Use of ethylene vinyl acetal as a binder for ceramic green sheets

Abstract

The present invention relates to the use of a specific ethylene vinyl acetal as a binder for printing ink. A suspension composition is disclosed that includes one or more inorganic pigments, one or more organic solvents, one or more binders, one or more plasticizers, and one or more dispersants, where the binder is an ethylene vinyl acetal containing 25-60 mol% of ethylene units. A method for producing a ceramic green sheet or a ceramic molded body using the suspension is also disclosed.

Description

[Technical field]

[0001] The present invention is directed to the use of ethylene vinyl acetal as a binder for ceramic green sheets.

[0002] Ceramic materials, such as ceramic capacitors for the electronics industry, are generally produced by sintering so-called green sheets, i.e. thin film-like bodies containing the ceramic material. For the production of such green sheets, a suspension of metal oxides, plasticizers, dispersants and binders in an organic solvent is produced. This suspension is then applied to the desired thickness by a suitable process (i.e. the doctor blade process) onto a carrier film and the solvent is removed. The green sheets thus obtained must be free of cracks, exhibit a smooth surface and still have a certain degree of elasticity.

[0003] Polyvinyl acetals, such as polyvinyl butyral, are frequently used as binders in the production of ceramic green sheets.For this reason, DE 40 03 198 A1 describes the production of casting slips for ceramic green films using polyvinyl butyral as binder with a residual polyvinyl acetate content of 0 to 2% by weight.

[0004] In recent years, multilayer ceramic capacitors (MLCCs) have become increasingly important in the electronics industry. MLCCs consist of several individual capacitors stacked in parallel and contacted via their terminal surfaces. Due to the miniaturization of electronic components, the size of powder particles can be as small as 10 nm. This calls for improved precision in the ceramic sheets used in the production. Furthermore, multilayer stacks of ceramic green sheets are often wound into rolls during the manufacturing process. To avoid delamination, the individual green sheets must have excellent properties in terms of binding strength and elongation at break. This calls for further improvements in the binders used in the suspensions.

[0005] Accordingly, one object of the present invention was to provide a binder for ceramic green sheets that provides improved adhesion, improved elongation at break, improved dispersion effectiveness, improved environmental and safety impacts, and / or a better economic profile in the manufacture and use of ceramic green sheets.

[0006] It has been found that these and other specific ethylene vinyl acetals are highly suitable as binders for the production of ceramic suspensions and thus for the production of ceramic green sheets.

[0007] Thus, the present invention relates to the use of ethylene vinyl acetal as a binder for the production of ceramic green sheets or ceramic molded bodies, wherein the ethylene vinyl acetal contains ethylene units in the range of 25-60 mol %.

[0008] The ethylene vinyl acetal of the present invention can be obtained by subjecting an aldehyde to an acetalization reaction with ethylene vinyl alcohol (EVOH). Such ethylene vinyl alcohol is known in the art and can be obtained by copolymerizing ethylene in the presence of an acid catalyst. Moreover, ethylene vinyl alcohol is commercially available.

[0009] Preferably, ethylene vinyl alcohol is obtained by copolymerizing ethylene and vinyl acetate and hydrolyzing the copolymer obtained. A conventionally known alkali catalyst or acid catalyst can be used for the hydrolysis reaction, and among them, a hydrolysis reaction using methanol as a solvent and caustic soda (NaOH) as a catalyst is simple.

[0010] Preferably, the percentage of ethylene units in the ethylene vinyl alcohol is from 25 to 60 mol %, more preferably from 30 to 55 mol %, even more preferably from 35 to 50 mol %.

[0011] The reaction product obtained after the acetalization reaction is neutralized with an alkali and then washed with water to obtain ethylene vinyl acetal.

[0012] The catalyst for the acetalization reaction is not particularly limited, and any of organic and inorganic acids can be used, examples of which include acetic acid, p-toluenesulfonic acid, nitric acid, sulfuric acid, hydrochloric acid, and carbonic acid.

[0013] The degree of saponification of the acetate group is not particularly limited, but is preferably 95 mol % or more, more preferably 98 mol % or more, even more preferably 99 mol % or more, and most preferably 99.9 mol % or more.

[0014] The percentage of ethylene units in the ethylene vinyl acetal is preferably 30 to 55 mol %, more preferably 35 to 50 mol %, and further preferably 50 to 60 mol %.

