High-performance waterborne polyurethane primer applied to optical-grade biaxially oriented polyester film and preparation method of high-performance waterborne polyurethane primer

Abstract

The invention discloses a high-performance waterborne polyurethane primer applied to an optical-grade biaxially oriented polyester film and a preparation method of the high-performance waterborne polyurethane primer, and belongs to the field of waterborne polyurethane primer. The primer is prepared from the following raw materials in parts by weight: 52 to 68 parts of polyester polyol, 4 to 7 parts of sulfonate polyester polyol, 1 to 3 parts of polyether polyol, 1 to 6 parts of carboxylic acid type hydrophilic compound, 16 to 38 parts of isocyanate, 0.1 to 0.5 part of alcohol chain extender, 1 to 5 parts of amine chain extender, 0.02 to 0.06 part of catalyst, 1 to 6 parts of neutralizer, 160 to 280 parts of acetone, 1340 to 1740 parts of deionized water, 0.3 to 2 parts of silane coupling agent, 0.3 to 1 part of defoaming agent, 1 to 5 parts of wetting agent and 260 to 300 parts of isopropanol. And 4-7 parts of a closed curing agent. The primer prepared by the invention has good high-temperature yellowing resistance on an optical-grade biaxially oriented polyester film, is free of stripes after being coated, has the adhesive force of grade 0, and also has the advantages of flame retardance, environment friendliness, no toxicity, low VOC (Volatile Organic Compounds), low odor and the like.

Description

Technical Field

[0001] This invention relates to the field of waterborne polyurethane primers, and more particularly to a high-performance waterborne polyurethane primer for optical-grade biaxially oriented polyester films and its preparation method. Background Technology

[0002] As is well known, optical-grade biaxially oriented polyester film (BOPET) has low surface tension, and surface treatment is generally required to increase it before use. Improving coating adhesion through corona treatment lacks long-term sustainability, and the adhesion gradually weakens, especially at high temperatures. To address this issue, a primer can be applied to the BOPET film as a base coat to act as a bridging agent, ensuring a tighter adhesion between the surface functional coating and the functional film. This improves the adhesion of the surface coating, enhancing properties such as printability, surface hardness, scratch resistance, and oil resistance, as well as maintaining the surface coating's adhesion for a longer period.

[0003] Optical-grade BOPET films possess characteristics such as high light transmittance, low haze, high brightness, non-yellowing, good adhesion, good flatness, no visible or hidden lines, resistance to high temperatures and ultraviolet radiation, good stiffness, resistance to burn-cracking, and resistance to breakage, leading to their widespread application in recent years. They are particularly indispensable raw materials in the LCD manufacturing industry. These functional BOPET-type optical-grade films are mainly obtained by coating the surface of BOPET films with various functional coatings. Therefore, developing various functional coatings for BOPET-type optical-grade biaxially oriented polyester films in the liquid crystal display field is one of the important research directions for optical-grade biaxially oriented polyester films.

[0004] Chinese patent CN108250925A discloses a primer and its preparation method. It uses raw materials including amine-functionalized acrylic copolymers, olefin-acrylonitrile copolymers, epoxy resins, polyester polyols, polycyclic heteroatomic compounds, additives, catalysts, and solvents, and prepares a primer suitable for BOPET films through physical blending. However, because the raw material system contains a large amount of odorous amine-functionalized acrylic copolymers and harmful isocyanate raw materials, it can cause negative effects such as environmental pollution and harm to the health of operators.

[0005] Chinese patent CN111944405B discloses a coating liquid for optical polyester film primers and its preparation method. It first synthesizes waterborne polyester, waterborne polyurethane, and modified waterborne polyurethane, then blends these three with melamine, epoxy, nano-ion and other additives in a certain proportion to obtain a primer suitable for optical polyester films. However, this approach requires the pre-synthesis of three different waterborne materials, making the process complex. Furthermore, the presence of aromatic segments in the polymer chains may cause yellowing and damage to optical properties upon prolonged exposure to high temperatures.

[0006] Chinese patent CN103205146B discloses a UV-curable PET film surface treatment primer using an acrylate system, its preparation method, and its application. The acrylate system used has a strong odor, is environmentally unfriendly, and is corrosive to workers' skin.

[0007] In their paper "Preparation and Performance Study of Aqueous Online Coating Liquid for Non-Corona-Treated Optical-Grade BOPET Pre-coated Film", Wu Dun et al. used four commercially available types of aqueous polyurethane dispersions as the main film-forming agents. They prepared an aqueous online coating liquid for non-corona-treated optical-grade BOPET pre-coated film by physical compounding with aqueous blocked isocyanate curing agent, surface wetting agent, anti-blocking agent and defoamer. However, this paper does not have the innovative synthesis of aqueous polyurethane dispersions.

