Carboxyl-modified water-soluble PVB resin, its preparation method and application

Abstract

This invention relates to the field of water-based functional paint technology, and more particularly to a carboxyl-modified water-soluble PVB resin, its preparation method, and its applications. Addressing the shortcomings of existing water-soluble PVB resins, such as a significant contradiction between water solubility and water resistance, insufficient adhesion, low film hardness, and poor storage stability, this invention first uses 0899 type general-purpose polyvinyl alcohol as a starting material, synthesizing a PVB resin with a narrow molecular weight distribution and controllable functional group content through low-temperature acidification and a gradient-temperature acetal reaction. Then, through a mild ring-opening esterification reaction between phthalic anhydride and the hydroxyl groups on the PVB resin molecular chain, hydrophilic carboxyl groups are quantitatively introduced into the PVB molecular chain, with the content controlled at 0.6~2.8 mmol / g. This process ensures the excellent water solubility of the carboxyl-modified water-soluble PVB resin while maximizing the preservation of its original mechanical properties and adhesion, endowing the water-based paint composition with advantages such as high adhesion, high water resistance, high hardness, and storage stability.

Description

Technical Field

[0001] This invention relates to the field of water-based functional paint technology, and in particular to a carboxyl-modified water-soluble PVB resin (WPVB resin), its preparation method, and its application. Background Technology

[0002] Polyvinyl butyral (PVB) resin contains three functional groups—butyral, hydroxyl, and acetyl—in its molecular chain, exhibiting excellent adhesion, flexibility, impact resistance, transparency, and chemical resistance. It is an important raw material for the preparation of high-grade paints, adhesives, and inks. Traditional PVB paints are solvent-based, releasing large amounts of volatile organic compounds (VOCs) during production and application, causing serious environmental pollution and occupational health hazards, and thus failing to meet increasingly stringent environmental protection requirements.

[0003] Modifying PVB resin to make it water-soluble and preparing water-based PVB paint is the fundamental way to solve the above problems. However, existing water-soluble PVB resins generally have the following drawbacks: 1) The contradiction between water solubility and water resistance is prominent: In order to improve water solubility, a large number of strong hydrophilic groups (such as sulfonic acid groups and amino groups) are introduced, which leads to a sharp decrease in water resistance after film formation. The coating film is prone to absorbing water, turning white, and peeling off.

[0004] 2) Insufficient adhesion: The molecular structure of the modified resin is severely damaged, resulting in a significant reduction in adhesion to substrates such as metal, wood, and plastic, and it is prone to delamination, especially in humid environments.

[0005] 3) Low coating hardness: Existing modification methods often lead to a decrease in the molecular weight of the resin or insufficient cross-linking, resulting in low coating hardness and poor wear resistance and scratch resistance.

[0006] 4) Poor storage stability: Aqueous PVB emulsions or solutions are prone to stratification and precipitation, resulting in a short shelf life, which is not conducive to industrial production and application.

[0007] Therefore, developing a water-soluble PVB resin and its water-based paint composition that combines excellent water solubility, high adhesion, good water resistance and hardness has significant market value and application prospects. Summary of the Invention

[0008] In view of this, the present invention provides a carboxyl-modified water-soluble PVB resin, its preparation method and application. The carboxyl-modified water-soluble PVB resin provided by the present invention has excellent water solubility, high adhesion, good water resistance and hardness.

[0009] This invention provides a method for preparing carboxyl-modified water-soluble PVB resin, comprising the following steps: (1) Mix 0899 type PVA with water, acidify, and mix with n-butyraldehyde to carry out acetal reaction to obtain PVB resin; (2) PVB resin is mixed with polar organic solvent, tertiary amine catalyst and phthalic anhydride for esterification modification to obtain carboxyl-modified water-soluble PVB resin.

[0010] Preferably, the degree of polymerization of 0899 type PVA is 750~850 and the degree of alcoholysis is 98~100 mol.

[0011] Preferably, the target pH value for acidification is 1 to 2; the acidifying agent used for acidification is concentrated hydrochloric acid; and the concentration of concentrated hydrochloric acid is 36 to 38 wt%.

[0012] Preferably, the PVB resin has a hydroxyl content of 19-24 wt%, a butyral content of 72-78 wt%, an acetyl content of 1-4 wt%, a number-average molecular weight of 40,000-80,000, and a molecular weight distribution index ≤2.2.

[0013] Preferably, the mass ratio of PVB resin to tertiary amine catalyst is 100:0.2~1.5; and the mass ratio of PVB resin to phthalic anhydride is 100:6~18.

