Optical composite film and method for manufacturing the same

Abstract

The application belongs to the technical field of optical film preparation, and discloses an optical composite film and a preparation method thereof. The optical composite film is sequentially provided with a first PC layer, a first modified solvent-free adhesive layer, a brightening core layer, a second modified solvent-free adhesive layer and a second PC layer, and is integrally formed into a composite structure symmetric in upper and lower directions. The first PC layer and the second PC layer are both optical-grade polycarbonate films. The brightening core layer is an APF acrylate polarizing film. The symmetric structure of the optical composite film makes the stress in the film layer balanced, and the size stability is strong. The symmetric optical compensation structure is relied on to eliminate the large-view-angle chromatic dispersion and stress birefringence, the white picture chromatic aberration ΔE is less than or equal to 2.0 at a large view angle of 45° to 85°, and problems such as redness and color deviation that can be seen by naked eyes are eliminated. In addition, the nano visible light absorption dopant selectively absorbs the lateral stray light, the lateral stray light transmittance is less than or equal to 3%, the problems of bright edges and side light leakage of the composite film are solved, and the picture purity is improved.

Description

Technical Field

[0001] This invention relates to the field of optical thin film preparation technology, and specifically to an optical composite film and its preparation method. Background Technology

[0002] APF acrylate polarizing film, with its high polarization efficiency, low color difference, thinness, bend resistance, and excellent optical stability, is widely used in mid-to-high-end display panels. It is often used in combination with PC polycarbonate film to achieve image polarization dimming and optical compensation. Currently, most mainstream products in the industry adopt a dual-layer asymmetric composite structure of PC / brightness enhancement core layer, and generally use solvent-based adhesive wet lamination process.

[0003] Existing technologies suffer from two major technical defects: First, solvent-based adhesives contain organic solvents, resulting in high VOC emissions and poor environmental performance during production. Solvent residues are easily present in the finished product, and defects such as bubbles, pinholes, and wrinkles are readily generated during coating and curing, leading to low product yield and poor product stability. Second, the traditional double-layer asymmetric structure exhibits uneven stress distribution, and the thermal expansion coefficients and optical parameters of the PC film and the brightness enhancement core layer are poorly matched. When observing a white screen at a large viewing angle of 45°–85°, selective transmission enhancement in the red light band and interface light interference dispersion easily occur, causing severe reddening and color shift problems. Simultaneously, conventional transparent optical adhesives lack stray light suppression capabilities, and oblique diffuse reflection and transmission light paths easily occur between film layers and on the sides, resulting in defects such as bright edges, light overflow, and side light leakage, severely affecting the image purity and visual effect of high-end displays.

[0004] The core defects of existing technologies are concentrated in two points: First, traditional solvent-based composite processes rely on large amounts of organic solvents, resulting in high VOCs, significant residues, and a tendency to generate bubbles and pinholes. Furthermore, solvent evaporation can cause micro-shrinkage of the film layer, inducing subsequent color shift and dimensional instability. Second, traditional double-layer structures are asymmetrical, lack stress control, and conventional thermosetting solvent-free adhesives result in high curing stress, poor curing uniformity, reddish tint at wide viewing angles, and severe side light leakage. Additionally, existing UV-curable optical films often employ single-power, single-wavelength curing, leading to issues such as over-curing of the surface layer, uncured inner layers, and high residual stress. Summary of the Invention

[0005] To overcome the above-mentioned defects, this invention provides an optical composite film and its preparation method. This invention is mainly applied to the production and manufacturing of core optical components such as polarizers and optical compensation films for OLED and LCD display panels. It eliminates the large-view-angle lateral light shift problem through symmetrical three-layer optical structure compensation, precise refractive index matching, and stress balance design. It also achieves selective absorption of stray light through nano-doped modified adhesive layers, thus eradicating side light leakage. The following technical solution is adopted:

[0006] In a first aspect, the present invention provides an optical composite film comprising a first PC layer, a first modified solvent-free adhesive layer, a brightness enhancement core layer, a second modified solvent-free adhesive layer, and a second PC layer stacked sequentially to form a symmetrical composite structure; both the first PC layer and the second PC layer are optical-grade polycarbonate films; the brightness enhancement core layer is an APF acrylate polarizing film. The optical composite film of the present invention has a haze of 3%–85%, an overall light transmittance ≥45%, a white screen color difference ΔE ≤2.0 at a wide viewing angle of 45°–85°, and a side stray light transmittance ≤3%.

