JP2011230943A - Ceramic green sheet and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a mechanically strong ceramic green sheet with cracks suppressed in punching, and a method for manufacturing the same.SOLUTION: The ceramic green sheet 3 is manufactured by binding ceramic powder 1 using a binder 2 made of an organic resin, wherein the binder 2 contains a first phase 2a mainly composed of a polyvinyl acetal chain and a second phase 2b mainly composed of a polyalkylene oxide chain. Because the polyvinyl acetal chain of the first phase 2a is block-copolymerized with the polyalkylene oxide chain of the second phase 2b, the ceramic green sheet 3 has a sea-island structure where the first phase 2a is a sea and the second phase 2b is an island. The first phase 2a makes the binder 2 mechanically strong, while the flexible second phase 2b suppresses development of cracks C.

Description

  The present invention relates to a ceramic green sheet for producing an insulating substrate made of a ceramic sintered body used in a wiring board such as an electronic component mounting board, and a method for producing the same.

  Conventionally, as a wiring board used for mounting electronic components such as semiconductor elements and surface acoustic wave elements, circuit-like wiring and penetration are formed on an insulating substrate made of an aluminum oxide sintered body by a method such as metallization or plating. A wiring board on which a wiring conductor such as a conductor is attached is often used. Such an insulating substrate is generally manufactured by laminating a plurality of ceramic green sheets and then firing the laminate. The wiring conductor is coated or filled with a paste of a metal material such as tungsten or copper (conductor paste) on the surface of the ceramic green sheet or inside the through hole formed by punching the ceramic green sheet. It is formed by co-firing with a sheet.

  Conventionally, a general ceramic green sheet is obtained by bonding ceramic powders of raw materials such as aluminum oxide, silicon oxide, and calcium oxide with a binder made of a polymer such as polyvinyl acetal such as polyvinyl butyral or an acrylic polymer.

  In addition, such a ceramic green sheet is usually prepared by first adding ceramic powder and the polymer used as the binder to an organic solvent and kneading to prepare a slurry mainly composed of the ceramic powder, the binder, and the organic solvent. Thereafter, the slurry is formed into a sheet by a method such as a doctor blade method or a lip coater method, and unnecessary organic solvents are removed by heating. In this slurry, the ceramic powder and the binder are almost uniformly dispersed in the organic solvent, and therefore, with the removal of the unnecessary organic solvent, the ceramic powder is almost uniformly dispersed and bonded in the binder. .

Japanese Patent Laid-Open No. 10-81657 JP 2000-34265 A

  However, the above-described conventional ceramic green sheet has the following problems.

  That is, when an acrylic polymer is used as the binder, the cohesive force of the acrylic polymer chain constituting the acrylic polymer is weak, and its elastic modulus is relatively low, so the mechanical strength of the ceramic green sheet tends to be low There was a problem that there was. In this case, problems such as swelling of the ceramic green sheet due to absorption of the solvent contained in the conductor paste at the time of printing the conductor paste and deformation when stacking a plurality of ceramic green sheets are likely to occur.

When polyvinyl acetal, for example, polyvinyl butyral, is used as the binder, polyvinyl butyral has a rigid molecular structure having a cyclic structure and a strong cohesive force, so that its elastic modulus is relatively high. Therefore, although the mechanical strength of the ceramic green sheet can be increased, since the tensile elongation is low, the ceramic green sheet tends to become brittle as a binder. For example, when punching and forming a through hole in a ceramic green sheet, the stress tends to cause cracks in the ceramic green sheet.

  For such a problem, for example, a means of mixing and using an acrylic polymer and polyvinyl butyral as a binder is conceivable (see, for example, Patent Document 1). However, since the solubility parameter differs between acrylic polymers (such as acrylic esters that become acrylic polymers by polymerization) and polyvinyl acetals (such as vinyl acetate that becomes polyvinyl butyral by polymerization and reaction with butyraldehyde), both Difficult to mix effectively with each other. Further, when the acrylic polymer and polyvinyl butyral are simply copolymerized (for example, see Patent Document 3), the mechanical strength of the ceramic green sheet can be increased, but the phase composed of the acrylic polymer chain There is a possibility that it is easy to macroscopically separate into a phase composed of polyvinyl butyral chains. For this reason, mechanical strength is partially increased and decreased in the binder, and it is difficult to effectively suppress the generation and progress of cracks such as the formation of the above-described through holes.