[0014] The present invention also provides a carboxyl-modified water-soluble PVB resin, which is prepared by the above-described method for preparing carboxyl-modified water-soluble PVB resin, in the form of an aqueous solution, with a solid content of 30-40 wt% and a carboxyl content of 0.6-2.8 mmol / g.

[0015] The present invention also provides an application of a carboxyl-modified water-soluble PVB resin in the field of water-based paints, wherein the carboxyl-modified water-soluble PVB resin is the carboxyl-modified water-soluble PVB resin described above.

[0016] The present invention also provides a water-based paint composition comprising, by weight parts: 50-70 parts of carboxyl-modified water-soluble PVB resin; 5-15 parts of water-based amino resin curing agent; 0-30 parts of pigments and fillers; 0.5-2 parts of dispersant; 0.1-0.5 parts of leveling agent; 0.1-0.5 parts of defoamer; 1-5 parts of film-forming aid; 5-20 parts of deionized water; the carboxyl-modified water-soluble PVB resin is the carboxyl-modified water-soluble PVB resin of the above scheme.

[0017] The present invention also provides a method for preparing the above-described water-based paint composition, comprising the following steps: (1) Mix the dispersant, defoamer and deionized water to obtain a premix; (2) After dispersing the premix and pigments and fillers, grind them to a fineness of ≤20μm to obtain a pigment and filler slurry; (3) Under stirring conditions, carboxyl-modified water-soluble PVB resin, water-based amino resin curing agent, leveling agent and film-forming aid are added to the pigment and filler slurry in sequence, stirred and mixed, and the viscosity is adjusted to 25~35s (25℃) of Fore-4 cup to obtain water-based paint composition.

[0018] The present invention also provides the application of the above-described water-based paint composition in the fields of metal corrosion protection, wood coating, or plastic primer.

[0019] Compared with the prior art, the present invention has achieved the following beneficial effects: To address the shortcomings of existing water-soluble PVB resins, such as a prominent contradiction between water solubility and water resistance, insufficient adhesion, low film hardness, and poor storage stability, this invention first uses 0899 type general-purpose polyvinyl alcohol (PVA) as the starting material and synthesizes a PVB resin with a narrow molecular weight distribution (PDI≤2.2) and controllable functional group content through low-temperature acidification and gradient temperature acetal reaction. Then, through a mild ring-opening esterification reaction between phthalic anhydride and the hydroxyl groups on the PVB resin molecular chain, hydrophilic carboxyl groups (content 0.6~2.8mmol / g) are quantitatively introduced into the PVB molecular chain. This ensures the excellent water solubility of the carboxyl-modified water-soluble PVB resin while maximizing the preservation of its original mechanical properties and adhesion.

[0020] The water-based paint composition obtained by combining carboxyl-modified water-soluble PVB resin with water-based amino resin curing agent, pigments, fillers, and additives provided by this invention has advantages such as low VOC, high adhesion, good water resistance and hardness, and storage stability. The VOC content is ≤50g / L, far below the national standard; the coating adhesion can reach grade 0, the pencil hardness is ≥2H, and there is no whitening, bubbling, or peeling after immersion at room temperature for 72 hours; the shelf life at room temperature is ≥6 months.

[0021] The preparation method provided by this invention uses readily available raw materials, is inexpensive, and has simple steps that are easy to industrialize. The prepared water-based paint composition has excellent comprehensive performance and can be widely used in fields such as metal corrosion protection, wood coating, and plastic primer. Attached Figure Description

[0022] To more clearly illustrate the technical solutions of this invention, the accompanying drawings used in the embodiments of this invention or in the prior art are briefly described below. For those skilled in the art, other drawings can be derived from the following drawings without creative effort, and all such drawings are within the protection scope of this invention.

[0023] Figure 1 This is a schematic diagram of the process flow for preparing the carboxyl-modified water-soluble PVB resin and water-based coating composition according to the present invention. Detailed Implementation

[0024] This invention provides a method for preparing carboxyl-modified water-soluble PVB resin, comprising the following steps: (1) Mix 0899 type PVA with water, acidify, and mix with n-butyraldehyde to carry out acetal reaction to obtain PVB resin; (2) PVB resin is mixed with polar organic solvent, tertiary amine catalyst and phthalic anhydride for esterification modification to obtain carboxyl-modified water-soluble PVB resin.