[0008] Furthermore, in optical-grade biaxially oriented polyester films, the primer coating is applied before the stretching zone. Under the high temperature and high speed conditions of the stretching zone, the film is stretched approximately four times its original length. If the primer is not suitable for these process conditions, streaks often appear on the film surface, rendering the film unusable. None of the aforementioned literature mentions whether streaks appear on the film surface after applying the primer.

[0009] In view of this, the present invention is hereby proposed. Summary of the Invention

[0010] The purpose of this invention is to provide a high-performance waterborne polyurethane primer for optical-grade biaxially oriented polyester films and its preparation method. This primer enables the optical-grade biaxially oriented polyester film to maintain high transparency, low haze, resistance to high-temperature yellowing, and a stripe-free coating surface, while achieving a zero-level adhesion between the primer and the BOPET film. Furthermore, it possesses excellent flame retardant and environmentally friendly properties, is non-toxic and safe, low in VOCs and odor, non-irritating to the skin, and friendly to the environment and operators, effectively solving the aforementioned technical problems existing in the prior art.

[0011] The objective of this invention is achieved through the following technical solution: A high-performance waterborne polyurethane primer for optical-grade biaxially oriented polyester films is made from the following raw materials in parts by weight: 52-68 parts of polyester polyol, 4-7 parts of sulfonate polyester polyol, 1-3 parts of polyether polyol, 1-6 parts of carboxylic acid hydrophilic compound, Isocyanate 16-38 parts, Alcohol chain extender 0.1-0.5 parts, 1-5 parts of amine chain extender Catalyst 0.02–0.06 parts, Neutralizing agent 1-6 parts, 160-280 parts acetone 1340–1740 parts of deionized water 0.3–2 parts of silane coupling agent, Defoamer 0.3-1 part, 3-5 parts wetting agent Isopropanol 260-300 parts, 4 to 7 parts of a sealed curing agent.

[0012] A method for preparing the high-performance waterborne polyurethane primer for optical-grade biaxially oriented polyester films according to the present invention includes the following steps: Step 1: According to the formulation of the high-performance waterborne polyurethane primer for optical grade biaxially oriented polyester film described in this invention, weigh out the following: polyester polyol, sulfonate polyester polyol, polyether polyol, carboxylic acid hydrophilic compound, isocyanate, alcohol chain extender, amine post-chain extender, catalyst, neutralizer, acetone, deionized water, silane coupling agent, defoamer, wetting agent, isopropanol, and blocking curing agent. Step 2: The polyester polyol, sulfonate polyester polyol, polyether polyol and carboxylic acid hydrophilic compound are added to the reaction apparatus. Dehydration is carried out for 40 to 50 minutes at 65 to 95°C and a vacuum of -0.085 to -0.098 MPa. The temperature is then lowered to 55 to 65°C. Isocyanate, alcohol chain extender and catalyst are added to the reaction apparatus. The reaction is carried out at 65 to 850°C for 2.5 to 4 hours until the -NCO content reaches 1.05% to 2%, thus obtaining the first intermediate. Step 3: Cool the first intermediate to 30-55°C, then add acetone to the first intermediate to adjust its viscosity, add a neutralizing agent to neutralize for 25-55 minutes, and then add deionized water to emulsify and obtain the second intermediate. Step 4: Control the temperature of the second intermediate at 35-45°C, then add the amine chain extender and silane coupling agent to the second intermediate and stir for 30 min to 1.5 h. Add the defoamer and stir for 15 min to 30 min, then remove acetone under reduced pressure. Step 5: Add the wetting agent, isopropanol and blocking curing agent to the second intermediate, stir for 20-30 minutes to ensure they are fully mixed, then filter to obtain a high-performance waterborne polyurethane primer for optical grade biaxially oriented polyester films.

[0013] Compared with the prior art, the high-performance waterborne polyurethane primer for optical-grade biaxially oriented polyester films and its preparation method provided by the present invention have the following advantages: A single aqueous polyurethane dispersion system was synthesized using aliphatic raw materials as a primer for optical-grade biaxially oriented polyester films. During the synthesis stage, all raw materials were free of aromatic components to avoid yellowing of the final product at high temperatures. Crystalline polyester, isocyanate, and amine chain extenders were introduced to enhance the crystallinity and rigidity of the polymer chains, improving the phase separation between the soft and hard segments of the polyurethane, thereby increasing adhesive strength and heat resistance. A small amount of polyether was introduced to provide flexibility and solvent resistance without affecting adhesion and bulk strength. A silane coupling agent with polyamine functional groups was introduced to provide flexibility and form an internal cross-linking structure, improving heat resistance. Appropriate amounts of solvent and wetting agent were introduced to improve the wetting and spreading properties of the polyester film, contributing to improved adhesion. A blocked curing agent was introduced to initiate polymerization after entering the drying tunnel, improving the heat resistance and strength of the primer coating. After coating and drying, no streaks were observed on the polyester film surface, and the coating adhesion to the polyester film was grade 0. This invention also possesses excellent safety and environmental protection properties, such as being non-flammable, environmentally friendly and non-toxic, low in VOCs, and low in odor. Detailed Implementation

