PVA optical film and preparation method thereof, and polaroid and preparation method thereof

Abstract

The invention relates to the technical field of high polymer chemistry, in particular to a PVA optical film, a preparation method of the PVA optical film, a polaroid and a preparation method of the polaroid. The PVA optical film comprises PVA resin, a plasticizer, a solvent and a surfactant, wherein the critical micelle concentration value CMC of the surfactant is 1 * 10 <-5 >-1 * 10 <-2 > M, the hydrophilic-lipophilic balance value HLB is 4-18, and the boiling point is greater than or equal to 100 DEG C. According to the method, the key performance indexes of the surfactant for preparing the PVA optical film are cooperatively regulated and controlled, so that the water absorption swelling degree of the PVA optical film is accurately controlled, stretching stripes are prevented from being formed in the subsequent stretching process due to excessive swelling of the PVA optical film due to water absorption, and the apparent quality of the polaroid is remarkably improved.

Description

Technical Field

[0001] This invention relates to the field of polymer chemistry technology, specifically to a PVA optical film and its preparation method, and a polarizer and its preparation method. Background Technology

[0002] Polyvinyl alcohol (PVA) optical film is the core raw material for manufacturing polarizers. Polarizers, as a key component of liquid crystal display panels, are widely used in various terminal products such as televisions, computer monitors, mobile phones, car navigation systems, and wearable electronic devices. As display technology rapidly develops towards thinner, more durable, and higher light transmittance, the market is placing increasingly stringent demands on the quality of PVA polarizers, especially on their appearance performance.

[0003] PVA polarizers are typically manufactured from PVA optical films through processes such as dyeing, stretching, cross-linking, and laminating with a protective film. During the uniaxial stretching of the PVA optical film, stretching streaks are a common surface defect. The formation mechanism is as follows: the PVA optical film first undergoes a water-absorbing and swelling treatment to improve its stretchability, followed by dyeing and high-ratio stretching. High tension exists during the longitudinal (MD) high-ratio stretching process, while shrinkage stress is generated in the transverse (TD) direction, causing narrowing in the TD direction and thus forming stretching streaks in the MD direction. In severe cases, the stretching streaks can accumulate and even form creases. This defect significantly affects the apparent yield of polarizers and has become a key issue restricting the production of high-quality polarizers.

[0004] Currently, industry solutions for stretching stripes on PVA polarizers mainly focus on the polarizer processing, such as adjusting the amount of boric acid added to promote PVA crosslinking and setting, or optimizing process parameters such as drying temperature. However, while these solutions can alleviate stretching stripes and creases to some extent, they inevitably introduce new drawbacks. For example, adjusting the amount of boric acid added can easily make the polarizer brittle and prone to cracking; optimizing the drying temperature will increase production costs or energy consumption, and some solutions may even cause the polarizer's optical performance to fail to meet standards.

[0005] Therefore, developing a PVA optical film preparation technology that is simple to process, precisely controlled, requires no complex chemical modification, and can fundamentally solve the stretching stripe defect has significant industrial value. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a PVA optical film and its preparation method, as well as a polarizer and its preparation method. By synergistically regulating the key performance indicators of the surfactant used in the preparation of the PVA optical film, precise control of the water absorption and swelling degree of the PVA optical film is achieved, avoiding the formation of stretching stripes during subsequent stretching due to excessive water absorption and swelling of the PVA optical film, thereby significantly improving the appearance quality of the polarizer.

[0007] To achieve the above objectives, in a first aspect, the present invention provides a PVA optical film comprising PVA resin, a plasticizer, a solvent, and a surfactant; wherein... The critical micelle concentration (CMC) of the surfactant is 1 × 10⁻⁶. -5 ~1×10 -2 M, with a hydrophilic-lipophilic balance value (HLB) between 4 and 18, and a boiling point ≥100℃.

[0008] Preferably, the water absorption swelling degree of the PVA optical film is 110~130%.

[0009] Preferably, the degree of polymerization of the PVA resin is 1700~3200, more preferably 2000~2800, and the degree of alcoholysis is 80~99.99 mol%, more preferably 90~99.99 mol%.

[0010] Preferably, the plasticizer is selected from one or more of glycerol, triacetin, acetone glycerol, polyglycerol, ethylene glycol, polyethylene glycol, propylene glycol, isopropanol, and dimethyl sulfate, with glycerol being the most preferred.

[0011] Preferably, the solvent is demineralized water and / or ultrapure water, with demineralized water being the most preferred.

[0012] Preferably, the surfactant is selected from one or more of sodium dodecylbenzenesulfonate, sodium dodecyl sulfate, sodium dodecyl sulfate, ammonium dodecyl sulfate, polyoxyethylene lauryl ether, polyoxyethylene oil ether, oleic acid diethanolamide, sodium lauryl polyoxyethylene ether sulfate, potassium salt of polyether phosphate, ethylene glycol fatty acid ester, lauryl alcohol polyoxyethylene ether, glyceryl monostearate, potassium oleate, polysorbate 20, polysorbate 80 and polyoxyethylene dioleate, preferably a binary compound system composed of two surfactants.

[0013] Preferably, the weight ratio of the PVA resin, solvent, plasticizer and surfactant is 1:1~3:0.2~0.05:0.0002~0.005.

[0014] Preferably, the weight ratio of the first surfactant to the second surfactant in the binary compound system is 1:0.3~3.

[0015] Preferably, the common logarithm of the CMC value of the first surfactant is Log(CMC) > -3.5, and the common logarithm of the CMC value of the second surfactant is Log(CMC) < -3.5.

