# Patent

## Title
Green sheet coating material, green sheet, production method of green sheet and production method of electronic device

## Abstract

A green sheet coating material including ceramic powder, a binder resin including a butyral based resin as the main component, and a solvent. The solvent includes a first solvent medium having a relatively low boiling point, wherein said binder resin is easy to be dissolved, and a second solvent medium having a relatively high boiling point. The boiling point of the second solvent medium is in a range of 130 to 230° C. The second solvent medium is included by 5 to 70 wt %, and more preferably 8 to 52 wt % with respect to 100 wt % of the entire solvent.

## Background
TECHNICAL FIELD
The present invention relates to a green sheet coating material, a green sheet, a production method of a green sheet and a production method of an electronic device, and particularly relates to a coating material, green sheet and a method capable of producing a green sheet without a pin hole, having excellent surface smoothness even in the case of an extremely thin sheet and being suitable to making an electronic device of a thin layer and multilayer.
BACKGROUND ART
In recent years, as a variety of electronic equipments become compact, electronic devices to be installed inside the electronic equipments have become more compact and higher in performance. As one of the electronic devices, there is a ceramic electronic device, such as a CR built-in substrate and a multilayer ceramic capacitor, and the ceramic electronic devices have been required to be more compact and higher in performance.
To pursue a more compact ceramic electronic device having a higher capacity, there is a strong demand for making a dielectric layer thinner. Recently, a thickness of a dielectric green sheet composing a dielectric layer has become several μm or less.
To produce a ceramic green sheet, normally, a ceramic coating material composed of ceramic powder, a binder (an acrylic based resin and a butyral based resin, etc.), a plasticizer (phthalate esters, glycols, adipic acids, and phosphoric esters) and an organic solvent (toluene, MEK and acetone, etc.). Next, the ceramic coating material coated on a carrier sheet (a supporting body made by PET and PP) by using the doctor blade method, etc. and dried by heating.
Also, a method of producing by preparing a ceramic suspension wherein the ceramic powder and binder are mixed in a solvent, then, extruding a film-shaped molded item obtained by molding the suspension by twin-screw has been considered in recent years.
A method of producing a multilayer ceramic capacitor by using the ceramic green sheet explained above will be explained in detail. An internal electrode conductive paste containing metal powder and a binder is printed to be a predetermined pattern on the ceramic green sheet and dried to form an internal electrode pattern. After that, the green sheet is peeled from the carrier sheet and stacked by a predetermined number of layers. Here, two methods are proposed, that are a method of peeling the green sheet from the carrier sheet before stacking in layers and a method of peeling the carrier sheet after stacking in layers and adhering by compression, but the difference is not large. Finally, the stacked body is cut to be chips, so that green chips are prepared. After firing the green chips, external electrodes are formed, so that a multilayer ceramic capacitor and other electronic devices are produced.
When producing a multilayer ceramic capacitor, an interlayer thickness of sheets formed with internal electrodes is in a range of 3 μm to 100 μm or so based on a desired capacitance required as a capacitor. Also, in a multilayer ceramic capacitor, a part not formed with internal electrodes is formed on an outer part in the stacking direction of the capacitor chip.
Generally, when a thickness of the green sheet becomes thin, there arise problems that smoothness on the surface of the sheet declines and stacking becomes difficult.
In recent years, as electronic equipments become more compact, electronic devices to be used therein have rapidly become more compact. In multilayer electronic devices as typified by a multilayer ceramic capacitor, rapid development has been made on increasing the number of layers to be stacked and attaining a thinner interlayer thickness. To respond to the technical trends, a thickness of a green sheet, which determines the interlayer thickness, has almost become 3 μm or less to 2 μm or less. Therefore, in a production process of a multilayer ceramic capacitor, it is necessary to handle extremely thin green sheets and to design very advanced green sheet properties.
As characteristics required as the properties of such an extremely thin green sheet, sheet strength, flexibility, smoothness, adhesiveness when being stacked, handlability (electrostatic property), etc. may be mentioned, and balance of a higher order is required.
Particularly, when the sheet becomes thin, roughness (unevenness) on the sheet surface cannot be ignored with respect to the thickness. Namely, there appears a portion where the sheet is thin. It is anticipated that this portion has susceptibility to a voltage application at firing and causes short-circuiting. Therefore, to produce a sheet having a unified thickness and smooth surface is essential element technique in producing a multilayer chip capacitor.
Note that, as described in the Japanese Unexamined Patent Publication No. 6-206756, there is known a technique of using a polyvinyl butyral resin having a polymerization degree of 1000 or more as a binder in green sheet slurry containing an aqueous solvent for a purpose of eliminating a short-circuiting defect.
However, the Japanese Unexamined Patent Publication No. 6-206756 is not for particularly attaining a thinner organic solvent based green sheet, and also has the problem that surface smoothness declines and stacking becomes difficult when a thickness of the green sheet is made thin.
Also, the Patent Publication No. 2866137 discloses a technique of using a solvent having a high evaporation rate to improve a surface property of the sheet by making the evaporation rate high. However, although the method of making the evaporation rate high is effective to obtain a thick sheet, it gives an adverse effect of deteriorating the surface property in the case of making the sheet thin.
Also, as disclosed in the Japanese Unexamined Patent Publication No. 2000-335971, there is known an invention of regulating a blending composition ratio, a defoaming condition and a drying temperature condition of the sheet by an aqueous coating material.
However, in this technique, a sheet having a desired property may not be able to be obtained due to the limited composition and the procedure becomes cumbersome and complicated because a defoaming step is added.
Furthermore, as disclosed in the Japanese Unexamined Patent Publication No. 2001-114568, there is also known a technique of improving a surface property by extending the sheet by applying pressure.
However, in this technique, the sheet may be damaged due to the applied pressure when the green sheet is made thin.
DISCLOSURE OF THE INVENTION
An object of the present invention is to provide a coating material, a green sheet and a method capable of producing a green sheet without a pin hole, having enough strength to be peeled from a supporting body and excellent surface smoothness even when the green sheet is extremely thin, and being suitable to make an electronic device thin and multilayer.
The present inventors have been committed themselves to study to attain the above objects, found that it was possible to produce a green sheet without a pin hole and having enough strength to be peeled from a supporting body and excellent surface smoothness even if the green sheet was extremely thin, by using as a binder a polyvinyl acetal resin or other butyral based resin and by making a second solvent medium having a relatively high boiling point contained as a solvent in addition to a first solvent medium having a relatively low boiling point, wherein a binder resin was easy to be dissolved, and completed the present invention.
