Cellulose ester film and polaroid prepared from cellulose ester film

Abstract

The cellulose ester film contains one or more than one additive (A) and one or more than one additive (B), the additive (A) is a sugar ester compound containing at least one of 1-12 pyranose structures or furanose structures, and the additive (B) is a trimethylolpropane triphenyl ester compound containing condensation of tribenzoic acid and trimethylolpropane. According to the cellulose ester film disclosed by the invention, the mechanical strength and the dimensional stability of the film are improved by optimizing a formula and a two-way stretching design, and good structural integrity can still be kept in a high-temperature and high-humidity environment; the cellulose ester film disclosed by the invention has low moisture permeability, can effectively block moisture permeation, and can prevent a polarizer from being degraded in a high-temperature and high-humidity environment when being attached to the polarizer; the cellulose ester film provided by the invention has excellent dimensional stability, can maintain good dimensional stability under the conditions of large size and thinness, and effectively solves the problem that the cellulose ester film is easy to deform in a high-temperature and high-humidity environment.

Description

Technical Field

[0001] This invention belongs to the field of optical film technology, specifically relating to a cellulose ester film and a polarizer made therefrom. Background Technology

[0002] In the construction of liquid crystal display (LCD) devices, the polarizer is one of the key components. To protect the polarizer's polarizer, a cellulose ester film is typically used as a protective film. Cellulose ester films possess excellent transmittance, optical homology, and mechanical properties, and have been widely applied. LCD devices are not only used in personal computer monitors but also in television displays, and their size and brightness have increased accordingly; simultaneously, the demand for thinner designs has also risen.

[0003] However, large-size, thin polarizers are susceptible to changes in environmental conditions such as temperature and humidity, leading to deterioration at the edges and highlighting of black areas in the image, thus reducing contrast. This aging of the polarizer may be due to shrinkage or dimensional changes in the protective film, necessitating improvements in the dimensional stability of the cellulose ester film.

[0004] Thinning of cellulose ester films can also increase the moisture permeability of the product, making it unable to adequately block moisture. When made into polarizing films, the adhesive or polarizer may sometimes deteriorate. Simply increasing the amount of plasticizer added will not sufficiently improve the moisture permeability and may also cause new problems such as changes in product size and precipitation.

[0005] In the invention patents with publication numbers JP5023837B2 and CN104603174B, although cellulose ester films with good optical anisotropy and excellent moisture permeability can be obtained by adding polymers or polyester resins with lactone ring structures, the durability of the products is poor and the dimensional change rate of the products is large under high temperature and high humidity conditions. Summary of the Invention

[0006] In response to the problems raised in the background art, this invention studies and designs a cellulose ester film and the polarizer prepared therefrom. The cellulose ester film contains one or more sugar ester compounds and one or more trimethylolpropane triphenyl ester compounds. It has low moisture permeability and can effectively block moisture. Even under the conditions of large size and thinness, the cellulose ester film can maintain good dimensional stability, good optical performance and low haze.

[0007] A cellulose ester membrane comprising one or more additives (A) and one or more additives (B),

[0008] Wherein, additive (A): contains at least one sugar ester compound with 1 to 12 pyranose or furanose structures, as shown in general formula (I):

[0009]

[0010] In the formula: R1 to R8 each represent a substituted or unsubstituted alkyl carbonyl or aryl carbonyl, and R1 to R8 can be the same or different;

[0011] Additive (B): A compound containing trimethylolpropane triphenyl ester, which is a product of the condensation of tribenzoic acid and trimethylolpropane, as shown in general formula (II):

[0012]

[0013] In the formula: R9, R 10 and R 11 It represents hydrogen atoms, alkyl groups with 1 to 4 carbon atoms, or alkoxy groups with 1 to 4 carbon atoms; n1 to n3 represent 1 to 3.

[0014] Preferably, the degree of substitution of the sugar ester compound represented by general formula (I) is 4.5 to 8.0, more preferably 5.0 to 7.5.

[0015] Preferably, R9 and R in the general formula (II) 10 and R 11 At least one is a hydrogen atom.

[0016] Preferably, the cellulose ester membrane, after being placed at 85°C and 85% RH for 1000 hours, exhibits a dimensional change rate of less than 0.5%, more preferably less than 0.3%.