  The present invention has been completed in view of such conventional problems, and the object thereof is to effectively increase the mechanical strength and, for example, the stress associated with the formation of a through-hole or the like. Even if it acts, it is providing the ceramic green sheet which can suppress generation | occurrence | production and progress of a crack effectively, and its manufacturing method.

  The ceramic green sheet of the present invention is a ceramic green sheet formed by bonding ceramic powder with a binder made of an organic resin, and the binder includes a first phase mainly composed of a polyvinyl acetal chain and a polyalkylene oxide chain. A second phase as a main component, and the first phase and the second phase are obtained by block copolymerization of the polyvinyl acetal chain of the first phase on the polyalkylene oxide chain of the second phase. A sea-island structure in which the first phase is the sea and the second phase is an island is bonded to each other.

  The ceramic green sheet of the present invention is characterized in that, in the above configuration, the polyvinyl acetal chain is a polyvinyl butyral chain, and the polyalkylene oxide chain is a polyethylene oxide chain.

The method for producing a ceramic green sheet according to the present invention comprises preparing a slurry by kneading a binder made of an organic resin and ceramic powder together with an organic solvent, and then forming the slurry into a sheet shape and removing the organic solvent to remove the ceramic. In the method for producing a ceramic green sheet in which powder is bonded with the binder,
Preparing the binder, a macroazo compound in which a plurality of polyethylene oxide chains are bonded via an azo group;
Using the azo group of the macroazo compound as a polymerization initiator, vinyl acetate is radically polymerized at the end of the polyethylene oxide chain and then saponified to prepare a water-soluble block copolymer of the polyethylene oxide chain and the polyvinyl alcohol chain. And a process of
A first phase mainly composed of polyvinyl butyral chain formed by acetalization of polyvinyl alcohol by selectively reacting butyraldehyde with the polyvinyl alcohol chain of the block copolymer using an organic carboxylic acid as a catalyst. And a step of preparing a copolymer having a sea-island structure in which the second phase mainly composed of the polyethylene oxide chain is an island.

  According to the ceramic green sheet of the present invention, by using a copolymer of a flexible polyalkylene oxide chain and a polyvinyl acetal chain having high mechanical strength as a binder, cracks are generated when punching through holes or the like. It is possible to provide a ceramic green sheet that is difficult to deform and has high mechanical strength (difficult to deform and has high dimensional stability). That is, the mechanical strength as the binder can be increased by the sea portion composed of the first phase mainly composed of the polyvinyl acetal chain having a relatively high mechanical strength. Further, even if cracks occur in the first phase, which is the sea mainly composed of this polyvinyl butyral chain, the progress of the cracks is mainly caused by the high elongation rate at the time of mechanical pulling and flexible polyalkylene oxide chains. It can suppress in the 2nd phase which is an island made into a component. The polyalkylene oxide chain has a flexible molecular structure because the ether bond is easy to move. Moreover, since the ether bond forms a hydrogen bond with the hydroxyl group on the surface of the metal oxide (such as aluminum oxide) of the ceramic powder, the ceramic particles can be dispersed well. Accordingly, the ceramic green sheet capable of effectively increasing the mechanical strength and effectively suppressing the occurrence and progression of cracks even when stress associated with the formation of through-holes acts, for example. Can be provided.

  Further, in the ceramic green sheet of the present invention, when the polyvinyl acetal chain is a polyvinyl butyral chain and the polyalkylene oxide chain is a polyethylene oxide chain, mechanical strength is improved and cracks are suppressed more reliably. Possible ceramic green sheets can be provided.

