Polyvinyl acetal resin and slurry composition thereof

Abstract

The invention discloses polyvinyl acetal resin and a slurry composition thereof, and relates to the technical field of polyvinyl alcohol. The polyvinyl acetal resin comprises the following raw materials: polyvinyl alcohol, a cross-linking agent and n-butyraldehyde. A cross-linking structure is constructed by adding the cross-linking agent, so that the mechanical strength of the resin is improved; the content of by-products is reduced by adopting a specific washing process, carbon residues are reduced, and the compatibility with organic solvents is improved. The slurry composition comprises the resin, inorganic powder, a plasticizer, toluene and ethanol, has excellent dispersibility, viscosity stability and green body formability, is suitable for an electronic ceramic tape casting process, can effectively prepare a high-quality multilayer ceramic capacitor green body, and improves production efficiency and product reliability.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of polyvinyl alcohol, in particular to a polyvinyl acetal resin and a slurry composition thereof. BACKGROUND

[0002] Polyvinyl acetal resin (PVB) is a partial condensation product of polyvinyl alcohol and n-butyraldehyde under acid catalysis, containing three functional groups, namely alcohol hydroxyl, butylal group and acetate group. In the field of electronic ceramics, especially in the flow casting process, it plays an indispensable key role and is a crucial film-forming adhesive. Modern electronic components such as chip multilayer ceramic capacitors (MLCC), varistors, substrates, etc. are developing towards multilayer, miniaturization and integration. The flow casting film forming technology is mostly used to manufacture multilayer ceramic element green sheet, and PVB resin is one of the core organic matters for preparing high-quality flow casting slurry. Chip multilayer ceramic capacitors can provide the maximum capacitance under the same volume, which is realized by using high dielectric constant ceramic materials and reducing the thickness of the medium to the nanometer level and stacking up to one thousand layers, meeting the extreme requirements of electronic equipment miniaturization for "board space" components, and is currently becoming the market mainstream. The PVB resin has very high requirements in the manufacturing process of slurry preparation and dispersion, flow casting drying, green sheet punching and lamination, glue removal and sintering, etc.

[0003] Therefore, PVB resin with excellent solubility, film-forming property and thermal decomposition is the key to preparing high-performance MLCC. If PVB resin fails to provide certain mechanical strength to ceramic powder, ceramic green sheet will crack during flow casting, and full sheet strength and softness cannot be obtained, which will cause damage during peeling or punching of ceramic green sheet, seriously affecting production efficiency. In the sintering and glue removal process, the carbon residue of PVB is mainly affected by the content of by-products and oxides formed by metal impurities, including unreacted butyraldehyde, butyraldehyde self-polymer generated under alkaline conditions and metal oxides, etc., which will cause the problem of reduced capacitance of the obtained laminated ceramic capacitor. In the face of the above problems, patent CN104662085B mentions mixing PVB resin with a methacrylic acid resin with a cross-linked structure to enhance the mechanical strength of the composition, which has complex components and high cost. Patent CN107406652B mentions modifying the PVB resin with an imine structure and using it in combination with an epoxy resin, which can improve the strength and adhesion of the resin, but the synthesis process is difficult and is not conducive to production. SUMMARY

[0004] The present application aims to provide a polyvinyl acetal resin to solve the problems of insufficient mechanical strength, high carbon residue and poor compatibility with organic solvents of polyvinyl acetal resin.

[0005] The polyvinyl acetal resin slurry composition of the present application can solve the problems of poor dispersibility, insufficient viscosity stability and poor green body formability of the existing slurry.

[0006] In a first aspect, the present application provides a polyvinyl acetal resin comprising the following raw materials by weight: 50-200 parts of polyvinyl alcohol, 0.01-10 parts of crosslinking agent, and 40-80 parts of n-butyraldehyde; The content of 2-ethylhexanal in the polyvinyl acetal resin is less than 100 ppm.

[0007] By adopting the above technical solution, polyvinyl alcohol is used as the resin matrix to provide sufficient hydroxyl sites for acetalization reaction and crosslinking reaction, thereby ensuring the basic film-forming property and adhesion of the resin; the crosslinking agent forms a three-dimensional network structure through crosslinking reaction between molecular chains, thereby significantly improving the cohesive strength of the resin and further enhancing the mechanical properties of the ceramic green body to avoid damage during casting and punching; n-butyraldehyde is used as an acetalization reagent to react with polyvinyl alcohol to form butyl acetal groups, thereby giving the resin excellent film-forming property and adhesion.