[0016] Preferably, the first surfactant has an HLB value of 6 to 10, and the second surfactant has an HLB value of 14 to 17.

[0017] Secondly, the present invention provides a method for preparing a PVA optical film as described herein, characterized in that the preparation method comprises: 1) In the presence of a solvent, PVA resin, plasticizer, and surfactant are dissolved to form a homogeneous PVA solution; 2) The homogeneous PVA solution is cast into a film and pre-dried to obtain a pre-dried film; 3) The pre-dried film is annealed to obtain a PVA optical film.

[0018] Preferably, in step 1), the degree of polymerization of the PVA resin is 1700~3200, more preferably 2000~2800, and the degree of alcoholysis is 80~99.99 mol%, more preferably 90~99.99 mol%.

[0019] Preferably, the plasticizer is selected from one or more of glycerol, triacetin, acetone glycerol, polyglycerol, ethylene glycol, polyethylene glycol, propylene glycol, isopropanol, and dimethyl sulfate, with glycerol being the most preferred.

[0020] Preferably, the solvent is demineralized water and / or ultrapure water, with demineralized water being the most preferred.

[0021] Preferably, the surfactant is selected from one or more of sodium dodecylbenzenesulfonate, sodium dodecyl sulfate, sodium dodecyl sulfate, ammonium dodecyl sulfate, polyoxyethylene lauryl ether, polyoxyethylene oil ether, oleic acid diethanolamide, sodium lauryl polyoxyethylene ether sulfate, potassium salt of polyether phosphate, ethylene glycol fatty acid ester, lauryl alcohol polyoxyethylene ether, glyceryl monostearate, potassium oleate, polysorbate 20, polysorbate 80 and polyoxyethylene dioleate, preferably a binary compound system composed of two surfactants.

[0022] Preferably, the weight ratio of the PVA resin, solvent, plasticizer and surfactant is 1:1~3:0.2~0.05:0.0002~0.005.

[0023] Preferably, the weight ratio of the first surfactant to the second surfactant in the binary compound system is 1:0.3~3.

[0024] Preferably, the common logarithm of the CMC value of the first surfactant is Log(CMC) > -3.5, and the common logarithm of the CMC value of the second surfactant is Log(CMC) < -3.5.

[0025] Preferably, the first surfactant has an HLB value of 6 to 10, and the second surfactant has an HLB value of 14 to 17.

[0026] Preferably, in step 2), the conditions for casting film formation include: the temperature of the casting roller is 80~100℃, preferably 85~95℃.

[0027] Preferably, the pre-drying conditions include: the temperature of the drying roller is 40~100℃, preferably 50~80℃.

[0028] Preferably, in step 3), the annealing conditions include: a temperature of 30~130℃, preferably 50~70℃; and a time of 1~3min.

[0029] Thirdly, the present invention provides a polarizer, which is made from the PVA optical film described in the present invention.

[0030] Fourthly, the present invention provides a method for preparing a polarizer, the method comprising: subjecting the PVA optical film of the present invention to swelling, dyeing, washing, stretching, color correction, water washing, drying, laminating, and secondary drying in sequence to obtain a polarizer.

[0031] Preferably, the swelling conditions include: immersing the PVA optical film in desalinated water at a temperature of 25~40°C for 60~150 seconds.

[0032] Preferably, the dyeing conditions include: dyeing the swollen PVA optical film for 6 to 200 seconds using a solution containing a dichroic substance at a temperature of 25 to 40°C.

[0033] Preferably, the solution containing the dichroic substance contains KI at a mass concentration of 1-4 wt%, I2 at a mass concentration of 0.02-0.2 wt%, and H3BO3 at a mass concentration of 0-4 wt%, preferably H3BO3 at a mass concentration of 1-3 wt%.

[0034] Preferably, the washing conditions include: washing the stained PVA optical film with a washing solution at a temperature of 25~50°C for 60~200s.

[0035] Preferably, the washing solution contains KI at a mass concentration of 1.5-4 wt% and H3BO3 at a mass concentration of 1-3 wt%.

[0036] Preferably, the stretching conditions include: using a stretching solution to stretch the cleaned PVA optical film for 60 to 120 seconds at a temperature of 50 to 65°C, with a total stretching ratio of 5 to 7 times.

[0037] Preferably, the extended solution contains KI at a mass concentration of 1.5-4 wt% and H3BO3 at a mass concentration of 2-5 wt%.

[0038] Preferably, the conditions for color correction include: using a color-correcting solution to correct the color of the extended PVA optical film for 30 to 60 seconds at a temperature of 25 to 40°C.

[0039] Preferably, the complementary color solution contains KI at a mass concentration of 2-5 wt% and H3BO3 at a mass concentration of 0.5-2.5 wt%.

[0040] Preferably, the washing conditions include immersing the color-corrected PVA optical film in a desalination aqueous solution at 15-40°C for 20-40 seconds.

[0041] Preferably, the drying conditions include: a temperature of 40~110℃, more preferably 40~80℃; and a time of 20~60s.

[0042] Preferably, the bonding conditions include: applying a protective film to both sides of the dried PVA optical film using an adhesive.

[0043] Preferably, the adhesive is selected from Z-200 (Mitsubishi) and WT-07 (Chongqing Spectrum).

[0044] Preferably, the protective film is selected from one or more of TAC, PET, PMMA, COP and COC.