[0025] The process flow for preparing the carboxyl-modified water-soluble PVB resin and water-based coating composition of this invention is as follows: Figure 1 As shown. In this invention, 0899 type PVA is mixed with water (denoted as the first mixture, yielding the first mixed solution), acidified, and then mixed with n-butyraldehyde (denoted as the second mixture) to undergo an acetal reaction to obtain PVB resin. In this invention, the degree of polymerization of 0899 type PVA can be 750~850, specifically 800, and the degree of alcoholysis can be 98~100 mol%, specifically 98.5 mol% or 99.5 mol%.

[0026] In this invention, the water can be deionized water.

[0027] In this invention, the temperature of the first mixing can be 90~95℃, specifically 93℃, and the time can be 2~3 hours, specifically 2.5 hours; the method of the first mixing can be stirring.

[0028] In this invention, the mass concentration of the first mixture can be 8-12%, specifically 10%.

[0029] In this invention, the first mixing may further include cooling the resulting product; the final cooling temperature may be 10~15°C, specifically 12°C.

[0030] In this invention, the target pH value for acidification can be 1 to 2, specifically 1.5; the acidifying agent used for acidification can be concentrated hydrochloric acid; the concentration of concentrated hydrochloric acid can be 36 to 38 wt%, specifically 37 wt%.

[0031] In this invention, the mass ratio of 0899 type PVA to n-butyraldehyde can be 100:45~65, specifically 100:48, 100:51, 100:55, 100:58, 100:60 or 100:63.

[0032] In this invention, the second mixing may include the following steps: adding n-butyraldehyde dropwise to the first mixture while stirring.

[0033] In this invention, the dripping time can be 1 to 2 hours, specifically 1.5 hours.

[0034] In this invention, the acetalization reaction temperature can be 50~65℃, specifically 55℃ or 60℃, and the time can be 3~6 hours, specifically 4 hours or 5 hours. This invention obtains a mixed system of PVB resin through the acetalization reaction, in which a large amount of white precipitate appears.

[0035] In this invention, the acetalization reaction may further include post-treatment of the resulting product, which may include neutralization, solid-liquid separation, water washing and drying in sequence.

[0036] In this invention, the neutralizing agent used for neutralization can be a sodium hydroxide solution; the concentration of the sodium hydroxide solution can be 10 wt%; the target pH value for neutralization can be 6.5~8, specifically 7~7.5.

[0037] In this invention, solid-liquid separation can be achieved through filtration. This invention obtains crude PVB product through solid-liquid separation.

[0038] In this invention, the water used for washing can be deionized water; the temperature of the deionized water can be 60~70℃; the target state of washing can be: the pH value of the filtrate is neutral (7~7.5) and no chloride ions are detected by silver nitrate test.

[0039] In this invention, the drying temperature can be 60~70℃, specifically 65℃, the vacuum degree can be -0.08~-0.095MPa, specifically -0.09MPa, and the time can be 12~24 hours, specifically 15 hours, 18 hours or 21 hours.

[0040] After obtaining PVB resin, this invention involves mixing the PVB resin with a polar organic solvent, a tertiary amine catalyst, and phthalic anhydride (referred to as the third mixture) for esterification modification to obtain carboxyl-modified water-soluble PVB resin. In this invention, the PVB resin can be pretreated before use, specifically by drying. The drying temperature can be 60~80℃, specifically 70℃; the vacuum degree can be -0.08~-0.095MPa, specifically -0.09MPa; and the time can be 12~24 hours, specifically 16 hours or 20 hours. This invention removes residual moisture through drying.

[0041] In this invention, the hydroxyl content of the PVB resin is 19-24 wt%, the butyral content is 72-78 wt%, the acetyl content is 1-4 wt%, the number average molecular weight is 40,000-80,000, and the molecular weight distribution index is ≤2.2.

[0042] In this invention, the polar organic solvent may include one or more of N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), and dimethyl sulfoxide (DMSO).

[0043] In this invention, the mass ratio of PVB resin to polar organic solvent can be 100:80~180, specifically 100:90, 100:100, 100:120, 100:140 or 100:160.

[0044] In this invention, the tertiary amine catalyst may include one or both of triethylamine and 4-dimethylaminopyridine (DMAP); when the tertiary amine catalyst is triethylamine and 4-dimethylaminopyridine, the mass ratio of triethylamine to 4-dimethylaminopyridine may be 0.9~1.1:1, specifically 1:1.

[0045] In this invention, the mass ratio of PVB resin to tertiary amine catalyst can be 100:0.2 to 1.5, specifically 100:0.4, 100:0.6, 100:0.8, 100:1 or 100:1.2.

[0046] In this invention, the mass ratio of PVB resin to phthalic anhydride can be 100:6 to 18, specifically 100:8, 100:10, 100:12, 100:14 or 100:16.

