Waterborne polyurethane dispersion as well as preparation method and application thereof

Abstract

The invention provides a waterborne polyurethane dispersion as well as a preparation method and application thereof. The waterborne polyurethane dispersion is prepared from the following raw materials: polyisocyanate, polyester polyol, a hydrophilic chain extender, a neutralizer and an optional micromolecular chain extender. According to the waterborne polyurethane dispersion, polyester polyol with a specific structure and molecular weight is adopted as a soft segment, and through formula optimization, the waterborne polyurethane dispersion is good in adhesion and bonding force to polymethyl methacrylate / polycarbonate base materials, high in hardness and resistant to scratches; meanwhile, the waterborne polyurethane dispersion is high in dry film full light transmittance and has wide application prospects in the fields of optical material assemblies, coatings and the like.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials technology, specifically to the field of waterborne polyurethane, and more specifically to a waterborne polyurethane dispersion, its preparation method, and its application. Background Technology

[0002] With the increasing global emphasis on green chemistry and low-carbon environmental protection, new materials and technologies that align with this international development trend have received widespread attention and application. Among them, waterborne polyurethane or polyurethane-polyurea aqueous dispersions, using water as the dispersion medium, have become a research hotspot due to their unique properties and advantages. This material not only meets national policy guidance and development needs but also produces no pollution during use, making it environmentally friendly and widely used in coatings, adhesives, and other fields.

[0003] The field of optical devices is increasingly demanding higher performance from coatings and adhesives, particularly in terms of overall light transmittance. Optical substrates such as PMMA (polymethyl methacrylate) and PC (polycarbonate) require surface treatment and bonding solutions with high light transmittance and low haze for applications in displays, lenses, and optical films. While common waterborne polyurethanes (such as polyester, polyether, and polycarbonate types) offer environmental advantages, their soft segments are prone to crystallization, leading to high haze and insufficient overall light transmittance in the coating, making it difficult to meet the stringent light transmission requirements of optical devices.

[0004] CN108250390B requires the use of crystalline polyester diols (such as 1,4-butanediol / 1,6-hexanediol and adipic acid copolymers) with a number average molecular weight of 1000-4000 and amorphous polycarbonate diols (such as 1,4-butanediol / 1,6-hexanediol and dimethyl carbonate copolymers), with a ratio of crystalline to amorphous diols of 1-25:1, preferably 5-10:1. This combination optimizes the flexibility, crystallinity, and compatibility of the polyurethane chain segments. By synergistically combining the ordered arrangement of the hard segments of the crystalline polyester with the flexible segments of the amorphous polycarbonate, heat resistance and flexibility are balanced. At the same time, the siloxane crosslinking points are embedded in the side chains, avoiding the reaction inertia caused by steric hindrance, thus solving the problems of complex operation and short open time in traditional two-component systems.

[0005] Patent CN107868204B relates to an anionic waterborne polyurethane resin, its preparation method, and its application. The patent requires that the polyester polyol segment (R3) must be derived from a specific series, including: terephthalic acid-isophthalic acid-adipic acid-neopentyl glycol series; terephthalic acid-isophthalic acid-adipic acid-hexanediol series; terephthalic acid-isophthalic acid-adipic acid-butanediol series; and terephthalic acid-isophthalic acid-adipic acid-methylpropylene glycol series. The number average molecular weight of the polyester polyol is strictly limited to between 2000 and 4000 to ensure that the polyurethane coating film has suitable mechanical properties and water resistance. Simultaneously, this water-soluble polyurethane is compounded with solvent-based polyurethane resin (mass ratio 1:1 to 5:1) and co-dispersed in water to form a stable waterborne emulsion. This compounding strategy resolves the contradiction between the water resistance of the waterborne polyurethane coating film and the water dispersibility of the resin.

[0006] In general, while existing waterborne polyurethane systems—whether polyester, polyether, or polycarbonate—have inherent advantages in VOC emission reduction and environmental compliance due to the use of water as the dispersion medium, the soft segments in their molecular chains (especially aliphatic segments with a molecular weight ≥ 1000 g·mol⁻¹) readily arrange themselves in an ordered manner within the conventional drying range of room temperature to 80°C, forming microcrystalline domains on the scale of 10–50 nm. The refractive index difference between these microcrystalline domains and the continuous phase (Δn ≈ 0.03–0.08) is sufficient to induce Rayleigh-Mie scattering, resulting in coating haze (Hz) generally > 2% and total light transmittance (T) low. t ≤90%. For optical devices such as foldable screen polarizers, AR diffractive waveguides, and automotive HUD composite prisms, industry specifications already require Hz <0.3% and T <90%. t ≥92% (@550nm, multi-angle integrating sphere). The optical loss caused by the intrinsic crystallization tendency of soft segments in existing waterborne polyurethane has become a technical bottleneck for its replacement of solvent-based high-transparency resins, and also constitutes a difficult point that urgently needs to be overcome in patents. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide an aqueous polyurethane dispersion, its preparation method, and its applications. By using adipic acid, terephthalic acid, isophthalic acid, neopentyl glycol, and ethylene glycol as comonomers, and a polyester polyol in a specifically designed ratio as the soft segment, the aqueous polyurethane dispersion can maintain excellent adhesion to polar substrates such as PMMA and PC, while providing high hardness and good wear resistance. More importantly, by limiting the types and ratios of polyester polyol comonomers, its crystallinity can be effectively controlled, thereby ensuring low haze and high total light transmittance to meet the requirements of optical device applications.

