A high moisture resistant scratch protective film base film for a polarizing sheet

Abstract

This invention relates to a high moisture-barrier and scratch-resistant protective film base for polarizers. The base film, from bottom to top, comprises a functional bonding layer: intercalated modified montmorillonite, graphene nanosheets, an antistatic agent, and optical-grade PET; an adhesive layer; and an outer wear-resistant layer: wear-resistant modified PET, functional nanofillers, UV absorbers, and optical-grade PET. The functional bonding layer of this invention contacts the pressure-sensitive adhesive of the polarizer. The unique intercalated modified montmorillonite combined with graphene nanosheets enhances the film's moisture barrier properties, providing long-term protection for the polarizer's core layer. Simultaneously, the introduction of an antistatic agent ensures no risk of electrostatic discharge damage during protective film peeling. The outer wear-resistant layer, through the synergistic effect of modified PET containing silicon and naphthalene rings and functional nanofillers, improves the film's hardness and scratch resistance. The intermediate adhesive layer effectively solves the compatibility problem between the functional bonding layer and the outer surface layer, ensuring the stability and strength of the multilayer co-extruded structure.

Description

Technical Field

[0001] This invention relates to the field of polarizer protective film technology, specifically to a high moisture resistance and scratch-resistant protective film base film for polarizers. Background Technology

[0002] Polarizing films are mainly used in various optical instruments such as displays, digital cameras, and projectors. They are multi-layered composite films, including a surface protective film, a polarizing substrate layer, an inner protective film, an optical pressure-sensitive adhesive layer, and a release film. The outer surface protective film of the polarizing film protects the film itself, thus requiring high mechanical properties, including high strength and scratch resistance. Furthermore, since the protective film needs to be removed before use, it also needs to be anti-static. Currently, research on polarizing film protective films mainly focuses on improving its strength and other properties. The effects of external environments such as moisture and ultraviolet radiation must also be considered during use and storage. However, current research in this area is relatively limited, with most efforts concentrated on improving the performance of the inner protective film. Summary of the Invention

[0003] To address the shortcomings of existing technologies, this invention integrates multiple functions, such as high moisture resistance, scratch resistance, and excellent mechanical properties, into a single PET substrate through an innovative multi-layer design.

[0004] To achieve the above objectives, the present invention provides the following technical solution:

[0005] A high moisture-resistant and scratch-resistant protective film base for polarizers, the base film comprising a 30-50 μm thick functional bonding layer from bottom to top: the materials include intercalated modified montmorillonite, graphene nanosheets, antistatic agent and optical grade PET;

[0006] A 5-15 μm thick adhesive layer: materials include PET-g-MAH and TPEE; and

[0007] 20~30 μm thick outer wear-resistant layer: materials include wear-resistant modified PET, functional nanofillers, ultraviolet absorbers and optical grade PET;

[0008] The intercalated modified montmorillonite is obtained by intercalating montmorillonite with an ATRP initiator that has cationic surface activity, and then grafting polymethyl methacrylate-dodecyl methacrylate-glycidyl methacrylate in situ between the layers and on the surface.

[0009] The wear-resistant modified PET is prepared by a series of esterification reactions, transesterification reactions, and polycondensation reactions of terephthalic acid, ethylene glycol, 1,4-cyclohexanediol, hydroxyl-terminated organosilicon glycol, and dimethyl terephthalate.

[0010] The functional nanofiller is nano-silica or nano-alumina modified with a silane coupling agent.

[0011] Furthermore, the material composition of the functional bonding layer is as follows by weight: 5-10 parts intercalated modified montmorillonite, 1-3 parts graphene nanosheets, 1-3 parts antistatic agent, and 100 parts optical grade PET.

[0012] Furthermore, the graphene nanosheets are hydroxylated graphene nanosheets with a sheet diameter of 1-5 μm; the antistatic agent is a polyether ester amide or an acrylate copolymer containing a quaternary ammonium salt structure.

[0013] Furthermore, the material ratio in the adhesive layer is as follows, by weight: 40-50 parts PET-g-MAH and 50-60 parts TPEE.

