High-viscosity-stability water gel for polaroid and preparation method of high-viscosity-stability water gel

Abstract

The invention discloses a high-viscosity-stability water adhesive for a polaroid and a preparation method of the water adhesive, and belongs to the technical field of high polymer materials and adhesives. The water gel for the polaroid is prepared from 2 to 8 parts of acetoacetyl modified PVA (Polyvinyl Alcohol), 0.01 to 0.2 part of bifunctional crosslinking agent, 0.01 to 0.1 part of coordination metal ion salt and 100 parts of deionized water. PVA is completely dissolved, and a Lewis base catalyst and a controllable dropwise adding process are matched, so that efficient and uniform grafting and high conversion rate of acetoacetyl are realized. The modified PVA has a synergistic effect with a cross-linking agent and a metal ion salt to form a stable dual cross-linked network, and after a damp-heat aging test, the weather-resistant polyvinyl alcohol adhesive still shows excellent weather resistance, and has excellent initial bonding strength and continuous and uniform film-forming characteristics at the same time. The method has the advantages of being environmentally friendly, stable in production process and the like, and is particularly suitable for preparing the polaroid of the high-end display device.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials and adhesives technology, specifically relating to a water-based adhesive for polarizing films with high viscosity stability and its preparation method. Background Technology

[0002] Polarizing films are a core component of modern display technologies such as liquid crystal displays (LCDs) and organic light-emitting diodes (OLEDs). A typical polarizing film has a sandwich structure, with a dichroic polyvinyl alcohol (PVA) optical film at its core. A layer of triacetate cellulose (TAC) film is usually bonded to both sides of this film via a water-based adhesive. This TAC layer protects the mechanically weak PVA film and imparts weather resistance. This adhesive layer is crucial in determining the polarizing film's resistance to damp heat, bonding reliability, and long-term service life. Traditional PVA, due to its high content of hydrophilic hydroxyl groups, has poor water resistance and is unsuitable for direct use as an adhesive. To overcome this deficiency, existing technologies typically chemically modify PVA. Acetylacetyl-modified PVA, in particular, has active methylene groups on its side chains that can cross-link with various functional groups and metal ions to form a water-insoluble three-dimensional network structure. This significantly improves the water resistance and bonding strength of the adhesive layer, making it an ideal raw material for water-based adhesives in polarizing films.

[0003] Patent CN105492471B discloses a method using diene as an acetylation reagent. Dienones are highly toxic and reactive, posing a serious challenge to production safety and environmental protection. Methods using relatively safe reagents such as acetoacetate esters, as described in patents CN108219035A and CN116057077A, typically involve reacting PVA in a swollen state rather than completely dissolved. Due to the poor compatibility between PVA and acetoacetate esters, the reactants do not come into sufficient contact in the swollen state, resulting in low grafting conversion rates of the acetoacetyl group (only 37.7% and 23.8%, respectively). This not only wastes raw materials and results in poor atom economy but also increases side reactions.

[0004] The aforementioned swelling synthesis process results in an uneven distribution of acetyl groups on the PVA molecular chain, forming a block-like modified structure. When this unevenly modified PVA is formulated into an adhesive with a crosslinking agent, the crosslinking reaction occurs rapidly in the highly modified chain segments, causing the adhesive viscosity to surge non-linearly in the early stages of storage. As the viscosity increases, the molecular chain motion slows down, which in turn further accelerates local crosslinking, creating a vicious cycle that ultimately leads to the adhesive gelling and completely failing within a short period.

[0005] Therefore, developing a novel technical solution for polarizer water adhesive that can simultaneously achieve high conversion rate, green and safe synthesis, and formulate polarizers with long-term viscosity stability has become an urgent technical problem to be solved by those skilled in the art. Summary of the Invention

[0006] One of the objectives of this invention is to provide a water-based adhesive for polarizing films with high viscosity stability, in order to solve the problems of unstable viscosity and easy gelation during storage caused by uneven modification of acetyl groups in existing water-based adhesives for polarizing films.

[0007] The second objective of this invention is to provide a method for preparing a water-based adhesive for polarizing films with high viscosity stability, which is used to prepare the aforementioned water-based adhesive for polarizing films with high viscosity stability.

[0008] The objective of this invention can be achieved through the following technical solutions: Firstly, a water-based adhesive for high-viscosity, stable polarizing film, comprising the following components by weight: Acetylacetyl modified PVA: 2-8 parts; Crosslinking agent: 0.01–0.2 parts; Metal ion salt: 0.01–0.1 parts; Deionized water: 100 parts.

[0009] Furthermore, the acetyl-modified PVA is prepared by the following steps: S1. Ingredients and Dissolution: Add PVA and solvent to the reactor, start stirring and heat to 70~130 ℃, while simultaneously introducing nitrogen gas into the reactor to remove oxygen until PVA is completely dissolved. S2. Addition of catalyst and reactants: After the PVA is completely dissolved, add the catalyst to the reaction system and add a compound containing acetyl groups dropwise. S3. Constant temperature reaction: After the addition is complete, maintain the reaction temperature and continue the reaction for 2-5 hours; S4. Precipitation and washing: After the reaction is complete, the reaction solution is cooled and poured into methanol to precipitate the solid. After multiple filtrations and washing with methanol, a wet solid is obtained. S5. Vacuum drying: The washed solid product is vacuum dried to obtain acetyl-modified PVA.

