Light diffusion type polyvinyl acetal composite film as well as preparation method and application thereof

Abstract

The invention relates to the technical field of polymer functional composite materials, in particular to a light diffusion type polyvinyl acetal composite film as well as a preparation method and application of the light diffusion type polyvinyl acetal composite film. The functional layer comprises the following components in parts by mass: 100 parts of polyvinyl acetal resin, 15-40 parts of a plasticizer, 5-25 parts of polymer optical microspheres and 0-5 parts of an ultraviolet absorbent; the refractive index difference between the polymer optical microspheres and the polyvinyl acetal resin is 0.02-0.08, and the volume average particle size D50 of the polymer optical microspheres is 2-8 [mu] m. Cooperative unification of high light transmittance and high haze is achieved, the haze can be precisely regulated and controlled within a wide range, the light diffusion requirements in the fields of building lighting, LED lighting, display devices and the like are met, the preparation method is simple and flexible, a single-layer or multi-layer structure film can be prepared, and continuous and large-scale industrial production is adapted.

Description

Technical Field

[0001] This invention relates to the field of polymer functional composite materials technology, and in particular to a light-diffusing polyvinyl acetal composite film, its preparation method, and its application. Background Technology

[0002] Polyvinyl acetal resin, especially polyvinyl butyral (PVB), has long been widely used as an interlayer in laminated glass in fields such as construction and transportation due to its excellent transparency, flexibility, impact resistance, strong adhesion to substrates such as glass, and safety performance. Existing technologies for improving polyvinyl acetal resin mainly focus on enhancing its weather resistance, reducing coloration, strengthening adhesion, and reducing foreign matter content. For example, patent WO2015019452A1 discloses a film containing polyvinyl acetal, which exhibits lower coloration upon heating, lower impurity (undissolved portion) content, and minimal increase in water vapor permeability even during long-term use.

[0003] All of the above improvements are based on maintaining the structural adhesive material's characteristics of high transparency and low haze. However, in fields such as building skylights, decorative glass partitions, LED flat panel lighting, advertising light boxes, and display backlight modules, optical films have a dual functional requirement of high light transmittance and high and uniform haze: on the one hand, high light transmittance is needed to ensure the brightness output of the light source, and on the other hand, high and uniform haze is needed to achieve soft light diffusion, eliminate glare from point or line light sources, and obtain a uniform light-emitting surface.

[0004] Currently, mainstream light diffusion materials on the market have many technical defects: Light diffusion plates with polycarbonate (PC) and polymethyl methacrylate (PMMA) as the matrix and inorganic particles such as barium sulfate and silica added have a core problem of mutual restriction between light transmittance and haze. Increasing the content of inorganic fillers can improve haze, but it will lead to a significant decrease in light transmittance. It is also prone to "cloudiness" due to interface scattering. In addition, inorganic fillers can damage the mechanical properties and processing fluidity of the matrix. On the other hand, thin films that achieve light diffusion through microstructures such as surface prisms and microlenses have complex preparation processes, high production costs, and the surface microstructures are easy to wear, affecting long-term performance.

[0005] The excellent bulk properties of polyvinyl acetal resin provide a foundation for the development of novel light-diffusing materials. However, directly introducing conventional light-diffusing fillers makes it difficult to overcome the constraints of transmittance and haze, and also easily leads to the loss of its original mechanical and adhesive properties. Therefore, developing a light-diffusing composite film with polyvinyl acetal resin as the matrix that combines high transmittance, high haze, and adjustable properties, while maintaining excellent mechanical properties, processability, and adhesion, has become an urgent technical problem to be solved in this field. Summary of the Invention

[0006] The purpose of this invention is to provide a light-diffusing polyvinyl acetal composite film, its preparation method, and its application. The composite film inherits the high transparency, toughness, and strong adhesion of polyvinyl acetal resin, and achieves a synergistic unity of high light transmittance and high haze. Moreover, the haze can be precisely controlled within a wide range, meeting the light diffusion requirements of fields such as architectural lighting, LED lighting, and display devices. The preparation method is simple and flexible, and can prepare single-layer or multi-layer structured films, making it suitable for continuous and large-scale industrial production.

