Method for improving reliability of phase delay film and phase delay film

Abstract

The invention discloses a method for improving the reliability of a phase delay film and the phase delay film, and belongs to the technical field of optics. According to the invention, the sulfur-sulfur alkyl chain-containing compound is adopted to perform molecular modification on the phase delay film, so that the adsorption and invasion rate of the phase delay film to water molecules can be reduced, and polymer swelling, plasticizing and hydrolysis effects caused by water vapor can be reduced; thermal motion of a polymer molecular chain in a high-humidity and high-temperature environment is inhibited, internal stress release and microstructure change are reduced, and then the problems of phase delay value drift, haze rising and surface physical degradation of the phase delay film in the high-humidity and high-temperature environment are solved; and the optical stability and the mechanical stability of the phase delay film in a high-humidity and high-temperature environment are improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of optical technology, and relates to a method for improving the reliability of a phase retardation film and the phase retardation film. BACKGROUND

[0002] The phase retardation film is a key element in an optical display system and is used for regulating the polarization state of light. When used or stored for a long time in a high-temperature and high-humidity (temperature 60-85 DEG C, relative humidity 85-95% RH) environment, the traditional phase retardation film often has problems such as phase retardation value (in-plane phase retardation value Re, thickness direction phase retardation value Rth) deviation, haze increase, surface wrinkling and even peeling. These instabilities are caused by the intensified movement of the molecular chains of the polymer materials (such as polycarbonate PC, cyclic olefin polymer COP, cellulose triacetate TAC or composite materials thereof) in the wet and hot conditions, the release of internal stress and the erosion of water vapor, which further changes the birefringence characteristics or physical structure, and finally leads to display defects such as color distortion and contrast reduction of the display device.

[0003] The current core methods for improving stability mainly include two types of bulk material modification and surface plating protective layer. In the aspect of bulk material modification, Nitto Electric Industrial Co., Ltd. discloses a polyacrylate optical compensation film containing a biphenyl structure through a patent (JP2018-156789A), which realizes performance optimization by means of rigid non-conjugated dihedral angle regulation; Sumitomo Chemical develops a fluorene group-containing norbornene resin composition (WO2017 / 168934A1) which can meet the demand for high weather resistance; Shanjing Optoelectronic Technology proposes a photosensitive liquid crystal polyurethane prepolymer in a patent (CN114887673A), which forms a stable cross-linked structure by triggering thiol-ene cross-linking through ultraviolet light; and 3M Company adopts a double-layer coating scheme (US20200311897A1) to improve the stability of the material by using a highly cross-linked structure in the surface layer. The surface plating protective layer method is also widely used, for example, the hard coating protection scheme disclosed in a patent (CN108975826A) controls the balance between hardness and cohesion of the double network structure, and a water-blocking layer can also be plated to achieve protection. However, bulk modification may increase the cost of materials, sacrifice optical performance or processing fluidity; the protective effect of the conventional plating layer is limited, the interfacial compatibility thereof may decrease in a high-humidity environment, and additional process steps and costs are increased. Therefore, there is an urgent need for a modification method which is simple to operate, compatible with existing processes and can significantly improve the intrinsic environmental stability of the phase retardation film. SUMMARY

[0004] In view of the above technical problems and defects, the application provides a method for improving the reliability of a phase delay film and a phase delay film, the method uses a sulfur-containing alkyl chain compound to modify the surface of the phase delay film, and the water resistance and heat resistance of the surface and near-surface of the film layer are strengthened without significantly changing the original optical properties and physical thickness of the film layer.

[0005] In a first aspect, the application provides a method for improving the reliability of a phase delay film, a sulfur-containing alkyl chain compound is reacted with a surface base material of the phase delay film to form a hydrophobic layer; The sulfur-containing alkyl chain compound is a sulfur-sulfur alkyl chain compound. The general formula of the sulfur-sulfur alkyl chain compound is R-(CH2) n -S-S-(CH2) m -R’, wherein R and R' are independently selected from C1-C20 alkyl, C2-C20 alkenyl, C6-C24 substituted or unsubstituted straight or branched aryl, and the substituent is C1-C18 straight or branched alkyl. n and m are independently selected from integers from 1 to 18.

[0006] Further, in the method for improving the reliability of the phase delay film, R and R' are independently selected from C1-C12 alkyl. n and m are independently selected from integers from 4 to 12.