[0010] Furthermore, in S1, the degree of polymerization of PVA is 500~3000, and the degree of hydrolysis is 88%~99%.

[0011] Furthermore, the solvent is formic acid, acetic acid, propionic acid, etc. N , N -Dimethylformamide, N , N -Diethylformamide, N , N -Dimethylacetamide, dimethyl sulfoxide, 2-pyrrolidone N One or more of methylpyrrolidone, etc.

[0012] Furthermore, the solid content of the PVA and solvent mixture is 5% to 30%.

[0013] Furthermore, in step S1, the time for introducing nitrogen gas to remove oxygen is 1 to 2 hours.

[0014] Furthermore, in S2, the catalyst is a Lewis base, and its addition amount is 1% to 5% of the mass of PVA.

[0015] Furthermore, the Lewis base is selected from ethylenediamine, dodecylamine, aniline, diethylamine, di-n-butylamine, piperidine, diphenylamine, etc. N -Methylaniline, triethylamine, triphenylamine, dodecylamine, dimethylaminopyridine N , N One or more of dimethylformamide, etc.

[0016] Furthermore, in S2, the compound containing an acetoacetyl group is one or more of the following: methyl acetoacetate, ethyl acetoacetate, n-propyl acetoacetate, isopropyl acetoacetate, allyl acetoacetate, isobutyl acetoacetate, sec-butyl acetoacetate, tert-butyl acetoacetate, isoamyl acetoacetate, n-hexyl acetoacetate, n-heptyl acetoacetate, n-octyl acetoacetate, benzyl acetoacetate, etc.

[0017] Furthermore, in step S2, the time for adding the compound containing acetyl groups is 1 to 3 hours.

[0018] Furthermore, in step S4, the amount of methanol used is 3 to 5 times the volume of the reaction liquid; the number of washing cycles is 3 to 5.

[0019] Furthermore, in step S5, the vacuum drying conditions are: temperature 40~100℃, pressure 0.05~0.1 MPa, and drying time 4~8 hours.

[0020] Furthermore, the crosslinking agent is a water-soluble compound containing at least two functional groups, selected from one or more of glyoxal, glutaraldehyde, ethylenediamine, 1,4-butanediamine, ethylene glycol, and 1,4-butanediol. The molar ratio of the crosslinking agent to the active functional groups in the acetylacetyl-modified PVA is controlled between 1:1 and 1:2.

[0021] Furthermore, the metal ion salt is a water-soluble, colorless metal salt, and its metal ion can form a coordinate bond with an oxygen atom, selected from one or more of aluminum sulfate, aluminum nitrate, magnesium chloride, magnesium sulfate, calcium chloride, zinc sulfate, and zinc chloride.

[0022] Secondly, a method for preparing a water-based adhesive for a polarizing film with high viscosity stability includes the following steps: S1. Mix acetyl-modified PVA with deionized water and stir at 70~90℃ until the modified PVA is completely dissolved to form a homogeneous solution. S2. Cool the homogeneous solution to room temperature, add the crosslinking agent and metal ion salt, stir and mix evenly to obtain a high viscosity and stable polarizing film water adhesive.

[0023] The beneficial effects of this invention are: (1) This invention achieves long-term controllable viscosity by precisely controlling each component and key parameters: the dosage of the core component, acetyl-modified PVA (2-8 parts), is adapted to the film formation and viscosity baseline, avoiding discontinuous film formation due to excessive dosage and molecular chain entanglement due to excessive dosage; the molar ratio of crosslinking agent (0.01-0.2 parts) to the active functional groups of modified PVA is controlled at 1:1 to 1:2, ensuring a dense crosslinking network while avoiding excessive crosslinking leading to gelation; the metal ion salt (0.01-0.1 parts) regulates the crosslinking rate and inhibits uneven local crosslinking by forming coordination bonds with oxygen atoms. Based on 100 parts of deionized water, standardized production can be achieved, ensuring consistent performance across different batches; under synergistic effect, the viscosity of the adhesive increases by ≤20% after 7 days and ≤50% after 30 days at 25℃, solving the problems of nonlinear viscosity growth and easy failure in the prior art, and meeting the industrial storage requirements for more than 30 days.

[0024] (2) This invention, by completely dissolving PVA in a solvent before modification, and supplementing it with a catalyst and a controllable dropping process, ensures uniform grafting of acetoacetyl groups onto the PVA molecular chains, fundamentally avoiding the problem of localized rapid crosslinking caused by uneven modification. Combined with an optimized crosslinking system and metal ion coordination crosslinking, the viscosity of the adhesive changes minimally during storage. Furthermore, the complete dissolution of PVA allows the PVA molecular chains to fully extend in the reaction system, increasing the probability of effective contact with acetoacetate molecules; simultaneously, the preferred Lewis base catalyst effectively promotes the transesterification reaction. The synergistic effect of these two factors significantly improves the conversion rate of acetoacetate.

[0025] (3) This invention avoids the use of highly toxic and high-risk chemicals such as diene ketones throughout the entire process, and instead uses acetoacetate esters as modifiers. The reaction conditions are mild and controllable, which greatly reduces the safety risks and environmental pollution in the production process, and is in line with the green and sustainable development direction of modern chemical industry. In addition, based on the high conversion rate and uniformly modified PVA raw materials, the prepared water adhesive not only has stable viscosity, but its final cross-linked and cured adhesive layer also shows excellent performance in terms of water resistance, bonding strength and compatibility with PVA / TAC film, which can meet the stringent requirements of high-end polarizers for reliability and durability. Detailed Implementation

[0026] 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.