[0047] In this invention, the third mixing may include the following steps: adding PVB resin to a polar organic solvent, heating and stirring under nitrogen protection to obtain a PVB solution, adding a tertiary amine catalyst to the PVB solution and stirring to mix, and then adding phthalic anhydride to the PVB solution in batches.

[0048] In this invention, the heating and stirring temperature can be 60~80℃, specifically 70℃.

[0049] In this invention, the batches added in batches can be 2 to 4, specifically 3, with an interval of 35 to 45 minutes between each addition, specifically 40 minutes.

[0050] In this invention, the esterification modification temperature can be 85~115℃, specifically 95℃ or 105℃, and the time can be 3~5 hours, specifically 4 hours.

[0051] In this invention, the esterification modification may further include post-treatment of the resulting product, which may include sequentially performing cooling, neutralization, phase inversion, and solvent removal.

[0052] In this invention, the final cooling temperature can be 40~60℃, specifically 50℃; the neutralizing agent used for neutralization can include one or more of triethylamine, diethanolamine, triethanolamine, and 2-amino-2-methyl-1-propanol (AMP-95); neutralization can include the following steps: stirring and mixing the neutralizing agent and the cooled esterified modified product for 15~30 minutes; the target pH value for neutralization can be 7.5~8.5; phase inversion can include the following steps: adding deionized water to the neutralized product under high-speed stirring to perform phase inversion, the high-speed stirring speed is 1200~1800 r / min, the mass ratio of PVB resin to deionized water can be 100:150~300, specifically 100:200 or 100:250; solvent removal can be by distillation; the distillation temperature can be 60~70℃, specifically 65℃, the vacuum degree can be -0.08~-0.095MPa, specifically -0.09MPa, and the time can be more than 2 hours. This invention removes residual organic solvents by solvent removal.

[0053] The present invention also provides a carboxyl-modified water-soluble PVB resin, which is prepared by the above-described method for preparing carboxyl-modified water-soluble PVB resin, in the form of an aqueous solution, with a solid content of 30-40 wt% and a carboxyl content of 0.6-2.8 mmol / g.

[0054] The present invention also provides an application of a carboxyl-modified water-soluble PVB resin in the field of water-based paints, wherein the carboxyl-modified water-soluble PVB resin is the carboxyl-modified water-soluble PVB resin described above.

[0055] The present invention also provides a water-based paint composition comprising, by weight parts: 50-70 parts of carboxyl-modified water-soluble PVB resin; 5-15 parts of water-based amino resin curing agent; 0-30 parts of pigments and fillers; 0.5-2 parts of dispersant; 0.1-0.5 parts of leveling agent; 0.1-0.5 parts of defoamer; 1-5 parts of film-forming aid; 5-20 parts of deionized water; the carboxyl-modified water-soluble PVB resin is the carboxyl-modified water-soluble PVB resin of the above scheme.

[0056] The water-based paint composition provided by the present invention comprises 50 to 70 parts by weight of carboxyl-modified water-soluble PVB resin, specifically 60 parts.

[0057] In this invention, the solid content of the carboxyl-modified water-soluble PVB resin can be 35 wt%.

[0058] Based on the mass fraction of carboxyl-modified water-soluble PVB resin, the water-based paint composition provided by the present invention includes 5 to 15 parts of water-based amino resin curing agent, specifically 10 parts.

[0059] In this invention, the waterborne amino resin curing agent may include one or more of hexamethoxymethyl melamine resin, butylated melamine-formaldehyde resin, and benzoated melamine-formaldehyde resin.

[0060] Based on the mass fraction of carboxyl-modified water-soluble PVB resin, the water-based paint composition provided by the present invention includes 0 to 30 parts of pigments and fillers, specifically 10 or 20 parts.

[0061] In this invention, pigments and fillers may include one or more of titanium dioxide, talc, calcium carbonate, barium sulfate, carbon black, and iron oxide red.

[0062] Based on the mass fraction of carboxyl-modified water-soluble PVB resin, the water-based paint composition provided by the present invention includes 0.5 to 2 parts of dispersant, specifically 1 part or 1.5 parts.

[0063] In this invention, the dispersant may include one or both of BYK-163 and BYK-190.

[0064] Based on the mass fraction of carboxyl-modified water-soluble PVB resin, the water-based paint composition provided by the present invention includes 0.1 to 0.5 parts of leveling agent, specifically 0.3 parts.

[0065] In this invention, the leveling agent may include one or more of BYK-348, BYK-333 and BYK-346.

