JP6633488B2 - Method of manufacturing conductive paste and substrate with conductive film - Google Patents

Description

  The present invention relates to a conductive paste useful for forming an electrode or circuit pattern by a transfer printing method using a screen plate such as screen offset printing, and a method for manufacturing a substrate with a conductive film using the paste.

  2. Description of the Related Art Conventionally, in the field of electronic components, there are a thick film method, a thin film method, a plating method, and the like as a method of forming a conductive film such as a wiring or an electrode on a surface of a film or a substrate. The thick film method is a method in which a conductive paste is formed by screen-printing a conductive paste to form a wiring electrode pattern, followed by curing or baking. The merit of this thick film method is that the conductive film can be formed at low cost as a whole because of the simplicity of the process and the low cost of the mask. Further, compared to other methods, a thick conductive film having a thickness of, for example, 10 μm or more can be easily formed. However, on the other hand, it is difficult to form a conductive film having an excellent shape, and the printed paste drips, resulting in a semi-cylindrical cross-sectional shape or a rough surface with traces of screen mesh remaining. Roll around.

  For such a thick film method, for example, there is a thin film method (sputtering method) capable of forming a thin film of 1 μm or less. Although a fine pattern can be precisely formed by the thin film method, it is not suitable because a vacuum process is required, so that the cost is high and the formation of a thick film takes too much time.

  There is a plating method as a method capable of precisely forming a fine pattern and forming a thick film. The formation of a thick film by plating is relatively easy, but a fine patterning requires a photolithography step and a subsequent etching step. In the plating method that goes through such a process, a photosensitive resist is applied to the surface of the conductive film plated on the base material, only necessary portions are exposed and cured, and unnecessary portions that are not cured are removed with a developer. After that, a method of chemical etching in a wet process, exposure and development after applying a resist to the substrate provided with a plating seed layer, plating only on the opening portion, the resist is peeled off and there is no plating There are two types of methods of forming a pattern by removing a portion of the seed layer by dry etching or the like. However, both methods require many steps and are low in economic efficiency.

  As described above, each of the methods has advantages and disadvantages, and therefore, at present, they are used properly according to the required quality and cost levels.

  By the way, since the electronic component market is intensely competitive worldwide, low cost is always required. In addition, the trend of miniaturization of electronic devices is still continuing, and accordingly, the miniaturization of wiring electrode patterns is further progressing. Furthermore, as the width of the conductor circuit is reduced due to miniaturization, the thickness of the conductive film is also increasing in order to secure the cross-sectional area of the current path by increasing the film thickness. In addition, for example, in a flip-chip mounting type LED (light emitting diode) element, the distance between the anode electrode and the cathode electrode is extremely narrow, and the distance between the electrodes on the substrate side on which the electrodes are mounted is adjusted accordingly. In addition to the necessity of a fine pattern (for example, 50 μm) which is narrower, the electrode tends to be thicker as the output of the LED increases. In addition, chip mounting requires a flat surface, and the above-described anode-cathode electrode distance must be achieved on the surface on which the chip is mounted, that is, the upper surface of the electrode. Since the distance between the electrodes on the electrode lower surface, that is, the contact surface with the substrate, is already too small, there is no margin, and the size of the electrode upper surface and the electrode lower surface needs to be substantially the same. In other words, the electrode cross-sectional shape is rectangular. Is required.

  In order to meet the demand for such a low-cost, fine-pattern, thick-film, smooth-surface, and rectangular-section conductive film, it is difficult to continue using the existing processes described above, and new processes are required. Is desired. Among them, the printing method is expected to have advantages such as the low cost and the advantage that resources can be effectively used because only the necessary portions need to be printed, and various advantages besides the screen printing method described above. Various printing methods are being studied.

  For example, the inkjet printing method does not require a plate or a mold, and has the advantage that data can be drawn as it is.Since the precise control of the amount of ink ejected from the nozzles enables printing of fine wiring, fine printing is possible. A simple pattern can be easily formed. However, since it is a method of drawing with fine dots, if a thick film or a large area is printed, the cost increases immediately.

  Gravure offset printing using intaglio printing is often studied for the purpose of forming fine patterns. However, since it is a method of transferring the ink filled in the concave plate, the ink transfer amount cannot be so large and the transfer film thickness is about 2 to 3 μm. For example, it is difficult to transfer a 10 μm thick film. It is. In addition, the ink adhering to the portion of the intaglio that is not filled with ink is scraped with a doctor blade so that the ink is not transferred to unnecessary portions.However, in order to completely scrape the ink, the viscosity of the ink is reduced to some extent. There is a need. Therefore, in the gravure offset printing, the amount of the solvent must be increased to reduce the solid content in the ink, which is one of the reasons why the film thickness cannot be increased. In addition, the ink adhering to the upper surface of the plate convex portion that is not filled with ink is scraped off by a doctor blade, but in recent years conductive metal inks and pastes used fine metal particles such as nano-sized metal for the purpose of improving conductivity. In some cases, such fine particles are transferred without being scraped off by a doctor blade, and the printed circuit may have poor insulation.

  As a method of overcoming such disadvantages of the printing method and making the most of the advantages, a transfer printing method using a screen plate such as a screen offset printing method or a screen pad printing method (a predetermined pattern on the screen plate is formed of silicone rubber). (A printing method of transferring by a transferred transfer member).

  The screen offset printing method is a method in which a predetermined pattern is printed on the surface of a silicone blanket (a blanket formed of silicone rubber) by screen printing, and this pattern is transferred to a substrate or film that is originally intended for printing to form a pattern. It is. According to this method, a thick film can be formed by first performing screen printing. Since this screen printing is performed once on the silicone blanket, the silicone blanket absorbs some of the solvent in the paste. For this reason, in screen printing, it is possible to prevent the paste from oozing or dripping and sticking to an adjacent pattern, or the cross-sectional shape of the film from becoming semi-cylindrical. Although mesh marks may be formed on the film surface, when the film is transferred to the object, the surface located on the surface is the side in contact with the silicone blanket, and the silicone blanket is smooth In addition, a smooth surface appears on the surface of the film. Therefore, in the screen offset printing method, a fine pattern having a smooth surface and a rectangular cross section can be printed. Also, in terms of cost, since printing is performed only once on the silicone blanket, there is no large loss, and the method can be implemented at low cost.

  On the other hand, in the screen pad printing method, a predetermined pattern is printed on the surface of a silicone blanket by screen printing, and the pattern is temporarily transferred to the silicone pad by pressing the silicone pad against the printed surface, and then the silicone pad is originally used for printing. This is a method of forming a pattern by transferring a pattern by pressing against a substrate or a film. This method has a smooth surface, and a cross-sectional shape can obtain a thick film pattern having a rectangular cross-sectional shape. There is also an advantage that a pattern can be formed even if there is a pattern. The reason is that this method is a method in which a soft silicone pad is pressed and transferred, and the silicone pad can follow a curved surface or unevenness. The characteristics required for the paste of the screen pad printing method are the same as those of the above-described screen offset printing method because the screen printing and the subsequent transfer method using a silicone blanket are common. In that sense, it can be said that a paste for gravure offset printing that does not use screen printing is not suitable for the screen pad printing method.