[0027] In some embodiments, a water-based adhesive for a high-viscosity, stable polarizing film comprises, by weight, the following components: Acetylacetyl modified PVA: 2-8 parts; Crosslinking agent: 0.01–0.2 parts; Metal ion salt: 0.01–0.1 parts; Deionized water: 100 parts.

[0028] Acetylacetyl-modified PVA is the core film-forming and bonding component of the adhesive, and its dosage directly determines the adhesive's film-forming properties, bonding strength, and viscosity. If the amount of modified PVA is too low, the film formation is discontinuous, making it impossible to effectively bond the PVA optical film and TAC film, and delamination is likely to occur. If the amount is too high, the initial viscosity of the adhesive is too high, making application difficult, and the viscosity may increase non-linearly in the later stages due to molecular chain entanglement.

[0029] The core function of the crosslinking agent is to form a crosslinking network with the acetyl groups on the modified PVA molecular chain, thereby improving the structural stability of the adhesive. Insufficient crosslinking agent results in a loose crosslinking network, making the adhesive susceptible to environmental humidity and causing large viscosity fluctuations. Excessive crosslinking leads to over-crosslinking, excessively high molecular chain crosslinking density, and rapid gelation of the adhesive, rendering it unusable.

[0030] Metal ion salts, acting as crosslinking aids, regulate the crosslinking reaction rate by forming coordination bonds with oxygen atoms on the modified PVA molecular chain. When no metal ions are added or the amount added is too low, the crosslinking reaction rate is uneven, with some areas exhibiting excessively rapid crosslinking, leading to viscosity fluctuations. Conversely, when the amount added is too high, excessive coordination of metal ions reduces the adhesive's flexibility and may even affect the optical properties of the bonding interface.

[0031] When using deionized water as a solvent, it is essential to ensure the uniform dispersion of modified PVA, crosslinking agent, and metal ion salts. If ordinary tap water is used, impurities in the water will interfere with the crosslinking and coordination reactions, leading to a decrease in viscosity stability. Using 100 parts as a baseline dosage can standardize the proportions of other components, ensuring consistent performance across different batches of adhesive. This also avoids situations where excessive solvent leads to insufficient adhesive concentration and bonding strength, or insufficient solvent results in incomplete dissolution of components and an uneven system.

[0032] In some embodiments, the acetoacetyl-modified PVA is prepared by the following steps: S1. Ingredients and Dissolution: Add PVA and solvent to the reactor, start stirring and heat to 70~130 ℃, while simultaneously introducing nitrogen gas into the reactor to remove oxygen until PVA is completely dissolved. Existing technologies often employ methods that swell PVA, resulting in insufficient exposure of hydroxyl groups and incomplete reactions. Complete dissolution of PVA allows the PVA molecular chains to fully extend and hydroxyl groups to be fully exposed, laying the foundation for subsequent transesterification reactions. 70–130 °C is the optimal temperature for dissolving PVA in DMSO: below 70 °C, the dissolution rate is extremely slow, leading to low production efficiency; above 130 °C, PVA molecular chains may undergo oxidative degradation. Introducing nitrogen gas for deoxygenation prevents the oxidation of hydroxyl groups in the PVA molecular chains at high temperatures, ensuring the modification reaction proceeds in a directed manner and avoiding the influence of oxidative impurities on product performance.

[0033] S2. Addition of catalyst and reactants: After the PVA is completely dissolved, add the catalyst to the reaction system and add a compound containing acetyl groups dropwise. Adding the catalyst only after PVA is completely dissolved ensures sufficient contact between the catalyst and the PVA molecular chains, preventing localized catalyst aggregation and low catalytic efficiency due to undissolved PVA. Directly adding the acetyl hydroxyl compound all at once can easily lead to excessively high local concentrations, triggering side reactions such as self-polymerization and reducing conversion rate. Dropwise addition allows for control of the reactant addition rate, ensuring uniform dispersion of the acetyl hydroxyl compound in the system, facilitating thorough transesterification with the PVA hydroxyl groups, guaranteeing uniform modification, and preventing over- or under-modification of localized molecular chains.

[0034] S3. Constant temperature reaction: After the addition is complete, maintain the reaction temperature and continue the reaction for 2-5 hours; After the addition is complete, the reaction temperature must be maintained at 70-130 °C to ensure that the transesterification reaction proceeds fully. If the reaction time is too short, the acetoacetyl compound will not react completely with the PVA hydroxyl groups, resulting in a low conversion rate; if the reaction time is too long, energy consumption will increase, and over-reaction may occur, leading to cross-linking of the PVA molecular chains and affecting subsequent solubility.

[0035] S4. Precipitation and washing: After the reaction is complete, the reaction solution is cooled and poured into methanol to precipitate the solid. After filtration and washing with methanol, a wet solid is obtained. Methanol is a poor solvent for modified PVA. Pouring the reaction solution into methanol allows the modified PVA to precipitate rapidly, achieving separation of the product from the solvent and unreacted raw materials. In existing technologies, insufficient washing can lead to solvent residue, catalyst, and unreacted reactants affecting the performance of subsequent adhesives. Precipitation after cooling avoids the aggregation of modified PVA molecular chains at high temperatures, ensuring uniform product particles and facilitating filtration and washing.

