Triacetylcellulose optical film and method for producing the same

Abstract

The application discloses a kind of cellulose triacetate optical films and preparation method thereof, cellulose triacetate optical film component includes cellulose triacetate resin and alicyclic oligocarbonate type optical additive, with the mass of cellulose triacetate as benchmark, the addition amount of the alicyclic oligocarbonate type optical additive is 5-10 wt%, and the number average molecular weight of the alicyclic oligocarbonate type optical additive is 900-1800.The optical film prepared from the composition of the application realizes the synergistic improvement of water vapor barrier property and hygrothermal haze stability without significantly sacrificing optical performance, and has stable and reliable and repeatable technical effect.

Description

Technical Field

[0001] This invention relates to the field of cellulose triacetate optical film compositions, and more specifically to a cellulose triacetate optical film and its preparation method. Background Technology

[0002] Cellulose triacetate (TAC) has long been widely used in polarizer protective films and related optical functional films in display devices such as liquid crystal displays (LCDs) and organic light-emitting diodes (OLEDs) due to its excellent optical uniformity, low birefringence, good mechanical properties, and mature solution casting processing technology. As display technology develops towards larger sizes, higher resolutions, and higher reliability, the service environments faced by display devices are becoming increasingly harsh, especially under high temperature and high humidity conditions. The dimensional stability, optical uniformity, and long-term reliability of TAC optical films have become critical issues that urgently need to be addressed. Among these, high water vapor transmission rate (WVTR) and increased haze during damp heat aging are significant technical bottlenecks restricting the further application of TAC optical films.

[0003] To reduce the water vapor transmittance of TAC optical films and improve their humid heat stability, various methods have been adopted, but existing technologies generally have the following shortcomings: First, it is difficult to balance moisture barrier performance and optical performance. Existing moisture barrier modification methods often reduce water vapor transmittance while increasing haze or enhancing light scattering, making it difficult to simultaneously meet the comprehensive performance requirements of low water vapor transmittance and low haze. In addition, most existing technologies are insufficient for systematically improving haze stability under high temperature and high humidity long-term service conditions.

[0004] Therefore, there is an urgent need to provide a new technology for modifying cellulose triacetate optical films to improve their moisture barrier and haze properties. Summary of the Invention

[0005] To address the aforementioned problems, the present invention aims to provide a cellulose triacetate optical film and its preparation method. The optical film prepared by the composition of the present invention achieves a synergistic improvement in water vapor barrier performance and humid heat haze stability without significantly sacrificing optical performance, and exhibits good haze stability under long-term service conditions of high temperature and high humidity.

[0006] This invention is achieved through the following technical solution: A cellulose triacetate optical film comprises cellulose triacetate resin and an alicyclic oligocarbonate optical additive. Based on the mass of cellulose triacetate, the alicyclic oligocarbonate optical additive is added at an amount of 5–10 wt%, and the number average molecular weight of the alicyclic oligocarbonate optical additive is 900–1800. In practice, commercially available plasticizers, such as glycoesters, polyesters, or acrylic plasticizers, can also be added to improve the film-forming properties and flowability of the solution during film formation.

[0007] The alicyclic oligocarbonate optical additive is added at an amount of 7–8 wt%. The number average molecular weight of the alicyclic oligocarbonate optical additive is 1500–1700.

[0008] The alicyclic oligocarbonate type optical additive is one or more of 1,4-cyclohexanedimethyl carbonate, hydrogenated bisphenol A carbonate, or norbornenedimethyl carbonate.

[0009] By introducing the alicyclic oligocarbonate-type optical additive into a cellulose triacetate matrix and adding it in controlled quantities Within the aforementioned specific range, the optical additive can form a stable and uniform distribution between cellulose triacetate molecular chains. Its alicyclic backbone (1,4-cyclohexanedimethyl, hydrogenated bisphenol A, or norbornene structure) endows the molecular chains with high rigidity and low polarizability. The carbonate groups achieve molecular-level uniform dispersion through dipole-dipole interactions and hydrogen bonding with the cellulose triacetate ester groups, avoiding light scattering caused by phase separation or local enrichment. At the same time, the number-average molecular weight of the oligocarbonate is precisely controlled within the range of 900–1800, which can effectively fill the free volume after film formation, reduce the diffusion rate of water molecules, and suppress the increase in haze caused by chain segment rearrangement under high temperature and high humidity conditions.

