Production of compressed polyvinyl acetal with low residual particles

Abstract

The present invention is directed to a method for producing a compressed powder of polyvinyl acetal with improved residual particle properties and its use as a binder for ceramic green sheets.A method for producing a final compact comprising polyvinyl acetal, the method comprising the steps of: a. compressing a raw powder comprising polyvinyl acetal; b. grinding the compressed polyvinyl acetal of step a. to produce a ground compressed polyvinyl acetal; and c. sieving the ground compressed polyvinyl acetal of step b. to obtain i. a fraction of the final compact having a lower and upper limit of a desired particle size range; ii. a coarse fraction having a particle size range with a lower limit equal to the upper limit of the desired particle size range of the final compact; and iii. a fine fraction having a particle size range from 0 μm to the lower limit of the desired particle size range of the final compact.

Description

[Technical field]

[0001] The present invention is directed to a method for making a compacted powder of polyvinyl acetal having improved residual particle properties and its use as a binder for ceramic green sheets.

[0002] 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 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. 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 required for the subsequent production steps.

[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 several individual capacitors stacked in parallel and contacted via their terminal surfaces. Due to the increasing miniaturization of electronic components, the size of the powder particles can be in the nanometer range. This calls for improved precision in the ceramic sheets used in their manufacture.

[0005] The PVB resins used to make the 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. 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 risk after flame ignition. To solve these problems, granular PVB has been introduced. For example, US Patent Application Publication No. 20080203593 describes the production of PVB granules to be used as binders for ceramic green sheets. However, when such granules are produced by melt extrusion, the high temperatures and high shear forces used in the extruder can cause partial decomposition of the PVB. Furthermore, the dissolution rate of such granules is generally higher than that of the corresponding powdered material, i.e., the granules dissolve slowly. This is because they have a smaller surface compared to powders with a high surface area.

[0006] Compressing PVB powder is a much gentler method that avoids the problems of using powdered PVB because it does not involve high temperature processes, and in addition, the pores on the surface of the powder material are not completely closed when compressed.

[0007] However, it has been found that the compaction process of polyvinyl acetal often results in a significant increase in residual particles, i.e. after dissolving the compacted body in the solvent (mixture) used to make the suspension used in green sheet production, when comparing the compacted material with the raw polyvinyl acetal powder. Such residual particles are becoming an increasing problem in the electronics industry due to the extremely high purity binder required for MLCC production.

[0008] It was therefore an object of the present invention to provide a polyvinyl acetal compact as a binder for ceramic green sheets with improved properties with respect to residual particles. A further object was to provide such a binder which results in 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.

[0009] Compaction is used to densify powders and form compacted bodies. One method for producing such compacted bodies is the use of roller compactors. This compaction process produces so-called "flakes", which are crushed in a second step by a crusher, for example by a hammer mill, to obtain compacted materials with various particle sizes. Since the electronics industry generally requires compacted materials with a certain particle size range, a sieving step is usually added as a third step. Thus, to obtain a compacted body with the desired particle size (hereinafter referred to as the "final compact"), the crushed material is subjected to a classification sieving.

[0010] In addition to the final compact, the sieving process results in a fraction of the compacted polyvinyl acetal having a particle size from about 0 μm to the lower end of the desired particle size range, hereinafter referred to as the "fines fraction." The amount of this fraction may represent 15-25% of the compacted material formed. Thus, in prior art compaction processes, these fines are recycled back into the feedstock.

[0011] To a lesser extent, the sieving process also produces a coarse fraction having a particle size above the upper end of the desired particle size range for the final compact.

[0012] To avoid raw material waste, as well as for environmental and safety reasons, the compactor / crusher / sieving units used for polyvinyl acetal and other materials are constructed with a dust-tight housing, so that no dust of the product or raw material can escape from the housing. The dust generated in the dust-tight housing is collected by suction and recycled to the raw material to improve the overall process yield. This fraction will be referred to as "dust" in the following of this specification.

[0013] The inventors have found that recycling the dust and coarse powder fractions as raw materials does not degrade the quality of the final compact, but recycling the fines from sieving significantly increases the number of residual particles in the final compact.

