Polarizer and preparation method thereof

Abstract

The preparation method comprises the following steps: providing a PVA (Polyvinyl Alcohol) film, and carrying out swelling, dyeing, crosslinking, stretching, washing and color complementing treatment on the PVA film to obtain an undried polarizing film; the undried polarizing film penetrates through a drying box to be dried, the water content is adjusted to range from 2% to 20%, and a dried polarizing film is obtained; wherein the drying box comprises a low-temperature pre-drying section, a high-temperature drying section and a plurality of groups of low-temperature drying sections through which an undried polarizing film sequentially penetrates; the drying treatment also comprises at least one group of damp and hot drying sections which are positioned among the plurality of groups of low-temperature drying sections; and pasting a protective film on the dried polarizing film, and carrying out drying maintenance to obtain the polaroid. The invention relates to the technical field of polaroid preparation, through the steps, a polarizing film in the prepared polaroid is not prone to shrinkage under the high-temperature and high-temperature and high-humidity conditions, and therefore the purpose of improving the weather resistance of the polaroid is achieved.

Description

Technical Field

[0001] The present invention belongs to the field of polarizers and relates to a polarizer preparation technology, in particular to a polarizer preparation method and a polarizer. Background Art

[0002] With the advancement of display technology, liquid crystal displays (LCDs) are widely used in computers, televisions, instruments, mobile phones, and automobiles. Polarizing film, a key material for LCDs, combines high transmittance with high polarization. This film is manufactured by subjecting polyvinyl alcohol films to various treatments, such as swelling, dyeing, crosslinking, stretching, and color correction, in different solutions at different temperatures, followed by cleaning and drying. Alternatively, a protective film, such as triacylcellulose, can be bonded to one or both sides of the polarizing film using an adhesive to create a polarizer suitable for display applications.

[0003] In recent years, with the development of display technology and the needs of various application scenarios, the use of LCDs has become more diverse, even in some relatively harsh environments such as high temperature, high humidity, and low temperature. At the same time, people have increasingly stringent requirements for display effects, such as visibility, and display stability under various conditions. This requires that the polarizers produced have high polarization degree, high transmittance, and high weather resistance.

[0004] In the prior art, to improve the weather resistance of polarizers, as specifically described in the current Chinese patent publication No. CN107407757B, a polarizing plate and image display device with a phase difference layer is proposed. To achieve a polarizer with suppressed shrinkage, a high-boric acid production process is employed, wherein a polyvinyl alcohol-based resin film is immersed in a solution containing a high boric acid concentration, ultimately producing a polyvinyl alcohol-based resin film with a boric acid content of approximately 25% by weight. By increasing the boric acid content in the polarizing film, the crosslinking degree of the polarizing film is increased, thereby achieving a polarizing film with suppressed shrinkage even when stored in a high-temperature, high-humidity environment for a long time.

[0005] However, due to the increased degree of cross-linking, the residual internal stress in the polarizing film during oven drying also increases, which in turn increases the shrinkage force during high-temperature weathering tests. Furthermore, when bonded to a glass substrate for high-temperature aging tests, the glass substrate can experience severe warping. Furthermore, during thermal cycling tests, the polarizing film is prone to fracture along the stretching direction, seriously affecting the polarizer's weathering performance.

[0006] In addition, as described in Japanese Patent Application Publication No. 2009-104062, a method is also proposed to obtain a polarizing film with excellent durability. Specifically, by reducing the amount of boric acid used in the stretching process of the polarizing film, the boron content in the polarizing film is reduced, thereby improving the weather resistance of the polarizing film. When conducting a weathering test, the absorption axis (stretching axis) direction of the polarizing film is used as the short side and cut into a size of 2mm×8mm. When heated to 80°C, the shrinkage force perpendicular to the absorption axis direction is less than 2.8N. Therefore, the polarizer prepared by the polarizing film has a small shrinkage force in the direction orthogonal to the stretching axis, making the polarizer less likely to break in a hot and cold shock test, thereby achieving an excellent durability effect.

[0007] However, since the polarizing film with excellent durability obtained by this method has a low boric acid content, the orthogonal hue of the polarizer is very likely to shift toward blue when used under high temperature and high humidity, affecting the appearance of the polarizer.