[0017] Preferably, the cellulose ester membrane, after being placed at 85°C and 85%RH for 1000 hours, has a deformation angle of less than 1°, more preferably less than 0.8°, and even more preferably less than 0.5°.

[0018] Preferably, the cellulose ester film is a biaxially oriented cellulose ester film.

[0019] Preferably, the moisture permeability of the cellulose ester membrane is 350–850 g / m²·d.

[0020] Preferably, the content of additives in the cellulose ester film is equivalent to 2-30 wt% of the mass of the cellulose resin, more preferably 5-20 wt%.

[0021] Preferably, the thickness of the cellulose ester film is 10–60 μm, more preferably 20–40 μm.

[0022] A polarizer having at least one of the cellulose ester films described above.

[0023] The beneficial effects of this invention are as follows: The cellulose ester membrane of this invention, through optimized formulation and biaxial stretching design, improves the mechanical strength and dimensional stability of the film, enabling it to maintain good structural integrity even under high temperature and high humidity environments; the cellulose ester membrane of this invention has low moisture permeability, which can effectively block moisture penetration; when the cellulose ester membrane is attached to the polarizer, it can prevent the deterioration of the polarizer under high temperature and high humidity environments; the cellulose ester membrane of this invention has excellent dimensional stability, maintaining good dimensional stability even under large-size and thin-film conditions, effectively solving the problem of easy deformation of cellulose ester membranes under high temperature and high humidity environments. Detailed Implementation

[0024] The present invention will be further described below with reference to specific embodiments.

[0025] (cellulose resin)

[0026] Cellulose resins used as raw materials for cellulose ester films include cotton pulp fibers and wood pulp (broadleaf wood pulp, softwood pulp), etc. Cellulose ester films obtained from cellulose resins of any raw materials can be used, or two or more cellulose resins can be mixed for use.

[0027] In the cellulose ester film prepared by this invention, the cellulose resin preferably comprises cellulose acetate, cellulose diacetate, cellulose triacetate, cellulose acetate propionate, cellulose acetate butyrate, cellulose acetate phthalate, polycaprolactone, and grafted cellulose acetate. Among these, acetylated celluloses such as cellulose acetate, cellulose diacetate, and cellulose triacetate are more preferred in terms of mechanical properties (tensile strength, flexural strength, and flexural elasticity).

[0028] When the cellulose is acetylated cellulose, the degree of polymerization is preferably 200–50, more preferably 250–400. If the polymerization degree of acetylated cellulose is too high, the viscosity of the acetylated cellulose solution will become too high, making it difficult to produce cellulose ester films through the casting process, and therefore this is not preferred. If the polymerization degree of acetylated cellulose is too low, the strength of the produced cellulose ester film will be reduced, and therefore this is also not preferred. The degree of acetylation is preferably 54.0%–62.5%, more preferably 58.0%–62.5%.

[0029] (glycoester compounds)

[0030] The cellulose ester membrane of the present invention contains at least one sugar ester compound having 1 to 12 pyranose or furanose structures, as shown in general formula (I):

[0031]

[0032] In the formula: R1 to R8 each represent a substituted or unsubstituted alkyl carbonyl or aryl carbonyl, and R1 to R8 can be the same or different.

[0033] The number average molecular weight of the sugar ester compound is preferably 200-3500, more preferably 200-3000, and even more preferably 250-2000. The degree of substitution of the sugar ester compound is preferably 4.5-8.0, more preferably 5.0-7.5. Specific examples of sugar ester compounds that can be preferably used in this invention are listed below, but the invention is not limited thereto.

[0034]

[0035] (Trimethylolpropane triphenyl ester compound)

[0036] The cellulose ester membrane of the present invention contains at least one trimethylolpropane triphenyl ester compound, as shown in general formula (II):

[0037]

[0038] In the formula: R9, R 10 and R 11 It represents hydrogen atoms, alkyl groups with 1 to 4 carbon atoms, or alkoxy groups with 1 to 4 carbon atoms; n1 to n3 represent 1 to 3.

[0039] R9 and R in general formula (II) 10 and R 11 At least one is a hydrogen atom.

[0040] The following are specific examples of trimethylolpropane triphenyl ester compounds that can be preferably used in this invention, but the invention is not limited thereto.

[0041]

[0042]

[0043] The preferred amount of the sugar ester compound and the trimethylolpropane triphenyl ester compound added is equivalent to 2 to 30 wt% of the mass of the cellulose resin, more preferably 5 to 20 wt%.