  By using the transfer printing method using a screen plate, a fine pattern can be formed at a lower cost than other printing methods, and a conductive film having a thick film, a smooth surface, and a rectangular cross section can be obtained. Despite the advantages obtained, there have been various problems in performing good printing by the transfer printing method that actually uses a screen plate. For example, as described above, in the screen offset printing method, the paste is printed on the silicone blanket and then transferred to the base material.However, this transfer is not performed or a part of the paste is transferred to the base material. However, the so-called "crying parting" phenomenon in which the paste remains on the blanket side is likely to occur. Further, even if the transfer is completed completely, the pattern accuracy is low. In an extreme case, the pattern may be stuck to an adjacent pattern or stringing may occur to bridge the adjacent pattern. Furthermore, even when a fine pattern can be transferred with high reproducibility, the cross-sectional shape is not rectangular but may be in a semicircular shape. The gravure offset printing method (one type of intaglio offset printing) is the same in that a silicone blanket is used, but the thickness of the film to be transferred is different, and the gravure offset is about 2 to 3 μm. On the other hand, since the screen offset is a thick film of at least about 10 μm, it is very difficult to obtain good transfer.

  For that reason, there has been no report that attempts have been made to solve the problem by a paste composition in a transfer printing method using a screen plate such as screen offset printing. As a paste for another printing method, for example, as a conductive paste for intaglio offset printing, JP-A-2007-250892 (Patent Document 1) discloses a conductive powder, a glass frit, a binder resin, and a solvent. Wherein the solvent is a mixed solvent of a good solvent and a poor solvent of the binder resin, and the ratio of the poor solvent is 5 to 40% by weight based on the total amount of the mixed solvent. Conductive paste is disclosed.

  Japanese Patent Application Laid-Open No. 2010-55807 (Patent Document 2) discloses a conductive paste used in an intaglio offset printing method using a silicone blanket having at least a surface made of silicone rubber, and includes a binder resin, a conductive powder, and at least a conductive paste. A mass change before and after immersing a sample obtained by cutting the silicone blanket into a 2 cm square at 23 ± 1 ° C. in a solvent for 5 hours at a temperature of 23 ± 1 ° C., including a mixed solvent comprising two kinds of solvents. A high swelling solvent having a ratio V (% by mass) of 40% by mass or more, and the other solvent is a low swelling solvent having a mass change ratio V (% by mass) of less than 40% by mass; The product V × R of the mass change rate V (mass%) of the solvent and the ratio R (mass%) of the total amount of the high swelling solvent to the total amount of the mixed solvent is 0.05 or more; A conductive paste of 0.70 or less is disclosed.

  However, these pastes are also gravure (intaglio) offset printing pastes, and do not disclose screen offset printing.

  Further, toluene as a poor solvent cited in Examples of Patent Document 1 has high volatility and is easy to dry, so it could not be used for screen offset printing.

  Further, glycol ether solvents and terpineols used in Examples as a solvent for swelling a silicone blanket in Patent Document 2 are actually solvents for swelling silicone rubber as described in Patent Document 2. Rather, it is a solvent that should be classified as the low swelling solvent in view of its chemical properties (polarity). Actually, the present inventor tried screen offset printing using these solvents as high swelling solvents, but the absorption to the silicone blanket was not sufficient, and a tearing-off phenomenon occurred, so that good transfer was not obtained. This can be presumed to be due to the reasons described above or to the difference between the gravure offset and the screen offset.

JP 2007-250892A (Claim 1) JP 2010-55807 A (Claim 1)

  Therefore, an object of the present invention is to provide a conductive paste and a method of manufacturing a substrate with a conductive film, which can transfer a pattern with high accuracy by transfer printing using a screen plate such as screen offset printing.

  Another object of the present invention is to transfer a fine and thick pattern having a smooth surface, a rectangular cross-section, and a fine and thick pattern by transfer printing using a screen plate with high accuracy, and tearing or yarn during transfer. An object of the present invention is to provide a method for manufacturing a conductive paste and a substrate with a conductive film that can also suppress a pulling phenomenon.

  The present inventor has conducted intensive studies to achieve the above object, and as a result, in a paste containing conductive particles, an acrylic resin and two types of organic solvents having different penetrating powers or affinities to a silicone blanket for transfer printing using a screen plate. It has been found that a pattern can be transferred with high precision by transfer printing using a screen plate, and the present invention has been completed.

That is, the conductive paste of the present invention is a conductive paste for transferring a pattern by a screen plate to a blanket at least a surface of which is formed of silicone rubber, and has conductive particles and a solid having a glass transition temperature of 10 ° C. or higher. A binder resin containing an acrylic resin, and an organic solvent containing a first organic solvent and a second organic solvent, wherein the first organic solvent has a boiling point of 120 ° C. or more, and swells the silicone rubber by 60%. % Or more, and the second organic solvent is a solvent that swells the silicone rubber at a swelling ratio of 30% or less. The boiling point of the second organic solvent may be 120 ° C. or higher. The mass ratio of the first organic solvent to the second organic solvent is about 1 / organic solvent / second organic solvent = 20/80 to 70/30. The conductive paste of the present invention may have a viscosity of 5 to 300 Pa · s measured at 25 ° C. and 10 rpm using a B-type viscometer. The first organic solvent may be an aliphatic hydrocarbon or an alicyclic hydrocarbon (particularly, a _C10-14 alkane, a _C10-14 alkene or a _C8-12 cycloalkane). The second organic solvent may be at least one selected from the group consisting of alcohols, ketones, esters, cellosolves, carbitols, and pyrrolidones. The ratio of the organic solvent is about 20 to 60% by volume based on the whole conductive paste. The binder resin may further include a liquid resin having a glass transition temperature of less than 10 ° C. The liquid resin may include a liquid acrylic resin. The ratio of the binder resin is about 5 to 30% by volume based on the whole conductive paste. The conductive particles may be formed of an alloy containing at least one or two or more selected from the group consisting of copper, silver, and nickel. The conductive paste of the present invention may further contain glass particles. The conductive particles may include active metal particles. The conductive paste of the present invention may be a screen offset printing paste or a screen pad printing paste.

  In the present invention, a printing step of printing the conductive paste through a screen plate on at least the surface of a blanket made of silicone rubber, a transfer step of transferring the printed paste film to an insulating substrate, And a baking step for baking the resulting paste film to form a conductive film on the surface of the insulating substrate.

  In the present invention, in the paste containing the conductive particles, an acrylic resin and two types of organic solvents having different penetration or swelling power with respect to the silicone blanket of screen offset printing are combined, so that screen offset printing or screen pad printing is used. A pattern can be transferred with high accuracy by transfer printing using a screen plate such as the one described above. In particular, a fine and thick pattern having a smooth surface, a rectangular cross section, and a fine and thick pattern can be transferred with high accuracy, and tearing and stringing can be suppressed during transfer.

[Organic solvent]
The conductive paste of the present invention has a different penetrating power to the silicone rubber constituting a blanket (a blanket having at least a surface formed of silicone rubber) used in transfer printing using a screen plate such as screen offset printing or screen pad printing. A solvent that easily swells the silicone rubber, that is, a solvent that is easily absorbed in the silicone rubber, as the first organic solvent. As the solvent, a solvent that hardly swells the silicone rubber, that is, a solvent that is hardly absorbed by the silicone rubber, is selected. As a result, the first organic solvent is quickly absorbed from the printed film of the conductive paste into the blanket, so that the viscosity of the printed film increases at the same time as printing, and the shape is less likely to collapse due to dripping and is necessary for transfer. High film strength. On the other hand, since the second organic solvent is hardly absorbed by the blanket and remains on the print film, the second organic solvent has such an adhesive property as to be able to adhere to the insulating substrate which is a transfer partner material when transferred, and also has the blanket and the print film. Since a small amount of liquid layer is formed at the interface with the blanket, it can be easily peeled off from the blanket.