[0007] Further, in the method for improving the reliability of the phase delay film, the surface base material of the phase delay film is selected from at least one of polycarbonate, cyclic olefin polymer and cellulose triacetate.

[0008] Further, in the method for improving the reliability of the phase delay film, the temperature of the heat reaction is 50-200 DEG C, and the time is 1-60 min.

[0009] Further, in the method for improving the reliability of the phase delay film, the method comprises cleaning the surface of the phase delay film, coating a modification liquid containing the sulfur-containing alkyl chain compound on the surface of the phase delay film, performing heat reaction on the phase delay film coated with the modification liquid, and cleaning and drying the phase delay film after the heat reaction.

[0010] Further, in the method for improving the reliability of the phase delay film, the modification liquid containing the sulfur-containing alkyl chain compound is made of the sulfur-containing alkyl chain compound and a mixed solvent. The mixed solvent is selected from one or more of alcohols, ketones, hydrocarbons and ethers.

[0011] Further, in the method for improving the reliability of the phase delay film, the mass percentage concentration of the modified liquid of the sulfur-containing alkyl chain compound is 0.5% to 1.0%.

[0012] Further, in the method for improving the reliability of the phase delay film, the coating method is slot coating or micro-gravure coating.

[0013] Further, in the method for improving the reliability of the phase delay film, the drying temperature is 40 to 60 DEG C, and the time is 30 to 60 min.

[0014] In a second aspect, the application provides a phase delay film prepared by the method for improving the reliability of the phase delay film.

[0015] Compared with the prior art, the technical scheme provided by the application has at least the following advantages: The application uses a sulfur-containing alkyl chain compound (sulfur-sulfur alkyl chain compound) to modify the phase delay film. The alkyl chain provides a good hydrophobic barrier to effectively prevent water vapor molecules from penetrating into the film layer. The -S-S- at the end exhibits excellent interface reactivity and can form stable chemical bonds (such as covalent bond S-C) or strong physical adsorption with specific functional groups (such as carbonyl, unsaturated bond, or active groups possibly generated in the surface treatment process) in the polymer film material. This combination allows the sulfur-containing alkyl chain to be tightly anchored to the surface and subsurface layer of the film material, thereby forming a dense hydrophobic surface layer with dual functions: on the one hand, it greatly reduces the adsorption and penetration rate of water vapor molecules, reducing the effects of polymer swelling, plasticization, and hydrolysis caused by water vapor; on the other hand, the strong bonding layer can effectively suppress the thermal motion amplitude of the polymer molecular chain when it is heated and humidified, reducing internal stress release and microstructure changes. This synergistic effect significantly suppresses the drift of the phase delay value in harsh environments, reduces the rise in haze, and reduces the risk of surface physical degradation, greatly improving the long-term optical and mechanical stability of the phase delay film in high-temperature and high-humidity environments. BRIEF DESCRIPTION OF DRAWINGS

[0016] In order to more clearly illustrate the technical solutions in the embodiments of the application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are only some embodiments of the application, and for those skilled in the art, other drawings can also be obtained without creative labor.

[0017] Figure 1 It is a schematic diagram of the phase delay film structure.

[0018] Figure 2 It is a preparation flowchart of the phase delay film. DETAILED DESCRIPTION

[0019] Hereinafter, the technical solutions of the present application will be described in conjunction with examples, but the present application is not limited to the following examples. The experimental methods and detection methods described in each example are all conventional methods unless otherwise specified; the reagents and materials described are all commercially available unless otherwise specified.

[0020] The method for improving the reliability of the phase retardation film involved in the following examples is shown in method 2 in the Figure 2 , and the modified phase retardation film is shown in the Figure 1 .

[0021] In the method 2 (method 1) in the Figure 2 , the method for preparing a liquid crystal layer on a substrate on which an alignment layer has been formed comprises, in sequence, a liquid crystal layer coating (such as gravure coating, reverse roll coating, knife roll coating, metering bar coating, slot die coating, immersion, curtain coating, air knife coating, etc.), a liquid crystal layer drying (oven heating / heating table heating, etc.), and a liquid crystal layer curing (ultraviolet light 365 nm / 395 nm) step. Each step will be described in detail below.

[0022] Liquid crystal layer coating: The coating liquid containing liquid crystal molecules and polymerizable components is uniformly applied to the surface of the alignment layer of the substrate by using film-forming techniques known in the art, such as but not limited to microgravure coating or slit extrusion coating, thereby forming a liquid crystal wet film.