[0066] Based on the mass fraction of carboxyl-modified water-soluble PVB resin, the water-based paint composition provided by the present invention includes 0.1 to 0.5 parts of defoamer, specifically 0.3 parts.

[0067] In this invention, the defoamer may include one or more of BYK-019, BYK-028 and BYK-024.

[0068] Based on the mass fraction of carboxyl-modified water-soluble PVB resin, the water-based paint composition provided by the present invention includes 1 to 5 parts of film-forming aid, specifically 2 or 4 parts.

[0069] In this invention, the film-forming aid may include one or more of propylene glycol methyl ether, propylene glycol butyl ether, dipropylene glycol butyl ether, and 12-ol ester.

[0070] Based on the mass fraction of carboxyl-modified water-soluble PVB resin, the water-based paint composition provided by the present invention includes 5 to 20 parts of deionized water, specifically 10 or 15 parts.

[0071] The present invention also provides a method for preparing the above-described water-based paint composition, comprising the following steps: (1) Mix the dispersant, defoamer and deionized water to obtain a premix; (2) After dispersing the premix and pigments and fillers, grind them to a fineness of ≤20μm to obtain a pigment and filler slurry; (3) Under stirring conditions, carboxyl-modified water-soluble PVB resin, water-based amino resin curing agent, leveling agent and film-forming aid are added to the pigment and filler slurry in sequence, stirred and mixed, and the viscosity is adjusted to 25~35s (25℃) of Fore-4 cup to obtain water-based paint composition.

[0072] This invention involves mixing a dispersant, an antifoaming agent, and deionized water to obtain a premix. In this invention, mixing can be achieved through stirring.

[0073] After obtaining the premix, the present invention disperses the premix and pigments / fillers and then grinds them to a fineness of ≤20μm to obtain a pigment / filler slurry. In the present invention, dispersion can be achieved by high-speed stirring, with a stirring speed of 2000~3000r / min, specifically 2500r / min, and a stirring time of 20~30 minutes, specifically 25 minutes.

[0074] After obtaining the pigment and filler slurry, the present invention, under stirring conditions, sequentially adds carboxyl-modified water-soluble PVB resin, water-based amino resin curing agent, leveling agent and film-forming aid to the pigment and filler slurry, stirs and mixes, and adjusts the viscosity to 25~35s (25℃) of Forecast cup 4 to obtain a water-based paint composition.

[0075] In this invention, the stirring speed can be 500~800 r / min, specifically 600 r / min or 700 r / min.

[0076] In this invention, the stirring and mixing time can be 20 to 30 minutes, specifically 25 minutes.

[0077] In this invention, the reagent used to adjust the viscosity can be deionized water.

[0078] In this invention, after adjusting the viscosity, the resulting product may also be filtered; the filter used for filtration may be a 200-mesh filter.

[0079] The present invention also provides the application of the above-described water-based paint composition in the fields of metal corrosion protection, wood coating, or plastic primer.

[0080] Overall, the carboxyl-modified water-soluble PVB resin, its preparation method, and the water-based paint composition provided by this invention have the following advantages: 1) Low and controllable raw material cost: This invention uses 0899 type general-purpose PVA as the starting material. The raw material is readily available and inexpensive. The prepared PVB resin has a narrow molecular weight distribution and stable functional group content. The subsequent carboxyl modification reaction has good controllability, and the water-based paint has high batch consistency.

[0081] 2) Excellent and stable water solubility: By controlling the amount of phthalic anhydride, this invention can precisely adjust the carboxyl content (0.6~2.8 mmol / g) of the carboxyl-modified water-soluble PVB resin. The resulting carboxyl-modified water-soluble PVB resin is transparent and stable, has a storage period of ≥6 months, does not exhibit stratification or precipitation, and is miscible with water in any proportion.

[0082] 3) Excellent adhesion: The carboxyl and hydroxyl groups in the molecular chain of carboxyl-modified water-soluble PVB resin can form strong hydrogen bonds and chemical bonds with the oxide film on the surface of metal substrates. It has strong mechanical adhesion to wood and plastic substrates, and the coating adhesion can reach grade 0 (GB / T 9286-1998).

[0083] 4) Good balance between water resistance and water solubility: The present invention uses phthalic anhydride monoesterification modification to avoid the introduction of strong hydrophilic groups; after film formation, the amino resin undergoes cross-linking reaction with carboxyl and hydroxyl groups to form a dense three-dimensional network structure. The coating film has excellent water resistance and does not whiten, bubble or peel off after immersion at room temperature for 72 hours.

