JP2013045874A - Ceramic paste and ceramic green sheet - Google Patents

Abstract

【選択図】なしDisclosed is a ceramic paste for a multilayer ceramic capacitor, which contains polyvinyl acetal and has both improved coating strength and viscosity stability.
A paste containing an organoboron compound having a partial structure represented by the following formula (I) in a molecule of 3 or more is used. In formula (I), m is 0 or 1, n is an integer of 1 to 3, R ¹ and R ² are each independently a hydrogen atom or an optionally substituted alkyl group. R ¹ and R ² may be bonded to each other.

[Selection figure] None

Description

  The present invention relates to a ceramic paste used for manufacturing a multilayer ceramic capacitor and a ceramic green sheet.

  Polyvinyl acetal typified by polyvinyl butyral is excellent in properties such as adhesion to a substrate, solubility in an organic solvent, and dispersibility of inorganic particles, and is therefore widely used as a binder component in various applications. An example of the application is a ceramic green sheet (hereinafter, also simply referred to as “green sheet”) used for manufacturing a multilayer ceramic capacitor.

  The green sheet is usually formed from a ceramic paste that is a mixture of ceramic powder, a binder resin and a solvent, and additives such as a plasticizer and a dispersant. Specifically, a ceramic paste is applied onto a support, and the solvent is evaporated to form a coating film. Then, the obtained coating film is peeled from the support. The said coating film containing ceramic powder and binder resin is a green sheet, and polyvinyl acetal is used for this binder resin. A multilayer ceramic capacitor is manufactured by laminating green sheets coated with a conductive paste on the surface, firing the obtained green sheet laminate to form a ceramic laminate, and adding external electrodes thereto. Multilayer ceramic capacitors are always required to have a higher capacity and a smaller size. In order to meet this requirement, it is necessary to reduce the thickness of the green sheet. In order to achieve a reduction in the thickness of the green sheet, a ceramic paste that exhibits high strength after coating (shows high coating strength) is required.

  By using a high molecular weight (high polymerization degree) polyvinyl acetal as a binder resin, the coating strength of the ceramic paste is improved. However, high molecular weight polyvinyl acetal has low solubility in a solvent. Even when the minimum solubility can be ensured, the viscosity of the ceramic paste using the high molecular weight polyvinyl acetal is high and tends to be inferior in coatability.

  On the other hand, in Patent Document 1, a crosslinkable polyvinyl acetal having a specific molecular structure and a coating film obtained by crosslinking the polyvinyl acetal by ultraviolet (UV) irradiation, electron beam irradiation or heat treatment using a specific cross-linking agent. A method for improving strength is disclosed. Patent Document 2 discloses an active energy ray-curable ink composition containing a crosslinkable polyvinyl acetal having a specific molecular structure. However, in the techniques disclosed in Patent Documents 1 and 2, after forming a coating film containing polyvinyl acetal, it is necessary to advance the crosslinking reaction by applying some post-treatment such as UV irradiation or heat treatment to the coating film. Further, the modified polyvinyl acetals disclosed in Patent Documents 1 and 2 have high cross-linking reactivity, and although the cross-linking reaction is suppressed in the state of a slurry or an ink composition by using the above specific cross-linking agent. The viscosity stability as the slurry or the ink composition is inferior to that when a general polyvinyl acetal is used. Slurries / compositions with poor viscosity stability have poor coatability and can result in reduced product quality and productivity. In the case of the ceramic paste, although the improvement of the coating film strength can be expected by the modified polyvinyl acetal, it is assumed that stable production of the thinned green sheet becomes difficult.

International Publication No. 2008/143286 JP 2004-269690 A

  Thus, in a coating film forming composition containing polyvinyl acetal as a binder resin, it is difficult to achieve both improvement in coating film strength and viscosity stability of the composition. An object of the present invention is to provide a ceramic paste for a multilayer ceramic capacitor containing polyvinyl acetal, which is compatible with improvement in coating film strength and viscosity stability. Another object of the present invention is to provide a ceramic green sheet for a multilayer ceramic capacitor exhibiting high film strength.

  The present inventors have found that the above object can be achieved by a combination of polyvinyl acetal as a binder resin and an organic boron compound having three or more specific partial structures containing a boron atom as a crosslinking agent, and based on this finding The present invention was completed through further studies.

  The ceramic paste for multilayer ceramic capacitors of the present invention contains an organoboron compound having three or more partial structures represented by the following formula (I) in the molecule, polyvinyl acetal, ceramic powder, and a solvent.

In the formula (I), m is 0 or 1, and n is an integer of 1 to 3. R ¹ and R ² are each independently a hydrogen atom or an optionally substituted alkyl group. R ¹ and R ² may be bonded to each other.

  The ceramic green sheet for a multilayer ceramic capacitor of the present invention is a green sheet obtained by coating the ceramic paste for a multilayer ceramic capacitor of the present invention.