[0015] Preferably, the acetal groups each have from 1 to 7 carbon atoms, ie, they are derived from a condensation reaction with an aldehyde having from 1 to 7 carbon atoms. More preferably, methanal (formaldehyde), acetaldehyde, n-propanal (propionaldehyde), n-butanal (butyraldehyde), isobutanal (2-methyl-1-propanal, isobutyraldehyde), n-pentanal (valeraldehyde), isopentanal (3-methyl-1-butanal), sec-pentanal (2-methyl-1-butanal), tert-pentanal (2,2,dimethyl-1-propanal), n-hexanal (capronaldehyde), isohexanal (2-methyl-1-pentanal, 3-methyl-1-pentanal, 4-methyl-1-pentanal), 2,2-dimethyl-1-butanal, 2,3-dimethyl-1-butanal, 3, The aldehydes are derived from the list consisting of 3-dimethyl-1-butanal, 2-ethyl-1-butanal, n-heptanal, 2-methyl-1-hexanal, 3-methyl-1-hexanal, 4-methyl-1-hexanal, 5-methyl-1-hexanal, 2,2-dimethyl-1-pentanal, 3,3-dimethyl-1-pentanal, 4,4-dimethyl-1-pentanal, 2,3-dimethyl-1-pentanal, 2,4-dimethyl-1-pentanal, 3,4-dimethyl-1-pentanal, 2-ethyl-1-pentanal, 2-ethyl-2-methyl-1-butanal, 2-ethyl-3-methyl-1-butanal, 3-ethyl-2-methyl-1-butanal, cyclohexylaldehyde and benzaldehyde. Most preferably, it is derived from a condensation reaction with isobutyraldehyde, acetaldehyde and / or n-butyraldehyde.

[0016] Also preferably, the ethylene vinyl acetal according to the present invention is a mixed acetal, i.e., contains at least two different acetal groups.In other words, the ethylene vinyl acetal used in the present invention contains a first acetal group derived from the reaction of two hydroxyl groups of each ethylene vinyl alcohol with an aldehyde, and at least one second acetal group derived from the reaction of the other two hydroxyl groups of each ethylene vinyl alcohol with a second aldehyde, and the first aldehyde is different from the second aldehyde.The preferred aldehydes are the same as those used in the acetal with one acetal group described above; the most preferred combination is a mixture of acetals derived from acetaldehyde and n-butyraldehyde.

[0017] The method for producing the ethylene vinyl acetal used in this embodiment of the present invention is not particularly limited, but it can be produced by a method in which an aldehyde is added to an ethylene vinyl alcohol solution under acidic conditions and the mixture is subjected to an acetalization reaction.

[0018] Preferably, the acetalization degree of the ethylene vinyl acetal used in the present invention is 5 mol% or more and less than 40 mol%, more preferably, the lower limit of the acetalization degree is more than 6 mol%, more than 7 mol%, more than 8 mol%, more than 9 mol%, and most preferably, more than 10 mol%. Furthermore, the upper limit of the acetalization degree is more preferably 38 mol% or less, 36 mol% or less, 34 mol% or less, and 32 mol% or less, in that order, and most preferably, less than 30 mol%.

[0019] Preferably, the percentage of vinyl alcohol units in the ethylene vinyl acetal resin of the present invention is 24 to 71 mol % based on the total monomer units constituting the resin.

[0020] The vinyl alcohol content and vinyl acetate content of ethylene vinyl acetal were determined according to DIN ISO 3681 (acetate content) and DIN ISO 53240 (PVA content). The vinyl acetal content is calculated as the sum of the vinyl alcohol content and the vinyl acetate content determined according to DIN ISO 53401 / 53240 and the remainder necessary to make 100 from ethylene. The degree of acetalization is calculated by dividing the vinyl acetal content by the sum of the vinyl alcohol content, the vinyl acetal content and the vinyl acetate content. The conversion from weight % to mol % is carried out using a formula known to those skilled in the art.