[0084] 5) Excellent overall performance of the coating: It retains the excellent flexibility and impact resistance of PVB resin, and the hardness of the coating after cross-linking and curing can reach above 2H. It has good wear resistance and scratch resistance, which solves the problem of low hardness of traditional water-based PVB paint.

[0085] 6) Good environmental performance: The entire production process uses little organic solvent and it can be recycled; the final paint VOC content is ≤50g / L, which is far below the national standard requirements.

[0086] 7) Simple steps, easy to industrialize: mild reaction conditions, no need for high temperature and high pressure, low equipment investment, suitable for large-scale continuous production.

[0087] To further illustrate the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings and embodiments.

[0088] Preparation Example 1: This preparation example uses type 0899 PVA as raw material to prepare PVB resin, as detailed below: 1) Dissolution: Add 100 parts of type 0899 PVA (degree of polymerization 750~850, degree of alcoholysis 98~100mol%) to 1000 parts of deionized water, stir and heat to 92℃, keep warm and stir for 2.5 hours until completely dissolved, to obtain a PVA aqueous solution with a mass concentration of 9.1%; 2) Cooling and acidification: Cool the prepared PVA aqueous solution to 12°C, and add 12 parts of concentrated hydrochloric acid (concentration of concentrated hydrochloric acid is 37wt%) to adjust the pH value of the system to 1.5; 3) Acetal reaction: 55 parts of n-butyraldehyde were added dropwise under stirring conditions, with the addition time controlled at 1.5 hours. After the addition was completed, the temperature was raised to 58°C and the reaction was maintained at this temperature for 4.5 hours. A large amount of uniform white precipitate appeared in the system. 4) Neutralization and washing: After the reaction is complete, add 15 parts of 10wt% sodium hydroxide solution to adjust the pH of the system to 7.0, filter, and obtain crude PVB product. Wash repeatedly with 65℃ deionized water 6 times until the pH of the filtrate is 7.0 and no chloride ions are detected by silver nitrate test. 5) Drying: The washed PVB product is dried in a vacuum drying oven at 65℃ and a vacuum degree of -0.08MPa for 18 hours to obtain PVB resin.

[0089] 6) Performance testing: The PVB resin prepared in this preparation example was tested and found to have a hydroxyl content of 21 wt%, a butyral content of 76 wt%, an acetyl content of 3 wt%, a number-average molecular weight of 65,000, and a molecular weight distribution index of 2.0.

[0090] Example 1: This embodiment prepared a carboxyl-modified water-soluble PVB resin, as detailed below: 1) Raw material pretreatment: 100 parts of the PVB resin prepared in Preparation Example 1 were dried in a vacuum drying oven at 70°C and a vacuum degree of -0.09MPa for 18 hours; 2) Solvent dissolution: Add the dried PVB resin to 120 parts of N,N-dimethylformamide, stir and heat to 70°C under nitrogen protection until the PVB is completely dissolved to obtain a PVB solution; 3) Esterification modification: Add 0.5 parts of triethylamine and 0.5 parts of DMAP as a compound catalyst to the above PVB solution, stir evenly, and then add 12 parts of phthalic anhydride in 3 portions, with an interval of 40 minutes between each addition. After the addition is complete, raise the temperature to 100℃ and keep the reaction at this temperature for 4 hours to obtain the reaction solution. 4) Neutralization and phase inversion: After the reaction is completed, the reaction solution is cooled to 50°C, 8 parts of triethanolamine are added for neutralization for 20 minutes, and then 200 parts of deionized water are added dropwise under high-speed stirring at 1500 r / min to carry out phase inversion; 5) Desolventization: The aqueous solution after phase inversion was distilled under reduced pressure at 65℃ and -0.09MPa for 2 hours to remove residual DMF, and a carboxyl-modified water-soluble PVB resin with a solid content of 35wt% (in aqueous solution form) was obtained.

[0091] 6) Performance testing: The carboxyl-modified water-soluble PVB resin prepared in this embodiment was tested and found to be a colorless and transparent liquid with a pH value of 8.0 and a carboxyl content of 1.5 mmol / g. Its storage stability showed no stratification or precipitation after 6 months of storage at room temperature, and its water solubility showed that it was miscible with water in any proportion.

[0092] Example 2: This embodiment prepares a water-based paint composition (water-based white metal anti-corrosion paint), as detailed below: 1) Formula: 60 parts of carboxyl-modified water-soluble PVB resin (35wt%) prepared in Example 1; 10 parts of hexamethoxymethyl melamine resin; 20 parts of rutile titanium dioxide; 1 part dispersant (BYK-190); Leveling agent (BYK-346) 0.3 parts; Defoamer (BYK-024) 0.2 parts; 3 parts of alcohol ester twelve; 5 parts deionized water.

