Use of modified polyvinyl acetals as binders in ceramic blanks

Abstract

The invention relates to the use of modified polyvinyl acetals as binders in ceramic blanks.

Description

[0001] The present invention relates to the use of modified polyvinyl acetals as binders in ceramic green sheets.

[0002] Ceramic materials, such as ceramic capacitors for the electronics industry, are usually produced by sintering so-called green sheets, i.e. film-like thin mouldings, comprising the ceramic material. For the production of these green sheets, a suspension of metal oxides, plasticizers, dispersants and binders in organic solvents is produced. Subsequently, the suspension is applied to a carrier film in the desired thickness by means of a suitable process, i.e. a doctor blade process, and the solvent is removed. The green sheets thus obtained must be free of cracks, show a smooth surface and still have a certain elasticity.

[0003] Polyvinyl acetals, such as polyvinyl butyral, are often used as binders for the production of ceramic green sheets. For this purpose, DE 4 003 198 A1 describes the production of a casting slip for ceramic green films, in which polyvinyl butyral with a residual polyvinyl acetate content of 0 to 2% by weight is used as a binder.

[0004] In recent years, multilayer ceramic capacitors (MLCC) have become increasingly important in the electronics industry. MLCCs are composed of many individual capacitors stacked in parallel and contacted via the terminal surfaces. Due to the miniaturization drive of electronic components, the size of the powder particles can be as small as 10 nm. Therefore, the precision of the ceramic sheets used in the production is increased. Furthermore, in the production process, the multilayer stack of ceramic green sheets is usually wound into a roll. In order to avoid delamination, the individual green sheets must have excellent properties in terms of adhesion and elongation at break. For this purpose, there is an industrial need for further improved binders for use in the suspension.

[0005] It was therefore an object of the present invention to provide a binder for ceramic green sheets which leads to improved adhesion, improved dispersion effects, improved environmental and safety influences and / or has better economics, in particular has improved elongation at break, in the production and use of ceramic green sheets.

[0006] Surprisingly, the present inventors have now found that the use of polyvinyl acetals modified with low concentrations of carboxylic acid groups in the polymer chain leads to excellent properties in the production of ceramic green sheets.

[0007] The present invention therefore relates to the use of acid-modified polyvinyl acetals as binders for the production of ceramic green sheets or ceramic mouldings, wherein the acid-modified polyvinyl acetals comprise carboxyl units in the range from 0.5 to 1.5 mol% and wherein the carboxyl units are derived from a dicarboxylic acid, and wherein the acid-modified polyvinyl acetals have a degree of polymerization of 1500 to 2000.

[0008] The term "comprising carboxylic acid units" is intended to mean that the polyvinyl acetal has carboxylic acid and / or carboxylic ester units somewhere in the polymer chain.

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

[0010] The degree of polymerization of the polyvinyl acetal is equivalent to that of the polyvinyl alcohol serving as a starting material in the acetalization reaction. The degree of polymerization of the polyvinyl alcohol is determined according to JIS-K6726.

[0011] "Polyvinyl alcohol" means a homopolymer having the idealized formula [CH2CH(OH)] n that is, copolymers - for example derived from copolymerization with ethylene - are not within the definition of "polyvinyl alcohol".

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

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

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

[0015] Although the degree of saponification of the acetate groups is not particularly limited, it is preferably 85 mol% or more, more preferably 95 mol% or more, still 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 more than 6 mol%, more than 7 mol%, more than 9 mol%, and most preferably more 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, and most preferably less than 30 mol%.

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

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

[0019] Preferably, the acetal groups each have 1 to 7 carbon atoms, i.e. they are derived from condensation reactions with aldehydes having 1 to 7 carbon atoms. More preferably, they are derived from the list consisting of formaldehyde (formaldehyde), acetaldehyde, n-propanal (propionaldehyde), n-butanal (butyraldehyde), isobutanal (2-methyl-1-propanal, isobutyraldehyde), n-pentanal (valeraldehyde), iso-pentanal (3-methyl-1-butanal), sec-pentanal (2-methyl-1-butanal), tert-pentanal (2,2-dimethyl-1-propanal), n-hexanal (hexanal), iso-hexanal (2-methyl-1-pentanal, 3-methyl-1-pentanal, 4-methyl-1-pentanal), 2,2-dimethyl-1-butanal, 2,3-dimethyl-1-butanal, 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, cyclohexan al and benzaldehyde. Most preferably, they are derived from condensation reactions with isobutyraldehyde, acetaldehyde and / or n-butyraldehyde. In particular, the acid-modified polyvinyl acetal is an acid-modified polyvinyl butyral.