Namely, green sheet coating material according to the present invention contains ceramic powder, a binder resin including a butyral based resin as the main component, and a solvent, wherein
the solvent contains a first solvent medium having a relatively low boiling point, wherein the binder resin is easy to be dissolved, and a second solvent medium having a relatively high boiling point.
By using a binder resin including a butyral based resin as the main component and by making a second solvent medium having a relatively high boiling point contained as a solvent in addition to a first solvent medium having a relatively low boiling point, wherein a binder resin is easy to be dissolved, it becomes possible to produce a green sheet without a pin hole and having enough strength to be peeled from a supporting body and excellent surface smoothness even if the green sheet is extremely thin. For example, a thickness of a dielectric layer after firing (a green sheet after firing) can be made as thin as 5 μm or less, preferably 3 μm or less, and furthermore preferably 2 μm or less. Also, the number of layers to be stacked can be increased. Furthermore, short-circuiting or other defects can be reduced.
Preferably, a vapor pressure of the second solvent medium at the room temperature (25° C.) is lower than that of the first solvent medium. It is liable that a vapor pressure generally becomes low in the solvent having a high boiling point.
Preferably, a boiling point of the second solvent medium is in a range of 130 to 230° C., and more preferably 135 to 210° C. When the boiling point is too low, it is liable that an evaporation rate of the solvent becomes high when drying the green sheet, and the sheet surface becomes rough. While, when the boiling point is too high, drying of the sheet takes time and there is a tendency that it becomes difficult to make a sheet.
Preferably, a vapor pressure of the second solvent medium at 25° C. is in a range of 1.3 to 667 Pa (0.01 to 5 Torr), and more preferably in a range of 10 to 300 Pa. When the vapor pressure is too low, drying of the sheet takes time and there is a tendency that it becomes difficult to make a sheet. While, when the vapor pressure is too high, an evaporation rate of the solvent becomes high when drying the green sheet and the sheet surface becomes rough.
Preferably, when assuming that a boiling point of the second solvent medium is T° C. and a vapor pressure of the second solvent medium at 25° C. is α Pa, a product of T×α is in a range of 2000 to 65000 (° C.×Pa), and more preferably in a range of 3000 to 50000. Since the rising rate of the boiling point is larger than the lowering rate of the vapor pressure, a product of T×α in the ranges is preferable. Note that there are some solvent, wherein the boiling point is high but the vapor pressure is also high. In the present invention, it is preferable that a solvent having a high boiling point and a low vapor pressure is included as a second solvent medium.
Preferably, the second solvent medium has a higher boiling point by 50 to 105° C. than a drying temperature at the time of making the green sheet coating material to be a sheet. By making the second solvent medium having such a high boiling point contained in the coating material, the effects of the present invention are enhanced.
Preferably, a drying temperature at the time of drying the green sheet is 50 to 100° C.
Preferably, the second solvent medium includes an organic solvent having a higher boiling point by 60 to 150° C. than that of alcohol having the lowest boiling point included in the first solvent medium. By making the second solvent medium having such a high boiling point contained in the coating material, the effects of the present invention are enhanced.
Preferably, the second solvent medium includes an organic solvent having a vapor pressure at 25° C. of 0.1 to 10% of that of alcohol having the highest vapor pressure at 25° C. included in the first solvent medium. By making the second solvent medium having such a low vapor pressure contained in the coating material, the effects of the present invention are enhanced.
Preferably, the second solvent medium is included by 5 to 70 wt %, more preferably 8 to 52%, and furthermore preferably 13 to 52 wt % with respect to 100 wt % of the entire solvent. When the content of the second solvent medium is too small, effects of the present invention are small, while when too much, it tends to be difficult to make a sheet.
Preferably, the second solvent medium is not particularly limited as far as it has a high boiling point and a butyral based resin is dissolved therein, but it includes at least one selected form the 1) to 3) below.
1) monohydric alcohol having a carbon number of 5 to 9
1-pentanol, 1-hexanol, 1-heptanol, 1-octanol, 1-nonanol, tarpineol
2) ketones containing a cyclic structure
cyclohexanon, isophorone
3) compound containing two or more functional groups selected from a —OH group, ether and ketone
2-ethoxyethanol, 2-butoxyethanol, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diacetone alcohol
The first solvent medium is not particularly limited as far as it has a low boiling point and a butyral based resin is dissolved therein. Preferably, at least one of ethanol and methanol is contained.
Preferably, the butyral based resin is a polybutyral resin; and
a polymerization degree of the polybutyral resin is 1000 or more and 1700 or less, a butyralation degree of the resin is 64% or higher and 78% or lower, and a residual acetyl group amount is less than 6%.
When the polymerization degree of the polybutyral resin is too low, it is liable that sufficient mechanical strength is hard to be obtained when the layer is made to be as thin as 5 μm or less, and preferably 3 μm or less. While, when the polymerization degree is too high, surface roughness tends to deteriorate when made to be a sheet. Also, when the butyralation degree of the polybutyral resin is too low, solubility to a coating material tends to deteriorate, while when too high, surface roughness of the sheet tends to deteriorate. Furthermore, when a residual acetyl group amount is too much, surface roughness of the sheet tends to deteriorate.
Preferably, the binder resin is included by 5 parts by weight or more and 6.5 parts by weight or less with respect to 100 parts by weight of the ceramic powder. When a content of the binder resin is too small, it is liable that the sheet strength declines and stackability (adhesiveness at the time of stacking) deteriorates. Also, when a content of the binder resin is too large, it is liable that segregation of the binder resin is caused to deteriorate the dispersibility, and sheet surface roughness declines.
Preferably, dioctyl phthalate as a plasticizer is contained by 40 parts by weight or more and 70 parts by weight or less with respect to 100 parts by weight of the binder resin. Comparing with other plasticizers, dioctyl phthalate is preferable in terms of both of sheet strength and sheet ductility, and particularly preferable because the release strength from a supporting body is small and it is easily peeled. Note that when a content of the plasticizer is too small, it is liable that sheet stretching becomes less and flexibility becomes less. Also, when the content is too large, it is liable that breedout of the plasticizer from the sheet is caused, segregation of the plasticizer is easily caused against the sheet, and the sheet dispersibility declines.
A production method of a ceramic green sheet according to the present invention comprises the steps of:
preparing the green sheet coating material; and
forming a ceramic green sheet by using the green sheet coating material.
A production method of a ceramic electronic device according to the present invention comprises the steps of:
preparing the green sheet coating material;
forming a ceramic green sheet by using the green sheet coating material;
drying the green sheet;
stacking the green sheets after drying via an internal electrode layer to obtain a green chip; and
firing the green chip.
The green sheet according to the present invention is produced by using the green sheet coating material explained above.



BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a schematic sectional view of a multilayer ceramic capacitor according to an embodiment of the present invention;
FIG. 2 is a sectional view of a key part showing a production procedure of the multilayer ceramic capacitor shown in FIG. 1; and
FIG. 3A and FIG. 3B are schematic views showing a production procedure of a green sheet.



BEST MODE FOR CARRYING OUT THE INVENTION
Below, the present invention will be explained based on an embodiment shown in the drawings.
First, as an embodiment of an electronic device produced by using a green sheet coating material (dielectric paste) and a green sheet according to the present invention, an overall configuration of a multilayer ceramic capacitor will be explained.
As shown in FIG. 1, a multilayer ceramic capacitor 2 according to the present embodiment comprises a capacitor element 4, a first terminal electrode 6 and a second terminal electrode 8. The capacitor element 4 comprises dielectric layers 10 and internal electrode layers 12, and the internal electrode layers 12 are stacked alternately between the dielectric layers 10. The alternately stacked internal electrode layers 12 on one side are electrically connected to inside of the first terminal electrode 6 formed at one end portion of the capacitor element 4. Also, the alternately stacked internal electrode layers 12 on the other side are electrically connected to inside of the second terminal electrode 8 formed at the other end portion of the capacitor element 4.
A material of the dielectric layer 10 is not particularly limited and composed of a dielectric material, for example, calcium titanate, strontium titanate and/or barium titanate, etc. A thickness of each of the dielectric layers 10 is not particularly limited, but those having a thickness of several μm to several hundreds of μm are general. Particularly in the present embodiment, it is made to be thin as preferably 5 μm or less, and more preferably 3 μm or less.
A material of the terminal electrodes 6 and 8 is not particularly limited, either, and copper, a copper alloy, nickel and a nickel alloy, etc. are normally used. Silver or an alloy of silver and palladium may be also used. A thickness of the terminal electrodes 6 and 8 is not particularly limited, either, but is normally 10 to 50 μm or so.
A shape and size of the multilayer ceramic capacitor 2 may be suitably determined in accordance with the object and use. When the multilayer ceramic capacitor 2 has a rectangular parallelepiped shape, it is normally a length (0.6 to 5.6 mm, preferably 0.6 to 3.2 mm)×width (0.3 to 5.0 mm, preferably 0.3 to 1.6 mm)×thickness (0.1 to 1.9 mm, preferably 0.3 to 1.6 mm) or so.
Next, an example of production methods of the multilayer ceramic capacitor 2 according to the present embodiment will be explained.
(1) First, a dielectric coating material (green sheet coating material) is prepared to produce a ceramic green sheet for composing the dielectric layers 10 shown in FIG. 1 after firing.
The dielectric coating material is composed of an organic solvent based coating material obtained by kneading a dielectric material (ceramic powder) and an organic vehicle.
The dielectric material is suitably selected from a variety of compounds which become composite oxides or oxides, such as carbonates, nitrites, hydroxides, and organic metal compounds, and mixed for use. The dielectric material is normally used as powder having an average particle diameter of 0.1 to 3 μm, and preferably 0.4 μm or less or so. Note that it is preferable to use finer powder than the green sheet thickness to form an extremely thin green sheet.
The organic vehicle is obtained by dissolving a binder resin in an organic solvent. As the binder resin used for the organic vehicle, a polyvinyl butyral resin is used in the present embodiment. A polymerization degree of the polybutyral resin is 1000 or higher and 1700 or lower, and preferably 1400 to 1700. Also, a butyralation degree of the resin is 64% or higher and 78% or lower, and preferably 64% or higher and 70% or lower, and the residual acetyl group amount is less than 6% and preferably 3% or less.
The polymerization degree of the polybutyral resin can be measured, for example, by a polymerization degree of a polyvinyl acetal resin as a material. Also, the butyralation degree can be measured, for example, based on the JISK6728. Furthermore, the residual acetyl group amount can be measured based on the JISK6728.
When the polymerization degree of the polybutyral resin is too low, it is liable that sufficient mechanical strength is hard to be obtained when made to be a thin film of, for example, 5 μm or less, and preferably 3 μm or less or so. Also, when the polymerization degree is too large, surface roughness tends to decline when made to be a sheet. Also, when the butyralation degree of the polybutyral resin is too low, solubility in a coating material tends to decline, while when too high, sheet surface roughness tends to decline. Furthermore, when the residual acetyl group amount is too large, sheet surface roughness tends to decline.
An organic solvent to be used for an organic vehicle includes a first solvent medium having a relatively low boiling point, wherein a binder resin is easy to be dissolved, and a second solvent medium having a higher boiling point than that of the first solvent medium. In the present invention, the low boiling-point and the high boiling point are based on a concept of relativity, and a solvent having a higher boiling point by 60 to 150° C. than that of alcohol having the lowest boiling point included in the first solvent medium can be defined as a solvent having a high boiling point, and a solvent having a lower boiling point than that can be defined as a solvent having a low boiling point.
Alternately, a solvent having a higher boiling point by 50 to 105° C. than a drying temperature at the time when the green sheet coating material is made to be a sheet is defined as a solvent having a high boiling point, and a solvent having a lower boiling point than that can be defined as a solvent having a low boiling point. Note that, temperature of drying the sheet is normally 50 to 100° C., more preferably 60 to 80° C.
Alternately, those having a higher boiling point in a range of 130 to 230° C., and more preferably in a range of 135 to 205° C. are defined as a solvent having a high boiling point, and those having a lower boiling point than that can be defined as a solvent having a lo boiling point.
A solvent having a high boiling point generally tends to have a low vapor pressure. Therefore, in the present embodiment, a vapor pressure of the second solvent medium is lower than that of the first solvent medium at a predetermined temperature close to the room temperature. For example, the vapor pressure of the second solvent medium is 0.1 to 10% of that of alcohol having the highest vapor pressure included in the first solvent medium. Specifically, a vapor pressure of the second solvent medium at 25° C. is in a range of 1.3 to 667 Pa (0.01 to 5 Torr), and more preferably in a range of 10 to 300 Pa.
When assuming that a boiling point of the second solvent medium is T° C. and a vapor pressure of the second solvent medium at 25° C. is α Pa, a product of T×α is in a range of 2000 to 65000 (° C.×Pa), and more preferably in a range of 3000 to 50000. Since a rising rate of a boiling point is larger than a lowering rate of a vapor pressure, the product of T×α in the ranges is preferable. Note that there are some solvents, wherein the vapor pressure is high even if the boiling point is high. In the present invention, it is preferable that the solvent having a high boiling point and a low vapor pressure is included as the second solvent medium.
The first solvent medium is not particularly limited as far as it has a low boiling point and a butyral based resin is dissolved therein. Preferably, at least one of ethanol and methanol is included.
The second solvent medium is not particularly limited as far as it has a high boiling point and a butyral based resin can be dissolved therein, but at least one selected from 1) to 3) below is included.
1) monohydric alcohol having a carbon number of 5 to 9
1-pentanol, 1-hexanol, 1-heptanol, 1-octanol, 1-nonanol, tarpineol
2) ketones containing a cyclic structure
cyclohexanon, isophorone
3) compound containing two or more functional groups selected from a —OH group, ether and ketone
2-ethoxyethanol, 2-butoxyethanol, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diacetone alcohol
Among them, as the second solvent medium, diethylene glycol monoethyl ether, 2-butoxyethanol, diacetone alcohol and 1-pentanol are particularly preferable.
The second solvent medium is included preferably by 5 to 70 wt %, and more preferably 30 to 70 wt % with respect to 100 wt % of the entire solvent. When the content of the second solvent medium is too small, effects of the present invention are small, while when too much, it tends to be difficult to make a sheet.
Furthermore, in the present embodiment, as a solvent, an alcohol based solvent and aromatic solvent are preferably included, and an aromatic solvent is included by 6 parts by weight or more and 20 parts by weight or less when assuming that the total weight of the alcohol based solvent and the aromatic solvent is 100 parts by weight. When the content of the aromatic solvent is too small, surface roughness of the sheet tends to increase, while when too much, the coating material filtration properties decline and sheet surface roughness also declines by increasing.
As an alcohol based solvent, methanol, ethanol, propanol and butanol, etc. may be mentioned. As an aromatic solvent, toluene, xylene and benzyl acetate, etc. may be mentioned.