[0093] 2) Preparation method: (1) Add the dispersant and defoamer to deionized water and stir evenly to obtain a premixed solution; (2) Add rutile titanium dioxide to the premixed liquid, disperse it at 2500 r / min for 25 minutes, and then grind it to a fineness of ≤15 μm to obtain pigment and filler slurry (white slurry). (3) Under low-speed stirring conditions of 600r / min, WPVB resin, hexamethoxymethyl melamine resin, leveling agent and alcohol ester dodecyl are added to the white slurry in sequence and stirred for 30 minutes to obtain the mixture; (4) Adjust the viscosity of the mixture with deionized water to 30s (25°C) in a Forte 4 cup, filter with a 200-mesh filter to obtain a water-based paint composition.

[0094] (5) Performance test: The water-based paint composition prepared in this embodiment was applied to the surface of the substrate. The substrate was cold-rolled steel plate. The curing conditions of the coating were 140°C for 30 minutes. The test results are shown in Table 1.

[0095] Table 1. Performance test results of the water-based paint composition prepared in Example 2:

[0096] As shown in Table 1, the water-based paint composition prepared using the carboxyl-modified water-soluble PVB resin of the present invention forms a smooth and flat coating with no obvious structural defects. It also exhibits excellent adhesion, good mechanical properties such as hardness and impact resistance, ideal water resistance and salt spray resistance, low VOC content, and is safe and environmentally friendly, meeting the performance requirements of water-based white metal anti-corrosion paint.

[0097] Example 3: This embodiment prepares a water-based paint composition (water-based transparent wood topcoat), as detailed below: 1) Formula: 65 parts of carboxyl-modified water-soluble PVB resin (35wt%) prepared in Example 1; Eight parts of butylated melamine-formaldehyde resin; Dispersant (BYK-190) 0.5 parts; Leveling agent (BYK-333) 0.2 parts; 0.3 parts of defoamer (BYK-028); 2 parts of propylene glycol butyl ether; 15 parts deionized water.

[0098] The preparation method and performance testing method of this embodiment are the same as those of Embodiment 2, except that the coating curing conditions are adjusted to 120°C for 20 minutes, the substrate is beech wood board, and the test results are shown in Table 2.

[0099] Table 2 Performance test results of the water-based paint composition prepared in Example 3:

[0100] As can be seen from Table 2, the water-based paint composition prepared using the carboxyl-modified water-soluble PVB resin provided by the present invention forms a transparent and glossy coating with no haze, exhibits excellent adhesion, and demonstrates good mechanical properties, water resistance, and alcohol resistance, meeting the relevant requirements for water-based transparent wood coatings.

[0101] Example 4: This embodiment prepares a water-based paint composition (water-based black ABS plastic primer), as detailed below: 1) Formula: 55 parts of carboxyl-modified water-soluble PVB resin (35wt%) prepared in Example 1; 7 parts of benzo-substituted melamine-formaldehyde resin; 8 parts of high-pigment carbon black; Dispersant (BYK-163) 1.2 parts; Leveling agent (BYK-348) 0.3 parts; Defoamer (BYK-019) 0.2 parts; 2.3 parts of dipropylene glycol butyl ether; 20 parts deionized water.

[0102] The preparation method and performance testing method of this embodiment are the same as those of Embodiment 2, except that the coating curing conditions are adjusted to 100°C for 15 minutes, the substrate is ABS plastic board, and the test results are shown in Table 3.

[0103] Table 3 Performance test results of the water-based paint composition prepared in Example 4:

[0104] As can be seen from Table 3, the water-based paint composition prepared by further processing the carboxyl-modified water-soluble PVB resin provided by the present invention forms a black, uniformly colored coating without structural defects such as particles or pinholes, and has good adhesion. Its mechanical properties, water resistance, and gasoline resistance meet the relevant performance requirements.

[0105] Comparative Example 1: This comparative example prepared an unmodified PVB solvent-based white paint. The formulation and preparation method were the same as in Example 2, except that an ethanol solution of unmodified PVB resin (35 wt%, the unmodified PVB resin was the PVB resin prepared in Preparation Example 1) was used instead of WPVB resin.