  The ceramic paste of the present invention has a property that the cross-linking reaction of polyvinyl acetal is suppressed in the state of a paste containing a solvent, while the cross-linking reaction sufficiently proceeds after the solvent evaporates and becomes a coating film. ing. Thereby, the favorable viscosity stability as a ceramic paste and the high coating-film intensity | strength compatible with this are brought about.

[Organic boron compounds]
The ceramic paste of the present invention has an organic boron compound (hereinafter simply referred to as “compound (a)”) having three or more partial structures represented by the following formula (I) (hereinafter also simply referred to as “partial structure X”) in the molecule. Also called). The compound (a) can function as a crosslinking agent.

In the formula (I), m is 0 or 1, and n is an integer of 1 to 3. R ¹ and R ² are each independently a hydrogen atom or an optionally substituted alkyl group. R ¹ and R ² may be bonded to each other.

The boron atom of the partial structure X possessed by the compound (a) has a vacant orbit, and the hydroxyl group of polyvinyl acetal is coordinated to the vacant orbit, and the OR ¹ or OR ² group is eliminated from the boron atom instead. As a result, the crosslinking reaction proceeds. Furthermore, another hydroxyl group of polyvinyl acetal may coordinately bond to a new vacant orbit generated in the boron atom, and the remaining OR ¹ group or OR ² group may be detached from the boron atom instead. However, the amount of hydroxyl groups contained in polyvinyl acetal is small compared to polyvinyl alcohol (PVA) before being acetalized, and in the presence of a solvent, this small number of hydroxyl groups is present in the solvent present around the polyvinyl acetal chain. The crosslinking reaction is suppressed by being blocked by molecules. For this reason, it is thought that the ceramic paste of this invention is excellent in viscosity stability.

  On the other hand, when the solvent is removed to form a coating film, the block due to the solvent molecules disappears and the crosslinking reaction proceeds. In the progress of this crosslinking reaction, application of a crosslinking trigger such as UV irradiation, electron beam irradiation and heat treatment to the coating film can be omitted. The compound (a) is an organic compound, and is highly compatible with polyvinyl acetal in a state where there is no block by a solvent. Moreover, in the said state, the compound (a) has the outstanding crosslinkability with respect to polyvinyl acetal. For this reason, it is thought that the coating strength is improved in the ceramic paste of the present invention.

  Furthermore, although the ceramic paste of this invention contains a solvent, the compound (a) is excellent in the solubility to such a solvent. For this reason, in the ceramic paste of this invention, the crosslinking reaction at the time of making it into a coating film advances more uniformly, and coating film strength improves. Moreover, the ceramic paste of the present invention is excellent in coatability, and can further reduce the thickness of the green sheet.

By the way, boric acid (B (OH) ₃ ) is known as a crosslinking agent that contains boron and promotes a crosslinking reaction via a hydroxyl group. However, boric acid is an inorganic substance and has low compatibility with polyvinyl acetal and low solubility in a solvent. For this reason, when boric acid is used as the cross-linking agent, high coating strength as in the ceramic paste of the present invention cannot be obtained.

In the partial structure X, the alkyl group before being substituted in the “optionally substituted alkyl group” which can be R ¹ or R ² is, for example, a methyl group, an ethyl group, an n-propyl group, an isopropyl group, n Carbon number such as -butyl group, isobutyl group, sec-butyl group, t-butyl group, n-pentyl group, n-hexyl group, n-octyl group, 2-ethylhexyl group, n-decyl group, n-dodecyl group 1 to 20 alkyl groups. The volatility of the leaving products (typically R ¹ —OH and R ² —OH) after coordination substitution accompanying the crosslinking reaction, more specifically, the ease of removal of the leaving products by volatilization From the viewpoint, an alkyl group having 1 to 8 carbon atoms is preferable, an alkyl group having 1 to 3 carbon atoms is more preferable, and a methyl group, an ethyl group, and an isopropyl group are more preferable.

The substituent in the “optionally substituted alkyl group” which can be R ¹ or R ² is, for example, an aryl group such as a phenyl group or a naphthyl group; a halogen atom such as a fluorine atom, a chlorine atom or a bromine atom. 0-3 are preferable, as for the number of the substituents in "the alkyl group which may be substituted", 0 or 1 is more preferable, and 0 is still more preferable. When the number of substituents is 0, such R ¹ or R ² is an alkyl group having no substituent.

R ¹ and R ² in the partial structure X may be bonded to each other. R ¹ and R ² are bonded to each other to form a ring structure including two oxygen atoms to which R ¹ and R ² are bonded, and a boron atom to which the two oxygen atoms are bonded. Can do. When the partial structure X has such a ring structure, the thermal stability of the compound (a) is improved, and the handleability of the ceramic paste of the present invention is improved. The form of specific bonding of R ¹ and R ² is not limited. For example, both R ¹ and R ² are “optionally substituted alkyl groups”, and one hydrogen atom from each alkyl group. It is a form corresponding to a structure in which atoms from which hydrogen atoms are removed are bonded to each other.