A binder resin is dissolved in an alcohol based solvent and filtrated to obtain a solution in advance, and dielectric powder and other components are added to the solution. A binder resin having a high polymerization degree is hard to be dissolved in a solvent, and dispersibility of a coating material tends to decline in a normal method. In a method of the present embodiment, a binder resin having a high polymerization degree is dissolved in the above good solvent and ceramic powder and other components are added to the solution, so that dispersibility of a coating material can be improved and generation of undissolved resin can be suppressed. Note that solid content concentration cannot be raised and changes of lacquer viscosity tend to become large over time in the case of a solvent other than the above solvents.
In the present embodiment, in the dielectric coating material, a xylene based resin is preferably added as a tackifier together with a binder resin. The xylene based resin is added in a range of 1.0 wt % or less, more preferably 0.1 wt % or more and 1.0 wt % or less, and particularly preferably in a range of more than 0.1 and 1.0 wt % or less with respect to 100 parts by weight of ceramic powder. When the adding quantity of the xylene based resin is too small, adhesiveness tends to decline. While when the adding quantity is too much, adhesiveness improves but it is liable that surface roughness of the sheet declines, stacking by a large number becomes difficult, tensile strength of the sheet declines, and handlability of the sheet decline.
In the dielectric coating material, additives selected from a variety of dispersants, plasticizers, antistatic agents, dielectrics, glass flit, and insulators may be included in accordance with need.
In the present embodiment, a dispersant is not particularly limited, but polyethylene glycol based nonionic dispersant is preferably used, and a hydrophile-lipophile balance (HLB) value thereof is 5 to 6. A dispersant is added by 0.5 part by weight or more and 1.5 parts by weight or less, and more preferably 0.5 part by weight or more and 1.0 part by weight or less with respect to 100 parts by weight of ceramic powder.
When the HLB is out of the above ranges, it is liable that coating material viscosity increases and sheet surface roughness increases. Also, in the case of a dispersant other than a polyethylene glycol based nonionic dispersant, coating material viscosity increases, sheet surface roughness increases and sheet ductility declines, so that it is not preferable.
When an adding quantity of a dispersant is too small, sheet surface roughness tends to increase, while when too large, sheet tensile strength and stackability tend to decline.
In the present embodiment, dioctyl phthalate is preferably used as a plasticizer and contained by an amount of preferably 40 parts by weight or more and 70 parts by weight or less, and more preferably 40 to 60 parts by weight with respect to 100 parts by weight of a binder resin. Comparing with other plasticizers, dioctyl phthalate is preferable in terms of both of sheet strength and sheet stretch and is particularly preferable for having weak peeling strength so as to be easily peeled from a supporting body. Note that when a content of the plasticizer is too small, it is liable that sheet stretch becomes less and flexibility becomes less. Also, when the content is too large, it is liable that breedout of a plasticizer from a sheet is caused, segregation of the plasticizer against the sheet easily arises and dispersibility of the sheet declines.
Also, in the present embodiment, the dielectric coating material contains water by 1 part by weight or more and 6 parts by weight or less, and preferably 1 to 3 parts by weight with respect to 100 parts by weight of dielectric powder. When a water content is too small, changes of coating material characteristics due to moisture absorbance over time becomes large, which is preferable, coating material viscosity tends to increase and filtration properties of the coating material tend to decline. While when the water content is too large, separation and precipitation of the coating material are caused, the dispersibility becomes poor and surface roughness of the sheet tends to decline.
Furthermore, in the present embodiment, at least any one of a hydrocarbon based solvent, industrial gasoline, kerosene, and solvent naphtha is added by preferably 3 parts by weight or more and 15 parts by weight, and more preferably 5 to 10 parts by weight with respect to 100 parts by weight of dielectric powder. By adding these additives, sheet strength and sheet surface roughness can be improved. When an adding quantity of these additives is too small, effects of adding is small, while when the adding quantity is too large, it is liable that sheet strength and sheet surface roughness are deteriorated inversely.
A binder resin is contained preferably by 5-parts by weight or more and 6.5 parts by weight or less with respect to 100 parts by weight of dielectric powder. When a content of the binder resin is too small, it is liable that the sheet strength declines and stackability (adhesiveness at the time of stacking in layers) also declines. While when a content of the binder resin is too large, it is liable that segregation of the binder resin is caused to make the dispersibility worse and sheet surface roughness tends to decline.
When assuming that total volume of the ceramic powder, binder resin and plasticizer is 100 volume %, a volume ratio accounted by the dielectric powder is preferably 62.42% or more and 72.69% or less, and more preferably 63.93% or more and 72.69% or less. When the volume ratio is too small, it is liable that segregation of the binder is easily caused to make the dispersibility worse and surface roughness declines. Also, when the volume ratio is too large, it is liable that the sheet strength declines and the stackability also declines.
Furthermore, in the present embodiment, the dielectric coating material preferably includes an antistatic agent, and the antistatic agent is preferably imidazoline based antistatic agent. When the antistatic agent is not an imidazoline based antistatic agent, the antistatic effect is small and the sheet-strength, sheet ductility or adhesiveness tends to decline.
An antistatic agent is contained by 0.1 part by weight or more and 0.75 part by weight or less, and more preferably 0.25 to 0.5 part by weight with respect to 100 parts by weight of ceramic powder. When an adding quantity of the antistatic agent is too small, the antistatic effect becomes small, while when too large, it is liable that surface roughness of the sheet declines and sheet strength declines. When the antistatic effect is too small, electrostatic easily arises when peeling the carrier sheet as a supporting body from the ceramic green sheet, and a disadvantage that the green sheet gets wrinkled, etc. easily arises.
By using the dielectric coating material, as shown in FIG. 2, a green sheet 10a is formed to be a thickness of preferably 0.5 to 30 μm, and more preferably 0.5 to 10 μm or so on the carrier sheet 30 as a second supporting sheet by the doctor blade method, etc. The green sheet 10a is dried after being formed on the carrier sheet 30.
Temperature of drying the green sheet is preferably 50 to 100° C. and drying time is preferably 1 to 20 minutes. A thickness of the green sheet after drying is contracted to 5 to 25% of that before drying. The thickness of the green sheet 10a after drying is preferably 3 μm or less.
When drying the green sheet 10a, in the present embodiment, as shown in FIG. 3B, as a solvent, other than the first solvent medium having a relatively low boiling point, wherein a binder resin is easy to be dissolved, a second solvent medium having a higher boiling point than that of the first solvent medium is included in the coating material. Accordingly, an evaporation rate of the solvent from the green sheet becomes low and the sheet surface becomes smooth even in the case of an extremely thin green sheet.
Note that, as shown in FIG. 3A, in the case of a coating material including only the first solvent medium as a solvent, the evaporation rate becomes high and the sheet surface tends to become rough.
(2) As shown in FIG. 2, a carrier sheet 20 as a first supporting sheet is prepared separately from the above carrier sheet 30, and a release layer 22 is formed thereon, and on top thereof, an electrode layer 12a having a predetermined pattern is formed. On a surface of the release layer 22 where the electrode layer 12a is not formed, a blank pattern layer 24 having substantially the same thickness as that of the electrode layer 12a is formed.
As the carrier sheets 20 and 30, for example, a PET film, etc. is used, and those coated with silicon, etc. are preferable to improve the release property. Thicknesses of the carrier sheets 20 and 30 are not particularly limited and are preferably 5 to 100 μm.
The release layer 22 preferably contains the same dielectric powder as the dielectric composing the green sheet 10a. Also, the release layer 22 contains a binder, a plasticizer and a release agent other than the dielectric powder. A particle diameter of the dielectric powder may be the same as that of the dielectric particles included in the green sheet but it is preferable to be smaller.
In the present embodiment, a thickness of the release layer 22 is preferably not more than a thickness of the electrode layer 12a, and more preferably, it is set to be a thickness of 60% or less, and further preferably 30% or less.
A method of applying the release layer 22 is not particularly limited, but it has to be formed to be extremely thin, so that an applying method using, for example, a wire bar coater or a die coater is preferable. Note that adjustment of the release layer 22 thickness can be made by selecting a wire bar coater having a different wire diameter. Namely, to make the thickness of the release layer to be applied thinner, it can be done by selecting one having a small wire diameter, inversely, to form it thick, one with a large wire diameter may be selected. The release layer 22 is dried after being applied. The drying temperature is preferably 50 to 100° C. and the drying time is preferably 1 to 10 minutes.