[0036] S5. Vacuum drying: The washed solid product is vacuum dried to obtain acetyl-modified PVA.

[0037] Conventional hot air drying easily leads to surface hardening of the product, making it difficult to remove residual methanol and moisture; furthermore, high temperatures can cause PVA oxidation. Vacuum drying lowers the boiling points of moisture and methanol, accelerating evaporation, while preventing the degradation or cross-linking of modified PVA molecular chains caused by high temperatures. The dried product has no solvent residue, ensuring a uniform system and stable viscosity during subsequent adhesive preparation, and preventing residual solvents from interfering with the cross-linking reaction.

[0038] In some embodiments, in S1, the degree of polymerization of PVA is 500-3000, the degree of alcoholysis is 88%-99%, and the mixed solid content of PVA and solvent is 5%-30%.

[0039] When the degree of polymerization is below 500, the film-forming properties are poor and the bonding strength is insufficient; when it is above 3000, PVA is difficult to dissolve in solvents and cannot fully expand even with heating. A degree of hydrolysis of 88%–99% ensures that there are enough hydroxyl groups on the PVA molecular chain to participate in the transesterification reaction: when the degree of hydrolysis is below 88%, the number of hydroxyl groups is small, the grafting rate of acetyl groups is low, and the modification effect is poor; when it is above 99%, PVA is too water-soluble, and the water resistance after modification is insufficient, affecting the moisture and heat resistance of the adhesive.

[0040] When the solid content is too low, the concentration of the reaction system is low, the production efficiency is low, and the subsequent precipitation and drying steps consume a lot of energy; when the solid content is too high, the viscosity of the system is too high, stirring is difficult, PVA is difficult to completely dissolve, and the acetyl group compound is unevenly dispersed, resulting in uneven modification.

[0041] In some embodiments, in step S1, nitrogen is introduced for deoxygenation for 1 to 2 hours.

[0042] If the nitrogen deoxygenation time is too short, the residual oxygen in the reactor will not be completely discharged, and the PVA molecular chains will be easily oxidized, resulting in a reduction in the number of hydroxyl groups and a decrease in conversion rate. If the time is too long, nitrogen resources will be wasted, production costs will increase, and the production cycle will be extended.

[0043] In some embodiments, in step S2, the catalyst is a Lewis base, and the amount added is 1% to 5% of the mass of PVA.

[0044] Existing technologies either do not use a catalyst or use an acidic catalyst, resulting in a slow transesterification reaction rate and low conversion rate. Lewis bases can capture protons on the hydroxyl groups of PVA, activating the hydroxyl groups and promoting the transesterification reaction with acetyl compounds. When the amount added is too low, the catalytic effect is not obvious, and the conversion rate improvement is limited; when the amount is too high, catalyst residue is difficult to remove and may cause side reactions, affecting product purity.

[0045] In some embodiments, the Lewis base is selected from one or more of ethylenediamine, dodecylamine, aniline, diethylamine, di-n-butylamine, piperidine, diphenylamine, N-methylaniline, triethylamine, triphenylamine, dodecylamine, dimethylaminopyridine, N,N-dimethylformamide, etc.

[0046] These Lewis bases possess suitable basicity, effectively catalyzing transesterification without causing PVA chain degradation due to excessive alkalinity. Furthermore, they exhibit good solvent compatibility, readily dissolving in the reaction system and dispersing uniformly to avoid localized catalytic efficiency differences; moreover, they can be subsequently removed by methanol washing, leaving no residue in the product.

[0047] In some embodiments, the compound containing an acetoacetyl group in S2 is one or more of the following: methyl acetoacetate, ethyl acetoacetate, n-propyl acetoacetate, isopropyl acetoacetate, allyl acetoacetate, isobutyl acetoacetate, sec-butyl acetoacetate, tert-butyl acetoacetate, isoamyl acetoacetate, n-hexyl acetoacetate, n-heptyl acetoacetate, n-octyl acetoacetate, benzyl acetoacetate, etc.

[0048] Existing technologies use highly toxic reagents such as diene ketones, posing significant safety risks. These compounds, however, exhibit low toxicity and moderate reactivity, containing active acetylacetyl groups that can undergo transesterification with the hydroxyl groups of PVA, allowing for the directional grafting of acetylacetyl groups. The carbon chain length of different compounds can adjust the hydrophilicity / hydrophobicity of modified PVA, adapting it to different polarizing film usage environments; further optimization of the modification effect can be achieved by blending multiple compounds, ensuring the viscosity stability and weather resistance of the adhesive.

[0049] In some embodiments, in step S2, the time for adding the compound containing acetyl groups is 1 to 3 hours.

[0050] If the dropping time is too short, the acetyl group compound will rapidly enter the system, resulting in excessively high local concentrations. This can easily lead to side reactions such as self-polymerization and hydrolysis, reducing the conversion rate and causing uneven modification. If the dropping time is too long, the production cycle will be prolonged, resulting in low efficiency. Furthermore, the PVA molecular chains may oxidize due to the prolonged high temperature of the reaction system. A dropping time of 1–3 hours ensures uniform dispersion of the reactants, minimizes side reactions, and maintains production efficiency.

[0051] In some embodiments, in step S4, the amount of methanol used is 3 to 5 times the volume of the reaction liquid; and the number of washing cycles is 3 to 5.

