Use of polyvinyl acetal with specific porosity as a binder for ceramic green sheets

Abstract

The present invention is directed to the use of a polyvinyl acetal powder having a specific porosity as a binder for ceramic green sheets. The polyvinyl acetal has a total pore volume of 1.5-5.0 ml / g as measured by mercury porosimetry according to the present specification and has a predominant population of pores with diameters centered between 10 and 100 μm. A suspension composition is produced 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 polyvinyl acetal. A method for producing a ceramic green sheet or ceramic compact, comprising compressing polyvinyl acetal and producing a suspension composition comprising the produced compressed body.

Description

[Technical field]

[0001] The present invention is directed to the use of polyvinyl acetal having a specific porosity as a binder for ceramic green sheets and to a method for making compacts using said polyvinyl acetal.

[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 consist of multiple individual capacitors stacked in parallel and contacted via their terminal surfaces. As electronic components become increasingly miniaturized, the size of powder particles can be as small as 10 nm. This calls for improved precision in the ceramic sheets used in their manufacture.

[0005] The PVB resins used in the manufacture of suspensions are generally supplied in the form of fine powders. However, such powders cannot be used in all industrial environments due to health and / or safety concerns. Therefore, to avoid these drawbacks, the PVB powder is compressed before use in certain applications.

[0006] Furthermore, PVB resins must exhibit extremely high purity to meet the stringent requirements of the electronics industry, but cleaning such polymer products to high purity in an economically feasible manner is not easy.

[0007] It was therefore an object of the present invention to provide a binder for ceramic green sheets that has improved washability and at the same time improved compressibility. A further object was to provide a binder that provides improved dissolution rate, 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.

[0008] The inventors have surprisingly found that these and other objectives are achieved by using PVB with a high total pore volume and at the same time with pores with a small average pore diameter. It is believed that a high total pore volume leads to good washability, since washing liquid can penetrate the powder. At the same time, the total pore volume is mainly contributed by pores with a relatively small pore diameter, which obviously leads to improved compressibility, i.e., it can be compressed to obtain a compact with a relatively low total pore volume and a relatively high density, expressed as bulk density or tap density.

[0009] Thus, a first aspect of the present invention relates to the use of polyvinyl acetal as a binder for the production of ceramic green sheets or ceramic moulded bodies, the polyvinyl acetal having a total pore volume of 1.5 to 5.0 ml / g, measured by mercury porosimetry according to the conditions described below, and a predominant population of pores with diameters centred between 10 and 100 µm. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 shows the results of porosimetry measurements of two polyvinyl acetal powder samples according to the invention, two compacts made from said polyvinyl acetal powders, and a prior art commercially available compact currently used in the electronics industry.

[0011] The term "main population of pores having a diameter centered around a value" is intended to mean that a curve plotting cumulative pore volume against pore diameter using porosimetry measurements as described below has an inflection point between the given values.

[0012] Preferably, the diameter is centered between 15 and 50 μm, more preferably between 20 and 40 μm, and more preferably between 30 and 80 μm, more preferably between 40 and 60 μm.

[0013] Preferably, the total pore volume is from 1.75 to 4.5 ml / g, more preferably from 2.0 to 4.0 ml / g, even more preferably from 2.0 to 3.0 ml / g, and most preferably from 2.5 to 3.0 ml / g.

[0014] The polyvinyl acetal preferably has an average pore diameter of 2.0 μm or less when measured by mercury porosimetry described below, and more preferably has an average pore diameter of 1.0 to 1.5 μm.

[0015] Preferably, the polyvinyl acetal has a molecular weight of ≧20,000 g / mol, as determined by gel permeation chromatography in accordance with DIN ISO 16014 1:2019-05.

[0016] The molecular weight is measured by gel permeation chromatography according to DIN ISO 16014 1:2019-05. Preferably, the molecular weight is 40,000 g / mol or more, more preferably 50,000 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.

[0017] Preferably, the acetal groups of the polyvinyl acetal each 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 a polyvinyl butyral or a mixed polyvinyl acetal derived from the condensation of n-butyraldehyde with acetaldehyde.

[0018] 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 the solution to an acetalization reaction.