  That is, since the polyvinyl butyral chain has high solubility in an organic solvent such as toluene, it is easier to knead with an organic solvent and ceramic particles to form a slurry (slurry). In addition, since the glass transition temperature is relatively low at about 50 to 60 ° C., it has good flexibility as a binder in the ceramic green sheet. Moreover, since the polyethylene oxide chain has a low glass transition temperature of about −50 ° C., the second phase that is an island can be made more flexible. In addition, since the polyethylene oxide chain has a high polarity and a high hydrogen bonding force among the polyalkylene oxide chains, the polyethylene oxide chain has a strong bonding force to the ceramic particles, which are metal oxides, and can disperse the ceramic powder more favorably.

  According to the method for producing a ceramic green sheet of the present invention, a binder is prepared by the above-described process, and a vinyl acetate radical is prepared using a azo group of a macroazo compound in which a plurality of polyethylene oxide chains are bonded via an azo group as a polymerization initiator. A block copolymer of a polyethylene oxide chain and a polyvinyl alcohol chain can be easily produced by performing polymerization and saponifying the vinyl acetate. Further, by using an organic carboxylic acid as a catalyst, butyraldehyde can be selectively reacted with the polyvinyl alcohol chain of the block copolymer. Therefore, it is easy to produce a block copolymer of a polyethylene oxide chain and a polyvinyl butyral chain, the first phase mainly comprising the polyvinyl butyral chain is the sea, and the second phase mainly comprising the polyethylene oxide chain is the island. It is easy to produce a binder as a sea-island structure copolymer. And since ceramic powder can be combined with this sea-island structure binder, a ceramic green sheet having high mechanical strength and capable of effectively suppressing defects such as cracks can be manufactured.

It is an expanded sectional view which expands and shows a part of section of the thickness direction about an example of an embodiment of a ceramic green sheet of the present invention. It is an expanded sectional view which expands and shows the part of the binder in FIG. It is sectional drawing which shows 1 process at the time of producing a ceramic substrate using the ceramic green sheet of this invention. (A)-(c) is a structural formula which shows typically an example of the chemical structure of the binder in the ceramic green sheet of this invention, respectively. It is a structural formula which shows typically the sea-island structure of the binder in the ceramic green sheet of this invention. (A)-(c) is reaction formula which shows typically the chemical reaction in the process of preparing a binder in the manufacturing method of the ceramic green sheet of this invention in order, respectively. It is a typical reaction formula for explaining in detail the chemical reaction in FIG. It is sectional drawing which shows an example of the process in which the slurry in the manufacturing method of the ceramic green sheet of this invention is shape | molded in a sheet form.

  The ceramic green sheet of the present invention will be described with reference to the accompanying drawings.

  FIG. 1 is an enlarged cross-sectional view showing a part of the cross section in the thickness direction of the ceramic green sheet of the present invention. FIG. 2 is an enlarged cross-sectional view showing the binder part in FIG. 1 further enlarged. . 1 and 2, 1 is a ceramic powder, and 2 is a binder including a first phase 2a and a second phase 2b. Ceramic powders 1 are bonded together via a binder 2 to form a ceramic green sheet 3.

  For example, as shown in FIG. 3, the ceramic green sheet 3 is subjected to processing such as formation of through holes 11 by mechanical punching and printing of the conductive paste 12, and a plurality of ceramic green sheets 3 as necessary. If the ceramic powders 1 are sintered while the binder 2 is decomposed and removed, the ceramic substrate (not shown) for mounting electronic components or the like is produced. FIG. 3 is a cross-sectional view showing a step in producing a ceramic substrate for mounting electronic components using the ceramic green sheet 3 of the present invention.

  In the ceramic green sheet 3 of the present invention, the binder 2 includes a first phase 2a mainly composed of a polyvinyl acetal chain and a second phase 2b mainly composed of a polyalkylene oxide chain, and the first phase 2a and The second phase 2b is a sea island in which the first phase 2a is the sea and the second phase 2b is the island by block copolymerization of the polyvinyl acetal chain of the first phase 2a to the polyalkylene oxide chain of the second phase 2b Forms a structure and bonds to each other.

  That is, in the binder 2 in the ceramic green sheet 3 of the present invention, a relatively high mechanical strength portion and a relatively flexible portion are combined in a sea-island microphase separation structure. Thus, it is possible to ensure the mechanical strength of the ceramic green sheet 3 and to suppress the progress of cracks and the like.