[0052] Too little methanol will prevent the modified PVA from precipitating completely, resulting in some product dissolving in the methanol and causing losses; too much methanol will lead to significant methanol waste and increase production costs. Washing 3-5 times ensures the removal of residual solvent, catalyst, and unreacted acetyl compounds.

[0053] In some embodiments, the vacuum drying conditions in step S5 are: temperature 40~100 ℃, pressure 0.05~0.1 MPa, and drying time 4~8 hours.

[0054] When the drying temperature is below 40℃, methanol and water evaporate slowly, resulting in excessively long drying time; when the temperature is above 100℃, the modified PVA molecular chains may undergo thermal degradation, affecting subsequent solubility. A vacuum of 0.05~0.1 MPa can lower the boiling point of methanol and water, accelerating evaporation, while preventing the product from being removed due to excessively high vacuum.

[0055] In some embodiments, the crosslinking agent is a water-soluble compound containing at least two functional groups, selected from one or more of glyoxal, glutaraldehyde, ethylenediamine, 1,4-butanediamine, ethylene glycol, and 1,4-butanediol. The molar ratio of the crosslinking agent to the active functional groups in the acetylacetyl-modified PVA is controlled between 1:1 and 1:2.

[0056] Crosslinking agents must possess at least two functional groups (such as dialdehyde, diamino, or dihydroxyl groups) to form a crosslinking network with the acetylacetyl groups on the modified PVA molecular chain (monofunctional compounds cannot form crosslinking structures). Water solubility ensures uniform mixing of the crosslinking agent and the adhesive system, avoiding uneven crosslinking caused by local aggregation. These compounds exhibit moderate reactivity, and the resulting crosslinking bonds (such as imine or ether bonds) are stable and not easily hydrolyzed, thus improving the adhesive's resistance to damp heat.

[0057] When the molar ratio is too low, the amount of crosslinking agent is insufficient, and the acetyl groups on the modified PVA molecular chain cannot be fully crosslinked, resulting in a loose crosslinking network and poor viscosity stability of the adhesive. When the ratio is too high, there is an excess of crosslinking agent, and unreacted crosslinking agent will remain in the system, potentially causing over-crosslinking, leading to a rapid increase in adhesive viscosity and gelation. A ratio of 1:1 to 1:2 ensures sufficient but not excessive crosslinking reaction, forming a dense and uniform crosslinking network, achieving long-term viscosity stability.

[0058] In some embodiments, the metal ion salt is a water-soluble, colorless metal salt, and its metal ion can form a coordinate bond with an oxygen atom, selected from one or more of aluminum sulfate, aluminum nitrate, magnesium chloride, magnesium sulfate, calcium chloride, zinc sulfate, and zinc chloride.

[0059] Water solubility ensures uniform dispersion of metal ion salts in the adhesive system, preventing excessively high local concentrations from affecting optical performance; colorlessness prevents the metal ion salts from introducing color, thus avoiding impact on the light transmittance of the polarizer. Metal ions can form coordination bonds with oxygen atoms on the modified PVA molecular chains, regulating the cross-linking reaction rate, preventing excessively rapid local cross-linking, and enhancing the stability of the cross-linked network. These metal salts have moderate coordination ability, preventing adhesive embrittlement due to excessive coordination, and are non-toxic, meeting the environmental protection requirements for display materials.

[0060] In some embodiments, a method for preparing a water-based adhesive for a polarizing film with high viscosity stability includes the following steps: S1. Mix acetyl-modified PVA with deionized water and stir at 70~90 ℃ until the modified PVA is completely dissolved to form a homogeneous solution; The dissolution temperature of modified PVA in deionized water needs to be controlled between 70 and 90 °C. Below 70 °C, the dissolution rate is slow and may not dissolve completely, resulting in solid particles in the system and defects during coating. Above 90 °C, water evaporates quickly, the system concentration fluctuates easily, and may cause slight degradation of the modified PVA molecular chains, affecting viscosity stability. Stirring can accelerate dissolution, ensure the formation of a homogeneous solution, avoid localized concentration unevenness, and lay the foundation for the uniform mixing of subsequent addition of crosslinking agents and metal ion salts.

[0061] S2. Cool the homogeneous solution to room temperature, add the crosslinking agent and metal ion salt, stir and mix evenly to obtain a high viscosity and stable polarizing film water adhesive.

[0062] Adding crosslinking agents and metal ion salts at high temperatures will cause the crosslinking reaction to proceed rapidly and uncontrollably, leading to a sudden increase in adhesive viscosity or even gelation, rendering the adhesive unusable. Cooling to room temperature reduces the crosslinking reaction rate, allowing the crosslinking agent and metal ion salts to disperse evenly before reacting gradually, ensuring a uniform and dense crosslinked network.

[0063] 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.

[0064] Example 1

[0065] This embodiment provides a water-based adhesive for polarizing films with high viscosity stability, which is prepared through the following steps: S1. Add PVA (10g, degree of polymerization / degree of hydrolysis 1700 / 99%) and dimethyl sulfoxide (90g) to the reactor. Heat to 80℃ and mix thoroughly. Simultaneously, purge the reactor with nitrogen gas to remove oxygen for 1 hour. After the PVA is fully dissolved, add triethylamine (0.2g) to the reactor. Add methyl acetoacetate (2.2g) dropwise over 2 hours. After the addition is complete, maintain the reaction temperature and continue the reaction for 3 hours. Then stop heating and allow it to cool to room temperature. Pour the reaction solution into methanol. A solid precipitates out. After filtering and washing several times, place it in a vacuum drying oven at 70℃ and 0.06MPa to dry again, obtaining acetoacetyl-modified PVA. Then, send the sample for 1H NMR spectroscopy to test the degree of acetoacetyl modification.