[0014] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the specific content of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments, which do not constitute a limitation of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0015] First, the following explanations are provided for the terms that may be used in this article: The term "and / or" means that either or both can be achieved simultaneously. For example, X and / or Y means that it includes both "X" or "Y" as well as the three cases of "X and Y".

[0016] The terms "comprising," "including," "containing," "having," or other similar semantic descriptions should be interpreted as non-exclusive inclusion. For example, including a technical feature element (such as raw material, component, ingredient, carrier, dosage form, material, size, part, component, mechanism, device, step, process, method, reaction conditions, processing conditions, parameter, algorithm, signal, data, product or article of manufacture, etc.) should be interpreted as including not only the expressly listed technical feature element, but also other technical feature elements that are not expressly listed and are well-known in the art.

[0017] The term "composed of" excludes any technical features not expressly listed. When used in a claim, it closes the claim to exclude all technical features other than those expressly listed, except for associated conventional impurities. If the term appears only in a clause of a claim, it limits the claim to the elements expressly listed in that clause; elements recited in other clauses are not excluded from the overall claim.

[0018] The term "parts by mass" indicates the mass ratio between multiple components. For example, if component X is described as x parts by mass and component Y as y parts by mass, then the mass ratio of component X to component Y is x:y. One part by mass can represent any mass; for example, one part by mass can be expressed as 1 kg or 3.1415926 kg, etc. The sum of the parts by mass of all components is not necessarily 100 parts; it can be greater than 100 parts, less than 100 parts, or equal to 100 parts. Unless otherwise stated, parts, proportions, and percentages mentioned herein are all measured by mass.

[0019] When concentration, temperature, pressure, size, or other parameters are expressed as numerical ranges, such ranges should be understood to specifically disclose all ranges formed by any pairing of upper limits, lower limits, or preferred values ​​within that range, regardless of whether the range is explicitly stated; for example, if the numerical range "2 to 8" is stated, then that range should be interpreted to include ranges such as "2 to 7", "2 to 6", "5 to 7", "3 to 4 and 6 to 7", "3 to 5 and 7", "2 and 5 to 7", etc. Unless otherwise stated, the numerical ranges described herein include both their endpoints and all integers and fractions within that range.

[0020] The solution provided by this invention will be described in detail below. Contents not described in detail in the embodiments of this invention are prior art known to those skilled in the art. Where specific conditions are not specified in the embodiments of this invention, they shall be performed according to conventional conditions in the art or conditions recommended by the manufacturer. Reagents or instruments used in the embodiments of this invention whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0021] This invention provides a high-performance waterborne polyurethane primer for optical-grade biaxially oriented polyester films, made from raw materials comprising the following parts by weight: 52-68 parts of polyester polyol, 4-7 parts of sulfonate polyester polyol, 1-3 parts of polyether polyol, 1-6 parts of carboxylic acid hydrophilic compound, Isocyanate 16-38 parts, Alcohol chain extender 0.1-0.5 parts, 1-5 parts of amine chain extender Catalyst 0.02–0.06 parts, Neutralizing agent 1-6 parts, 160-280 parts acetone 1340–1740 parts of deionized water 0.3–2 parts of silane coupling agent, Defoamer 0.3-1 part, 3-5 parts wetting agent Isopropanol 260-300 parts, 4 to 7 parts of a sealed curing agent.

[0022] In some preferred embodiments, the primer comprises at least one of polybutylene adipate diol, polyhexyl adipate diol, poly(neopentyl adipate-1,6-hexylene glycol adipate diol), polycaprolactone diol, polypropylene carbonate diol, and polyhexyl sebacate diol. The number average molecular weight of this polyester polyol is 1000–3000.

[0023] In some preferred embodiments, the sulfonate polyester polyol in the above-mentioned primer is BY3305B from Baiyuan Chemical, with a number average molecular weight of 2000.

[0024] In some preferred embodiments, the ether polyol in the primer is at least one selected from polypropylene glycol (PPG) and polytetrahydrofuran (PTMEG). The number average molecular weight of the polyether polyol is 1000 to 3000.

