples. In Figure 2, a graph showing the above evaluation results. In Fig. 2, "◆" is an example, and "口" is a comparative example. Examples 1 to 11 are located on the lower side than the formula (1) shown in FIG. 2 and are conductive pastes that satisfy them. Comparative Examples 1 to 6 are conductive pastes of comparative examples that are located on the upper side of formula (1) or on the right side of the viscosity of 3.0 (Pa·s), which do not satisfy the scope of the present invention.

As shown in the above evaluation results, when the viscosity is 0.1 to 3.0 (Pa.s) and the contact angle is 14 to 39 (°), the surface roughness of the printed body can be obtained by satisfying the above formula (1) viscosity and contact angle It is a very good result of 0.003~0.016 (μm). Therefore, when the internal electrode (conductor layer 14) of the MLCC 10 is formed by using such a conductive paste, it is possible to obtain a good transferability on the printed surface by gravure printing. As a result, a thinner and smooth surface can be easily obtained. The continuous film, so it is possible to obtain a small, high-capacity MLCC10 with a high manufacturing yield. In addition, in Example 11, the Ni-plating platemaking was also evaluated, and it was possible to obtain the same good results as the Cr-plating platemaking. When the conductive paste is prepared in a way to meet the formula (1), Cr plating system Either the plate or the Ni-plated plate can similarly obtain a thin continuous film with a smooth surface.

On the contrary, even in the range of viscosity of 0.2 to 3.0 (Pa.s) in Comparative Examples 1 to 4, the contact angle is 22 to 72 (°) because it does not satisfy the above formula (1). In combination with the contact angle, the transferability of plate making from gravure printing is poor and the surface roughness Ra of the printed body becomes a large value of 0.021 to 0.194 (μm). The surface roughness Ra indicates the size of the unevenness of the printed film surface. Since the thickness of the conductor layer 14 is very thin, about 0.5 (μm), the large unevenness mentioned above means that the printed film cannot Get continuity. That is, in the conductive paste system of the comparative example, it is difficult to obtain a thin continuous film with a smooth surface.

In addition, the viscosity of Comparative Examples 5 and 6 is very high at 5.3 to 6.9 (Pa.s), and the contact angle is 51 to 61 (°) and is located on the lower side of the aforementioned formula (1). However, when gravure printing is performed using these, the surface roughness Ra of the printed film is a relatively large value and is 0.036 to 0.095 (μm). As in Comparative Examples 1 to 4, a continuous film cannot be obtained. Even at the lower side of formula (1), the transferability is poor when the viscosity is greater than 3.0 (Pa·s).

As mentioned above, according to this embodiment, because the conductive paste system viscosity x (Pa.s) and the contact angle y (°) to the test surface with the arithmetic mean roughness Ra of 0.010 (μm) or less satisfy the aforementioned (1) Therefore, when the conductive paste is used to perform gravure printing on a ceramic green sheet, the conductive paste can be quickly and uniformly transferred from the gravure printing plate. As a result, since the surface of the paste becomes smooth immediately after transfer and the film thickness is easily thinned while maintaining continuity, it is possible to form a continuous and thinner internal electrode suitable for small high-capacity MLCC10 Conductor film 14 of film thickness.

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

Moreover, according to the above Table 1 and Figure 2, the lower limit of the preferred viscosity is 0.1 (Pa.s). It is difficult to make the conductive paste have a lower viscosity. 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 located above the formula (2) in Figure 2, that is It is better to satisfy y>8.8x+12.4. The smaller the contact angle y, the higher the wettability and the worse the handleability, the lower the viscosity x, the lower the contact angle y can be allowed.

The above has been described in detail with reference to the drawings, but the present invention can also be implemented in other aspects, and various changes can be made without departing from the spirit of the invention.

Claims (2)

A conductive paste, a conductive paste for gravure printing containing conductive powder, adhesive, and organic solvent, characterized in that the viscosity at 25 (℃) and a shear rate of 40 (1/s) is set to x (Pa. s). The contact angle when 10 (μL) is dropped on the horizontal test surface is set as y(°), and x and y satisfy the following formula: y<17.6x+19.1 (but 0.1≦x≦3.0, 10< y<40); The test surface has been subjected to Cr or Ni plating, and the arithmetic average roughness Ra of 1.0 (mm) of the test surface with a boundary value of 80 (μm) is less than 0.010 (μm). A method for forming a conductive film, which is characterized by comprising the following steps: preparing a conductive paste containing conductive powder, adhesive, and organic solvent; filling the conductive paste in the recess of the gravure printing plate and transferring it to the printed The step of printing on the surface; and the step of calcining the printed film to form a conductive film on the printed surface by calcining the printed film; wherein, the step of preparing the conductive paste is to perform the conductive paste under the following conditions Modulation: Viscosity x (Pa.s) at 25 (℃) and shear rate of 40 (1/s), contact angle y (°) when dropping 10 (μL) on the test surface, the x and y satisfy y<17.6x+19.1 (but 0.1≦x≦3.0, 10<y<40); the test surface is the one that has been plated with Cr or Ni, and the test surface is the same as the outermost peripheral surface of the aforementioned gravure printing plate The materials are arranged horizontally so as to have the same surface state.

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