[0010] Therefore, this invention also discloses the use of alicyclic oligocarbonates as additives in optical films to synergistically optimize the haze and moisture-blocking properties of optical films. The preparation method of alicyclic oligocarbonates can be as follows: an alicyclic dihydroxy compound and a carbonate reagent undergo a polycondensation reaction in a reactor equipped with stirring, condensation, and vacuum control devices (e.g., alicyclic dihydroxy compounds such as 1,4-cyclohexanediethanol, hydrogenated bisphenol A, or norbornenediethanol react with reagents such as diphenyl carbonate, dimethyl carbonate, or diethyl carbonate in an equimolar ratio for 3-6 hours under the action of a catalyst). The temperature is raised to 120-160 °C under nitrogen protection, and vacuum is gradually applied to remove reaction byproducts. After the reaction is completed, the material is cooled and discharged to obtain the alicyclic oligocarbonate product. The catalyst is zinc acetylacetonate Zn(Acac)2 (0.2 wt% of the total reactants) and cesium carbonate Cs2CO3 (0.05 wt% of the total reactants), with a mass ratio of 4:1. The alicyclic oligocarbonates prepared by this method have a number-average molecular weight of 900–1800 and a molecular weight distribution (Mw / Mn) of 1.8–2.5. Furthermore, the Mw / Mn distribution of 1.8–2.5 completely eliminates the influence of end-molecule components, thereby achieving extremely low migration rates and very high consistency in moisture barrier properties and haze between batches, with stable haze changes after damp heat aging.

[0011] An optical element comprising a cellulose triacetate optical film as described in any of the preceding claims. The optical element may be a polarizer, a liquid crystal display panel, a phase compensation film, etc.

[0012] A method for preparing a cellulose triacetate optical thin film includes the following steps: (1) Solvent preparation and cotton glue preparation: Dichloromethane, methanol and butanol are mixed in a mass ratio of 90-91%:8-10%:0.10-0.15% to form a mixed solvent. Cellulose triacetate resin is dissolved in the mixed solvent to prepare a cotton glue solution with a mass fraction of 10-15 wt%. (2) Adding optical additives: Add 5-10 wt% of alicyclic oligocarbonate type optical additives to the cotton glue solution, stir to dissolve and form a homogeneous solution, cast the homogeneous cotton glue solution into a film, stretch and dry the film to obtain a cellulose triacetate optical film.

[0013] Compared with the prior art, the present invention has the following advantages and beneficial effects: The optical films prepared by the compositions of this invention significantly reduce the water vapor transmittance of cellulose triacetate optical films under low addition conditions, effectively suppress the increase of film haze under high temperature and high humidity aging conditions, and maintain excellent optical uniformity. In this invention, the moisture barrier performance and haze control do not show a simple linear improvement relationship with the increase of addition amount, but rather exhibit a synergistic optimization effect based on the combination window of specific molecular weight and addition amount of additives. When the parameters deviate from this combination window, it is difficult to simultaneously achieve both moisture barrier performance and optical performance of the film. The alicyclic oligocarbonate type optical additives used in this invention have good compatibility with the cellulose triacetate system, strong process adaptability, and are suitable for industrial scale-up applications. Detailed Implementation

[0014] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the embodiments. The illustrative embodiments and descriptions of this invention are only used to explain this invention and are not intended to limit this invention.

[0015] Example 1: (1) Solvent preparation and cotton glue preparation: Dichloromethane, methanol and butanol were mixed in a mass ratio of 90%:9.9%:0.1% to form a mixed solvent. 100 g of cellulose triacetate was weighed and dissolved in the mixed solvent to prepare a cotton glue solution with a mass fraction of 15 wt%.

[0016] (2) Adding optical additives: 1,4-cyclohexanedimethyl carbonate with a number average molecular weight of 900 is selected and added to the cotton glue solution at an amount of 5 wt% of the mass of cellulose triacetate. The solution is stirred and dissolved at room temperature to form a homogeneous solution.