  Specifically, the swelling ratio of the silicone rubber by the first organic solvent is 60% or more (for example, 60 to 150%), preferably 80% or more (for example, 80 to 130%), and more preferably 100% or more. (For example, 100 to 110%). If the swelling ratio of the first organic solvent is too small, the penetrating power of the blanket of the first organic solvent decreases, and the accuracy of the transferred pattern shape decreases.

  On the other hand, the swelling ratio of the silicone rubber by the second organic solvent is 30% or less (for example, 0 to 30%), preferably 20% or less (for example, 1 to 20%), more preferably 10% or less (for example, 5 to 5%). 10%). If the swelling ratio due to the second organic solvent is too large, the penetrating power of the second organic solvent into the blanket increases, and the transfer accuracy to the insulating substrate decreases.

  In the present invention, the swelling ratio can be calculated from the volume change rate before and after immersion of a silicone rubber test piece in an organic solvent at 25 ° C. for 72 hours, and is measured in detail by the method described in Examples described later. it can. The silicone rubber test piece is a silicone rubber constituting a blanket used in screen offset printing, and may be, for example, methyl silicone rubber.

  The boiling point of the first organic solvent is 120 ° C. or higher (eg, 120 to 300 ° C.), preferably 150 ° C. or higher (eg, 150 to 280 ° C.), more preferably 180 ° C. or higher, from the viewpoint of screen printability on a blanket. (For example, 180 to 250 ° C.). If the boiling point of the first organic solvent is too low and the volatility is too high, the paste will dry too quickly at the stage of screen printing on the blanket, making it difficult for the paste to pass through the screen mesh, and the printed matter will be blurred.

  The boiling point of the second organic solvent may be 120 ° C. or higher (eg, 120 to 300 ° C.), preferably 150 ° C. or higher (eg, 150 to 280 ° C.), more preferably, from the viewpoint of transferability to the insulating substrate. It is 180 ° C or higher (for example, 180 to 250 ° C). If the boiling point of the second organic solvent is low and the volatility is too high, the printed film of the paste may be immediately dried at the stage before the transfer, and the adhesiveness to the insulating substrate may be lost, so that the transfer may be difficult.

The first organic solvent is not particularly limited as long as it has a boiling point of 120 ° C. or more and satisfies the swelling property. Specifically, as the first organic solvent having a high penetrating power or swelling power with respect to the silicone rubber, A hydrocarbon solvent or the like can be preferably used. As the hydrocarbon solvent, any of linear, branched or cyclic aliphatic hydrocarbons and aromatic hydrocarbons can be used. For example, aliphatic hydrocarbons [saturated aliphatic hydrocarbons (octane, decane, dodecane, tetradecane, _{C 8-18} alkane, etc.), such as octadecane; unsaturated aliphatic hydrocarbons (octene, decene, _{C 8-18} alkene such as dodecene; and _{C 8-18} alkynes such as octyne), etc.], alicyclic hydrocarbons Examples thereof include hydrogen (eg, C _8-18 cycloalkane such as cyclooctane and cyclodecane), and aromatic hydrocarbon (eg, xylene, ethylbenzene). These hydrocarbon solvents may be isomers. These solvents can be used alone or in combination of two or more.

Among these hydrocarbon solvents, solvents that have a high molecular weight and are difficult to volatilize are preferable from the viewpoint that drying of the paste on the screen plate during storage or during continuous printing can be suppressed, and aliphatic hydrocarbons (e.g., dodecane and the like) C _10-14 alkanes, such as _{C 10-14} alkenes such as dodecene), alicyclic hydrocarbons (e.g., _{C 8-12,} etc. cycloalkane) are preferred, such as cyclodecane, _{C 11-13} alkanes such as dodecane, dodecene, etc. Particularly preferred are C _9-11 cycloalkanes such as C _11-13 alkenes and cyclodecane.

  The second organic solvent is not particularly limited as long as it satisfies the swelling property. Specifically, as the second organic solvent having a low osmotic power or swelling power with respect to the silicone rubber and having a boiling point of 120 ° C. or more, for example, , Alcohols [aliphatic alcohols (octanol, decanol, diacetone alcohol, etc.); aliphatic polyhydric alcohols (ethylene glycol, diethylene glycol, dipropylene glycol, butanediol, triethylene glycol, glycerin, etc.); alicyclic alcohols (cyclo Cycloalkanols such as hexanol; terpene alcohols such as terpineol and dihydroterpineol (monoterpene alcohols); aromatic alcohols (benzyl alcohol and the like); ketones (cyclohexanone, cycloheptanone, iso- Alicyclic ketones such as Ron), esters (aliphatic carboxylic esters such as ethyl lactate and butyl acetate; aromatic carboxylic esters such as dibutyl phthalate and dioctyl phthalate), cellosolves (methyl cellosolve, ethyl cellosolve) , Butyl cellosolve and the like; cellosolves such as ethyl cellosolve acetate and butyl cellosolve acetate; carbitols (carbitols such as carbitol, methyl carbitol and ethyl carbitol; carbitols such as ethyl carbitol acetate and butyl carbitol acetate) Acetates), nitrogen-containing heterocyclic compounds (imidazoles such as dimethylimidazole and dimethylimidazolidinone; 2-pyrrolidone, 3-pyrrolidone, N-methyl-2) Pyrrolidones such as pyrrolidone, etc.), and the like. These solvents can be used alone or in combination of two or more.

Among these solvents, alcohols (C _8-12 alkanol such as decanol, alicyclic alcohols such as terpineol, etc.), ketones (alicyclic ketones such as isophorone, etc.), esters (aliphatic such as methyl lactate, etc.) such as carboxylic acid esters), _{C 2-6} alkyl cellosolve such as cellosolve (butyl cellosolve), _{C 2-6} alkyl carbitol acetate such as carbitol (butyl carbitol acetate), pyrrolidones (N- methyl-2 N-C _1-3 alkylpyrrolidone such as -pyrrolidone) is widely used, and terpene alcohols such as terpineol; C _2-6 alkyl carbitol acetates such as butyl carbitol acetate; -Methyl-2-pyrrolidone and the like _{N-C 1-3} alkylpyrrolidones are preferred.

  The mass ratio of the first organic solvent to the second organic solvent is, for example, (first organic solvent / second organic solvent) = 20/80 to 70/30, preferably 25/75 to 65/35, and more preferably 30/80. It is about 70 to 60/40. If the amount of the first organic solvent is too small, a large amount of the organic solvent remains in the print film on the blanket, so that the cross-sectional shape of the print film may become semicylindrical under the influence of the surface tension of the organic solvent. In an extreme case, a tearing phenomenon may occur between the blanket and the insulating substrate. Conversely, if the amount of the first organic solvent is too large, most of the organic solvent is absorbed by the blanket, so that the printed film may be too dry, lose its tackiness, and may not be transferred.