[0014] Furthermore, the material composition of the outer wear-resistant layer is as follows by weight: 30-50 parts wear-resistant modified PET, 2-8 parts functional nanofillers, 1-5 parts ultraviolet absorber, and 50 parts optical grade PET.

[0015] Furthermore, the ATRP initiator with cationic surface activity has the following structural formula: The molar ratio of the three monomers, polymethyl methacrylate, dodecyl methacrylate, and glycidyl methacrylate, is 10:3~6:4~7.

[0016] Furthermore, the preparation process of the intercalated modified montmorillonite is as follows:

[0017] 1) Disperse sodium montmorillonite in deionized water to prepare a 3-5 wt% suspension. Stir at high speed at 80°C for 24 h. Then add an equal volume of THF and continue stirring for 2 h. Dissolve the cationic surface-active ATRP initiator in THF and add it dropwise to the above suspension. Continue stirring for 8-12 h. Cool down, centrifuge, wash repeatedly with hot ethanol aqueous solution, vacuum dry, grind and sieve.

[0018] 2) Add N,N,N',N'',N'''-pentamethyldivinyltriamine, cuprous bromide, sieved powder, and THF to a reaction flask, and mix thoroughly by ultrasonication. Then add methyl methacrylate, dodecyl methacrylate, and glycidyl methacrylate. Purge nitrogen gas to remove oxygen from the reaction flask. Under nitrogen protection, heat to 70°C and react for 8-24 hours. After the reaction is complete, centrifuge to separate the solid, wash with THF multiple times, and vacuum dry to obtain the intercalated modified montmorillonite.

[0019] Furthermore, the specific preparation process of the wear-resistant modified PET is as follows:

[0020] 1) In a reaction vessel, terephthalic acid, ethylene glycol, 1,4-cyclohexanediol, and terminal hydroxyl organosilicon glycol with a molecular weight of 800-1500 are added. Antimony acetate catalyst and triphenyl phosphite stabilizer are also added. Under nitrogen protection, the temperature is gradually raised to 240-260℃ to carry out the esterification reaction and obtain product 1.

[0021] 2) In a reaction vessel, dimethyl p-naphthalenedicarboxylate, ethylene glycol, zinc acetate, and the stabilizer triphenyl phosphite are added, and the temperature is gradually raised to 170~215℃ to carry out the transesterification reaction to obtain product 2;

[0022] 3) Transfer product 2 to the product 1 system, draw a low vacuum, reduce the pressure to below 100 Pa, raise the temperature to 270-285℃, and carry out a polycondensation reaction for 2-4 hours. After the reaction is completed, release the vacuum, discharge the material, cool it, and granulate it to obtain wear-resistant modified PET resin.

[0023] Further, in step 1), the molar ratio of terephthalic acid, ethylene glycol, and 1,4-cyclohexanediethanol is 1:0.9~1.1:0.1~0.3; the amount of the terminal hydroxyl organosilicon glycol added is 0.5~2% of the molar amount of terephthalic acid; in step 2), the molar ratio of dimethyl phthalate and ethylene glycol is 1:2.1~2.2; and the mass ratio of product 2 to product 1 is 0.1~0.2:1.

[0024] Compared with existing technologies, the beneficial effects of this invention are as follows: This invention prepares three composite layers with different functions through a one-time co-extrusion molding process. The functional bonding layer is in contact with the polarizer pressure-sensitive adhesive. The moisture resistance of the film is improved by using a unique intercalation-modified montmorillonite combined with graphene nanosheets, providing long-term protection for the core layer of the polarizer. At the same time, an antistatic agent is introduced to ensure that there is no risk of electrostatic discharge damage when the protective film is peeled off. The wear-resistant layer on the outer surface improves the hardness and scratch resistance of the film by introducing modified PET with silicon and naphthalene ring structures and functional nanofillers. The middle adhesive layer effectively solves the compatibility problem between the functional bonding layer and the outer surface layer, ensuring the stability and strength of the multi-layer co-extruded structure. Detailed Implementation

[0025] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0027] Most of the raw materials used in this application were purchased from the market, and a small portion were produced in-house, as described in detail below. Some of the raw materials may affect the product due to their properties, and their sources are provided below:

[0028]

[0029] In addition, MAH-g-PET can be custom-produced with manufacturers, or obtained through the following methods:

[0030] 100 parts by weight of PET are fed into the main feed port. 2 parts of maleic anhydride, 0.2 parts of DCP initiator and 0.5 parts of styrene are mixed evenly and injected into the extruder through the side feed port. The mixture is melt-extruded at a melting temperature of 260~280℃, stretched, water-cooled, pelletized and dried to obtain MAH-g-PET.