[0008] In addition, 2-ethylhexanal contained in the polyvinyl acetal resin is a byproduct of the self-polymerization of n-butyraldehyde under acidic conditions, and its long branched chain structure can destroy the regularity of the PVB molecular chain, reduce the tensile strength and worsen the compatibility with organic solvents, and also easily pyrolyze at high temperatures to form carbon residues affecting the capacitance performance; controlling the content of 2-ethylhexanal to be less than 100 ppm can not only avoid the above negative effects, but also improve the flexibility of the resin by means of the slight plasticizing effect of a small amount of 2-ethylhexanal, thereby balancing the mechanical strength and processability.

[0009] Preferably, the crosslinking agent comprises one or a combination of ethanedial, glutaraldehyde, bisphenol A type epoxy resin, ethylene glycol diglycidyl ether, toluene diisocyanate, and diphenyl methane diisocyanate.

[0010] The average polymerization degree of the polyvinyl alcohol is 2000-4000.

[0011] More preferably, the crosslinking agent is glutaraldehyde.

[0012] Preferably, the polyvinyl acetal resin is prepared by the following method: A1, dissolving polyvinyl alcohol in water to obtain a polyvinyl alcohol aqueous solution; A2, adding a crosslinking agent and a catalyst to the polyvinyl alcohol aqueous solution, stirring, then adding n-butyraldehyde, and finally adding a lye to react to obtain a polyvinyl acetal resin slurry; A3, washing the polyvinyl acetal resin slurry with water to obtain the polyvinyl acetal resin.

[0013] Preferably, the water washing comprises the following steps: A301. The polyvinyl alcohol acetal resin slurry is subjected to solid-liquid separation. 15-30 wt% sodium hydroxide is added to the solid part until the pH value of the system is 2-7. The mixture is stirred for 10-60 min to obtain a polyvinyl alcohol acetal resin solution. A302. Wash the polyvinyl acetal resin solution with hot water at 40-80℃ 1-15 times. After each wash, centrifuge and dry. Maintain the system temperature at 40-80℃. Pump the material into the second-stage washing tank and mix it with cleaner water from the third stage for washing. Centrifuge and dry again. Repeat this process until the material finally enters the last stage. A303. Reduce the system temperature to 20-25℃ and wash with water 3-15 times. Centrifuge and dry after each wash until the system pH value is 7-9.

[0014] More preferably, in step A301, the pH value of the system is 5 to 7.

[0015] More preferably, in step A302, the system temperature is 60–80°C, and the number of water washes is 5–10.

[0016] Preferably, the ratio of the amounts of polyvinyl alcohol, water, crosslinking agent, catalyst and n-butyraldehyde, by weight, is (50-200): (1000-1500): (0.01-10): (40-80).

[0017] Preferably, in step A1, the dissolution temperature is 80–98°C.

[0018] Preferably, in step A2, the temperature of the polyvinyl alcohol aqueous solution is 20–40°C.

[0019] Preferably, in step A2, the acid catalyst includes hydrochloric acid, nitric acid, and sulfuric acid.

[0020] Preferably, in step A2, n-butyraldehyde is added in two parts. The first part of n-butyraldehyde is added after stirring for 30 to 120 minutes, and the second part of n-butyraldehyde is added after the system temperature drops to 5 to 15°C. The mass ratio of the first part of n-butyraldehyde to the second part of n-butyraldehyde is 1:(3 to 4).

[0021] Preferably, after adding the second part of n-butyraldehyde, the reaction is carried out at 5-15°C for 30-120 min, the system temperature is raised to 50-80°C over 1-4 h and then stirred for another 1-4 h, and then an alkaline solution is added, which is a 15-30 wt% sodium hydroxide solution.

[0022] Preferably, in step A2, the alkaline solution is added and the reaction is carried out by stirring for 30 to 60 minutes.

[0023] Secondly, the present invention also provides a polyvinyl acetal resin slurry composition comprising the following raw materials in parts by weight: 1-20 parts polyvinyl acetal resin, 100 parts inorganic powder, 1-10 parts plasticizer, 5-200 parts toluene, and 5-200 parts ethanol.

[0024] By adopting the above technical solutions, 1-20 parts of polyvinyl acetal resin can fully coat 100 parts of inorganic powder to form a stable bonding system and ensure mechanical strength; plasticizer can reduce the intermolecular forces of resin and improve flexibility and processability. The dosage of 1-10 parts can balance flexibility and mechanical strength and avoid excessive green body sticking; toluene and ethanol are used as mixed solvents. Ethanol can improve the solubility of resin, and toluene can adjust the viscosity of slurry. The synergistic effect of the two makes the slurry have suitable fluidity, which is suitable for casting molding process and ensures uniform green body thickness.

[0025] Preferably, the inorganic powder includes one or a combination of several of barium titanate, alumina, ferrite, silicon carbide and zirconium oxide.