[0014] Thus, a first aspect of the present invention is a method for producing a final compact comprising polyvinyl acetal, the method comprising the steps of: a. compressing a raw material powder containing polyvinyl acetal; b. grinding the compressed polyvinyl acetal of step a. to produce a ground compressed polyvinyl acetal; c. Sifting the pulverized compressed polyvinyl acetal of step b. i. a fraction of the final compact having a lower and upper limit of a desired particle size range; ii. a coarse fraction having a particle size range with a lower limit equal to the upper limit of the desired particle size range of the final compact; iii. a fine fraction having a particle size range of 0 μm to the lower end of the desired particle size range for the final compact; and Including, The fine fraction obtained in step c) is not recycled to the raw powder used in step a). [Brief description of the drawings]

[0015] [Figure 1] Measurements of the raw powder, the fine fraction from the sieving process, dust, and residual particles in the final compact with and without the fine fraction being recycled are shown (all in solution). [Diagram 2] The results of particle size distribution measurements of the raw powder, dust, and fine fraction are shown.

[0016] As can be seen from Figures 1 and 2, the residual particle count appears to be coupled with the particle size distribution. Surprisingly, the fine fraction resulting from the sieving process shows a sharp increase in particles between 200 and 2000 μm in size, with the number of particles in this range maximizing at approximately 600 μm. This increase appears to be the cause of the deterioration of the dissolution properties / solubility and thus the large increase in the residual particle count.

[0017] Therefore, in a preferred embodiment of the present invention, the percentage of particles in the range of 200 to 2000 μm in the raw material powder is less than 25 vol.% when measured by the method described below. More preferably, the percentage is less than 20 vol.%, even more preferably less than 15 vol.%, most preferably less than 15 vol.%, and especially less than 10 vol.%.

[0018] Preferably, the lower limit of the desired particle size range is 0.5 mm or more and the upper limit of the desired particle size range is 4.0 mm or less.More preferably, the desired particle size range is 0.75 to 3.5 mm.

[0019] Also preferably, the percentage of particles in the 200-2000 μm range of the fine fraction is greater than 25% by volume, expressed as a percentage of the volume density measured by the method described herein, more preferably the percentage is greater than 30%, even more preferably greater than 35%.

[0020] Preferably, the polyvinyl acetal of the compact has a molecular weight of ≧20,000 g / mol, as determined by gel permeation chromatography in accordance with DIN ISO 16014 1:2019-05.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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).

[0029] 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.

[0030] In a second aspect, the present invention provides a method for producing a final compact comprising polyvinyl acetal, the method comprising the steps of: a. compressing a polyvinyl acetal containing a raw powder having a percentage of particles in the range of 200 to 2000 μm of less than 25% by volume, expressed as a percentage of the volume density as measured by the method described herein; b. grinding the compressed polyvinyl acetal of step a. to produce a ground compressed polyvinyl acetal; c. Sifting the pulverized compressed polyvinyl acetal of step b. i. a fraction of the final compact having a lower and upper limit of a desired particle size range; ii. a coarse fraction having a particle size range with a lower limit equal to the upper limit of the desired particle size range of the final compact; iii. a fine fraction having a particle size range of 0 μm to the lower end of the desired particle size range for the final compact; and The present invention relates to a method comprising the steps of:

[0031] In a third aspect, the present invention provides a method for producing a final compact comprising polyvinyl acetal, the method comprising the steps of: a. compressing a polyvinyl acetal containing a raw powder having a percentage of particles in the range of 200 to 2000 μm of less than 25% by volume, expressed as a percentage of the volume density as measured by the method described herein; b. grinding the compressed polyvinyl acetal of step a. to produce a ground compressed polyvinyl acetal; c. Sifting the pulverized compressed polyvinyl acetal of step b. i. a fraction of the final compact having a lower and upper limit of a desired particle size range; ii. a coarse fraction having a particle size range with a lower limit equal to the upper limit of the desired particle size range of the final compact; iii. a fine fraction having a particle size range of 0 μm to the lower end of the desired particle size range for the final compact; and Including, wherein the residual particle count in the final compact, for particles having a particle size of 2 to 500 μm in a 2 wt. % solution in a 1:1 mixture of toluene and ethanol, as measured by the method described herein, is equal to or less than 10% higher than the corresponding residual particle count in the raw powder.