[0044] (UV absorber)

[0045] The cellulose ester film of the present invention may contain an ultraviolet absorber, which is intended to improve durability by absorbing ultraviolet light below 400 nm. Particularly preferred is a transmittance of 10% or less at a wavelength of 380 nm, more preferably 5% or less, and even more preferably 2% or less.

[0046] The ultraviolet absorbers used in this invention are not particularly limited, but it is preferable to contain two or more ultraviolet absorbers. Examples include benzotriazole compounds, salicylates, benzophenone compounds, cyanoacrylate compounds, and triazine compounds. Benzotriazole ultraviolet absorbers, benzophenone ultraviolet absorbers, and triazine ultraviolet absorbers are preferred for use in this invention, with benzotriazole ultraviolet absorbers and benzophenone ultraviolet absorbers being particularly preferred. Furthermore, compounds having a 1,3,5-triazine ring are also preferred as ultraviolet absorbers.

[0047] The ultraviolet absorber can be dissolved in alcohols such as methanol, ethanol, and butanol, or organic solvents such as dichloromethane, methyl acetate, acetone, and dioxolane, or a mixture thereof, and then added to the cellulose solution, or it can be added directly to the cellulose solution. The amount of ultraviolet absorber used varies depending on the type of ultraviolet absorber and the conditions of use. Preferably, the amount of ultraviolet absorber added is equivalent to 0.5 wt% to 5.0 wt% of the mass of the cellulose resin, more preferably 0.6 wt% to 2.5 wt%.

[0048] (Antioxidant)

[0049] Antioxidants are also known as degradation inhibitors. When liquid crystal display devices or similar devices are placed under high temperature and high humidity conditions, the cellulose ester film may degrade. Antioxidants in cellulose ester films can effectively delay or prevent the decomposition of the cellulose ester film caused by the presence of residual halogens in the solvent or phosphoric acid plasticizers (such as phosphate esters). Therefore, it is preferable that the cellulose ester film contains antioxidants.

[0050] As antioxidants, hindered phenolic compounds are preferred, such as: 2,6-di-tert-butyl-p-cresol, pentaerythritol tetra[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], triethylene glycol bis[3-(3-tert-butyl-5-methyl-4-hydroxyphenyl)propionate], 1,6-hexanediol bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], 2,4-bis(n-octylthio)-6-(4-hydroxy-3,5-di-tert-butylaniline)-1 3,5-triazine, 2,2-thiodiethylene bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, N,N'-hexamethylene bis(3,5-di-tert-butyl-4-hydroxyhydrocinnamoamide), 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene, tris(3,5-di-tert-butyl-4-hydroxybenzyl)triisocyanate, etc.

[0051] Particularly preferred are 2,6-di-tert-butyl-p-cresol, pentaerythritol tetra[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and triethylene glycol bis[3-(3-tert-butyl-5-methyl-4-hydroxyphenyl)propionate]. Additionally, combinations can be used, such as hydrazine metal passivators like N,N'-bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl]hydrazine, and phosphorus processing stabilizers like tris(2,4-di-tert-butylphenyl) phosphate.

[0052] Preferably, the amount of antioxidant added is equivalent to 0.1wt% to 2.0wt% of the cellulose resin mass, and more preferably 0.2wt% to 1.0wt%.

[0053] (Matte agent)

[0054] The cellulose ester film may contain microparticles as a matting agent. Preferably, the particle size of the matting agent is 0.1 μm to 2.0 μm, more preferably 0.1 μm to 1.0 μm. As a matting agent, it is preferable to contain silicon, particularly silica. Preferred silica microparticles in the cellulose ester film of the present invention include, for example, Aerosil R972, R972V, R974, R812, 200, 200V, 300, R202, OX50, and TT600 (manufactured by Nippon Aerosil Co., Ltd.), with Aerosil 200V, R972, R972V, R974, R202, and R812 being preferred. As an organic compound matting agent, silicone resins, fluoropolymers, and acrylic resins are preferred, with silicone resins being more preferred. Particularly preferred are silicone resins with a three-dimensional network structure, such as Tospearl 103, Tospearl 105, Tospearl 108, Tospearl 120, Tospearl 145, Tospearl 3120, and Tospearl 240 (manufactured by Momentive Advanced Materials Group). The amount of matting agent added is preferably 0.05–2 wt% of the mass of the cellulose resin, more preferably 0.08–1.5 wt%.