  The organic solvent may include a third organic solvent (the organic solvent having a swelling ratio of more than 30% and less than 60%) as long as the effects of the present invention are not impaired. The total ratio of the first organic solvent and the second organic solvent to the whole organic solvent may be 50% by mass or more, preferably 80% by mass or more, more preferably 90% by mass or more, and 100% by mass or more. (Only the first organic solvent and the second organic solvent).

  The proportion of the organic solvent is not particularly limited, but is, for example, about 20 to 60% by volume, preferably about 25 to 55% by volume, and more preferably about 30 to 50% by volume, based on the whole conductive paste. If the proportion of the organic solvent is too small, not only does the screen printing become difficult because the paste becomes hard, but also when printed and absorbed on a blanket, the printed film becomes too dry and loses its tackiness and can be transferred. There is a risk of disappearing. On the other hand, if the amount of the organic solvent is too large, even if the first organic solvent is absorbed, a large amount of the second organic solvent remains in the printed film, the increase in viscosity is suppressed, and the printed film drips and the shape becomes accurate. There is a possibility that the image is not transferred. In an extreme case, a tearing phenomenon may occur between the blanket and the insulating substrate.

[Binder resin]
The binder resin includes a solid acrylic resin having a glass transition temperature of 10 ° C. or higher. The reason for using solid acrylic resin is that solid acrylic resin has many types of soluble organic solvents, and it is easy to use two types of solvents with greatly different properties. The points where the polarities are opposite are large. In other words, silicone rubber has a property of easily absorbing a nonpolar organic solvent and a property of hardly absorbing a polar organic solvent, whereas a solid acrylic resin has many soluble solvents, Specifically, it is easily compatible with the second organic solvent as a polar solvent, and hardly compatible with the first organic solvent as a nonpolar solvent. Therefore, when the silicone blanket comes into contact with the solid acrylic resin binder containing the first organic solvent and the second organic solvent, a state in which the first organic solvent easily migrates to the silicone blanket can be prepared.

Examples of the solid acrylic resin include acrylic monomers forming a homopolymer having a glass transition temperature of 10 ° C. or higher, such as methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, t-butyl methacrylate, and methacrylic acid. Homopolymers and copolymers containing, as constituent units, an acrylic monomer such as _C1-4 alkyl methacrylate such as isobutyl and t-butyl acrylate are exemplified. The solid acrylic resin may contain another copolymerizable monomer as a constituent unit as long as the effects of the present invention are not impaired.

Other copolymerizable monomers include, for example, acrylic monomers [C _1-4 alkyl acrylates such as methyl acrylate, ethyl acrylate, n-butyl acrylate, and isobutyl acrylate; (meth) C- _5-12 alkyl (meth) acrylates such as pentyl acrylate, hexyl (meth) acrylate, octyl (meth) acrylate, 2-ethylhexyl (meth) acrylate], olefin-based monomers, and styrene-based Monomers (styrene, vinyl toluene, etc.), vinyl ester monomers, (anhydride) maleic acid or alkyl esters thereof, and the like.

These solid acrylic resins can be used alone or in combination of two or more. Among these solid acrylic resins, polymethacrylic acid is excellent in solubility in the second organic solvent and having a certain degree of solubility in the first organic solvent, thereby suppressing gelation of the paste. Polyalkyl _C1-4 alkyl esters such as butyl (e.g., poly n-butyl methacrylate) are preferred.

  The glass transition temperature of the solid acrylic resin is, for example, about 10 to 120 ° C, preferably about 15 to 110 ° C, and more preferably about 20 to 100 ° C. In the present description and claims, the glass transition temperature can be measured using a differential scanning calorimeter (DSC).

  The weight average molecular weight of the solid acrylic resin is not particularly limited, and is, for example, about 1000 to 20,000, preferably about 3,000 to 10,000, and more preferably about 5,000 to 8,000 in terms of polystyrene by gel permeation chromatography.

  The binder resin may further include a liquid resin in addition to the solid acrylic resin. By combining the solid acrylic resin and the liquid resin, the problem common to transfer printing using a silicone blanket is also greatly improved. The problem common to transfer printing is the lack of continuous printability when repeating printing on a large number of works, and this problem is that silicone rubber absorbs a part of the solvent contained in the paste or ink. This causes the blanket rubber to gradually swell and saturate, resulting in a decrease in the amount of solvent absorbed or an inability to absorb the solvent. More specifically, since the solvent is less likely to be absorbed by the blanket, the film before transfer cannot obtain appropriate drying, and eventually a tearing-off phenomenon occurs and transfer becomes impossible. Therefore, in the actual printing operation, the operation must be stopped periodically during continuous printing to replace the blanket or the solvent in the blanket must be removed, so that there is a disadvantage that productivity is not improved. The liquid resin is effective against such disadvantages for the following reasons.

  The reason that the above problem can be improved by adding a liquid resin to the paste is that the amount of the solvent (the first organic solvent in the present invention) to be absorbed by the blanket can be reduced. When using only an organic vehicle produced by dissolving a solid resin in an organic solvent without using a liquid resin, a large amount of the organic solvent must be added to obtain a viscosity suitable for screen printing of the paste, and the amount of the binder resin is required. Tend to decrease naturally. The smaller the amount of the binder resin, the weaker the stickiness and stiffness of the film, the more difficult it is for the entire film to be completely transferred, and the more likely it is to “break apart”. Even in such a case, a proper balance between dryness and tackiness cannot be obtained, but it is difficult to maintain the state as described above in the process of continuous printing. On the other hand, if a liquid resin is used, a viscosity suitable for screen printing can be obtained with a configuration in which a large amount of binder resin is used. It becomes difficult to do. In addition, since the liquid resin itself has adhesiveness, the balance between dryness and adhesiveness required for transfer can be largely shifted to the adhesive side, and the first necessary for drying the film (to increase the viscosity). The amount of the organic solvent (absorbing solvent) required is smaller than when no liquid resin is used. Furthermore, even if the transfer balance shifts to the sticky side and the absorption of the first solvent is slightly reduced, if the shift is not shifted to the sticky side, it will break apart, but it shifts to the sticky side. Because of this, the transfer can be performed, and the continuous printability is further improved.

  Although the type of the liquid resin is not particularly limited, a liquid acrylic resin, a liquid epoxy resin, a liquid phenol resin, a liquid silicone resin, a liquid terpene resin, or the like can be used. These liquid resins can be used alone or in combination of two or more. Above all, liquid acrylic resin is preferable in consideration of compatibility with the acrylic resin and solubility in a solvent.

Examples of the liquid acrylic resin include C _1-4 alkyl acrylates such as methyl acrylate, ethyl acrylate, n-butyl acrylate, and isobutyl acrylate; pentyl (meth) acrylate, hexyl (meth) acrylate, _Homopolymers and copolymers containing, as constituent units, acrylic monomers such as (meth) acrylic acid C _5-12 alkyl esters such as octyl (meth) acrylate and 2-ethylhexyl (meth) acrylate are exemplified. Can be The liquid acrylic resin may contain another copolymerizable monomer as long as the effects of the present invention are not impaired.

Examples of other copolymerizable monomers include, for example, acrylic monomers (methyl methacrylate C _1-4 such as methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, t-butyl methacrylate, and isobutyl methacrylate). Alkyl esters, t-butyl acrylate, etc.), olefin monomers, styrene monomers (styrene, vinyl toluene, etc.), vinyl ester monomers, (anhydride) maleic acid or its alkyl esters, and the like. .