[0008] To achieve this objective, the present invention adopts the following technical solution:

[0009] This invention provides an aqueous polyurethane dispersion, wherein the raw materials for preparing the aqueous polyurethane dispersion include polyisocyanate, polyester polyol, hydrophilic chain extender, neutralizer and optional small molecule chain extender.

[0010] The polyester polyol comprises five structural units, A, E, and D, where A is a structural unit derived from diacid, B is a structural unit derived from terephthalic acid, C is a structural unit derived from isophthalic acid, D is a structural unit derived from neopentyl glycol, and E is a structural unit derived from ethylene glycol.

[0011] In the polyester polyol, the molar percentage of structural unit A is denoted as a, the molar percentage of structural unit B as b, the molar percentage of structural unit C as c, the molar percentage of structural unit D as d, and the molar percentage of structural unit E as e. The molar percentage of each structural unit is the sum of the molar percentages of structural units A, B, C, D, and E. Where a, b, c, d, and e are all non-zero; 0 < a < d, and 1 ≤ c / b ≤ 2, and d / e ≥ 1, and a + b + c < d + e.

[0012] Specifically, c / b can be 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9 or 2.0, as well as specific point values ​​between the above point values. Due to space limitations and for the sake of brevity, this invention will not exhaustively list the specific point values ​​included in the range.

[0013] Specifically, d / e can be 1, 1.2, 1.5, 1.8, 2.0, 2.2, 2.5, etc., as well as specific point values ​​between the above point values, with 1 ≤ d / e < 2.5 being preferred.

[0014] Preferably, the number average molecular weight of the polyester polyol is 1000-2500 g / mol, for example, it can be 1000 g / mol, 1200 g / mol, 1400 g / mol, 1500 g / mol, 1800 g / mol, 2000 g / mol, 2200 g / mol, 2400 g / mol or 2500 g / mol, preferably 1500-2500 g / mol.

[0015] In this invention, the polyester polyol can be prepared by polyester polyol condensation polymerization methods known in the art.

[0016] The aqueous polyurethane dispersion provided by this invention utilizes a polyester polyol with a specific structural composition as the soft segment, introducing a large number of rigid aromatic ring structures into the polymer. This allows for a significant increase in the cohesive energy of the polymer segments through π-π stacking. Specifically, after film formation, π-π stacking microregions with a face-to-face distance of 0.35–0.38 nm can be formed, with a microregion interaction energy of 8–12 kJ mol⁻¹, resulting in a cohesive energy density (CED) increase of ≥120 J cm⁻¹ compared to conventional aliphatic segments. -3 This invention achieves a tensile strength of >35MPa without the need for external crosslinking agents. By precisely controlling the molar ratio (c / b) of structural units derived from isophthalic acid and terephthalic acid (c / b = 1.0–2.0, 1 ≤ c / b ≤ 2), the 120° bond angle of isophthalic acid introduces a "knot" structure in the amorphous region, preventing the chain segments from forming continuous crystalline domains ≥10nm and disrupting the crystallinity of the polyester polyol. Simultaneously, by designing the proportion of amorphous diol (neopentyl glycol) to be no less than that of crystalline diol (ethylene glycol) (d / e ≥ 1), the crystallinity of the polyester polyol can be further reduced, ensuring both mechanical properties and chain segment flexibility. Ethylene glycol is chosen because its short methylene segments ensure a high density of hydrogen bond acceptor ester bonds when copolymerized into polyester. Thus, the aqueous polyurethane dispersion possesses both tuned and optimized weak crystallinity and the high cohesive energy of polyester products, with a simple process and easy preparation.

[0017] Through the synergistic design of the above molecular structure, the waterborne polyurethane dispersion achieves precise control of crystallization ability under the premise of simple process and easy preparation. It retains the high cohesive energy characteristics of polyester materials, and by inhibiting crystallization, it can effectively reduce light scattering caused by crystallization regions in the coating, thereby giving the coating excellent light transmittance. It has broad application prospects in the field of optical device coatings or adhesives.

[0018] Preferably, in the raw materials for preparing the aqueous polyurethane dispersion of the present invention, the polyisocyanate includes any one or a combination of at least two of aliphatic diisocyanates, alicyclic diisocyanates, and aromatic diisocyanates.

[0019] Preferably, the polyisocyanate includes any one or a combination of at least two of toluene diisocyanate, diphenylmethane diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate, and dicyclohexylmethane diisocyanate, and more preferably isophorone diisocyanate.

[0020] Preferably, the hydrophilic chain extender is a compound containing hydroxyl and carboxyl groups, more preferably any one or a combination of at least two of 3-hydroxypropionic acid, dimethylolpropionic acid, dimethylolbutyric acid, dimethylolacetic acid, trihydroxysulfonic acid, and dihydroxysuccinic acid, and more preferably dimethylolpropionic acid.

