Composite membrane for high-brightness small-size backlight module and preparation method of composite membrane

Abstract

The invention belongs to the technical field of backlight modules, and particularly relates to a composite membrane for a high-brightness small-size backlight module and a preparation method of the composite membrane. The invention aims to solve the problems of non-uniform thermal expansion coefficient and interface optical loss of the existing composite membrane. The designed and prepared composite membrane sequentially comprises the following functional layers: a diffusion layer, a bonding layer, a second prism layer, a bonding layer, a first prism layer, a PET base material and a back coating layer. After surface treatment is carried out on a PET base material, a layer of functional UV curing resin is coated on the back surface to form a back coating layer, prism layer resin is processed on the front surface through UV nanoimprint lithography to obtain a first prism diaphragm, and after a second prism diaphragm is prepared through the same process, the second prism diaphragm is attached and laminated to obtain the double-layer prism composite structure. And further laminating to obtain a diffusion layer, and finally obtaining a composite membrane product. The prepared composite membrane is small in internal stress difference, small in interface optical loss and good in application value.

Description

Technical Field

[0001] This invention belongs to the field of backlight module technology, specifically relating to a composite film for a high-brightness, small-size backlight module and its preparation method. Background Technology

[0002] As consumer electronics continue to evolve towards thinner, lighter, higher-quality, and lower-power products, backlight modules, as a core component of LCD modules, have undergone significant technological changes. Among these changes, the emergence of composite optical films is a key element. These films integrate the functions traditionally achieved by stacking multiple independent optical films into a single component, playing a crucial role in achieving high-brightness, ultra-thin small-sized displays, especially in the application of next-generation backlight technologies represented by Mini LED.

[0003] Traditional backlight modules typically require stacking at least three films: a bottom diffuser film for uniform light distribution and two orthogonal prism films for enhanced brightness. Composite films, through precise manufacturing processes, integrate these functional layers along with adhesive and protective layers. Designed to meet the market's urgent need for thinner, brighter, and more efficient displays, composite films are highly concentrated in space-constrained and performance-critical applications. They significantly reduce thickness and weight while simplifying the supply chain and assembly, and improving optical coupling efficiency. Despite their significant advantages, the highly integrated design and manufacturing of composite films present significant technical challenges. Optically, the regular microarrays on the prism film can easily interfere with the pixel grid of the LCD panel, producing moiré patterns; the adhesive layer of the composite film can lead to interfacial optical losses; and mechanically, composite films are laminated from multiple polymer materials, and differences in the thermal expansion coefficients between these materials can cause internal stress imbalances, potentially leading to warping, curling, or even delamination of the film.

[0004] To address the issues of uneven thermal expansion coefficients and interfacial optical losses in existing composite films, a high-brightness, small-size composite film for backlight modules and its fabrication method are proposed. Summary of the Invention

[0005] The purpose of this invention is to provide a composite film for a high-brightness, small-size backlight module and its preparation method. The composite film designed and prepared according to this invention sequentially comprises the following functional layers: a diffusion layer, an adhesive layer, a second prism layer, an adhesive layer, a first prism layer, a PET substrate, and a back coating layer. This invention involves surface treating the PET substrate, coating the back with a functional UV-curable resin to form a back coating layer, and then processing the prism layer resin on the front using UV nanoimprint lithography to obtain a first prism film. A second prism film is then prepared using the same process and laminated to obtain a double-prism composite structure. Finally, a diffusion layer is laminated onto the second prism film to obtain the final composite film product.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A method for preparing a composite film for a high-brightness, small-size backlight module includes the following steps:

[0008] Unless otherwise specified, the parts in this invention refer to parts by mass.

[0009] At the beginning of the production line, optical-grade PET substrate rolls are unrolled and surface-treated.

[0010] Among them, the light transmittance of PET substrate rolls is >92%, and the haze is <1%.

[0011] A layer of functional UV-curable resin is applied to the back of the PET substrate using a slot coating process to form a back coating. This is followed by low-energy pre-curing and annealing, and then a high-energy first UV curing.

[0012] The back coating has a thickness of 3-5 μm, and the functional UV-curable resin includes: 40 parts of bisphenol A epoxy acrylate with an average molecular weight of 1000-1500 g / mol; 30 parts of pentaerythritol hexaacrylate; 20 parts of isoborneol acrylate; 3 parts of fumed silica; 3 parts of 1-hydroxycyclohexylphenyl ketone; 1.5 parts of diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide; and 0.5 parts of polyether-modified polydimethylsiloxane.