  In the partial structure X, m is 0 or 1, and n is an integer of 1 to 3. As long as this condition is satisfied, the combination of m and n is not particularly limited. Since the synthesis of the compound (a) is relatively easy, a combination of m = 1 and n = 3, a combination of m = 0 and n = 2 is preferable, and a combination of m = 1 and n = 3 is more preferable.

  Specific examples of the partial structure X are shown in the following formulas (I-1) to (I-12).

  Among the partial structures X represented by the formulas (I-1) to (I-12), the partial structure represented by the formula (I-9) and the partial structure represented by the formula (I-10) are preferable. In this case, the synthesis of the compound (a) is relatively easy, and the compound (a) having the partial structure X has particularly high crosslinkability with respect to polyvinyl acetal. Further, the stability of the ceramic paste containing the compound (a) is stable. Especially high.

  The compound (a) has 3 or more partial structures X in the molecule. When the number of partial structures X in the molecule is 2 or less, sufficient crosslinkability for polyvinyl acetal cannot be obtained. From the viewpoint of crosslinkability with respect to polyvinyl acetal, the number of partial structures X that the compound (a) has in the molecule is preferably 3 to 6, and more preferably 3 or 4. The partial structures X in the molecule of the compound (a) may all be the same structure, some partial structures X may be different, or all partial structures X may be different from each other. From the viewpoint of facilitating the synthesis of the compound (a), it is preferable that all have the same structure.

  The structure of the portion other than the partial structure X in the compound (a) (hereinafter, the portion is referred to as “mother nucleus”) is not particularly limited, but an atom bonded to the partial structure X in the mother nucleus is substituted for the partial structure X. When a hydrogen atom is bonded, a mother nucleus that becomes an optionally substituted aliphatic hydrocarbon and a mother nucleus that becomes an optionally substituted aromatic hydrocarbon are preferable. This optionally substituted aliphatic hydrocarbon includes an optionally substituted alicyclic hydrocarbon. Examples of the substituent in the mother nucleus that becomes an optionally substituted aliphatic hydrocarbon and the mother nucleus that becomes an optionally substituted aromatic hydrocarbon include, for example, a hydroxyl group, an alkoxy group, an amino group, a carboxyl group, and a sulfonic acid group. Amide group, urethane group, urea group and mercapto group. 0-3 are preferable and, as for the number of a substituent, 0 or 1 is more preferable.

  1-10 are preferable and, as for carbon number of a mother nucleus, 2-6 are more preferable.

  Specific examples of the mother nucleus are shown in the following formulas (II-1) to (II-5). The asterisk (*) in the formulas (II-1) to (II-5) indicates a place where the partial structure X is bonded. In addition, an atom does not exist in the position of the asterisk in the mother nucleus of Formula (II-1)-(II-5). When the compound (a) is used, for example, the oxygen atom of the partial structure X (when m in Formula (I) is 1) is located at this position.

  Among the mother nuclei represented by the formulas (II-1) to (II-5), the compound (a) having a crosslinking property necessary for obtaining the effects of the present invention can be prepared at a relatively low cost. The mother nucleus shown in -1) is preferred.

200-5000 are preferable, as for the molecular weight of a compound (a), 300-2500 are more preferable, and 500-1500 are more preferable. When the molecular weight of the compound (a) is excessively small, the boiling point of the compound (a) is low, the compound (a) is easily volatilized during coating of the ceramic paste, and it becomes difficult to play a role as a crosslinking agent. Tend. In addition, when a lower alcohol is contained in the solvent, the boiling point of the compound (a) tends to be lower due to coordination exchange of the OR ¹ group and OR ² group bonded to the boron atom by the lower alcohol. A relatively large molecular weight is desired. When the molecular weight of the compound (a) is excessively large, the solubility in a solvent and the compatibility with polyvinyl acetal tend to decrease.

  The content of boron atoms in the compound (a) (ratio of the mass of all boron atoms of the compound (a) to the mass of the compound (a)) is preferably 1 to 15% by mass, and preferably 2 to 10% by mass. More preferably, 3-7 mass% is further more preferable. When the said content rate is too small, there exists a tendency for the crosslinking | crosslinked property with respect to the polyvinyl acetal of a compound (a) to fall. When the said content rate is too large, there exists a tendency for stability of the ceramic paste containing the said compound to fall.

  Preferred specific examples of the compound (a) are shown in the following formulas (a-1) to (a-15).

  Among the compounds (a) represented by the formulas (a-1) to (a-15), since the synthesis is relatively easy and the performance as a crosslinking agent is particularly high, the formula (a-3), At least one selected from the compounds represented by each of (a-6), (a-9), (a-12) and (a-15) is preferred, and the formulas (a-3) and (a-6) are preferred. , (A-9) and (a-12) are more preferably at least one selected from the compounds represented by each.

