Use of compressed polyvinyl acetal as a binder for ceramic green sheets.

Abstract

Disclosed is the use of a compact comprising polyvinyl acetal as a binder for the production of ceramic green sheets or ceramic shaped bodies, wherein the polyvinyl acetal has a molecular weight of 50,000 g / mol or more, as measured by gel permeation chromatography according to DIN ISO 16014-1:2019-05, and 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 a compact.

Description

[Technical field]

[0001] The present invention is directed to the use of compressed powders of polyvinyl 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. a 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 (PVB), 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 PVB 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 are made up of several individual capacitors stacked in parallel and contacted via their terminal surfaces. Due to the ever-increasing miniaturization of electronic components, the size of powder particles can be as small as 10 nm. This places manufacturing demands on the precision of the ceramic sheets used therein. 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 bond strength and breaking elongation.

[0005] To achieve these goals, high molecular weight PVB, i.e., PVB with a high degree of polymerization, is preferred because it provides a suspension with a sufficiently high viscosity, but it has a poorer solubility than short-chain PVB, which increases the overall time required to prepare the suspension.

[0006] The PVB resins used to manufacture the suspensions are generally supplied in the form of a fine powder. However, such powders cannot be used in all industrial environments due to health and / or safety concerns. Depending on the particle size of the powder, the particles can easily be inhaled into the lungs of employees handling the material. Furthermore, powdered materials usually present an explosion hazard after flame ignition.

[0007] To solve these problems, granular PVB has been introduced. For example, US Patent Application Publication No. 20080203593 describes the preparation of PVB granules to be used as a binder for ceramic green sheets.

[0008] However, when such granules are produced by melt extrusion, the high temperatures and high shear forces used in the extruder can lead to partial decomposition of the PVB. Furthermore, the granules dissolve much slower than the corresponding powders. The use of such granular PVB is not recommended in the ceramic industry, since the high molecular weight PVB is already inferior in terms of dissolution rate.

[0009] It was therefore an object of the present invention to provide a binder for ceramic green sheets that has an improved dissolution rate. A further object was to provide a binder that provides improved adhesion, improved handling, improved elongation at break, improved dispersion effect, improved environmental, health and safety effects, and / or a better economic profile in the manufacture and use of ceramic green sheets.

[0010] The present inventors have surprisingly discovered that the use of compressed PVB achieves these and other objectives.

[0011] Thus, a first aspect of the present invention relates to the use of a compact comprising polyvinyl acetal as a binder for the production of ceramic green sheets or ceramic shaped bodies, wherein the polyvinyl acetal has a molecular weight of 50,000 g / mol or more, as determined by gel permeation chromatography according to DIN ISO 16014 1:2019-05.

[0012] The molecular weight is measured by gel permeation chromatography in accordance with DIN ISO 16014 1:2019-05. Preferably, the molecular weight is 60,000 g / mol or more, more preferably 70,000 g / mol or more. Also preferably, the molecular weight is 200,000 g / mol or less, more preferably 175,000 g / mol or less, most preferably 150,000 g / mol or less, in particular 100,000 g / mol or less. Also preferably, the molecular weight is 50,000 to 150,000 g / mol, more preferably 60,000 to 125,000 g / mol.

[0013] The term "compacted body" as used herein is intended to refer to a compacted powder of polyvinyl acetal that has undergone a compaction process in which dry powder is pressed without the use of solvents or melting of the powder. Such compaction processes are also called dry granulation, as opposed to wet granulation, which uses a solution or slurry, or extrusion processes, which use a melt of the polyvinyl acetal material.

[0014] Preferably, the acetal groups individually have from 1 to 7 carbon atoms, ie, the acetal groups are derived from a condensation reaction with an aldehyde having from 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 (capronaldehyde), isohexanal (2-methyl-1-pentanal, 3-methyl-1-pentanal, 4-methyl-1-pentanal), 2,2-dimethyl-1-butanal, 2,3-dimethyl-1-butanal. The list of 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, cyclohexylaldehyde and benzaldehyde. More preferably, the acetal groups are derived from a condensation reaction with isobutyraldehyde, acetaldehyde and / or n-butyraldehyde. Most preferably, the polyvinyl acetal is polyvinyl butyral.

[0015] The method for producing the polyvinyl 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 a polyvinyl alcohol solution under acidic conditions to subject it to an acetalization reaction. Polyvinyl acetals are also commercially available, such as Mowital® polyvinyl acetal available from Kuraray Europe GmbH.

[0016] The degree of acetalization of the polyvinyl acetal used in the present invention is preferably 50 mol% or more and less than 90 mol%, more preferably the lower limit of the degree of acetalization is more than 60 mol% or more than 70 mol%, and more preferably the upper limit of the degree of acetalization is 90 mol% or less, 85 mol% or less, 80 mol% or less, or 75 mol% or less.

[0017] The percentage of vinyl alcohol units in the polyvinyl acetal of the present invention is preferably 10 to 50 mol %, more preferably 15 to 35 mol %, based on the total monomer units constituting the resin.

[0018] The vinyl alcohol content and vinyl acetate content of the polyvinyl acetals were determined in accordance with DIN ISO 3681 (acetate content) and DIN ISO 53240 (PVA content).

[0019] Preferably, the compressed body has a median particle size of 0.5 to 5 mm, more preferably 2 to 4 mm. The particle size is determined by optical inspection using a specified amount of particles, measuring the diameter if the particles are spherical, or the longest horizontal axis if the particles are non-spherical.

[0020] 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 a compact comprising the polyvinyl acetal described above.

[0021] Preferably, the acetal group has 2 to 7 carbon atoms and is derived from the same aldehydes as mentioned above, most preferably, the acetal group is derived from n-butyraldehyde.