[0013] On the front side of the PET substrate with the back coating, the prism layer resin is processed by UV nanoimprint lithography. Using a master engraving mold with various spacing and height combinations, the first quasi-randomized prism array is replicated to obtain the first prism film. After repeating the above process, the PET carrier film is removed to obtain a second prism film with the same process parameters.

[0014] The prism mold has three different spacing and height combinations: all prism apex angles are 90°; Unit A has a spacing of 45 μm and a height of 22.5 μm; Unit B has a spacing of 55 μm and a height of 27.5 μm; and Unit C has a spacing of 65 μm and a height of 32.5 μm. The prism layer resin includes: 50 parts of bisphenol A epoxy acrylate with an average molecular weight of 500-1000 g / mol; 20 parts of 2-phenoxyethyl acrylate; 20 parts of trimethylolpropane triacrylate; 5 parts of isoborneol acrylate; 3 parts of 1-hydroxycyclohexylphenyl ketone; and 2 parts of diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide.

[0015] The first prism diaphragm was subjected to online plasma treatment.

[0016] The UV adhesive is transferred through an intermediate carrier roller to the prism tip peak of the first prism film;

[0017] The second prism film is precisely aligned with the first one so that their prism directions are orthogonal, and then laminated together.

[0018] The UV adhesive includes: 50 parts of aliphatic polyurethane acrylate, CAS number 68987-79-1, with an average molecular weight of 2500-3500 g / mol; 30 parts of isoborneol acrylate; 15 parts of 2-hydroxyethyl acrylate; 2 parts of γ-methacryloyloxypropyltrimethoxysilane; 2 parts of 1-hydroxycyclohexylphenyl ketone; and 1 part of diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide.

[0019] The second UV curing process completely cures the UV adhesive at the tip of the prism, forming a double-layer prism composite structure.

[0020] The UV adhesive is transferred to the prism tip of the second prism film through an intermediate carrier roller, and then laminated and finally cured after being bonded to the diffusion film to obtain the diffusion layer. All the film layers from the back coating layer to the diffusion layer are combined to form a composite film product.

[0021] The diffusion membrane comprises: 60 parts of bisphenol A epoxy acrylate with an average molecular weight of 1000-1500 g / mol; 35 parts of trimethylolpropane triacrylate; 4 parts of 1-hydroxycyclohexylphenyl ketone; 1 part of diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide; and 25 parts of polymethyl methacrylate microspheres with a D50 of 5 μm.

[0022] Preferably, the pre-curing operating parameters are: ultraviolet wavelength of 395nm and irradiance of 120-150mW / cm². 2 The exposure energy is 80 mJ / cm. 2The annealing parameters were: hold the back coating at 110℃ for 30 seconds, then cool to 25℃; the first UV curing parameters were: use a high-pressure mercury lamp as the light source, with a lamp power of 120W / cm, and a cumulative exposure energy of 1000mJ / cm in the UVA band. 2 The operating parameters for the second UV curing are as follows: a high-pressure mercury lamp is used as the light source, with a lamp power of 120-140 W / cm², and the cumulative exposure energy in the UVA band is 1200 mJ / cm². 2 The final curing parameters were: a high-pressure mercury lamp as the light source, a lamp power of 160W / cm, and a cumulative exposure energy of 1200mJ / cm in the UVA band. 2 .

[0023] Preferably, the surface treatment process is as follows: using 15-20 W·min / m 2 With a power density of 1.5 mm and an electrode gap of 1.5 mm, the surface of the PET substrate is subjected to corona treatment under atmospheric pressure.

[0024] Preferably, the online plasma treatment process is as follows: a mixed gas with a nitrogen to oxygen volume ratio of 4:1 is used as the working fluid, the flow rate is 20L / min, the radio frequency power is 400W, and the distance between the plasma nozzle and the prism diaphragm surface is maintained at 8mm.