[0031] Example: A high moisture-resistant and scratch-resistant protective film base for polarizers, wherein the base film comprises a 30-50 μm thick functional bonding layer from bottom to top: the material comprises 5-10 parts intercalated modified montmorillonite, 1-3 parts graphene nanosheets, 1-3 parts antistatic agent and 100 parts optical grade PET;

[0032] A 5-15 μm thick adhesive layer: the material comprises 40-50 parts PET-g-MAH and 50-60 parts TPEE; and

[0033] 20~30 μm thick outer wear-resistant layer: 30~50 parts wear-resistant modified PET, 2~8 parts functional nanofillers, 1~5 parts ultraviolet absorber and 50 parts optical grade PET.

[0034] The preparation process of the intercalated modified montmorillonite is as follows:

[0035] 1) Disperse 10g of sodium montmorillonite in deionized water to prepare a 5wt% suspension. Stir at high speed at 80℃ for 24h, then add an equal volume of THF and continue stirring for 2h. Add 4.2g of ATRP initiator with cationic surface activity ( (Referring to the synthesis of ATRP initiators with cationic surface activity, Chinese Journal of Synthetic Chemister, Vol 18, 2010, 741-744) was dissolved in THF and then added dropwise to the above suspension. The mixture was stirred for 8-12 h, cooled, centrifuged, washed repeatedly with hot ethanol aqueous solution, vacuum dried, ground and sieved.

[0036] 2) Add 0.64 g N,N,N',N'',N'''-pentamethyldivinyltriamine, 0.53 g cuprous bromide, 5 g sieved powder, and 200 ml THF to a reaction flask, and mix thoroughly by ultrasonication. Then add 10 g methyl methacrylate, 15.24 g dodecyl methacrylate, and 5.69 g glycidyl methacrylate (molar ratio 10:6:4). Purge nitrogen gas to remove oxygen from the reaction flask, and react at 70 °C for 16 h under nitrogen protection. After the reaction is complete, centrifuge to separate the solid, wash repeatedly with THF, and vacuum dry to obtain the intercalated modified montmorillonite.

[0037] While the original layered montmorillonite sheets possess inherent barrier properties, the strong interlayer forces make them difficult to peel off and uniformly disperse in polymers, easily leading to agglomeration and defects. This approach addresses this by intercalating with an ATRP (Atom Transfer Radical Polymerization) initiator and grafting polymers in situ. First, a cationic ATRP initiator is selected to facilitate insertion between montmorillonite sheets, widening the interlayer spacing. Subsequently, graft polymerization of PMMA-PEGMA-GMA is initiated, forming numerous nanoscale layered structures. This imparts hydrophobicity to the montmorillonite surface, reducing water molecule adsorption. Simultaneously, the polymer groups and PET segments create interfacial bonding, resolving the agglomeration problem of montmorillonite. Furthermore, hydroxylated graphene nanosheets serve as complementary materials, synergistically constructing a denser layered barrier network, significantly reducing water vapor permeability.

[0038] The specific preparation process of the wear-resistant modified PET is as follows:

[0039] 1) In a reaction vessel, add 2 mol terephthalic acid, 2.4 mol ethylene glycol, 0.4 mol 1,4-cyclohexanediol, and 0.04 mol terminal hydroxyl organosilicon glycol (molecular weight 1000), add 0.6 g antimony acetate catalyst and 0.4 g triphenyl phosphite stabilizer, and under nitrogen protection, gradually raise the temperature to 250℃ to carry out the esterification reaction to obtain product 1;

[0040] 2) In a reaction vessel, add 0.2 mol of dimethyl p-naphthalenecarboxylate, 0.42 mol of ethylene glycol, 0.05 g of zinc acetate, and 0.05 g of the stabilizer triphenyl phosphite, and gradually raise the temperature to 190 °C to carry out the transesterification reaction to obtain product 2;

[0041] 3) Transfer all of product 2 to the product 1 system, draw a low vacuum, reduce the pressure to below 100 Pa, raise the temperature to 270-285℃, and carry out a polycondensation reaction for 3 hours. After the reaction is completed, release the vacuum, discharge the material, cool it, and granulate it to obtain wear-resistant modified PET resin.