  According to such a ceramic green sheet 3, a copolymer of a flexible polyalkylene oxide chain (main component of the second phase 2b) and a polyvinyl acetal chain (main component of the first phase 2a) having high mechanical strength. By using as a binder 2, it is possible to provide a ceramic green sheet 3 which is flexible and hardly cracks when punching through holes, and is not easily deformed and has high dimensional stability. That is, the mechanical strength as the binder 2 can be increased by the portion of the first phase 2a which is the sea mainly composed of polyvinyl acetal chains. Further, even if a crack C as shown in FIG. 2 is generated in the sea portion mainly composed of the polyvinyl acetal chain, for example, the progress of the crack C is caused by a flexible polyalkylene having a high mechanical elongation. It can suppress in the 2nd phase 2b which is an island consisting of an oxide chain.

  In this case, when the polyvinyl acetal (for example, polyvinyl butyral) and polyalkylene oxide (for example, polyethylene oxide) produced separately are mixed and used as a binder, both are separated macroscopically (for example, in two upper and lower layers). However, in the ceramic green sheet 3 of the present invention, a copolymer of a polyvinyl acetal chain PVAc and a polyalkylene oxide chain PAO is formed, for example, as shown in FIGS. 4 (a) to 4 (c). Therefore, as shown in FIG. 5, a sea-island structure binder 2 composed of a first phase 2a mainly composed of polyvinyl acetal chain PVAc and a second phase 2b mainly composed of polyalkylene oxide chain PAO can be used. ing. 4A to 4C are structural formulas schematically showing the chemical structure of the binder 2 of the ceramic green sheet 3 of the present invention. FIG. 5 is a structural formula schematically showing the sea-island structure of the binder 2 in the ceramic green sheet 3 of the present invention. In FIG. 4, R2 represents an alkylene group, and R represents an alkyl group or H. 5, parts similar to those in FIGS. 1 and 2 are denoted by the same reference numerals.

  In addition, as for the copolymer of polyvinyl acetal chain PVAc and polyalkylene oxide chain PAO, either one bonded to each other as shown in FIG. 4 (a) or either as shown in FIG. 4 (b). Either one of them may be a plurality of ones, or a plurality of ones may be coupled to each other as shown in FIG. 4 (c).

  The polyvinyl acetal chain PVAc that is the main component of the first phase 2a of the binder 2 is a portion for increasing the mechanical strength of the binder 2, and as described above, the polyalkylene oxide that is the main component of the second phase 2b. Block copolymerized with chain PAO. As the polyvinyl acetal chain PVAc, for example, a polyvinyl formal chain or a polyvinyl butyral chain can be used.

  The polyvinyl acetal chain PVAc can be formed, for example, by reacting an aldehyde such as formaldehyde or butyraldehyde with a polyvinyl alcohol chain to cause acetalization. In this case, not all of the alcohol (hydroxyl group) portion of the polyvinyl alcohol chain is acetalized, so the first phase 2a of the binder 2 is mainly composed of polyvinyl acetal PVAc and contains some other structural portions. It has become a thing.

The number average molecular weight of the polyvinyl acetal chain PVAc is preferably 5000 to 100,000 if the polyvinyl acetal chain PVAc is a polyvinyl butyral chain and the ceramic powder 1 is aluminum oxide, borosilicate glass, or the like. 100000-500000 is more preferable. If the number average molecular weight of the polyvinyl acetal chain PVAc is 50000 or more, the mechanical strength as the binder 2 can be ensured better, and if it is 1000000 or less, it is more effective that the viscosity of the slurry becomes too high. Therefore, it becomes easier to form a sheet more satisfactorily (for example, by suppressing variation in thickness and variation in filling degree of the ceramic powder 1). The number average molecular weight of such polyvinyl acetal chain PVAc can be controlled by the amount of polymerization initiator and the amount of chain transfer agent used during polymerization.