[0032] In a fourth aspect, the present invention relates to a polyvinyl acetal compressed body having a residual particle count of particles having a particle size of 2 to 500 μm in a 2% by mass solution in a 1:1 mixture of toluene and ethanol of 300 counts / ml or less, as measured by the method described herein, preferably 250 counts / ml or less, more preferably 200 counts / ml or less.

[0033] Also preferably, in the fourth embodiment, the percentage of particles in the range of 200-2000 μm is less than 25% by volume when expressed as a percentage of the volume density measured by the method described herein.

[0034] Also preferably, the polyvinyl acetal compressed body has a percentage of particles in the range of 20 to 200 μm, expressed as a percentage of the volume density measured by the method described herein, of more than 80 vol. %, more preferably 90 vol. % or more, and most preferably 95 vol. % or more.

[0035] The compressed polyvinyl acetal product preferably has a particle size of 0.5 mm or more and 4.0 mm or less, more preferably 1.0 to 3.0 mm.

[0036] 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 ingredients to be compacted are moisture or heat sensitive. Compaction is used to densify the powder and form the compacted body. This process is generally carried out using a slugging tool or a roller compactor machine. The slugging process usually results in "flakes", which are typically 25 mm in diameter and 10-15 mm thick. Hammer mills are ideal for crushing the flakes. The compacted material can be further processed by classification sieving to obtain compacted bodies with the desired particle size.

[0037] 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.

[0038] Another aspect of the present invention relates to the use of the polyvinyl acetal compacts according to the invention as binders for the production of ceramic green sheets or ceramic molded bodies.

[0039] For the production of such green sheets, a suspension of metal oxide, plasticizer, dispersant and binder in an organic solvent is prepared.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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. EXAMPLES

[0047] [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.

[0048] 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.

[0049] Polyvinyl Butyral (PVB 3) 100 parts by weight of polyvinyl alcohol with a viscosity of 26 mPas (measured according to DIN 53015 at 20° C., 4 w / w% in aqueous solution) and a degree of hydrolysis of 99 mol % were dissolved in 1075 parts by weight of water while heating to 90° C. At a temperature of 40° C., 57 parts by weight of n-butylaldehyde were added and at a temperature of 10° C., 75 parts by weight of 20% hydrochloric acid were added while stirring. After precipitation of polyvinyl butyral (PVB), the mixture was heated to 70° C. and stirred at this temperature for 1 hour. After cooling to room temperature, the PVB was separated, washed to neutrality with water and dried. A PVB with a polyvinyl alcohol content of 20.0% by weight (28.8 mol %) and a polyvinyl acetate content of 1.4% by weight (1 mol %) was obtained.

[0050] [PVB compression body 1] Polyvinyl butyral PVB 3 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 0.5-1.0 cm thick sheet was then crushed and further reduced in size using a granulator to obtain a compact with a median particle size of 1-3 mm after classification and sieving.

[0051] [Particle count] 2 g of PVB compacts were dissolved in 98 g of a solvent mixture (1:1 mixture of ethanol and toluene) using a tilt / rotate mixer. After 24 hours, a 50 mL sample was 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.

[0052] Figure 1 shows the results of the particle count analysis. The raw powder and dust show values ​​of about 300 counts / ml, while the fine fraction shows significantly higher values ​​of about 600 counts / ml. Thus, the residual particle count of the final compact without fines recycling shows a significantly improved behavior in particle counts compared to the final compact with fines recycling.

[0053] [Particle size distribution] The particle sizes of all powder samples were measured by laser diffraction using a Mastersizer 3000 (Malvern Panalytical) in the angular range of 0.015 to 144 degrees (corresponding to a particle size range of 0.01 to 3500 μm).

[0054] Figure 2 shows the particle size distribution. The raw powder and dust each have no or low particle counts in the range of 200-2000 μm, while the fine fraction shows a large peak around 600 μm. This second mode of particle size is believed to be the cause of the deterioration of the dissolution properties.