[0007] Furthermore, neither the first PC layer nor the second PC layer has a stretching orientation direction, a thickness of 40–200 μm, an in-plane phase difference Re ≤ 5 nm, a thickness direction phase difference Rth of -20–-50 nm, a birefringence Δn ≤ 0.001, a transmittance ≥ 90%, and a thickness deviation of ≤ ± 1 μm between the two PC layers, with symmetrical optical parameters.

[0008] Furthermore, both the first and second modified solvent-free adhesive layers are cured from modified solvent-free polyurethane optical adhesive, with a hardness of Shore A 60-80 after curing and an interfacial bonding force ≥1.5N / 25mm. The thickness of both the first and second modified solvent-free adhesive layers is 5-15μm, and the refractive index n is 1.58-1.60, with a refractive index difference ≤0.01 between the first and second modified solvent-free adhesive layers and the PC layer and the brightening core layer.

[0009] Furthermore, the modified solvent-free polyurethane optical adhesive comprises, by weight, 94.0–96.0 parts of polyurethane acrylate matrix, 0.8–1.5 parts of nano-visible light absorbing dopant, 0.3–0.6 parts of photoinitiator, 0.2–0.5 parts of dispersant, and 2.0–4.0 parts of silane coupling agent; the viscosity of the modified solvent-free polyurethane optical adhesive is 800–1200 cps.

[0010] Furthermore, the visible light absorbing dopant is a compound system of surface-modified nano-carbon black and nano-organic black pigment, wherein the mass ratio of surface-modified nano-carbon black to nano-organic black pigment is 1:3 to 1:5, and the particle size is 20 to 50 nm; the photoinitiator is a UV photoinitiator.

[0011] Furthermore, the polarization axis of the brightening core layer is set parallel to the reference direction of the film surface.

[0012] Secondly, the present invention also provides a method for preparing the optical composite film described in the first aspect, comprising the following steps:

[0013] The first PC layer, the second PC layer and the brightening core layer are left to stand to eliminate substrate curling and internal stress, and then a single-sided corona activation treatment is performed.

[0014] The modified solvent-free polyurethane optical adhesive was degassed and then coated.

[0015] PC, modified solvent-free polyurethane optical adhesive, brightening core layer, modified solvent-free polyurethane optical adhesive, and PC are simultaneously laminated on both the top and bottom layers using a silicone hot press roller.

[0016] The modified solvent-free polyurethane optical adhesive is pre-cured under low-pressure mercury lamp UV to initially shape the adhesive surface and prevent sagging, and then deeply cured under high-pressure mercury lamp UV, followed by segmented heat curing.

[0017] Optical composite films are obtained by slitting.

[0018] Furthermore, the static temperature is 21–25°C and the humidity is 45–55%; the corona power of the single-sided corona activation treatment is 300–400W and the processing speed is 12–18m / min, so that the surface tension of the substrate is ≥42mN / m.

[0019] Furthermore, the dispersion rate of the degassing treatment is 1200–1500 r / min, the temperature is 50–60℃, and the vacuum degree is -0.08–-0.1 MPa; the ambient humidity of the coating environment is 45%–60%, the temperature of the silicone coating hot press roller is 52–58℃, the adhesive layer transfer linear speed is 10–15 m / min, and the single-sided dry adhesive coating amount is 8–12 g / m². 2 The composite temperature is 55–65°C, and the pressure is 0.3–0.5 MPa.

[0020] Furthermore, the ultraviolet pre-curing uses ultraviolet light with a main wavelength of 360–370 nm, and the low-pressure mercury lamp has a power of 80–120 W / cm and an irradiation energy of 300–500 mJ / cm. 2 The pre-curing speed is 10–15 m / min; the ultraviolet deep curing uses a dual-band composite irradiation with the main peak at 360–370 nm and 400–410 nm, the power of the high-pressure mercury lamp is 200–300 W / cm, and the total irradiation energy is 800–1200 mJ / cm. 2 The segmented heat treatment includes pre-cooking and deep cooking; the slitting tension is 20-30N.

