A high-transmittance soft-light haze film based on water-based resin compounding, a preparation method and application thereof

Abstract

This invention discloses a high-transmittance, soft-light matte film based on an aqueous resin compound, its preparation method, and its applications. The invention involves mixing an aqueous solution of polyvinyl alcohol (PVA) with a molecular weight of 50,000 to 100,000 with an aqueous polyurethane prepolymer with a molecular weight of 2,000 to 5,000 at a solid-to-mass ratio of 1:1 to 1:7, followed by defoaming, coating, and drying to form a film. This invention utilizes the order-of-magnitude difference in molecular weight between the two materials, as well as the strong hydrogen bonding between hydroxyl and urethane bonds, to induce controllable microphase separation during film curing. This achieves high haze while maintaining high light transmittance. The method eliminates the need for inorganic matting agents, solving the powder agglomeration problem and providing excellent adhesion and mechanical properties. It can be widely applied in fields such as displays and LED anti-glare films.

Description

Technical Field

[0001] This invention relates to the field of optical translucent film technology, specifically to a high-transmittance soft-light matte film formed by compounding waterborne resins with large molecular weights without adding inorganic matting fillers, its preparation method, and its application. Background Technology

[0002] Optical matte film is the unsung hero behind achieving a healthy and comfortable lighting environment. LED lights are typical high-brightness light sources, which are very glaring when viewed directly. Optical matte film can make the light emitted by LEDs more uniform and softer, achieving a comfortable effect where you can see the light but not the lamp itself.

[0003] Currently, there are two main preparation methods for LED anti-glare films: one is to add inorganic matting powder (such as silica powder) to achieve a matte effect. However, this traditional powder-addition matte process has some problems. The powder filler is prone to agglomeration and uneven dispersion in the resin system, directly resulting in uneven haze and large local differences in light transmission in the finished film, which seriously affects the optical appearance. The powder has poor compatibility with the organic resin matrix, and long-term use can easily lead to problems such as filler precipitation, whitening of the film surface, and decreased adhesion, shortening the service life of the film. At the same time, adding a large amount of powder will directly reduce the overall light transmittance of the film, making it impossible to achieve both high light transmittance and uniform haze at the same time, which is difficult to meet the needs of high-end optical soft light transmission scenarios. The second method is to form through microstructure molds (such as embossing). Although this method can stably control light, the mold development cost is high and the flexibility is poor, making it difficult to fit irregularly shaped light sources such as curved LED light strips.

[0004] Chinese invention patent CN108467507 A discloses a matte film, its preparation method, and a haze adjustment method. By adjusting the difference in refractive index between the organic particles in the matte layer and the non-matte layer, secondary refraction of light is achieved, thereby adjusting the overall haze. However, regarding the surface roughness caused by the large number of particles in the matte layer, an additional layer of UV adhesive is needed as a non-matte layer for masking. While this effectively reduces surface roughness, it also introduces engineering problems such as complex processes, increased costs, difficulty in thickness control, and environmental pressures. These problems arise because the filler particles have relatively large particle sizes.

[0005] While existing research includes studies on PVA / WPU blend films (such as "Preparation of Polyvinyl Alcohol / Waterborne Polyurethane Blend Films," Packaging Engineering, 2020, No. 13), these studies primarily focus on the impact of blending on mechanical properties and water resistance, and lack systematic exploration of the synergistic control of light transmittance and haze. More importantly, existing blend systems typically employ designs using two resins with similar or comparable molecular weights, resulting in homogeneous structures or randomly distributed phase regions after film formation, making controllable microscopic phase separation impossible.

[0006] In summary, there is an urgent need in this field to develop a pure resin-based matte film that can generate stable and uniform haze by relying solely on the formulation design and film-forming process control of pure resin without adding any inorganic matting powder. This film should also have high light transmittance, strong adhesion, excellent mechanical properties, and a delicate appearance. Summary of the Invention

[0007] To address the shortcomings of existing haze films, this invention aims to provide a method for preparing a soft-optical haze film that is simple to process, safe and environmentally friendly, widely adaptable, and with adjustable haze.