[0042] For the protective film base film for polarizers in this application, the inventors designed a wear-resistant modified PET. This is achieved through a copolymerization reaction at the molecular level. First, an esterification reaction is performed, with the addition of 1,4-cyclohexanediol and terminal hydroxyl organosilicon glycol to moderately reduce crystallinity, improve toughness, and enhance surface elasticity, thus reducing the coefficient of friction. A small amount of transesterification introduces a naphthalene ring structure to increase the material's hardness. By separating the esterification and transesterification reactions and then performing them together in a condensation process, a balance between hardness and toughness is effectively achieved. In addition, a certain amount of functional nanofiller is added. Modified with a silane coupling agent, the wear-resistant modified PET is uniformly dispersed in the matrix, providing a certain degree of support.

[0043] The functional nanofiller is silane coupling agent modified nano-silica or nano-alumina, and the specific preparation process is as follows:

[0044] A certain amount of nano-silica or nano-alumina is first activated with 2M potassium hydroxide, then dispersed in deionized water and an equal mass of KH570 is added. The mixture is stirred at 50℃ for 24 hours, filtered, washed, dried and ground to obtain KH570 modified nano-silica or KH570 modified nano-alumina.

[0045] Example 1: 50 μm thick functional bonding layer: The material includes 5 parts intercalated modified montmorillonite, 1 part graphene nanosheets, 1 part antistatic agent and 100 parts optical grade PET;

[0046] 10 μm thick adhesive layer: The material consists of 40 parts PET-g-MAH and 50 parts TPEE;

[0047] 20 μm thick outer wear-resistant layer: 30 parts wear-resistant modified PET, 2 parts KH570 modified nano silica, 1 part benzotriazole UV absorber and 50 parts optical grade PET.

[0048] The three layers of raw material are extruded separately through a screw extruder, with the temperatures of each layer set as follows: functional bonding layer 280℃, adhesive layer 275℃, and outer wear-resistant layer 265℃. The three-layer melt is then extruded onto a 50℃ cooling roller through a three-layer co-extrusion distributor and die to form a cast sheet.

[0049] The casting is preheated to 90°C and then longitudinally stretched at a stretching temperature of 95°C and a stretching ratio of 3.5. Then it is preheated to 105°C and transversely stretched at a stretching temperature of 110°C and a stretching ratio of 3.7.

[0050] Heat setting was performed at 210℃, and the film was wound up to obtain a three-layer co-extruded protective film base film with a total thickness of approximately 80 μm.

[0051] Example 2: 50 μm thick functional bonding layer: The material includes 8 parts intercalated modified montmorillonite, 2 parts graphene nanosheets, 2 parts antistatic agent and 100 parts optical grade PET;

[0052] 10 μm thick adhesive layer: The material consists of 45 parts PET-g-MAH and 55 parts TPEE;

[0053] 20 μm thick outer wear-resistant layer: 40 parts wear-resistant modified PET, 6 parts KH570 modified nano alumina, 3 parts UV absorber and 50 parts optical grade PET.

[0054] Example 3: 50 μm thick functional bonding layer: The material includes 10 parts intercalated modified montmorillonite, 3 parts graphene nanosheets, 3 parts antistatic agent and 100 parts optical grade PET;

[0055] A 10 μm thick adhesive layer: the material consists of 50 parts PET-g-MAH and 60 parts TPEE; and

[0056] 20 μm thick outer wear-resistant layer: 50 parts wear-resistant modified PET, 8 parts KH570 modified nano silica, 5 parts UV absorber and 50 parts optical grade PET.