[0021] Beneficial effects

[0022] 1. Stable performance and excellent weather resistance: The symmetrical structure ensures balanced internal stress and strong dimensional stability; the finished product has a light transmittance of ≥45% and a haze of 3%-85%, with no defects such as bubbles, pinholes, or wrinkles; after being tested for 500 hours of high temperature aging at 80℃ and damp heat aging at 60℃ / 90%RH, the optical performance shows no attenuation, no delamination, no secondary light leakage, and no color deviation.

[0023] 2. Improved optical image quality: This invention relies on a symmetrical optical compensation structure to eliminate large-view chromatic aberration and stress birefringence. The color difference ΔE of the white image at a large viewing angle of 45° to 85° is ≤2.0, with no visible redness or color shift. By selectively absorbing lateral stray light through a nano-doped modified adhesive layer, the lateral stray light transmittance is ≤3%, solving the problems of bright edges and side light leakage, thus improving the purity of the image.

[0024] 3. High stability: This invention uses 365nm / 405nm ultraviolet bands and high and low pressure mercury lamps for graded curing, first shaping, then deep curing, and then stress release, which solves the defects of traditional solvent-free thermosetting, such as slow curing, large residual stress, and uneven adhesive layer; the product size and optical performance are stable for a long time.

[0025] 4. Green and environmentally friendly, with no residual pollution: The entire process of this invention adopts a solvent-free composite process, with zero VOC emissions and no solvent residue, which meets international environmental protection standards and is compatible with the environmental access requirements of high-end display products.

[0026] 5. Controllable cost and high mass production yield: The process of this invention is simple and the parameters are controllable. There is no need to add a complex optical compensation structure. The production efficiency is 30% higher than that of traditional solvent processes, and the mass production yield is ≥95%, which greatly reduces the production cost and is suitable for large-scale industrial application. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the cross-sectional structure of the optical composite film of the present invention;

[0028] Figure 2 This is a comparison curve of the color deviation ΔE of the white screen under different viewing angles between Embodiment 1 of the present invention and a traditional double-layer composite film;

[0029] Figure 3 This is a schematic diagram of the microstructure of the nano-visible light absorbing dopant used in this invention to suppress light leakage. Detailed Implementation

[0030] The present invention will be further described in detail below with reference to specific embodiments. The described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0031] Example 1

[0032] Environment: Temperature 23℃, Humidity 50%, Cleanliness Class 100;

[0033] Membrane structure (such as) Figure 1The first and second PC layers are both 60 μm thick and have the same optical parameters; the upper and lower modified solvent-free adhesive layers are both 10 μm thick; the brightening core layer is 42 μm thick and has a polarization efficiency of 99.0%.

[0034] Adhesive layer composition (parts by weight): 95.7 parts polyurethane acrylate matrix, 1.1 parts nano visible light absorbing dopant, 0.4 parts photoinitiator, 0.3 parts dispersant, 2.5 parts silane coupling agent; nano carbon black: nano organic black pigment = 1:4, particle size 40nm.

[0035] Process parameters: Corona power 350W, surface tension 45mN / m; adhesive viscosity 1000cps, vacuum degassing -0.09MPa; coating weight 10g / m² 2 Composite pressure 0.4MPa, composite temperature 60℃; UV curing: 365nm / 405nm main wavelength band, low-pressure mercury lamp 100W / cm, energy 400mJ / cm. 2 High-pressure mercury lamp 250W / cm, dual-band total energy 1000mJ / cm 2 Segmented heat curing: The first segment is pre-cured at 40℃ for 12 hours to release composite stress, and the second segment is deep-cured at 48-50℃ for 12-36 hours with a cutting tension of 25N.

[0036] Performance testing: 70° wide viewing angle ΔE=1.2, side stray light transmittance 2.1%, light transmittance 45.5%, haze 0.8%, interface bonding force 2.0N / 25mm, no light leakage, no visible color shift, and excellent optical uniformity.

[0037] Example 2

[0038] The difference between this embodiment and Embodiment 1 is that the composition of the nano visible light absorbing dopant is 1.1 parts and the polyurethane acrylate matrix is ​​96.0 parts, while the other parameters are the same as those in Embodiment 1.