[0008] In summary, the above methods all have certain defects, so a method for preparing a polarizer and a polarizer are proposed herein to solve the above problems. Summary of the Invention

[0009] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, the present invention proposes a method for preparing a polarizer and a polarizer to effectively improve the weather resistance of the polarizer. The present invention adds a wet heat drying section in the middle of the drying process of the undried polarizing film, so that the PVA molecular chains that are over-oriented in the front drying process of the polarizing film can be promoted to move and properly rearranged under the action of water molecules in the wet heat drying process, so that some of the over-stretched PVA molecular chains shrink, thereby improving the polarizing film due to excessive stress in the PVA molecular chains, so that the polarizing film is not easy to shrink under high temperature and high temperature and high humidity conditions, thereby achieving the purpose of improving the weather resistance of the polarizer.

[0010] To achieve the above object, the first aspect of the present invention provides a method for preparing a polarizer, comprising the following steps:

[0011] Providing a PVA film, and performing swelling, dyeing, cross-linking, stretching, washing, and color-correcting treatment on the PVA film to obtain an undried polarizing film;

[0012] Passing the undried polarizing film through a drying oven for drying, adjusting the moisture content to 2%-20%, and obtaining a dried polarizing film;

[0013] The drying box includes a low-temperature pre-drying section, a high-temperature drying section, and multiple groups of low-temperature drying sections for the undried polarizing film to pass through in sequence;

[0014] The drying process further comprises at least one group of moist heat drying sections, wherein the moist heat drying sections are located between the multiple groups of low temperature drying sections;

[0015] A protective film is attached to the dried polarizing film, and drying and curing are performed to obtain a polarizer.

[0016] Furthermore, the following steps are included:

[0017] Before drying the undried polarizing film, the undried polarizing film is pretreated to adjust the water content of the undried polarizing film to 20%-60%.

[0018] Furthermore, the pretreatment method of the undried polarizing film includes water-cutting roller extrusion and / or air knife drying.

[0019] Furthermore, the heating temperature of the low-temperature pre-drying section is 25°C-60°C, the drying time is 25s-200s, and the drying humidity is 10%RH-50%RH;

[0020] The heating temperature of the high temperature drying section is 60°C-110°C, the drying time is 30s-150s, and the drying humidity is 2%RH-45%RH;

[0021] The low-temperature drying section is provided with two groups, and the two groups of low-temperature drying sections are respectively provided as a first low-temperature drying section and a second low-temperature drying section;

[0022] The heating temperature of the first low-temperature drying section is 35°C-70°C, the drying time is 25s-120s, and the drying humidity is 2%RH-45%RH;

[0023] The heating temperature of the wet heat drying section is 35°C-70°C, the drying time is 25s-120s, and the drying humidity is 40%RH-90%RH;

[0024] The heating temperature of the second low-temperature drying section is 20° C.-60° C., the drying time is 25 s-180 s, and the drying humidity is 2% RH-40% RH.

[0025] Furthermore, the drying treatment method includes heating drying, far infrared drying, hot air drying or microwave drying.

[0026] Furthermore, a temperature and humidity sensor is provided on the wet heat drying section for feeding back the temperature and humidity in the wet heat drying section so that the temperature and humidity in the wet heat drying section are always within a preset range.

[0027] Furthermore, the wet heat drying section is provided with a tension adjustment mechanism for controlling the tension of the undried polarizing film at the inlet of the wet heat drying section to be smaller than the tension of the undried film at the inlet of the drying box, and the tension of the drying film at the outlet of the wet heat drying section to be smaller than the tension of the undried film at the outlet of the drying box.

[0028] The tension on the undried polarizing film at the inlet and outlet of the wet heat drying section is 5 MPa-18 MPa.

[0029] Furthermore, the tension adjustment mechanism includes clamping rollers which are arranged at the inlet and outlet of the wet heat drying section and have adjustable rotation speeds.

[0030] Furthermore, the protective film is attached to the surface of the dried polarizing film by using a water-based adhesive or a light-curing adhesive.

[0031] Furthermore, the drying and curing temperature is 30° C.-92° C., and the drying time is 100s-1000s.

[0032] On the other hand, a polarizer is also proposed. The polarizer is prepared using the method for preparing a polarizer described in the above embodiment.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] By adding a wet heat drying section in the middle of the drying process of the undried polarizing film, the PVA molecular chains that are over-oriented in the polarizing film during the previous drying process can be promoted to move and properly rearrange the PVA molecular chains of the polarizing film under the action of water molecules formed in the wet heat drying section, so that some of the over-stretched PVA molecular chains shrink, resulting in irreversible stress relaxation of the PVA molecular chains, thereby improving the polarizing film caused by excessive stress in the PVA molecular chains. In this way, the polarizing film is less likely to shrink under high temperature and high temperature and high humidity conditions, thereby achieving the purpose of improving the weather resistance of the polarizer.