[0026] Preferably, the plasticizer comprises one or a combination of several of dioctyl phthalate, dibutyl phthalate, diisononyl phthalate and dioctyl adipate.

[0027] Preferably, the slurry composition is prepared by the following method: A polyvinyl acetal resin solution is obtained by mixing 1-20 parts of polyvinyl alcohol acetal resin, 1-10 parts of plasticizer, 5-200 parts of toluene and 5-200 parts of ethanol evenly. 100 parts by weight of inorganic powder is added, and the mixture is stirred and ball-milled for 2-3 hours to obtain a polyvinyl alcohol acetal resin slurry composition.

[0028] The beneficial effects of this invention are: 1. This invention provides a polyvinyl acetal resin and its slurry composition, which is a slurry composition containing inorganic powder, polyvinyl acetal resin, plasticizer, toluene, and ethanol. It comprises: a step of preparing a polyvinyl acetal resin solution, a step of dispersing the inorganic powder in the above mixed solution, a polyvinyl acetal resin synthesis process, and a matching water washing process, which can reduce the content of by-reaction products during synthesis. The polyvinyl acetal resin solution exhibits good dispersibility for the inorganic powder, a low viscosity change rate, and provides excellent mechanical strength for the molding of ceramic inorganic powders, and the film has low carbon residue at high temperatures.

[0029] 2. Currently, common methods to improve the mechanical strength of diaphragms involve modifying the ends of polyvinyl acetal resin molecules to include sulfonyl, alkylsulfonyl, aromatic sulfonyl, sulfinyl, imidazolinyl, carboxyl, amide, and amino groups, which are difficult to synthesize. Alternatively, adding methylpropionic acid resin with cross-linking structures results in complex compositions and increases production costs. In this invention, a small amount of cross-linking agent is added during the PVB resin synthesis process to give the synthesized polyvinyl acetal resin a cross-linking structure, thereby improving the resin's mechanical strength.

[0030] 3. In the synthesis of polyvinyl acetal resin, the byproduct 2-ethylhexanal, generated during this invention, undergoes pyrolysis at high temperatures, ultimately forming polycyclic aromatic hydrocarbons and even coke, affecting the carbon residue of PVB resin. This invention found that when the 2-ethylhexanal content reaches 300 ppm or higher, the carbon residue of PVB resin is significantly higher, a conclusion confirmed by gas chromatography detection of polyvinyl acetal resin with high carbon residue. The byproduct 2-ethylhexanal is mainly produced by the self-condensation reaction of the raw material n-butyraldehyde under acidic conditions. This patent initially removes the residual butyraldehyde in the system by washing with water, then softens and swells the polyvinyl acetal resin by heating to 60-80℃, repeatedly washing with water at this temperature to remove the residual n-butyraldehyde in the polyvinyl acetal particles, and then cooling to room temperature for washing with water to stabilize the particles, thereby reducing the byproduct 2-ethylhexanal. Furthermore, 2-ethylhexanal, due to its long branched molecular structure, disrupts the regularity of the molecular chain, causing PVB to maintain a higher degree of amorphous state, increasing its plasticity, making it "softer," and significantly reducing its tensile strength. Simultaneously, 2-ethylhexanal reacts with the hydroxyl groups on the PVB molecular chain, forming a newly formed long-chain alkyl acetal structure with stronger hydrophobicity, leading to reduced compatibility of PVB with organic solvents. Therefore, reducing the 2-ethylhexanal content to below 100 ppm is crucial for controlling carbon residue in PVB resin.

[0031] 4. The process of this invention is simple and low-cost. Compared with existing production processes, this invention does not require the addition of other thixotropic agents or other additives that may affect product performance during the slurry manufacturing process. Furthermore, this invention can improve the mechanical strength of the resin without modifying existing production equipment. According to this invention, a polyvinyl acetal resin and its slurry composition can be provided, which contains no undissolved micelles. It exhibits good adhesion to inorganic materials when preparing ceramic slurries, and the system has good uniformity and stability. It can improve the formability of ceramic powder and possesses excellent mechanical strength, enabling the fabrication of highly reliable multilayer ceramic capacitors. This significantly improves production efficiency and can be applied to the fabrication of electronic ceramic green bodies, conductive pastes, ink printing, and piezoelectric actuators. Detailed Implementation

[0032] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below.