[0021] The ethylene content of ethylene-vinyl acetate copolymer is measured by NMR spectroscopy. First, ethylene vinyl acetal resin is dissolved in ethanol, 2N aqueous hydroxylamine hydrochloride solution and hydrochloric acid are added, the mixture is stirred in a water bath under reflux with a condenser for 4 hours, and after cooling, aqueous ammonia is added. Then, methanol is added to precipitate the polymer, which is washed and dried to obtain an acetylated ethylene vinyl alcohol copolymer. Next, this acetylated ethylene vinyl alcohol copolymer is dissolved in DMSO (dimethyl sulfoxide) at 120 ° C., cooled to room temperature, and then N,N-dimethyl-4-aminopyridine and acetic anhydride are added to it, followed by stirring for 1 hour, and then precipitated with ion-exchanged water and acetone and dried to obtain an ethylene vinyl acetate copolymer. This polymer is dissolved in DMSO-d6 and measured with a 400 MHz proton NMR spectrometer. The obtained spectrum was accumulated 256 times. The molar ratio of ethylene units in the ethylene-vinyl alcohol copolymer is calculated from the intensity ratio of methine protons derived from ethylene units and vinyl acetate units (peaks at 1.1 to 1.9 ppm) to the terminal methine protons derived from vinyl acetate units (peak at 2.0 ppm). Since ethylene units are not affected by the acetalization reaction, the molar ratio (n) of ethylene units in the ethylene-vinyl alcohol copolymer before the acetalization reaction is equal to the molar ratio (n) of ethylene units in the ethylene vinyl acetal resin obtained after the acetalization reaction.

[0022] In a second aspect, the present invention relates to a suspension composition comprising one or more inorganic pigments, one or more organic solvents, one or more binders, one or more plasticizers, and one or more dispersants, wherein the binder is an ethylene vinyl acetal comprising ethylene units in the range of 25-60 mol %.

[0023] Preferably, the acetal groups have 2 to 7 carbon atoms and are derived from the same aldehydes as mentioned above. Most preferably, the ethylene vinyl acetal contains n-butyraldehyde and / or acetaldehyde acetal groups.

[0024] The inorganic pigments can be selected from finely ground granules of paraelectric or ferroelectric materials, titanium dioxide (rutile), preferably modified with additives of zinc, zirconium, niobium, magnesium, tantalum, cobalt and / or strontium, as well as MgNb2O6, ZnNb2O6, MgTa2O6, ZnTa2O6, (ZnMg)TiO3, (ZrSn)TiO4 and Ba2Ti9O 20 or BaTiO3 (barium titanate).The average particle size of the inorganic pigment is preferably about 0.01 to 1 μm.

[0025] The organic solvent may be selected from aromatic compounds such as toluene, xylene, alcohol compounds such as ethyl alcohol, isopropyl alcohol, butyl alcohol, and more preferably mixtures thereof.

[0026] Suitable dispersants include fish oil, phosphate esters, and functional polymers having polyoxyalkylene groups in the side chains, such as the MALIALIM™ series available from NOF America Cooperation.

[0027] In addition to the binder according to the invention, the suspension may contain other components chosen in particular from other binders such as cellulose resins, acrylic resins, vinyl acetate resins, polyvinyl alcohol resins; plasticizers such as polyethylene glycols or phthalates and / or antifoamers.

[0028] The method for producing the suspension composition is not particularly limited. Various dispersion methods can be used, such as a method using a medium mill such as a bead mill, a ball mill, an attritor, a paint shaker, or a sand mill, a method of kneading powdered ceramic, a dispersion medium, a dispersant, a binder, a plasticizer, and the like; and a method using a three-roll mill. The method using a three-roll mill includes a method of dispersing a powdered inorganic pigment together with a dispersant, a binder, a plasticizer, and the like in an organic solvent (mixture).

[0029] Preferably, the powdered ceramic, the dispersant and the solvent (mixture) are premixed and dispersed such that the dispersant is adsorbed on the powdered ceramic. In a second step, the binder is added to the mixture thus formed, followed by mixing and dispersion again.

[0030] The coating film produced by these steps may have a thickness of 0.25 to 25 μm, typically 0.5 to 10 μm. EXAMPLES

[0031] Example 1 - Ethylene Vinyl Acetal 100 parts by weight of an ethylene vinyl alcohol copolymer synthesized by the method described in JP 2016-28139 A was dispersed in 315 parts by weight of 1-propanol containing 44 mol% ethylene units (saponification degree: 99%), and the temperature of the solution was raised to 60°C while stirring. Then, while maintaining the temperature at 60°C, 40 parts by weight of 1M hydrochloric acid was added, followed by 34.2 parts by weight of n-butylaldehyde. As the reaction proceeded, the ethylene vinyl alcohol copolymer dissolved, and the reaction mixture became a homogeneous solution. After 36 hours, 6.4 parts by weight of sodium bicarbonate was added to stop the reaction. 500 parts by weight of 1-propanol was added to the reaction solution to make it uniform, and then 2000 parts by weight of water was added dropwise to precipitate the resin. Then, the filtration and water washing operations were repeated three times, and the obtained solid was vacuum dried at 60°C for 8 hours. The ethylene vinyl acetal thus obtained had an ethylene unit content of 44 mol% and an acetalization degree of 46 mol%.