  The liquid acrylic resin may be a straight acrylic resin in which a modification or a functional group is not introduced into a side chain, or a modified acrylic resin such as silicone-modified acrylic, and may have a hydroxyl group, a carboxyl group, an epoxy group. Resin having an alkyl group, an alkoxysilyl group, or the like in a side chain. These liquid acrylic resins may be appropriately selected according to the compatibility and the strength of interaction with other constituent materials in the paste, or the requirements of the printed film of the final target. These liquid acrylic resins can be used alone or in combination of two or more.

  The glass transition temperature of the liquid resin (particularly the liquid acrylic resin) may be less than 10 ° C, for example, -100 ° C or more and less than 10 ° C, preferably -90 ° C to 0 ° C, more preferably -80 ° C to -10 ° C. It is about.

  The weight average molecular weight of the liquid resin (particularly the liquid acrylic resin) is not particularly limited. For example, in gel permeation chromatography, in terms of polystyrene, for example, about 1,000 to 20,000, preferably about 3,000 to 10,000, and more preferably about 5,000 to 8,000. It is.

  Although the ratio of the liquid resin is not particularly limited, the mass ratio between the solid acrylic resin and the liquid resin (particularly, the liquid acrylic resin) can be selected from the range of solid acrylic resin / liquid resin 100/0 to 1/99, For example, it is about 95/5 to 5/95, preferably about 90/10 to 10/90, and more preferably about 80/20 to 20/80. If the ratio of the liquid resin is too large, tearing or stringing may occur, or the cross-sectional shape of the printed film may be in a semi-cylindrical shape.

  As long as the binder resin does not impair the effects of the present invention, other binder resins (for example, olefin resin, vinyl resin, styrene resin, polyether resin, polyester resin, polyamide resin, A thermoplastic resin such as a cellulose derivative; a thermosetting resin such as a thermosetting acrylic resin, an epoxy resin, a phenol resin, an unsaturated polyester resin, or a polyurethane resin). The total ratio of the solid acrylic resin and the liquid resin to the entire binder resin may be 50% by mass or more, preferably 80% by mass or more, more preferably 90% by mass or more, and 100% by mass (solid (Acrylic resin and liquid resin only).

  Although the ratio of the binder resin is not particularly limited, it is, for example, about 5 to 30% by volume, preferably about 7 to 25% by volume, and more preferably about 10 to 20% by volume, based on the whole conductive paste. If the proportion of the binder resin is too small, even if the viscosity of the printed film is sufficient at the time of transfer, there is little binder to keep the film, so that the film may be broken and transfer may not be possible. On the other hand, if the amount of the binder resin is too large, the adhesiveness becomes strong, a stringing phenomenon occurs when the paste printed on the blanket is transferred to the screen plate, and the printed pattern becomes mustache or extremely In such a case, the beard may be bridged to an adjacent pattern.

[Conductive particles]
The conductive particles are not particularly limited as long as they can form a good conductive film, and are usually conductive metal particles. Examples of the conductive metal include transition metals [for example, metals of Group 4A of the periodic table such as titanium and zirconium; metals of Group 5A of the periodic table such as vanadium, niobium, and tantalum]; and metals of Group 6A of the periodic table such as molybdenum and tungsten. A periodic table group 7A metal such as manganese; a periodic table group 8 metal such as iron, cobalt, nickel, ruthenium, rhodium, palladium, rhenium, iridium and platinum; a periodic table group 1B metal such as copper, silver and gold Etc.], periodic table group 2B metals (eg, zinc, cadmium, etc.), periodic table group 3B metals (eg, aluminum, gallium, indium, etc.), periodic table group 4B metals (eg, germanium, tin, lead, etc.) ), And metals of Group 5B of the periodic table (for example, antimony, bismuth, and the like). These conductive metals can be used alone or in combination of two or more, and may be an alloy.

  Among these conductive metals, copper, silver, and nickel are preferable in that a conductive film having good conductivity can be obtained. Copper, silver and nickel may be a combination of two or more, and in particular, an alloy of two or more.

  Further, the conductive particles may be adhered to an insulating substrate in addition to particles formed of an alloy containing at least one or two or more selected from the group consisting of copper, silver and nickel (good conductive metal particles). The active metal particles may be further included from the viewpoint that the property can be improved.

  The active metal is a metal belonging to Group 4A of the periodic table, and may be a compound containing this metal. Examples of the metal include titanium, zirconium, and hafnium. These active metals and active metal compounds can be used alone or in combination of two or more.

  The ratio of the active metal particles may be 50 parts by mass or less, for example, 0.1 to 50 parts by mass, preferably 0.3 to 30 parts by mass, and more preferably 100 parts by mass with respect to 100 parts by mass of the good conductive metal particles. It is about 0.5 to 10 parts by mass (particularly 1 to 5 parts by mass). If the ratio of the active metal particles is too large, the conductivity of the conductive film may be reduced.

  The shape of the conductive particles is not particularly limited, and may be spherical (true spherical or substantially spherical), elliptical (elliptical spherical), polygonal (polygonal such as pyramidal, cubic or rectangular), plate Shape (flat, scale, flake, etc.), rod shape or rod shape, fibrous shape, irregular shape, etc. The shape of the metal particles is usually spherical, elliptical, polygonal, irregular, or the like.

  Although the particle size of the conductive particles is not particularly limited, it is more advantageous to use conductive particles having a small particle size in view of excellent paste uniformity and screen printing without clogging. The center particle diameter (D50) of the conductive particles is, for example, about 0.05 to 10 μm, preferably about 0.08 to 8 μm, and more preferably about 0.1 to 5 μm (particularly about 0.2 to 3 μm). If the particle size of the conductive particles is too small, the economics may be reduced and the dispersibility in the paste may be reduced. If the particle size is too large, the printability and dispersibility of the paste may be reduced.

  In particular, the conductive particles may be a combination of small particles having a particle size of less than 1 μm (for example, 1 nm or more and less than 1 μm) and large particles having a particle size of 1 μm or more (for example, 1 to 50 μm) from the viewpoint of the conductivity of the conductive film. . The central particle size of the small particles can be selected from a range of about 0.01 to 0.9 μm (particularly 0.1 to 0.8 μm). The central particle size of the large particles can be selected from a range of about 1.5 to 30 μm (particularly 2 to 10 μm). The mass ratio of small particles to large particles can be selected from the range of small particles / large particles = 1/99 to 90/10, for example, 5/95 to 80/20, preferably 10/90 to 70/30, More preferably, it is about 15/85 to 50/50 (particularly about 20/80 to 30/70).

[Inorganic binder]
The conductive paste may further include an inorganic binder (or a sintering aid). Glass particles (glass frit) can be preferably used as the inorganic binder. The glass particles are preferably low-melting glass particles having a softening point lower than the firing temperature, and the softening point of the low-melting glass particles is about 400 to 800 ° C, preferably about 420 to 700 ° C, and more preferably about 450 to 600 ° C. is there.

  Examples of the low-melting glass particles include conventional low-melting glass particles such as borosilicate glass particles, zinc borosilicate glass particles, zinc glass particles, bismuth glass particles, and lead glass particles. These low-melting glass particles can be used alone or in combination of two or more. Among these low-melting glass particles, zinc-based glass particles, bismuth-based glass particles, and the like are widely used.