[0055] (Method for manufacturing cellulose ester membranes)

[0056] The cellulose ester film of the present invention is manufactured by solution casting. Cellulose resin and additives are dissolved in a solvent to prepare a cellulose solution. The cellulose solution is cast onto a seamless metal support. The cast cellulose solution is made into a sheet and dried. It is peeled off from the metal support, stretched, dried, and the completed film is wound up.

[0057] The prepared cellulose solution will be described. A high concentration of cellulose resin in the cellulose solution reduces the drying burden after casting onto the metal support, which is preferred. However, if the concentration of cellulose resin is too high, it will increase the burden during filtration, resulting in poor filtration accuracy. A concentration that balances both of these factors is preferably 10-35 wt%, and more preferably 15-25 wt%.

[0058] The solvent used in the cellulose solution can be a single solvent or a combination of two or more solvents. From the perspective of production efficiency, it is preferable to use a mixture of good and bad solvents. From the perspective of the solubility of cellulose resin, it is preferable to use more good solvents.

[0059] The preferred mixing ratio of benign solvent to unfavorable solvent is 70-98 wt% benign solvent and 2-30 wt% unfavorable solvent. The benign solvent and unfavorable solvent are defined as follows: a solvent that can dissolve the cellulose resin used when used alone is defined as a benign solvent; a solvent that swells or does not dissolve the cellulose resin used when used alone is defined as an unfavorable solvent.

[0060] There are no particular limitations on the benign solvents used in this invention, but preferred solvents include organohalogen compounds such as dichloromethane, dioxanes, acetone, methyl acetate, and methyl acetoacetate. Dichloromethane and methyl acetate are particularly preferred. Furthermore, there are no particular limitations on the undesirable solvents used in this invention, but preferred solvents include methanol, ethanol, n-butanol, cyclohexane, and cyclohexanone.

[0061] Conventional methods can be used to dissolve cellulose resin when preparing the aforementioned cellulose solution. Combining heating and pressurization allows heating to be performed above the atmospheric boiling point. Dissolving the solvent while stirring during heating within a temperature range above the atmospheric boiling point and where the solvent does not boil under pressure prevents the formation of lumpy, undissolved substances, often referred to as gels or lumps. Pressurization can be achieved by introducing an inert gas such as nitrogen, or by increasing the solvent vapor pressure through heating. Heating is preferably performed externally; for example, temperature control is easily achieved when using a sheathed heating device.

[0062] Next, the cellulose solution is filtered using a suitable filter material such as filter paper. To remove insoluble matter, a material with a low absolute filtration precision is preferred; however, if the absolute filtration precision is too low, clogging of the filter material can easily occur. Therefore, filter materials with an absolute filtration precision of 0.008 mm or less are preferred, those with an absolute filtration precision of 0.001 to 0.008 mm are more preferred, and those with an absolute filtration precision of 0.003 to 0.006 mm are even more preferred. Filtration removes or reduces impurities, especially bright particles, contained in the raw cellulose resin.

[0063] The following describes the casting process for cellulose ester films.

[0064] The metal support used in the casting process is preferably a support with a mirror-finished surface. Stainless steel strips or rollers with plated surfaces made from castings are preferred as the metal support. The casting width can be 1–4 m, preferably 1.4–4 m, and more preferably 1.6–3 m. The surface temperature of the metal support in the casting process is preferably 0–55°C, more preferably 25–50°C. Higher temperatures accelerate the drying speed of the cellulose ester film, which is therefore preferred; however, excessively high temperatures may cause foaming and deterioration of the planarity of the cellulose ester film.

[0065] There are no particular limitations on the method for controlling the temperature of the metal support, including methods such as blowing in warm or cold air or contacting the back side of the metal support with warm water. Using warm water allows for efficient heat conduction and shortens the time required for the metal support to reach a constant temperature, therefore it is preferred.

[0066] In order to make the cellulose ester film exhibit good planarity, the residual solvent content when peeling the cellulose ester film from the metal support is preferably 10-150 wt%, more preferably 60-130 wt%, and even more preferably 70-120 wt%.

[0067] In this invention, the residual solvent amount is defined by the following formula.