  The synthesis method of the compound (a) is not limited, and can be appropriately synthesized by applying a known reaction. For example, a compound (a) having a partial structure X with m = 1 and n = 3 prepares a synthetic precursor in which all the parts that become the partial structure X after the reaction are allyloxy groups, and the precursor is pinacol. It can be easily synthesized by advancing a hydroboration reaction using a boron compound such as borane. For example, a compound (a) having a partial structure X of m = 0 and n = 2 is prepared as a synthetic precursor in which all the parts that become the partial structure X after the reaction are vinyl groups, and the precursor is pinacol. It can be easily synthesized by advancing a hydroboration reaction using a boron compound such as borane. After the synthesis of compound (a), it can be purified by a technique such as distillation, if necessary.

  The ceramic paste of this invention may contain only 1 type of compound (a), and may contain 2 or more types. Moreover, the ceramic paste of the present invention may contain a crosslinking agent other than the compound (a). Crosslinking agents other than compound (a) are boric acid and its salt, for example. The content of the crosslinking agent other than the compound (a) in the ceramic paste of the present invention is preferably 50% by mass or less, and preferably 20% by mass or less based on the total mass of the crosslinking agent other than the compound (a) and the compound (a). More preferably, it is more preferably 5% by mass or less, and particularly preferably 0% by mass (that is, not including a crosslinking agent other than the compound (a)). When the ceramic paste of the present invention contains a cross-linking agent other than the compound (a), depending on the type of the cross-linking agent, in order to advance the cross-linking reaction by the cross-linking agent, after the ceramic paste of the present invention is applied, It may be preferable to apply a trigger. The trigger for crosslinking is, for example, UV irradiation, electron beam irradiation, or heat treatment.

  The content of the compound (a) in the ceramic paste of the present invention is preferably 0.1 to 30 parts by mass, more preferably 0.5 to 20 parts by mass, and 1.0 to 10 parts by mass with respect to 100 parts by mass of the polyvinyl acetal. Part is more preferred.

[Polyvinyl acetal]
The ceramic paste of the present invention contains polyvinyl acetal. Polyvinyl acetal can function as a binder for ceramic powder. Polyvinyl acetal can be obtained by reacting (acetalizing) polyvinyl alcohol (PVA) and an aldehyde in water and / or an organic solvent in the presence of an acid catalyst. PVA is a polymer having vinyl alcohol units as main structural units, and the ratio of the number of moles of vinyl alcohol units to the total number of moles of all structural units constituting PVA is, for example, 50 mol% or more.

  The PVA used for the production of polyvinyl acetal is not particularly limited, and known PVA can be used. PVA is, for example, vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl isobutyrate, vinyl pivalate, vinyl versatate, vinyl caproate, vinyl caprylate, vinyl laurate, vinyl palmitate, vinyl stearate, PVA obtained by saponifying a polymer of vinyl ester monomers such as vinyl oleate, vinyl benzoate and isopropenyl acetate; these vinyl ester monomers and ethylene, propylene, butylene, isopropylene, isobutylene, etc. PVA obtained by saponifying a copolymer of the α-olefins. The vinyl ester monomer is preferably vinyl acetate. In the case of PVA obtained by saponifying a copolymer with α-olefins, ethylene is preferable as the α-olefins.

  PVA may contain a structural unit derived from another monomer other than the monomers described above. The other monomers include, for example, acrylic acid and salts thereof; methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, t-butyl acrylate, Acrylic esters such as 2-ethylhexyl acrylate, dodecyl acrylate, octadecyl acrylate; methacrylic acid and its salts; methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, Methacrylic acid esters such as isobutyl methacrylate, t-butyl methacrylate, 2-ethylhexyl methacrylate, dodecyl methacrylate, octadecyl methacrylate; acrylamide, N-methylacrylamide, N-ethylacrylamide, , N-dimethylacrylamide, diacetone acrylamide, acrylamide propane sulfonic acid and its salts, acrylamide propyl dimethylamine and its salts (quaternary salt etc.), N-methylol acrylamide and acrylamide derivatives such as derivatives thereof; methacrylamide, N-methyl Methacrylamide derivatives such as methacrylamide, N-ethylmethacrylamide, methacrylamidepropanesulfonic acid and salts thereof, methacrylamidepropyldimethylamine and salts thereof (quaternary salts, etc.), N-methylolmethacrylamide and derivatives thereof; methyl vinyl ether, Ethyl vinyl ether, n-propyl vinyl ether, isopropyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, t-butyl vinyl Vinyl ethers such as ether, dodecyl vinyl ether and stearyl vinyl ether; vinyl cyanides such as acrylonitrile and methacrylonitrile; vinyl halides such as vinyl chloride and vinyl fluoride; vinylidene halides such as vinylidene chloride and vinylidene fluoride; allyl acetate; Allyl compounds such as allyl chloride; maleic acid and its salts, esters and acid anhydrides; vinylsilyl compounds such as vinyltrimethoxysilane.