  The shape of the glass particles is not particularly limited, and may be spherical (true spherical or substantially spherical), elliptical (elliptical spherical), polygonal (polygonal pyramid, tetragonal or rectangular parallelepiped, etc.), plate, or the like. Shape (flat, scale, flake, etc.), rod shape or rod shape, fibrous shape, irregular shape, etc. The shape of the glass particles is usually spherical, elliptical, polygonal, irregular, and the like. The center particle diameter (D50) of the glass particles is not particularly limited, and is, for example, about 0.1 to 20 μm, preferably about 0.5 to 10 μm, and more preferably about 1 to 5 μm (particularly about 2 to 4 μm).

  The proportion of the inorganic binder may be 50 parts by mass or less based on 100 parts by mass of the conductive particles, for example, 1 to 50 parts by mass, preferably 2 to 30 parts by mass, more preferably 3 to 10 parts by mass (particularly 3 to 10 parts by mass) 3 to 8 parts by mass). If the proportion of the inorganic binder is too large, the conductivity of the conductive film may be reduced.

[Other components]
The conductive paste may further include a curing agent for the acrylic resin (for example, a melamine resin or an organic peroxide such as benzoyl peroxide) or a conventional additive. Conventional additives include, for example, colorants (such as dyes and pigments), hue improvers, dye fixing agents, gloss imparting agents, metal corrosion inhibitors, stabilizers (such as antioxidants and ultraviolet absorbers), and surfactants. Or dispersants (anionic surfactants, cationic surfactants, nonionic surfactants, amphoteric surfactants, etc.), dispersion stabilizers, viscosity modifiers or rheology modifiers, humectants, thixotropic agents, Examples include leveling agents, defoamers, bactericides, and fillers. These other components can be used alone or in combination of two or more. The ratio of the other components can be selected according to the type of the components, and is usually about 10% by mass or less (for example, 0.01 to 10% by mass) based on the whole paste.

[Viscosity of conductive paste]
The conductive paste of the present invention can be prepared by dispersing conductive particles and a binder resin in an organic solvent by a conventional method such as stirring, and the viscosity characteristics are such that a good pattern can be screen-printed on the blanket surface. I just need. Specifically, the viscosity measured at 25 ° C. and 10 rpm using a B-type viscometer (“HBDV-2 Pro” manufactured by Brookfield) may be about 5 to 300 Pa · s, preferably 10 to 250 Pa. S, more preferably about 20 to 200 Pa · s (particularly 30 to 150 Pa · s). In particular, the viscosity is, for example, 30 to 250 Pa · s, preferably 50 to 200 Pa · s, more preferably 80 to 150 Pa · s (particularly 100 to 130 Pa · s) from the viewpoint that high pattern accuracy and transferability can be highly compatible. s). If the viscosity is too low, bleeding or spreading of the printed pattern may occur and pattern collapse may occur, or even if the pattern accuracy is maintained, the cross-sectional shape of the printed film may become a semicylindrical shape due to the effect of the surface tension of the solvent. is there. On the other hand, if the height is too high, the paste lacks fluidity in the process of coming out of the screen mesh and contacting the blanket, so that the paste is not completely printed at every corner of the pattern edge and the edge line is not linear but easily wavy There is a fear.

[Method of manufacturing substrate with conductive film]
The method for manufacturing a substrate with a conductive film according to the present invention includes a printing step of printing the conductive paste on a silicone blanket surface through a screen plate, a transfer step of transferring the printed paste film to an insulating substrate, and a transferred paste. A baking step for baking the film to form a conductive film on the surface of the insulating substrate.

  In the printing step, as a screen printing method, a conventional method, for example, a method described in JP-A-4-364953 can be used. The coating thickness (thickness after drying) is about 3 to 50 μm, preferably about 5 to 30 μm, and more preferably about 7 to 20 μm (particularly about 8 to 15 μm). Further, in the present invention, even a fine pattern can be printed. For example, the width (diameter) of the pattern may be, for example, about 10 to 500 μm, preferably about 20 to 300 μm, and more preferably about 30 to 100 μm. The screen plate may have, for example, about 100 to 1000 mesh, preferably about 200 to 800 mesh, and more preferably about 300 to 600 mesh.

  The silicone rubber constituting the blanket may have a polyorganosiloxane skeleton, and examples thereof include methyl silicone rubber, vinyl silicone rubber, phenyl silicone rubber, methyl phenyl silicone rubber, and phenyl vinyl silicone rubber.

  In the transfer step, the insulating substrate is not particularly limited as long as it is formed of a material that can be fired, and various materials such as ceramics such as silica, alumina, alumina zirconium, aluminum nitride, and silicon nitride, glass, and metal A substrate formed of an inorganic material such as an organic material such as an engineering plastic or the like can be used. Among these substrates, heat-resistant substrates and ceramic green sheets are widely used, and ceramic substrates such as an alumina substrate and an aluminum nitride substrate are preferable from the viewpoint of excellent adhesion to a conductive paste.

  The thickness of the insulating substrate may be appropriately selected depending on the application, and is, for example, about 0.001 to 10 mm, preferably about 0.01 to 5 mm, and more preferably about 0.05 to 3 mm (particularly about 0.1 to 1 mm). There may be.

  As a method of transferring the printed paste film, a conventional transfer method in offset printing or pad printing can be used.

  The transferred paste film may be naturally dried before the baking treatment, or may be dried by heating. The heating temperature can be selected according to the type of the organic solvent, and is, for example, about 50 to 200 ° C, preferably about 80 to 180 ° C, and more preferably about 100 to 150 ° C. The heating time is, for example, about 1 minute to 3 hours, preferably 5 minutes to 2 hours, and more preferably about 10 minutes to 1 hour.

  In the firing step, the firing temperature may be any temperature at which the metal as the conductive particles can be sintered, for example, 500 ° C. or higher (eg, 500 to 2000 ° C.), preferably 550 to 1500 ° C., more preferably 600 to 1200 ° C. (particularly 700 to 1200 ° C.). 1100 ° C.). The heat treatment time (heating time) may be, for example, about 1 minute to 48 hours, preferably about 5 minutes to 8 hours, and more preferably about 10 to 120 minutes, depending on the heat treatment temperature and the like.

  The firing atmosphere may be appropriately selected according to the type of the conductive particles contained in the paste.For example, when the conductive particles are silver particles, the firing may be performed in an air atmosphere, and the copper particles are easily oxidized. When the particles are used, they may be fired in an inert gas (for example, nitrogen gas, argon gas, helium gas, or the like) or in a vacuum.

  Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples. In the following examples, the materials used in the examples, the patterns of the evaluation substrates, the methods for measuring the properties, and the evaluation methods in screen offset printing are shown below.

[Material used]
(Conductive particles)
Cu particles (5 μm): copper particles having a central particle diameter of 5 μm Cu particles (0.5 μm): copper particles having a central particle diameter of 0.5 μm Ag particles (3 μm): silver particles having a central particle diameter of 3 μm Ag particles (0.1 μm) : Silver particles having a central particle diameter of 0.1 μm Ni particles (0.7 μm): nickel particles having a central particle diameter of 0.7 μm CuAg particles (5 μm): alloy particles of copper and silver having a central particle diameter of 5 μm, Ag / Cu = 72/28 (mass ratio)
Titanium hydride particles (7 μm): Titanium hydride particles with a central particle diameter of 7 μm (binder)
Solid acrylic resin: poly n-butyl methacrylate Liquid acrylic resin: hydroxyl-containing acrylic resin, glass transition temperature -47 ° C., weight average molecular weight 6,000
(Sintering aid)
Glass particles (3 μm): glass particles having a central particle diameter of 3 μm.