[0025] Preferably, the operating parameters for UV nanoimprint lithography are as follows: imprint pressure of 0.3-0.5 MPa, prism resin thickness of 35-40 μm, and production line speed maintained at 10 m / min; after imprinting, a high-pressure mercury lamp is used during the curing process, with a lamp power of 160 W / cm and a cumulative exposure energy of 600-900 mJ / cm in the UVA band. 2 .

[0026] A composite film for a high-brightness, small-size backlight module comprises the following functional layers in sequence: a diffusion layer, an adhesive layer, a second prism layer, an adhesive layer, a first prism layer, a PET substrate, and a back coating layer. The prism directions of the first and second prism layers are orthogonal to each other.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] 1. At the beginning of the roll-to-roll production line, the PET substrate undergoes surface treatment, and a layer of functional UV-curable resin is coated on the back side of the PET substrate using a slot coating process. The back coating is then pre-cured and annealed. In other words, a low-energy UV curing process initially cures the back coating, followed by a precisely temperature-controlled annealing unit to release the internal stress generated during manufacturing and coating, and finally, complete UV curing. This back coating not only provides protection, but its thickness and curing shrinkage rate are precisely designed to counteract the asymmetric stress generated during the subsequent curing of the multi-layer optical structure on the front side, thus balancing the stress distribution across the entire film.

[0029] 2. After the first layer of quasi-randomized prism array is cured and formed, it undergoes online plasma treatment, followed by lamination with the second layer of prism film. The purpose of plasma treatment is to change the inert surface chemical properties of the cured acrylic resin layer, generating a large number of active functional groups on its surface. When the UV composite adhesive is subsequently coated, the accelerator molecules in the adhesive can chemically bond with these newly generated active functional groups, significantly improving the adhesion between the composite layers. This lays the foundation for the diffusion layer in subsequent lamination and ensures that the composite film product will not delaminate during subsequent processing.

[0030] 3. On the front side of the PET substrate, microstructures are formed using UV nanoimprint lithography. Using a master engraving mold with various combinations of spacing and height, UV resin is replicated into a quasi-randomized prism array. This structural design aims to break optical interference conditions to suppress moiré patterns that may occur when superimposed on the LCD pixel grid. Next, in the lamination process, a micron-thick layer of UV adhesive is first applied to an intermediate carrier roller. Then, the prism tips of the first prism film are brought into contact with the carrier roller, selectively transferring the adhesive to the prism peaks. Finally, the second prism film is orthogonally stacked and subjected to a second UV curing. This discontinuous lamination method preserves the functional air gaps in the prism valleys, maintaining total internal reflection conditions and avoiding brightness loss due to adhesive filling.

[0031] 4. On top of the composite double-layer prism structure, the top diffusion layer is bonded and laminated using the same lamination process and UV adhesive. This diffusion layer is composed of UV resin containing microbeads of specific size and concentration. Structurally, the diffusion layer is placed on the top layer where light exits, below which is the double-layer orthogonal prism structure, creating synergy in light processing. This layering arrangement ensures that light emitted from the backlight is first fully scattered and homogenized by the diffusion layer, eliminating uneven highlights and masking potential texture defects in the lower layers. The homogenized diffused light then enters the lower prism array for collimation and brightening. This "homogenization first, brightening later" structure ensures that the prism structure does not amplify the inhomogeneity of the light source itself, thus providing a high-brightness and uniform visual performance for the entire display screen. Attached Figure Description

[0032] Figure 1 This is a flowchart illustrating the preparation method of the composite film for high-brightness small-size backlight module in this invention. Detailed Implementation

[0033] The technical solution of the present invention will be clearly and completely described below through some embodiments and experimental examples. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0034] Reference Figure 1 The process flow diagram shown illustrates that this invention provides a composite film for high-brightness, small-size backlight modules and its preparation method. The technical solution is as follows:

[0035] Example 1

[0036] At the beginning of the production line, optical-grade PET substrate rolls are unrolled and surface-treated. Specifically, 15 W·min / m 2 With a power density of 1.5 mm and an electrode gap of 1.5 mm, the surface of the PET substrate is subjected to corona treatment under atmospheric pressure.

[0037] A functional UV-curable resin is applied to the back of the PET substrate using a slot coating process to form a back coating. This is followed by low-energy pre-curing, annealing, and then a high-energy first UV curing. The pre-curing parameters are: UV wavelength of 395nm and irradiance of 120mW / cm². 2 The exposure energy is 80 mJ / cm. 2The annealing parameters were: hold the back coating at 110℃ for 30 seconds, then cool to 25℃; the first UV curing parameters were: use a high-pressure mercury lamp as the light source, with a lamp power of 120W / cm, and a cumulative exposure energy of 1000mJ / cm in the UVA band. 2 .