  In addition, the polyalkylene oxide chain PAO, which is the main component of the second phase 2b of the binder 2, improves the flexibility as the binder 2 as described above, and suppresses the progress of cracks in the ceramic green sheet 3. Part. Polyethylene oxide, polypropylene oxide, etc. can be used as the polyalkylene oxide chain PAO.

The polyalkylene oxide chain PAO is produced by cationic polymerization of a corresponding monomer, alkylene oxide. For example, in the case of a polyethylene oxide chain, it is produced by cationic polymerization of ethylene oxide.

  In this case, since the polymerization initiator and the like necessary for the polymerization of the polyalkylene oxide chain PAO are included in the second phase 2b, the second phase 2b is composed mainly of polyethylene oxide PAO, and other products such as a decomposition product of the polymerization initiator. It contains some ingredients.

  The number average molecular weight of the polyalkylene oxide chain PAO is preferably 5000 to 100,000 when the ceramic powder 1 is aluminum oxide, borosilicate glass or the like in the case of polyethylene oxide, for example. If the number average molecular weight is 5,000 or more, the chain length of the polyalkylene oxide chain PAO is sufficiently long, which is advantageous in effectively improving the flexibility as the binder 2, and if it is 100,000 or less, the first phase Copolymerization of 2a with polyvinyl acetal chain PVAc and formation of a sea-island structure with the first phase 2a as the sea and the second phase 2b as an island are easier.

  The number average molecular weight of the polyalkylene oxide chain PAO can be controlled by, for example, the ratio between the polymerization initiator and the monomer (ethylene glycol or the like). That is, if the ratio of the polymerization initiator is increased, the number average molecular weight can be decreased, and if the ratio is decreased, the number average molecular weight can be increased.

  The ceramic powder 1 includes aluminum oxide, silicon oxide, magnesium oxide, calcium oxide, borosilicate glass, lithium glass, ferrite, forsterite, steatite, mullite, zirconia, barium titanate, aluminum nitride, silicon nitride. Etc. are used.

  In addition to the ceramic powder 1 and the binder 2, various additives may be added to the ceramic green sheet 3. Examples of such additives include coloring materials such as titanium oxide, chromium oxide, iron oxide, and molybdenum oxide, phosphate esters such as tributyl phosphate and triphenyl phosphate, DOP (dioctyl phthalate), DBP (dibutyl phthalate), and the like. Plasticizers such as phthalates, and dispersants such as polyacrylic acid, polymethacrylic acid, and polyvinylamine are suitably used.

  The ratio of the first phase 2a and the second phase 2b in the binder 2 may be appropriately set according to the material, the particle size, the shape of the ceramic powder 1 to be used, and the use conditions such as the processing density of the through holes. For example, if the ceramic powder 1 has a small particle size and a large surface area, the ratio of the second phase 2b mainly composed of the polyalkylene oxide chain PAO, which is a flexible component, should be set to about 40 to 80% by mass. That's fine.

The second phase 2b which is an island in the binder 2 is, for example, a spherical or elliptical sphere having a particle size of about 0.1 to 2 μm, and is distributed almost uniformly within the first phase 2a which is the sea.

  Further, the second phase 2b that is an island may be independent of each other, or may be a part of each other bonded together. In the case where the plurality of second phases 2b are partially bonded to each other, for example, the plurality of second phases 2b have a structure connected in a network, so that the mechanical strength of the entire ceramic green sheet 3 is increased. It is more effective for improvement.

  Further, in the ceramic green sheet 3 of the present invention, when the polyvinyl acetal chain PVAc is a polyvinyl butyral chain and the polyalkylene oxide chain PAO is a polyethylene oxide chain, the mechanical strength is improved more reliably, cracks, etc. It is possible to provide the ceramic green sheet 3 capable of suppressing the above.

  That is, since the polyvinyl butyral chain has high solubility in an organic solvent such as toluene, it is easier to knead with an organic solvent and ceramic particles to form a slurry (slurry). In addition, since the glass transition temperature is relatively low at about 50 to 60 ° C., the ceramic green sheet 3 has good flexibility as the binder 2. Further, since the polyethylene oxide chain has a low glass transition temperature of about −50 ° C., the second phase 2b that is an island can be made more flexible. In addition, since the polyethylene oxide chain has a high polarity and a high hydrogen bond strength among the polyalkylene oxide chains PAO, the bond strength to the ceramic particles 1 which are metal oxides is strong, and the ceramic powder 1 can be more favorably dispersed. .