[0045] Preferably, the secondary drying conditions include: drying the PVA optical film with the protective film attached at a temperature of 40~100℃ for 50~400s.

[0046] In the above technical solution, the PVA optical film of the present invention achieves precise control over the water absorption and swelling of the PVA optical film by synergistically regulating the critical micelle concentration (CMC), hydrophilic-lipophilic balance (HLB), and boiling point of the surfactant. This fundamentally solves the defects of stretching stripes and creases in polarizers prepared from PVA optical films after dyeing and stretching. The PVA optical film prepared using the method of the present invention produces polarizers with excellent appearance quality and no defects such as stretching stripes.

[0047] Meanwhile, the PVA optical film preparation process of the present invention is simple, requires no complex chemical modification, uses commercially available conventional products, has controllable costs, and does not require special equipment during the preparation process, making it easy to scale up for industrial production.

[0048] Moreover, the polarizer preparation method of the present invention has clear procedures and controllable parameters. The polarizer produced not only has excellent appearance performance, but also good optical and mechanical properties, which can meet the application requirements of various high-end display panels.

[0049] Furthermore, the technical solution of the present invention avoids the problems of polarizer brittleness, increased cost, and substandard optical performance caused by adjusting the amount of boric acid added or the drying temperature in the prior art, and has significant technical advantages and industrial application value.

[0050] Other features and advantages of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0051] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the following detailed description to explain the invention, but do not constitute a limitation thereof. In the drawings: Figure 1 The appearance of the polarizer prepared in Example 1; Figure 2 The appearance of the polarizer prepared in Comparative Example 1 is shown. Figure 3 The appearance of the polarizer prepared in Comparative Example 3 is shown. Detailed Implementation

[0052] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0053] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0054] In a first aspect, the present invention provides a PVA optical film, the PVA optical film comprising PVA resin, plasticizer, solvent, and surfactant; wherein... The critical micelle concentration (CMC) of the surfactant is 1 × 10⁻⁶. -5 ~1×10 -2 M, with a hydrophilic-lipophilic balance value (HLB) between 4 and 18, and a boiling point ≥100℃.

[0055] The PVA optical film of this invention achieves precise control over the water absorption and swelling of the PVA optical film by synergistically regulating the critical micelle concentration (CMC), hydrophilic-lipophilic balance (HLB), and boiling point of the surfactant. This fundamentally solves the defects of stretching stripes and creases in polarizers prepared from PVA optical films after dyeing and stretching. The PVA optical film prepared using the method of this invention produces polarizers with excellent appearance quality and no stretching stripes or other defects.

[0056] The CMC value determines the form of the surfactant at a given concentration. When the surfactant concentration is below the CMC value, it exists in a monomolecular state, mainly affecting the surface energy of the PVA chains. When the concentration is above the CMC value, the surfactant forms micelles. These micelles easily aggregate in the PVA network to form opaque patches, leading to a decrease in the optical performance of the PVA optical film. Furthermore, micelles with high HLB values ​​act as "hydrophilic reservoirs" and "relay stations" for moisture transport, accelerating the swelling of the PVA film and causing excessive swelling or rapid swelling, resulting in wrinkles. This invention limits the CMC value of the surfactant to 1 × 10⁻⁶. -5 ~1×10 -2 Between M, excessive micelle formation can be avoided, while ensuring appropriate adjustment of the surface energy of the PVA optical film.

[0057] The HLB value determines the final orientation of the surfactant at the PVA-water interface. Surfactant molecules with low HLB values ​​(<10) tend to anchor their hydrophilic chains to PVA segments, with the hydrophobic groups facing outwards, forming a hydrophobic barrier that inhibits water molecule penetration and reduces swelling after water absorption. However, low HLB surfactants have poor water solubility and low CMC values, making them prone to forming micelles. During rapid drying and film formation, they do not have enough time to migrate / distribute evenly, resulting in aggregated streaks. Surfactants with high HLB values ​​(>13) have good water solubility and can strongly bind water molecules, forming hydrophilic channels in the PVA network, promoting water penetration, and increasing water absorption rate and swelling. This invention optimizes surfactants with HLB values ​​between 4 and 18, especially by using a first surfactant with an HLB value of 6 to 10 and a second surfactant with an HLB value of 14 to 17 to form a binary compound system. This balances the effects of the hydrophobic barrier and the hydrophilic channels, achieving precise control of swelling.

[0058] Since PVA solutions need to be cast and dried to form PVA optical films, if the boiling point of the surfactant is below 100°C, it is prone to boiling during the drying process, forming bubbles or holes within the film, affecting the integrity and optical properties of the film. Therefore, this invention limits the boiling point of the surfactant to ≥100°C to ensure the stability of the film formation process.

[0059] In this invention, the PVA optical film needs to meet the high magnification stretch of 5 to 7 times, which requires controlling the water absorption swelling degree of the PVA optical film to be 110 to 130% to avoid the formation of stretching stripes during the stretching process.

[0060] In this invention, the degree of polymerization of the PVA resin is 1700~3200, preferably 2000~2800, and the degree of alcoholysis is 80~99.99 mol%, preferably 90~99.99 mol%. For example, it can be a PVA resin with a degree of polymerization of 1700 and a degree of hydrolysis of 80 mol%, a degree of polymerization of 2000 and a degree of hydrolysis of 85 mol%, a degree of polymerization of 2200 and a degree of hydrolysis of 90 mol%, a degree of polymerization of 2500 and a degree of hydrolysis of 89 mol%, a degree of polymerization of 2800 and a degree of hydrolysis of 95 mol%, a degree of polymerization of 3000 and a degree of hydrolysis of 94 mol%, or a degree of polymerization of 3200 and a degree of hydrolysis of 99 mol%, etc.