[0007] To achieve the above objectives, the present invention provides a light-diffusing polyvinyl acetal composite film. The composite film includes a functional layer, the components of which, by mass parts, include: 100 parts of polyvinyl acetal resin, 15-40 parts of plasticizer, 5-25 parts of polymer optical microspheres, and 0-5 parts of ultraviolet absorber; the refractive index difference between the polymer optical microspheres and the polyvinyl acetal resin is 0.02-0.08, and the volume average particle size D50 of the polymer optical microspheres is 2μm-8μm.

[0008] Preferably, the polymer optical microspheres include one of cross-linked polymethyl methacrylate microspheres, cross-linked polystyrene microspheres, and silicone resin microspheres.

[0009] Preferably, the ultraviolet absorber is one of nano-inorganic ultraviolet shielding agents and organic ultraviolet absorbers. The nano-inorganic ultraviolet shielding agents include one of nano-cerium oxide, nano-zinc oxide, and nano-titanium dioxide, and the organic ultraviolet absorbers include one of benzotriazole ultraviolet absorbers, benzophenone ultraviolet absorbers, and triazine ultraviolet absorbers.

[0010] Preferably, the composite film is a co-extruded film having at least two layers, wherein at least one layer of the co-extruded film is a functional layer.

[0011] Preferably, the co-extruded film has a three-layer symmetrical structure, including a core layer in the middle and surface layers located on both sides of the core layer, wherein the core layer is a functional layer, and the components of the surface layer include, by mass parts: 100 parts of polyvinyl acetal resin and 15-40 parts of plasticizer.

[0012] Preferably, the polyvinyl acetal resin is polyvinyl butyral resin.

[0013] Preferably, the plasticizer is one of triethylene glycol di-2-ethylhexanoate, triethylene glycol di-2-ethylbutanoate, triethylene glycol di-n-heptanoate, and dihexyl adipate.

[0014] This invention also provides a method for preparing a light-diffusing polyvinyl acetal composite film, comprising the following steps: S1. Premix 100 parts of polyvinyl acetal resin, 15-40 parts of plasticizer, 5-25 parts of polymer optical microspheres, and 0-5 parts of ultraviolet absorber in a high-speed mixer to obtain a premix. S2. The premixed material is fed into a twin-screw extruder for melt blending, extrusion granulation, and then the functional masterbatch is obtained. S3. The functional masterbatch is fed into the die head through an extruder, and after co-extrusion casting, cooling and shaping, traction and winding, a composite film is obtained.

[0015] Preferably, S3 further includes extruding and granulating polyvinyl acetal resin and plasticizer for the surface layer, and feeding them and functional masterbatch into a multi-layer co-extrusion die through an extruder, and then co-extruding, casting, cooling and shaping, drawing and winding to obtain a composite film.

[0016] This invention also provides an application of a light-diffusing polyvinyl acetal composite film, used in building decorative lighting panels, LED flat panel lights, light diffusion plates for panel lights, and diffusion films for display backlight modules.

[0017] Mechanism of the invention: This invention introduces a combination of polymer optical microspheres and a polyvinyl acetal resin matrix, utilizing the specific refractive index difference (0.02-0.08) and microsphere particle size (2-8 μm) between the two to construct a uniform and controllable light scattering interface within the matrix. When light passes through the film, the microspheres induce efficient Mie scattering, ensuring uniform light diffusion. Simultaneously, the moderate refractive index difference avoids light energy loss caused by excessive reflection, thus achieving a wide range of adjustable haze while maintaining high light transmittance, truly realizing a synergistic improvement of both components.