[0022] The inorganic pigments can be selected from finely divided granules of paraelectric or ferroelectric materials, titanium dioxide (rutile), preferably modified with additives of zinc, zirconium, niobium, magnesium, tantalum, cobalt and / or strontium, and MgNb 2 O 6 , ZnNb 2 O 6 , MgTa 2 O 6 , ZnTa 2 O 6 , (ZnMg)TiO 3 , (ZrSn)TiO 4 , BaTiO 3 and Ba 2 Ti 9 O 20 The inorganic pigment preferably has an average particle size of about 0.01 to 1 μm.

[0023] 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. Most preferably, the organic solvent is a mixture of ethanol and toluene.

[0024] 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.

[0025] 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.

[0026] The method for producing the suspension composition is not particularly limited. Various dispersion methods can be used, such as a method using a media-type mill such as a bead mill, a ball mill, an attritor, a paint shaker, or a sand mill, a method of kneading a 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 in an organic solvent (mixture) together with a dispersant, a binder, a plasticizer, and the like. The mixture is compressed and kneaded by passing through a small gap between a first roll and a second roll that roll independently of each other and are adjacent to each other with a small gap therebetween, and then the mixture is further compressed and kneaded by passing through a gap between the second roll and a third roll that rolls and is adjacent to the second roll with a gap smaller than the gap between the first roll and the second roll.

[0027] 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.

[0028] The dry thickness of the coating film produced by these steps may be 0.25 to 25 μm, and is typically 1 to 15 μm.

[0029] Compacted bodies can be produced by dry granulation processes known in the art, i.e., processes that form granules without the use of liquid solutions. Such processes are superior when the ingredients being compacted are moisture or heat sensitive. Compaction is used to densify the powders and form the compacted bodies. This process is generally carried out using a slugging tool or roller compactor machine. The slugging process usually results in a "slug," which is typically 25 mm in diameter and 10-15 mm thick. A hammer mill is ideal for crushing the slugs to produce the final compacted bodies.

[0030] Preferably, the compact manufacturing process uses a roller compactor. In this machine, the powder is pressed through two counter-rotating rollers to form a compacted sheet. The sheet is brittle and easily crumbles into flakes. Careful processing is required to break the flakes into compacts, which can then be ground to the desired size. Roller compaction machines offer a wide range of pressures and roll types to achieve the proper densification. EXAMPLES

[0031] [Example 1 - PVB compressed body 1] Polyvinyl butyral powder (Mowital® B75H, molecular weight 100,000 g / mol±10,000 g / mol) is drawn between two counter-rotating water-cooled rollers using a roller compactor with a linear pressure of 15 kN / cm at a temperature of 45° C. The resulting 0.5-1.0 cm thick sheet is then crushed and then further reduced in size using a granulator to obtain a compact with a median particle size of 1-3 mm.

[0032] [Comparison of dissolution behavior between PVB powder and PVB compact] 10 g of PVB powder or compact was mixed with 90 g of a mixed solvent (1:1 mixture of ethanol and toluene). A rotary tilt mixer was used for the dissolution process (supplier: IKA, model: rotary tilt mixer, digital, 6). After a given period (0 h, 3 h, 6 h, 18 h, and 24 h), the mixer was stopped, 1 g of the supernatant was taken, and the solvent was evaporated in an oven to determine the solid content. A digital precision balance was used for the analysis.

[0033] [Table 1]

[0034] [result] Compact 1 was completely dissolved already after 3 hours, whereas the corresponding powder material required a dissolution time of more than 6 hours to completely dissolve.

[0035] [Comparison of particle counts in solution between PVB powder and PVB compact] Compact 2 was prepared as described above for compact 1, except that Mowital® B30HH, a PVB with a molecular weight of 35,000 g / mol±10,000 g / mol available from Kuraray Europe GmbH, was used.

[0036] 2 g of PVB powder or compacts, respectively, were dissolved in 98 g of a solvent mixture (1:1 mixture of ethanol and toluene) using a tilt / rotate mixer. After 24 h, 50 mL samples were taken and analyzed by single particle measurement by laser focus using an Accusizer™ 780 from Soliton GmbH. Only particles in the size range of 2-500 μm were counted.

[0037] [Table 2]

[0038] [result] Residual particles of size 2-500 μm can be a major problem in the production of ceramic green sheets and so their presence in the binder solution must be minimized. The compression process for compact 1 results in only a small increase in particle size, but when the low molecular weight PVB material (compact 2) is compressed, there is surprisingly a very large increase in particle count from powder to compact.

Claims

1. 1. Use of a compact comprising polyvinyl acetal as a binder for producing ceramic green sheets or ceramic shaped bodies, wherein the polyvinyl acetal has a molecular weight of 50,000 g / mol or more, as determined by gel permeation chromatography in accordance with DIN ISO 16014-1:2019-05.

2. 2. The use according to claim 1, wherein the polyvinyl acetal is polyvinyl butyral.

3. 2. The use according to claim 1, wherein the polyvinyl acetal has a molecular weight of 50,000 g / mol to 150,000 g / mol, as determined by gel permeation chromatography according to DIN ISO 16014-1:2019-05.

4. 2. The use according to claim 1, wherein the compact has a median particle size of 1 to 5 mm.

5. 5. 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 a compact according to any one of claims 1 to 4.

6. 1. A compressed body comprising a polyvinyl acetal having a molecular weight of 50,000 g / mol or more, as determined by gel permeation chromatography in accordance with DIN ISO 16014-1:2019-05.

7. The compressed body according to claim 6, having a median particle size of 1 to 5 mm.

8. 8. A method for producing the compressed body of claim 7, comprising the step of compressing polyvinyl acetal powder in a roll mill.