[0008] To achieve the above objectives, the present invention provides a method for preparing a high-transmittance soft-light matte film based on an aqueous resin compound, comprising the following steps:

[0009] Step 1: Preparation of polyvinyl alcohol aqueous dispersion: Add polyvinyl alcohol (PVA) resin to deionized water, heat to 90-95℃ and stir continuously until completely dissolved to form a pure transparent polyvinyl alcohol aqueous solution with a solid content of 8-12%, for later use. The molecular weight of the polyvinyl alcohol resin is 50,000-100,000.

[0010] Step 2: Preparation of waterborne polyurethane prepolymer: Polycarbonate diol and isophorone diisocyanate are added to a reaction vessel and stirred at 75-80℃; then the temperature is lowered to 60-65℃ and 2,2-dimethylolpropionic acid is added and the reaction is continued with stirring; then dibutyltin dilaurate is added and the reaction is stirred; after the reaction is completed, the residual -NCO content and -OH content are measured respectively, and the temperature is lowered to room temperature for later use when the reaction reaches the theoretical endpoint; wherein, the initial -NCO / -OH molar ratio set for the reaction is 1.2-1.5; the molecular weight of the waterborne polyurethane prepolymer is at least one order of magnitude different from the molecular weight of the polyvinyl alcohol resin in Step 1; preferably, the number average molecular weight of the waterborne polyurethane prepolymer is 2000-5000;

[0011] The amount of 2,2-dimethylolpropionic acid added is 3-6% of the total mass of polycarbonate diol and isophorone diisocyanate; the amount of dibutyltin dilaurate added is 0.1-0.2% of the total mass of the resin system.

[0012] Step 3: Neutralizing the prepolymer: Take the room temperature waterborne polyurethane prepolymer from Step 2, control the reaction system temperature at 15-25℃, slowly add the neutralizing agent and continuously stir until uniform to obtain the neutralized prepolymer; the neutralizing agent is preferably polyetheramine or triethylamine;

[0013] The molar ratio of the neutralizing agent to the 2,2-dimethylolpropionic acid in step 2 is 1~1.1:1. When polyetheramine is used as the neutralizing agent, the reaction system temperature should be controlled at 15-25℃ and the addition should be slow. When triethylamine is used as the neutralizing agent, the preferred molar ratio of triethylamine to the 2,2-dimethylolpropionic acid in step 2 is 1.1:1.

[0014] Step 4, preparing the matte film resin compound: The polyvinyl alcohol aqueous solution obtained in Step 1 is slowly added dropwise to the neutralized prepolymer obtained in Step 3 under high-speed stirring. After the addition is complete, stirring is continued until fully compounded. Then, deionized water is added to dilute and the overall solid content is adjusted to 9-11% to obtain the resin compound. The predetermined ratio is: the mass ratio of polyvinyl alcohol solids to waterborne polyurethane solids is 1:1 to 1:7.

[0015] Step 5, Post-processing: Place the resin compound in a vacuum degassing mixer for degassing treatment, and then cure at room temperature for 1-2 hours to fully remove air bubbles from the system;

[0016] Step 6, Coating and Film Formation: The matured matte film resin compound is uniformly coated on the PET substrate and dried at 80℃-100℃ for 1~3 minutes to obtain a high-transmittance soft matte film.

[0017] As a preferred embodiment, in step 2, the molecular weight of the polycarbonate diol is 1000~3000;

[0018] As a preferred embodiment, in step 3, the neutralizing agent is polyetheramine D400, which is used at a temperature controlled between 15-25°C.

[0019] As a preferred embodiment, in step 4, the mass ratio of the polyvinyl alcohol solids to the waterborne polyurethane solids is preferably 1:4 to 1:6.5.

[0020] As a preferred embodiment, the difference between the refractive index of the polyvinyl alcohol resin film and the refractive index of the waterborne polyurethane prepolymer film is less than 0.03.

[0021] A high-transmittance, soft-light matte film based on an aqueous resin compound prepared according to the above method.