[Evaluation board pattern]
On a 50 mm × 50 mm × 0.4 mm aluminum nitride substrate surface, two 1 mm × 2 mm rectangular patterns of conductive film were arranged at 0.05 mm (50 μm) intervals to form a pair of patterns. A total of 324 pairs arranged in 18 rows × 18 columns at 0.4 mm intervals were used as evaluation substrates.

[Swelling ratio of silicone blanket to organic solvent]
A test cut out from an organic solvent shown in Table 1 into a size of about 2 mm x 5 mm x 10 mm from a silicone blanket made of a polyorganosiloxane compound (trade name: MB500, manufactured by Mino Group Co., Ltd., material: methyl silicone rubber) The pieces were dipped. It was immersed in a thermostat at 25 ° C. for 72 hours. Before and after immersion, the volume of each test piece was determined by the Archimedes method and used for calculating the swelling ratio. That is, the value obtained by subtracting the weight in water (g) from the weight in air (g) was taken as the volume of the test piece (cm ³ ), and the swelling ratio was determined by the following equation. The results are shown in Table 1.

    Swelling ratio (%) = (volume of test piece after immersion−volume of test piece before immersion) / (volume of test piece before immersion) × 100

  Among the organic solvents shown in Table 1, cyclodecane, dodecane, and dodecene were selected as the first organic solvent, and N-methyl-2-pyrrolidone, butyl carbitol acetate, and terpineol were selected as the second organic solvent. Examples and Comparative Examples , A conductive paste to be subjected to screen offset printing was prepared.

[Viscosity of conductive paste]
About the conductive paste prepared by the Example and the comparative example, the viscosity was measured on 25 degreeC and 10 rpm conditions using the Brookfield viscometer ("HBDV-2 Pro, SC-14 spindle"). .

[Thickness of conductive film]
In the examples and comparative examples, the height profile from the substrate surface to the opposite substrate back surface beyond the conductive film (1 mm width) was measured with a roughness meter (Co., Ltd.) for the evaluation substrate manufactured using the conductive paste. It was measured by ULVAC “DEKTAK6M”). Four points and five points at the center of the substrate were measured. The average of five points of the height obtained by subtracting the height (substrate thickness) connecting the front surface and the back surface of the substrate from the average height of the conductive film in the scanning direction was defined as the thickness of the conductive film.

[Print / Transfer status]
In the screen offset process, the state of printing / transfer to the aluminum nitride substrate was observed, and the state of the defect was classified into the following states.

Not transferred (non-transferred)… Not transferred at all Film tearing… Partially transferred, but the film is torn and partly left on the blanket side Weeping… Trying to move entirely to the substrate side, but split inside the film The paste film is separated on both the substrate and the blanket. Threading: There is no residue on the blanket side, and the transfer appears to be good at first glance. It is growing.

  The number (ratio) at which these defects were observed was measured for the evaluation pattern 324 pair, and each defect was evaluated according to the following criteria.

：: Less than 10 defects (less than about 3%)
：: 10 or more defects and less than 33 defects (about 3 to 10%)
Δ: Number of defects is 33 or more and less than 100 (about 10 to 30%)
×: 100 or more defects (about 30% or more).

[Pattern accuracy]
For the example in which the transfer state was good, the width between a pair of rectangular patterns (design value: 50 μm) was measured on the evaluation substrate, and evaluated according to the following criteria. The width was measured based on an image enlarged by a stereoscopic microscope, and a total of five pairs located at the four corners and the center of the substrate were measured, and the average was defined as the width between the patterns. In addition, there was no example of 70 μm or more.

：: in the range of 40 to 60 μm for the design value of 50 μm ：: in the range of 30 to 40 μm or 60 to 70 μm for the design value of 50 μm △: in the range of 20 to 30 μm for the design value of 50 μm : Narrower than 20 μm with respect to the designed value of 50 μm.

[Cross-sectional shape]
The width of the flat region of the profile of the conductive film (width 1 mm) in the film thickness measurement was evaluated based on the following criteria for the example in which the transfer state was good. The width was also measured at five points in the same manner as in the film thickness measurement, and the average was taken. Note that the “flat region” was a profile length in which a height not lower than 3 μm from the maximum height in the profile continued.

◎: The width of the flat region is 0.95 mm or more ：: The width of the flat region is in the range of 0.9 to 0.95 mm Δ: The width of the flat region is in the range of 0.8 to 0.9 mm ×: Flat The width of the region is shorter than 0.8 mm.

[Continuous printability]
The continuous printability was evaluated by repeating printing while sequentially replacing the printed substrates. The number of times until the tearing-off mode finally becomes x based on the above-described determination criterion was recorded. When the number of printings was 100 or more, it was determined that sufficient continuous printability was obtained, and the evaluation was completed.

Example 1
(Preparation of conductive paste)
As shown in Table 2, the mixed solvent obtained by weighing the first organic solvent and the second organic solvent so as to have a mass ratio of 50:50 was stirred with a propeller in a 60 ° C. water bath while the solid acrylic resin powder was mixed. It was added slowly. After the entire amount of the acrylic resin was added, stirring was continued for 20 minutes to completely dissolve the mixture in the mixed solvent to obtain an organic vehicle. Cu particles as conductive particles and glass particles as a sintering aid were added to this organic vehicle, mixed with a mixer, and then uniformly dispersed with three rolls to prepare a conductive paste.

(Screen offset printing)
The above conductive paste was screen-printed on a silicone blanket at a squeegee speed of 50 mm / sec using a 400-mesh stainless mesh screen and a urethane squeegee. Subsequently, the printing film on the blanket was immediately pressed against the aluminum nitride substrate, and then slowly peeled off and transferred. The substrate to which the printed film was transferred was dried in an oven at 120 ° C. for 20 minutes to completely remove the solvent.

(Fired)
The dried substrate was fired in a belt-conveying tunnel furnace in which nitrogen gas was replaced, under the condition of maintaining the peak temperature at 900 ° C. for 10 minutes to obtain a substrate with a conductive film. Even in the case of a conductive film produced through screen offset printing, the conductivity and adhesion to a substrate were equivalent to those of a conductive film produced by ordinary screen printing. A film having a thickness of about 10 μm was formed as intended. When the pattern accuracy and the cross-sectional shape of the conductive film were evaluated by the above method, the pattern accuracy was good and the cross-sectional shape was rectangular.

Examples 2-3
A substrate with a conductive film was manufactured in the same manner as in Example 1 except that the ratio between the first organic solvent and the second organic solvent was changed. The results were also generally good.

Example 4
A substrate with a conductive film was manufactured in the same manner as in Example 1 except that the proportions of the first organic solvent and the second organic solvent were increased. The results were also generally good.

Examples 5 to 6
A substrate with a conductive film was manufactured in the same manner as in Example 1 except that the ratio of the organic solvent in the conductive paste was changed. The results were also generally good.

Examples 7 and 8
A substrate with a conductive film was manufactured in the same manner as in Example 1 except that the ratio of the binder resin in the conductive paste was changed. The results were also generally good.

