Use of modified polyvinyl acetal as a binder in ceramic green sheets

Abstract

This invention relates to the use of modified polyvinyl acetal as a binder in ceramic green sheets.

Description

Technical Field

[0001] The present invention relates to the use of modified polyvinyl acetal as a binder in a ceramic green sheet.

[0002] Ceramic materials such as ceramic capacitors for the electronics industry are generally produced by sintering a so-called green sheet, i.e., a thin film-shaped molded body containing a ceramic material. For the production of this green sheet, a suspension of metal oxides, plasticizers, dispersants and binders in an organic solvent is produced. Then, this suspension is applied onto a carrier film with a desired thickness by an appropriate process (i.e., doctor blade method), and the solvent is removed. The green sheet thus obtained must be crack-free, have a smooth surface and further have a certain elasticity.

[0003] Polyvinyl acetals such as polyvinyl butyral are often used as binders for producing ceramic green sheets. For this purpose, German Patent Application Publication No. 4003198 describes the production of a casting slip for a ceramic green film in which polyvinyl butyral having a residual polyvinyl acetate content of 0 wt% to 2 wt% is used as a binder.

[0004] In recent years, multilayer ceramic capacitors (MLCCs) have become increasingly important to the electronics industry. An MLCC consists of numerous individual capacitors stacked parallel to each other and in contact via their terminal surfaces. Due to the miniaturization of electronic components, powder particle sizes can be reduced to as small as 10 nm. Therefore, the manufacturing of electronic components requires increased precision in the ceramic sheets used within them. In addition, stacks of ceramic green sheets are often wound into rolls during the manufacturing process. To avoid delamination, individual green sheets must possess excellent properties in terms of bonding and elongation at break. For this purpose, the industry is seeking further improved binders for use in suspensions.

[0005] Therefore, one object of the present invention was to provide a binder for ceramic green sheets that results in improved adhesion, improved dispersion effect, improved environmental and safety impact, and / or has a better economic profile in the manufacture and use of ceramic green sheets, and in particular has improved elongation at break.

[0006] Surprisingly, the inventors have now discovered that using polyvinyl acetal modified with a low concentration of carboxylic acid groups in the polymer chain yields excellent performance in the production of ceramic green sheets.

[0007] Accordingly, the present invention relates to the use of acid-modified polyvinyl acetal as a binder for producing ceramic green sheets or ceramic molded articles, wherein the acid-modified polyvinyl acetal contains carboxyl units in the range of 0.5 mol% to 1.5 mol%, the carboxyl units are derived from dicarboxylic acid, and the degree of polymerization of the acid-modified polyvinyl acetal is 1500 to 2000.

[0008] The term "containing carboxyl units" is intended to mean that the polyvinyl acetal has carboxyl acid and / or carboxylate units somewhere in its polymer chain.

[0009] The acid-modified polyvinyl acetal of the present invention can be obtained by acetalizing an aldehyde with an acid-modified polyvinyl alcohol. Such acid-modified polyvinyl alcohols are known in the art and can be commercially available or prepared by copolymerization in the presence of an unsaturated carboxylic acid.

[0010] The degree of polymerization of polyvinyl acetal is equivalent to that of polyvinyl alcohol, the starting material in the acetalization reaction. The degree of polymerization of polyvinyl alcohol was measured according to JIS-K6726.

[0011] "Polyvinyl alcohol" is given by the idealized formula [CH2CH(OH)] n This refers to homopolymers represented by [formula]. In other words, copolymers (e.g., copolymers derived from copolymerization with ethylene) are not included in the definition of "polyvinyl alcohol".

[0012] Useful unsaturated carboxylic acids in this regard include, for example, maleic acid, itaconic acid, acrylic acid, and methacrylic acid. Acid-modified polyvinyl alcohol can be produced by copolymerizing a carboxylic acid and / or a suitable ester thereof with a vinyl ester monomer, and then saponifying the resulting acid-modified polyvinyl ester copolymer.

[0013] Preferably, the acid-modified polyvinyl acetal contains carboxyl units in the range of 0.6 mol% to 1.4 mol%, 0.7 mol% to 1.3 mol%, and most preferably 0.8 mol% to 1.2 mol%.

[0014] Preferably, the degree of polymerization of the acid-modified polyvinyl acetal is 1500 to 2000, most preferably 1700 to 1800.

[0015] There are no particular restrictions on the degree of saponification of the acetyl group, but it is preferably 85 mol% or more, more preferably 95 mol% or more, even more preferably 98 mol% or more, and most preferably 99 mol% or more. Preferably, the acid-modified polyvinyl acetal has a polyvinyl acetate content of 1.0% to 15% by weight, more preferably 1.5% to 2.5% by weight, or 10% to 15% by weight, or 12% to 13% by weight.

[0016] Preferably, the degree of acetalization is 5 mol% or more and less than 40 mol%, more preferably the lower limit of the degree of acetalization is greater than 6 mol%, greater than 7 mol%, greater than 8 mol%, greater than 9 mol%, and most preferably greater than 10 mol%. Furthermore, the upper limit of the degree of acetalization 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%.