  The aldehyde used for the acetalization of PVA is not particularly limited. For example, formaldehyde (including paraformaldehyde), acetaldehyde (including paraacetaldehyde), propionaldehyde, n-butyraldehyde, amylaldehyde, hexylaldehyde, heptylaldehyde, 2- It is ethylhexyl aldehyde, cyclohexyl aldehyde, furfural, glyoxal, glutaraldehyde, benzaldehyde, 2-methylbenzaldehyde, 3-methylbenzaldehyde, 4-methylbenzaldehyde, p-hydroxybenzaldehyde, m-hydroxybenzaldehyde, phenylacetaldehyde, β-phenylpropionaldehyde. . In the acetalization of PVA, one of these aldehydes may be used alone or two or more of them may be used in combination. Among these aldehydes, formaldehyde, acetaldehyde, and n-butyraldehyde are preferable, and n-butyraldehyde is more preferable from the viewpoint of easy production of polyvinyl acetal.

  The polyvinyl acetal is, for example, polyvinyl formal, polyvinyl acetoacetal, or polyvinyl butyral.

  Although the polymerization degree of the polyvinyl acetal which the ceramic paste of this invention contains is not specifically limited, It is preferable that it is 100-3000, The lower limit is more preferable 300 or more, The upper limit has more preferable 2500 or less. If the degree of polymerization of the polyvinyl acetal is too small, sufficient coating strength cannot be ensured, and the strength of the formed green sheet may decrease. When the polymerization degree of polyvinyl acetal is excessively large, the viscosity as a ceramic paste increases, and the coatability may decrease. Since the degree of polymerization of polyvinyl acetal coincides with the degree of polymerization of PVA before being acetalized, the degree of polymerization of polyvinyl acetal is determined by determining the degree of polymerization of PVA. In the present specification, the degree of polymerization of PVA before acetalization is an average degree of polymerization measured in accordance with the provisions of JIS K6726-1994, and the PVA before acetalization is re-saponified and purified. Later, it can be determined from the intrinsic viscosity measured in a constant temperature bath maintained at 30 ° C.

  The acetalization degree of the polyvinyl acetal contained in the ceramic paste of the present invention is preferably 50 to 95 mol%, more preferably 50 to 85 mol%, still more preferably 55 to 80 mol%, and particularly preferably 60 to 75 mol%. When the degree of acetalization is excessively small, the solubility in a solvent is lowered, the coating film strength is lowered, and the formation of a ceramic paste may be difficult. When the degree of acetalization is excessively large, the density of the hydroxyl group contained in the polyvinyl acetal is decreased, and the bonding point with the compound (a) is decreased, so that the coating film strength may be decreased. In addition, polyvinyl acetal having an excessively high degree of acetalization is inferior in productivity because long-time acetalization is required for its synthesis.

  The degree of acetalization of polyvinyl acetal is the ratio of the number of moles of the structural unit constituting the acetal unit to the total number of moles of the structural unit constituting the acetal unit, the vinyl alcohol unit and the vinyl ester unit. Here, the acetal unit and the structural unit constituting the acetal unit are considered as follows. The acetal unit is usually formed by acetalizing two vinyl alcohol units. Therefore, the number of moles of the structural unit constituting the acetal unit is usually twice the number of moles of the acetal unit. Moreover, a vinyl ester unit is based on the structural unit derived from said vinyl ester type monomer which PVA used for manufacture of a polyvinyl acetal can have, for example. In the present specification, the number of moles of all structural units constituting the polyvinyl acetal is calculated based on the number of moles of structural units constituting the acetal unit, not the number of moles of the acetal unit.

  The content of vinyl alcohol units in polyvinyl acetal (ratio of the number of moles of vinyl alcohol units to the number of moles of all structural units constituting polyvinyl acetal) is preferably 3 to 50 mol% from the viewpoint of the productivity of polyvinyl acetal, 5-45 mol% is more preferable and 10-40 mol% is further more preferable.

  As for content of polyvinyl acetal in the ceramic paste of this invention, 1-50 mass parts is preferable with respect to 100 mass parts of ceramic powder.

[Ceramic powder]
The ceramic powder contained in the ceramic paste of the present invention is not particularly limited. For example, various ceramic powders such as barium titanate, alumina, zirconia, aluminum silicate, titanium oxide, zinc oxide, magnesia, sialon, spinel, mullite, glass, silicon carbide, silicon nitride, and aluminum nitride. The ceramic paste of the present invention may contain only one kind of ceramic powder, or may contain two or more kinds of ceramic powder.

  The average particle diameter of the ceramic powder is appropriately selected according to the thickness of the green sheet to be formed. The average particle size of the ceramic powder is preferably 10 μm or less, and more preferably 1 μm or less. The average particle diameter of the ceramic powder can be measured by a light scattering method.

  The content rate of the ceramic powder in the ceramic paste of the present invention is not particularly limited. The content is preferably 20 to 80% by mass, and more preferably 30 to 75% by mass.