[0023] Liquid crystal layer drying The liquid crystal wet film is subjected to a drying process. This step uses conventional drying processes, such as vacuum drying or multi-stage hot air convection drying, to remove volatile solvents in the coating liquid. In this process, the liquid crystal molecules are self-assembled and oriented under the induction of the underlying alignment layer, forming a pre-arrangement structure with the desired optical anisotropy.

[0024] Liquid crystal layer curing The pre-arrangement liquid crystal layer formed after drying is subjected to a curing process. This step uses conventional curing techniques such as photocuring or thermal curing to initiate crosslinking polymerization of the polymerizable components, thereby permanently fixing the oriented arrangement of the liquid crystal molecules and obtaining a structurally stable optical retardation layer.

[0025] The surface substrate of the phase retardation film involved in the following examples includes but is not limited to at least one polymeric material of polycarbonate, cyclic olefin polymer, cellulose triacetate, or a blend thereof.

[0026] The modifying liquid involved in the following examples is composed of a sulfur-containing alkyl chain compound and a mixed solvent; The sulfur-containing alkyl chain compound is a sulfur-sulfur alkyl chain compound; Specifically, the sulfur-sulfur alkyl chain compound has a general formula of R-(CH2) n -S-S-(CH2) m -R’, wherein R and R’ are independently selected from H, C1-C20 alkyl, C2-C20 alkenyl, C6-C24 substituted or unsubstituted straight or branched aryl, the substituent being C1-C18 straight or branched alkyl, preferably C1-C12 alkyl; n and m are integers of 1-18, preferably integers of 4-12.

[0027] The mixed solvent includes, but is not limited to, alcohols (such as methanol, ethanol, isopropanol, n-butanol, sec-butanol, etc.), ketones (such as acetone, methyl ethyl ketone, cyclopentanone, cyclohexanone, etc.), hydrocarbons (such as toluene), ethers, or a mixture of any two or more thereof.

[0028] Example 1 The present example provides a method for improving the reliability of a phase delay film S1. Pre-treatment of the phase delay film: Take a piece of polycarbonate (PC) phase delay film with a thickness of 50 μm, and carefully wipe and clean both sides with an isopropanol-ethanol mixture and a dust-free cloth.

[0029] S2. Preparation of the sulfur-containing alkyl chain compound-modified solution: Dissolve the diallyl disulfide in toluene to prepare a sulfur-containing alkyl chain compound-modified solution with a concentration of 0.5% (w / v).

[0030] S3. Coating of the protective layer: Uniformly coat the sulfur-containing alkyl chain compound-modified solution on the surface of the cleaned PC film (coating only on one side) by using a slot coating method.

[0031] S4. Drying of the protective layer: Place the PC film coated with the protective layer in an 80°C oven for heat treatment for 30 min.

[0032] S5. Post-treatment of the phase delay film: Immerse the heat-treated PC film in anhydrous ethanol for ultrasonic cleaning for 3 min, remove the unreacted diallyl disulfide and toluene, and then place it in a 50°C oven for drying for 60 min to obtain the modified phase delay film sample A.

[0033] Comparative Example 1 This comparative example is the same as Example 1, except that the PC film in this comparative example is not treated with the sulfur-containing alkyl chain compound-modified solution, i.e., immerse the PC film in anhydrous ethanol for ultrasonic cleaning for 3 min, and then place it in a 50°C oven for drying for 60 min to obtain the phase delay film sample B. Figure 2 (method 1) in the specification).

[0034] Example 2 The present example provides a method for improving the reliability of a phase retardation film S1. Pretreatment of the phase retardation film: Take a piece of triacetate cellulose (TAC) phase retardation film with a thickness of 40 μm, and clean both sides carefully with isopropyl alcohol and a dust-free cloth.

[0035] S2. Preparation of the modification liquid containing the sulfur-containing alkyl chain compound: Dissolve bis (undecyl) disulfide ((CH3(CH2) 12 S)2) in acetone to prepare a modification liquid containing the sulfur-containing alkyl chain compound with a concentration of 1.0% (w / v).

[0036] S3. Coating of the protective layer: Uniformly coat the modification liquid containing the sulfur-containing alkyl chain compound on the surface of the cleaned TAC film (coating only on one side) by micro-gravure coating.

[0037] S4. Drying of the protective layer: Place the TAC film coated with the protective layer in a 120°C oven and heat treat for 15 min.