[0061] In this invention, the plasticizer can be selected from commonly used plasticizers in the art, such as glycerol, triacetin, acetone glycerol, polyglycerol, ethylene glycol, polyethylene glycol, propylene glycol, isopropanol, and dimethyl sulfate, or one or more of these. However, glycerol is a commonly used plasticizer for PVA films, exhibiting excellent compatibility with PVA resin. It can effectively insert itself between PVA molecular chains, weakening the hydrogen bonding between molecular chains, improving the flexibility and tensile properties of the film, and preventing the film from breaking under high-ratio stretching. Therefore, glycerol is preferably the plasticizer used in this invention.

[0062] In this invention, the solvent is demineralized water and / or ultrapure water, preferably demineralized water.

[0063] In this invention, the surfactant is selected from one or more of sodium dodecylbenzenesulfonate, sodium dodecyl sulfate, sodium dodecyl sulfate, ammonium dodecyl sulfate, polyoxyethylene lauryl ether, polyoxyethylene oil ether, oleic acid diethanolamide, sodium lauryl polyoxyethylene ether sulfate, potassium salt of polyether phosphate, ethylene glycol fatty acid ester, lauryl alcohol polyoxyethylene ether, glyceryl monostearate, potassium oleate, polysorbate 20, polysorbate 80, and polyoxyethylene dioleate.

[0064] In a preferred embodiment of the present invention, a binary compound surfactant system is adopted, and the first surfactant is limited to Log(CMC)>-3.5 and HLB value 6~10, and the second surfactant is limited to Log(CMC)<-3.5 and HLB value 14~17, with a weight ratio of 1:0.3~3. This can achieve the complementary advantages of the two surfactants, further precisely control the water absorption and swelling, and avoid the defects caused by the use of a single surfactant.

[0065] In this invention, the weight ratio of the PVA resin, solvent, plasticizer and surfactant is 1:1~3:0.2~0.05:0.0002~0.005.

[0066] Secondly, the present invention provides a method for preparing a PVA optical film as described herein, characterized in that the preparation method comprises: 1) In the presence of a solvent, PVA resin, plasticizer, and surfactant are dissolved to form a homogeneous PVA solution; 2) The homogeneous PVA solution is cast into a film and pre-dried to obtain a pre-dried film; 3) The pre-dried film is annealed to obtain a PVA optical film.

[0067] The PVA optical film preparation process of this invention is simple, requires no complex chemical modification, uses commercially available conventional products, has controllable costs, and does not require special equipment during the preparation process, making it easy to scale up for industrial production.

[0068] In this invention, in step 1), the degree of polymerization of the PVA resin is 1700~3200, preferably 2000~2800, and the degree of alcoholysis is 80~99.99 mol%, preferably 90~99.99 mol%. For example, it can be a PVA resin with a degree of polymerization of 1700 and a degree of hydrolysis of 80 mol%, a degree of polymerization of 2000 and a degree of hydrolysis of 85 mol%, a degree of polymerization of 2200 and a degree of hydrolysis of 90 mol%, a degree of polymerization of 2500 and a degree of hydrolysis of 89 mol%, a degree of polymerization of 2800 and a degree of hydrolysis of 95 mol%, a degree of polymerization of 3000 and a degree of hydrolysis of 94 mol%, or a degree of polymerization of 3200 and a degree of hydrolysis of 99 mol%, etc.

[0069] In this invention, the plasticizer can be selected from commonly used plasticizers in the art, such as glycerol, triacetin, acetone glycerol, polyglycerol, ethylene glycol, polyethylene glycol, propylene glycol, isopropanol, and dimethyl sulfate, or one or more of these. However, glycerol is a commonly used plasticizer for PVA films, exhibiting excellent compatibility with PVA resin. It can effectively insert itself between PVA molecular chains, weakening the hydrogen bonding between molecular chains, improving the flexibility and tensile properties of the film, and preventing the film from breaking under high-ratio stretching. Therefore, glycerol is preferably the plasticizer used in this invention.

[0070] In this invention, the solvent is demineralized water and / or ultrapure water, preferably demineralized water.

[0071] In this invention, the surfactant is selected from one or more of sodium dodecylbenzenesulfonate, sodium dodecyl sulfate, sodium dodecyl sulfate, ammonium dodecyl sulfate, polyoxyethylene lauryl ether, polyoxyethylene oil ether, oleic acid diethanolamide, sodium lauryl polyoxyethylene ether sulfate, potassium salt of polyether phosphate, ethylene glycol fatty acid ester, lauryl alcohol polyoxyethylene ether, glyceryl monostearate, potassium oleate, polysorbate 20, polysorbate 80, and polyoxyethylene dioleate.

[0072] In a preferred embodiment of the present invention, a binary compound surfactant system is adopted, and the first surfactant is limited to Log(CMC)>-3.5 and HLB value 6~10, and the second surfactant is limited to Log(CMC)<-3.5 and HLB value 14~17, with a weight ratio of 1:0.3~3. This can achieve the complementary advantages of the two surfactants, further precisely control the water absorption and swelling, and avoid the defects caused by the use of a single surfactant.

[0073] In this invention, the weight ratio of the PVA resin, solvent, plasticizer and surfactant is 1:1~3:0.2~0.05:0.0002~0.005.