A binder for the release layer 22 is composed, for example, of an acrylic resin, polyvinyl butyral, polyvinyl acetal, polyvinyl alcohol, polyolefin, polyurethane, polystyrene, or an organic composed of a copolymer of these or emulsion. The binder contained in the release layer 22 may be the same as the binder contained in the green sheet 10a or may be different from that, but preferably the same.
A plasticizer for the release layer 22 is not particularly limited and, for example, phthalate ester, dioctyl phthalate, adipic acid, phosphate ester and glycols, etc. may be mentioned. The plasticizer to be contained in the release layer 22 may be the same as that contained in the green sheet or may be different from that.
A release agent for the release layer 22 is not particularly limited and, for example, paraffin, wax and silicone oil, etc. may be mentioned. A release agent contained in the release layer 22 may be the same as that contained in the green sheet or may be different from that.
A binder is contained in the release layer 22 by preferably 2.5 to 200 parts by weight, more preferably 5 to 30 parts by weight, and particularly preferably 8 to 30 parts by weight or so with respect to 100 parts by weight of dielectric particle.
A plasticizer is preferably contained in the release layer 22 by 0 to 200 parts by weight, preferably 20 to 200 parts by weight, and more preferably 50 to 100 parts by weight with respect to 100 parts by weight of the binder.
A release agent is preferably contained in the release layer 22 by 0 to 100 parts by weight, preferably 2 to 50 parts by weight, and more preferably 5 to 20 parts by weight with respect to 100 parts by weight of the binder.
After forming the release layer 22 on the surface of the carrier sheet, an electrode layer 12a to compose an internal electrode layer 12 after firing is formed to be a predetermined pattern on the surface of the release layer 22. A thickness of the electrode layer 12a is preferably 0.1 to 2 μm, and more preferably 0.1 to 1.0 μm or so. The electrode layer 12a may be configured by a single layer or two or more layers having different compositions.
The electrode layer 12a can be formed on the surface of the release layer 22 by a thick film formation method, such as a printing method using an electrode coating material, or a thin film method, such as evaporation and sputtering. When forming the electrode layer 12a on the surface of the release layer 22 by a screen printing method or a gravure printing method as a kind of thick film method, it is as follows.
First, an electrode coating material is prepared. The electrode coating material is fabricated by kneading a conductive material composed of a variety of conductive metals and alloys, or a variety of oxides, organic metal compounds or resinates, etc. to be conductive materials after firing with an organic vehicle.
As a conductive material to be used when producing the electrode coating material, Ni, a Ni alloy and a mixture of these are used. A shape of the conductive materials is not particularly limited and may be a spherical shape and scale-like shape, etc. or a mixture of these shapes. Those having an average particle diameter of the conductive material of normally 0.1 to 2 μm, and preferably 0.2 to 1 μm or so may be used.
An organic vehicle contains a binder and a solvent. As the binder, for example, ethyl cellulose, an acrylic resin, polyvinyl butyral, polyvinyl acetal, polyvinyl alcohol, polyolefin, polyurethane, polystyrene, or a copolymer of these may be mentioned. Particularly, butyrals, such as polyvinyl butyral, are preferable.
The binder is contained in the electrode coating material by preferably 8 to 20 parts by weight with respect to 100 parts by weight of the conductive material (metal powder). As a solvent, any of well-known ones, such as terpionel, butylcarbitol and kerosene, may be used. A content of the solvent is preferably 20 to 55 wt % or so with respect to the entire coating material.
To improve the adhesiveness, the electrode coating material preferably contains a plasticizer. As a plasticizer, benzylbutyl phthalate (BBP) and other phthalate esters, adipic acids, phosphoric esters, and glycols, etc. may be mentioned. The plasticizer in the electrode coating material is preferably 10 to 300 parts by weight, and more preferably 10 to 200 parts by weight with respect to 100 parts by weight of the binder. Note that when an adding quantity of the plasticizer or adhesive is too large, it is liable that strength of the electrode layer 12a remarkably declines. Also, to improve transferability of the electrode layer 12a, it is preferable to improve adhesiveness and/or adherence of the electrode coating material by adding a plasticizer and/or adhesive in the electrode coating material.
After or before forming the electrode coating material layer in a predetermined pattern on the surface of the release layer 22 by a printing method, a blank pattern layer 24 is formed to be substantially the same thickness as that of the electrode layer 12a on the surface of the release layer 22 not formed with the electrode layer 12a. The blank pattern layer 24 is composed of the same material as that of the green sheet and formed by the same method. The electrode layer 12a and the blank layer 24 are dried in accordance with need. The drying temperature is not particularly limited, but is preferably 70 to 120° C., and the drying time is preferably 5 to 15 minutes.
(3) After that, the electrode layer 12a is adhered to the surface of the green sheet 10a. For that purpose, the electrode layer 12a and the blank pattern layer 24 are pressed against the surface of the green sheet 10a together with the carrier sheet 20, heated and pressed to transfer the electrode layer 12a and the blank pattern layer 24 to the surface of the green sheet 10a. Note that when seeing from the green sheet side, the green sheet 10a is transferred to the electrode layer 12a and the blank pattern layer 24.
Heating and pressing at the time of transferring may be pressing and heating by a press or by a calendar roll, but is preferably performed by a pair of rolls. The heating temperature and the pressing force are not particularly limited.
By stacking single-layered green sheets formed with an electrode layer 12a of a predetermined pattern on a green sheet 10a, a stacked block, wherein a large number of the electrode layers 12a and the green sheet 10a are alternately stacked, is obtained. After that, an outer layer green sheet (a little thicker stacked body, wherein a plurality of green sheets not formed with an electrode layer are stacked) is stacked on the lower surface of the stacked body. After that, an outer layer green sheet is formed in the same way on the upper side of the stacked body, then, a final pressing is performed.
Pressure at the time of the final pressing is preferably 10 to 200 MPa. Also, the heating temperature is preferably 40 to 100° C. After that, the multilayer body is cut to be a predetermined size to form green chips. The green chips are subjected to binder removal processing and firing processing, then, thermal treatment is performed in order to re-oxidize the dielectric layer.
The binder removal processing may be performed under a normal condition, but when using a base metal, such as Ni and a Ni alloy, as a conductive material of the internal electrode layer, it is preferably performed under the specific condition below.
temperature rising rate: 5 to 300° C./hour, particularly 10 to 50° C./hour
holding temperature: 200 to 400° C., particularly 250 to 350° C.
holding time: 0.5 to 20 hours, particularly 1 to 10 hours
atmosphere: a mixed gas of wet N2 and H2 
A firing condition is preferably as below.
temperature rising rate: 50 to 500° C./hour, particularly 200 to 300° C./hour
holding temperature: 1100 to 1300° C., particularly 1150 to 1250° C.
holding time: 0.5 to 8 hours, particularly 1 to 3 hours
cooling rate: 50 to 500° C./hour, particularly 200 to 300° C./hour
atmosphere gas: a mixed gas of wet N2 and H2, etc.
Note that oxygen partial pressure in an atmosphere in the air at firing is preferably 10−2 Pa or less, particularly 10−2 to 10−8 Pa. When exceeding the above ranges, the internal electrode layer tends to oxidize, while when the oxygen partial pressure is too low, abnormal sintering is caused in an electrode material of the internal electrode layer to be broken.
The thermal treatment after performing such firing is preferably performed with a holding temperature or highest temperature of 1000° C. or higher, more preferably 1000 to 1100° C. When the holding temperature or the highest temperature at the time of the thermal treatment is lower than the above ranges, it is liable that oxidization of the dielectric material is insufficient to make the insulation resistance lifetime short, while when exceeding the above ranges, Ni in the internal electrode oxidizes and the capacity decreases, moreover, Ni reacts with a dielectric base and the lifetime also tends to become short. The oxygen partial pressure at the time of thermal treatment is higher than a higher oxygen partial pressure than a reducing atmosphere at the time of firing, preferably 10−3 Pa to 1 Pa, and more preferably 10−2 Pa to 1 Pa. When it is lower than the above range, re-oxidization of the dielectric layer 2 becomes difficult, while when exceeding the above ranges, the internal electrode layer 3 tends to oxidize. Other condition of the thermal treatment is preferably as below.
holding time: 0 to 6 hours, particularly 2 to 5 hours
cooling rate: 50 to 500° C./hour, particularly 100 to 300° C./hour
atmosphere gas: wet N2 gas, etc.