[0038] S5. Post-treatment of the phase retardation film: After heat treatment, immerse the TAC film in acetone and ultrasonically clean for 2 min, repeat the cleaning for 2 times, remove the unreacted n-dodecanethiol and toluene, and then place in a 50°C oven to dry for 60 min to obtain the modified phase retardation film sample C.

[0039] Comparative Example 2 This comparative example is the same as Example 2, except that the modification liquid containing the sulfur-containing alkyl chain compound is not used in this comparative example. That is, immerse the TAC film in acetone and ultrasonically clean for 2 min, repeat the cleaning for 2 times, and then place in a 50°C oven to dry for 60 min to obtain the phase retardation film sample D.

[0040] Place samples A, B, C, and D in a constant temperature and humidity chamber for high temperature and high humidity aging test under the conditions of 85°C / 85% RH. Take out at 0 hours (initial), 250 hours, and 500 hours, respectively, and after equilibrating in a standard temperature and humidity environment (23°C / 50% RH) for 24 hours, measure the in-plane phase retardation value (Re), haze (Haze), and observe the surface morphology. The test results are shown in Table 1.

[0041] Table 1 Test results of the in-plane phase retardation value, haze, and surface morphology of the phase retardation film after aging

[0042] The above data show that after the phase retardation film samples (A and C) treated by the modifier containing the sulfanyl chain of the application are aged in an environment of 85°C, 85% RH for 500h, the change rates of Re of sample A and sample C are +1.3% and +1.8% respectively, which are far lower than the serious drifts of unmodified sample B (-12.2%) and sample D (-11.7%), and completely meet the application requirements (absolute value of Re change rate <5%). The haze increase of the modified samples is extremely small (1.0% for sample A and 1.5% for sample C), while the haze of the unmodified samples increases significantly (6.5% for sample B and 7.2% for sample D). The surfaces of the modified sample A and sample C after aging are still smooth, and no wrinkles, shrinkage, peeling or discoloration is observed; while the unmodified sample B and sample D have different degrees of physical deformation and visual defects.

[0043] Example 3 The present example provides a method for improving the reliability of a phase retardation film S1. Pretreatment of the phase retardation film: take a piece of cyclo-olefin polymer (COP) phase retardation film with a thickness of 50 μm, and carefully wipe and clean both sides with an isopropyl alcohol-ethanol mixture and a dust-free cloth.

[0044] S2. Preparation of the modification liquid containing the sulfanyl chain compound: dissolve methylpropyl disulfide in isopropyl alcohol to prepare a modification liquid containing the sulfanyl chain compound with a concentration of 0.8% (w / v).

[0045] S3. Coating of the protective layer: uniformly coat the modification liquid containing the sulfanyl chain compound on the surface of the cleaned COP film (coating only one side) by slot coating.

[0046] S4. Drying of the protective layer: place the COP film coated with the protective layer in an oven at 180°C and heat treat for 10 min.

[0047] S5. Post-treatment of the phase retardation film: immerse the heat-treated COP film in anhydrous ethanol and ultrasonically clean for 3 min to remove unreacted methylpropyl disulfide and isopropyl alcohol, and then place it in an oven at 40°C and dry for 60 min to obtain the modified phase retardation film sample, which has a Re change rate of 1.3% after being aged in an environment of 85°C, 85% RH for 500h.

[0048] Example 4 The present example provides a method for improving the reliability of a phase retardation film S1. Pretreatment of the phase retardation film: take a piece of polycarbonate and triacetate cellulose blend phase retardation film with a thickness of 75 μm, and carefully wipe and clean both sides with an isopropyl alcohol-ethanol mixture and a dust-free cloth.

[0049] S2. Preparation of the modifying solution of the sulfur-containing alkyl chain compound: Dissolve di-sec-butyl disulfide in a mixture of isopropyl alcohol and ethanol (volume ratio of isopropyl alcohol to ethanol is 73:17) to prepare a modifying solution of the sulfur-containing alkyl chain compound with a concentration of 0.7% (w / v).

[0050] S3. Protective layer coating: uniformly coat the modifying solution of the sulfur-containing alkyl chain compound on the surface of the cleaned polycarbonate and cellulose triacetate blend film (coating only on one side) by using a slot coating method.

[0051] S4. Protective layer drying: place the polycarbonate and cellulose triacetate blend film coated with the protective layer in an oven at 80°C and heat treat for 30 min.