[0074] In this invention, in step 2), before casting the film, the PVA solution is coarsely filtered and then extruded into an extruder, filtered again, and then cast into the die head of the casting machine.

[0075] In this invention, in step 2), the casting temperature must be sufficient to maintain good fluidity of the PVA solution, facilitating uniform spreading on the casting roller to form a PVA optical film of uniform thickness. If the temperature is below 80°C, the PVA solution has high viscosity and poor fluidity, resulting in an uneven thickness of the obtained PVA optical film. If the temperature is above 100°C, the solvent evaporates too quickly, and defects such as cracking and bubbles easily appear on the surface of the PVA optical film. The casting conditions include: the temperature of the casting roller is 80~100°C, preferably 85~95°C.

[0076] In this invention, the pre-drying temperature should be able to quickly remove most of the solvent in the membrane, while avoiding excessively rapid solvent evaporation that could lead to uneven membrane shrinkage. The pre-drying conditions include: a drying roller temperature of 40~100℃, preferably 50~80℃; hot air drying or far-infrared drying methods can be used.

[0077] In this invention, in step 3), the annealing conditions include: a temperature of 30~130℃, preferably 50~70℃; and a time of 1~3min.

[0078] Thirdly, the present invention provides a polarizer, which is made from the PVA optical film described in the present invention.

[0079] Fourthly, the present invention provides a method for preparing a polarizer, the method comprising: subjecting the PVA optical film of the present invention to swelling, dyeing, washing, stretching, color correction, water washing, drying, laminating, and secondary drying in sequence to obtain a polarizer.

[0080] The polarizer preparation method of the present invention has a clear process and controllable parameters. The polarizer prepared not only has excellent appearance performance, but also has good optical and mechanical properties, which can meet the application requirements of various high-end display panels.

[0081] In this invention, in order to remove dust from the surface of the PVA optical film or plasticizer contained in the film, and to cause the PVA optical film to swell in order to improve the stretching efficiency, the swelling conditions include: immersing the PVA optical film in desalinated water at a temperature of 25~40°C for 60~150s.

[0082] In this invention, the dyeing conditions include: dyeing the swollen PVA optical film for 6 to 200 seconds using a solution containing a dichroic substance at a temperature of 25 to 40°C.

[0083] In this invention, the solution containing the dichroic substance contains 1-4 wt% KI, 0.02-0.2 wt% I2, and 0-4 wt% H3BO3, preferably 1-3 wt% H3BO3. For example, the solution containing the dichroic substance may contain 1 wt% KI, 0.02 wt% I2, 2 wt% KI, 0.02 wt% I2, and 0.5 wt% H3BO3. t% H3BO3; 3wt% KI, 0.05wt% I2, and 2wt% H3BO3; 4wt% KI, 0.1wt% I2, and 2wt% H3BO3; 2wt% KI, 0.15wt% I2, and 3wt% H3BO3; 2wt% KI, 0.2wt% I2, and 4wt% H3BO3, etc.

[0084] In this invention, the dyed PVA optical film undergoes a washing process to remove free iodine molecules physically adsorbed on the film surface, preventing over-dyeing and allowing the initially stretched PVA optical film to undergo preliminary cross-linking. The washing conditions include: washing the dyed PVA optical film with a washing solution at a temperature of 25~50℃ for 60~200s, preferably 90~120s.

[0085] In this invention, the washing solution contains KI at a mass concentration of 1.5-4 wt% and H3BO3 at a mass concentration of 1-3 wt%.

[0086] In this invention, iodine, as a dichroic substance, will sublimate and escape after being adsorbed by PVA in a humid and hot environment. Therefore, it is necessary to crosslink the PVA molecular chains to form a crosslinked network to lock in the iodine molecules. In addition, in order to orient the iodine molecules adsorbed by the PVA molecular chains, a certain degree of stretching is required. The crosslinking reaction is carried out simultaneously in this process. To avoid the film being difficult to stretch after crosslinking, this process needs to be stretched at the maximum stretching ratio. The stretching conditions include: using a stretching solution at a temperature of 50~65°C, stretching the cleaned PVA optical film for 60~120s, with a total stretching ratio of 5~7 times.

[0087] In this invention, the extended solution contains KI at a mass concentration of 1.5 to 4 wt%, preferably 2 wt%, and H3BO3 at a mass concentration of 2 to 5 wt%, preferably 3 wt%.

[0088] In this invention, after the PVA optical film is stretched at a high ratio in the stretching groove, relative sliding occurs between its molecular chains, which amplifies the problem of uneven dyeing during the dyeing process. Therefore, it is necessary to correct the insufficiently dyed PVA optical film. The conditions for color correction include: using a color correction solution at a temperature of 25~40℃ to correct the color of the stretched PVA optical film for 30~60s.

[0089] In this invention, the complementary color solution contains KI at a mass concentration of 2-5 wt%, preferably 3 wt%, and H3BO3 at a mass concentration of 0.5-2.5 wt%, preferably 1.5 wt%.

[0090] In this invention, in order to remove the residues such as free potassium iodide and boric acid that adhered to the surface of the PVA optical film in the previous steps, the washing conditions include: immersing the color-corrected PVA optical film in a desalination aqueous solution at 15~40℃ for 20~40s.

[0091] In this invention, the wet film is dried using methods such as hot air drying or far-infrared drying. The film after the drying process is named a polarizing film. The drying conditions include: a temperature of 40~110℃, preferably 40~80℃; and a time of 20~60s.