[0032] (Comparative Example 1 - n-Butyl Acetal) Mowital® polyvinyl acetal resin B75H obtained from Kuraray Europe GmbH contains acetal units generated from n-butyraldehyde and polyvinyl alcohol with no ethylene units in the polymer chain, and is used to prepare the PVB solution. This PVB solution is used as the binder solution for the production of ceramic green sheets. A detailed description of the production of the green sheets is given in the following section.

[0033] Preparation of inorganic dispersions 1.3 g of polyoxyalkylene dispersant (MALIALIM (trademark) series, name: SC-0505K, supplier: NOF) was added to a mixed solvent of 25 g of toluene and 25 g of ethanol, and dissolved by stirring. Next, 130 g of barium titanate powder (manufactured by Fuji Titanium Industry, UQBT-20) and 500 g of ZrO2 beads (diameter: 2 mm) were added to the resulting solution. This organic dispersion was mixed with a roller mixer for 6 to 8 hours.

[0034] Preparation of resin solution A resin solution was prepared by adding 10.4 g of (polyvinyl) acetal resin and 3.95 g of plasticizer 3G8 to a mixed solvent of 59.8 g of ethanol and 59.8 g of toluene. The mixture was stirred to dissolve the resin.

[0035] ·Ceramic green sheet manufacturing The resin solution was added to the obtained inorganic dispersion, and the mixture was mixed for 10 hours using a roller block mixer to obtain a composition for ceramic green sheets.

[0036] The ZrO2 beads were separated from the dispersion using a nylon screen / filter.

[0037] The resulting dispersion was degassed and cast by doctor blade process using an automatic film applicator. Silicone-treated PET (Hostaphan® RN 2 SLK, thickness 75 μm) was used as the casting support. After casting, the film was dried in air for 24 hours (temperature: 23° C., relative humidity: 50%) and then drawn off.

[0038] The resulting film had a thickness of 15 μm and was free of cracks, blisters and defects upon optical evaluation.

[0039] Suitable tensile specimens in the so-called "dogbone" shape were punched out of the green sheets. Eight tensile specimens per type of film were punched out crosswise to the casting direction and inspected by human eyes. For both Example 1 and Comparative Example 1, the four specimens that were considered to have the least scratches due to the punching process were selected for measurement. A universal tensile tester was used for the tensile force measurements. The measurements were carried out under controlled conditions at 23 °C and 50% relative humidity according to DIN EN ISO 527-1 and DIN EN ISO 527-3.

[0040] [Table 1]

[0041] As a result of the tensile test, the breaking elongation of the ceramic green sheet obtained using ethylene vinyl acetal was more than twice as high as that obtained using the standard PVB.

Claims

1. Use of ethylene vinyl acetal as a binder for producing ceramic green sheets or ceramic molded bodies, wherein the ethylene vinyl acetal contains 25 to 60 mol % of ethylene units.

2. 2. The use according to claim 1, wherein the acetal group has 2 to 7 carbon atoms.

3. 3. The use according to claim 1, wherein the ethylene vinyl acetal contains n-butyraldehyde and / or isobutyraldehyde acetal groups.

4. 3. The use according to claim 1, wherein the residual vinyl alcohol in the ethylene vinyl acetal is 15 to 40 mol %.

5. 1. A suspension composition comprising one or more inorganic pigments, one or more organic solvents, one or more binders, one or more plasticizers, and one or more dispersants, wherein the binder is an ethylene vinyl acetal containing ethylene units in the range of 25 to 60 mol %.

6. 6. The suspension composition of claim 5, wherein the acetal group has 2 to 7 carbon atoms.

7. 7. The suspension composition of claim 5 or 6, wherein the ethylene vinyl acetal contains n-butyraldehyde and / or acetaldehyde acetal groups.

8. A method for producing a ceramic green sheet or a ceramic molded body using the suspension composition according to claim 5 or 6.