[0021] Preferably, the small molecule chain extender is a small molecule amine chain extender.

[0022] Preferably, the molecular weight of the small molecule chain extender is 60-500 g / mol, for example, it can be 60 g / mol, 70 g / mol, 80 g / mol, 90 g / mol, 100 g / mol, 150 g / mol, 200 g / mol, 250 g / mol, 300 g / mol, 350 g / mol, 400 g / mol, 450 g / mol, 480 g / mol or 500 g / mol, as well as specific values ​​between the above values. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range.

[0023] Preferably, the small molecule chain extender is a linear diamine chain extender.

[0024] In this invention, "linear diamine chain extender" means that the molecular structure of the diamine chain extender does not contain a branched cross-linked structure, and the diamine chain extender includes any one or a combination of at least two of aliphatic diamine chain extenders, alicyclic diamine chain extenders, and aromatic diamine chain extenders.

[0025] As a preferred embodiment of the present invention, the small molecule chain extender is a linear diamine chain extender containing active hydrogen. The reactivity of diamine chain extenders is generally less than that of triamines and tetraamines, resulting in better chain extension effect on polymers.

[0026] Preferably, the small molecule chain extender includes any one or a combination of at least two of ethylenediamine, hexamethylenediamine, pentamethylenediamine, isophoronediamine, 4,4'-diphenylmethanediamine, and 4,4'-diaminodicyclohexylmethane, and more preferably isophoronediamine.

[0027] Preferably, the neutralizing agent is an organic or inorganic alkaline compound, more preferably any one or a combination of at least two of the following: triethylamine, triethanolamine, dimethylethanolamine, 2-amino-2-methyl-1-propanol, N-methyldiethanolamine, dimethylcyclohexylamine, sodium hydroxide, potassium hydroxide, lithium hydroxide, and calcium hydroxide, and more preferably triethylamine.

[0028] Preferably, based on the total mass of the polyisocyanate, polyester polyol, hydrophilic chain extender, small molecule chain extender, and neutralizing agent as 100%, the mass content of the polyisocyanate is 16.0-38.0 wt%, for example, it can be 16 wt%, 16.5 wt%, 17 wt%, 17.5 wt%, 18.0 wt%, 18.5 wt%, 19 wt%, 20 wt%, 21 wt%, 22 wt%, 25 wt%, 28 wt%, 30 wt%, 32 wt%, 35 wt%, or 38 wt%, as well as specific values ​​between the above values. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range, but it is further preferred to be 24.0-34.0 wt%.

[0029] Preferably, based on the total mass of the polyisocyanate, polyester polyol, hydrophilic chain extender, small molecule chain extender and neutralizer as 100%, the mass content of the polyester polyol is 46.0-72.0 wt%, for example, 46 wt%, 48 wt%, 50 wt%, 52 wt%, 55 wt%, 58 wt%, 61 wt%, 63 wt%, 66 wt%, 69 wt% or 72 wt%, and specific values ​​between the above values. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range, but is further preferably 50.0-66.0 wt%.

[0030] Preferably, based on the total mass of the polyisocyanate, polyester polyol, hydrophilic chain extender, small molecule chain extender, and neutralizing agent as 100%, the mass content of the hydrophilic chain extender is 6.0-15.0 wt%, for example, 6.0 wt%, 7.0 wt%, 7.5 wt%, 8.0 wt%, 9.0 wt%, 9.5 wt%, 10.5 wt%, 11.0 wt%, 12.0 wt%, 12.5 wt%, 13.0 wt%, 14.0 wt%, or 15.0 wt%, as well as specific values ​​between the above values. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range, but is further preferably 7.5-13.0 wt%.

[0031] Preferably, based on the total mass of the polyisocyanate, polyester polyol, hydrophilic chain extender, small molecule chain extender, and neutralizing agent as 100%, the mass content of the small molecule chain extender is ≤6.0wt%, for example, it can be 0, 0.2wt%, 0.5wt%, 0.8wt%, 1wt%, 1.2wt%, 1.5wt%, 1.7wt%, 2wt%, 2.2wt%, 2.5wt%, 2.8wt%, 3.7wt%, 4.5wt%, 5.1wt%, 5.5wt%, 6wt%, and specific values ​​between the above values. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range, but it is further preferred to be 0.1-4.5wt%.

[0032] Preferably, based on the total mass of the polyisocyanate, polyester polyol, hydrophilic chain extender, small molecule chain extender, and neutralizer as 100%, the mass content of the neutralizer is 2.0-11.0 wt%, for example, 2.0 wt%, 3.0 wt%, 4.0 wt%, 5.0 wt%, 6.0 wt%, 7.0 wt%, 8.0 wt%, 9.0 wt%, 10.0 wt%, or 11.0 wt%, as well as specific values ​​between the above values. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range, but 2.8-9.8 wt% is further preferred.