[solvent]
The solvent contained in the ceramic paste of the present invention is not particularly limited, and a solvent capable of dissolving the compound (a) and polyvinyl acetal can be used. Specific examples of the solvent are methanol, ethanol, propanol, butanol, toluene, xylene, acetone, methyl ethyl ketone, dioxane, tetrahydrofuran, and ethyl acetate. Among these solvents, a protic polar solvent is preferable because methanol has a strong effect of suppressing the crosslinking reaction by the compound (a) in the paste state, and methanol and ethanol are particularly preferable. The ceramic paste of the present invention may contain only one type of solvent, or may contain two or more types of solvent. The content rate of a solvent is not specifically limited, 10-80 mass% of the whole ceramic paste containing a solvent is preferable, and 15-70 mass% is more preferable.

[Additive]
The ceramic paste of this invention can contain an additive as needed. Additives are, for example, plasticizers, dispersants, lubricants, antistatic agents, and antifoaming agents. When the ceramic paste of the present invention contains an additive, the content of the additive in the ceramic paste is preferably 0.1 to 3% by mass, more preferably 0.1 to 1% by mass, excluding the plasticizer.

  The plasticizer is not particularly limited, and examples thereof include phthalic acid plasticizers such as dioctyl phthalate, benzylbutyl phthalate, dihexyl phthalate, di (2-ethylhexyl) phthalate, and di (2-ethylbutyl) phthalate; adipic acid Adipic acid plasticizers such as dihexyl; glycol plasticizers such as ethylene glycol and triethylene glycol; triethylene glycol dibutyrate, triethylene glycol di (2-ethylbutyrate), triethylene glycol di (2-ethylhexano) Glycol ester plasticizers such as Only one type of plasticizer may be used, or two or more types may be used in combination. When the ceramic paste of this invention contains a plasticizer, 0.1-10 mass% is preferable and, as for the content rate of the plasticizer in a ceramic paste, 1-8 mass% is more preferable.

[Method of forming ceramic paste]
The ceramic paste of the present invention can be formed by mixing the above-mentioned compound (a), polyvinyl acetal and ceramic powder, and, if necessary, an additive with a solvent. For mixing, a mixing device such as a ball mill can be used, and mixing may be performed while applying heat as necessary. For example, the above-described materials are mixed at a temperature of 0 to 100 ° C. for 1 to 100 hours. You may perform various processes, such as a defoaming process, after mixing as needed.

[Green sheet]
The green sheet of the present invention is manufactured by applying the ceramic paste of the present invention. Coating is performed, for example, on a support. In the coating film of the ceramic paste of the present invention formed by coating, the cross-linking reaction of polyvinyl acetal with the compound (a) proceeds with the volatilization of the solvent, and a green sheet having high film strength is produced. The support is preferably made of polyester such as polyethylene terephthalate (PET). The polyester support is excellent in the peelability of the green sheet obtained by coating. The support is, for example, a sheet or a film.

  The green sheet of the present invention usually contains a ceramic powder and a cross-linking reaction product of compound (a) and polyvinyl acetal. In such a green sheet, the ceramic powder is dispersed in the crosslinking reaction product.

  Hereinafter, the present invention will be described in more detail with reference to examples. The present invention is not limited to the following examples.

  First, a method for evaluating the characteristics of the ceramic paste and the green sheet produced in this example will be described.

[Viscosity stability]
The viscosity stability of the produced ceramic paste was evaluated as follows.

  Using a viscometer (Brookfield, LVDV-II + Pro), the viscosity of the prepared ceramic paste was measured immediately after the paste was prepared, and when the paste was left at 25 ° C. for two weeks, and at two points in time. The case where the viscosity after standing was 3 times or more compared with the viscosity immediately after production was judged as unacceptable (x), and the case where it was less than 3 times was judged as good (◯).

[Membrane strength]
A test piece having a size of 8 cm × 1 cm was cut out from the produced green sheet, and a tensile test was performed on the test piece using an autograph (manufactured by Shimadzu Corporation, AG5000-B). The tensile speed of the test piece was 8 mm / min, and the test piece was pulled in the long side direction. The tensile test was performed 5 times while exchanging the test pieces with respect to the same green sheet, and the average of the maximum tensile strength values measured each time was defined as the film strength (N / mm ² ) of the green sheet.

(Synthesis Example 1)
In Synthesis Example 1, an organoboron compound (a) represented by the following formula (a-3) was synthesized.

After 4.6 parts by mass of glycerin, 20 parts by mass of sodium hydroxide, 5.8 parts by mass of tetrabutylammonium bromide and 20 parts by mass of water were stirred and stirred, 27.6 parts by mass of allyl chloride was added, The mixture was further stirred at 60 ° C. for 12 hours. Ethyl acetate and saturated brine were added to the obtained mixture and stirred, and then the organic layer was taken out by liquid separation, concentrated, and distilled under reduced pressure to obtain glycerin triallyl ether. The analysis results of proton nuclear magnetic resonance ( ¹ H-NMR, 270 MHz, heavy solvent: deuterated chloroform (CDCl ₃ ), reference substance: tetramethylsilane (TMS)) for the obtained glycerin triallyl ether are shown below.