[0018] Therefore, the present invention, employing the above-mentioned light-diffusing polyvinyl acetal composite film, its preparation method, and its application, has the following beneficial effects: (1) This invention solves the technical problem of mutual constraint between transmittance and haze in traditional light diffusion materials. By precisely controlling the refractive index difference, particle size and addition amount of polymer optical microspheres, the visible light transmittance of the film is always not lower than 86% while the haze is adjustable in a wide range of 20%-85%. Even when the haze reaches 85%, the transmittance is still maintained above 86%, and the light diffusion uniformity is good, with no obvious bright spots, dark areas and particle sensation, effectively eliminating glare and forming a soft and uniform surface light source. (2) The present invention uses polyvinyl acetal resin as the matrix. The polymer optical microspheres introduced have good compatibility with polyvinyl acetal resin and do not damage the mechanical structure of polyvinyl acetal resin. The film maintains the inherent high tensile strength, high elongation at break and high tear strength of polyvinyl acetal resin, while also having excellent flexibility, impact resistance and excellent adhesion to substrates such as glass, thus overcoming the drawback of significant decline in mechanical properties of traditional inorganic filler-type light diffusion materials. (3) The present invention can prepare films with different structures through single-layer or multi-layer co-extrusion processes. Single-layer films are simple and low-cost, while multi-layer composite films take into account both surface properties and light diffusion function, and can be flexibly adjusted according to the needs of different application scenarios. (4) The present invention adopts mature polymer melt blending, extrusion granulation and casting co-extrusion molding process, uses conventional polymer processing equipment, the raw materials are readily available and have good compatibility, the production process is continuous and stable, and large-scale industrial production can be realized, and the production cost is controllable. (5) The composite film of the present invention can be widely used in fields that require soft and uniform surface light sources, such as high-end building lighting decoration, glare-free LED lighting fixtures, liquid crystal display backlight modules, etc., and has significant market competitiveness.

[0019] The technical solution of the present invention will be further described in detail below through embodiments. Detailed Implementation

[0020] The present invention will be further described below with reference to embodiments. Unless otherwise defined, the technical or scientific terms used in this invention should have the ordinary meaning understood by one of ordinary skill in the art. The features mentioned above or in the specific examples mentioned in this invention can be combined arbitrarily, and these specific embodiments are only used to illustrate the invention and are not intended to limit the scope of the invention.

[0021] A light-diffusing polyvinyl acetal composite film, comprising a functional layer, wherein the functional layer comprises, by mass parts: 100 parts polyvinyl acetal resin, 15-40 parts plasticizer, 5-25 parts polymer optical microspheres, and 0-5 parts ultraviolet absorber; the refractive index difference (Δn) between the polymer optical microspheres and the polyvinyl acetal resin is 0.02-0.08, and the volume average particle size D50 of the polymer optical microspheres is 2μm-8μm.

[0022] In this invention, polyvinyl acetal resin is used as the matrix resin, serving as the continuous phase framework of the light-diffusing composite film, providing the film with mechanical properties, basic optical properties, and substrate adhesion properties; plasticizer is used to adjust the flexibility and processing fluidity of the matrix resin.

[0023] In this invention, the refractive index difference between the polymer optical microspheres and the polyvinyl acetal resin is controlled within the range of 0.02-0.08. If the refractive index difference is too small (Δn<0.02), the scattering ability is weak and it is difficult to achieve high haze; if the refractive index difference is too large (Δn>0.08), it will lead to severe interface reflection, significantly reduce the light transmittance and may cause strong glare.

[0024] In this invention, the volume average particle size D50 of the polymer optical microspheres is controlled within the range of 2μm-8μm. This particle size range can produce effective Mie scattering of visible light, achieving high haze while having a relatively small impact on light transmittance, and avoiding obvious graininess or mechanical weaknesses caused by excessively large particle size.

[0025] Preferably, the polymer optical microspheres include one of cross-linked polymethyl methacrylate microspheres, cross-linked polystyrene microspheres, and silicone resin microspheres.

[0026] In this invention, polymer optical microspheres serve as the core light-diffusing filler, a key component for achieving the light scattering effect of the composite film. By controlling the refractive index difference and volume average particle size D50 between the microspheres and polyvinyl acetal resin, efficient and controllable Mie scattering of visible light is achieved. This ensures high light transmittance while transforming point and line light sources into uniform and soft surface light sources, effectively eliminating glare. Furthermore, the polymer optical microspheres exhibit excellent compatibility with polyvinyl acetal resin, and their dispersion does not significantly disrupt the continuous phase structure of the matrix resin. This allows for the preservation of the matrix's mechanical toughness and adhesion properties to the greatest extent possible while imparting excellent light diffusion performance to the film. Moreover, by adjusting the amount added, precise control of the composite film's haze can be achieved, adapting to the optical requirements of different application scenarios. In addition, compared to traditional inorganic light-diffusing fillers, polymer optical microspheres do not suffer from the "cloudiness" problem caused by interface scattering, further enhancing the optical quality and light diffusion uniformity of the composite film. This allows the composite film to maintain clear light transmission even under high haze conditions, avoiding brightness loss and visual blurring during light transmission.