[0033] Preferably, the raw materials for preparing the waterborne polyurethane dispersion further include a catalyst, and the amount of catalyst is preferably greater than 0.01 wt% and less than 1 wt% of the total mass of polyisocyanate, polyester polyol, hydrophilic chain extender, small molecule chain extender and neutralizer, and more preferably less than 0.8 wt%.

[0034] In this invention, the type of catalyst is not specifically limited, and any catalyst known in the art that can catalyze the reaction of active hydrogen with NCO groups to generate carbamate groups is applicable to this invention.

[0035] Preferably, the catalyst comprises an organobismuth catalyst and / or an organotin catalyst, exemplary including but not limited to: any one or a combination of at least two of Bi@8108 (a leading US company), dimethyltin dinedecanoate, dibutyltin dilaurate, and dioctyltin dilaurate, further preferably Bi@8108 (a leading US company) and / or dimethyltin dinedecanoate, more preferably dimethyltin dinedecanoate.

[0036] Preferably, the raw materials for preparing the aqueous polyurethane dispersion also include an organic solvent.

[0037] Preferably, the boiling point of the organic solvent is 40-85℃, for example, it can be 40℃, 45℃, 50℃, 55℃, 60℃, 65℃, 70℃, 75℃, 80℃ or 85℃, and specific values ​​between the above points. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range.

[0038] Preferably, the organic solvent includes ketone solvents, more preferably acetone and / or butanone, and even more preferably acetone.

[0039] Preferably, based on the total mass of the polyisocyanate, polyester polyol, hydrophilic chain extender, small molecule chain extender and neutralizer as 100%, the mass content of the organic solvent is 100-300 wt%, for example, it can be 100 wt%, 120 wt%, 150 wt%, 180 wt%, 200 wt%, 220 wt%, 250 wt%, 280 wt% or 300 wt%, and specific values ​​between the above values. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range.

[0040] Preferably, the raw materials for preparing the aqueous polyurethane dispersion further include water, and the amount of water is such that the solid content in the final aqueous polyurethane dispersion product is 10-40 wt%, for example, it can be 10 wt%, 12 wt%, 15 wt%, 18 wt%, 20 wt%, 22 wt%, 25 wt%, 28 wt%, 30 wt%, 32 wt%, 35 wt%, 38 wt%, or 40 wt%, as well as specific values ​​between the above values. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range, but it is further preferred to be 15-30 wt%.

[0041] Preferably, the particle size of the solids in the aqueous polyurethane dispersion product is 10-500 nm, for example, it can be 10 nm, 30 nm, 40 nm, 50 nm, 60 nm, 80 nm, 100 nm, 120 nm, 150 nm, 180 nm, 200 nm, 220 nm, 250 nm, 280 nm, 300 nm, 350 nm, 400 nm, 450 nm or 500 nm, as well as specific values ​​between the above values. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range, and it is further preferred to be 15-250 nm.

[0042] The aforementioned phrase "based on the total mass of the polyisocyanate, polyester polyol, hydrophilic chain extender, small molecule chain extender, and neutralizer being 100%" specifically means: when the system contains a small molecule chain extender, the total mass of the polyisocyanate, polyester polyol, hydrophilic chain extender, small molecule chain extender, and neutralizer is taken as 100%; when the system does not contain a small molecule chain extender, the total mass of the polyisocyanate, polyester polyol, hydrophilic chain extender, and neutralizer is taken as 100%.

[0043] In a second aspect, the present invention provides a method for preparing an aqueous polyurethane dispersion as described in the first aspect, the preparation method comprising the following steps:

[0044] (1) Polyisocyanate, polyester polyol and hydrophilic chain extender are polymerized to obtain prepolymer;

[0045] (2) After the prepolymer is neutralized by the neutralizing agent, it is chain extended by an optional small molecule chain extender, and then water is added to disperse it to obtain the waterborne polyurethane dispersion.

[0046] Preferably, the polymerization reaction in step (1) is carried out in the presence of an organic solvent.

[0047] Preferably, the polymerization reaction in step (1) is carried out in the presence of a catalyst.

[0048] Preferably, the preparation method includes the following steps:

[0049] S1. Polyisocyanate, polyester polyol, hydrophilic chain extender, some organic solvent and optional catalyst are mixed and polymerized to obtain prepolymer;

[0050] S2. After mixing the prepolymer with the remaining organic solvent, neutralize it with a neutralizing agent.

[0051] S3. The product of the neutralization reaction is subjected to a chain extension reaction with an optional small molecule chain extender, and then water is added to disperse it to obtain an emulsion; the organic solvent in the emulsion is removed to obtain the aqueous polyurethane dispersion.

[0052] As a preferred embodiment of the present invention, the organic solvent is added to the system in two stages. The first stage serves as the solvent (medium) for the polymerization reaction. Taking the total amount of organic solvent added as 100%, the amount added during the polymerization reaction stage (step S1) is 20-80 wt%, for example, 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%, 45 wt%, 50 wt%, 55 wt%, 60 wt%, 65 wt%, 70 wt%, 75 wt%, or 80 wt%, and specific values ​​between these ranges are not exhaustively listed here for space limitations and for the sake of brevity. The remaining organic solvent is added in step S2 and mixed with the prepolymer to dilute it.