[0033] A polyvinyl acetal resin, comprising the following raw materials in parts by weight: Polyvinyl alcohol 50-200 parts, crosslinking agent 0.01-10 parts, n-butyraldehyde 40-80 parts; The 2-ethylhexanal content in polyvinyl alcohol acetal resin is <100 ppm. By adopting the above technical solutions, polyvinyl alcohol, as the resin matrix, provides sufficient hydroxyl sites for acetalization and crosslinking reactions, ensuring the basic film-forming properties and adhesion of the resin; the crosslinking agent constructs a three-dimensional network structure through crosslinking reactions between molecular chains, significantly improving the cohesive strength of the resin, thereby enhancing the mechanical properties of the ceramic green body and avoiding breakage during casting and die-cutting processes; n-Butyral, as an acetalizing agent, reacts with polyvinyl alcohol to form butyral groups, giving the resin excellent film-forming properties and adhesion.

[0034] Furthermore, 2-ethylhexanal, contained in polyvinyl alcohol acetal resin, is a byproduct of the self-polymerization of n-butyraldehyde under acidic conditions. Its long branched structure can disrupt the regularity of PVB molecular chains, reduce tensile strength, and worsen compatibility with organic solvents. At high temperatures, it is also prone to pyrolysis, forming carbon residues that affect capacitance performance. Controlling the content of 2-ethylhexanal to below 100 ppm can avoid the above-mentioned negative effects and improve the resin's flexibility by utilizing the slight plasticizing effect of trace amounts of 2-ethylhexanal, thus balancing mechanical strength and processability.

[0035] In some embodiments, the crosslinking agent includes one or more of glyoxal, glutaraldehyde, bisphenol A epoxy resin, ethylene glycol diglycidyl ether, toluene diisocyanate, and diphenylmethane diisocyanate; more preferably, the crosslinking agent is glutaraldehyde. As a bifunctional crosslinking agent, glutaraldehyde has moderate reactivity with the hydroxyl groups on the polyvinyl alcohol molecular chain, and can efficiently construct a stable three-dimensional network structure. While improving the mechanical strength of the resin, it will not cause a decrease in resin solubility or an increase in brittleness due to excessive crosslinking. Moreover, glutaraldehyde is inexpensive, has mild reaction conditions, can achieve stable crosslinking without special processes, and has few residual impurities.

[0036] In some embodiments, the average degree of polymerization of polyvinyl alcohol is 2000–4000. If the degree of polymerization is less than 2000, the viscosity of the prepared resin solution is low, which cannot effectively bind the inorganic powder. During the casting process, it cannot provide sufficient mechanical strength to ensure further thinning of the green body, leading to cracking and brittleness of the green body. If the degree of polymerization is greater than 4000, the resin dissolves slowly in the organic solvent, and the solution viscosity is too high. This reduces the dispersibility of the inorganic powder in the solution, and the viscosity of the slurry composition is too high. During the green body preparation process, the slurry has poor fluidity and is difficult to form a film.

[0037] In some embodiments, polyvinyl acetal resin is prepared by the following method: A1. Dissolve 50-200 parts of polyvinyl alcohol in 1000-1500 parts of pure water, and stir at 80-98°C until fully dissolved to obtain a polyvinyl alcohol aqueous solution; A2. Cool the polyvinyl alcohol aqueous solution to 20-40°C, add 0.01-10 parts of crosslinking agent and 30-50 parts of catalyst with a concentration of 20-40 wt%, stir for 30-120 min, add the first part of n-butyraldehyde, lower the system temperature to 5-15°C, add the second part of n-butyraldehyde, react at this temperature for 30-240 min, then raise the temperature of the reaction system to 50-80°C for 1-4 h, and stir the reaction at this temperature for 1-4 h, add 15-30 wt% sodium hydroxide to the reaction solution, and stir for 30-60 min to obtain polyvinyl alcohol acetal resin slurry; A3. The polyvinyl alcohol acetal resin slurry is obtained by washing with water.

[0038] By adopting the above technical solutions, the high-temperature stirring in step A1 ensures complete dissolution of polyvinyl alcohol, avoiding the impact of undissolved particles on reaction uniformity; in step A2, the cross-linking reaction is carried out first, followed by the staged addition of n-butyraldehyde, and the reaction process is controlled by temperature regulation to reduce the formation of by-products. Subsequent heating can promote the complete acetalization reaction, and the addition of sodium hydroxide can neutralize hydrochloric acid and terminate the reaction; the water washing process in step A3 can effectively remove residual impurities and by-products, ensuring resin purity. This preparation method, by precisely controlling the reaction temperature, feeding sequence, and reaction time, achieves effective control over the degree of acetalization, cross-linking density, and by-product content, providing a process guarantee for obtaining polyvinyl alcohol acetal resin with high mechanical strength and low impurity content.