Chemical shifts δ (ppm): 3.5-3.6 (4H , OCHCH * 2 O), 3.65-3.75 (1H, OCH * CH 2 O), 4.0-4.1 (4H, ^{_{CH 2 OCH * 2 CH = CH}} 2), 4.1-4.2 (2H, CHOCH * 2 CH = CH 2), 5.1-5.3 (6H, OCH 2 CH = CH * 2), 5 ^{_{.8-6.0 (3H, OCH 2 CH *}} = CH 2)

Next, 1.75 parts by mass of tris (triphenylphosphine) rhodium chloride, 84 parts by mass of tetrahydrofuran, and 8.7 parts by mass of pinacol borane were charged into another reactor, and 4.0 glycerin triallyl ether prepared as described above was added thereto. After adding part by mass and stirring at room temperature for 1 hour, the mixture was further heated to reflux for 1 hour. After adding ethyl acetate and water to the obtained mixture and stirring, the organic layer was taken out by liquid separation, concentrated, and distilled under reduced pressure to obtain an organoboron compound represented by the formula (a-3). The analysis results of proton nuclear magnetic resonance ( ¹ H-NMR, 270 MHz, heavy solvent: DMSO-d ₆ , reference substance: tetramethylsilane (TMS)) for the obtained organic boron compound are shown below.

Chemical shifts δ (ppm): 0.9-1.0 (6H , CH 2 CH * 2 B), 1.27 (36H, BOCCH * 3), 1.5-1.7 (6H, OCH 2 CH * _{2 CH 2 B), 3.3-3.6 (} 11H, OCHCH * 2 O, OCH * CH 2 O, OCH * 2 CH 2 CH 2 B)

(Synthesis Example 2)
In Synthesis Example 2, an organoboron compound (a) represented by the following formula (a-12) was synthesized.

50 parts by mass of pentaerythritol triallyl ether, 36 parts by mass of sodium hydroxide, 7.0 parts by mass of tetrabutylammonium bromide and 36 parts by mass of water were added to the reactor and stirred, and then 27.7 parts by mass of allyl chloride was added. The mixture was further stirred at 60 ° C. for 9 hours. Ethyl acetate and saturated brine were added to the obtained mixture and stirred, and then the organic layer was taken out by liquid separation, concentrated, and distilled under reduced pressure to obtain pentaerythritol tetraallyl ether. The analysis results of proton nuclear magnetic resonance ( ¹ H-NMR, 270 MHz, heavy solvent: deuterated chloroform (CDCl ₃ ), reference substance: tetramethylsilane (TMS)) for the obtained pentaerythritol tetraallyl ether are shown below.

Chemical shifts δ (ppm): 3.47 (8H , CCH * 2 O), 3.9-4.0 (8H, OCH * 2 CH = CH 2), 5.1-5.3 (8H, OCH 2 _{^{CH = CH * 2), 5.8-6.0}} (4H, OCH 2 CH * = CH 2)

Next, 1.5 parts by mass of tris (triphenylphosphine) rhodium chloride, 88.4 parts by mass of tetrahydrofuran and 17.7 parts by mass of pinacolborane were charged into another reactor, and the pentaerythritol tetraallyl ether prepared above was added thereto. 10.0 parts by mass was added, and the mixture was stirred at room temperature for 1 hour, and then further heated to reflux for 1 hour. After adding ethyl acetate and water to the obtained mixture and stirring, the organic layer was taken out by liquid separation, concentrated, and distilled under reduced pressure to obtain an organoboron compound represented by the formula (a-12). The analysis results of proton nuclear magnetic resonance ( ¹ H-NMR, 270 MHz, heavy solvent: DMSO-d ₆ , reference substance: tetramethylsilane (TMS)) for the obtained organic boron compound are shown below.

Chemical shifts δ (ppm): 0.85-0.95 (8H , CH 2 CH * 2 B), 1.27 (48H, BOCCH * 3), 1.5-1.7 (8H, OCH 2 CH * ₂ CH ₂ B), 3.3-3.5 (16H, CCH ^* ₂ O, OCH ^* ₂ CH ₂ CH ₂ B)