(Production method)
Next, the manufacturing method of the ceramic green sheet of this invention is demonstrated, referring drawings. 6 (a) to 6 (c) are reaction formulas schematically showing the chemical reaction in the step of preparing the binder in the ceramic green sheet manufacturing method of the present invention in order of steps.

  In the method for producing a ceramic green sheet of the present invention, a binder made of an organic resin and ceramic powder are kneaded together with an organic solvent to prepare a slurry, and then the slurry is formed into a sheet and the organic solvent in the slurry is removed. For example, in the manufacturing method in which the ceramic powder 1 is bonded with the binder 2 as shown in FIG. 1, the binder 2 is prepared in the following steps.

  The slurry is formed by a doctor blade method, for example, as shown in FIG. In FIG. 8, 21 is a hopper that holds a certain amount of slurry (no symbol), 22 is a roller, and 23 is a strip of paper. By feeding the belt-like paper 23 at a constant speed by the roller 22 and applying the slurry on the belt-like paper 23 with a constant thickness from the hopper 21, the slurry is formed into a sheet. The coating thickness of the slurry is adjusted by moving (sliding) the doctor blade 24 arranged at the slurry outlet in the hopper 21 up and down. In addition, FIG. 8 is sectional drawing which shows an example of the process of shape | molding a slurry in a sheet form in the manufacturing method of the ceramic green sheet of this invention.

  First, as shown in FIG. 6A, a macro azo compound MA is prepared in which a plurality of polyethylene oxide chains PEO are bonded via an azo group.

  The macroazo compound MA can be synthesized, for example, by a transesterification reaction between dimethyl 2,2′-azobisisobutyrate and a hydroxyl group at the end of the polyethylene oxide chain PEO.

  In this case, the plurality of polyethylene oxide chains PEO to be bonded may have the same molecular weight (number average molecular weight, etc.), or may have different molecular weights.

  Next, as shown in FIG. 6 (b), vinyl acetate VAc is radically polymerized at the end of polyethylene oxide chain PEO using the azo group of macroazo compound MA as a polymerization initiator, and then saponified to form polyethylene oxide chain PEO and polyvinyl oxide. A water-soluble block copolymer with an alcohol chain PVA is prepared.

This step is a preliminary copolymerization and saponification for block copolymerization of the polyvinyl butyral chain PVB to be the first phase 2a of the binder 2 with the polyethylene oxide chain PEO to be the second phase 2b of the binder 2. It is a process. That is, since the polyvinyl butyral chain PVB cannot be directly copolymerized with the polyethylene oxide chain PEO, the polyvinyl alcohol chain PVA is first block copolymerized with the polyethylene oxide chain PEO in this step, and the polyvinyl alcohol chain PVA is converted into polyvinyl in the next step. Butyral chain P
Acetalizes to VB.

  In order for the azo group of the macroazo compound MA to act as the polymerization initiator, for example, the vinyl acetate VAc as a monomer is added to the macroazo compound MA, the macroazo compound MA is 20% by mass, and the vinyl acetate VAc is 80% by weight. And the mixture is stirred at 80 ° C. for 8 hours in an organic solvent under a nitrogen atmosphere to cleave the macroazo compound MA at the azo group portion to generate radicals to radically polymerize vinyl acetate VAc. Good.

  In this case, since a plurality of polyethylene oxide chains PEO were bonded at the azo group part, each polyethylene oxide chain PEO was separated individually as the azo group was cleaved, and vinyl acetate VAc was sequentially radicalized at these ends. Since polymerization is performed, a block copolymer of polyethylene oxide chain PEO and polyvinyl acetate chain (not shown) can be easily produced.

  A block copolymer of polyethylene oxide chain PEO and polyvinyl alcohol chain PVA can be easily prepared by saponifying the block copolymer of polyethylene oxide chain PEO and polyvinyl acetate chain with an alkaline aqueous solution or the like. it can.