[0039] In some embodiments, washing includes the following steps: A301. The polyvinyl alcohol acetal resin slurry is subjected to solid-liquid separation. 15-30 wt% sodium hydroxide is added to the solid part until the pH value of the system is 2-7. The mixture is stirred for 10-60 min to obtain a polyvinyl alcohol acetal resin solution. A302. Wash the polyvinyl acetal resin solution with hot water at 40-80℃ 1-15 times. After each wash, centrifuge and dry. Maintain the system temperature at 40-80℃. Pump the material into the second-stage washing tank and mix it with cleaner water from the third stage for washing. Centrifuge and dry again. Repeat this process until the material finally enters the last stage. A303. Reduce the system temperature to 20-25℃ and wash with water 3-15 times. Centrifuge and dry after each wash until the system pH value is 7-9.

[0040] In some embodiments, in step A301, the pH value of the system is 5 to 7.

[0041] In some embodiments, in step A302, the system temperature is 60–80°C, and the number of water washes is 5–10.

[0042] By adopting the above technical solution, the residual n-butyraldehyde in the system is initially washed away by water washing. Then, the polyvinyl alcohol acetal resin is softened and swollen by heating to 60-80℃. At this temperature, the residual n-butyraldehyde in the polyvinyl alcohol acetal particles is removed by multiple water washings. Finally, the temperature is lowered to room temperature for water washing to stabilize the particles, thereby reducing the byproduct 2-ethylhexanal.

[0043] In some embodiments, the catalyst includes hydrochloric acid, nitric acid, and sulfuric acid; by selecting the above-mentioned acidic substances as catalysts for the acetal reaction, the reaction rate can be precisely controlled, and the condensation reaction of n-butyraldehyde and polyvinyl alcohol hydroxyl groups can be determined.

[0044] In some embodiments, in step A2, the mass ratio of the first part of n-butyraldehyde to the second part of n-butyraldehyde is 1:(3-4). This mass ratio can balance the acetalization reaction rate and the generation of byproducts. The first part of a small amount of n-butyraldehyde reacts rapidly at a higher temperature to form the basic framework, while the second part of a large amount of n-butyraldehyde reacts slowly at a lower temperature to ensure uniform acetalization and avoid local over-acetalization that leads to a decrease in resin solubility. At the same time, it effectively inhibits the self-polymerization of n-butyraldehyde and reduces the yield of 2-ethylhexanal.

[0045] A polyvinyl acetal resin slurry composition comprising the following raw materials in parts by weight: 1-20 parts polyvinyl acetal resin, 100 parts inorganic powder, 1-10 parts plasticizer, 5-200 parts toluene, and 5-200 parts ethanol.

[0046] By adopting the above technical solutions, 1-20 parts of polyvinyl acetal resin can fully coat 100 parts of inorganic powder to form a stable bonding system and ensure mechanical strength; plasticizer can reduce the intermolecular forces of resin and improve flexibility and processability. The dosage of 1-10 parts can balance flexibility and mechanical strength and avoid excessive green body sticking; toluene and ethanol are used as mixed solvents. Ethanol can improve the solubility of resin, and toluene can adjust the viscosity of slurry. The synergistic effect of the two makes the slurry have suitable fluidity, which is suitable for casting molding process and ensures uniform green body thickness.

[0047] In some embodiments, the inorganic powder includes one or more of barium titanate, alumina, ferrite, silicon carbide and zirconium oxide; the selected inorganic powder is well adapted to the performance requirements of the slurry composition and has good compatibility with polyvinyl acetal resin.

[0048] In some embodiments, the plasticizer includes one or more of dioctyl phthalate, dibutyl phthalate, diisononyl phthalate, and dioctyl adipate; the selected plasticizer has good compatibility with polyvinyl acetal resin, can fully exert its plasticizing effect, and synergistically improve the processing rheology of the resin solution and the flexibility of the final green film, so that it has excellent resistance to breakage during subsequent peeling, punching and lamination processes.

[0049] In some embodiments, the slurry composition is prepared by the following method: A polyvinyl acetal resin solution is obtained by mixing 1-20 parts of polyvinyl alcohol acetal resin, 1-10 parts of plasticizer, 5-200 parts of toluene and 5-200 parts of ethanol evenly. 100 parts by weight of inorganic powder is added, and the mixture is stirred and ball-milled for 2-3 hours to obtain a polyvinyl alcohol acetal resin slurry composition.

[0050] By adopting the above technical solution, the preparation process ensures that the resin and plasticizer are completely dissolved in the solvent to form a uniform binder phase. Then, the inorganic powder is highly uniformly dispersed in this binder phase through ball milling, thereby obtaining a stable, homogeneous, and high-performance ceramic slurry suitable for casting.

[0051] The specific embodiments of the present invention will be described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments.