Example 1
Barium titanate particles as ceramic particles (average particle size 0.1 μm (measured by light scattering method using dynamic light scattering device “DLS-7000” manufactured by Otsuka Electronics Co., Ltd.), Sakai Chemical Industry, BT-01) 25 g 15 g of acetone and 15 g of toluene as a solvent, polyvinyl butyral (a polyvinyl alcohol having a polymerization degree of 300 acetalized with n-butyraldehyde. Degree of acetalization: 63.5 mol%, vinyl alcohol unit content: 35 mol%, 1% of vinyl acetate unit content: 1.5 mol%), 0.5 g of Marialim AKM (manufactured by NOF Corporation) as a dispersant, 1 g of benzylbutyl phthalate as a plasticizer, and the organoboron compound prepared in Synthesis Example 1 Put 0.03g in a ball mill, temperature 20 ° C, rotation speed 100rpm Mixed 20 hours to obtain a ceramic paste (P1). Next, the obtained ceramic paste (P1) was applied on a support sheet made of polyethylene terephthalate (PET) so that the film thickness after drying was 25 μm, and the whole was dried at 30 ° C. for 5 hours. It dried at 120 degreeC for 2 hours, the coating film formed on the support sheet was peeled from the said sheet | seat, and the green sheet (G1) was obtained.

(Example 2)
A ceramic paste (P2) and a green sheet (G2) were obtained in the same manner as in Example 1 except that 0.03 g of the organic boron compound prepared in Synthesis Example 2 was used instead of the organic boron compound prepared in Synthesis Example 1. )

(Comparative Example 1)
A ceramic paste (P3) and a green sheet (G3) were obtained in the same manner as in Example 1 except that no organic boron compound was added.

(Comparative Example 2)
A ceramic paste (P4) and a green sheet (G4) were obtained in the same manner as in Example 1 except that 0.03 g of boric acid was used instead of the organic boron compound prepared in Synthesis Example 1.

(Comparative Example 3)
The ceramic paste (P5) and the green sheet (G5) were the same as in Example 1 except that 0.03 g of hexamethylene diisocyanate (manufactured by Tokyo Chemical Industry Co., Ltd.) was used instead of the organoboron compound prepared in Synthesis Example 1. Got.

(Comparative Example 4)
A ceramic paste (P6) and a green sheet (in the same manner as in Example 1 except that 0.03 g of pyromellitic dianhydride (manufactured by Tokyo Chemical Industry Co., Ltd.) was used instead of the organoboron compound prepared in Synthesis Example 1. G6) was obtained.

  The evaluation results of the viscosity stability of the ceramic pastes (P1) to (P6) and the film strengths of the ceramic green sheets (G1) to (G6) of Examples and Comparative Examples thus prepared are shown in Table 1 below. . In Table 1, the content of polyvinyl acetal in the produced ceramic paste is 100 parts by mass, and the content (parts by mass) of the organic boron compound, boric acid, hexamethylene diisocyanate or pyromellitic dianhydride with respect to the content is shown. Also shown.

  As shown in Table 1, although the ceramic pastes (P3) and (P4) of Comparative Examples 1 and 2 were good in terms of viscosity stability, the films of the green sheets (G3) and (G4) obtained from the ceramic paste The strength was inferior. On the other hand, although the film strength of the green sheets (G5) and (G6) obtained from the ceramic pastes (P5) and (P6) of Comparative Examples 3 and 4 was high, the viscosity stability of the ceramic paste was low. On the other hand, the ceramic pastes (P1) and (P2) of the examples are excellent in viscosity stability and high in coating strength, and both properties are compatible. The green sheets (G1) obtained from the ceramic paste ) And (G2) film strength was high.

  The ceramic paste for a multilayer ceramic capacitor of the present invention is suitable for forming a ceramic green sheet used for manufacturing a multilayer ceramic capacitor. The ceramic green sheet for a multilayer ceramic capacitor of the present invention is used for manufacturing a multilayer ceramic capacitor.

Claims (7)

A ceramic paste for multilayer ceramic capacitors, comprising an organic boron compound having a partial structure represented by the following formula (I) in a molecule of 3 or more, polyvinyl acetal, ceramic powder, and a solvent.

In the formula (I), m is 0 or 1, and n is an integer of 1 to 3. R ¹ and R ² are each independently a hydrogen atom or an optionally substituted alkyl group. R ¹ and R ² may be bonded to each other.   The ceramic paste for a multilayer ceramic capacitor according to claim 1, wherein the number of the partial structures of the organoboron compound is 3 or more and 6 or less.   The ceramic paste for multilayer ceramic capacitors according to claim 1 or 2, wherein m in the formula (I) is 1 and n is 3. The organic boron compound is at least one selected from compounds represented by each of the following formulas (a-3), (a-6), (a-9) and (a-12): The ceramic paste for multilayer ceramic capacitors as described.

  The ceramic paste for multilayer ceramic capacitors according to any one of claims 1 to 4, wherein the degree of acetalization of the polyvinyl acetal is 50 to 95 mol%.   The ceramic paste for multilayer ceramic capacitors according to any one of claims 1 to 5, wherein the ceramic paste contains 0.1 to 30 parts by mass of the organoboron compound with respect to 100 parts by mass of the polyvinyl acetal.   A ceramic green sheet for a multilayer ceramic capacitor obtained by coating the ceramic paste for a multilayer ceramic capacitor according to any one of claims 1 to 6.