[0055] [Table 1]

Claims

1. 1. A method for producing a final compact comprising polyvinyl acetal, said method comprising: a) compressing a raw material powder containing the polyvinyl acetal; b. grinding the compressed polyvinyl acetal of step a. to produce a ground compressed polyvinyl acetal; c. Sifting the pulverized compressed polyvinyl acetal of step b. i. a fraction of the final compact having a lower and upper limit of a desired particle size range; ii. a coarse fraction having a particle size range with a lower limit equal to the upper limit of the desired particle size range of the final compact; iii. a fine fraction having a particle size range of from 0 μm to the lower limit of the desired particle size range of the final compact; and a process of obtaining Including, The fine fraction obtained in step c) is not recycled to the raw powder used in step a).

2. 10. The method of claim 1, wherein the percentage of particles in the raw powder range of 200 to 2000 μm is less than 25% by volume as measured by the method described herein.

3. 2. The method of claim 1, wherein the lower limit of the desired particle size range is 0.5 mm or greater and the upper limit of the desired particle size range is 4.0 mm or less.

4. 10. The method of claim 1, wherein step a. comprises roll compaction in a roll mill.

5. 2. The method of claim 1, wherein the percentage of particles in the range of 200-2000 μm in the fines fraction is greater than 25% by volume when expressed as a percentage of the volume density as measured by the method described herein.

6. 1. A method for producing a final compact comprising polyvinyl acetal, said method comprising: a. compressing a polyvinyl acetal comprising a raw powder having a percentage of particles in the range of 200-2000 μm of less than 25% by volume, expressed as a percentage of the bulk density as measured by the method described herein; b. grinding the compressed polyvinyl acetal of step a. to produce a ground compressed polyvinyl acetal; c. Sifting the pulverized compressed polyvinyl acetal of step b. i. a fraction of the final compact having a lower and upper limit of a desired particle size range; ii. a coarse fraction having a particle size range with a lower limit equal to the upper limit of the desired particle size range of the final compact; iii. a fine fraction having a particle size range of from 0 μm to the lower limit of the desired particle size range of the final compact; and a process of obtaining A method comprising:

7. 7. The method of claim 6, wherein the lower limit of the desired particle size range is 0.5 mm or greater and the upper limit of the desired particle size range is 4.0 mm or less.

8. 1. A method for producing a final compact comprising polyvinyl acetal, said method comprising: a. compressing a polyvinyl acetal comprising a raw powder having a percentage of particles in the range of 200-2000 μm of less than 25% by volume, expressed as a percentage of the bulk density as measured by the method described herein; b. grinding the compressed polyvinyl acetal of step a. to produce a ground compressed polyvinyl acetal; c. Sifting the pulverized compressed polyvinyl acetal of step b. i. a fraction of the final compact having a lower and upper limit of a desired particle size range; ii. a coarse fraction having a particle size range with a lower limit equal to the upper limit of the desired particle size range of the final compact; iii. a fine fraction having a particle size range of from 0 μm to the lower limit of the desired particle size range of the final compact; and a process of obtaining Including, wherein the residual particle count of particles 2 to 500 μm in size in a 2 wt. % solution in a 1:1 mixture of toluene and ethanol in the final compact, as measured by the method described herein, is equal to or less than 10% higher than the corresponding residual particle count in the raw powder.

9. 9. A polyvinyl acetal compressed body produced by the method of any one of claims 1 to 8, having a residual particle count of particles having a particle size of 2 to 500 µm in a 2% by weight solution in a 1:1 mixture of toluene and ethanol of 300 counts / ml or less, when measured by the method described herein.

10. 10. The polyvinyl acetal compressed body according to claim 9, wherein the residual particle count is 250 counts / ml or less.

11. A polyvinyl acetal compressed body as described in claim 9, wherein the percentage of particles in the range of 200 to 2000 μm is less than 25 volume % when expressed as a percentage of the volume density measured by the method described in this specification.

12. A polyvinyl acetal compressed body as described in claim 9, wherein the percentage of particles in the range of 20 to 200 μm is greater than 80 volume % when expressed as a percentage of the volume density measured by the method described in this specification.

13. The polyvinyl acetal compressed product according to claim 9, having a particle size of 0.5 mm or more and 4.0 mm or less.

14. 10. Use of the polyvinyl acetal compressed body according to claim 9 as a binder for producing ceramic green sheets or ceramic molded bodies.

15. 9. The method of claim 1, wherein the polyvinyl acetal is polyvinyl butyral or a mixed polyvinyl acetal derived from the condensation of n-butyraldehyde and acetaldehyde.

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