Use of compacted polyvinyl acetals as binder in ceramic green sheets, a suspension composition, a compactate, and a method for preparing the compactate

Abstract

This invention relates to the use of compacted polyvinyl acetal powder as an adhesive on ceramic green sheets.

Description

Technical field

[0001] The invention relates to the use of a compacted powder (compacted powder) of polyvinyl acetal in a ceramic green sheet as a binder. Prior technology

[0002] Ceramic materials such as ceramic capacitors used in the electronics industry are usually manufactured by resorting to sintering of so-called green sheets (i.e., membrane-like, thin molded bodies) containing ceramic materials. Suspensions of metal oxides, plasticizers, dispersants and adhesives in organic solvents are fabricated in order to make such bioblast sheets. The suspension is then applied to the desired thickness on the carrier film using a suitable procedure (i.e., a doctor blade process) and the solvent is removed. The raw embryos thus obtained shall be free from cracking, exhibit a smooth surface and still have some elasticity.

[0003] Polyvinyl acetal such as polyvinyl butyral (PVB) is often used as a binder for the manufacture of ceramic bioblasts. For this purpose, DE 4 003 198 A1 describes the fabrication of casting slips of ceramic bioblast films, in which PVB with a residual polyvinyl acetate (polyvinyl acetate) content of 0 to 2% by weight is used as the adhesive.

[0004] In recent years, multi-layer ceramic capacitors (MLCCs) have become increasingly important in the electronics industry. The MLCC consists of numerous individual capacitors stacked together in parallel and in contact through the termination surface. Due to the advanced miniaturization of the electronic components, the size of the powder particles can be as small as 10 nm. Therefore, the manufacturing requires improved precision of the ceramic sheets used therein. In addition, the multilayer stacking of ceramic bioblasts during the process is often entangled into rolls. In order to avoid delamination, individual bioblasts must have excellent properties regarding adhesion and elongation-at-break.

[0005] To achieve these goals, high molecular weight (i.e., high degree of polymerization) PVB is preferred because it forms a suspension with sufficiently high viscosity. However, the dissolution rate of high molecular weight PVB is worse than that of short-chain PVB, resulting in an overall increase in the time required to prepare the suspension.

[0006] PVB resin used to prepare suspensions is typically supplied in fine powder form. However, due to health and / or safety concerns, these powders cannot be used in all industrial settings. Depending on the particle size, particles may be easily inhaled into the lungs of employees handling the material. Furthermore, materials in powder form often pose an explosion risk after being ignited by a flame.

[0007] To address these issues, PVB in granular form has been introduced. For example, US20080203593A1 describes the manufacture of PVB granules used as an adhesive for ceramic green sheets.

[0008] However, manufacturing these granules using melt extrusion results in partial decomposition of PVB due to the high temperatures and shear forces used in the extruder. Furthermore, the granules dissolve much more slowly than the corresponding powder. Because high molecular weight PVB already has a poor dissolution rate, the ceramics industry discourages the use of PVB in granular form. Summary of the Invention

[0009] Therefore, one object of the present invention is to provide an adhesive for ceramic green sheets with an improved dissolution rate. Another object is to provide an adhesive that achieves improved adhesion, improved processing, improved elongation at break, improved dispersion, improved environmental, health and safety effects and / or a better economic profile in the manufacture and use of ceramic green sheets.

[0010] The inventors of this case have now surprisingly discovered that using compacted PVB can solve these and other purposes.

[0011] Therefore, the first aspect of the present invention relates to the use of a compactate comprising polyvinyl acetal as an adhesive in the production of ceramic green sheets or ceramic molded bodies, wherein the polyvinyl acetal has a molecular weight equal to or greater than 50,000 g / mol when measured by gel permeation chromatography according to DIN ISO 16014 1:2019-05.

[0012] The molecular weight was determined by gel permeation chromatography according to DIN ISO 16014 1:2019-05. Preferably, the molecular weight is equal to or greater than 60,000 g / mol, more preferably 70,000 g / mol. Even more preferably, the molecular weight is equal to or less than 200,000 g / mol, more preferably equal to or less than 175,000 g / mol, most preferably equal to or less than 150,000 g / mol, and particularly equal to or less than 100,000 g / mol. Even more preferably, the molecular weight is from 50,000 to 150,000 g / mol, more preferably from 60,000 to 125,000 g / mol.