[0052] Preparation Example

[0053] Preparation Example 1: A polyvinyl acetal resin was prepared by the following method: 100g of polyvinyl alcohol with an average degree of polymerization of 3000 (degree of hydrolysis 99.0 mol%) was dissolved in 1150.0g of pure water and stirred at 95℃ for 3h to ensure complete dissolution. The solution was cooled to 30℃, and 0.4g of glutaraldehyde and 47.2g of 31wt% hydrochloric acid were added. The reaction was allowed to proceed at this temperature for 0.5h, followed by the addition of 12.0g of n-butyraldehyde. The system temperature was then further reduced to 15℃, and the remaining 48.0g of butyraldehyde was added. The reaction system was then heated to 60℃ after 4h and stirred at this temperature for 2h. Finally, 200g of 15wt% sodium hydroxide aqueous solution was added, and the mixture was stirred for 30min.

[0054] After the reaction, the slurry was allowed to stand, all the original liquid was discharged, and the mixture was centrifuged to dryness. 15 wt% sodium hydroxide was added until the system pH reached 6, and the mixture was stirred for 30 minutes. The system was then heated to 70°C and washed 10 times with water, centrifuging to dryness after each wash. The system temperature was maintained at 70°C, and the material was pumped into a second-stage washing vessel to mix and wash with cleaner water from the third stage. This process was repeated until the material entered the final stage. The temperature was then lowered to 25°C, and the washing process was repeated 10 times, centrifuging to dryness after each wash, until the system pH reached 7, yielding a polyvinyl alcohol acetal resin.

[0055] Preparation Example 2: A polyvinyl acetal resin, which differs from Example 1 only in that the amount of glutaraldehyde added is 0.1g.

[0056] Preparation Example 3: A polyvinyl acetal resin, which differs from Example 1 only in that the amount of glutaraldehyde added is 0.25g.

[0057] Preparation Example 4: A polyvinyl acetal resin, which differs from Example 1 only in that the temperature of the first 10 water washes is 80°C.

[0058] Preparation Example 5: A polyvinyl alcohol acetal resin, which differs from Example 1 only in that the average degree of polymerization of polyvinyl alcohol is 3000.

[0059] Preparation Example 6: A polyvinyl acetal resin, which differs from Example 1 only in that glutaraldehyde is not added.

[0060] Preparation Example 7: A polyvinyl acetal resin, which differs from Example 1 only in that the temperature of the first 10 water washes is 20°C.

[0061] Preparation Example 8: A polyvinyl acetal resin, which differs from Example 1 only in that the first water wash is performed 5 times.

[0062] Example

[0063] Example 1: A polyvinyl acetal resin slurry composition was prepared by the following method: Five parts of the polyvinyl acetal resin prepared in Preparation Example 1 were added to 47.5 parts of toluene and swollen for 1 hour. Then, 47.5 parts of ethanol solution were added and stirred for 2 hours. Finally, 4 parts of dioctyl phthalate (DOP) were added, and the mixture was stirred continuously until the resin was completely dissolved to prepare a polyvinyl acetal resin solution. 100 parts by weight of barium titanate powder were added to the polyvinyl acetal resin solution and stirred using a ball mill for 3 hours to obtain a slurry composition.

[0064] Example 2, a polyvinyl acetal resin slurry composition, differs from Example 1 only in that the polyvinyl acetal resin prepared in Preparation Example 2 is used to replace the polyvinyl acetal resin in Example 1 with the same weight.

[0065] Example 3, a polyvinyl acetal resin slurry composition, differs from Example 1 only in that the polyvinyl acetal resin prepared in Preparation Example 3 is used to replace the polyvinyl acetal resin in Example 1 with the same weight.

[0066] Example 4, a polyvinyl acetal resin slurry composition, differs from Example 1 only in that the polyvinyl acetal resin prepared in Preparation Example 4 is used instead of the polyvinyl acetal resin in Example 1.

[0067] Example 5: A polyvinyl acetal resin slurry composition, which differs from Example 1 only in that the polyvinyl acetal resin prepared in Preparation Example 5 is used instead of the polyvinyl acetal resin in Example 1.

[0068] Example 6: A polyvinyl acetal resin slurry composition was prepared by the following method: Ten parts of the polyvinyl acetal resin prepared in Preparation Example 1 were added to 45 parts of toluene and swollen for 1 hour. Then, 45 parts of ethanol solution were added and stirred for 2 hours. Finally, 5 parts of DOP were added, and the mixture was stirred continuously until the resin was completely dissolved to prepare a polyvinyl acetal resin solution. 100 parts by weight of barium titanate powder were added to the polyvinyl acetal resin solution and stirred using a ball mill for 3 hours to obtain a slurry composition.