[0020] It is also preferred that the acid-modified polyvinyl acetal according to the present application is a mixed acetal class, i.e. they comprise at least two different acetal groups. The most preferred combination is a mixture of acetal groups derived from acetaldehyde and n-butyraldehyde.

[0021] In a second aspect, the present application 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 comprising carboxyl units in the range of 0.5 to 1.5 mol%.

[0022] Preferably, the acetal group has 2 to 7 carbon atoms and is derived from the same aldehyde(s) as described above. Most preferably, the ethylene-vinyl alcohol comprises n-butyraldehyde acetal groups and / or acetaldehyde acetal groups.

[0023] The inorganic pigments can be selected from finely ground particles of paraelectric or ferroelectric stock and include titanium dioxide (rutile), preferably modified by additives of zinc, zirconium, niobium, magnesium, tantalum, cobalt and / or strontium and compounds selected from the group consisting of MgNb2O6, ZnNb2O6, MgTa2O6, ZnTa2O6, (ZnMg)TiO3, (ZrSn)TiO4 and Ba2Ti9O 20 The average particle size of the inorganic pigments is preferably about 0.01 to 1 μm.

[0024] The organic solvent can be selected from aromatic compounds such as toluene and xylene; and alcohol compounds such as ethanol, isopropanol and butanol, more preferably mixtures thereof.

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

[0026] In addition to the binder according to the present application, the suspension can also comprise further components, in particular selected from other binders (such as cellulose resins, acrylic resins, vinyl acetate resins, polyvinyl alcohol resins); plasticizers such as polyethylene glycol or phthalates and / or antifoams.

[0027] The method for producing the suspension composition is not particularly limited. Various dispersion methods can be used, for example, a method using a media-type mill such as a bead mill, a ball mill, a mortar mill, a paint shaker and 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. Using a three-roll mill, the method comprises dispersing the powdered inorganic pigment and the dispersant, binder, plasticizer and the like together in the organic solvent (mixture). The mixture is compressed and kneaded by the small gap between a first roll and a second roll which roll independently of each other and adjacent to each other with a small gap therebetween, and subsequently, the mixture is passed through between the second roll and a third roll which rolls and is adjacent to the second roll with a gap therebetween which is smaller than the gap between the first roll and the second roll, so as to be further compressed and kneaded.

[0028] Preferably, the powdered ceramic, dispersant and solvent (mixture) are pre-mixed and dispersed so that the dispersant is adsorbed on the powdered ceramic. In a second step, the binder is added to the mixture thus formed, and subsequently, mixing and dispersion are carried out again.

[0029] The coating film produced by these processes can have a thickness of 0.25 to 25 pm, and is usually 1 to 10 pm. Examples

[0030] Synthesis of acid-modified poly(vinyl butyral) - Example 1

[0031] 100 parts by weight of a polyvinyl alcohol having a viscosity of 32 mPas (measured in a 4 w / w% aqueous solution at 20°C according to DIN 53015) and 1 mol% carboxyl functions, a hydrolysis degree of 98 mol% and a degree of polymerization of 1750, KURARAY POVAL® 32-97 KL, was dissolved in 1333 parts by weight of water and heated to 90°C. After complete dissolution of the polyvinyl alcohol powder, the temperature was continuously reduced and at a temperature of 40°C, 52.5 parts by weight of n-butyraldehyde were added and at a temperature of 10°C, 150 parts by weight of 20% hydrochloric acid were added while stirring. The mixture was heated to 40°C. After stirring for 2 hours at this temperature, the formed precipitate was isolated after cooling to room temperature, washed with water to neutrality and dried. An acid-modified polyvinyl butyral having a polyvinyl alcohol content of 20.5 wt% (29.5 mol%) and a polyvinyl acetate content of 2.6 wt% (1.9 mol%) was obtained.