[0092] In this invention, the bonding conditions include: applying a protective film to both sides of the dried PVA optical film using an adhesive.

[0093] In this invention, the adhesive is acetylated polyvinyl alcohol, specifically Z-200 (produced by Mitsubishi Chemical Corporation, Japan) or WT-07 (produced by Chongqing Spectrum New Materials Technology Co., Ltd.).

[0094] In this invention, the protective film is selected from one or more of TAC, PET, PMMA, COP and COC.

[0095] In this invention, after the protective film is laminated, in order to remove the moisture contained in the adhesive, the three-layer film structure needs to be dried to promote the adhesion between the protective film and the polarizing film. This can be done using methods such as hot air drying or far-infrared drying. The conditions for the secondary drying include drying the PVA optical film with the protective film laminated at a temperature of 40~100℃ for 50~400 seconds.

[0096] In this invention, the test method for the water absorption and swelling degree of the PVA optical film is as follows: after the PVA optical film passes through the swelling tank, the original film width L0 and the width L1 after swelling are measured, and the swelling degree is calculated as (L1 / L0)×100%.

[0097] The present invention will be described in detail below through examples. In the following examples, the pharmaceuticals and agents are all conventional commercially available products.

[0098] Preparation Example 1 Accurately weigh 40 parts of PVA resin with a degree of polymerization of 2500 and a degree of hydrolysis of 99.9 mol%, 100 parts of deionized water, 4 parts of glycerol as plasticizer, 0.025 parts of polyoxyethylene dioleate (Log(CMC)=-3.1, HLB=7.5) as the first surfactant, and 0.025 parts of polysorbate 20 (Log(CMC)=-4.7, HLB=16) as the second surfactant. Mix and dissolve to form a homogeneous PVA solution. The homogeneous PVA solution is coarsely filtered and then extruded into an extruder. After being filtered again, it is cast into a casting die at 85°C. After drying with an 85°C drying roller, it is then dried in an 80°C oven for 2 minutes to obtain the finished PVA optical film, denoted as M1.

[0099] Preparation Example 2 The preparation was carried out according to Preparation Example 1, except that "0.025 parts of polysorbate 20 (Log(CMC)=-4.7, HLB=16) as the second surfactant" in Preparation Example 1 was replaced with "0.025 parts of polyoxyethylene lauryl ether (Log(CMC)=-4.0, HLB=13.3) as the second surfactant". All other steps remained the same, and the finished PVA optical film was obtained, which was denoted as M2.

[0100] Preparation Example 3 The preparation was carried out according to Preparation Example 1, except that "0.025 parts of polysorbate 20 (Log(CMC)=-4.7, HLB=16) as the second surfactant" in Preparation Example 1 was replaced with "0.025 parts of sodium dodecyl sulfate (Log(CMC)=-6.0, HLB=40) as the second surfactant". All other steps remained the same, and the finished PVA optical film was obtained, which was denoted as M3.

[0101] Preparation Example 4 The preparation was carried out according to Preparation Example 1, except that "0.025 parts of polyoxyethylene dioleate (Log(CMC)=-3.1, HLB=7.5) as the first surfactant and 0.025 parts of polysorbate 20 (Log(CMC)=-4.7, HLB=16) as the second surfactant" was replaced with "0.025 parts of glyceryl monostearate (Log(CMC)=-5.0, HLB=5.5) as the first surfactant and 0.025 parts of potassium oleate (Log(CMC)=-3.0, HLB=20) as the second surfactant". All other steps remained the same, and the finished PVA optical film was obtained, denoted as M5.

[0102] Preparation Example 5 The preparation was carried out according to Preparation Example 1, except that "0.025 parts of polyoxyethylene dioleate (Log(CMC)=-3.1, HLB=7.5) as the first surfactant" was replaced with "0.025 parts of ethylene glycol fatty acid ester (Log(CMC)=-5.0, HLB=2.1) as the first surfactant". All other steps remained the same, and the finished PVA optical film was obtained, denoted as M4.

[0103] Example 1 S1. Swelling: The unstretched PVA optical film M1 from Preparation Example 1 is immersed in a swelling tank filled with demineralized water to remove dust and excess plasticizer from the surface of the PVA optical film, causing the PVA optical film to swell and improve the stretching efficiency; wherein, the temperature of the demineralized water in the swelling tank is 28°C and the swelling time is 120s. S2, Staining: The swollen PVA optical film from S1 is placed into a staining tank, and the PVA optical film is immersed in a staining tank containing a dichroic substance solution. The dichroic substance solution contains KI / I2 / H3BO3, wherein the mass concentration of KI is 2wt%, the mass concentration of I2 is 0.1wt%, the mass concentration of H3BO3 is 2wt%, the staining temperature is 30℃, and the staining time is 120s. S3. Washing: The PVA optical film dyed in S2 is washed in a washing tank, and the initially stretched PVA optical film is initially cross-linked; wherein, the mass concentration of KI in the washing tank is 2.5wt%, the mass concentration of H3BO3 is 2wt%, the temperature is 30℃, and the time is 120s. S4. Stretching: The PVA optical film washed in S3 is stretched in a stretching tank. The stretching tank contains KI / H3BO3, wherein the mass concentration of KI is 2.5wt% and the mass concentration of H3BO3 is 3.5wt%. The total stretching ratio is 6 times, the stretching temperature is 50℃, and the stretching time is 90s. S5, Color Complementation: The PVA optical film stretched at a high magnification in the stretching tank in S4 is immersed in the color complementation solution in the color complementation tank for color complementation; the mass concentration of KI in the color complementation solution is 3.5wt%, the mass concentration of H3BO3 is 1.5wt%, the color complementation temperature is 30℃, and the color complementation time is 45s. S6. Water washing: Immerse the PVA optical film after color correction in S5 in a water washing tank filled with desalinated water to remove the free potassium iodide, boric acid and other residues that adhered to the surface of the PVA optical film in the previous steps; the temperature of the water washing tank is 30℃. S7. Drying: The wet film washed with water in S6 is dried with hot air at 75°C for 40 seconds to obtain the initial polarizing film. S8. Lamination: Use Z-200 to laminate the TAC protective film onto both sides of the polarizing film after S7 has been dried. S9. Secondary drying: Dry the polarizing film with the protective film attached in S8 with hot air at 70℃ for 220s to make a polarizing film, denoted as PL-M1.