[0057] Comparative Example 1: 50 μm thick functional bonding layer: 100 parts optical grade PET;

[0058] A 10 μm thick adhesive layer: the material consists of 50 parts PET-g-MAH and 60 parts TPEE; and

[0059] 20 μm thick outer wear-resistant layer: 40 parts wear-resistant modified PET, 6 parts KH570 modified nano alumina, 3 parts UV absorber and 50 parts optical grade PET.

[0060] Comparative Example 2: 50 μm thick functional bonding layer: The materials include 8 parts intercalated modified montmorillonite, 2 parts graphene nanosheets, 2 parts antistatic agent and 100 parts optical grade PET;

[0061] A 10 μm thick adhesive layer: the material consists of 50 parts PET-g-MAH and 60 parts TPEE; and

[0062] 20 μm thick outer wear-resistant layer: 8 parts KH570 modified nano silica, 5 parts ultraviolet absorber and 50 parts optical grade PET.

[0063] Comparative Example 3: 50 μm thick functional bonding layer: The material includes 2 parts graphene nanosheets, 2 parts antistatic agent and 100 parts optical grade PET;

[0064] A 10 μm thick adhesive layer: the material consists of 50 parts PET-g-MAH and 60 parts TPEE; and

[0065] 20 μm thick outer wear-resistant layer: 5 parts UV absorber and 50 parts optical grade PET.

[0066] The following performance tests were performed on the protective film base film prepared above: 1. Water vapor transmission rate: Tested according to standard ASTM F1249 under the conditions of temperature 38°C and relative humidity 90%.

[0067] 2. Light transmittance and haze: Tested using a haze meter according to standard ASTM D1003;

[0068] 4. Hardness: Scratch test using the pencil hardness method;

[0069] 5. Scratch resistance: The scratch resistance of the coating is determined by placing sandpaper on the coating surface and applying different loads on the sandpaper, with the minimum mass required to produce a noticeable scratch.

[0070] 6. Surface resistance: Tested using a high resistance meter.

[0071] The results are recorded in Table 1.

[0072] Table 1

[0073]

[0074] The water vapor transmission rates of Examples 1-3 were significantly lower than those of Comparative Examples 1 and 3, demonstrating the outstanding synergistic barrier effect of the intercalated modified montmorillonite and graphene nanosheets. Comparative Example 1, lacking this functional layer, showed no improvement in moisture barrier properties, while Comparative Example 3, containing only graphene nanosheets, showed a slight improvement in moisture barrier properties. Observing Examples 1-3, with the increase of functional fillers, the light transmittance slightly decreased, while the haze increased, but the hardness and scratch resistance significantly improved. Comparative Example 3, lacking wear-resistant modified PET and functional nanofillers, showed a significant deterioration in hardness and scratch resistance; Comparative Example 2, containing only functional nanofillers, showed a slight improvement in scratch resistance, but its performance was still inferior to Example 3, demonstrating the crucial role of the wear-resistant modified PET resin in surface properties. Furthermore, the addition of antistatic agents and UV absorbers also improved the antistatic and UV absorption properties of the film.

[0075] Although the embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details.

Claims

1. A high moisture-resistance and scratch-resistant protective film base for polarizers, characterized in that, The base film comprises a 30-50 μm thick functional bonding layer from bottom to top: the materials include intercalated modified montmorillonite, graphene nanosheets, antistatic agent and optical grade PET; A 5-15 μm thick adhesive layer: materials include PET-g-MAH and TPEE; and 20~30 μm thick outer wear-resistant layer: materials include wear-resistant modified PET, functional nanofillers, ultraviolet absorbers and optical grade PET; The intercalated modified montmorillonite is obtained by intercalating montmorillonite with an ATRP initiator that has cationic surface activity, and then grafting polymethyl methacrylate-dodecyl methacrylate-glycidyl methacrylate in situ between the layers and on the surface. The preparation process of the intercalated modified montmorillonite is as follows: 1) Disperse sodium montmorillonite in deionized water to prepare a 3-5 wt% suspension. Stir at high speed at 80°C for 24 h. Then add an equal volume of THF and continue stirring for 2 h. Dissolve the cationic surface-active ATRP initiator in THF and add it dropwise to the above suspension. Continue stirring for 8-12 h. Cool down, centrifuge, wash repeatedly with hot ethanol aqueous solution, vacuum dry, grind and sieve. 2) Add N,N,N',N'',N'''-pentamethyldivinyltriamine, cuprous bromide, sieved powder, and THF to a reaction flask, and mix thoroughly by ultrasonication. Then add methyl methacrylate, dodecyl methacrylate, and glycidyl methacrylate. Purge nitrogen gas to remove oxygen from the reaction flask. Under nitrogen protection, heat to 70°C and react for 8-24 h. After the reaction is complete, centrifuge to separate the solid, wash with THF multiple times, and vacuum dry to obtain the intercalated modified montmorillonite. The wear-resistant modified PET is prepared by a series of esterification reactions, transesterification reactions, and polycondensation reactions of terephthalic acid, ethylene glycol, 1,4-cyclohexanediol, hydroxyl-terminated organosilicon glycol, and dimethyl terephthalate. The functional nanofiller is nano-silica or nano-alumina modified with a silane coupling agent.