[0032] Comparative Example 1 - unmodified poly(vinyl butyral)

[0033] A PVB solution was prepared using Mowital® polyvinyl butyral resin B 75H obtained from Kuraray Europe GmbH, comprising acetal units prepared from n-butyraldehyde and a polyvinyl alcohol having no acid functions in / on the polymer chain. This PVB solution was used as binder solution to prepare ceramic green sheets.

[0034] Preparation of inorganic dispersion

[0035] 1.3 g of a polyoxyalkylene dispersant (MALIALIM TM 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 Zr02beads (diameter: 2 mm) were added to the obtained solution. The organic dispersion was mixed on a roll mixer for 6 to 8 hours.

[0036] Preparation of resin solution

[0037] 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.

[0038] Production of ceramic green sheets

[0039] The resin solution was added to the obtained inorganic dispersion and mixed for 10 hours using a roll block mixer to obtain a composition for ceramic green sheets. Zr02beads were separated from the dispersion using a nylon mesh / filter.

[0040] The obtained dispersion was degassed and casted according to the doctor blade process using an automatic film coater. Siliconized PET (Hostaphan® RN 2 SLK, thickness 75 pm) was used as casting support. After casting, the film was dried overnight. To remove residual solvents, the film was dried in an oven at 50 °C for 1 hour followed by a pull out.

[0041] The thickness of the obtained film was 19 pm and cracks, blisters or defects occurred during optical evaluation.

[0042] From the involved green sheets, suitable tensile specimens according to DIN EN ISO 527-3, type 2 (150 mm x 20 mm) in the form of so-called “strips” were punched out. 8 tensile specimens of each type of film were punched out crosswise to the casting direction and checked by the human eye. For both, Example 1 and Comparative Example 1, 5 specimens were chosen which appeared to have the least defects from the punching process for measurement.

[0043] Before measurement, the samples were conditioned for 24 hours at a temperature of 23 °C and a humidity of 50%.

[0044] A universal tensile testing machine (ZwickiLine Z0,5 TN from Zwick / Roell) was used for tensile force measurements. The measurements were carried out according to DIN EN ISO 527-1 and DIN EN ISO 527-3 under controlled conditions at 23 °C and 50% relative humidity.

[0045]

[0046] Table 1: Results of tensile test

[0047] The results of the tensile test show that the elongation at break values of the ceramic green sheets obtained with acid-modified polyvinyl acetal are more than three times greater than the values obtained with PVB standard.

Claims

1. Use of an acid-modified polyvinyl acetal as a binder for the production of ceramic green sheets or ceramic moldings, wherein the acid-modified polyvinyl acetal comprises carboxyl units in the range of 0.5 to 1.5 mol% and wherein the carboxyl units originate from a dicarboxylic acid and wherein the acid-modified polyvinyl acetal has a degree of polymerization of 1500 to 2000.

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

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

4. Use according to any of the preceding claims, wherein the acid-modified polyvinyl acetal has a degree of polymerization of 1700 to 1800.

5. Use according to any of the preceding claims, wherein the acid-modified polyvinyl acetal has a polyvinyl alcohol content of 15 to 25 wt.%.

6. Use according to any of the preceding claims, wherein the acid-modified polyvinyl acetal has a polyvinyl acetate content of 1.0 to 15 wt.%.

7. Use according to any of the preceding claims, wherein the acid-modified polyvinyl acetal is an 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 comprising carboxyl units in the range of 0.5 to 1.5 mol% and wherein the carboxyl units originate from a dicarboxylic acid and wherein the acid-modified polyvinyl acetal has a degree of polymerization of 1500 to 2000.

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

10. Suspension according to any of claims 8 to 9, wherein the acid-modified polyvinyl acetal has a polyvinyl alcohol content of 15 to 25 wt.%.

11. Process for the production of ceramic green sheets or ceramic moldings using a suspension according to any of claims 8 to 10.

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