[0025] In some preferred embodiments, the isocyanate in the primer is at least one selected from isoflavone diisocyanate (IPDI), cyclohexane-1,4-diisocyanate (CHDI), 4,4-diisocyanate dicyclohexylmethane (HMDI), and HDI trimer.

[0026] In some preferred embodiments, the alcohol chain extender in the above-mentioned primer is at least one selected from 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, diethylene glycol, dipropylene glycol, and 1,2-propanediol.

[0027] In some preferred embodiments, the amine chain extender in the primer is at least one of isophorone diamine (IPDA), diethylenetriamine (DETA), ethylenediamine, and propylenediamine.

[0028] In some preferred embodiments, the carboxylic acid hydrophilic compound in the above-mentioned primer is at least one of dimethylolpropionic acid (DMPA) and dimethylolbutyric acid (DMBA).

[0029] In some preferred embodiments, the catalyst in the above-mentioned primer is at least one of organotin catalysts, stannous octoate catalysts, and organobismuth catalysts.

[0030] In some preferred embodiments, the neutralizing agent in the above-mentioned primer is at least one selected from triethylamine, dimethylethanolamine, N-methylethanolamine, sodium hydroxide, and sodium carbonate.

[0031] In some preferred embodiments, the defoamer in the above-mentioned primer is at least one of BASFFoamaster8034, BYK018, BYK019, BYK093, AFCONA 2590, Sangjing Chemical SKCDF942, and Sangjing Chemical SKC DF677.

[0032] In some preferred embodiments, the silane coupling agent in the above-mentioned primer is at least one of N-aminoethyl-γ-aminopropyltriethoxysilane (KH791) and (3-trimethoxysilylpropyl)diethylethylenediamine (NQ-62).

[0033] In some preferred embodiments, the wetting agent in the above-mentioned primer is one or more of the following: Evonik's TEGO WET KL245, BYK's BYK345, BYK's BYK346, BYK's BYK349, and BYK's BYK378.

[0034] In some preferred embodiments, the sealing curing agent in the above-mentioned primer is Covestro's sealing curing agent Desmodur® BL 3175 A.

[0035] This invention also provides a method for preparing the above-mentioned high-performance waterborne polyurethane primer for optical-grade biaxially oriented polyester films, comprising the following steps: Step 1: According to the above formulation for high-performance waterborne polyurethane primer applied to optical-grade biaxially oriented polyester film, weigh out the following: polyester polyol, sulfonate polyester polyol, polyether polyol, carboxylic acid hydrophilic compound, isocyanate, alcohol chain extender, amine post-chain extender, catalyst, neutralizer, acetone, deionized water, silane coupling agent, defoamer, wetting agent, isopropanol, and blocking curing agent. Step 2: The polyester polyol, sulfonate polyester polyol, polyether polyol, and carboxylic acid hydrophilic compound are added to the reaction apparatus. Dehydration is carried out for 40-50 minutes at 65-95°C and a vacuum of -0.085 to -0.098 MPa. The temperature is then lowered to 55-65°C. Isocyanate, alcohol chain extender, and catalyst are added to the reaction apparatus. The reaction is carried out at 65-85°C for 2.5-4 hours until the -NCO content reaches 1.05%-2%, thus obtaining the first intermediate. Step 3: Cool the first intermediate to 30-55°C, then add acetone to the first intermediate to adjust its viscosity, add a neutralizing agent to neutralize for 25-55 minutes, and then add deionized water to emulsify and obtain the second intermediate. Step 4: Control the temperature of the second intermediate at 35-45°C, then add the amine chain extender and silane coupling agent to the second intermediate and stir for 30 min to 1.5 h. Add the defoamer, stir for 15 min to 30 min, and then remove acetone under reduced pressure.

[0036] Step 5: Add the wetting agent, isopropanol and blocking curing agent to the second intermediate, stir for 20-30 minutes to ensure they are fully mixed, and then filter to obtain a high-performance waterborne polyurethane primer for optical grade biaxially oriented polyester film.

[0037] In summary, the present invention, applied to high-performance waterborne polyurethane primers for optical-grade biaxially oriented polyester films and its preparation method, has at least the following advantages: (1) During the synthesis stage, the raw materials introduced do not contain aromatic components, thus avoiding the phenomenon that the final product is prone to yellowing at high temperatures.

[0038] (2) Introducing crystalline polyester, isocyanate, and amine chain extenders enhances the crystallinity and rigidity of the polymer chains, improves the phase separation between the soft and hard segments of polyurethane, thereby increasing the bonding strength and heat resistance. Introducing a small amount of polyether provides a certain degree of flexibility and solvent resistance without affecting the bonding and bulk strength. Introducing silane coupling agents with polyamino functional groups provides a certain degree of flexibility and forms an internal cross-linking structure, improving heat resistance.