[0017] (3) Cotton glue treatment: Heat the cotton glue solution to 80°C for high-temperature dissolution, maintain for 15 min and then cool to 35°C, and remove impurities by filtration multiple times.

[0018] (4) Casting film: The treated cotton glue solution is pumped to the casting machine and cast on a stainless steel strip (temperature <80℃, initial liquid film solvent content is about 81%, and wet film solvent content drops to 30% after drying).

[0019] (5) Stretching and drying: After the wet film is peeled off, it is stretched (temperature <130℃, solvent reduced to 10%), trimmed once (temperature about 60℃, solvent reduced to 8-9%) and then put into the drying oven (temperature <140℃) to dry to a solvent content of 3%.

[0020] (6) Post-processing: After secondary edge trimming, edge embossing, online inspection, and balanced winding, the dry film thickness was controlled to 60 μm to obtain a cellulose triacetate optical film. The solvent volatilized during the drying process was recovered and reused by condensation at -42℃.

[0021] Water vapor transmission rate was tested at 40 ℃ and 90%RH; haze change was measured before and after aging at 85 ℃ and 95%RH for 120 h. The resulting film had a water vapor transmission rate of 520 g / m²·24 h and a haze change of 0.05%.

[0022] Example 2: The method of Example 1 was followed, except that the ratio of dichloromethane, methanol and butanol in the mixed solvent was 91%:8.85%:0.15%, and 1,4-cyclohexanedimethyl carbonate with a number average molecular weight of 1300 was added to the cellulose triacetate system at an addition amount of 6 wt% of the cellulose triacetate mass to prepare an optical film.

[0023] The water vapor transmission rate of the obtained film was 500 g / m²·24 h, and the haze change was 0.04%.

[0024] Example 3: The method of Example 1 was followed, except that 1,4-cyclohexanedimethyl carbonate with a number average molecular weight of 1500 was added to the cellulose triacetate system at an addition amount of 7 wt% of the mass of cellulose triacetate to prepare an optical film.

[0025] The water vapor transmission rate of the obtained film was 480 g / m²·24 h, and the haze change was 0.03%.

[0026] Example 4: The method of Example 1 was followed, except that 1,4-cyclohexanedimethyl carbonate with a number average molecular weight of 1700 was added to the cellulose triacetate system at an addition amount of 8 wt% of the cellulose triacetate mass to prepare an optical film.

[0027] The water vapor transmission rate of the obtained film was 470 g / m²·24 h, and the haze change was 0.04%.

[0028] Example 5: The method of Example 1 was followed, except that hydrogenated bisphenol A carbonate with a number average molecular weight of 1200 was added to the cellulose triacetate system at an addition amount of 9 wt% of the cellulose triacetate mass to prepare an optical film.

[0029] The water vapor transmission rate of the obtained film was 460 g / m²·24 h, and the haze change was 0.06%.

[0030] Example 6: The method of Example 1 was followed, except that norbornene dimethyl carbonate with a number average molecular weight of 1400 was added to the cellulose triacetate system at an addition amount of 10 wt% of the cellulose triacetate mass to prepare an optical film.

[0031] The water vapor transmission rate of the obtained film was 450 g / m²·24 h, and the haze change was 0.07%.

[0032] Example 7: The method of Example 1 was followed, except that 1,4-cyclohexanedimethyl carbonate with a number average molecular weight of 1800 was added to the cellulose triacetate system at an addition amount of 6 wt% of the mass of cellulose triacetate to prepare an optical film.

[0033] The water vapor transmission rate of the obtained film was 510 g / m²·24 h, and the haze change was 0.05%.

[0034] Comparative Example 1 The procedure was carried out according to Example 1, except that no alicyclic oligocarbonate optical additives were added, while all other conditions remained the same.

[0035] The water vapor transmission rate of the obtained film was 650 g / m²·24 h, and the haze change was 0.12%.

[0036] Comparative Example 2 The method was carried out as in Example 1, except that 1,4-cyclohexanedimethyl carbonate with a number average molecular weight of 640 was introduced into the cellulose triacetate system at an addition amount of 6 wt%.