  In this case, although the portion of the polyvinyl alcohol chain PVA is hardly soluble in water, since the polyethylene oxide chain PEO is hydrophilic (water-soluble), the polymer is precipitated even if saponification progresses because it is water-soluble as a whole. This is effectively suppressed. Therefore, the saponification degree with respect to the polyvinyl acetate chain can be advanced to about 100%.

  And as shown in FIG.6 (c), butyraldehyde BuAld was made to react selectively with the polyvinyl alcohol chain PVA of the said water-soluble block copolymer using organic carboxylic acid as a catalyst, and the polyvinyl alcohol chain PVA was made. By forming a sea-island copolymer having a first phase 2a mainly composed of acetalized polyvinyl butyral chain PVB as a sea and a second phase 2b mainly composed of a polyethylene oxide chain PEO as an island, a binder is obtained. 2 can be prepared.

  In this step, it is important to use an organic carboxylic acid as a catalyst in order to selectively react butyraldehyde BuAld with the polyvinyl alcohol chain PVA of the water-soluble block copolymer. This is because the block copolymer of polyethylene oxide chain PEO and polyvinyl alcohol chain PVA is water-soluble and highly reactive in aqueous solution. For example, when a strong acid such as hydrochloric acid is used as a catalyst for acetalization, its catalytic action As a result, a side reaction such as cross-linking between molecules occurs, and the solvent becomes insoluble and the dispersion force to the ceramic particles 1 decreases.

  On the other hand, for example, as shown in FIG. 7, if malic acid, citric acid, succinic acid, tartaric acid, acetic acid or the like (malic acid in the example shown in FIG. 7), which is a weak acid organic carboxylic acid, is used as a catalyst, Since the catalytic action is small, the reaction proceeds only at the hydroxyl part in the molecule of the polyvinyl alcohol chain PVA, which is the part that is most likely to react (acetalization). Therefore, it is possible to selectively acetalize the polyvinyl alcohol chain PVA. FIG. 7 is a schematic reaction formula for explaining the chemical reaction in FIG. 6C in detail.

Also in this case, since the polyethylene oxide chain PEO is water-soluble, it is effective that the copolymer of polyethylene oxide chain PEO and polyvinyl butyral chain PVB generated by the reaction precipitates in the aqueous solution containing the weak acid. The acetalization (butyralization) can be advanced by about 100% (relative to the hydroxyl group to be saponified).

  In the binder 2, the polyethylene oxide chain PEO, which is the main component of the second phase 2b, generally has a linear structure and the molecular chain itself is linear, but is a block copolymer as described above. As a result, due to the action of reducing the surface (surface tension or the like), the islands are gathered into a granular shape such as a spherical shape or an elliptical spherical shape.

  One embodiment of the ceramic green sheet of the present invention will be described.

The ceramic powder used was a powder of an aluminum oxide sintered body having an average particle diameter of 1.7 μm as a main component, to which about 3% by mass of silicon oxide and calcium oxide borosilicate glass powder was added. The ceramic green sheet contains 90% by mass of the ceramic powder and 10% by mass of the binder, and the thickness is adjusted to about 100 μm and is produced by a doctor blade method.

In the examples described below, the chemical structure of the binder is analyzed by ¹ H-NMR (proton-nuclear magnetic resonance), and the shape of the second phase that is an island in the first phase that is the sea that constitutes the binder. The confirmation was performed by thinly cutting the ceramic green sheet to obtain a sample, coloring this with an osmium salt, and then observing it with a TEM (transmission electron microscope).

  In the present example, the first phase constituting the binder contained about 99% by mass of the main component polyvinyl butyral chain, and the number average molecular weight was 135,000.

  The first phase contained about 3 mol% of polyvinyl alcohol chains remaining in an unreacted state in the step of converting the polyvinyl alcohol chain into a butyral to form a polyvinyl butyral chain.

The second phase contained about 98 mol% of the main component polyethylene oxide chain. The number average molecular weight of the polyethylene oxide chain was adjusted to 980000 by adding about 0.1 mol% of 2-mercaptoethylamine as a polymerization initiator to the ethylene glycol monomer as the second phase.