[0035] Furthermore, by installing a moisture sensor on the wet heat drying section and using the monitoring of the moisture sensor, the temperature and humidity of the wet heat treatment section can be quickly controlled manually, so as to better promote the retraction of the over-stretched PVA molecular chains generated in the drying process of the polarizing film in the previous section, thereby further improving the weather resistance of the polarizer.

[0036] Furthermore, by installing a tension adjustment mechanism in the wet-heat drying section, the polarizing film is prevented from excessive shrinkage due to high humidity, which could affect its deflection. Furthermore, the tension adjustment mechanism prevents wrinkling or curling of the polarizing film due to water absorption, thereby improving the polarizer's weather resistance while effectively preventing any impact on its optical properties and appearance. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0038] Figure 1 Schematic diagram of the process of a method for preparing a polarizer according to one embodiment of the present invention;

[0039] Figure 2 FIG. 4 is a flow chart of a method for preparing a polarizer in one embodiment of the present invention.

[0040] Figure Number:

[0041] 10. PVA film; 20. Undried polarizing film; 21. Low-temperature pre-drying section; 22. High-temperature drying section; 23. First low-temperature drying section; 24. Wet-heat drying section; 241. Temperature and humidity sensor; 242. Tension adjustment mechanism; 25. Second low-temperature drying section; 30. Dried polarizing film; 31. Protective film. DETAILED DESCRIPTION

[0042] The technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0043] The production of iodine-based polarizers typically uses a wet process to process the polyvinyl alcohol (PVA) film, which serves as the base film. This process includes swelling, dyeing, cross-linking, stretching, color correction, and drying. The drying process primarily adjusts the moisture content of the polarizing film to facilitate lamination. After stretching, the PVA film reaches a magnification of 4-7 times, at which point the PVA molecular chains are highly oriented. After stretching, the polarizing film enters a drying oven for drying. When the water content in the polarizing film decreases to a certain value, the PVA molecular chains in the polarizing film begin to rapidly form crystal nuclei and crystallize. However, at this point, the water content in the polarizing film is low, and many of the molecular chains are oriented due to stretching, limiting their mobility. Therefore, during the rapid crystallization, the PVA molecular chains near the crystal nuclei are forced into the nuclei. When the crystals grow near the oriented molecular chains, they attract the oriented molecular chains into the crystal lattice. However, since the oriented molecular chains cannot fit into the nuclei, they are pulled by the crystals. Combined with the drying process, the polarizing film will shrink in volume. As the volume shrinks, the highly oriented PVA molecular chains, which are pulled by the crystals, will further orient themselves. Ultimately, these molecular chains become over-oriented, generating internal stress. After drying, the molecular chains are frozen by the effects of boric acid, polyiodide ions, and other factors, preventing them from releasing internal stress, resulting in high internal stress in the polarizing film. This internal stress will cause the weather resistance of the polarizer to deteriorate. For example, the polarizing film will shrink under high temperature or high temperature and high humidity conditions, causing light leakage at the edge of the display or even bending of the display.

[0044] Currently, most polarizer manufacturers primarily dry polarizing film using a three-stage drying oven with a temperature setting of low temperature, high temperature, and low temperature. The oven heats the polarizing film using a heating element, hot air, infrared radiation, or heated rollers, while a fan removes moisture from the drying oven. This drying method offers high efficiency and can quickly dry stretched polarizing film.

[0045] However, the above analysis and actual production results show that this drying method can cause a large amount of internal stress to remain in the polarizing film, resulting in poor weather resistance of the produced polarizer. In this case, if the stress at both ends of the oven is reduced, the molecular orientation of the entire molecular chain will be reduced throughout the drying process, resulting in optical performance that cannot meet the requirements.

[0046] From the above analysis, it can be seen that the main reason for the internal stress in the polarizer is that during the drying process of the polarizing film of the polarizer, the crystal network and boric acid cross-linking network formed inside the polarizer due to drying will cause a large number of PVA molecular chains to be excessively oriented due to extension due to the water content.

[0047] Therefore, in response to the causes of the above-mentioned internal stress, the inventors proposed a method for preparing a polarizer through the following embodiments to improve the situation where a large number of PVA molecular chains are excessively oriented due to extension, thereby obtaining a polarizer with better weather resistance, as shown below.