[0038] The functional UV-curable resin includes: 40 parts of bisphenol A epoxy acrylate with an average molecular weight of 1000-1500 g / mol; 30 parts of pentaerythritol hexaacrylate; 20 parts of isoborneol acrylate; 3 parts of fumed silica; 3 parts of 1-hydroxycyclohexylphenyl ketone; 1.5 parts of diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide; and 0.5 parts of polyether-modified polydimethylsiloxane.

[0039] On the front side of the PET substrate with the back coating, the prism layer resin is processed by UV nanoimprint lithography. Using a master engraving mold with various spacing and height combinations, the first quasi-randomized prism array is replicated to obtain the first prism film. After repeating the above process, the PET carrier film is removed to obtain a second prism film with the same process parameters.

[0040] The operating parameters for UV nanoimprint lithography are as follows: imprinting pressure of 0.3 MPa, prism resin thickness of 35 μm, and production line speed maintained at 10 m / min. After imprinting, a high-pressure mercury lamp with a power of 160 W / cm is used during the curing process, and the cumulative exposure energy in the UVA band is 600 mJ / cm. 2 .

[0041] The prism molds include three combinations of spacing and height: all prism apex angles are 90°; unit A has a spacing of 45 μm and a height of 22.5 μm; unit B has a spacing of 55 μm and a height of 27.5 μm; and unit C has a spacing of 65 μm and a height of 32.5 μm. These three prism molds are randomly distributed. The prism layer resin includes: 50 parts bisphenol A epoxy acrylate; 20 parts 2-phenoxyethyl acrylate; 20 parts trimethylolpropane triacrylate; 5 parts isoborneol acrylate; 3 parts 1-hydroxycyclohexylphenyl ketone; and 2 parts diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide.

[0042] The first prism diaphragm was subjected to online plasma treatment, specifically: a mixture of nitrogen and oxygen in a volume ratio of 4:1 was used as the working fluid, with a flow rate of 20 L / min, a radio frequency power of 400 W, and the distance between the plasma nozzle and the surface of the prism diaphragm was maintained at 8 mm.

[0043] The UV adhesive is transferred through an intermediate carrier roller to the prism tip peak of the first prism film.

[0044] The second prism film is precisely aligned with the first one so that their prism directions are orthogonal, and then laminated together.

[0045] A second UV curing process completely cures the UV adhesive at the prism tip, forming a double-layer prism composite structure. The operating parameters for the second UV curing are: a high-pressure mercury lamp as the light source, a lamp power of 120W / cm, and a cumulative exposure energy of 1200mJ / cm in the UVA band. 2 .

[0046] The UV adhesive is transferred to the prism tip of the second prism film through an intermediate carrier roller, and then laminated and finally cured with the diffusion film to obtain the diffusion layer. All film layers from the back coating layer to the diffusion layer, namely the diffusion layer, adhesive layer, second prism layer, adhesive layer, first prism layer, PET substrate, and back coating layer, are combined to form a composite film product.

[0047] The final curing parameters are as follows: a high-pressure mercury lamp is used as the light source, with a lamp power of 160W / cm, and the cumulative exposure energy in the UVA band is 1200mJ / cm. 2 .

[0048] Examples 2-16 differ from Example 1 in operating parameters, but the other process steps and the range of raw material selection are the same.

[0049] The specific changes in operating parameters are summarized in Table 1.

[0050]

[0051] Comparative Example 1

[0052] Unlike Example 1, no back coating is provided, but all other process parameters are the same.

[0053] Comparative Example 2

[0054] Unlike Example 1, no pre-curing and annealing steps were performed; instead, the first UV curing was performed directly, while all other process parameters remained the same.

[0055] Comparative Example 3

[0056] Unlike Example 5, online plasma treatment was not performed, but all other process parameters remained the same.

[0057] Comparative Example 4

[0058] Unlike Example 5, the UV adhesive formulation does not use γ-methacryloyloxypropyltrimethoxysilane, while all other process parameters remain the same.