[0053] Preferably, the neutralizing agent is added to the reaction system in the form of an aqueous solution of the neutralizing agent.

[0054] Preferably, the neutralizing agent in the aqueous solution has a mass percentage content of 5-50 wt%, for example, it can be 5 wt%, 8 wt%, 10 wt%, 12 wt%, 15 wt%, 18 wt%, 20 wt%, 22 wt%, 25 wt%, 28 wt%, 30 wt%, 32 wt%, 35 wt%, 38 wt%, 40 wt%, 45 wt%, 48 wt%, or 50 wt%, as well as specific values ​​between the above values. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range.

[0055] Preferably, the small molecule chain extender is added to the reaction system in the form of an aqueous solution of the small molecule chain extender.

[0056] Preferably, the mass percentage of the small molecule chain extender in the aqueous solution is 5-50 wt%, for example, it can be 5 wt%, 8 wt%, 10 wt%, 12 wt%, 15 wt%, 18 wt%, 20 wt%, 22 wt%, 25 wt%, 28 wt%, 30 wt%, 32 wt%, 35 wt%, 38 wt%, 40 wt%, 45 wt%, 48 wt%, or 50 wt%, as well as specific values ​​between the above values. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range.

[0057] Preferably, the polymerization reaction temperature is 70-90℃, for example, it can be 70℃, 72℃, 75℃, 78℃, 80℃, 82℃, 85℃, 88℃ or 90℃, and specific values ​​between the above points. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range, but it is more preferably 75-85℃.

[0058] Preferably, the polymerization reaction time is the time required for the NCO groups in the product (prepolymer) to reach the theoretical value.

[0059] Preferably, the NCO group content in the prepolymer is 0.8-2.5 wt%, for example, it can be 0.8 wt%, 0.82 wt%, 0.85 wt%, 0.88 wt%, 0.9 wt%, 0.92 wt%, 0.95 wt%, 0.98 wt%, 1 wt%, 1.02 wt%, 1.05 wt%, 1.08 wt%, 1.1 wt%, 1.2 wt%, 1.3 wt%, 1.4 wt%, 1.5 wt%, 1.6 wt%, 1.8 wt%, 2 wt%, 2.1 wt%, 2.2 wt%, 2.4 wt%, or 2.5 wt%, as well as specific values ​​between the above values. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range.

[0060] Preferably, the temperature of the neutralization reaction is 30-50°C, for example, it can be 30°C, 32°C, 35°C, 38°C, 40°C, 42°C, 45°C, 48°C or 50°C, as well as specific values ​​between the above points. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range, but it is more preferably 35-45°C.

[0061] Preferably, the neutralization reaction time is 5-40 min, for example, it can be 5 min, 8 min, 10 min, 12 min, 15 min, 18 min, 20 min, 25 min, 30 min, 35 min, 38 min or 40 min, as well as specific values ​​between the above values. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range. More preferably, it is 10-20 min.

[0062] Preferably, the temperature of the chain extension reaction is 35-60°C, for example, it can be 35°C, 38°C, 40°C, 42°C, 45°C, 48°C, 50°C, 52°C, 55°C, 58°C or 60°C, as well as specific values ​​between the above points. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range, but it is further preferred to be 40-55°C.

[0063] Preferably, the chain extension reaction time is 5-40 min, for example, it can be 5 min, 8 min, 10 min, 12 min, 15 min, 18 min, 20 min, 25 min, 30 min, 35 min or 40 min, as well as specific values ​​between the above points. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range. More preferably, it is 10-20 min.

[0064] Preferably, the pH value of the emulsion in step S3 is >6, for example, it can be 6.2, 6.5, 6.8, 7, 7.2, 7.5, 7.8, 8, etc., and preferably the pH value is 6.5-8.

[0065] Preferably, the method for removing organic solvents includes vacuum distillation.

[0066] Thirdly, the present invention provides an application of the aqueous polyurethane dispersion as described in the first aspect, wherein the aqueous polyurethane dispersion is applied to a coating or adhesive for optical devices.

[0067] Fourthly, the present invention provides an aqueous polyurethane optical formulation coating, the formulation comprising commonly used coating additives and an aqueous polyurethane dispersion as described in the first aspect.

[0068] Preferably, the waterborne polyurethane optical formulation coating includes auxiliary substances and additives known in coating and adhesive technologies. Examples include emulsifiers, light stabilizers (e.g., UV absorbers and sterically hindered amines (HALS)), antioxidants, fillers, antisettling agents, defoamers and / or wetting agents, flow modifiers, reactive diluents, plasticizers, neutralizers, catalysts, auxiliary solvents, thickeners, pigments, dyes, matting agents, tackifiers, etc. Additives and / or auxiliary agents can be added before / after polymerization or after dispersion; the present invention does not impose any particular limitation on the aforementioned reagents.

[0069] As a preferred embodiment of the present invention, the aqueous polyurethane dispersion exhibits excellent adhesion to high surface energy substrates such as PMMA or PC. Furthermore, as a coating or adhesive for optical devices, it provides a device haze (Hz) < 0.3% and a total light transmittance (T0.05). t ≥92.0%.