[0066] S2. Mix the synthesized acetyl-modified PVA (4g) and deionized water (100g) evenly, and heat to 90℃ while stirring. After the modified PVA is completely dissolved, add glyoxal (0.14g) and aluminum sulfate (0.03g) and mix evenly to obtain a water-based adhesive for polarizing film with high viscosity stability.

[0067] Example 2

[0068] The difference between this embodiment and Example 1 is that the solvent "dimethyl sulfoxide" is replaced with " N , N - Dimethylformamide (160 g); replace the catalyst "triethylamine" with "piperidine"; replace the compound containing acetoacetyl groups "methyl acetoacetate" with "tert-butyl acetoacetate" (2.3 g); at the same time, when preparing the hydrogel, replace the crosslinking agent "glyoxal" with "ethylenediamine" (0.12 g); replace the metal ion salt "aluminum sulfate" with "magnesium chloride" (0.03 g).

[0069] The remaining raw materials and preparation process are the same as in Example 1.

[0070] Example 3

[0071] The difference between this embodiment and Example 1 is that the solvent "dimethyl sulfoxide" is replaced with " N -Methylpyrrolidone (dosage: 100 g); the PVA specification was changed from "degree of polymerization 1700, degree of hydrolysis 99%" to "degree of polymerization 500, degree of hydrolysis 99%"; the compound containing acetoacetyl group "methyl acetoacetate" was changed to "ethyl acetoacetate" (dosage: 2.4 g); the dropping time was changed to 1.5 hours; the amount of catalyst triethylamine was changed to 0.15 g; at the same time, when preparing the water-based adhesive, the crosslinking agent "glyoxal" was changed to "glutaraldehyde" (dosage: 0.16 g); the metal ion salt "aluminum sulfate" was changed to "aluminum nitrate" (dosage: 0.02 g).

[0072] The remaining raw materials and preparation process are the same as in Example 1.

[0073] Example 4

[0074] Compared with Example 1, the difference in this embodiment is that the solvent "dimethyl sulfoxide" is replaced with "acetic acid" (120g); the PVA specification is changed from "degree of polymerization 1700, degree of hydrolysis 99%" to "degree of polymerization 3000, degree of hydrolysis 88%"; the catalyst "triethylamine" is replaced with "dimethylaminopyridine" (0.3g); the dropping time is changed to 3 hours; and when preparing the water-based adhesive, the crosslinking agent "glyoxal" is replaced with "1,4-butanediamine" (0.15g); and the metal ion salt "aluminum sulfate" is replaced with "zinc sulfate" (0.04g).

[0075] The remaining raw materials and preparation process are the same as in Example 1.

[0076] Example 5

[0077] Compared with Example 1, the difference in this embodiment is that the amount of methyl acetoacetate, a compound containing acetoacetyl groups, is changed from "2.2 g" to "1.5 g". At the same time, when preparing the water-based adhesive, the amount of glyoxal, a crosslinking agent, is changed from "0.14 g" to "0.08 g", and the amount of aluminum sulfate, a metal ion salt, is changed from "0.03 g" to "0.02 g".

[0078] The remaining raw materials and preparation process are the same as in Example 1.

[0079] Example 6

[0080] Compared with Example 1, the difference in this embodiment is that the amount of methyl acetoacetate, a compound containing acetoacetyl groups, is changed from "2.2 g" to "3.0 g". At the same time, when preparing the water-based adhesive, the amount of glyoxal, a crosslinking agent, is changed from "0.14 g" to "0.20 g", and the amount of aluminum sulfate, a metal ion salt, is changed from "0.03 g" to "0.05 g".

[0081] The remaining raw materials and preparation process are the same as in Example 1.

[0082] Comparative Example 1

[0083] The difference between this comparative example and Example 2 is that the solvent is used... N , N The dosage of dimethylformamide has been changed from "160 g" to 20 g, and PVA is used in small amounts. N , N -Dimethylformamide can only swell but cannot completely dissolve.

[0084] The remaining raw materials and preparation process are the same as in Example 1.

[0085] Comparative Example 2

[0086] The difference between this comparative example and Example 1 is that the catalyst "triethylamine" was not added.

[0087] The remaining raw materials and preparation process are the same as in Example 1.

[0088] Comparative Example 3

[0089] The difference between this comparative example and Example 1 is that the method of adding methyl acetoacetate was changed from "dropping over 2 hours" to "adding it all at once".

[0090] The remaining raw materials and preparation process are the same as in Example 1.

[0091] Comparative Example 4

[0092] The difference between this comparative example and Example 1 is that, in the preparation of the water-based adhesive, the crosslinking agent "ethylenediamine" was replaced with the monofunctional "ethanol" (0.12 g).

[0093] The remaining raw materials and preparation process are the same as in Example 1.

[0094] Comparative Example 5

[0095] The difference between this comparative example and Example 1 is that, in the preparation of the hydrogel, the metal ion salt "magnesium chloride" was replaced with "sodium chloride" (0.03 g).