[0022] The film is a pure organic resin structure, and micro-phase separation occurs due to the molecular weight difference, refractive index and intermolecular hydrogen bond network between polyvinyl alcohol resin and waterborne polyurethane. The film does not contain inorganic powder fillers.

[0023] The present invention also provides the application of the above-mentioned high-transmittance soft-light matte film in the preparation of LED anti-glare film, display screen soft-light film or optical diffusion plate.

[0024] During the formation of waterborne polyurethane in a polyvinyl alcohol aqueous dispersion, the hydroxyl groups of polyvinyl alcohol provide hydrogen bond donors, while the carbonyl groups in the urethane bonds of the waterborne polyurethane act as excellent hydrogen bond acceptors. This allows them to form strong hydrogen bonds, significantly improving the stability of the two resin blends. Simultaneously, the molecular weight of polyvinyl alcohol (PVA1799) is 50,000-100,000, while the waterborne polyurethane adjusts the -NCO / -OH molar ratio of the prepolymer reaction to 1.2-1.5 to control the chain extension, resulting in waterborne polyurethane oligomers with molecular weights tens of times different from polyvinyl alcohol. During the drying process, the curing and crosslinking rates of different resin segments vary, gradually forming a uniform structure alternating between dense and porous phases. The hazy appearance is achieved through the light refraction at the interlayer interface. Finally, as an optical film material, it undergoes defoaming and curing post-treatments to improve haze uniformity and stability.

[0025] The present invention forms a strong hydrogen bond network between the hydroxyl groups of polyvinyl alcohol (PVA1799) and the urethane bonds of waterborne polyurethane (WPU), thereby ensuring high light transmittance while exhibiting uniform haze.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0027] (1) This invention is completely different from the traditional technical approach of adding inorganic matting powder. It only utilizes the difference in film-forming aggregation behavior of two transparent functional resins and generates light-controlling microstructures by microphase separation induced by the molecular weight difference of pure resins. There is no need to add additional powder fillers such as matting powder and fogging powder, which simplifies the formula and improves the uniformity of light transmission of the film layer, avoiding the damage to light transmission performance and mechanical properties caused by filler agglomeration.

[0028] (2) Pure resin film formation avoids problems such as agglomeration of inorganic powders. The film surface obtained by this invention is delicate, with low variance and no mottled haze in multi-point tests. Moreover, under the condition that no wetting agent is added and PET does not require pretreatment, the coating exhibits excellent wettability and adhesion, and is not easy to crack or fall off.

[0029] (3) The pure resin formulation of the present invention does not contain inorganic fillers, so the film thickness is not constrained by the particle size of the fillers and can be flexibly adjusted. The resin ratio can be adjusted to precisely control the haze size and adapt to the needs of different application scenarios. At the same time, there are no inorganic fillers in the film layer, so the adhesion to the substrate is strong and it is not easy to fall off, crack, bloom, etc., and the service life is longer. The compounded resins are all polar materials, and strong hydrogen bonds are formed between the molecular chains of the two resins, which helps to stabilize the compounded system and prevent macroscopic phase separation. Attached Figure Description

[0030] Figure 1 Optical effect diagram of the high-transmittance soft-light matte film prepared in Example 7 of the present invention;

[0031] Figure 2This is an optical effect diagram of the PVP / PVA blend film prepared in Comparative Example 4 of the present invention. Detailed Implementation

[0032] The present invention will be further described in detail below with reference to specific embodiments. The testing standards used in the following embodiments are as follows: haze and transmittance are tested according to GB / T 2410-2008 standard; adhesion is tested according to GB / T 9286-2021 standard using the cross-cut adhesion test. The polyvinyl alcohol resin is PVA1799 with a molecular weight of 50,000-100,000; the polycarbonate diol has a molecular weight of 2,000.

[0033] In this embodiment, the PET substrate has a refractive index of approximately 1.635; the pure polyvinyl alcohol (PVA1799) coating has a refractive index of approximately 1.52; and the synthesized pure waterborne polyurethane (WPU) prepolymer has a refractive index of approximately 1.5 after curing.