Note that to wet a N2 gas or a mixed gas, etc., for example, a wetter, etc. may be used. In this case, the water temperature is preferably 0 to 75° C. or so. Also, the binder removal processing, firing and thermal treatment may be performed continuously or separately. When performing continuously, the atmosphere is changed without cooling after the binder removal processing, continuously, the temperature is raised to the holding temperature at firing to perform firing. Next, it is cooled and the thermal treatment is preferably performed by changing the atmosphere when the temperature reaches to the holding temperature of the thermal treatment. On the other hand, when performing them separately, after raising the temperature to the holding temperature at the binder removal processing in an atmosphere of a N2 gas or a wet N2 gas, the atmosphere is changed, and the temperature is furthermore raised. After cooling the temperature to the holding temperature at the thermal treatment, it is preferable that the cooling continues by changing the atmosphere again to a N2 gas or a wet N2 gas. Also, in the thermal treatment, after raising the temperature to the holding temperature under the N2 gas atmosphere, the atmosphere may be changed, or the entire process of the thermal processing may be in a wet N2 gas atmosphere.
The thus obtained sintered body (element body 4) is subjected to end surface polishing, for example, by barrel polishing and sand-blast, etc., then, a terminal electrode coating material is burnt to form terminal electrodes 6 and 8. For example, a firing condition of the terminal electrode coating material is preferably in a mixed gas of wet N2 and H2 at 600 to 800° C. for 10 minutes to 1 hour or so. In accordance with need, soldering, etc. is performed on the terminal electrodes 6 and 8 to form a pad layer. Note that the terminal electrode coating material may be fabricated in the same way as the electrode coating material explained above.
A multilayer ceramic capacitor of the present invention produced as above is mounted on a print substrate, etc. by soldering, etc. and used for a variety of electronic equipments.
In a method of producing a multilayer ceramic capacitor using the dielectric coating material (green sheet coating material) and the green sheet according to the present embodiment, by using a binder resin including a butyral based resin as the main component and by containing the second solvent medium having a higher boiling point than that of the first solvent medium other than the first solvent medium having a relatively low boiling point, wherein the binder resin is easy to be dissolved, it becomes possible to produce a green sheet without a pin hole having enough strength to be peeled from a supporting body and excellent surface smoothness even if the green sheet was extremely thin. For example, a thickness of a dielectric layer after firing (a green sheet after firing) can be made as thin as 5 μm or less, preferably 3 μm or less, and furthermore preferably 2 μm or less. Also, the number of layers to be stacked can be increased. Furthermore, short-circuiting or other defects can be reduced.
Also, in a production method of a multilayer ceramic capacitor using the dielectric coating material (green sheet coating material) and the green sheet according to the present embodiment, a specific kind of dispersant having a specific range of HLB is used. Therefore, even an extremely thin green sheet of, for example, 5 μm or thinner is strong enough to be peeled from the carrier sheet and has preferable adhesiveness and handlability. Also, surface roughness of the sheet is small and stackability is excellent. Therefore, it becomes easy to stack a large number of green sheets via electrode layers.
Furthermore, in a production method of a multilayer ceramic capacitor using the dielectric coating material (green sheet coating material) and the green sheet according to the present embodiment, an antistatic agent is contained in the dielectric coating material, and the antistatic agent is an imidazoline based antistatic agent. Therefore, even in the case of an extremely thin green sheet of, for example, 5 μm or thinner, it is possible to produce a green sheet having sufficient strength to be peeled from the carrier sheet, wherein static electricity generated at the time of being peeled from the carrier sheet is suppressed, and the adhesiveness and handlability are preferable. Also, surface roughness of the sheet is small and stackability is excellent. Therefore, it becomes easy to stack a large number of green sheets via electrode layers.
Also, in a production method of a multilayer ceramic capacitor according to the present embodiment, a dry type electrode layer can be easily and highly accurately transferred to the surface of the green sheet without damaging or deforming the green sheet.
Note that the present invention is not limited to the above embodiments and may be variously modified within the scope of the present invention.
For example, a method of the present invention is not limited to the production method of multilayer ceramic capacitors and may be applied as a production method of other multilayer type electronic devices.
Below, the present invention will be explained based on further detailed examples, but the present invention is not limited to the examples.
EXAMPLE 1a
Production of Green Sheet Coating Material
As a starting material of ceramic powder, BaTiO3 powder (BT-02 made by Sakai Chemical Industry Co., Ltd.) was used. A ceramic powder subcomponent-additives were prepared to satisfy (Ba0.6Ca0.4)SiO3: 1.48 parts by weight, Y2O3: 1.01 parts by weight, MgCO3: 0.72 wt %, Cr2O3: 0.13 wt % and V2O5: 0.045 wt % with respect to 100 parts by weight of the BaTiO3 powder.
First, only the subcomponent additives were mixed by a ball-mill to obtain slurry. Namely, the subcomponent additives (total amount 8.8 g), 15 g of a solvent, wherein a ratio of ethanol, n-propanol and xylene is 42.5:42.5:15, a dispersant (0.1 g) and a binder (2 wt % (1.1 g as a lacquer adding quantity) of the subcomponent additives) were preliminary ground by a ball-mill for 20 hours, and preliminary ground slurry was obtained.
Next, with respect to 191.2 g of BaTiO3, the preliminary ground slurry of the subcomponent additives: 24 g, ethanol: 123 g, n-propanol: 123 g, xylene: 56 g, diethylene glycol monoethyl ether (DGME): 136 g, mineral spirit: 15 g, a dispersant: 1.4 g, DOP (dioctyl phthalate): 6 g, an imidazoline based antistatic agent: 0.8 g, lacquer of BH-6 (a polyvinyl butyral resin BH-6 made by Sekisui Chemical Co., Ltd. was dissolved in ethanol/n-propanol=1:1): 80 g were mixed by a ball mill for 20 hours to obtain a ceramic coating material (green sheet coating material).
Note that, as a dispersant, a polyethylene glycol based nonionic dispersant (HLB=5 to 6) was used. As a binder, 15% lacquer (BH6 made by Sekisui Chemical Co., Ltd. was dissolved in ethanol/n-propanol=1:1) of BH6 made by Sekisui Chemical Co., Ltd. (polybutyral resin (PVB)) was added as a solid content.
Solvent components in the ceramic coating material include a solvent having a low boiling point composed of ethanol and n-propanol (a first solvent medium) and a solvent having a high boiling point composed of DGME (a second solvent medium). A content of the solvent having a high boiling point (the second solvent medium) in the solvent was 26 wt % with respect to the entire solvent of 100 wt %. Note that a boiling point and a vapor pressure at 25° C. are shown in Table 1.
A polymerization degree of the polybutyral resin as a binder resin was 1400, a butyralation degree thereof was 69±3%, and a residual acetyl group amount thereof was 3±2%. The binder resin was contained by 6 parts by weight in the ceramic coating material with respect to 100 parts by weight of ceramic powder (including ceramic powder subcomponent additives). Also, when assuming that total volume of the ceramic powder, binder resin and plasticizer in the ceramic coating material was 100 volume %, the volume ratio accounted by the ceramics powder was 67.31 volume %.
Also, DOP as a plasticizer was contained in the ceramic coating material by 50 parts by weight with respect to 100 parts by weight of the binder resin. Water was contained by 2 parts by weight with respect to 100 parts by weight of the ceramic powder. The polyethylene glycol based nonionic dispersant as a dispersant was contained by 0.7 part by weight with respect to 100 parts by weight of the ceramic powder.
Also, in the coating material, mineral spirit of at least any one of a hydrocarbon based solvent, industrial gasoline, kerosene and solvent naphtha was added by 5 parts by weight with respect to 100 parts by weight of the ceramic powder.
Viscosity of the coating material was 180 mPa·S. The viscosity of the coating material was measured by using a B-type viscosimeter and using S21 as a rotor, and measurement was made at a temperature of 25° immediately after the coating material was obtained. The rotation rate at the time of measurement was 50 rpm.
Production of Green Sheet
The coating material obtained as above was applied to a PET film as a supporting film by a wire bar coater and dried, so that a green sheet having a thickness of 1 μm was produced. The applying rate was 50 m/min. and the drying condition was a temperature in the drying furnace of 60° C. to 70° C. and drying time of 2 minutes.
Evaluation of Green Sheet
After that, a degree of brilliancy of the green sheet was measured. The degree of brilliancy was obtained by measuring a degree of brilliancy on the green sheet surface by using VGS-1D made by Nippon Denshoku Co., Ltd. based on the JIS Z-8741 (1983) method. The higher a percentage of the degree of brilliance is, the more excellent in surface smoothness. The results are shown in Table 1. In the measurement of the degree of brilliance, those with 38% or higher were determined to be good (o) and the rest were determined to be defect (x).