[0096] The remaining raw materials and preparation process are the same as in Example 1.

[0097] Comparative Example 6

[0098] The difference between this comparative example and Example 1 is that the PVA specification was changed from "degree of polymerization 1700, degree of hydrolysis 99%" to "degree of polymerization 1700, degree of hydrolysis 70%".

[0099] The remaining raw materials and preparation process are the same as in Example 1.

[0100] Performance testing

[0101] The performance of the acetoacetyl-modified PVA and its formulated adhesive prepared in all the above examples and comparative examples was tested.

[0102] 1. Calculation of degree of modification: Nuclear magnetic resonance analysis: using DMSO- d 6 is a deuterated reagent. NMR analysis was performed. In the 1H NMR spectrum, the chemical shift δ=2.17ppm is the characteristic peak of the methyl group in the acetoacetyl group, and its peak area is denoted as a. The chemical shift δ=1.0~1.8ppm is the characteristic peak of the methylene group on the PVA main chain, and its peak area is denoted as b. Therefore, the degree of modification of the acetoacetyl group is c1= (a / 3) / (b / 2).

[0103] Calculate the conversion rate of acetoacetate, where the mass of PVA is m, the molecular weight of the repeating unit of vinyl alcohol in PVA is 44, the mass of acetoacetate is m, the molecular weight of acetoacetate is M, the degree of modification of the acetoacetyl group when acetoacetate is completely reacted is c2=(m / M) / (m / 44), and the conversion rate of acetoacetate is c1 / c2.

[0104] 2. Water Resistance Test: The prepared adhesive was used to bond the PVA polarizing film and the TAC protective film. After drying, the polarizing film was obtained. The polarizing film was then bonded to a glass plate and immersed in 40°C water. o In water at C, and at 40 o Store the PVA polarizing film under C conditions and record the dissolution of the PVA polarizing film over time. If the PVA polarizing film does not dissolve after 24 hours of soaking, it is considered to have good water resistance; if the PVA polarizing film dissolves after 24 hours of soaking, it is considered to have poor water resistance.

[0105] 3. Adhesive strength test: Apply the prepared adhesive to bond two sheets of TAC, then immerse them in a 40°C immersion tank. o Immerse the TAC in a constant temperature water bath for 4 minutes, then remove it and test the peel strength between TACs according to GB / T 2792-2014 standard. If the peel strength is greater than 1.0 N / 25 mm, it is considered to have high adhesive strength; if the peel strength is between 0.5 and 1.0 N / 25 mm, it is considered to have medium adhesive strength; if the peel strength is less than 0.5 N / 25 mm, it is considered to have poor adhesive strength.

[0106] The results are shown in Table 1: Table 1

[0107]

[0108] As shown in Table 1, the acetoacetyl-modified PVA prepared in Examples 1-6 of this invention exhibited acetoacetate conversion rates ranging from 61.6% to 75.7%. The conversion rates of Comparative Examples 1-3 and Comparative Example 6 were significantly lower, ranging from 18.2% to 45.3%. This significant difference in conversion rates directly stems from the synergistic effect of key technical features. The conversion rate of Comparative Example 1 was much lower than all other examples, confirming that in a heterogeneous reaction system, the hydroxyl groups within the PVA molecular chain cannot be fully exposed and contacted with the reactants. In contrast, this invention completely dissolves PVA, creating a homogeneous reaction environment, which is a fundamental prerequisite for achieving high conversion rates. Although the conversion rate of Comparative Example 2 was higher than that of Comparative Example 1, it was significantly lower than any of the examples using a Lewis base catalyst. This demonstrates that the Lewis base significantly reduces the activation energy of the reaction by activating the hydroxyl groups of PVA and promoting the formation of the transition state in the transesterification reaction, playing a key catalytic role in achieving high conversion rates. The conversion rate of Comparative Example 3 was lower than that of the example using the dropwise addition method, indicating that the controllable dropwise addition process can effectively maintain the low concentration of reactants in the reaction system, suppress side reaction pathways to the maximum extent, thereby improving the selectivity of the reaction and the conversion rate of the main reaction.

[0109] Examples 1-6 exhibited good water resistance, with no PVA polarizing film dissolving, while Comparative Examples 1-6 showed poor water resistance, with all PVA optical films dissolving. This superior performance is attributed to the double cross-linked network structure formed in this invention. Covalent cross-linking provides a stable network framework, while the metal ion coordination bonds possess dynamic reversible properties, allowing stress to be released through bond rearrangement under humid and hot conditions, thus preventing permanent damage to the cross-linked network structure.

[0110] The peel strength of Examples 1-6 reached 1.12–1.70 N / 25 mm, significantly higher than the 0.09–0.73 N / 25 mm of Comparative Examples 1-6. This difference is directly attributable to the uniform grafting of acetyl groups. By completely dissolving PVA and using a controlled drop-feeding process, active sites are uniformly distributed on the PVA chain, forming a dense and uniform cross-linked network, thereby providing higher cohesive strength.

[0111] 5. Viscosity test: The viscosity of the prepared adhesive was tested at 25°C (initial, 7 days, 15 days and after 30 days) using a rotational viscometer.