[0104] Example 2 The method described in Example 1 was carried out, except that "preparation of unstretched PVA optical film M1 in Example 1" in S1 was replaced with "preparation of unstretched PVA optical film M2 in Example 2", and other conditions remained unchanged, and a polarizer was obtained, denoted as PL-M2.

[0105] Comparative Example 1 The method described in Example 1 was carried out, except that "preparation of unstretched PVA optical film M1 in Example 1" in S1 was replaced with "preparation of unstretched PVA optical film M3 in Example 3", and other conditions remained unchanged, and a polarizer was obtained, denoted as PL-M3.

[0106] Comparative Example 2 The method described in Example 1 was carried out, except that "preparation of unstretched PVA optical film M1 in Example 1" in S1 was replaced with "preparation of unstretched PVA optical film M4 in Example 4", and other conditions remained unchanged, and a polarizer was obtained, denoted as PL-M4.

[0107] Comparative Example 3 The method described in Example 1 was carried out, except that "the unstretched PVA optical film M1 in Example 1" in S1 was replaced with "the unstretched PVA optical film M5 in Example 5", and other conditions remained unchanged. A polarizer was then prepared and denoted as PL-M5.

[0108] Detection Example 1 The swelling degree of the PVA optical films prepared in Examples 1-5 was calculated respectively, and the dyeing and appearance of the polarizers prepared in Examples 1-2 and Comparative Examples 1-3 were tested. The results are shown in Table 1 and 2. Figure 1-3 As shown.

[0109] Table 1

[0110] Depend on Figure 1 The results show that the polarizer prepared in Example 1 of the present invention has no stretching stripes; Depend on Figure 2 The results show that the polarizer prepared in Comparative Example 1 of this invention has severe creases. Depend on Figure 3 The results show that the polarizer prepared in Comparative Example 3 of this invention has severe stretching stripes.

[0111] As can be seen from the test results in Table 1, the polarizers prepared in Examples 1-2 of this invention have a normal appearance and no stretching stripes.

[0112] In Comparative Example 1, the excessive HLB content of the second surfactant caused the PVA optical film to rapidly absorb water and swell during the swelling process, reaching a swelling degree of up to 140%. This resulted in excessive lateral expansion, causing the PVA optical film to narrow during stretching and produce stretch marks and even creases. Comparative Example 3 also suffered from severe stretching stripes on the polarizer due to excessive swelling of the PVA optical film.

[0113] Although the polarizer of Comparative Example 2 did not have stretching stripes, the PVA optical film was difficult to absorb water and was not easy to dye during the swelling process due to the strong hydrophobicity of the first surfactant and the amount used far exceeding its CMC value. Therefore, the polarizer of Comparative Example 2 was unqualified.

[0114] In summary, the present invention limits and coordinates the CMC value of the surfactant and further limits its HLB value, which can effectively reduce the water absorption and swelling of the PVA optical film, so that the obtained PVA polarizer has better appearance performance.

[0115] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0116] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0117] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A PVA optical film characterized by, The PVA optical film comprises PVA resin, plasticizer, solvent, and surfactant; wherein, The critical micelle concentration value CMC of the surfactant is 1 x 10 -5 ~1 x 10 -2 M, the hydrophilic-lipophilic balance value HLB is between 4~18, and the boiling point is ≥ 100℃.

2. The PVA optical film according to claim 1, wherein, The water absorption and swelling degree of the PVA optical film is 110~130%.

3. The PVA optical film according to claim 1 or 2, characterized in that, The degree of polymerization of the polyvinyl alcohol in the PVA resin is 1700-3200, preferably 2000-2800, and the degree of alcoholysis is 80-99.99 mol%, preferably 90-99.99 mol%. The plasticizer is selected from one or more of glycerol, triacetin, acetone glycerol, polyglycerol, ethylene glycol, polyethylene glycol, propylene glycol, isopropanol and dimethyl sulfate, preferably glycerol; The solvent is demineralized water and / or ultrapure water, preferably demineralized water; The surfactant is selected from one or more of sodium dodecylbenzenesulfonate, sodium dodecyl sulfonate, sodium dodecyl sulfate, ammonium dodecyl sulfate, polyoxyethylene lauryl ether, polyoxyethylene oil ether, oleic acid diethanolamide, sodium lauryl polyoxyethylene ether sulfate, potassium salt of polyether phosphate, ethylene glycol fatty acid ester, lauryl polyoxyethylene ether, glyceryl monostearate, potassium oleate, polysorbate 20, polysorbate 80 and polyoxyethylene dioleate, preferably a binary compound system composed of two surfactants; Preferably, the weight ratio of the PVA resin, solvent, plasticizer, and surfactant is 1:1~3:0.2~0.05:0.0002~0.005; More preferably, the weight ratio of the first surfactant to the second surfactant in the binary compound system is 1:0.3~3; More preferably, the common logarithm Log(CMC) of the CMC value of the first surfactant is >-3.5, and the common logarithm Log(CMC) of the CMC value of the second surfactant is <-3.5; More preferably, the first surfactant has an HLB value of 6 to 10, and the second surfactant has an HLB value of 14 to 17.