[0037] The water vapor transmission rate of the obtained film was 560 g / m²·24 h, and the haze change was 0.10%.

[0038] Comparative Example 3 The method was carried out as in Example 1, except that 1,4-cyclohexanedimethyl carbonate with a number average molecular weight of 2200 was introduced into the cellulose triacetate system at an addition amount of 6 wt%.

[0039] The water vapor transmission rate of the obtained film was 540 g / m²·24 h, and the haze change was 0.11%.

[0040] Comparative Example 4 The method was carried out as in Example 1, except that 1,4-cyclohexanedimethyl carbonate with a number average molecular weight of 1300 was introduced into the cellulose triacetate system at an addition amount of 3 wt%.

[0041] The water vapor transmission rate of the obtained film was 580 g / m²·24 h, and the haze change was 0.09%.

[0042] Comparative Example 5 The method was carried out as in Example 1, except that 1,4-cyclohexanedimethyl carbonate with a number average molecular weight of 1300 was introduced into the cellulose triacetate system at an addition amount of 12 wt%.

[0043] The resulting film had a water vapor transmission rate of 470 g / m²·24 h and a haze change of 0.15%. When the addition amount exceeded 10 wt%, although the water vapor transmission rate may continue to decrease, the haze deteriorated significantly and could no longer meet the comprehensive requirements of optical films for low haze.

[0044] The results of the above embodiments and comparative examples are shown in Table 1.

[0045]

[0046] The above examples and comparative examples clearly demonstrate that only when the molecular weight and dosage of the alicyclic oligocarbonate optical additive are both within the combined window range defined by this invention can the water vapor transmittance be significantly reduced while effectively controlling haze changes, thus demonstrating a synergistic optimization effect between moisture barrier performance and optical performance. When the molecular weight or dosage deviates from this window range, at least one performance indicator shows significant deterioration, making it impossible to simultaneously achieve both moisture barrier performance and optical performance. Looking at a 5%-10% change in dosage, the water vapor transmittance shows a decreasing trend, while the haze change first decreases and then increases, requiring a specific range of conditions to achieve synergistic optimization of moisture barrier performance and haze change.

[0047] The above embodiments and comparative examples fully demonstrate the effectiveness, stability, and synergistic optimization effect of the technical solution of the present invention within a specific combination window range. In actual implementation, the triacetate cellulose optical film of the present invention can also be further improved by adding commercially available plasticizers to enhance the flowability and film-forming processing performance of the cellulose adhesive solution.

[0048] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A cellulose triacetate optical film, characterized in that, Its components include cellulose triacetate resin and alicyclic oligocarbonate optical additives. Based on the mass of cellulose triacetate, the amount of alicyclic oligocarbonate optical additives added is 5–10 wt%, and the number average molecular weight of alicyclic oligocarbonate optical additives is 900–1800.

2. The cellulose triacetate optical film according to claim 1, characterized in that, The amount of the alicyclic oligocarbonate optical additive added is 7–8 wt%.

3. The cellulose triacetate optical film according to claim 1, characterized in that, The number average molecular weight of alicyclic oligocarbonate optical additives is 1500-1700.

4. The cellulose triacetate optical film according to claim 1, characterized in that, The alicyclic oligocarbonate type optical additive is one or more of 1,4-cyclohexanedimethyl carbonate, hydrogenated bisphenol A carbonate, or norbornenedimethyl carbonate.

5. The method for preparing cellulose triacetate optical thin films according to any one of claims 1-4, characterized in that, Includes the following steps: (1) Solvent preparation and cotton glue preparation: Dichloromethane, methanol and butanol are mixed in a mass ratio of 90-91%:8-10%:0.10-0.15% to form a mixed solvent. Cellulose triacetate resin is dissolved in the mixed solvent to prepare a cotton glue solution with a mass fraction of 10-15wt%. (2) Adding optical additives: Add 5-10 wt% of alicyclic oligocarbonate type optical additives to the cotton glue solution, stir to dissolve and form a homogeneous solution, cast the homogeneous cotton glue solution into a film, stretch and dry the film to obtain a cellulose triacetate optical film.

6. An optical element, characterized in that, Including cellulose triacetate optical films as described in any one of claims 1-4.

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