[0039] Adhesive layer components (parts by weight): 96.0 parts polyurethane acrylate matrix, 0.8 parts nano visible light absorbing dopant, 0.4 parts photoinitiator, 0.3 parts dispersant, and 2.5 parts silane coupling agent.

[0040] Performance testing: 70° wide viewing angle ΔE=1.9, side stray light transmittance 2.8%, light transmittance 46.2%, haze 1.2%, interface adhesion 1.9N / 25mm.

[0041] Example 3

[0042] The difference between this embodiment and Embodiment 1 is that the composition of the nano visible light absorbing dopant is 1.5 parts and the polyurethane acrylate matrix is ​​95.3 parts, while the other parameters are the same as those in Embodiment 1.

[0043] Adhesive layer components (parts by weight): 95.3 parts polyurethane acrylate matrix, 1.5 parts nano visible light absorbing dopant, 0.4 parts photoinitiator, 0.3 parts dispersant, and 2.5 parts silane coupling agent.

[0044] Performance test: 70° wide viewing angle ΔE=1.0, side stray light transmittance 1.8%, light transmittance 43.1%, haze 1.5%, interface bonding force 1.7N / 25mm, the light leakage suppression effect is the best, but the light transmittance is slightly reduced.

[0045] Example 4

[0046] The difference between this embodiment and Embodiment 1 is that the power of the ultraviolet low-pressure curing mercury lamp is 80W / cm and the irradiation energy is 300mJ / cm. 2 The remaining parameters are the same as in Example 1.

[0047] UV low-pressure curing parameters: Mercury lamp power 80W / cm, irradiation energy 300mJ / cm 2 The curing speed is 12 m / min; the high-pressure curing parameters remain unchanged (250 W / cm, 1000 mJ / cm). 2 ).

[0048] Performance testing: Adhesive layer crosslinking degree 90%, 70° wide viewing angle ΔE=1.8, side stray light transmittance 2.6%.

[0049] Example 5

[0050] The difference between this embodiment and Embodiment 1 is that the power of the mercury lamp used for ultraviolet low-pressure curing is 120W / cm, and the irradiation energy is 500mJ / cm. 2 The remaining parameters are the same as in Example 1.

[0051] Performance testing: The cross-linking degree of the adhesive layer is 98%, the ΔE is 1.1 at a 70° wide viewing angle, and the side stray light transmittance is 2.0%; however, local UV over-curing has increased the micro-stress of the film layer, and the haze has slightly increased to 1.1%.

[0052] Example 6

[0053] The difference between this embodiment and Embodiment 1 is that the power of the ultraviolet high-pressure curing mercury lamp is 200W / cm, and the total irradiation energy is 800mJ / cm. 2 The remaining parameters are the same as in Example 1.

[0054] Performance testing: The adhesive layer is not fully cured in the deep layers, with a cross-linking degree of 92%, a 70° wide viewing angle ΔE=1.7, a side light transmittance of 2.5%, and average long-term weather resistance.

[0055] Example 7

[0056] The difference between this embodiment and Embodiment 1 is that the power of the ultraviolet high-pressure curing mercury lamp is 300W / cm, and the total irradiation energy is 1200mJ / cm. 2 The remaining parameters are the same as in Example 1.

[0057] Performance testing: Complete curing with no residue, but the ultra-high energy caused slight thermal stress in the adhesive layer, resulting in a slight decrease in film smoothness and an increase in haze to 1.3%.

[0058] Example 8

[0059] The difference between this embodiment and Embodiment 1 is that the single-sided dry adhesive coating amount is adjusted to 8g / m². 2 The remaining parameters are the same as in Example 1.

[0060] Performance testing: The adhesive layer thickness is relatively thin and the uniformity is average. Local light leakage suppression is uneven. The side stray light transmittance is 2.9%, and the interface bonding strength is 1.6N / 25mm.

[0061] Example 9

[0062] The difference between this embodiment and Embodiment 1 is that the single-sided dry adhesive coating amount is 12g / m². 2 The remaining parameters are the same as in Example 1. Performance test: The adhesive layer is thicker, the curing stress is increased, the maximum visual aberration increases slightly to 1.4, and the haze is 1.2%.