[0027] Preferably, the ultraviolet absorber is one of nano-inorganic ultraviolet shielding agents and organic ultraviolet absorbers. The nano-inorganic ultraviolet shielding agents include one of nano-cerium oxide, nano-zinc oxide, and nano-titanium dioxide, and the organic ultraviolet absorbers include one of benzotriazole ultraviolet absorbers, benzophenone ultraviolet absorbers, and triazine ultraviolet absorbers.

[0028] Furthermore, the nano-inorganic UV shielding agent is loaded onto a porous carrier to prevent aggregation and achieve long-lasting and stable UV shielding function, thereby extending the lifespan of the composite film in outdoor applications.

[0029] Preferably, the composite film is a co-extruded film having at least two layers, wherein at least one layer of the co-extruded film is a functional layer.

[0030] Preferably, the co-extruded film has a three-layer symmetrical structure, including a core layer in the middle and surface layers located on both sides of the core layer, wherein the core layer is a functional layer, and the components of the surface layer include, by mass parts: 100 parts of polyvinyl acetal resin and 15-40 parts of plasticizer.

[0031] The co-extruded film of this invention uses pure polyvinyl acetal resin material or polyvinyl alcohol acetal resin material containing a small amount of additives in the surface layer to provide excellent surface hardness, gloss and bonding interface; the core layer is rich in polymer optical microspheres, which serve as the main light diffusion functional layer, and can optimize the mechanical properties and surface characteristics of the composite film while ensuring the best optical effect.

[0032] Preferably, the polyvinyl acetal resin is polyvinyl butyral resin.

[0033] Preferably, the plasticizer is one of triethylene glycol di-2-ethylhexanoate, triethylene glycol di-2-ethylbutanoate, triethylene glycol di-n-heptanoate, and dihexyl adipate.

[0034] This invention also provides a method for preparing a light-diffusing polyvinyl acetal composite film, comprising the following steps: S1. Premix 100 parts of polyvinyl acetal resin, 15-40 parts of plasticizer, 5-25 parts of polymer optical microspheres, and 0-5 parts of ultraviolet absorber in a high-speed mixer to obtain a premix. S2. The premixed material is fed into a twin-screw extruder for melt blending, extrusion granulation, and then the functional masterbatch is obtained. S3. The functional masterbatch is fed into the die head through an extruder, and after co-extrusion casting, cooling and shaping, traction and winding, a composite film is obtained.

[0035] Preferably, S3 further includes extruding and granulating polyvinyl acetal resin and plasticizer for the surface layer, and feeding them and functional masterbatch into a multi-layer co-extrusion die through an extruder, and then co-extruding, casting, cooling and shaping, drawing and winding to obtain a composite film.

[0036] Preferably, in S3, the extruder is a single-screw extruder or a twin-screw extruder, and the cooling and shaping are performed using a three-roll calender.

[0037] The preparation method of this invention mainly includes melt blending and extrusion molding. High-speed premixing and twin-screw extrusion are used to achieve uniform dispersion of polymer optical microspheres in a polyvinyl acetal resin matrix. Then, the microspheres are formed into a film through single-layer casting or multi-layer co-extrusion. Process parameters (such as processing temperature, screw speed, and cooling roller temperature) need to be optimized according to the specific formulation to ensure the integrity and good dispersion of the microsphere structure and to obtain a smooth and glossy film surface.

[0038] This invention also provides an application of a light-diffusing polyvinyl acetal composite film, used in building decorative lighting panels, LED flat panel lights, light diffusion plates for panel lights, and diffusion films for display backlight modules.