  A binder was prepared from the first phase and the second phase, and a ceramic green sheet was prepared by a doctor blade method using the binder.

  The ratio of the second phase in the binder (the ratio of the area in the sample cross section) (%) and the size of the second phase (maximum passing dimension on the observation surface of the sample) (μm) were adjusted to the values in Table 1, About each, the mechanical strength of the ceramic green sheet produced using the binder and the presence or absence of the crack at the time of through-hole formation were confirmed.

The mechanical strength of the ceramic green sheet was confirmed with a tensile measuring instrument. The through hole is formed by mechanical punching using a metal pin, and the opening diameter is 100 μm □
Were arranged vertically and horizontally in a 100 × 100 arrangement so that the distance between adjacent ones was 100 μm. And the presence or absence of the crack was performed by the microscopic inspection by a coloring test.

  The test results are shown in Table 1. In Table 1, the columns * V and * A indicate the ceramic green sheets of the comparative examples, respectively, * V is produced using only polyvinyl butyral as the binder, and * A is only methyl methacrylate as the binder. It was made using.

  As can be seen from the results shown in Table 1, in any of the ceramic green sheets of the present invention, the mechanical strength was high and the occurrence of cracks was effectively suppressed. On the other hand, the ceramic green sheet of the comparative example was produced using only polyvinyl butyral as a binder. * V has high mechanical strength, but a large number of cracks occur to the extent that it cannot be measured, and methyl methacrylate as a binder. In the case of * A produced by using only the material, cracks were suppressed, but the mechanical strength was low. In addition, when a ceramic green sheet is produced under the above conditions, a mechanical strength of about 1 MPa or more is required to suppress deformation during lamination. As described above, it was confirmed that the ceramic green sheet of the present invention has high mechanical strength and can effectively suppress the occurrence of cracks.

DESCRIPTION OF SYMBOLS 1 ... Ceramic powder 2 ... Binder 2a ... First phase 2b ... Second phase 3 ... Ceramic green sheet PAO ... Polyalkylene oxide chain PVAc ... Polyvinyl acetal chain MA ... Macroazo compound PEO・ Polyethylene oxide chain VAc ・ ・ Vinyl acetate PVA ・ ・ Polyvinyl alcohol chain BuAld ・ ・ Butyraldehyde PVB ・ ・ Polyvinyl butyral chain

Claims (3)

A ceramic green sheet formed by bonding ceramic powder with a binder made of an organic resin, wherein the binder includes a first phase mainly composed of polyvinyl acetal chains and a second phase mainly composed of polyalkylene oxide chains. Including
The first phase and the second phase are obtained by block copolymerization of the polyvinyl acetal chain of the first phase to the polyalkylene oxide chain of the second phase, so that the first phase is the sea, A ceramic green sheet characterized by forming a sea-island structure in which two phases are islands and bonding to each other.   The ceramic green sheet according to claim 1, wherein the polyvinyl acetal chain is a polyvinyl butyral chain, and the polyalkylene oxide chain is a polyethylene oxide chain. A ceramic green sheet in which a binder made of an organic resin and a ceramic powder are kneaded with an organic solvent to prepare a slurry, and then the slurry is formed into a sheet and the organic solvent is removed and the ceramic powder is bonded with the binder. In the production method, the step of preparing the binder, a macroazo compound in which a plurality of polyethylene oxide chains are bonded via an azo group;
Using the azo group of the macroazo compound as a polymerization initiator, radical polymerization of vinyl acetate at the end of the polyethylene oxide chain followed by saponification produces a water-soluble block copolymer of the polyethylene oxide chain and polyvinyl alcohol chain And a process of
A first phase mainly composed of polyvinyl butyral chain formed by acetalization of polyvinyl alcohol by selectively reacting butyraldehyde with the polyvinyl alcohol chain of the block copolymer using an organic carboxylic acid as a catalyst. And a step of preparing a sea-island-structure copolymer having the second phase mainly composed of the polyethylene oxide chain as an island.

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