[0017] Preferably, the acid-modified polyvinyl acetal has a polyvinyl alcohol content of 15% to 25% by weight, more preferably 17% to 23% by weight, and most preferably 18% to 22% by weight.

[0018] The vinyl alcohol content and vinyl acetate content were measured according to DIN ISO 3681 (acetate content) and DIN ISO 53240 (PVA content). The vinyl acetal content was calculated as the remainder of the sum of the vinyl alcohol content and vinyl acetate content measured according to DIN ISO 53401 / 53240.

[0019] Preferably, each acetal group has 1 to 7 carbon atoms, i.e., it is derived from a condensation reaction with an aldehyde having 1 to 7 carbon atoms. More preferably, the acetal group is 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 (caproaldehyde), isohexanal (2-methyl-1-pentanal, 3-methyl-1-pentanal, 4-methyl-1-pentanal), 2,2-dimethyl-1-butanal, 2,3-dimethyl-1-butanal Derived from a list consisting of 3,3-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, the acetal group is derived from a condensation reaction with isobutyraldehyde, acetaldehyde, and / or n-butyraldehyde. Specifically, the acid-modified polyvinyl acetal is acid-modified polyvinyl butyral.

[0020] Preferably, the acid-modified polyvinyl acetal according to the present invention is a mixed acetal, that is, it contains at least two different acetal groups. The most preferred combination is a mixture of acetals derived from acetaldehyde and n-butyraldehyde.

[0021] 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 acid-modified polyvinyl acetal containing carboxyl units in the range of 0.5 mol% to 1.5 mol%.

[0022] Preferably, the acetal group has 2 to 7 carbon atoms and is derived from the same aldehyde as above. Most preferably, the ethylene vinyl acetal contains an n-butyraldehyde and / or acetaldehyde acetal group.

[0023] Inorganic pigments can be selected from granules obtained by finely grinding paraelectric or ferroelectric raw materials, preferably titanium dioxide (rutile) modified with additives such as zinc, zirconium, niobium, magnesium, tantalum, cobalt, and / or strontium, as well as MgNb2O6, ZnNb2O6, MgTa2O6, ZnTa2O6, (ZnMg)TiO3, (ZrSn)TiO4, and Ba2Ti9O 20 It contains compounds selected from the following. The average particle size of the inorganic pigment is preferably about 0.01 μm to 1 μm.

[0024] The organic solvent can be selected from aromatic compounds such as toluene and xylene, alcohol compounds such as ethyl alcohol, isopropyl alcohol, and butyl alcohol, and more preferably mixtures thereof.

[0025] Suitable dispersants include fish oil, phosphate esters, and functional polymers containing polyoxyalkylene groups in their side chains, such as the MALIALIM® series, commercially available from NOF America Cooperation.

[0026] In addition to the binder according to the present invention, the suspension may contain, inter alia, other binders such as cellulose resins, acrylic resins, vinyl acetate resins, polyvinyl alcohol resins; plasticizers such as polyethylene glycol or phthalic esters, and / or other components selected from defoamers.

[0027] The method for producing the suspension composition is not particularly limited. Various dispersion methods can be used, for example, methods using media mills such as bead mills, ball mills, attritors, paint shakers, and sand mills; methods of kneading powdered ceramics, dispersion media, dispersants, binders, plasticizers, etc.; and methods using three-roll mills. The method includes dispersing a powdered inorganic pigment in an organic solvent (mixture) together with a dispersant, a binder, a plasticizer, etc. using a three-roll mill. The mixture is passed through the small gap between the first roll and the second roll that rotate independently of each other and have a small gap between them, and is squeezed and kneaded, and then the above mixture is passed between the second roll and the third roll adjacent to the second roll with a gap smaller than the gap between the first roll and the second roll, and is further squeezed and kneaded.

[0028] Preferably, the powdered ceramic, the dispersant, and the solvent (mixture) are premixed and dispersed so that the dispersant is adsorbed on the powdered ceramic. In the second step, after adding a binder to the mixture thus formed, mixing and dispersion are performed again.

[0029] The thickness of the coating film produced by these processes may be 0.25 μm or more and 25 μm or less, typically 1 μm or more and 10 μm or less.

Examples

[0030] (Synthesis of Acid-Modified Polyvinyl Butyral - Example 1) A polyvinyl alcohol KURARAY POVAL (registered trademark) 32-97KL having a viscosity of 32 mPas (measured at 20 °C according to DIN 53015, concentration of 4% by weight in an aqueous solution), 1 mol% of carboxyl functional groups, a degree of hydrolysis of 98 mol%, and a degree of polymerization of 1750, was dissolved in 1333 parts by weight of water and heated to 90 °C. After the polyvinyl alcohol powder was completely dissolved, the temperature was continuously lowered, and at a temperature of 40 °C, 52.5 parts by weight of n-butyl aldehyde was added. At a temperature of 10 °C, 150 parts by weight of 20% hydrochloric acid was added under stirring. The mixture was heated to 40 °C. After stirring at this temperature for 2 hours, the formed precipitate was separated after cooling to room temperature, washed until neutral with water, and dried. An acid-modified polyvinyl butyral having a polyvinyl alcohol content of 20.5% by weight (29.5 mol%) and a polyvinyl acetate content of 2.6% by weight (1.9 mol%) was obtained.