[0039] Example 1 This invention provides a light-diffusing polyvinyl acetal composite film, the components of which, by mass parts, include: 100 parts of polyvinyl butyral resin (degree of butyralization 68%, degree of polymerization 1700, refractive index approximately 1.485), 30 parts of triethylene glycol di-2-ethylhexanoate, and 15 parts of cross-linked polymethyl methacrylate microspheres (PMMA microspheres, volume average particle size D50 = 5 μm, refractive index 1.495, the refractive index difference between the microspheres and the polyvinyl acetal resin Δn ≈ 0.01).

[0040] The above-mentioned method for preparing a light-diffusing polyvinyl acetal composite film includes the following steps: S1. 100 parts of polyvinyl butyral resin, 30 parts of triethylene glycol di-2-ethylhexanoate, and 15 parts of cross-linked polymethyl methacrylate microspheres are premixed in a high-speed mixer at 1000 rpm for 5 minutes to obtain a premix.

[0041] S2. The premixed material is fed into a twin-screw extruder and melt-blended, extruded and granulated at a temperature of 190℃ and a speed of 300rpm. It is then dried at 80℃ for 4 hours to obtain functional masterbatch.

[0042] S3. The functional masterbatch is fed into a T-die through a single screw extruder and melt-extruded at 195°C. It is then cast to a three-roll calender at 25°C for cooling and shaping, followed by traction and winding to produce a single-layer light-diffusing composite film with a thickness of 0.80 mm containing only the functional layer.

[0043] Example 2 The difference from Example 1 is that the polymer optical microspheres are cross-linked silicone resin microspheres (refractive index approximately 1.43, with a refractive index difference of Δn≈0.055 between them and polyvinyl butyral resin), with a volume average particle size D50=8μm, and an addition amount of 20 parts. All other aspects are the same as in Example 1.

[0044] Example 3 The difference from Example 1 lies in step S3 of the preparation method. 100 parts of polyvinyl acetal resin and 25 parts of plasticizer for the surface layer are premixed evenly in a high-speed mixer, then fed into a twin-screw extruder for melt blending, extrusion granulation, and drying at 80°C for 4 hours to obtain a surface masterbatch. The surface masterbatch and functional masterbatch are then co-extruded using two single-screw extruders and a three-layer co-extrusion die (ABA flow channel). The surface masterbatch is supplied by one extruder and split into two surface layers, while the functional masterbatch is supplied by the other extruder. They are combined and co-extruded within the three-layer co-extrusion die, and cooled and shaped using a three-roll calender to obtain a light-diffusing composite film with a total thickness of 0.80 mm. The thicknesses of the two surface layers are approximately 0.10 mm each, and the core layer thickness is approximately 0.60 mm. All other steps are the same as in Example 1.

[0045] Example 4 The difference from Example 1 is that the mass fraction of the cross-linked polymethyl methacrylate microspheres is 5 parts, while the rest are the same as in Example 1.

[0046] Example 5 The difference from Example 1 is that the mass fraction of triethylene glycol di-2-ethylhexanoate is 35 parts and the mass fraction of cross-linked polymethyl methacrylate microspheres is 25 parts, while the rest are the same as in Example 1.

[0047] Example 6 The difference from Example 1 is that it also includes 2 parts of benzotriazole organic ultraviolet absorber (UV-328), and the amount of cross-linked polymethyl methacrylate microspheres is adjusted to 18 parts. Preparation method S1 involves premixing 100 parts of polyvinyl butyral resin, 30 parts of triethylene glycol di-2-ethylhexanoate, 18 parts of cross-linked polymethyl methacrylate microspheres, and 2 parts of UV-328 in a high-speed mixer at 1000 rpm for 5 minutes to obtain a premix. All other steps are the same as in Example 1.

[0048] Comparative Example 1 The difference from Example 1 is that no cross-linked polymethyl methacrylate microspheres were added; otherwise, they are the same as in Example 1.

[0049] Comparative Example 2 The difference from Example 1 is that the volume average particle size D50 of the cross-linked polymethyl methacrylate microspheres is 15 μm, while the rest are the same as in Example 1.

[0050] Comparative Example 3 The difference from Example 1 is that the volume average particle size D50 of the cross-linked polymethyl methacrylate microspheres is 0.5 μm, while the rest are the same as in Example 1.