[0039] (3) Introducing appropriate amounts of solvents and wetting agents improves the wetting and spreading properties of the polyester film, which helps to improve the adhesion of the polyester film. Introducing a closed-type curing agent initiates polymerization after entering the drying tunnel, improving the heat resistance and strength of the base coating.

[0040] (4) After the water-based polyurethane primer of the present invention is coated and dried, there are no streaks on the surface of the polyester film, and the adhesion of the coating to the polyester film is grade 0.

[0041] (5) The water-based polyurethane primer of the present invention is a water-based emulsion containing a large amount of water. It is a non-flammable system with excellent flame retardant safety. The adhesive itself is non-irritating to the skin and is friendly to operators. Small molecule compounds such as amines have already entered the molecular chain through chemical reaction, minimizing the possibility of their volatilization. It has the advantages of being environmentally friendly, non-toxic, safe, low in VOCs, and low in odor.

[0042] To more clearly demonstrate the technical solution and its effects provided by the present invention, the following detailed description of the high-performance waterborne polyurethane primer for optical-grade biaxially oriented polyester films and its preparation method is provided by the present invention with specific embodiments.

[0043] Example 1 This embodiment provides a high-performance waterborne polyurethane primer for optical-grade biaxially oriented polyester films, the preparation method of which may include the following steps: Step A1: Weigh out the raw materials for preparing the waterborne polyurethane primer of this embodiment according to the required amounts; Step A2: 55g of poly(adipate-neopentyl glycol-1,6-hexanediol) diol (number average molecular weight 2000), 2g of sulfonate polyester polyol BY3305B, 1g of polytetrahydrofuran (number average molecular weight 2000), 1g of polypropylene glycol (number average molecular weight 2000), and 4g of dimethylolpropionic acid from the raw materials are added to the reaction apparatus. The mixture is first dehydrated at 90℃ and a vacuum of -0.09MPa for 50 minutes, then cooled to 55℃. Next, 5.5g of cyclohexane-1,4-diisocyanate and 4.5g of... 4,4-Diisocyanate dicyclohexylmethane, 0.2 g HDI trimer, 9.5 g isoflavone diisocyanate, 0.3 g 1,4-butanediol, and 0.04 g dibutyltin dilaurate were reacted at 75 °C for 3.5 hours until the -NCO content reached 1.1%, thus obtaining the first intermediate. Step A3: Cool the first intermediate to 40°C, then add 240g of acetone to the first intermediate to adjust the prepolymer viscosity, add 3.02g of triethylamine, and stir for 40 minutes. Then add 1400g of deionized water for emulsification to obtain the second intermediate; Step A4: Control the temperature of the second intermediate at 45°C, then add 0.6g of isophorone diamine (IPDA), 0.7g of diethylenetriamine, 1g of ethylenediamine, and 1g of N-aminoethyl-γ-aminopropyltriethoxysilane to the second intermediate, stir for 60 min, add 0.5g of defoamer BASF Foamaster 8034, stir for 20 min, and then remove acetone under reduced pressure. Step A5: Add 3g of wetting agent BYK345, 265g of isopropanol and 5g of sealing curing agent Desmodur® BL 3175 A to the second intermediate, stir for 20 minutes to ensure they are fully mixed, then filter to obtain a high-performance waterborne polyurethane primer for optical grade biaxially oriented polyester films.