2. The high moisture resistance and scratch-resistant protective film base film for polarizers according to claim 1, characterized in that, The material composition of the functional bonding layer is as follows by weight: 5-10 parts intercalated modified montmorillonite, 1-3 parts graphene nanosheets, 1-3 parts antistatic agent, and 100 parts optical grade PET.

3. The high moisture resistance and scratch-resistant protective film base film for polarizers according to claim 1, characterized in that, The graphene nanosheets are hydroxylated graphene nanosheets with a sheet diameter of 1-5 μm; the antistatic agent is a polyether ester amide or an acrylate copolymer containing a quaternary ammonium salt structure.

4. The high moisture resistance and scratch-resistant protective film base film for polarizers according to claim 1, characterized in that, The material composition of the adhesive layer is as follows, by weight: 40-50 parts PET-g-MAH and 50-60 parts TPEE.

5. The high moisture resistance and scratch-resistant protective film base film for polarizers according to claim 1, characterized in that, The material composition of the outer wear-resistant layer is as follows by weight: 30-50 parts wear-resistant modified PET, 2-8 parts functional nanofillers, 1-5 parts ultraviolet absorber, and 50 parts optical grade PET.

6. The high moisture resistance and scratch-resistant protective film base film for polarizers according to claim 1, characterized in that, The ATRP initiator with cationic surface activity has the following structural formula: The molar ratio of the three monomers, polymethyl methacrylate, dodecyl methacrylate, and glycidyl methacrylate, is 10:3~6:4~7.

7. The high moisture resistance and scratch-resistant protective film base film for polarizers according to claim 1, characterized in that, The specific preparation process of the wear-resistant modified PET is as follows: 1) In a reaction vessel, terephthalic acid, ethylene glycol, 1,4-cyclohexanediol, and terminal hydroxyl organosilicon glycol with a molecular weight of 800-1500 are added. Antimony acetate catalyst and triphenyl phosphite stabilizer are also added. Under nitrogen protection, the temperature is gradually raised to 240-260℃ to carry out the esterification reaction and obtain product 1. 2) In a reaction vessel, dimethyl p-naphthalenedicarboxylate, ethylene glycol, zinc acetate, and the stabilizer triphenyl phosphite are added, and the temperature is gradually raised to 170~215℃ to carry out the transesterification reaction to obtain product 2; 3) Transfer product 2 to the product 1 system, draw a low vacuum, reduce the pressure to below 100 Pa, raise the temperature to 270-285℃, and carry out a polycondensation reaction for 2-4 hours. After the reaction is completed, release the vacuum, discharge the material, cool it, and granulate it to obtain wear-resistant modified PET resin.

8. The high moisture resistance and scratch-resistant protective film base film for polarizers according to claim 7, characterized in that, In step 1), the molar ratio of terephthalic acid, ethylene glycol, and 1,4-cyclohexanediethanol is 1:0.9~1.1:0.1~0.3; the amount of terminal hydroxyl organosilicon glycol added is 0.5~2% of the molar amount of terephthalic acid; in step 2), the molar ratio of dimethyl phthalate and ethylene glycol is 1:2.1~2.2; the mass ratio of product 2 to product 1 is 0.1~0.2:1.

Images