[0019] Preferably, the degree of acetalization of the polyvinyl acetal used in the present invention is 50 mol% or more and less than 90 mol%, more preferably the lower limit of the degree of acetalization is more than 60 mol%, even more preferably more than 70 mol%, and most preferably more than 80 mol%. Furthermore, the upper limit of the degree of acetalization is more preferably 90 mol% or less, and most preferably 85 mol% or less.

[0020] The percentage of vinyl alcohol units in the polyvinyl acetal of the present invention is preferably 10 to 25 mol %, more preferably 15 to 20 mol %, based on the total monomer units constituting the resin.

[0021] 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).

[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 a polyvinyl acetal as described above.

[0023] 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 or a mixture of n-butyraldehyde and acetaldehyde.

[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, BaTiO3 and Ba2Ti9O 20 The inorganic pigment preferably has an average particle size of 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. Most preferably, the organic solvent is a mixture of ethanol and toluene.

[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 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.

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

[0031] The inventors have found that compacts can be advantageously produced from the above-mentioned polyvinyl acetals. The PVB powders exhibit a high total pore volume and at the same time a small average pore diameter. A high total pore volume leads to better washability of the powders, since the washing liquid, usually in the form of demineralized water, can penetrate the PVB powder to a greater extent, which results in an excellent impurity profile of the PVB powder and thus of the compacts obtained. On the other hand, the smaller pores of the PVB powders result in compacts with a significantly higher compression level.

[0032] Therefore, a third aspect of the present invention relates to a method for producing a compressed body using the aforementioned polyvinyl acetal.

[0033] Preferably, the compact has an average pore diameter of 0.01 to 0.5 μm, measured by mercury porosimetry according to the method described below. The lower limit of the average pore diameter is more preferably 0.05, 0.1, or 0.15 μm. The upper limit of the average pore diameter is more preferably 0.4 μm, and most preferably 0.3 μm. In particular, the average pore diameter is 0.1 to 0.3 μm.

[0034] Preferably, the compact has a bulk density, measured according to the method described below, of at least 0.50 g / ml, more preferably at least 0.55 g / ml, most preferably at least 0.60 g / ml, especially at least 0.65 g / ml.

[0035] Preferably, the compressed body has a median particle size of 0.5 to 5 mm, more preferably 1 to 3 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.

[0036] 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.

[0037] Compacted bodies can be produced by processes known in the art, i.e., processes that form compacted bodies without the use of liquid solutions. Such processes are superior when the components to be compacted are moisture or heat sensitive. Compaction is used to densify the powder and form a compacted body. This process is generally carried out using a slugging tool or a 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. The compacted material can be further processed by classification sieving to obtain compacted bodies with the desired particle size.

[0038] 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.

[0039] A fourth aspect of the present invention is a method for producing a ceramic green sheet or a ceramic molded body, comprising the steps of: a. compressing the polyvinyl acetal by the method described above; b. preparing a suspension composition comprising the compacts prepared in step a.; The present invention relates to a method comprising the steps of: EXAMPLES

[0040] [Porosimetry] Total pore volume, median pore diameter, average pore diameter and bulk density were measured by mercury intrusion porosimetry using a porosimeter instrument AutoPore V 9600 (available from Micromeritics) in accordance with ISO 15901-1:2016. The contact angle of mercury was 130° and the surface tension was 485 dynes / cm. An equilibration time of 10 seconds and an initial packing pressure of 0.24 psia were used. The measured pressure range was 0.24-33.063 psia, which corresponds to pore diameters of 752-0.00581 μm. The total pore volume is defined as the cumulative intrusion volume measured in this range. The median pore diameter (related to volume) is defined as the pore diameter for which 50% of the pore volume is smaller or larger than this value. The average pore diameter is defined as "4 x pore volume / pore area", assuming that the pores are perfectly cylindrical. Bulk density is defined as the density at which the filling pressure of the measurement cell is 0.24 psia, at which pressure mercury is only trapped and does not permeate the sample.