[0034] Example 1

[0035] Step 1: Add 100 g of polyvinyl alcohol resin to 900 g of pure water and stir continuously in a 90 ℃ water bath until completely dissolved to form a pure transparent polyvinyl alcohol aqueous solution with a solid content of 10%, for later use.

[0036] Step 2: Preparation of waterborne polyurethane prepolymer: Take a clean, anhydrous, and oil-free 1L three-necked flask, and add 355 g of polycarbonate diol and 120 g of isophorone diisocyanate to the flask sequentially. Control the oil bath temperature at 75-80 ℃ and stir at 600 rpm for 2 hours. Cool down to 65 ℃, add 25 g of 2,2-dimethylolpropionic acid to the flask, and stir for 1 hour. Add 0.5 g of dibutyltin dilaurate and stir for 2 hours. After the reaction is complete, titrate the -NCO content using the di-n-butylamine method and the -OH content using the acylation method, and then calculate the molar ratio of the two to determine the -NCO / -OH molar ratio to 1.48 (the theoretical number-average molecular weight of the waterborne polyurethane prepolymer is approximately 2800). Take out all of it and store it in a clean, anhydrous, and oil-free glass bottle until it cools to room temperature for later use.

[0037] Step 3: Neutralize the prepolymer: Take 500 g of the room temperature waterborne polyurethane prepolymer from Step 2, add 20.73 g of triethylamine, stir evenly with a dispersion pan, and the solid content is 100%.

[0038] Step 4: Preparation of the matte film resin composite: Take 100 g of the 10% polyvinyl alcohol aqueous solution obtained by thermal dissolution in Step 1, place it under a dispersion pan, and stir at 1500 rpm. Take 10 g of the prepolymer prepared in Step 3 and slowly add it dropwise to the 10% polyvinyl alcohol aqueous solution being stirred at high speed. After the addition is complete, continue stirring at 1500 rpm for 30 minutes to ensure thorough compounding. A matte film resin composite with uniformly compounded resins is obtained. Dilute with deionized water to adjust the overall solid content to 10%, with a polyvinyl alcohol to waterborne polyurethane solid ratio of 1:1.

[0039] Step 5: Defoaming: Use a vacuum defoaming mixer at 1200 rpm for 90 seconds, with a vacuum of -75 kPa and a rotation ratio of 60% to remove bubbles, followed by curing at room temperature for 1 hour.

[0040] Step 6: Preparation of optical haze film. Using a 100 μm coater, the cured haze film resin compound from Step 5 is uniformly coated onto a PET substrate. After drying in an 80°C oven for 3 minutes, an optical haze film with a thickness of approximately 10 μm is obtained.

[0041] Example 2

[0042] The preparation method of the optical haze film in Example 2 is the same as that in Example 1, except that in step 4, the amount of waterborne polyurethane prepolymer added is 20 g, that is, the solid ratio of polyvinyl alcohol and waterborne polyurethane is 1:2. Other operations are the same as in Example 1.

[0043] Example 3

[0044] The preparation method of the optical haze film in Example 3 is the same as that in Example 1, except that in step 4, the amount of waterborne polyurethane prepolymer added is 40 g, that is, the solid ratio of polyvinyl alcohol and waterborne polyurethane is 1:4, and other operations are the same as in Example 1.

[0045] Example 4

[0046] The preparation method of the optical haze film in Example 4 is the same as that in Example 1, except that: in step 4, the amount of waterborne polyurethane prepolymer added is 45 g, that is, the solid ratio of polyvinyl alcohol and waterborne polyurethane is 1:4.5, and other operations are the same as in Example 1.

[0047] Example 5

[0048] The preparation method of the optical haze film in Example 5 is the same as that in Example 1, except that in step 4, the amount of waterborne polyurethane prepolymer added is 50 g, that is, the solid ratio of polyvinyl alcohol and waterborne polyurethane is 1:5, and other operations are the same as in Example 1.

[0049] Example 6

[0050] The preparation method of the optical haze film in Example 6 is the same as that in Example 1, except that in step 4, the amount of waterborne polyurethane prepolymer added is 55 g, that is, the solid ratio of polyvinyl alcohol and waterborne polyurethane is 1:5.5, and other operations are the same as in Example 1.