[0070] Compared with the prior art, the present invention has the following beneficial effects:

[0071] (1) In the waterborne polyurethane dispersion provided by the present invention, the composition of polyester polyol is precisely controlled to effectively destroy crystallinity, prevent the formation of large-size crystal domains, and reduce light scattering, thereby giving the coating excellent light transmittance, which is suitable for optical device coatings and other fields.

[0072] (2) The molecular structure design is simple and easy to prepare; at the same time, the flexibility of the chain segments is maintained by inhibiting crystallinity and the high cohesive energy characteristics of polyester materials are guaranteed, thus achieving a balance between mechanical properties and processability, and can be applied on a large scale in industry.

[0073] (3) The production process of the waterborne polyurethane dispersion provided by the present invention is simple, easy to operate, safe and non-toxic. Detailed Implementation

[0074] The present invention will be further illustrated below with specific embodiments. These embodiments are merely illustrative and do not limit the scope of the invention.

[0075] I. Main raw material sources for the example:

[0076] 4,4'-Dicyclohexylmethane diisocyanate (HMDI): Industrial grade, Wanhua Chemical;

[0077] Isophorone diisocyanate (IPDI): Industrial grade, Wanhua Chemical;

[0078] Dimethyltin dinedecanoate: analytical grade, Sinopharm Chemical Reagent Co., Ltd.;

[0079] Isophorone diamine (IPDA): Analytical grade, Sinopharm Chemical Reagent Co., Ltd.;

[0080] Ethylenediamine (EDA): Analytical grade, Sinopharm Chemical Reagent Co., Ltd.;

[0081] Triethylamine (TEA): Analytical grade, Sinopharm Chemical Reagent Co., Ltd.;

[0082] Dimethylolpropionic acid (DMPA): Industrial grade, Persto Chemical Company;

[0083] Acetone: Industrial grade, Wanhua Chemical;

[0084] Crosslinking agent WS-700: Nippon Shokubai;

[0085] Dispersant Solsperse 41000: Lubrizol;

[0086] Silica particles: Fusang Chemicals.

[0087] Polyester polyols (1)-(6) were prepared according to the proportions shown in Table 1 below. In a reaction flask equipped with a thermometer, reflux condenser, and nitrogen tube, terephthalic acid, isophthalic acid, adipic acid, neopentyl glycol, and ethylene glycol were added sequentially according to the proportions in Table 1. The mixture was stirred and heated to 250°C under a nitrogen stream. The reaction was terminated when the acid value reached below 5, yielding polyester polyols (1)-(6).

[0088] Table 1

[0089]

[0090] II. Performance Testing Methods

[0091] Solid content: According to HG / T4758, take 1g of waterborne polyurethane sample, put it in an oven at 105℃ for 3h and weigh it. Calculate the solid content.

[0092] Particle size: Malvern particle size analyzer was used in accordance with GB / T 19077-2016;

[0093] pH: Tested using a Mettler pH meter according to GB / T 9724-2007;

[0094] Haze: The haze of the PMMA film was measured using a haze meter (HGM-2DP, Suga);

[0095] Transmittance: The PMMA film sample was placed in a visible spectrophotometer (VAP-8010, JASCO) for measurement;

[0096] Peel strength: After bonding the PMMA film sample to the PVA substrate using a known method, a polarizing film substrate is obtained. The test piece is cut to a size of 15cm×15mm, and the peel strength between the PMMA film and PVA is tested using a tensile testing machine (MTS-E42) at a peel speed of 1000mm / min. This is used to determine the adhesion of the coating liquid.

[0097] Example 1

[0098] 100g of IPDI, 186g of polyester polyol (1), 35g of DMPA, 120g of acetone, and 0.8g of dimethyltin dinedecanoate were sequentially added to a four-necked flask equipped with a condenser, thermometer, and stirrer. The polymerization reaction was carried out at 80°C. When the NCO reached the theoretical value of 1.4%, a polyurethane prepolymer was obtained. The prepolymer was cooled to 50°C, and 426g of acetone was added. The mixture was stirred at 45°C for 20 minutes. 22g of TEA was added for neutralization reaction for 10 minutes. After neutralization, 6g of chain extender IPDA was added, and the mixture was reacted at 40°C for 20 minutes. Finally, 650g of water was slowly added for shear dispersion to obtain a crude polyurethane emulsion. Finally, the acetone in the crude emulsion was removed by vacuum distillation to obtain an aqueous polyurethane dispersion PUD-1.

[0099] Example 2

[0100] 90g of IPDI, 203g of polyester polyol (2), 30g of DMPA, 120g of acetone, and 0.8g of dimethyltin dinedecanoate were sequentially added to a four-necked flask equipped with a condenser, thermometer, and stirrer. The polymerization reaction was carried out at 75°C. When the NCO reached the theoretical value of 1.7%, a polyurethane prepolymer was obtained. The prepolymer was cooled to 50°C, and 426g of acetone was added. The mixture was stirred at 40°C for 20 minutes. 19g of TEA was added for neutralization reaction for 15 minutes. After neutralization, 7g of chain extender IPDA was added, and the mixture was reacted at 45°C for 15 minutes. Finally, 650g of water was slowly added for shear dispersion to obtain a crude polyurethane emulsion. Finally, the acetone in the crude emulsion was removed by vacuum distillation to obtain an aqueous polyurethane dispersion PUD-2.