[0041] [Synthesis of polyvinyl acetal] Polyvinyl Butyral (PVB 1) 100 parts by weight of polyvinyl alcohol with a viscosity of 19 mPas (measured according to DIN 53015 at 20° C., 8 w / w% in aqueous solution) and a degree of hydrolysis of 98 mol % were dissolved in 1000 parts by weight of water while heating to 90° C. At a temperature of 40° C., 65 parts by weight of n-butylaldehyde were added and, under stirring, at a temperature of 5° C., 250 parts by weight of 20% hydrochloric acid were added. The mixture was heated to 40° C. After precipitation of polyvinyl butyral (PVB), the mixture was stirred at this temperature for 48 hours. After cooling to room temperature, the PVB was separated, washed to neutrality with water and dried. A PVB with a polyvinyl alcohol content of 12.7% by weight (19.1 mol %) and a polyvinyl acetate content of 2.3% by weight (1.8 mol %) was obtained.

[0042] Mixed Polyvinyl Acetal (PVB 2) 100 parts by weight of polyvinyl alcohol with a viscosity of 50 mPas (measured according to DIN 53015 at 20° C., 8 w / w% in aqueous solution) and a degree of hydrolysis of 99 mol % were dissolved in 1000 parts by weight of water while heating to 90° C. At a temperature of 40° C., 200 parts by weight of 20% hydrochloric acid were added and at a temperature of 12° C., first 22 parts by weight of acetaldehyde and then 30 parts by weight of n-butyraldehyde were added while stirring. The mixture was heated to 40° C. After precipitation of polyvinyl butyral (PVB), the mixture was stirred at this temperature for 48 hours. After cooling to room temperature, the PVB was separated, washed to neutrality with water and dried. A PVB with a polyvinyl alcohol content of 12.5% ​​by weight (18.8 mol %) and a polyvinyl acetate content of 1.7% by weight (1.3 mol %) was obtained.

[0043] Compression process - PVB compression bodies 1 and 2 The polyvinyl butyral powder was 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 sheets of 0.5 to 1.0 cm thickness were then crushed, then further reduced in size using a granulator, and finally passed through a classification sieve to obtain compacts with a median particle size of 1 to 3 mm.

[0044] [Table 1]

Claims

1. 1. Use of polyvinyl acetal as a binder for producing ceramic green sheets or ceramic molded bodies, wherein the polyvinyl acetal has a total pore volume of 1.5 to 5.0 ml / g, as measured by mercury porosimetry in accordance with the present specification, and has a predominant population of pores with diameters centered between 10 and 100 μm.

2. 2. Use according to claim 1, wherein the total pore volume measured by mercury porosimetry according to the present specification is between 2.0 and 3.5 ml / g.

3. 2. Use according to claim 1, wherein the total pore volume measured by mercury porosimetry according to the present specification is between 2.5 and 3.0 ml / g.

4. 2. The use according to claim 1, wherein said diameter is centered at a value between 15 and 50 μm.

5. 2. The use according to claim 1, wherein the polyvinyl acetal has an average pore diameter of less than or equal to 2.0 μm as measured by mercury porosimetry according to the present specification.

6. 2. The use according to claim 1, wherein the polyvinyl acetal has an average pore diameter of 1.1 to 1.5 μm as measured by mercury porosimetry according to the present specification.

7. 2. The use according to claim 1, wherein the polyvinyl acetal is polyvinyl butyral or a mixed polyvinyl acetal derived from n-butyraldehyde and acetaldehyde.

8. 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 a polyvinyl acetal according to any one of claims 1 to 7.

9. A method for producing a ceramic green sheet or a ceramic molded body, comprising: a. compressing the polyvinyl acetal of any one of claims 1 to 7; b. Producing a suspension composition comprising the compacts produced in step a.; A method comprising:

10. 10. The method of claim 9, wherein the compacted body has a bulk density of 0.55 g / ml or greater when measured according to the present specification.

11. 10. The method of claim 9, wherein the compact has a total pore volume of from 0.25 ml / g to 0.75 ml / g.

12. A method for producing a compressed body using the polyvinyl acetal according to any one of claims 1 to 7.

13. 13. The method of claim 12, wherein the compacted body has a bulk density of 0.55 g / ml or greater when measured according to the present specification.

14. 13. The method of claim 12, wherein the compacted body has a total pore volume of from 0.25 ml / g to 0.75 ml / g.

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