[0044] Example 2 This embodiment provides a high-performance waterborne polyurethane primer for optical-grade biaxially oriented polyester films, the preparation method of which may include the following steps: Step B1: Weigh out the raw materials for preparing the waterborne polyurethane primer of this embodiment according to the required amounts; Step B2: 52g of poly(adipate-neopentyl glycol-1,6-hexanediol) diol (number average molecular weight 2000), 5g of sulfonate polyester polyol BY3305B, 2g of polytetrahydrofuran (number average molecular weight 2000), 1g of polypropylene glycol (number average molecular weight 2000), and 4.2g of dimethylolbutyric acid (DMBA) from the raw materials are added to the reaction apparatus. The mixture is first dehydrated at 90℃ and a vacuum of -0.085MPa for 40 minutes, then cooled to 60℃. Next, 4.2g of cyclohexane-1,4-diisocyanate, 8.8g of 4,4-diisocyanate dicyclohexylmethane, 0.3g of HDI trimer, 8g of isoflurane diisocyanate, 0.2g of 1,4-butanediol, and 0.2g of... 1,6-Hexanediol and 0.04 g of stannous octoate were reacted at 70 °C for 4 hours until the -NCO content reached 1.8%, thus obtaining the first intermediate. Step B3: Cool the first intermediate to 35°C, then add 250g of acetone to the first intermediate to adjust the viscosity of the prepolymer. Add 2.9g of triethylamine, stir for 50 minutes, then add 1500g of deionized water for emulsification to obtain the second intermediate; Step B4: Control the temperature of the second intermediate at 40°C, then add 0.5g of isophorone diamine (IPDA), 1g of diethylenetriamine, 2g of ethylenediamine, and 1.2g of N-aminoethyl-γ-aminopropyltriethoxysilane (KH791) to the second intermediate, stir for 55 min, add 0.9g of defoamer AFCONA 2590, stir for 20 min, and then remove acetone under reduced pressure. Step B5: Add 4g of wetting agent BYK346, 270g of isopropanol and 6g of sealing curing agent Desmodur® BL 3175 A to the second intermediate, stir for 30 min to ensure they are fully mixed, then filter to obtain a high-performance waterborne polyurethane primer for optical grade biaxially oriented polyester films.

[0045] Example 3 This embodiment provides a high-performance waterborne polyurethane primer for optical-grade biaxially oriented polyester films, the preparation method of which may include the following steps: Step C1: Weigh out the raw materials for preparing the waterborne polyurethane primer of this embodiment according to the required amounts; In step C2, 56g of polycaprolactone (number average molecular weight 2000), 7g of sulfonate polyester polyol BY3305B, 1g of polytetrahydrofuran (number average molecular weight 2000), 1.5g of polypropylene glycol (number average molecular weight 2000), and 4.5g of dimethylolpropionic acid from the raw materials are added to the reaction apparatus, and dehydration is carried out for 50 minutes at 95°C and a vacuum of -0.09MPa. The temperature was lowered to 55°C, and then 5.3g of cyclohexane-1,4-diisocyanate, 11.6g of 4,4-diisocyanate dicyclohexylmethane, 0.2g of HDI trimer, 9g of isoflavone diisocyanate, 0.2g of 1,4-butanediol, 0.3g of diethylene glycol, and 0.06g of dibutyltin dilaurate were added to the reaction apparatus. The reaction was carried out at 80°C for 3.5 hours until the -NCO content reached 1.9%, thus obtaining the first intermediate. Step C3: Cool the first intermediate to 40°C, then add 270g of acetone to the first intermediate to adjust the prepolymer viscosity. Add 3.39g of triethylamine and stir for 40 minutes. Then add 1680g of deionized water for emulsification to obtain the second intermediate; Step C4: Control the temperature of the second intermediate at 45°C, then add 0.5g isophorone diamine (IPDA), 1.5g diethylenetriamine, 1.5g ethylenediamine, and 1.4g (3-trimethoxysilylpropyl)diethylethylenediamine (NQ-62) to the second intermediate, stir for 50 minutes, add 1g of defoamer BYK019 from BYK, stir for 30 minutes, and then remove acetone under reduced pressure. Step C5: Add 5g of wetting agent BYK378, 280g of isopropanol and 6g of sealing curing agent Desmodur® BL 3175 A to the second intermediate, stir for 20 minutes to ensure they are fully mixed, then filter to obtain a high-performance waterborne polyurethane primer for optical grade biaxially oriented polyester films.

[0046] Comparative Example This comparative example provides a high-performance waterborne polyurethane primer for optical-grade biaxially oriented polyester films, the preparation method of which may include the following steps: Step D1: Weigh out the raw materials for preparing the comparative example waterborne polyurethane primer according to the required amounts; In step D2, 53g of polypentyl terephthalate diol (number average molecular weight 2000), 5g of sulfonate polyester polyol BY3305B, 1g of polytetrahydrofuran (number average molecular weight 2000), 2g of polypropylene glycol (number average molecular weight 2000), and 4g of dimethylolpropionic acid from the raw materials were added to the reaction apparatus. The mixture was first dehydrated at 90°C and a vacuum of -0.085MPa for 50 minutes, then cooled to 55°C. Next, 22g of isoflavone diisocyanate, 0.4g of 1,4-butanediol, and 0.04g of dibutyltin dilaurate were added to the reaction apparatus. The mixture was then reacted at 75°C for 4 hours until the -NCO content reached 1.5%, thus obtaining the first intermediate. Step D3: Cool the first intermediate to 40°C, then add 240g of acetone to the first intermediate to adjust the prepolymer viscosity, add 3.02g of triethylamine, and stir for 40 minutes. Then add 1400g of deionized water for emulsification to obtain the second intermediate; Step D4: Control the temperature of the second intermediate at 45°C, then add 1.5g of ethylenediamine to the second intermediate, stir for 60 minutes, add 0.5g of defoamer BASF Foamaster 8034, stir for 30 minutes, and then remove acetone under reduced pressure.