[0051] Example 7

[0052] The preparation method of the optical haze film in Example 7 is the same as that in Example 1, except that in step 4, the amount of waterborne polyurethane prepolymer added is 60 g, that is, the solid ratio of polyvinyl alcohol and waterborne polyurethane is 1:6, and other operations are the same as in Example 1.

[0053] Example 8

[0054] The preparation method of the optical haze film in Example 8 is the same as that in Example 1, except that in step 4, the amount of waterborne polyurethane prepolymer added is 65 g, that is, the solid ratio of polyvinyl alcohol and waterborne polyurethane is 1:6.5, and other operations are the same as in Example 1.

[0055] Example 9

[0056] The preparation method of the optical haze film in Example 9 is the same as that in Example 1, except that in step 4, the amount of waterborne polyurethane prepolymer added is 70 g, that is, the solid ratio of polyvinyl alcohol and waterborne polyurethane is 1:7, and other operations are the same as in Example 1.

[0057] Comparative Example 1

[0058] In this comparative example, no resin was coated; only the transmittance and haze of the blank substrate PET film were tested.

[0059] Comparative Example 2

[0060] This comparative example only coated with 10% polyvinyl alcohol aqueous dispersion to obtain a pure polyvinyl alcohol film.

[0061] Comparative Example 3

[0062] In this comparative example, 90g of deionized water was placed under a high-speed dispersion plate at 1500 rpm, and 10g of the waterborne polyurethane prepolymer neutralized by polyetheramine D400 in step three was slowly added dropwise. After the addition was completed, the mixture was stirred at the same speed for 0.5 h to prepare a waterborne polyurethane dispersion with a solid content of 10%.

[0063] Defoaming: Vacuum defoaming mixer, speed 1200 rpm, time 90 s, vacuum degree -75 kPa, rotation ratio 60%; Curing: Curing at room temperature for 1 hour.

[0064] Using a 100 μm coater, the cured waterborne polyurethane resin is uniformly coated onto a PET substrate. After drying in an 80 °C oven for 3 minutes, a transparent waterborne polyurethane film is obtained.

[0065] Comparative Example 4

[0066] A 10% solids aqueous dispersion of polyvinylpyrrolidone (PVP K30, molecular weight 40,000-50,000) was prepared to replace the aqueous polyurethane in Example 7. Polyvinyl alcohol aqueous solution (molecular weight 50,000-100,000, solids content 10%) was then compounded with the above-mentioned polyvinylpyrrolidone aqueous dispersion, controlling the mass ratio of polyvinyl alcohol solids to polyvinylpyrrolidone solids to be 1:6 (1 part polyvinyl alcohol, 6 parts polyvinylpyrrolidone). After thorough mixing, degassing, coating, and drying / curing operations were performed as in Example 7.

[0067] The coating of Comparative Example 4 was completely transparent and did not exhibit a soft, matte finish.

[0068] The haze and transmittance test results of the optical haze film in each embodiment and comparative example are shown in the table below.

[0069] Table 1. Test results of transmittance and haze under different blending ratios of polyurethane and polyvinyl alcohol

[0070]

[0071] Note: Light transmittance and haze were tested at nine points on the same film, and the average value and variance were calculated.

[0072] As can be seen from the data results of each embodiment in the table, by adjusting the compounding of the two transparent resins, the haze of the coating film can be controlled. Within a certain range, the haze increases with the increase of the proportion of waterborne polyurethane, while the light transmittance of the film is almost unaffected by the haze. In addition, in the data of the embodiments, the light transmittance of the coated film is higher than that of the substrate film because the PVA / WPU coating reduces interfacial reflection loss through refractive index matching and surface smoothing effect.