[0063] Comparative Example 1

[0064] This comparative example uses a traditional PC / APF dual-layer solvent-based composite membrane.

[0065] Composite structure: 60μm PC layer + 15μm solvent-based acrylic adhesive layer + 42μm APF layer, prepared by traditional solvent coating wet composite process, without UV curing and without nano-doping modification.

[0066] Performance test results: 70° wide-view white screen ΔE=5.8, severe redness observed by the naked eye; side stray light transmittance 18.6%, obvious light leakage and bright edge defects at the edges; overall light transmittance 43.5%; haze 2.5%; interface adhesion 1.2N / 25mm; after aging, slight delamination, color shift and increased light leakage occurred.

[0067] According to Examples 1-3, as the mass fraction of the nano-visible light absorbing dopant increases, the side stray light transmittance gradually decreases, the light transmittance gradually decreases, and the interfacial bonding force gradually increases. Overall, when the mass fraction of the nano-visible light absorbing dopant is 1.1, the leakage suppression, light transmittance, and interfacial bonding force reach the optimal balance.

[0068] According to Examples 1, 4, and 5, as the power and irradiation energy of the UV low-pressure curing mercury lamp increase, the degree of cross-linking of the adhesive layer gradually increases, the 70° wide viewing angle ΔE gradually increases, and the side stray light transmittance gradually decreases. Therefore, when the power of the UV low-pressure curing mercury lamp is 100 W / cm and the irradiation energy is 400 mJ / cm, the cross-linking degree of the adhesive layer gradually increases, the 70° wide viewing angle ΔE gradually increases, and the side stray light transmittance gradually decreases. 2 When cured evenly without dripping, it shows no performance degradation after 500 hours of aging, exhibiting optimal overall performance.

[0069] According to Examples 1, 6, and 7, as the power and irradiation energy of the ultraviolet high-pressure curing mercury lamp increase, the degree of cross-linking of the adhesive layer gradually increases, while the smoothness of the film gradually decreases. Therefore, when the power of the ultraviolet high-pressure curing mercury lamp is 250 W / cm and the total irradiation energy is 1000 mJ / cm, the cross-linking degree of the adhesive layer gradually increases, while the smoothness of the film gradually decreases. 2 At this time, light transmittance, haze, and bonding strength all reach the optimal balance.

[0070] According to Examples 1, 8, and 9, as the coating amount increases, the adhesive layer thickness gradually increases, and the curing stress also increases accordingly. Therefore, when the coating amount is 10 g / m², the adhesive layer thickness gradually increases, and the curing stress also increases accordingly. 2 At this time, the adhesive layer thickness is uniform, the stress is balanced, and the interfacial bonding strength is the highest.

[0071] According to Example 1 and Comparative Example 1, as Figure 2 The horizontal axis represents the viewing angle (0°, 30°, 60°, 70°, 85°), and the vertical axis represents the color difference value ΔE of the white screen. Among them, the curve of the composite film of the present invention is stable and low throughout, with a maximum ΔE ≤ 2.0; the curve of the traditional double-layer composite film increases sharply with the increase of the viewing angle, with ΔE ≥ 5.0 at a large viewing angle, which directly verifies the redness improvement effect of the present invention at a large viewing angle.

[0072] like Figure 2 As shown, the rectangular area is a modified solvent-free polyurethane optical adhesive, and the ellipse represents uniformly and discretely distributed nano-visible light absorbing doped particles. The vertical display light path penetrates the adhesive layer vertically without affecting the front light transmission display; the side stray light is intercepted and absorbed after contacting the nanoparticles, reflecting the selective optical control principle of "high front light transmission and side light leakage suppression".

[0073] In summary, using a nano-visible light absorbing dopant with a mass fraction of 1.1 parts, a low-pressure curing mercury lamp with a power of 100 W / cm, and an irradiation energy of 400 mJ / cm, the optimal method was successful. 2 The high-pressure mercury curing lamp has a power of 250W / cm and a total irradiation energy of 1000mJ / cm. 2 The coating amount is 10g / m² 2 When the optical composite film of the present invention is in use, all optical properties are optimal.