[0013] As used herein, the term "compactate" refers to compacted polyvinyl acetal powder that has undergone a compacting process involving pressing dry powder without the use of solvents or melting the powder. This compaction process is also known as dry granulation, rather than wet granulation using solutions or slurries, or extrusion using a melt of polyvinyl acetal material.

[0014] Preferably, the acetal group individually 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, it is derived from the following list: formaldehyde, acetaldehyde, n-propanal, n-butanal, iso-butanal, and n-pentanal. Isopentanal (3-methyl-1-butanal), sec-pentanal (2-methyl-1-butanal), tert-pentanal (2,2,dimethyl-1-propanal), n-hexanal (capronaldehyde), isopentanal (2-methyl-1-pentanal) 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-heptane Aldehydes (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-pentanal4-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, they are derived from condensation reactions with isobutyraldehyde, acetaldehyde, and / or n-butyraldehyde. The optimal form of polyvinyl acetal is polyvinyl butyral.

[0015] While there are no particular limitations on the method used to manufacture the polyvinyl acetal in this embodiment of the invention, it can be manufactured by adding an aldehyde to a polyvinyl alcohol solution under acidic conditions to carry out an acetalization reaction. Polyvinyl acetal is also commercially available, for example, Mowital® polyvinyl acetal sold by Kuraray Europe GmbH.

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

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

[0018] The vinyl alcohol content and vinyl acetate content of polyvinyl acetal were determined according to DIN ISO 3681 (acetic acid content) and DIN ISO 53240 (PVA content).

[0019] Preferably, the median particle size of the compacted material is 0.5 to 5 mm, more preferably 2 to 4 mm. The particle size is measured using a defined particle quantity and by optical inspection of the particle diameter (in the case of a spherical shape) or the longest lateral axis (in the case of a non-spherical shape).

[0020] In the second embodiment, 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 dispersing agents, wherein the binder is a compactate comprising polyvinyl acetal as described above.

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

[0022] Inorganic pigments can be selected from finely ground granules of paraelectric or ferroelectric raw materials, and preferably modified with additives of zinc, zirconium, niobium, magnesium, tantalum, cobalt and / or strontium, and compounds selected from MgNb₂O₆, ZnNb₂O₆, MgTa₂O₆, ZnTa₂O₆, (ZnMg)TiO₃, (ZrSn)TiO₄, BaTiO₃, and Ba₂Ti₉O₂₀. The average particle diameter of the inorganic pigments is preferably about 0.01 to 1 μm.

[0023] The organic solvent can be selected from aromatic compounds (such as toluene and xylene) and alcohol compounds (such as ethanol, isopropanol, and butanol), 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 with polyoxyalkylene groups on their side chains, such as the MALIALIM™ series sold by NOF America Cooperation.

[0025] In addition to the adhesive according to the invention, the suspension may contain other components, particularly selected from other adhesives (such as cellulose resin, acrylic resin, vinyl acetate resin, polyvinyl alcohol resin); plasticizers (such as polyethylene glycol or phthalic ester); and / or defoamers.

[0026] There are no particular limitations on the methods used to manufacture the suspension composition. Various dispersion methods can be used, such as methods using media-type mills (e.g., bead mills, ball mills, attritors, paint shakers, and sand mills); methods of kneading powdered ceramics, dispersing media, dispersants, binders, plasticizers, etc.; and methods using three-roll mills. Using a three-roll mill, this method involves dispersing powdered inorganic pigments together with dispersants, binders, plasticizers, etc., in an organic solvent (mixture). The mixture is compressed and kneaded by passing it through a small gap between the first roller and the second roller (the rollers roll independently of each other and are adjacent to each other with the small gap between them). Then, the mixture is further compressed and kneaded by passing it through a gap between the second roller and the third roller (the third roller rolls and is adjacent to the second roller, and the gap between them is smaller than the gap between the first and second rollers).

[0027] Preferably, the powdered ceramic, dispersant, and solvent (mixture) are pre-mixed and dispersed to allow the dispersant to adsorb onto the powdered ceramic. In the second step, a binder is added to the mixture thus formed, followed by further mixing and dispersion.

[0028] The dry film thickness of the coating film produced by these processes can be 0.25 to 25 micrometers, typically 1 to 15 micrometers.