4. A method for preparing a PVA optical film as described in any one of claims 1-3, characterized in that, The preparation method includes: 1) In the presence of a solvent, PVA resin, plasticizer, and surfactant are dissolved to form a homogeneous PVA solution; 2) The homogeneous PVA solution is cast into a film and pre-dried to obtain a pre-dried film; 3) The pre-dried film is annealed to obtain a PVA optical film.

5. The preparation method according to claim 4, characterized in that, In step 1), the degree of polymerization of the PVA resin is 1700~3200, preferably 2000~2800, and the degree of alcoholysis is 80~99.99 mol%, preferably 90~99.99 mol%. The plasticizer is selected from one or more of glycerol, triacetin, acetone glycerol, polyglycerol, ethylene glycol, polyethylene glycol, propylene glycol, isopropanol and dimethyl sulfate, preferably glycerol; The solvent is demineralized water and / or ultrapure water, preferably demineralized water; The surfactant is selected from one or more of sodium dodecylbenzenesulfonate, sodium dodecyl sulfonate, sodium dodecyl sulfate, ammonium dodecyl sulfate, polyoxyethylene lauryl ether, polyoxyethylene oil ether, oleic acid diethanolamide, sodium lauryl polyoxyethylene ether sulfate, potassium salt of polyether phosphate, ethylene glycol fatty acid ester, lauryl polyoxyethylene ether, glyceryl monostearate, potassium oleate, polysorbate 20, polysorbate 80 and polyoxyethylene dioleate, preferably a binary compound system composed of two surfactants; Preferably, the weight ratio of the PVA resin, solvent, plasticizer, and surfactant is 1:1~3:0.2~0.05:0.0002~0.005; More preferably, the weight ratio of the first surfactant to the second surfactant in the binary compound system is 1:0.3~3; More preferably, the common logarithm Log(CMC) of the CMC value of the first surfactant is >-3.5, and the common logarithm Log(CMC) of the CMC value of the second surfactant is <-3.5; More preferably, the first surfactant has an HLB value of 6 to 10, and the second surfactant has an HLB value of 14 to 17.

6. The preparation method according to claim 4 or 5, characterized in that, In step 2), the conditions for casting film formation include: the temperature of the casting roller is 80~100℃, preferably 85~95℃; Preferably, the pre-drying conditions include: the temperature of the drying roller is 40~100℃, preferably 50~80℃.

7. The preparation method according to any one of claims 4-6, characterized in that, In step 3), the annealing conditions include: a temperature of 30~130℃, preferably 50~70℃; and a time of 1~3min.

8. A polarizer, characterized in that, The polarizer is made from the PVA optical film as described in any one of claims 1-3.

9. A method for preparing a polarizer, characterized in that, The preparation method includes: subjecting the PVA optical film according to any one of claims 1-3 to swelling, dyeing, washing, stretching, color correction, water washing, drying, lamination, and secondary drying in sequence to obtain a polarizer.

10. The preparation method according to claim 9, characterized in that, The swelling conditions include: immersing the PVA optical film in desalinated water at a temperature of 25~40℃ for 60~150s; The dyeing conditions include: dyeing the swollen PVA optical film for 6 to 200 seconds using a solution containing a dichroic substance at a temperature of 25 to 40°C. Preferably, the solution containing the dichroic substance contains KI at a mass concentration of 1-4 wt%, I2 at a mass concentration of 0.02-0.2 wt%, and H3BO3 at a mass concentration of 0-4 wt%, preferably H3BO3 at a mass concentration of 1-3 wt%. The washing conditions include: washing the stained PVA optical film with a washing solution at a temperature of 25~50℃ for 60~200s; Preferably, the washing solution contains KI at a mass concentration of 1.5-4 wt% and H3BO3 at a mass concentration of 1-3 wt%. The stretching conditions include: using a stretching solution to stretch the cleaned PVA optical film for 60 to 120 seconds at a temperature of 50 to 65°C, with a total stretching ratio of 5 to 7 times. Preferably, the extended solution contains KI at a mass concentration of 1.5-4 wt% and H3BO3 at a mass concentration of 2-5 wt%. The conditions for color correction include: using a color-correcting solution to correct the color of the extended PVA optical film for 30 to 60 seconds at a temperature of 25 to 40°C; Preferably, the complementary color solution contains KI at a mass concentration of 2-5 wt% and H3BO3 at a mass concentration of 0.5-2.5 wt%. The washing conditions include immersing the color-corrected PVA optical film in a desalination aqueous solution at 15-40°C for 20-40 seconds; The drying conditions include: a temperature of 40~110℃, preferably 40~80℃; and a time of 20~60s. The bonding conditions include: applying a protective film to both sides of the dried PVA optical film using an adhesive. Preferably, the adhesive is acetylated polyvinyl alcohol; The protective film is selected from one or more of TAC, PET, PMMA, COP, and COC; The conditions for the secondary drying include: drying the PVA optical film with the protective film attached at a temperature of 40~100℃ for 50~400s.

Images