[0048] Example 1

[0049] See also Figure 1 and Figure 2 The first embodiment of the present invention provides a method for preparing a polarizer, comprising the following steps:

[0050] A PVA film 10 is provided, and the PVA film 10 is subjected to swelling, dyeing, cross-linking, stretching, washing, and color correction treatment to obtain an undried polarizing film 20;

[0051] Passing the undried polarizing film 20 through a drying oven for drying, adjusting the moisture content to 2%-20%, and obtaining a dried polarizing film 30;

[0052] The drying box includes a low-temperature pre-drying section 21, a high-temperature drying section 22 and a plurality of low-temperature drying sections for the undried polarizing film 20 to pass through in sequence;

[0053] The drying process further comprises at least one group of moist heat drying sections, wherein the moist heat drying section 24 is located between the multiple groups of low temperature drying sections;

[0054] A protective film 31 is attached to the dried polarizing film 30 , and the polarizing film is dried and cured to obtain a polarizer.

[0055] In the above steps, by adding a wet heat drying section 24 in the middle position of the drying process of the undried polarizing film 20, the PVA molecular chains that are over-oriented in the previous drying process of the polarizing film can be promoted to move and properly rearranged under the action of water molecules formed in the wet heat drying section 24, so that some of the over-stretched PVA molecular chains shrink, causing the PVA molecular chains to produce irreversible stress relaxation, thereby improving the polarizing film caused by excessive stress in the PVA molecular chains, so that the polarizing film is not easy to shrink under high temperature and high temperature and high humidity conditions, thereby achieving the purpose of improving the weather resistance of the polarizer.

[0056] In this embodiment, in order to facilitate the subsequent process of making the moisture content of the polarizing film 30 after drying be between 2% and 20%, the preparation method of the polarizer is further limited.

[0057] Specifically, the method for preparing the polarizer further includes the following steps:

[0058] Before drying the undried polarizing film 20, the undried polarizing film 20 is pre-treated to adjust the moisture content of the undried polarizing film 20 to 20%-60%. By limiting the moisture content of the undried polarizing film 20 before drying, the dried polarizing film 30 with a moisture content of 2%-20% can be efficiently obtained without excessive restrictions on drying conditions during the subsequent drying process, thus better preparing the dried polarizing film 30 for subsequent production.

[0059] In one example, the pretreatment method of the undried polarizing film 20 includes water-cutting roller extrusion and / or air knife drying.

[0060] In other examples, other contact or non-contact methods may be used to achieve the above function, that is, it is only necessary to ensure that the undried polarizing film 20 does not dry out during the moisture content adjustment process.

[0061] In a further example, a method for detecting the moisture content of the polarizing film is proposed, so as to cooperate with the above method to adjust the moisture content of the undried polarizing film 20 .

[0062] Specifically, the method for detecting the moisture content of the polarizing film includes the following steps:

[0063] Cut the polarizing film to be tested into several samples of about 50mm×50mm in size, and measure the initial weight of the sample (take 1g-3g).

[0064] The sample was then dried at 120°C for 2 hours, and the weight of the dried sample was measured;

[0065] Repeat multiple sets of measurements and determine the average value of moisture content according to the formula.

[0066] The formula is as follows:

[0067] Moisture content (weight %) = (initial weight - dry weight) / initial weight × 100%.

[0068] In summary, the moisture content of the undried polarizing film 20 can be quickly adjusted by using the polarizing film moisture content detection method and the water-cutting roller extrusion and / or air knife drying methods.

[0069] In a further embodiment, the heating temperature, drying time and drying humidity of each drying section are further limited to improve the drying effect of the undried polarizing film 20 and improve the molding quality of the polarizing film 30 after drying.

[0070] Specifically, the low-temperature pre-drying section 21 has a heating temperature of 25°C-60°C, a drying time of 25s-200s, and a drying humidity of 10%-50% RH. The low-temperature pre-drying section 21 facilitates uniform evaporation of moisture from the surface and interior of the undried polarizing film 20. Under these conditions, the undried polarizing film 20 is less likely to curl and dimensional change, resulting in a better appearance for the subsequently formed polarizing film. Furthermore, the moisture content of the polarizing film can be adjusted to 10%-30%.

[0071] In a further example, the heating temperature, drying time and drying humidity of the low-temperature pre-drying section 21 may be further limited, such as a heating temperature of 35°C-60°C, a drying time of 35s-120s, and a drying humidity of 15%RH-40%RH.