[0051] Comparative Example 4 The difference from Example 1 is that the polymer optical microspheres are cross-linked polystyrene microspheres (volume average particle size D50 = 5 μm, refractive index 1.590, and the refractive index difference between the microspheres and polyvinyl acetal resin Δn ≈ 0.105), while the rest are the same as in Example 1.

[0052] Comparative Example 5 The difference from Example 1 is that the cross-linked polymethyl methacrylate microspheres are replaced with precipitated barium sulfate (volume average particle size D50 = 1.5 μm), otherwise they are the same as in Example 1.

[0053] Performance testing The composite films prepared in Examples 1-6 and Comparative Examples 1-5 were tested for optical properties, mechanical properties, and diffusion uniformity. The test results are shown in Table 1. The test methods are as follows: Optical properties (transmittance and haze): The total light transmittance (Tt) and haze of the film samples were tested using a haze meter according to ASTM D1003 standard. Five points were measured for each sample, and the average value was taken. Mechanical properties (tensile strength, elongation at break and tear strength): According to GB / T 1040.3 standard, the composite film was cut into dumbbell-shaped strips, and the tensile strength and elongation at break were tested using a universal testing machine at a tensile speed of 500 mm / min; the tear strength was tested according to GB / T 529 standard (Elmendorf method). Diffusion uniformity (subjective evaluation): The composite film is tightly adhered to the surface of a standard LED light panel (color temperature 6000K), lit in a dark room, and the bright spots, dark areas, or graininess of the emitting surface are observed to evaluate the uniformity and softness of light diffusion. It is categorized as: Excellent (very uniform, no graininess), Good (uniform, slight graininess), Medium (visible unevenness in brightness and darkness), and Poor (severe unevenness or strong graininess).

[0054] Table 1 Performance test results of different composite films

[0055] As shown in Table 1, Example 1 (Δn≈0.01) maintained a high transmittance of 88.5% when the haze reached 68.3%, achieving a synergistic improvement in both haze and transmittance. Comparative Example 4 (Δn≈0.105), although exhibiting higher haze, suffered significant transmittance loss (down to 75.0%) and poor uniformity, demonstrating that an excessively large refractive index difference Δn led to excessive light reflection loss. Comparative Example 2 (PMMA microspheres with a volume average particle size D50=15μm) showed a decrease in haze and a noticeable grainy appearance, while Comparative Example 3 (PMMA microspheres with a volume average particle size D50=0.5μm) showed almost no light diffusion effect, with a haze of only 12.3%, indicating that the polymer optical microspheres need to be at a suitable visible light wavelength scale for effective scattering. Comparative Example 5, using barium sulfate as a filler, produced the worst-performing composite film, exhibiting low transmittance, a cloudy appearance, and significant mechanical losses, highlighting the significant advantages of polymer optical microspheres over traditional inorganic fillers.

[0056] In Examples 1, 4, and 5 of this invention, the amounts of polymer optical microspheres added were 15 parts, 5 parts, and 25 parts, respectively. The haze of the resulting composite films was 68.3%, 25.4%, and 82.7%, respectively, and the transmittance was higher than 86%. This indicates that by adjusting the amount of polymer optical microspheres added, a wide range of haze control can be achieved while ensuring high transmittance. Moreover, the haze increases steadily with the increase of the amount of polymer optical microspheres added, without any sharp increase or sudden drop in transmittance. This achieves linear and controllable adjustment of optical performance, adapting to the differentiated optical needs of different application scenarios.

[0057] The composite films prepared using polymer optical microspheres in Examples 1-5 and Comparative Examples 2-4 of this invention all exhibit better mechanical properties than the composite film prepared using inorganic fillers in Comparative Example 5. This indicates that the compatibility between polymer optical microspheres and the polyvinyl acetal resin matrix is ​​far superior to that of traditional inorganic fillers. When dispersed within the matrix, the polymer optical microspheres do not disrupt the continuous phase skeleton structure of the resin, thus preserving the mechanical properties of the matrix to the greatest extent. In contrast, inorganic fillers are prone to interfacial defects with the matrix, leading to a significant decrease in the tensile and tearing mechanical properties of the film. This highlights the technical advantage of using polymer optical microspheres as light diffusion fillers in this invention.