Examples 9 to 12
A substrate with a conductive film was manufactured in the same manner as in Example 1 except that the types of the first organic solvent and the second organic solvent were changed as shown in Table 2. The results were all good.

Examples 13 and 14
A substrate with a conductive film was manufactured in the same manner as in Example 1 except that the conductive particles were changed to Ag particles or Ni particles. As a result, the results of Example 13 were all good, and the results of Example 14 were also generally good.

Example 15
A conductive paste was prepared by mixing a titanium compound as active metal particles, replacing a part of the Cu particles with CuAg particles as a brazing agent. Screen offset printing was the same as in Example 1. The firing was performed in vacuum (1 × 10 ⁻⁴ Pa) at 900 ° C. for 1 hour (4 hours including heating and cooling). The results were all good.

Comparative Example 1
A substrate with a conductive film was manufactured in the same manner as in Example 1 except that the first organic solvent was not used. As a result, a tearing phenomenon occurred during transfer in screen offset printing, and a printed matter was not obtained.

Examples 16 to 17
A substrate with a conductive film was manufactured in the same manner as in Example 1 except that the amount of the first organic solvent was reduced. The results were better than Comparative Example 1, but lower than Examples 1 to 3.

Example 18
A substrate with a conductive film was manufactured in the same manner as in Example 1 except that the amount of the second organic solvent was reduced. The results were better than Comparative Example 2 described below, but decreased as compared with Examples 1 to 3.

Comparative Example 2
A substrate with a conductive film was manufactured in the same manner as in Example 1 except that the second organic solvent was not used. As a result, the paste film was too dry on the blanket and was not transferred.

Example 19
A substrate with a conductive film was manufactured in the same manner as in Example 1 except that the ratio of the organic solvent in the paste was significantly reduced. The results were better than Comparative Examples 1 and 2, but were lower than Example 1.

Examples 20 to 21
A substrate with a conductive film was manufactured in the same manner as in Example 1 except that the ratio of the organic solvent in the paste was significantly increased. The results were better than Comparative Examples 1 and 2, but were lower than Example 1.

Example 22
A substrate with a conductive film was manufactured in the same manner as in Example 1, except that the ratio of the binder resin in the conductive paste was significantly reduced. The results were better than Comparative Examples 1 and 2, but were lower than Example 1.

Example 23
A substrate with a conductive film was manufactured in the same manner as in Example 1 except that the ratio of the binder resin in the conductive paste was significantly increased. The results were better than Comparative Examples 1 and 2, but were lower than Example 1.

Comparative Example 3
A substrate with a conductive film was manufactured in the same manner as in Example 11 except that toluene used in the example of Patent Document 1 was used instead of dodecane as the first organic solvent, and the ratio with the second organic solvent was changed. did. As a result, drying of the paste was remarkable at the stage of screen printing on the blanket, and the printed matter on the blanket was blurred.

Comparative Example 4
Terpineol, which is used as a highly swellable solvent in the examples of Patent Document 2 in place of dodecane, which is the first organic solvent, is used as the first organic solvent, and the ratio with butyl carbitol acetate, which is the second organic solvent, is changed. A substrate with a conductive film was manufactured in the same manner as in Example 11 except for performing the above. As a result, she almost completely broke up.

Examples 24 to 26
As shown in Table 3, a substrate with a conductive film was manufactured in the same manner as in Example 1, except that part of the solid acrylic resin was changed to liquid acrylic resin and the ratio of the first organic solvent was changed. The results of Examples 24 and 25 were all good, and the result of Example 26 was also generally good.

  Tables 2 and 3 summarize the results of the examples and comparative examples.

  In addition, as a result of evaluating the continuous printability of Example 1 and Examples 24 to 26, the number of Examples 1 to 55 was 55, whereas the number of Examples 24 to 26 was 100 or more.

  Table 4 shows the results of evaluation of Examples 1 to 3 by performing the following screen pad printing instead of the screen offset printing. The results of Example 1 were all good, and the results of Examples 2 and 3 were also generally good.

(Screen pad printing)
The above conductive paste was screen-printed on a silicone blanket at a squeegee speed of 50 mm / sec using a 400-mesh stainless mesh screen and a urethane squeegee. Subsequently, the silicone pad was pressed against the printed film, and then quickly pressed against the aluminum nitride substrate, and then slowly peeled off and transferred. The substrate to which the printed film was transferred was dried in an oven at 120 ° C. for 20 minutes to completely remove the solvent.

  The conductive paste of the present invention includes a chip resistor, a module with a built-in resistor, a substrate with a built-in resistor, a thick film resistor such as a ceramic heater, and a resistor provided with the thick film resistor (for example, a resistor and a copper electrode are provided. Resistors, etc.) or electronic components.

Claims (16)

  A conductive paste for transferring a pattern by a screen plate to a blanket at least a surface of which is formed of silicone rubber, a conductive resin, a binder resin containing a solid acrylic resin having a glass transition temperature of 10 ° C. or more, An organic solvent containing 1 organic solvent and a second organic solvent, wherein the first organic solvent has a boiling point of 120 ° C. or more, and swells the silicone rubber at a swelling rate of 60% or more; A conductive paste, wherein the second organic solvent is a solvent that swells the silicone rubber at a swelling ratio of 30% or less.   The conductive paste according to claim 1, wherein a boiling point of the second organic solvent is 120C or higher.   The conductive paste according to claim 1 or 2, wherein the mass ratio of the first organic solvent to the second organic solvent is (first organic solvent / second organic solvent) = 20/80 to 70/30.   The conductive paste according to any one of claims 1 to 3, wherein the viscosity measured at 25 ° C and 10 rpm using a B-type viscometer is 5 to 300 Pa · s.   The conductive paste according to any one of claims 1 to 4, wherein the first organic solvent is an aliphatic hydrocarbon or an alicyclic hydrocarbon. The conductive paste according to any one of claims 1 to 5, wherein the first organic solvent is a _C10-14 alkane, a _C10-14 alkene or a _C8-12 cycloalkane.   The conductive paste according to any one of claims 1 to 6, wherein the second organic solvent is at least one selected from the group consisting of alcohols, ketones, esters, cellosolves, carbitols, and pyrrolidones.   The conductive paste according to any one of claims 1 to 7, wherein the proportion of the organic solvent is 20 to 60% by volume based on the entire conductive paste.   The conductive paste according to any one of claims 1 to 8, wherein the binder resin further includes a liquid resin having a glass transition temperature of less than 10 ° C.   The conductive paste according to claim 9, wherein the liquid resin includes a liquid acrylic resin.   The conductive paste according to any one of claims 1 to 10, wherein a ratio of the binder resin is 5 to 30% by volume based on the whole conductive paste.   The conductive paste according to any one of claims 1 to 11, wherein the conductive particles are formed of an alloy containing at least one or two or more selected from the group consisting of copper, silver, and nickel.   The conductive paste according to claim 1, further comprising glass particles.   The conductive paste according to claim 1, wherein the conductive particles include active metal particles.   The conductive paste according to any one of claims 1 to 14, which is a screen offset printing paste or a screen pad printing paste.   A printing step of printing the conductive paste according to any one of claims 1 to 15 on a surface of a blanket having at least a surface formed of silicone rubber through a screen plate, and a transfer of transferring the printed paste film to an insulating substrate. A method of manufacturing a substrate with a conductive film, comprising: a step of baking the transferred paste film to form a conductive film on the surface of the insulating substrate.