Claims

1. An optical composite film, characterized in that, The first PC layer, the first modified solvent-free adhesive layer, the brightness enhancement core layer, the second modified solvent-free adhesive layer, and the second PC layer are stacked sequentially to form a symmetrical composite structure. The first PC layer and the second PC layer are both optical-grade polycarbonate films. The brightness enhancement core layer is an APF acrylate polarizing film.

2. The optical composite film according to claim 1, characterized in that, Both the first and second PC layers have no stretching orientation, a thickness of 40–200 μm, an in-plane phase difference Re ≤ 5 nm, a thickness-direction phase difference Rth of -20–-50 nm, a birefringence Δn ≤ 0.001, a transmittance ≥ 90%, and a thickness deviation of ≤ ± 1 μm between the two PC layers, with symmetrical optical parameters.

3. The optical composite film according to claim 1, characterized in that, Both the first modified solvent-free adhesive layer and the second modified solvent-free adhesive layer are cured from modified solvent-free polyurethane optical adhesive, and the hardness after curing is Shore A 60-80. The thickness of both the first and second modified solvent-free adhesive layers is 5-15 μm, the refractive index n is 1.58-1.60, and the difference in refractive index between the first and second modified solvent-free adhesive layers and the PC layer and the brightening core layer is ≤0.

01.

4. The optical composite film according to claim 3, characterized in that, The modified solvent-free polyurethane optical adhesive comprises, by weight, 94.0–96.0 parts of polyurethane acrylate matrix, 0.8–1.5 parts of nano-visible light absorbing dopant, 0.3–0.6 parts of photoinitiator, 0.2–0.5 parts of dispersant, and 2.0–4.0 parts of silane coupling agent; the viscosity of the modified solvent-free polyurethane optical adhesive is 800–1200 cps.

5. The optical composite film according to claim 4, characterized in that, The visible light absorbing dopant is a compound system of surface-modified nano carbon black and nano organic black pigment, wherein the mass ratio of surface-modified nano carbon black to nano organic black pigment is 1:3 to 1:5, and the particle size is 20 to 50 nm; the photoinitiator is a UV photoinitiator.

6. The optical composite film according to claim 1, characterized in that, The polarization axis of the brightening core layer is set parallel to the reference direction of the film surface.

7. A method for preparing an optical composite film according to any one of claims 1-6, characterized in that, Includes the following steps: After the first PC layer, the second PC layer and the brightening core layer are left to stand, a single-sided corona activation treatment is performed. The modified solvent-free polyurethane optical adhesive was degassed and then coated. PC, modified solvent-free polyurethane optical adhesive, brightening core layer, modified solvent-free polyurethane optical adhesive, and PC are simultaneously laminated on both the top and bottom layers using a silicone hot press roller. The modified solvent-free polyurethane optical adhesive was subjected to UV pre-curing and UV deep curing, followed by segmented thermal curing. Optical composite films are obtained by slitting.

8. The preparation method according to claim 7, characterized in that, The static temperature is 21–25°C, and the humidity is 45–55%. The corona power of the single-sided corona activation treatment is 300–400W, and the processing speed is 12–18 m / min.

9. The preparation method according to claim 7, characterized in that, The degassing treatment involves a dispersion rate of 1200–1500 r / min, a temperature of 50–60°C, and a vacuum degree of -0.08–-0.1 MPa. The coating environment has a humidity of 45%–60%, a silicone hot press roller temperature of 52–58°C, an adhesive layer transfer linear speed of 10–15 m / min, and a single-sided dry adhesive coating weight of 8–12 g / m². 2 The composite temperature is 55–65°C, and the pressure is 0.3–0.5 MPa.

10. The preparation method according to claim 7, characterized in that, The ultraviolet pre-curing process uses ultraviolet light with a main wavelength of 360–370 nm, a low-pressure mercury lamp with a power of 80–120 W / cm, and an irradiation energy of 300–500 mJ / cm. 2 The pre-curing speed is 10–15 m / min; the ultraviolet deep curing uses a dual-band composite irradiation with a main peak of 360–370 nm and 400–410 nm, the power of the high-pressure mercury lamp is 200–300 W / cm, and the total irradiation energy is 800–1200 mJ / cm. 2 The segmented heat treatment includes pre-cooking and deep cooking; the slitting tension is 20-30N.

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