[0072] The high-temperature drying section 22 has a heating temperature of 60°C-110°C, a drying time of 30s-150s, and a drying humidity of 2% RH-45% RH. The high-temperature drying section 22 helps remove bound water from the undried polarizing film 20, which is difficult to dry at low temperatures. Furthermore, while promoting water evaporation, the high temperature facilitates the crystallization of the PVA molecular chains within the undried polarizing film 20 and the cross-linking reaction between the PVA molecular chains and boric acid. Both crystallization and cross-linking reactions help stabilize the orientation of the PVA molecular chains, and thus the orientation of the polyiodide ions. This stabilizes the dimensions and optical properties of the polarizing film and can adjust the moisture content of the polarizing film to 8%-25%.

[0073] In a further example, the heating temperature, drying time and drying humidity of the high temperature drying section 22 may be further limited, such as a heating temperature of 60° C.-100° C., a drying time of 35s-120s, and a drying humidity of 8% RH-25% RH.

[0074] In addition, in this embodiment, two groups of low-temperature drying sections are provided, and the two groups of low-temperature drying sections are respectively provided as a first low-temperature drying section 23 and a second low-temperature drying section 25 .

[0075] Among them, the wet heat drying section 24 is located between the first low-temperature drying section 23 and the second low-temperature drying section 25. By setting two low-temperature drying sections and making the wet heat drying section 24 located between the first low-temperature drying section 23 and the second low-temperature drying section 25, it is convenient to adjust the moisture content of the polarizing film through the second low-temperature drying section 25, so as to avoid the polarizing film having too high water content after passing through the wet heat drying section 24, resulting in the occurrence of composite lines and other undesirable conditions in the subsequent process of combining with the protective film 31, thereby affecting the molding quality of the polarizer.

[0076] In this embodiment, the heating temperature of the first low-temperature drying section 23 is 35°C-70°C, the drying time is 25s-120s, and the drying humidity is 2%-45% RH. This first low-temperature drying section 23 helps lower the temperature of the polarizing film, preventing the subsequent wet-heat drying section 24 from experiencing adverse effects due to large temperature fluctuations, i.e., excessive humidification. Furthermore, the first low-temperature drying section 23 can adjust the moisture content of the polarizing film to 2%-20%.

[0077] In a further example, the heating temperature, drying time and drying humidity of the first low-temperature drying section 23 may be further limited, such as a heating temperature of 40°C-65°C, a drying time of 35s-100s, and a drying humidity of 8%RH-30%RH.

[0078] The heating temperature of the wet heat drying section 24 is 35°C-70°C, the drying time is 25s-120s, and the drying humidity is 40%-90% RH. The wet heat drying section 24 facilitates irreversible stress relaxation of over-oriented PVA molecular chains during the stretching and drying process of the polarizing film, thereby releasing the internal stress of the PVA molecular chains. The resulting polarizer has improved dimensional and optical stability under high temperature and high humidity conditions. Furthermore, the wet heat drying section 24 can adjust the moisture content of the polarizing film to 5%-25%.

[0079] In a further example, the heating temperature, drying time and drying humidity of the wet heat drying section 24 may be further limited, such as a heating temperature of 40° C.-65° C., a drying time of 35s-100s, and a drying humidity of 65% RH-85% RH.

[0080] It should be noted that, since the drying humidity and drying temperature of the wet heat drying section 24 are relatively high, the changes in temperature and humidity during drying must be strictly controlled during production to prevent the polarizing film from being unable to release internal stress or causing the necessary orientation of the PVA molecular chains of the polarizing film to relax due to too little or too much humidity, thereby ultimately leading to degradation of the optical properties of the polarizing film. Therefore, the wet heat drying section 24 is further defined herein.

[0081] Specifically, a temperature and humidity sensor 241 is provided on the wet heat drying section 24 for feeding back the temperature and humidity in the wet heat drying section 24 . The temperature and humidity in the wet heat drying section 24 are manually controlled to always be within a preset range, thereby ensuring the drying effect of the polarizing film.

[0082] In other examples, the above-mentioned control work can also be completed in a system automation manner. This is existing technology and will not be described in detail here.

[0083] It should be noted that the preset range is the heating temperature and drying humidity of the wet heat drying section 24. Specifically, the heating temperature is 40° C.-65° C., and the drying humidity is 65% RH-85% RH.

[0084] In order to further enhance the stress release effect of the polarizing film and avoid wrinkles on the surface of the polarizing film, the wet heat drying section 24 is further limited.

[0085] Specifically, the wet heat drying section 24 is provided with a tension adjustment mechanism 242, which is used to control the tension of the undried polarizing film 20 at the inlet of the wet heat drying section 24 to be smaller than the tension of the undried polarizing film 20 at the inlet of the drying box, and to control the tension of the undried polarizing film 20 at the outlet of the wet heat drying section 24 to be smaller than the tension of the undried polarizing film 20 at the outlet of the drying box.