[0112] The results are shown in Table 2: Table 2

[0113] The water-based adhesives prepared in Examples 1-6 of this invention, after being stored at 25 °C for 30 days, showed viscosity increases ranging from 16.0% to 48.6%, all meeting the technical requirement of ≤50%. The adhesives in Comparative Examples 1 and 2 showed viscosity increases exceeding 75% within 15 days and gelled within 30 days. The adhesives in Comparative Examples 4 and 5 showed no significant viscosity change throughout the storage period, remaining at a consistently low viscosity level. Comparative Examples 1 and 2, due to the non-uniformity of their modified PVA, exhibited locally highly active regions after adhesive preparation, where the crosslinking reaction preferentially and accelerated, leading to a viscosity surge and eventual gelation. In contrast, the embodiments of this invention, with their high conversion rate and uniformly modified PVA, ensured a uniform distribution of crosslinking active sites on the molecular chain, enabling the crosslinking network to be constructed smoothly and synchronously, achieving long-term viscosity stability. The adhesives in Comparative Examples 4 and 5 failed to establish an effective three-dimensional network structure, resulting in extremely low viscosity with no growth, completely losing their function as structural adhesives. This proves that specific bifunctional crosslinking agents and coordinating metal ion salts are essential components for forming a stable crosslinked network.

[0114] 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 water-based adhesive for polarizing films with high viscosity stability, characterized in that, By weight, it includes the following components: Acetylacetyl modified PVA: 2-8 parts; Crosslinking agent: 0.01–0.2 parts; Metal ion salts: 0.01–0.1 parts; Deionized water: 100 parts.

2. The water-based adhesive for high viscosity stability of polarizers according to claim 1, characterized in that, The acetylacetyl-modified PVA is prepared by the following steps: S1. Add PVA and solvent to the reaction vessel, start stirring and heat to 70~130 ℃, while simultaneously introducing nitrogen gas into the reaction vessel to remove oxygen, until PVA is completely dissolved; S2. After the PVA is completely dissolved, add the catalyst to the reaction system and add a compound containing acetyl groups dropwise. S3. After the addition is complete, maintain the reaction temperature and continue the reaction for 2 to 5 hours. S4. After the reaction is complete, the reaction solution is cooled and poured into methanol to precipitate solid. After filtration and washing with methanol, a wet solid is obtained. S5. The washed solid product is vacuum dried to obtain acetyl-modified PVA.

3. The water-based adhesive for high viscosity stability of polarizing films according to claim 2, characterized in that, In S1, the degree of polymerization of PVA is 500-3000, and the degree of alcoholysis is 88%-99%; the solvent is formic acid, acetic acid, propionic acid, etc. N , N -Dimethylformamide, N , N -Diethylformamide, N , N -Dimethylacetamide, dimethyl sulfoxide, 2-pyrrolidone N One or more of methylpyrrolidone, etc.; the solid content of the PVA and solvent mixture is 5% to 30%; Nitrogen gas is introduced for deoxygenation for 1 to 2 hours.

4. The water-based adhesive for high viscosity stability of polarizers according to claim 2, characterized in that, In S2, the catalyst is a Lewis base, and its addition amount is 1% to 5% of the mass of PVA; The Lewis base is selected from one or more of ethylenediamine, dodecylamine, aniline, diethylamine, di-n-butylamine, piperidine, diphenylamine, N-methylaniline, triethylamine, triphenylamine, dodecyl tertiaryamine, dimethylaminopyridine, N,N-dimethylformamide, etc.

5. The water-based adhesive for high viscosity stability of polarizing films according to claim 2, characterized in that, In S2, the compound containing acetoacetyl groups is one or more of the following: methyl acetoacetate, ethyl acetoacetate, n-propyl acetoacetate, isopropyl acetoacetate, allyl acetoacetate, isobutyl acetoacetate, sec-butyl acetoacetate, tert-butyl acetoacetate, isoamyl acetoacetate, n-hexyl acetoacetate, n-heptyl acetoacetate, n-octyl acetoacetate, benzyl acetoacetate, etc.; the time for adding the compound containing acetoacetyl groups is 1 to 3 hours.

6. The water-based adhesive for high viscosity stability of polarizers according to claim 2, characterized in that, In step S4, the amount of methanol used is 3 to 5 times the volume of the reaction liquid; the number of washing cycles is 3 to 5.

7. The water-based adhesive for high viscosity stability of polarizers according to claim 2, characterized in that, In step S5, the vacuum drying conditions are: temperature 40~100 ℃, pressure 0.05~0.1 MPa, and drying time 4~8 hours.

8. The water-based adhesive for high viscosity stability of polarizers according to claim 1, characterized in that, The crosslinking agent is one or more of glyoxal, glutaraldehyde, ethylenediamine, 1,4-butanediamine, ethylene glycol, and 1,4-butanediol.

9. The water-based adhesive for high viscosity stability of polarizing film according to claim 1, characterized in that, The metal ion salt is one or more of aluminum sulfate, aluminum nitrate, magnesium chloride, magnesium sulfate, calcium chloride, zinc sulfate, and zinc chloride.

10. A method for preparing a water-based adhesive for a polarizing film with high viscosity stability, characterized in that, The water-based adhesive for preparing the high viscosity stability polarizer according to any one of claims 1-9 comprises the following steps: S1. Mix acetyl-modified PVA with deionized water and stir at 70~90 ℃ until the modified PVA is completely dissolved to form a homogeneous solution; S2. Cool the homogeneous solution to room temperature, add the crosslinking agent and metal ion salt, stir and mix evenly to obtain a high viscosity and stable polarizing film water adhesive.

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