[0047] Step D5: Add 4g of wetting agent BYK346, 270g of isopropanol and 6g of sealing curing agent Desmodur® BL 3175 A to the second intermediate, stir for 30 min to ensure they are fully mixed, then filter to obtain a waterborne polyurethane primer for polyester film.

[0048] This comparative example is only intended to demonstrate that the waterborne polyurethane primer in the comparative example exhibits yellowing at high temperatures when containing aromatic polyester raw materials. When the proportions of the raw materials are not appropriate, the streaking phenomenon is not eliminated, the adhesion between the primer layer and the polyester film is not optimal, and it cannot meet the requirements for use as a high-performance waterborne polyurethane primer for optical-grade biaxially oriented polyester films.

[0049] Performance testing: Take 5g of the primer prepared in each example and comparative example, place it in a crystallizing dish, dry it in an oven at 60℃ to form a film, then put it in an oven at 120℃ for 4 hours, take it out and cool it, and observe whether the film has yellowing.

[0050] The following performance tests were performed on the high-performance waterborne polyurethane primers for optical-grade biaxially oriented polyester films prepared in Examples 1-3 of this invention, as well as the waterborne polyurethane primers prepared in the comparative examples: Coated film surface streaks: In a dark room, fix the coated and dried film, shine a light from behind, and observe the film surface from the front to see if there are streaks.

[0051] The films were coated using the primers obtained in each of the embodiments and comparative examples, and the transmittance, haze, and adhesion of the coating to the polyester film were tested.

[0052] Among them, the AT-4725 transmission haze meter from BYK GmbH, Germany, was used, and ASTM D1003 was used as the test standard to test the transmittance and haze. The adhesion between the primer coating and the polyester film was tested using the test method specified in GB / T9286-98. The adhesion results were graded as follows: 0 > 1 > 2 > 3 > 4 > 5. The test results are shown in Table 1.

[0053] Table 1 shows the test results.

[0054] As shown in Table 1 above, the waterborne polyurethane primers prepared in Examples 1-3 of this invention did not exhibit yellowing after continuous heating at 120°C for 4 hours. The films after the coating process exhibited good high light transmittance and low haze performance, and the film surface was free of streaks. Under the above high-performance conditions, the adhesion between the primer layer and the substrate layer was grade 0. In contrast, the waterborne polyurethane primer prepared in the comparative example exhibited yellowing after continuous heating at 120°C for 4 hours. The film after the coating process showed streaks on the film surface. The adhesion between the primer layer and the substrate layer was grade 1, which is slightly poor. This indicates that the waterborne polyurethane primers in the comparative example cannot meet the coating requirements for optical-grade biaxially oriented polyester films.

[0055] In summary, the high-performance waterborne polyurethane primer used in this invention is suitable for coating optical-grade biaxially oriented polyester films. It maintains high transparency, low haze, and resistance to high-temperature yellowing, while achieving a zero-level adhesion between the primer and the BOPET film, provided the coated film surface is free of streaks. Furthermore, as a waterborne polyurethane system, this invention also offers advantages such as flame retardancy, environmental friendliness, non-toxicity, safety, low VOCs, and low odor.

[0056] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims. The information disclosed in the background section is intended only to enhance the understanding of the overall background technology of the present invention and should not be construed as an admission or implication in any way that such information constitutes prior art known to those skilled in the art.

Claims

1. A high-performance waterborne polyurethane primer for optical-grade biaxially oriented polyester films, characterized in that, Made from the following raw materials in parts by weight: 52-68 parts of polyester polyol, 4-7 parts of sulfonate polyester polyol, 1-3 parts of polyether polyol, 1-6 parts of carboxylic acid hydrophilic compound, Isocyanate 16-38 parts, Alcohol chain extender 0.1-0.5 parts, 1-5 parts of amine chain extender Catalyst 0.02–0.06 parts, Neutralizing agent 1-6 parts, 160-280 parts of acetone 1340–1740 parts of deionized water 0.3–2 parts of silane coupling agent, Defoamer 0.3-1 part, 3-5 parts wetting agent 260-300 parts of isopropanol 4 to 7 parts of a sealed curing agent.