[0029] Compactate can be prepared using dry granulation processes known in the prior art (i.e., processes that form particles without the aid of any liquid solution). These processes are preferred when the component to be compacted is sensitive to moisture or heat. Compaction is used to densify powder and form compactate. This process is typically carried out using a slugging tool or a roller compactor machine. The slugging method often forms "slugs" typically 25 mm in diameter and 10-15 mm in thickness. Hammer mills are well-suited for breaking up slugs to produce the final compactate.

[0030] Preferably, the process for manufacturing compacted objects uses a roller compactor. In this device, powder is squeezed by two counter-rotating rollers to form compressed sheets. These sheets are brittle and easily break into flakes. These flakes need to be carefully handled to break them into compacted objects, which can then be ground to the desired size. Roller compaction equipment offers a wide range of pressures and roller types to achieve proper densification. Implementation

[0031] [Example] [] Example 1 - PVB Compactor 1

[0032] Polyvinyl butyral powder (Mowital® B 75 H with a molecular weight of 100,000 g / mol ± 10,000 g / mol) was drawn between two counter-rotating water-cooled rollers at 45 °C using a roller compactor with a line pressure of 15 kN / cm. The resulting 0.5–1.0 cm thick flakes were then crushed and subsequently further reduced in size using a granulator to obtain compactate with a median particle size of 1–3 mm. [] Dissolution behavior of PVB powder and PVB compacts

[0033] 10 g of PVB powder or compressed material was mixed with 90 g of solvent mixture (1:1 mixture of ethanol and toluene). A dissolution process was performed using a rotating and tilting mixer (supplier: IKA, model: Kipp- / Rollenmischer, digital, 6). After defined time periods (0h, 3h, 6h, 18h, and 24h), the mixer was stopped, and over 1 g of supernatant was collected. The solid content was determined by evaporating the solvent in an oven. Analysis was performed using a digital precision balance. [] result

[0034] The compacted material 1 completely dissolved after 3 hours. On the other hand, the corresponding powder material required a dissolution time of more than 6 hours to completely dissolve. Particle count in solutions of PVB powder and PVB compacts

[0035] Compactor 2 was prepared in the same manner as compactor 1, but using Mowital® B 30 HH, which is a type of PVB with a molecular weight of 35,000 g / mol + / - 10,000 g / mol sold by Kuraray Europe GmbH. 2 g of PVB powder or compact was dissolved in 98 g of a solvent mixture (1:1 mixture of ethanol and toluene) using a tilting / rotating mixer. After 24 hours, 50 mL of the sample was taken and analyzed using a Soliton GmbH Accusizer™ 780 with laser focus for single particle measurement. Only particles in the range of 2–500 µm in size were counted. [] result:

[0036] Residual particles ranging in size from 2 to 500 µm are a major problem in the manufacture of ceramic green sheets, and therefore their presence in the binder solution must be minimized. Although the compacting process for compact 1 only showed a moderate increase in particle size, compacting PVB material with a lower molecular weight (compact 2) surprisingly resulted in a higher increase in particle count from powder to compact.

Claims

1. The use of a compactate containing polyvinyl acetal as an adhesive in the production of ceramic green sheets or ceramic molded bodies, wherein, According to DIN ISO 16014-1:2019-05, when measured by gel permeation chromatography, the polyvinyl acetal has a molecular weight of 50,000 to 150,000 g / mol; and the compacted mass has a median particle size of 0.5 to 5 mm.

2. As in the purpose of request item 1, wherein, The polyvinyl acetal is polyvinyl butyral.

3. As in the purpose of request item 1 or 2, wherein, According to DIN ISO 16014-1:2019-05, when measured by gel permeation chromatography, the polyvinyl acetal has a molecular weight of 50,000 g / mol or greater and 150,000 g / mol or less.

4. As in the purpose of request item 1 or 2, wherein, The compacted material has a median particle size of 1 to 5 mm.

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 adhesive is a press-fitting material as claimed in any of claims 1 to 4.

6. A compressed body comprising polyvinyl acetal having a molecular weight of 50,000 to 150,000 g / mol as measured by gel permeation chromatography according to DIN ISO 16014-1:2019-05; and the compressed body having a median particle size of 0.5 to 5 mm.

7. The compacted material as requested in item 6 has a median particle size of 1 to 5 mm.

8. A method for preparing a compacted object as claimed in claim 7, comprising the step of compacting polyvinyl acetal powder using a roller mill.