[0086] In the prior art, the tension applied to the undried polarizing film 20 at the inlet and outlet of the drying oven is generally 8MPa-23MPa. In one example, the tension applied to the undried polarizing film 20 at the inlet and outlet of the wet heat drying section 24 is 5MPa-18MPa. By making the tension applied to the undried polarizing film 20 at the inlet and outlet of the wet heat drying section 24 slightly smaller than the tension applied to the undried polarizing film 20 at the inlet and outlet of the drying oven, the internal stress formed in the polarizing film due to excessive orientation can be released, and the polarization degree and appearance quality of the produced polarizing film can be effectively guaranteed.

[0087] In one example, the tension adjustment mechanism 242 includes nip rollers with adjustable speeds provided at the inlet and outlet of the wet heat drying section 24 , and the tension of the undried polarizing film 20 at the inlet and outlet of the wet heat drying section 24 is adjusted by adjusting the speed of the nip rollers.

[0088] In this embodiment, the heating temperature of the second low-temperature drying section 25 is 20°C-60°C, the drying time is 25s-180s, and the drying humidity is 2% RH-40% RH. The second low-temperature drying section 25 not only removes excess moisture from the polarizing film, but also helps adjust the moisture content of the polarizing film to a range suitable for lamination. For example, the second low-temperature drying section 25 can adjust the moisture content of the polarizing film to 8%-17%, facilitating the subsequent bonding of the polarizing film 30 and the protective film 31 after drying. This prevents undesirable conditions such as composite lines during bonding due to excessive moisture content in the polarizing film 30 after drying, thereby improving product yield.

[0089] In the above drying stage, the drying treatment methods adopted include heating drying in the drying oven, far infrared drying, hot air drying or microwave drying.

[0090] In this embodiment, the protective film 31 is attached to the surface of the dried polarizing film 30 by a water-based adhesive or a light-curing adhesive. When the protective film 31 is combined with the dried polarizing film 30 for drying and curing, the drying and curing temperature is 30°C-92°C, and the drying time is 100s-1000s.

[0091] The drying and curing temperature is set to 30°C-92°C, which effectively prevents the protective film 31 from separating from the polarizing film 30 after drying and prevents the polarizing film from deteriorating. In addition, the drying and curing temperature can be adjusted to 200s-700s to increase production speed.

[0092] Example 2

[0093] This embodiment further provides a polarizer based on the embodiment 1. The polarizer is prepared by the method for preparing a polarizer described in the embodiment 1.

[0094] In order to explore the changes in polarizer performance under different parameters and to better prepare polarizers with better weather resistance, multiple groups of polarizer examples prepared based on the polarizer preparation method in Example 1 are listed here to explore the changes in polarizer performance under different parameters, as shown below:

[0095] Example 1

[0096] A polarizer is provided, which is prepared using the polarizer preparation method described in Example 1. The drying temperature of the wet heat drying section 24 is 40°C, the drying time is 40 seconds, and the drying humidity is 75% RH. The tensions at the inlet and outlet of the polarizing film drying oven are set to 12 MPa and 12.5 MPa, respectively, and the tensions at the inlet and outlet of the wet heat drying section 24 are set to 10 MPa and 10.5 MPa, respectively.

[0097] Example 2

[0098] A polarizer is provided, which is prepared by the method for preparing the polarizer described in Example 1. The drying temperature of the wet heat drying section 24 is 65° C., and the remaining parameters remain the same as those in Example 1.

[0099] Comparative Example 1

[0100] A polarizer is provided, which is prepared by the method for preparing the polarizer described in Example 1. The drying temperature of the wet heat drying section 24 is 24° C., and the remaining parameters remain the same as those in Example 1.

[0101] Comparative Example 2

[0102] A polarizer is provided, which is prepared by the method for preparing the polarizer described in Example 1. The drying temperature of the wet heat drying section 24 is 71° C., and the remaining parameters remain the same as those in Example 1.

[0103] Example 3

[0104] A polarizer is provided, which is prepared by the method for preparing the polarizer described in Example 1. The drying humidity in the wet heat drying section 24 is 45% RH, and the remaining parameters remain the same as those in Example 1.

[0105] Comparative Example 3

[0106] A polarizer is provided, which is prepared by the method for preparing the polarizer described in Example 1. The drying humidity in the wet heat drying section 24 is 35% RH, and the remaining parameters remain the same as those in Example 1.