[0068] Residual solvent content (mass%) = {(MN) / N} × 100

[0069] Where M is the mass of the cellulose ester film taken at any time during or after manufacturing, and N is the mass of M after heating at 115°C for 1 hour.

[0070] Furthermore, the cellulose ester film can be sequentially or simultaneously biaxially or uniaxially stretched in both the width direction (transverse) and the casting direction (longitudinal). The preferred stretching ratios are 1.0 to 2.5 times in the width direction and 0.8 to 1.5 times in the casting direction. The preferred stretching temperature is 120°C to 200°C, more preferably 130°C to 180°C. Stretching is preferably performed when the residual solvent in the film is 0 to 20%, more preferably 0 to 15%.

[0071] There are no particular limitations on the method for stretching the cellulose ester film. For example, a method that uses the difference in circumferential speed between multiple rollers to stretch the film; a method that uses clamps or pins to fix both ends of the cellulose ester film and then stretches the film by opening the gaps between the clamps or pins along the direction of travel; of course, these methods can also be used in combination. For producing the cellulose ester film of the present invention, it is particularly preferred to stretch the film in the width direction (lateral direction) using a tenter frame that clamps both ends of the cellulose ester film with clamps or the like.

[0072] In the film drying process, the following methods can generally be adopted: drying by roller drying (where the cellulose ester film is alternately passed through multiple rollers arranged above and below for drying) or drying while conveying the cellulose ester film using a tenter frame. There are no particular limitations on the method of drying the cellulose ester film; hot air, infrared radiation, heated rollers, microwaves, etc., can generally be used, with hot air drying being preferred. As for the drying temperature in the cellulose ester film drying process, it is preferred to increase the temperature in stages within the range of 40 to 200°C. After drying, the cellulose ester film preferably has a residual solvent content of less than 1 wt%, more preferably less than 0.1 wt%, and even more preferably less than 0 to 0.01 wt%.

[0073] There are no particular limitations on the thickness of the cellulose ester membrane, but a thickness of 10–60 μm is preferred, and 20–40 μm is even more preferred.

[0074] (Polarizing filter)

[0075] The polarizer of the present invention is obtained by attaching the cellulose ester film of the present invention to at least one side of a polarizer. Typical polarizers are known to be polyvinyl alcohol polarizing films, including polarizing films obtained by iodine dyeing or dichroic dye dyeing.

[0076] The polarizer can use a membrane that has undergone the following treatment: a membrane is prepared by an aqueous solution of polyvinyl alcohol, and the membrane is then uniaxially stretched and dyed, or dyed and then uniaxially stretched. The membrane thickness of the polarizer is preferably 5–30 μm, more preferably 10–20 μm.

[0077] The polarizer of the present invention can be manufactured using conventional methods, preferably the following method: the cellulose ester film of the present invention is subjected to alkali saponification treatment, and then laminated with a fully saponified polyvinyl alcohol aqueous solution onto at least one side of the polarizer, which has been impregnated and stretched by iodine solution or dye. For the other side of the polarizer, it is preferable to also use the cellulose ester film, or laminate with other films.

[0078] Example 1

[0079] Preparation of cellulose solution:

[0080] Cellulose resin: 100 parts by weight

[0081] Sugar ester compound (I-1): 4.0 parts by weight

[0082] Trimethylolpropane triphenyl ester compound (II-1): 8.0 parts by weight

[0083] UV absorber UV928: 2.5 parts by weight

[0084] Dichloromethane: 300 parts by weight

[0085] Methanol: 40 parts by weight

[0086] The above raw materials are mixed to form a cellulose solution. After filtration, the cellulose solution is cast onto a seamless metal support through a casting mold. Once the cast film on the support has the support properties, the cast film is peeled off from the casting support to form a wetted film. The film is then stretched, dried, formed into a film, and wound up to obtain a cellulose ester film with a thickness of 40 μm.

[0087] Other embodiments were prepared in the same manner as in Example 1, except that the sugar ester compound and trimethylolpropane triphenyl ester compound in the cellulose solution were different. Specific embodiments are shown in Table 1 below, and Examples 2-12 and Comparative Examples 1-6 were prepared.

[0088] Table 1. Components and amounts of glycolipid compounds and trimethylolpropane triphenyl ester compounds in each embodiment.