[0031] (Comparative Example 1 - Unmodified Polyvinyl Butyral) A PVB solution was prepared using Mowital (registered trademark) polyvinyl butyral resin B75H obtained from Kuraray Europe GmbH, which contains acetal units produced from n-butyl aldehyde and polyvinyl alcohol having no acid functional groups in / on the polymer chain. The PVB solution is used as a binder solution for producing ceramic green sheets.

[0032] Preparation of Inorganic Dispersion 1.3 g of a 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 obtained solution. The organic dispersion was mixed with a roller mixer for 6 to 8 hours.

[0033] 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.

[0034] Manufacturing of ceramic green sheets The resin solution was added to the obtained inorganic dispersion and mixed for 10 hours using a roller block mixer to obtain a composition for ceramic green sheets. ZrO2 beads were separated from the dispersion using a nylon screen / filter.

[0035] The resulting dispersion was degassed and cast using an automated film coating machine according to the doctor blade method. Silicone-treated PET (Hostaphan® RN 2 SLK, 75 μm thick) was used as the casting support. After casting, the film was dried overnight. To remove residual solvent, the film was dried in an oven at 50°C for 1 hour and then peeled off.

[0036] The resulting film had a thickness of 19 μm and exhibited cracks, blisters, or defects during optical evaluation.

[0037] From the green sheet, appropriate tensile test specimens in the form of so-called "stripe" were punched out according to DIN EN ISO 527-3, Type 2 (150 mm × 20 mm). Eight tensile test specimens were punched out for each film type in a direction intersecting the casting direction and inspected by human eye. Five specimens that appeared to have the fewest defects from the punching process were selected for measurements for both Example 1 and Comparative Example 1.

[0038] The samples were calibrated for 24 hours at a temperature of 23°C and a relative humidity of 50% before measurement.

[0039] A universal tensile testing machine (Zwick / Roell, ZwickiLine Z0.5 TN) was used for tensile force measurements. The measurements were performed under controlled conditions of 23°C and 50% relative humidity, in accordance with DIN EN ISO 527-1 and DIN EN ISO 527-3.

[0040] [Table 1]

[0041] The tensile test results show that the ceramic green sheet obtained using acid-modified polyvinyl acetal has a fracture elongation value that is more than three times the value obtained using the PVB standard.

Claims

1. Use of acid-modified polyvinyl acetal as a binder for manufacturing ceramic green sheets or ceramic molded articles, wherein the acid-modified polyvinyl acetal contains carboxyl units in the range of 0.5 mol% to 1.5 mol%, the carboxyl units are derived from dicarboxylic acid, and the degree of polymerization of the acid-modified polyvinyl acetal is 1500 to 2000.

2. The use according to claim 1, wherein the acid-modified polyvinyl acetal contains carboxyl units in the range of 0.8 mol% to 1.2 mol%.

3. The use according to claim 1 or 2, wherein the acid-modified polyvinyl acetal is obtained by acetalizing polyvinyl alcohol produced in a copolymerization step using maleic acid or itaconic acid.

4. The use according to any one of claims 1 to 3, wherein the degree of polymerization of the acid-modified polyvinyl acetal is 1700 or more and 1800 or less.

5. The use according to any one of claims 1 to 4, wherein the acid-modified polyvinyl acetal has a polyvinyl alcohol content of 15% by weight or more and 25% by weight or less.

6. The use according to any one of claims 1 to 5, wherein the acid-modified polyvinyl acetal has a polyvinyl acetate content of 1.0% by weight or more and 15% by weight or less.

7. The use according to any one of claims 1 to 6, wherein the acid-modified polyvinyl acetal is acid-modified polyvinyl butyral.

8. 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 acid-modified polyvinyl acetal containing carboxyl units in the range of 0.5 mol% to 1.5 mol%, the carboxyl units are derived from dicarboxylic acids, and the degree of polymerization of the acid-modified polyvinyl acetal is 1500 to 2000.

9. The suspension according to claim 8, wherein the acid-modified polyvinyl acetal is obtained by acetalizing polyvinyl alcohol produced in a copolymerization step using maleic acid or itaconic acid.

10. The suspension according to claim 8 or 9, wherein the acid-modified polyvinyl acetal has a polyvinyl alcohol content of 15% by weight or more and 25% by weight or less.

11. A method for producing a ceramic green sheet or a ceramic molded article using the suspension described in any one of claims 8 to 10.

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