TABLE 1









Sheet of 1 μm













Vapor Pressure at 25° C.

Evaluation
















Name of
Boiling

Boiling Point ×
Degree
on Degree




Solvent Having
Point
Vapor Pressure
Vapor Pressure
of Brilliance
of Brilliance



High Boiling Point
[° C.]
[Pa]
[° C. · Pa]
[%]
[∘ or x]


















Comparative Example 1a
1-decanol
231
0.8
185
—
x
Not Dried


Example la
DGME
202
17.3
3501
66.1
∘


Example 1b
2BE
170
113.6
19333
59.2
∘


Example 1c
DAA
168
226.6
38100
55.5
∘


Example 1d
1P
138
290.0
40017
50.3
∘


Comparative Example 1b
1-butanol
118
861.8
101433
32.1
x


Comparative Example 1c
xylene
140
1100.4
154062
36.0
x









EXAMPLE 1b
Other than using 2-butoxy ethanol (2BE) instead of DGME as a solvent having a high boiling point, a green sheet was produced in the same way as in the example 1a, and the same evaluation was made. The results are shown in Table 1.
EXAMPLE 1c
Other than using diacetone alcohol (DAA) instead of DGME as a solvent having a high boiling point, a green sheet was produced in the same way as in the example 1a, and the same evaluation was made. The results are shown in Table 1.
EXAMPLE 1d
Other than using 1-pentanol (1P) instead of DGME as a solvent having a high boiling point, a green sheet was produced in the same way as in the example 1a, and the same evaluation was made. The results are shown in Table 1.
COMPARATIVE EXAMPLE 1a
Other than using 1-decanol instead of DGME as a solvent having a high boiling point, a green sheet was produced in the same way as in the example 1a, and the same evaluation was made. The results are shown in Table 1.
COMPARATIVE EXAMPLE 1b
Other than using 1-butanol instead of DGME as a solvent having a high boiling point, a green sheet was produced in the same way as in the example 1a, and the same evaluation was made. The results are shown in Table 1.
COMPARATIVE EXAMPLE 2a
Except that a solvent having a high boiling point is not included, a green sheet was produced in the same way as in the example 1a, and the same evaluation was made. The results are shown in Table 2.