[0089] Example Sugar ester compounds Trimethylolpropane triphenyl ester compound Example 1 I-1: 4.0 parts by weight II-1: 8.0 parts by weight Example 2 I-2: 5.5 parts by weight II-3: 9.8 parts by weight Example 3 I-3: 6.2 parts by weight II-7: 8.4 parts by weight Example 4 I-4: 6.0 parts by weight II-10: 3.6 parts by weight Example 5 I-5: 7.2 parts by weight II-6: 5.2 parts by weight Example 6 I-6: 8.4 parts by weight II-8: 4.8 parts by weight Example 7 I-7: 5.6 parts by weight II-7: 7.2 parts by weight Example 8 I-8: 8.5 parts by weight II-12: 8.2 parts by weight Example 9 I-9: 2.7 parts by weight II-5: 8.8 parts by weight Example 10 I-10: 8.0 parts by weight II-9: 2.1 parts by weight Example 11 I-11: 4.7 parts by weight II-11: 8.9 parts by weight Example 12 I-12: 7.6 parts by weight II-2: 5.4 parts by weight Comparative Example 1 I-3: 1.5 parts by weight II-2: 1.9 parts by weight Comparative Example 2 I-5: 12.4 parts by weight II-7: 10.5 parts by weight Comparative Example 3 / II-4: 15.4 parts by weight Comparative Example 4 I-8: 3.5 parts by weight / Comparative Example 5 / II-10: 2.6 parts by weight Comparative Example 6 I-11: 8.5 parts by weight /

[0090] The evaluation method for the performance testing of the cellulose ester membranes prepared in the above embodiments is as follows:

[0091] 1. Water vapor permeability

[0092] The moisture permeability of cellulose ester membranes was determined according to the JIS Z0208 moisture permeability test (cup method) in an atmosphere with a temperature of 40℃ and a relative humidity of 90%RH, measuring the amount of water vapor passing through the sample over 24 hours. This is converted to a per-sample area of ​​1m². 2 The amount of water vapor that permeates within 24 hours, with a membrane thickness of 40 μm.

[0093] Water vapor permeability (WVT) calculation formula:

[0094]

[0095] in:

[0096] t—time interval between two mass increments after the latter has stabilized, in hours;

[0097] A—The area of ​​the sample through which water vapor passes, in meters. 2 (28.26×10 -4 m 2 );

[0098] The mass increment during the time interval Δm—t, in g.

[0099] 2. Membrane dimensional change rate

[0100] The dimensional change rate of the cellulose ester membrane of the present invention is determined by dividing the dimensional change by the initial length after placing the sample at 85°C and 85%RH for 1000 hours.

[0101] The dimensional change rate of the cellulose ester membrane of the present invention can be determined using the following method. First, a membrane sample with a length of 15 cm and a width of 5 cm is cut along the longitudinal direction of the cellulose ester membrane. A cross grid is drawn on the sample at 10 cm intervals. After being placed at 25°C and 60% RH for 2 hours, the grid interval is measured using a fully automatic image measuring instrument (model: JYT-3020Z, Beijing Jitai Scientific Instruments Testing Equipment Co., Ltd.) (the measured value is set as L0). Next, the sample is placed at 85°C and 85% RH for 1000 hours, then removed and placed at 25°C and 60% RH for 2 hours. The grid interval is then measured again using the fully automatic image measuring instrument (the measured value is set as L1). Using these measured values, the dimensional change rate is calculated using the following formula.

[0102] Dimensional change rate % = |(L1-L0) / L0| × 100

[0103] 3. Membrane deformation angle

[0104] The deformation angle of the cellulose ester film of the present invention is determined by placing the sample at 85°C and 85%RH for 1000 hours and measuring the absolute value of the difference in deformation angle before and after the placement.

[0105] The deformation angle of the cellulose ester membrane of the present invention can be determined using the following method. First, a membrane sample with a length of 6 cm and a width of 4 cm is cut at a 45° angle along the longitudinal direction of the cellulose ester membrane. After being placed at 25°C and 60% RH for 2 hours, the membrane angle is measured using a fully automatic image measuring instrument (model: JYT-3020Z, Beijing Jitai Scientific Instruments Testing Equipment Co., Ltd.) (the measured value is set as θ0). Next, the sample is placed at 85°C and 85% RH for 1000 hours, then removed and placed at 25°C and 60% RH for 2 hours. The membrane angle is then measured again using the fully automatic image measuring instrument (the measured value is set as θ1). Using these measured values, the deformation angle is calculated using the following formula.