[0069] Example 7: A polyvinyl acetal resin slurry composition, differing from Example 1 only in that the same weight of ferrite is used to replace barium titanate in Example 1.

[0070] Example 8: A polyvinyl acetal resin slurry composition, differing from Example 1 only in that barium titanate in Example 1 is replaced with the same weight of alumina.

[0071] Comparative Example

[0072] Comparative Example 1 is a polyvinyl acetal resin slurry composition, which differs from Example 1 only in that the polyvinyl acetal resin prepared in Preparation Example 6 is used instead of the polyvinyl acetal resin in Example 1.

[0073] Comparative Example 2 is a polyvinyl acetal resin slurry composition, which differs from Example 1 only in that the polyvinyl acetal resin prepared in Preparation Example 7 is used instead of the polyvinyl acetal resin in Example 1.

[0074] Comparative Example 3 is a polyvinyl acetal resin slurry composition, which differs from Example 1 only in that the polyvinyl acetal resin prepared in Preparation Example 8 is used instead of the polyvinyl acetal resin in Example 1.

[0075] Comparative Example 4: A polyvinyl acetal resin slurry composition was prepared by the following method: 15 parts of the polyvinyl acetal resin prepared in Preparation Example 1 were added to 42.5 parts of toluene and swollen for 1 hour. Then, 42.5 parts of ethanol solution were added and stirred for 2 hours. Finally, 7.5 parts of DOP were added, and the mixture was stirred continuously until the resin was completely dissolved to prepare a polyvinyl acetal resin solution. 100 parts by weight of barium titanate powder were added to the polyvinyl acetal resin solution and stirred using a ball mill for 3 hours to obtain a slurry composition.

[0076] Comparative Example 5, a polyvinyl acetal resin slurry composition, was prepared by the following method: 15 parts of the polyvinyl acetal resin prepared in Preparation Example 1 were added to a mixed solution of 42.5 parts toluene / ethanol and stirred for 3 hours. Then, 7.5 parts of DOP were added, and the mixture was stirred continuously until the resin was completely dissolved to prepare a polyvinyl acetal resin solution. 100 parts by weight of barium titanate powder were added to the polyvinyl acetal resin solution and stirred using a ball mill for 3 hours to obtain a slurry composition.

[0077] Performance testing: 1. The polyvinyl acetal resins prepared in Preparation Examples 1 to 8 were subjected to the following tests, and the results are listed in Table 1: (1) Viscosity: 10g of polyvinyl alcohol acetal resin was dissolved in toluene / ethanol = 1:1 solvent to prepare a 5wt% solid content solution, and tested at 20℃ using a rotational viscometer. (2) Mechanical properties: Polyvinyl alcohol acetal resin was made into 0.7 mm thin sheets using a hot press, and the mechanical strength of the sheets was tested by a universal tensile tester; (3) 2-Ethylhexanol content: detected by gas chromatography; (4) Carbon residue: TGA test, measured at room temperature to 800°C under nitrogen atmosphere; 2. The polyvinyl alcohol acetal resin slurry compositions prepared in Examples 1 to 8 and Comparative Examples 1 to 5 were subjected to the following tests, and the results are listed in Table 2: (1) Storage stability: After one month of storage at 25°C and 50% humidity, the state of the slurry composition was confirmed; (2) Viscosity stability: The viscosity was measured after storing the product in a constant temperature room at 25°C for one month. (3) Evaluation of raw sheets: Preparation of raw sheets: The slurry composition was cast onto a PET film using a coating machine and dried to form 20 μm resin sheets. The obtained ceramic raw sheets were peeled off from the PET film, and their condition was visually observed. The integrity was evaluated using the following criteria. 1. It can be completely peeled off from the film, and no cracks or damage are visible on the sheet; 2. The sheet can be completely peeled off from the film, but it is cracked or damaged; 3. It cannot be peeled off from the membrane, and after peeling, there are a lot of cracks and damage.

[0078] Table 1. Test Results of Polyvinyl Aldehyde Resin Performance

[0079] Table 2. Performance Test Results of Polyvinyl Aldehyde Resin Slurry Composition

[0080] The test results above show that the present invention effectively constructs a three-dimensional network structure by introducing a crosslinking agent, significantly improving the mechanical strength of the resin, which is far higher than that of Comparative Example 1 without the crosslinking agent, thus ensuring the integrity of the green body during casting and die-cutting. Furthermore, the unique gradient heating and washing process efficiently removes residual n-butyraldehyde, successfully controlling the content of the key byproduct 2-ethylhexanal below 100 ppm. This not only directly reduces high-temperature carbon residue but also improves the compatibility of the resin with organic solvents, resulting in excellent viscosity stability and green body formation properties in the slurry composition. The slurry stratification and performance degradation in Comparative Examples 4 and 5 caused by excessive resin or improper mixing processes demonstrate the synergistic necessity of the formulation and preparation method of the present invention. Overall, the present invention achieves the preparation of high-strength, low-impurity PVB resin through the synergistic effect of crosslinking enhancement and deep purification, meeting the technical requirements of high-end electronic ceramic casting.