[0107] Comparative Example 4

[0108] A polarizer is provided, which is prepared by the method for preparing the polarizer described in Example 1. The drying humidity in the wet heat drying section 24 is 98% RH, and the remaining parameters remain the same as those in Example 1.

[0109] Example 4

[0110] A polarizer is provided, which is prepared by the method for preparing the polarizer described in Example 1. The drying time of the wet heat drying section 24 is 115 seconds, and the remaining parameters remain the same as those in Example 1.

[0111] Comparative Example 5

[0112] A polarizer is provided, which is prepared by the method for preparing the polarizer described in Example 1. The drying time of the wet heat drying section 24 is 24 seconds, and the remaining parameters remain the same as those in Example 1.

[0113] Comparative Example 6

[0114] A polarizer is provided, which is prepared by the method for preparing the polarizer described in Example 1. The drying time of the wet heat drying section 24 is 121 seconds, and the remaining parameters remain the same as those in Example 1.

[0115] Comparative Example 7

[0116] A polarizer is provided, which is prepared using the method for preparing a polarizer described in Example 1. The tensions at the inlet and outlet of the wet heat drying section 24 are set to 14 MPa and 14.5 MPa, respectively. The remaining parameters remain the same as those in Example 1.

[0117] Comparative Example 8

[0118] A polarizer is provided, which is prepared using the method for preparing a polarizer described in Example 1. The tensions at the inlet and outlet of the wet heat drying section 24 are set to 4 MPa and 4.5 MPa respectively, and the remaining parameters remain the same as in Example 1.

[0119] Comparative Example 9

[0120] A polarizer is provided, which is prepared using the method for preparing a polarizer described in Example 1. The tensions at the inlet and outlet of the wet heat drying section 24 are set to 0 MPa and 0 MPa respectively, and the remaining parameters remain the same as in Example 1.

[0121] In summary, through Example 1 to Comparative Example 2, the influence of the wet heat drying section 24 on the performance of the polarizer at different drying temperatures is explored; through Example 1 and Example 3 to Comparative Example 4, the influence of the wet heat drying section 24 on the performance of the polarizer at different drying humidity is explored; through Example 1 and Example 4 to Comparative Example 6, the influence of the wet heat drying section 24 on the performance of the polarizer at different drying times is explored; through Example 1 and Comparative Examples 7 to Comparative Example 9, the influence of the wet heat drying section 24 on the performance of the polarizer at different inlet and outlet tensions is explored.

[0122] The performance of the polarizer was explored by testing the polarization degree of the polarizing film in the polarizer in the above example and the shrinkage of the polarizer during high-temperature testing, as shown in the following table.

[0123]

[0124]

[0125] According to the data of Example 1 to Comparative Example 2, when the heating temperature of the wet heat drying section 24 is 40°C-65°C, the polarization degree of the polarizing film is higher and the prepared polarizer has the smallest shrinkage under high temperature test, that is, the weather resistance is the best.

[0126] According to the data of Example 1 and Example 3 to Comparative Example 4, when the drying humidity of the wet heat drying section 24 is 65% RH-85% RH, the polarization degree of the polarizing film is higher and the prepared polarizer shrinks the least under high temperature testing, that is, the weather resistance is the best.

[0127] According to the data of Example 1 and Example 4 to Comparative Example 6, when the drying time of the wet heat drying section 24 is 35s-100s, the polarization degree of the polarizing film is higher and the prepared polarizer shrinks the least under high temperature testing, that is, the weather resistance is the best.

[0128] According to the data of Example 1 and Comparative Examples 7 to 9, when the tension applied to the undried polarizing film 20 at the inlet and outlet of the wet heat drying section 24 is 5MPa-18MPa, the polarization degree of the polarizing film is high and the prepared polarizer has the smallest shrinkage under high temperature test, that is, the weather resistance is the best.

[0129] In addition, as shown in the data of comparative example nine in the above table, it should be noted that when the tension applied to the undried polarizing film 20 at the inlet and outlet of the wet heat drying section 24 is 0 MPa, that is, when the tension adjustment mechanism 242 is not used to apply tension to the undried polarizing film 20, the polarizer prepared therefrom will have wrinkles and curling phenomena in a high temperature environment, which is defective.

[0130] Therefore, through the data in the above table, we can complete the influence of various parameters on the performance of polarizers, so as to better prepare polarizers with better weather resistance.

[0131] In addition, according to the polarization degree of the polarizing film and the shrinkage of the polarizer in the high temperature test in Example 1, Example 2, Example 3 and Example 4 in the above table, it can be clearly seen that the polarizer prepared by the polarizer preparation method in Example 1 in this embodiment has significantly improved high temperature resistance compared with the ordinary polarizer, that is, it has stronger weather resistance.