2. The high-performance waterborne polyurethane primer for optical-grade biaxially oriented polyester films according to claim 1, characterized in that, The polyester polyol is at least one of polybutylene adipate diol, polyhexyl adipate diol, polyhexyl adipate-neopentyl glycol-1,6-hexylene adipate diol, polycaprolactone diol, polypropylene carbonate diol, and polyhexyl sebacate. The sulfonate polyester polyol used is BY3305B from Baiyuan Chemical, with a number average molecular weight of 2000. The polyether polyol is at least one of polypropylene glycol and polytetrahydrofuran.

3. The high-performance waterborne polyurethane primer for optical-grade biaxially oriented polyester films according to claim 1 or 2, characterized in that... The number average molecular weights of the polyether polyol and the polyester polyol are both 1000 to 3000.

4. The high-performance waterborne polyurethane primer for optical-grade biaxially oriented polyester films according to claim 1 or 2, characterized in that... The isocyanate is at least one of isoflavone diisocyanate, cyclohexane-1,4-diisocyanate, 4,4-diisocyanate dicyclohexylmethane, and HDI trimer.

5. The high-performance waterborne polyurethane primer for optical-grade biaxially oriented polyester films according to claim 1 or 2, characterized in that... The alcohol chain extender is at least one selected from 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, diethylene glycol, dipropylene glycol, and 1,2-propanediol. The amine chain extender is at least one of isophorone diamine, diethylenetriamine, ethylenediamine, and propylenediamine.

6. The high-performance waterborne polyurethane primer for optical-grade biaxially oriented polyester films according to claim 1 or 2, characterized in that... The carboxylic acid hydrophilic compound is at least one of dimethylolpropionic acid and dimethylolbutyric acid; The neutralizing agent is at least one of triethylamine, dimethylethanolamine, N-methylethanolamine, sodium hydroxide, and sodium carbonate.

7. The high-performance waterborne polyurethane primer for optical-grade biaxially oriented polyester films according to claim 1 or 2, characterized in that... The catalyst is at least one of organotin catalysts, stannous octoate catalysts, and organobismuth catalysts.

8. The high-performance waterborne polyurethane primer for optical-grade biaxially oriented polyester films according to claim 1 or 2, characterized in that... The defoamer is at least one of BASF Foamaster8034, BYK018, BYK019, BYK093, AFCONA 2590, Sangjing Chemical SKC DF942, and Sangjing Chemical SKC DF677. The wetting agent is one or more of Evonik's TEGO WET KL245, BYK's BYK345, BYK's BYK346, BYK's BYK349, and BYK's BYK378. The blocked curing agent is Covestro's blocked curing agent Desmodur® BL 3175 A.

9. The high-performance waterborne polyurethane primer for optical-grade biaxially oriented polyester films according to claim 1 or 2, characterized in that... The silane coupling agent is at least one of N-aminoethyl-γ-aminopropyltriethoxysilane and (3-trimethoxysilylpropyl)diethylethylenediamine.

10. A method for preparing the high-performance waterborne polyurethane primer for optical-grade biaxially oriented polyester films according to any one of claims 1-9, characterized in that, Includes the following steps: Step 1: According to the formulation of the high-performance waterborne polyurethane primer for optical grade biaxially oriented polyester film as described in any one of claims 1-9, weigh out the following: polyester polyol, sulfonate polyester polyol, polyether polyol, carboxylic acid hydrophilic compound, isocyanate, alcohol chain extender, amine post-chain extender, catalyst, neutralizer, acetone, deionized water, silane coupling agent, defoamer, wetting agent, isopropanol, and blocking curing agent; Step 2: The polyester polyol, sulfonate polyester polyol, polyether polyol, and carboxylic acid hydrophilic compound are added to the reaction apparatus. Dehydration is carried out for 40-50 minutes at 65-95°C and a vacuum of -0.085 to -0.098 MPa. The temperature is then lowered to 55-65°C. Isocyanate, alcohol chain extender, and catalyst are added to the reaction apparatus. The reaction is carried out at 65-85°C for 2.5-4 hours until the -NCO content reaches 1.05%-2%, thus obtaining the first intermediate. Step 3: Cool the first intermediate to 30-55°C, then add acetone to the first intermediate to adjust its viscosity, add a neutralizing agent to neutralize for 30-60 minutes, and then add deionized water to emulsify and obtain the second intermediate. Step 4: Cool the first intermediate to 30-55°C, then add acetone to the first intermediate to adjust its viscosity, add a neutralizing agent to neutralize for 25-55 minutes, and then add deionized water to emulsify and obtain the second intermediate. Step 5: Add the wetting agent, isopropanol and blocking curing agent to the second intermediate, stir for 20-30 minutes to ensure they are fully mixed, and then filter to obtain a high-performance waterborne polyurethane primer for optical grade biaxially oriented polyester film.

Images