[0081] The above-disclosed embodiments are merely a few specific examples of the present invention. However, the embodiments of the present invention are not limited thereto, and any variations that can be conceived by those skilled in the art should fall within the protection scope of the present invention.

Claims

1. A polyvinyl acetal resin, characterized in that, Including the following parts by weight of raw materials: Polyvinyl alcohol 50-200 parts, crosslinking agent 0.01-10 parts, n-butyraldehyde 40-80 parts; The polyvinyl acetal resin contains less than 100 ppm of 2-ethylhexanal.

2. The polyvinyl acetal resin according to claim 1, characterized in that, The crosslinking agent includes one or more of glyoxal, glutaraldehyde, bisphenol A epoxy resin, ethylene glycol diglycidyl ether, toluene diisocyanate, and diphenylmethane diisocyanate.

3. The polyvinyl acetal resin according to claim 1, characterized in that, The average degree of polymerization of the polyvinyl alcohol is 2000-4000.

4. The polyvinyl acetal resin according to claim 1, characterized in that, The polyvinyl acetal resin is prepared by the following method: A1. Dissolve polyvinyl alcohol in water to obtain a polyvinyl alcohol aqueous solution; A2. Add crosslinking agent and acid catalyst to polyvinyl alcohol aqueous solution, stir, add n-butyraldehyde, and finally add alkaline solution to react and obtain polyvinyl alcohol acetal resin slurry. A3. The polyvinyl alcohol acetal resin slurry is obtained by washing with water.

5. The polyvinyl acetal resin according to claim 4, characterized in that, The water washing includes the following steps: A301. Separate the polyvinyl acetal resin slurry into solid and liquid components, add 15-30 wt% sodium hydroxide to the solid component until the pH value of the system is 2-7, and stir for 10-60 min to obtain a polyvinyl acetal resin solution. A302. Wash the polyvinyl acetal resin solution with hot water at 40-80℃ 1-15 times. After each wash, centrifuge and dry. Maintain the system temperature at 40-80℃. Pump the material into the second-stage washing tank and mix it with cleaner water from the third stage for washing. Centrifuge and dry again. Repeat this process until the material finally enters the last stage. A303. Reduce the system temperature to 20-25℃ and wash with water 3-15 times. Centrifuge and dry after each wash until the system pH value is 7-9.

6. The polyvinyl acetal resin according to claim 4, characterized in that, The amounts of polyvinyl alcohol, water, crosslinking agent, catalyst and n-butyraldehyde, by weight, are (50-200): (1000-1500): (0.01-10): (40-80); the acid catalyst includes hydrochloric acid, nitric acid and sulfuric acid.

7. The polyvinyl acetal resin according to claim 4, characterized in that, The n-butyraldehyde is added in two parts. The first part of n-butyraldehyde is added after stirring for 30 to 120 minutes, and the second part of n-butyraldehyde is added after the system temperature drops to 5 to 15°C. The mass ratio of the first part of n-butyraldehyde to the second part of n-butyraldehyde is 1:(3 to 4).

8. A polyvinyl acetal resin slurry composition, using the polyvinyl acetal resin according to any one of claims 1-7, characterized in that, Including the following parts by weight of raw materials: 1-20 parts polyvinyl acetal resin, 100 parts inorganic powder, 1-10 parts plasticizer, 5-200 parts toluene, and 5-200 parts ethanol.

9. The polyvinyl acetal resin slurry composition according to claim 8, characterized in that, The inorganic powder comprises one or more of barium titanate, alumina, ferrite, silicon carbide, and zirconium oxide; the plasticizer comprises one or more of dioctyl phthalate, dibutyl phthalate, diisononyl phthalate, and dioctyl adipate.

10. The polyvinyl acetal resin slurry composition according to claim 8, characterized in that, The slurry composition was prepared by the following method: A polyvinyl acetal resin solution is obtained by mixing 1-20 parts of polyvinyl alcohol acetal resin, 1-10 parts of plasticizer, 5-200 parts of toluene and 5-200 parts of ethanol evenly. 100 parts by weight of inorganic powder is added, and the mixture is stirred and ball-milled for 2-3 hours to obtain a polyvinyl alcohol acetal resin slurry composition.

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