[0101] Example 3

[0102] 100g of IPDI, 186g of polyester polyol (3), 35g of DMPA, 120g of acetone, and 0.8g of dimethyltin dinedecanoate were sequentially added to a four-necked flask equipped with a condenser, thermometer, and stirrer. The polymerization reaction was carried out at 80°C. When the NCO reached the theoretical value of 1.4%, a polyurethane prepolymer was obtained. The prepolymer was cooled to 50°C, and 426g of acetone was added. The mixture was stirred at 45°C for 20 minutes. 22g of TEA was added for neutralization reaction for 10 minutes. After neutralization, 6g of chain extender IPDA was added, and the mixture was reacted at 40°C for 20 minutes. Finally, 650g of water was slowly added for shear dispersion to obtain a crude polyurethane emulsion. Finally, the acetone in the crude emulsion was removed by vacuum distillation to obtain an aqueous polyurethane dispersion PUD-3.

[0103] Example 4

[0104] 100g of IPDI, 186g of polyester polyol (4), 35g of DMPA, 120g of acetone, and 0.8g of dimethyltin dinedecanoate were sequentially added to a four-necked flask equipped with a condenser, thermometer, and stirrer. The polymerization reaction was carried out at 80°C. When the NCO reached the theoretical value of 1.4%, a polyurethane prepolymer was obtained. The prepolymer was cooled to 50°C, and 426g of acetone was added. The mixture was stirred at 45°C for 20 minutes. 22g of TEA was added for neutralization reaction for 10 minutes. After neutralization, 6g of chain extender IPDA was added, and the mixture was reacted at 40°C for 20 minutes. Finally, 650g of water was slowly added for shear dispersion to obtain a crude polyurethane emulsion. Finally, the acetone in the crude emulsion was removed by vacuum distillation to obtain an aqueous polyurethane dispersion PUD-4.

[0105] Example 5

[0106] 110g of HMDI, 189g of polyester polyol (1), 27g of DMPA, 120g of acetone, and 0.8g of dimethyltin dinedecanoate were sequentially added to a four-necked flask equipped with a condenser, thermometer, and stirrer. The polymerization reaction was carried out at 82°C. When the NCO reached the theoretical value of 1.9%, a polyurethane prepolymer was obtained. The prepolymer was cooled to 50°C, and 426g of acetone was added. The mixture was stirred at 48°C for 20 minutes. 20g of TEA was added for neutralization reaction for 10 minutes. After neutralization, 3g of chain extender EDA was added, and the mixture was reacted at 50°C for 20 minutes. Finally, 650g of water was slowly added for shear dispersion to obtain a crude polyurethane emulsion. Finally, the acetone in the crude emulsion was removed by vacuum distillation to obtain the waterborne polyurethane dispersion PUD-5.

[0107] Comparative Example 1

[0108] Comparative Example 1 is based on Example 1, but the polyester polyol (1) in the formulation is replaced with polyester polyol (5) to synthesize waterborne polyurethane. The rest is the same as in Example 1, and waterborne polyurethane dispersion PUD-6 is obtained.

[0109] Comparative Example 2

[0110] Comparative Example 2 is based on Example 1, but the polyester polyol (1) in the formulation is replaced with polyester polyol (6) to synthesize waterborne polyurethane, and the rest is the same as in Example 1, to obtain waterborne polyurethane dispersion PUD-7.

[0111] 15 parts of the aqueous polyurethane dispersion, 5 parts of crosslinking agent, 0.5 parts of dispersant, 3.5 parts of silica particles, and 120 parts of deionized water from the above examples and comparative examples were mixed evenly to obtain a coating liquid containing aqueous polyurethane. The coating liquid was uniformly coated on the surface of a PMMA substrate with a thickness of approximately 40 micrometers and dried at 80°C to obtain a PMMA film, wherein the thickness of the coating liquid after drying was approximately 400 nm.

[0112] Table 2

[0113]

[0114] As can be seen from Examples 1-5, the coating liquid of the aqueous polyurethane dispersion of the present invention has good performance after film formation. The haze of the PMMA film is less than 2.2%, the transmittance is greater than 93.5%, and the peel force is high, indicating that the film has good adhesion to the substrate.

[0115] It is readily understood that the above embodiments are merely illustrative examples for clear explanation and do not imply that the invention is limited thereto. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. An aqueous polyurethane dispersion, characterized in that, The raw materials for preparing the aqueous polyurethane dispersion include a polyisocyanate, a polyester polyol, a hydrophilic chain extender, a neutralizing agent, and optionally a small molecule chain extender; The polyester polyol comprises five structural units of A, B, C, D, and E, wherein A is a structural unit derived from adipic acid, B is a structural unit derived from terephthalic acid, C is a structural unit derived from isophthalic acid, D is a structural unit derived from neopentyl glycol, and E is a structural unit derived from ethylene glycol; In the polyester polyol, the molar percentage of each of the structural units A-E, based on 100% of the total molar amount of the five structural units A-E, is denoted as a, b, c, d, and e, respectively, and satisfies 1≤c / b≤2 and d / e≥1. The number average molecular weight of the polyester polyol is 1000-2500 g / mol.