TABLE 2









Sheet of 1 μm












Name of
Adding

Evaluation



Solvent Having
Quantity
Degree of
on Degree



High Boiling
Ratio
Brilliance
of Brilliance



Point
[wt %]
[%]
[∘ or x]















Comparative
non-addition
0.0
36.0
x


Example 2a


Example 2a
DAA
8.8
38.0
∘


Example 2b
DAA
13.0
38.2
∘


Example 2c
DAA
26.1
46.6
∘


Example 2d
DAA
39.1
52.0
∘


Example 2e
DAA
52.1
55.5
∘


Example 2f
DAA
63.0
42.5
∘


Comparative
DAA
75.0
—
x


Example 2b









EXAMPLES 2a to 2f and COMPARATIVE EXAMPLE 2b
Other than using DAA instead of DGME as a solvent having a high boiling point and changing the adding quantity (including xylene) to 8.8 to 75 wt % with respect to 100 wt % of the entire solvent, a green sheet was produced in the same way as in the example 1a, and the same evaluation was made. The results are shown in Table 2. Note that since an adding quantity was too much in the comparative example 2b, it was not possible to make a sheet without drying.
Evaluation
As shown in Table 1, as a result that a solvent having a high boiling point, wherein the boiling point was in a range of 130 to 230° C., was included in the ceramic coating material, it was confirmed that a degree of brilliance of the sheet improved and surface smoothness of the sheet improved.
Also, as shown in Table 1, when assuming that a boiling point of a solvent is T° C. and a vapor pressure of the second solvent medium at 25° C. is α Pa, it was confirmed that a degree of brilliance of the sheet improved and surface smoothness of the sheet improved when a product of T×α is in a range of 2000 to 65000 (° C. ×Pa), and more preferably in a range of 3000 to 50000 (° C.×Pa).
Furthermore, as shown in Table 2, as a result that a solvent having a high boiling point was included by 5 to 70 wt %, and more preferably 8 to 52 wt % with respect to 100 wt % of the entire solvent, it was confirmed that a degree of brilliance of the sheet improved and surface smoothness of the sheet improved.
As explained above, according to the present invention, it is possible to provide a coating material, a green sheet and a method capable of producing a green sheet without a pin hole, having enough strength to be peeled from a supporting body and excellent surface smoothness even when the green sheet is extremely-thin, and being suitable to make an electronic device thinner and multilayered.

## Claims

1. A green sheet coating material containing ceramic powder, a binder resin including a butyral based resin as the main component, and a solvent, wherein
said solvent contains a first solvent medium having a relatively low boiling point, wherein said binder resin is easy to be dissolved, and a second solvent medium having a relatively high boiling point.

2. The green sheet coating material as set forth in claim 1, wherein said second solvent medium contains at least one selected from 1) monohydric alcohol having a carbon number of 5 to 9, 2) ketones containing a cyclic structure and 3) compounds containing two or more functional groups selected from a —OH group, ether and ketone.

3. The green sheet coating material as set forth in claim 1, wherein a vapor pressure of said second solvent medium at the room temperature is lower than that of said first solvent medium.

4. The green sheet coating material as set forth in claim 1, wherein a boiling point of said second solvent medium is in a range of 130 to 230° C.

5. The green sheet coating material as set forth in claim 1, wherein a vapor pressure of said second solvent medium at 25° C. is in a range of 1.3 to 667 Pa.

6. The green sheet coating material as set forth in claim 1, wherein, when assuming that a boiling point of said second solvent medium is T° C. and a vapor pressure of said second solvent medium at 25° C. is α Pa, a product of T×α is in a range of 2000 to 65000 (° C.×Pa).

7. The green sheet coating material as set forth in claim 1, wherein said second solvent medium has a higher boiling point by 50 to 105° C. than a drying temperature at the time of making said green sheet coating material to be a sheet.

8. The green sheet coating material as set forth in claim 1, wherein said second solvent medium is included by 5 to 70 wt % with respect to 100 wt % of the entire solvent.

9. The green sheet coating material as set forth in claim 1, wherein said second solvent medium includes an organic solvent having a higher boiling point by 60 to 150° C. than that of alcohol having the lowest boiling point included in said first solvent medium.

10. The green sheet coating material as set forth in claim 1, wherein said second solvent medium includes an organic solvent having a vapor pressure at 25° C. of 0.1 to 10% of that of alcohol having the highest vapor pressure at 25° C. included in said first solvent medium.

11. The green sheet coating material as set forth in claim 1, wherein said second solvent medium includes at least one selected from the 1) to 3) below.
1) monohydric alcohol having a carbon number of 5 to 9
1-pentanol, 1-hexanol, 1-heptanol, 1-octanol, 1-nonanol, tarpineol
2) ketones containing a cyclic structure
cyclohexanon, isophorone
3) compound containing two or more functional groups selected from a —OH group, ether and ketone
2-ethoxyethanol, 2-butoxyethanol, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diacetone alcohol.

12. The green sheet coating material as set forth in claim 1, wherein said butyral based resin is a polybutyral resin; and
a polymerization degree of said polybutyral resin is 1000 or more and 1700 or less, a butyralation degree of the resin is 64% or higher and 78% or lower, and a residual acetyl group amount is less than 6%.

13. The green sheet coating material as set forth in claim 1, wherein said binder resin is included by 5 parts by weight or more and 6.5 parts by weight or less with respect to 100 parts by weight of said ceramic powder.

14. A production method of a ceramic green sheet, comprising the steps of:
preparing a green sheet coating material as set forth in claim 1; and
forming a ceramic green sheet by using said green sheet coating material.

15. The production method of a ceramic green sheet as set forth in claim 14, wherein a drying temperature at the time of forming a ceramic green sheet by using said green sheet coating material is 50 to 100° C.

16. A production method of a ceramic electronic device, comprising the steps of:
preparing a green sheet coating material as set forth in claim 1;
forming a ceramic green sheet by using said green sheet coating material;
drying said green sheet;
stacking the green sheets after drying via an internal electrode layer to obtain a green chip; and
firing said green chip.

17. The production method of a ceramic electronic device as set forth in claim 16, wherein a drying temperature at the time of drying said green sheet is 50 to 100° C.

18. A green sheet produced by using a green sheet coating material as set forth in claim 1.