[0059] Comparative Example 5

[0060] Unlike Example 5, the thickness of the prism resin was adjusted to 30 μm, while all other process parameters remained the same.

[0061] Comparative Example 6

[0062] Unlike Example 9, only the prism mold assembly of Unit A is used, while all other process parameters are the same.

[0063] Comparative Example 7

[0064] Unlike Example 9, the UV adhesive is directly applied to the first and second prism films without the intermediate carrier roller transfer process, while all other process parameters remain the same.

[0065] Comparative Example 8

[0066] Unlike Example 9, only unit A and unit C are arranged alternately as a prism mold, while other process parameters are the same.

[0067] Comparative Example 9

[0068] Unlike Example 13, the diffusion layer is placed below the double-layer prism composite structure, that is, the diffusion film is directly laminated on the PET substrate, and then subsequent processes are performed on the surface of the diffusion film. All other process parameters are the same.

[0069] Comparative Example 10

[0070] Unlike Example 13, no diffusion layer was used, but all other process parameters were the same.

[0071] Experimental Example 1

[0072] The warpage and peel strength of the composite films prepared in Examples 1-4 and Comparative Examples 1-2 were tested, and the relevant results are summarized in Table 2.

[0073] The warpage test method is as follows: The composite film samples prepared in Examples 1-4 and Comparative Examples 1-2 are cut into 100mm×100mm sizes to obtain test specimens, and the maximum height (mm) of the four corner points of each specimen relative to the platform is measured. For products with uniform film thickness, the smaller the maximum height, the better the stress balance effect and the higher the flatness.

[0074] The peel strength test method is as follows: cut a 25mm wide sample strip, refer to the relevant test method of ASTM D3330 standard, peel the composite film at a rate of 300mm / min, and record the average force value (N / 25mm) during the stable phase of peeling. The larger the value, the stronger the interlayer adhesion.

[0075]

[0076] As shown in Table 2, the composite films prepared in Examples 1-4 are significantly better than those in Comparative Examples 1 and 2 in terms of flatness, indicating that the present invention has obvious advantages in balancing the internal stress of the composite film and improving the flatness of the product by setting a back coating and adopting a specific curing and annealing process.

[0077] Comparative Example 1, lacking a back coating, exhibited the most severe warping. This demonstrates that significant asymmetric stress is generated when curing a multilayer optical structure on the front side of a PET substrate. The absence of a precisely designed back coating to counteract this stress is the direct cause of the severe deformation. Comparative Example 2, although equipped with a back coating, omitted pre-curing and annealing steps. Its warping was still significantly greater than the examples. This indicates that without low-energy pre-curing and precisely temperature-controlled annealing to release the internal stress generated between the substrate and coating during processing, subsequent curing shrinkage cannot effectively balance the stress generated by the front optical structure, resulting in poor stress balancing.

[0078] In summary, this invention involves coating a layer of functional UV-curable resin onto the back of a PET substrate at the beginning of the production line, followed by low-energy pre-curing, annealing, and high-energy final curing. This back coating and its specific processing technology produce a significant synergistic effect: the back coating itself is precisely designed so that its curing shrinkage can offset the asymmetric stress generated by the multi-layer structure on the front side; while the pre-curing combined with annealing effectively releases and manages the internal stress generated in the substrate and during the coating process, ensuring that the back coating can optimally balance stress, ultimately resulting in a more balanced stress distribution throughout the composite film and significantly improving the flatness of the product.

[0079] Experimental Example 2

[0080] The peel strength of the composite film products prepared in Examples 5-8 and Comparative Examples 3-5 was tested, and the relevant results are summarized in Table 3.

[0081] The test method for peel strength is the same as that in Experimental Example 1.

[0082]

[0083] As shown in Table 3, the peel strength of the composite film products prepared in Examples 5-8 is significantly higher than that of Comparative Examples 3, 4 and 5, indicating that the present invention has a significant advantage in improving the interlayer adhesion of composite films through the combination of online plasma treatment and specific UV adhesive formulation.

[0084] Comparative Example 3, which did not undergo online plasma treatment, exhibited the worst peel strength. This demonstrates the inert chemical properties of the cured acrylate resin layer surface. Without treatment to generate active functional groups, it cannot form a strong bond with the subsequent UV adhesive. Comparative Example 4, which did not use γ-methacryloyloxypropyltrimethoxysilane in its UV adhesive, also showed a significant decrease in peel strength. This indicates that the silane coupling agent is a key accelerator molecule; without it, the adhesive cannot effectively chemically bond with the active functional groups generated on the surface after plasma treatment.