[0073] It is worth noting that when the solid ratio of waterborne polyurethane to polyvinyl alcohol is 1:1, the proportion of waterborne polyurethane is relatively low, resulting in a weaker driving force for phase separation. Therefore, the transmittance uniformity is slightly lower than that of samples with a higher proportion. When the solid ratio of waterborne polyurethane to polyvinyl alcohol reaches 6:1, the haze of the coating film exhibits a significant peak (84.03%). The microstructure is extremely sensitive to changes in the ratio, leading to a slight increase in haze fluctuation, with a relative deviation of <5%, which is acceptable. Further increasing the proportion of waterborne polyurethane actually reduces the haze. This nonlinear haze variation indicates that the evolution of the microstructure is not a simple proportional function, but rather is affected nonlinearly by the relative content of the two resins. When the proportion of waterborne polyurethane is too high, the originally loose phase gradually becomes denser, the phase interface density decreases, and thus the haze falls back. This phenomenon confirms that the interaction between the two resins in this invention is not a simple physical blending. The phase structure evolution of this system is controlled by the nonlinear coupling of multiple factors, including molecular weight difference, hydrogen bond density, curing rate, etc. Its behavior cannot be predicted from the linear extrapolation of existing blending systems. There is a specific structural control window. The resin ratio needs to be finely controlled during the resin ratio adjustment process to control the hydrogen bond density and phase morphology.

[0074] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a high-transmittance, soft-light matte film based on an aqueous resin compound, characterized in that, Prepared by the following steps: (1) Add polyvinyl alcohol resin with a molecular weight of 50,000 to 100,000 to deionized water to prepare a polyvinyl alcohol aqueous solution with a solid content of 8 to 12%. (2) Polycarbonate diol and isophorone diisocyanate are stirred and reacted at 75~80℃, then cooled to 60~65℃ and 2,2-dimethylolpropionic acid is added to continue the reaction. Dibutyltin dilaurate is added and stirred for 1~3 hours. After the reaction is completed, the temperature is lowered to room temperature to prepare waterborne polyurethane prepolymer. The initial -NCO / -OH molar ratio set for the reaction is 1.2~1.

5. The molecular weight of the waterborne polyurethane prepolymer is at least one order of magnitude different from the molecular weight of polyvinyl alcohol in step (1). (3) Add a neutralizing agent dropwise to the waterborne polyurethane prepolymer and stir continuously until homogeneous to obtain a neutralized prepolymer; (4) The polyvinyl alcohol aqueous solution obtained in step (1) and the neutralized prepolymer obtained in step (3) are compounded under high-speed stirring; then deionized water is added to dilute and the solid content is adjusted to 9~11% to obtain resin compound; wherein, the mass ratio of polyvinyl alcohol to waterborne polyurethane is 1:1~1:

7. (5) The resin compound is placed in a vacuum degassing mixer for degassing treatment, and then cured at room temperature for 1 to 2 hours; (6) The matured matte film resin compound is evenly coated on a PET substrate and dried at 80℃-100℃ for 1~3 minutes to obtain a high-transmittance soft matte film.

2. The preparation method according to claim 1, characterized in that, In step (2), the amount of 2,2-dimethylolpropionic acid added is 3 to 6% of the total mass of polycarbonate diol and isophorone diisocyanate; the amount of dibutyltin dilaurate added is 0.1 to 0.2% of the total mass of the resin system.

3. The preparation method according to claim 1, characterized in that, In step (2), the molecular weight of the polycarbonate diol is 1000~3000; the number average molecular weight of the waterborne polyurethane prepolymer is 2000~5000.

4. The preparation method according to claim 1, characterized in that, In step (3), the neutralizing agent is triethylamine or polyetheramine; the molar ratio of the neutralizing agent to 2,2-dimethylolpropionic acid in step (2) is 1~1.1:

1.

5. The preparation method according to claim 1, characterized in that, In step (4), the mass ratio of polyvinyl alcohol to waterborne polyurethane is 1:4 to 1:6.

5.

6. A high-transmittance, soft-light matte film based on an aqueous resin compound, prepared by the preparation method according to any one of claims 1-5.

7. The application of the high-transmittance soft-light matte film based on water-based resin compound according to claim 6 in the preparation of LED anti-glare film, display screen light film or optical diffusion plate.

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