2. The aqueous polyurethane dispersion according to claim 1, characterized in that, In the polyester polyol, a<b and a+b+c<d+e are also satisfied.

3. The aqueous polyurethane dispersion according to claim 1 or 2, characterized in that, The polyisocyanate includes any one or a combination of at least two of toluene diisocyanate, diphenylmethane diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate, and dicyclohexylmethane diisocyanate; The hydrophilic chain extender is a compound containing a hydroxyl group and a carboxyl group, and is preferably any one or a combination of at least two of 3-hydroxypropionic acid, dimethylolpropionic acid, dimethylolbutyric acid, dimethylolacetic acid, trihydroxy sulfonic acid, and dihydroxy succinic acid; The neutralizing agent is an organic or inorganic alkaline compound, and is preferably any one or a combination of at least two of triethylamine, triethanolamine, dimethyl ethanolamine, 2-amino-2-methyl-1-propanol, N-methyl diethanolamine, dimethylcyclohexylamine, sodium hydroxide, potassium hydroxide, lithium hydroxide, and calcium hydroxide; The small molecule chain extender is a small molecule amine chain extender, and the molecular weight thereof is preferably 60-500 g / mol, and more preferably, the small molecule chain extender is any one or a combination of at least two of ethylenediamine, hexamethylenediamine, pentamethylenediamine, isophorone diamine, 4,4'-diphenylmethane diamine, and 4,4'-diaminodicyclohexylmethane.

4. The aqueous polyurethane dispersion according to claim 3, characterized in that, The mass content of the polyisocyanate is 16.0-38.0 wt%, and is preferably 24.0-34.0 wt%, based on 100% of the total mass of the polyisocyanate, the polyester polyol, the hydrophilic chain extender, the small molecule chain extender, and the neutralizing agent; The mass content of the polyester polyol is 46.0-72.0 wt%, and is preferably 50.0-66.0 wt%; The mass content of the hydrophilic chain extender is 6.0-15.0 wt%, and is preferably 7.5-13 wt%; The mass content of the small molecule chain extender is 0-6.0 wt%, and is preferably 0.1-4.5 wt%; The mass content of the neutralizing agent is 2.0-11.0 wt%, and is preferably 2.8-9.8 wt%.

5. The aqueous polyurethane dispersion according to claim 4, characterized in that, The raw materials for preparing the aqueous polyurethane dispersion further include a catalyst, and the catalyst includes an organic bismuth catalyst and / or an organic tin catalyst. And / or, the raw materials for preparing the waterborne polyurethane dispersion further include an organic solvent, and the organic solvent includes a ketone solvent, preferably acetone and / or butanone.

6. The aqueous polyurethane dispersion according to claim 5, characterized in that, The raw materials for preparing the waterborne polyurethane dispersion further include water, and the amount of water is such that the solid content of the waterborne polyurethane dispersion is 10-40 wt%, preferably 15-35 wt%. Preferably, the particle size of the solid in the waterborne polyurethane dispersion is 10-500 nm, preferably 15-250 nm.

7. A process for the preparation of an aqueous polyurethane dispersion as defined in any one of claims 1 to 6, characterized in that, The preparation method includes the following steps: (1) polymeric reaction of polyisocyanate, polyester polyol and hydrophilic chain extender to obtain a prepolymer; (2) neutralization reaction of the prepolymer with a neutralizing agent, chain extension reaction with optional small molecule chain extender, and then water dispersion to obtain the waterborne polyurethane dispersion.

8. The production method according to claim 7, characterized by, The preparation method includes the following steps: S1, polymeric reaction of polyisocyanate, polyester polyol, hydrophilic chain extender, part of the organic solvent and optional catalyst to obtain a prepolymer; S2, mixing of the prepolymer with the remaining organic solvent, and then neutralization reaction with a neutralizing agent; S3, water dispersion of the product of the neutralization reaction, and then chain extension reaction with optional small molecule chain extender to obtain an emulsion; removal of the organic solvent in the emulsion to obtain the waterborne polyurethane dispersion.

9. The production method according to claim 8, characterized by, The temperature of the polymeric reaction is 70-90℃, preferably 75-85℃; And / or, the mass percentage content of NCO groups in the prepolymer is 0.8-2.5 wt%; And / or, the temperature of the neutralization reaction is 30-50℃, preferably 35-45℃; And / or, the time of the neutralization reaction is 5-40 min, preferably 10-20 min; And / or, the temperature of the chain extension reaction is 35-60℃, preferably 40-55℃; And / or, the time of the chain extension reaction is 5-40 min, preferably 10-20 min.

10. Use of an aqueous polyurethane dispersion according to any one of claims 1 to 6, characterized in that The waterborne polyurethane dispersion is applied to the field of high light transmittance coating or adhesive for polymethyl methacrylate or polycarbonate substrates.

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