[0106] Performance test results show that the unmodified PVB solvent-based white paint prepared in this comparative example forms a smooth and even film with an adhesion grade of 1, a pencil hardness of H, and exhibits whitening after 48 hours of water resistance. Its VOC content is 450 g / L. Compared to Example 2 of this invention, its adhesion is worse, its water resistance is poorer, its VOC content is higher, and its environmental friendliness is insufficient.

[0107] Comparative Example 2: The comparative example is a commercially available sulfonated modified water-soluble WPVB water-based white anti-corrosion paint. The performance test results show that the appearance is slightly cloudy, the adhesion is grade 2, the pencil hardness is B, the water resistance is whitening and bubbling after 24 hours, and the storage stability is delamination after 3 months. All aspects of the performance are poor.

[0108] As can be seen from the above embodiments and comparative examples, the carboxyl-modified water-soluble PVB resin and its water-based paint composition prepared by the present invention based on 0899 type PVA have significantly better performance than existing products in terms of adhesion, hardness, water resistance and environmental protection. They have excellent comprehensive performance and can be widely used in water-based paint fields such as metal corrosion protection, wood coating, and plastic primer.

[0109] The embodiments of the present invention have been described above; however, these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. All other embodiments obtained by those skilled in the art based on the above embodiments of the present invention without inventive effort are within the protection scope of the present invention.

Claims

1. A method for preparing a carboxyl-modified water-soluble PVB resin, characterized in that, Includes the following steps: (1) Mix 0899 type PVA with water, acidify, and mix with n-butyraldehyde to carry out acetal reaction to obtain PVB resin; (2) PVB resin is mixed with polar organic solvent, tertiary amine catalyst and phthalic anhydride for esterification modification to obtain carboxyl-modified water-soluble PVB resin.

2. The method for preparing carboxyl-modified water-soluble PVB resin according to claim 1, characterized in that, The degree of polymerization of 0899 type PVA is 750~850, and the degree of alcoholysis is 98~100 mol%.

3. The method for preparing carboxyl-modified water-soluble PVB resin according to claim 1, characterized in that, The target pH value for acidification is 1~2; the acidifying agent used for acidification is concentrated hydrochloric acid; the concentration of concentrated hydrochloric acid is 36~38wt%.

4. The method for preparing carboxyl-modified water-soluble PVB resin according to claim 1, characterized in that, The PVB resin has a hydroxyl content of 19-24 wt%, a butyral content of 72-78 wt%, an acetyl content of 1-4 wt%, a number-average molecular weight of 40,000-80,000, and a molecular weight distribution index ≤2.

2.

5. The method for preparing carboxyl-modified water-soluble PVB resin according to claim 1, characterized in that, The mass ratio of PVB resin to tertiary amine catalyst is 100:0.2~1.5; the mass ratio of PVB resin to phthalic anhydride is 100:6~18.

6. A carboxyl-modified water-soluble PVB resin, characterized in that, The PVB resin was prepared using any one of the carboxyl-modified water-soluble resins according to claims 1 to 5. It was in the form of an aqueous solution with a solid content of 30 to 40 wt% and a carboxyl content of 0.6 to 2.8 mmol / g.

7. The application of a carboxyl-modified water-soluble PVB resin in the field of water-based paints, characterized in that, The carboxyl-modified water-soluble PVB resin is the carboxyl-modified water-soluble PVB resin of claim 6.

8. A water-based paint composition, characterized in that, Based on parts by mass, it includes the following components: The mixture comprises 50-70 parts of carboxyl-modified water-soluble PVB resin; 5-15 parts of water-based amino resin curing agent; 0-30 parts of pigments and fillers; 0.5-2 parts of dispersant; 0.1-0.5 parts of leveling agent; 0.1-0.5 parts of defoamer; 1-5 parts of film-forming aid; and 5-20 parts of deionized water. The carboxyl-modified water-soluble PVB resin is the carboxyl-modified water-soluble PVB resin of claim 6.

9. A method for preparing a water-based paint composition, characterized in that, The water-based paint composition of claim 8 comprises the following steps: (1) Mix the dispersant, defoamer and deionized water to obtain a premix; (2) After dispersing the premix and pigments and fillers, grind them to a fineness of ≤20μm to obtain a pigment and filler slurry; (3) Under stirring conditions, carboxyl-modified water-soluble PVB resin, water-based amino resin curing agent, leveling agent and film-forming aid are added to the pigment and filler slurry in sequence, stirred and mixed, and the viscosity at 25°C is adjusted to 25~35s at Forte 4 cup to obtain water-based paint composition.

10. The application of a water-based paint composition in the fields of metal corrosion protection, wood coating, or plastic primer, characterized in that, The water-based paint composition is the water-based paint composition of claim 8.

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