[0085] In summary, this invention involves online plasma treatment after the first layer of quasi-randomized prism array has been cured and formed. This is combined with a UV adhesive containing specific accelerator molecules, resulting in a significant synergistic effect: the plasma treatment alters the inert surface of the cured resin layer, generating a large number of active functional groups; and the silane coupling agent in the UV adhesive can chemically bond with these newly generated active functional groups. This synergistic design of the process and materials creates a strong chemical bond between the composite layers, significantly improving adhesion and ensuring that the composite film product does not delamination during subsequent processing.

[0086] Experimental Example 3

[0087] The composite film products prepared in Examples 9-12 and Comparative Examples 6-8 were tested for moiré patterns and brightness gain after being assembled onto the backlight module. The relevant results are summarized in Table 4.

[0088] The moiré pattern evaluation method is as follows: Place the sample on a standard backlight module, and use a high-resolution two-dimensional luminance meter to capture the screen image at 50% grayscale. Perform two-dimensional Fast Fourier Transform (FFT) analysis on the captured luminance image. Record the peak intensity (dB) in the low-frequency region of the FFT spectrum. The lower the peak intensity, the less obvious the moiré pattern. To eliminate the influence of the background light source, a normalized comparison method is used to determine the intensity of the moiré pattern. That is, divide the peak frequency (dB) of the moiré pattern by the amplitude (dB) of the DC component to obtain a normalized amplitude (%). The smaller the normalized amplitude, the lower the intensity of the moiré pattern.

[0089] The brightness gain test method is as follows: In a dark room, use a luminance meter to test the center point brightness (L0) when only one standard diffuser is placed on the standard backlight module, and the center point brightness (L1) after replacing it with each sample. Calculate L1 / L0. The larger the value, the better the brightness improvement effect.

[0090]

[0091] As shown in Table 4, the composite films prepared in Examples 9-12 exhibit excellent performance in both moiré stripe suppression and brightness gain, significantly outperforming Comparative Examples 6, 7, and 8. This demonstrates that the present invention, through the use of a quasi-randomized prism array and a selective adhesive transfer composite process, has a clear advantage in improving optical performance.

[0092] Comparative Example 6, using a prism mold with only a single spacing, exhibits severe moiré pattern phenomena. Comparative Example 8, using a prism mold with two different unit spacing arrangements, shows some improvement in moiré pattern phenomena, but they remain noticeable. This demonstrates that the design of this invention, using a master engraving mold with three combinations of spacing and height to replicate and form a quasi-randomized prism array, can effectively break the optical interference conditions to suppress moiré patterns generated when superimposed on the LCD pixel grid. Comparative Example 7, by directly applying UV adhesive to the prism film, shows a significant reduction in brightness gain, indicating that adhesive filling the prism valleys disrupts the total internal reflection conditions, leading to severe brightness loss.

[0093] In summary, this invention employs UV nanoimprint lithography and uses a master engraving mold with various combinations of spacing and height to replicate UV resin into a quasi-randomized prism array. Simultaneously, in the lamination process, UV adhesive is selectively transferred to the prism peaks via an intermediate carrier roller for discontinuous lamination. These two processes produce a significant synergistic effect: the quasi-randomized structural design aims to break optical interference conditions and suppress moiré fringes; while the discontinuous lamination method preserves the functional air gaps in the prism valleys, maintaining total internal reflection conditions and avoiding brightness loss due to adhesive filling. This synergistic design ensures that the product achieves high brightness gain while suppressing moiré fringes.

[0094] Experiment Example 4

[0095] The brightness uniformity and brightness gain of the composite films prepared in Examples 13-16 and Comparative Examples 9-10 were tested, and the relevant results are summarized in Table 5.

[0096] For the test method of brightness gain, please refer to Experiment Example 3.

[0097] The test method for brightness uniformity is as follows: Place each numbered sample on a standard backlight module and illuminate it. Measure the brightness values ​​of nine specified points on the screen using the ANSI 9-point method. Record the brightness of all points and calculate the brightness uniformity (%) = (lowest brightness among the nine points / highest brightness among the nine points) × 100%. The higher the value, the more uniform the screen brightness and the better the visual effect.