[0106] Deformation angle °=|θ1-θ0|

[0107] 4. Elastic modulus and elongation at break

[0108] First, cut the cellulose ester film into rectangular samples (no fewer than 10 pieces) measuring 250mm (MD direction) × 15mm (TD direction). Condition the samples for 24 hours at a temperature of (23±2)℃ and a relative humidity of 45%–55%. Using a WDW-5 electronic universal testing machine with the clamp distance set to 180mm, stretch the conditioned samples along the MD direction and test the elastic modulus and elongation at break in the MD direction.

[0109] The performance test results of the cellulose ester membranes prepared in the above embodiments are shown in Table 2:

[0110] Table 2 shows the performance test results of the cellulose ester films prepared in Examples 1-12 and Comparative Examples 1-6.

[0111]

[0112] As can be seen from the test results of Examples 1 to 12 in Table 2, after adding the optimized sugar ester compound and trimethylolpropane triphenyl ester compound to the cellulose ester film, it has good dimensional stability and deformation angle under high temperature and high humidity conditions, effectively solving the problem of easy deformation of cellulose ester film under high temperature and high humidity conditions. Moreover, it has low moisture permeability, which can effectively block moisture penetration. When the cellulose ester film is attached to the polarizer, it can prevent the deterioration of the polarizer under high temperature and high humidity conditions. Comparative Examples 1 and 2 show that when the amounts of sugar ester compound and trimethylolpropane triphenyl ester compound are small, the moisture permeability of the cellulose ester membrane is large, and it cannot effectively prevent water vapor from passing through. When the amounts of sugar ester compound and trimethylolpropane triphenyl ester compound are large, the dimensional change rate and deformation angle of the cellulose ester membrane are large, and the durability of the cellulose ester membrane under high temperature and high humidity conditions is poor. Comparative Examples 3 to 6 show that when sugar ester compound or trimethylolpropane triphenyl ester compound is added alone, either the moisture permeability of the cellulose ester membrane is high, or the dimensional change rate and deformation angle are large. That is, the moisture permeability, dimensional change rate and deformation angle of the cellulose ester membrane cannot meet the requirements at the same time.

Claims

1. A cellulose ester membrane, characterized in that: Contains one or more additives (A) and one or more additives (B). Wherein, additive (A): contains at least one sugar ester compound with 1 to 12 pyranose or furanose structures, as shown in general formula (I): In the formula: R1 to R8 each represent a substituted or unsubstituted alkyl carbonyl or aryl carbonyl, and R1 to R8 can be the same or different; Additive (B): A compound containing trimethylolpropane triphenyl ester, which is a product of the condensation of tribenzoic acid and trimethylolpropane, as shown in general formula (II): In the formula: R9, R 10 and R 11 It represents hydrogen atoms, alkyl groups with 1 to 4 carbon atoms, or alkoxy groups with 1 to 4 carbon atoms; n1 to n3 represent 1 to 3.

2. The cellulose ester membrane as described in claim 1, characterized in that: The degree of substitution of the sugar ester compound represented by general formula (I) is 4.5 to 8.

0.

3. The cellulose ester membrane as described in claim 1, characterized in that: In the general formula (II), R9, R 10 and R 11 At least one is a hydrogen atom.

4. The cellulose ester membrane as described in claim 1, characterized in that: The cellulose ester membrane, after being placed at 85°C and 85% RH for 1000 hours, exhibited a dimensional change rate of less than 0.5%.

5. The cellulose ester membrane as described in claim 1, characterized in that: The cellulose ester membrane, when placed at 85°C and 85%RH for 1000 hours, exhibits a deformation angle of less than 1°, more preferably less than 0.8°.

6. The cellulose ester membrane as described in claim 1, characterized in that: The cellulose ester membrane is a biaxially oriented cellulose ester membrane.

7. The cellulose ester membrane according to claim 1, characterized in that: The moisture permeability of the cellulose ester membrane is 350–850 g / m²·d.

8. The cellulose ester membrane as described in claim 1, characterized in that: The additive content in the cellulose ester film is equivalent to 2-30 wt% of the cellulose resin mass.

9. The cellulose ester membrane as described in claim 1, characterized in that: The thickness of the cellulose ester film is 10–60 μm.

10. A polarizer, characterized in that: It possesses at least the cellulose ester membrane described in any one of claims 1 to 9.

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