[0058] Example 6, after adding a UV absorber, still maintains a high transmittance of 87.8% and a haze of 72.5%. Both optical and mechanical properties are within the preferred range of this invention, proving that the introduction of the UV absorber does not damage the light diffusion function and mechanical structure of the film, and is expected to improve the weather resistance of the film.

[0059] In summary, the light-diffusing polyvinyl acetal composite film provided by this invention achieves a combination of high light transmittance and medium-to-high haze, and has good diffusion uniformity. Among them, Example 1 (single layer, 15 parts PMMA microspheres) and Example 4 (multilayer structure) show the most balanced performance in terms of optics, mechanics and appearance.

[0060] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A light-diffusing polyvinyl acetal composite film, characterized in that: The composite film includes a functional layer, the components of which, by mass parts, include: 100 parts of polyvinyl acetal resin, 15-40 parts of plasticizer, 5-25 parts of polymer optical microspheres, and 0-5 parts of ultraviolet absorber; the refractive index difference between the polymer optical microspheres and the polyvinyl acetal resin is 0.02-0.08, and the volume average particle size D50 of the polymer optical microspheres is 2μm-8μm.

2. The light-diffusing polyvinyl acetal composite film according to claim 1, characterized in that: Polymer optical microspheres include one of cross-linked polymethyl methacrylate microspheres, cross-linked polystyrene microspheres, and silicone resin microspheres.

3. The light-diffusing polyvinyl acetal composite film according to claim 1, characterized in that: The ultraviolet absorber is one of the following: nano-inorganic ultraviolet shielding agents and organic ultraviolet absorbers. Nano-inorganic ultraviolet shielding agents include one of nano-cerium oxide, nano-zinc oxide, and nano-titanium dioxide. Organic ultraviolet absorbers include one of benzotriazole ultraviolet absorbers, benzophenone ultraviolet absorbers, and triazine ultraviolet absorbers.

4. The light-diffusing polyvinyl acetal composite film according to claim 1, characterized in that: The composite film is a co-extruded film with at least two layers, and at least one layer of the co-extruded film is a functional layer.

5. The light-diffusing polyvinyl acetal composite film according to claim 4, characterized in that: The co-extruded film has a three-layer symmetrical structure, including a core layer in the middle and surface layers on both sides of the core layer. The core layer is a functional layer, and the surface layer consists of the following components by mass: 100 parts of polyvinyl acetal resin and 15-40 parts of plasticizer.

6. The light-diffusing polyvinyl acetal composite film according to claim 5, characterized in that: Polyvinyl acetal resin is polyvinyl butyral resin.

7. The light-diffusing polyvinyl acetal composite film according to claim 5, characterized in that: The plasticizer is one of triethylene glycol di-2-ethylhexanoate, triethylene glycol di-2-ethylbutanoate, triethylene glycol di-n-heptanoate, and dihexyl adipate.

8. A method for preparing a light-diffusing polyvinyl acetal composite film according to any one of claims 1-7, characterized in that: Includes the following steps: S1. Premix 100 parts of polyvinyl acetal resin, 15-40 parts of plasticizer, 5-25 parts of polymer optical microspheres, and 0-5 parts of ultraviolet absorber in a high-speed mixer to obtain a premix. S2. The premixed material is fed into a twin-screw extruder for melt blending, extrusion granulation, and then the functional masterbatch is obtained. S3. The functional masterbatch is fed into the die head through an extruder, and after co-extrusion casting, cooling and shaping, traction and winding, a composite film is obtained.

9. The method for preparing a light-diffusing polyvinyl acetal composite film according to claim 8, characterized in that: S3 also includes extruding and granulating polyvinyl acetal resin and plasticizer for the surface layer, and feeding them and functional masterbatch into a multi-layer co-extrusion die through an extruder, and then producing a composite film through co-extrusion casting, cooling and shaping, traction and winding.

10. The application of a light-diffusing polyvinyl acetal composite film as described in any one of claims 1-7, characterized in that: Applications include architectural decorative lighting panels, LED flat panel lights, light diffusion plates for panel lights, and diffusion films for display backlight modules.

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