[0098]

[0099] As shown in Table 5, the composite films prepared in Examples 13-16 achieved high brightness uniformity while maintaining high brightness gain, and their overall performance was significantly better than that of Comparative Examples 9 and 10. This indicates that the layer sequence design of placing the diffusion layer above the double-layer prism structure in this invention has a significant advantage in optimizing visual effects.

[0100] Comparative Example 10, which does not use a diffusion layer, exhibits the worst brightness uniformity. This demonstrates that the double-prism structure itself amplifies the non-uniformity of the backlight. The diffusion layer, composed of UV resin containing specific microbeads, plays a crucial role in eliminating uneven brightness and achieving light uniformity. Comparative Example 9, which places the diffusion layer below the double-prism composite structure, also shows a significant decrease in brightness uniformity compared to the examples. This indicates that the layer sequence is critical; if the light is brightened first and then uniformized, the non-uniformity amplified by the prism structure cannot be completely corrected by the lower diffusion layer.

[0101] In summary, the present invention, in its structural design, places the diffuser layer at the top layer of light emission, below which is a double-layered orthogonal prism structure, forming a synergistic effect in light processing. Light emitted from the backlight first undergoes thorough scattering and homogenization by the diffuser layer, and then, after being homogenized and diffused, enters the prism array below for collimation and brightening. This structure, which first homogenizes and then brightens, ensures that the prism structure does not amplify the inherent non-uniformity of the light source itself. This synergistic design provides the entire display screen with a high-brightness and uniform visual performance.

[0102] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a composite film for a high-brightness, small-size backlight module, characterized in that: The preparation method is as follows: Surface treatment of PET substrate; A layer of functional UV-curable resin is coated on the back of the PET substrate to form a back coating. The prism layer resin is processed by UV nanoimprint lithography on the front side of the PET substrate to obtain the first prism film. The UV nanoimprint lithography process was repeated on the new PET carrier film, and the second prism film was obtained after removing the PET carrier film. After the first prism film is subjected to online plasma treatment, UV adhesive is attached to the surface of the first prism film; the second prism film is precisely aligned with the first prism film so that their prism directions are orthogonal to each other, and then laminated together. The UV adhesive is attached to the surface of the second prism film, and after lamination and final curing, the composite film is obtained.

2. The method for preparing a composite film for a high-brightness, small-size backlight module according to claim 1, characterized in that: After the back coating is formed, it undergoes pre-curing, annealing, and first UV curing in sequence.

3. The method for preparing a composite film for a high-brightness, small-size backlight module according to claim 1, characterized in that: In the UV nanoimprint lithography process, a master engraving mold with three combinations of spacing and height is used.

4. The method for preparing a composite film for a high-brightness, small-size backlight module according to claim 1, characterized in that: The bonding process between the first prism film and the second prism film is as follows: the UV adhesive is transferred to the prism tip peak of the first prism film through an intermediate carrier roller; after the first prism film and the second prism film are bonded together, a second UV curing treatment is performed to form a double-layer prism composite structure.

5. The method for preparing a composite film for a high-brightness, small-size backlight module according to claim 1, characterized in that: The bonding process between the second prism film and the diffusion film is as follows: the UV adhesive is transferred to the prism tip peak of the second prism film through an intermediate carrier roller, and after being laminated with the diffusion film, it is finally cured to obtain the composite film.

6. The method for preparing a composite film for a high-brightness, small-size backlight module according to claim 1, characterized in that: The UV adhesive comprises: aliphatic polyurethane acrylate and 1-hydroxycyclohexylphenyl ketone.

7. The method for preparing a composite film for a high-brightness, small-size backlight module according to claim 1, characterized in that: The diffusion membrane comprises: bisphenol A epoxy acrylate, trimethylolpropane triacrylate, and polymethyl methacrylate microspheres.

8. A composite film for a high-brightness, small-size backlight module, comprising, in sequence, the following functional layers: a diffusion layer, an adhesive layer, a second prism layer, an adhesive layer, a first prism layer, a PET substrate, and a back coating layer; characterized in that: The high-brightness small-size backlight module composite film is prepared by the preparation method described in any one of claims 1-7.

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