[0052] S5. Post-processing of the phase retardation film: after heat treatment, immerse the polycarbonate and cellulose triacetate blend film in anhydrous ethanol and ultrasonically clean for 3 min to remove unreacted di-sec-butyl disulfide, isopropyl alcohol and ethanol, then place in a 50°C oven and dry for 60 min to obtain a modified phase retardation film sample, which has a change rate of Re of 1.8% after aging in an environment of 85°C and 85% RH for 500 h.

[0053] Example 5 The present example provides a method for improving the reliability of a phase retardation film S1. Pre-treatment of the phase retardation film: take a polycarbonate (PC) phase retardation film with a thickness of 50 μm, carefully clean both sides with a mixture of isopropyl alcohol and ethanol and a dust-free cloth.

[0054] S2. Preparation of the modifying solution of the sulfur-containing alkyl chain compound: dissolve dipropyl disulfide in a mixture of diethylene glycol diethyl ether to prepare a modifying solution of the sulfur-containing alkyl chain compound with a concentration of 1.0% (w / v).

[0055] S3. Protective layer coating: uniformly coat the modifying solution of the sulfur-containing alkyl chain compound on the surface of the cleaned PC film (coating only on one side) by using a slot coating method.

[0056] S4. Protective layer drying: place the PC film coated with the protective layer in an oven at 200°C and heat treat for 10 min.

[0057] S5. Post-processing of the phase retardation film: after heat treatment, immerse the PC film in anhydrous ethanol and ultrasonically clean for 3 min to remove unreacted dipropyl disulfide and diethylene glycol diethyl ether, then place in a 50°C oven and dry for 60 min to obtain a modified phase retardation film sample, which has a change rate of Re of 2.2% after aging in an environment of 85°C and 85% RH for 500 h.

[0058] The above-described embodiments are merely some of the embodiments of the present application, but not all the embodiments. The detailed description of the embodiments of the present application is not intended to limit the scope of the claimed application, but merely represents selected embodiments of the application. All other embodiments obtained by persons of ordinary skill in the art based on the concept of the present application, without making creative labor, are within the scope of the present application.

Claims

1. A method for improving the reliability of a phase retardation film, characterized in that, A hydrophobic layer is formed by thermally reacting a sulfur-containing alkyl chain compound with a phase retardation film substrate. The sulfur-containing alkyl chain compound is a sulfur-sulfoalkyl chain compound; The general formula for the sulfur-thioalkyl chain compound is R-(CH2). n -SS-(CH2) m -R', Wherein, R and R' are independently selected from C1~C20 alkyl, C2~C20 alkenyl, C6~C24 substituted or unsubstituted straight or branched aryl groups, and the substituents are C1~C18 straight or branched alkyl groups. n and m are each independently selected from integers from 1 to 18.

2. The method for improving the reliability of a phase retardation film according to claim 1, characterized in that, R and R' are each independently selected from C1 to C12 alkyl groups; The n and m are each independently selected from integers from 4 to 12.

3. The method for improving the reliability of a phase retardation film according to claim 1, characterized in that, The substrate for the phase delay film is selected from at least one of polycarbonate, cyclic olefin polymer and cellulose triacetate.

4. The method for improving the reliability of a phase retardation film according to claim 1, characterized in that, The temperature of the thermal reaction is 80~200℃, and the time is 10~60min.

5. The method for improving the reliability of a phase retardation film according to claim 1, characterized in that, include: Clean the surface of the phase retardation film; A modified liquid containing sulfur-containing alkyl chain compounds was coated onto the surface of a phase retardation film; A thermal reaction was carried out on the phase retardation film coated with the modified liquid; The phase retardation film after thermal reaction is cleaned and dried.

6. The method for improving the reliability of a phase delay film according to claim 5, characterized in that, The modified liquid of the sulfur-containing alkyl chain compound is made from the sulfur-containing alkyl chain compound and a mixed solvent; The mixed solvent is selected from one or more of alcohols, ketones, hydrocarbons, and ethers.

7. The method for improving the reliability of a phase retardation film according to claim 5, characterized in that, The mass-volume percentage concentration of the modified liquid containing the sulfur-containing alkyl chain compound is 0.5% to 1.0%.

8. The method for improving the reliability of a phase retardation film according to claim 5, characterized in that, The coating method is slot coating or microgravure coating.

9. The method for improving the reliability of a phase retardation film according to claim 5, characterized in that, The drying temperature is 40~60℃ and the time is 30~60min.

10. A phase retardation film prepared by any one of the methods for improving the reliability of a phase retardation film as claimed in claims 1 to 9.

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