[0132] In other embodiments, further research is conducted on the effects of the wet heat drying section 24 at different positions in the drying oven on the preparation of the polarizer, as shown below:

[0133] Comparative Example 10

[0134] The wet heat drying section 24 is set between the low-temperature pre-drying section 21 and the high-temperature drying section 22, and the drying temperature, drying time, drying humidity, tension of the entire inlet and outlet of the polarizing film drying box, and tension of the inlet and outlet of the wet heat drying section 24 remain the same as those in Example 1.

[0135] Comparative Example 11

[0136] The wet heat drying section 24 is set at the end of the drying box, and the drying temperature, drying time, drying humidity, tension of the polarizing film drying box as a whole, and tension of the wet heat drying section 24 at the inlet and outlet remain the same as those in Example 1.

[0137] Among them, the polarization degree of the polarizing film in the polarizer in the above comparative example (such as by using a spectrophotometer to test the polarization degree of the polarizing film) and the shrinkage of the polarizer during high temperature testing (such as cutting and edge grinding the polarizer into a size of 66×114 mm, attaching it to optical glass with an adhesive, and placing it in a constant temperature test box at a temperature of 80°C for 1000 hours. The polarizer is taken out and the width of the black edge caused by the shrinkage of the polarizer edge is measured with an optical image measuring instrument) are tested to complete the exploration of the performance of the polarizer, as shown in the following table:

[0138]

[0139]

[0140] It can be clearly seen from the data in the above table that when the wet heat drying section 24 is set before the high-temperature drying section 22 or at the very end of the drying oven, the polarizers prepared therefrom have certain defects. Specifically, the polarizer prepared by the method in Comparative Example 10 has a low polarization degree of the polarizing film and a large shrinkage of the polarizer at high temperatures. The polarizer prepared by the method in Comparative Example 11 has a polarizing film that exhibits composite lines during the bonding process with the protective film 31 due to excessive humidity.

[0141] In summary, the polarizer prepared by the method described in Example 1 in this embodiment (as shown in Example 1 in the above table) effectively improves the situation of excessive stress in the PVA molecular chain of the polarizing film, thereby making the polarizing film less likely to shrink under high temperature and high temperature and high humidity conditions, thereby achieving the purpose of improving the weather resistance of the polarizer.

[0142] The above embodiments are only used to illustrate the technical method of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical method of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical method of the present invention.

Claims

1. A method for preparing a polarizer, characterized in that: The steps include: Providing a PVA film, and subjecting the PVA film to swelling, dyeing, cross-linking, stretching, washing, and color-correcting treatment to obtain an undried polarizing film; Passing the undried polarizing film through a drying oven for drying, adjusting the water content to 2%-20%, and obtaining a dried polarizing film; Wherein, the drying box comprises a low-temperature pre-drying section, a high-temperature drying section and a plurality of groups of low-temperature drying sections for the undried polarizing film to pass through in sequence; The drying process further comprises at least one group of wet heat drying sections, wherein the wet heat drying sections are located between the multiple groups of low temperature drying sections; A protective film is attached to the dried polarizing film, and drying and curing are performed to obtain a polarizer.

2. The method for preparing a polarizer according to claim 1, characterized in that: The following steps are also included: Before drying the undried polarizing film, the undried polarizing film is pretreated to adjust the water content of the undried polarizing film to 20%-60%.

3. The method for preparing a polarizer according to claim 2, characterized in that: The pretreatment method of the undried polarizing film includes water-cutting roller extrusion and / or air knife drying.

4. The method for preparing a polarizer according to claim 1, characterized in that: The heating temperature of the low-temperature pre-drying section is 25°C-60°C, the drying time is 25s-200s, and the drying humidity is 10%RH-50%RH; The heating temperature of the high temperature drying section is 60°C-110°C, the drying time is 30s-150s, and the drying humidity is 2%RH-45%RH; The low-temperature drying section is provided with two groups, and the two groups of low-temperature drying sections are respectively provided as a first low-temperature drying section and a second low-temperature drying section; The heating temperature of the first low-temperature drying stage is 35°C-70°C, the drying time is 25s-120s, and the drying humidity is 2%RH-45%RH; The heating temperature of the wet heat drying section is 35°C-70°C, the drying time is 25s-120s, and the drying humidity is 40%RH-90%RH; The heating temperature of the second low-temperature drying stage is 20° C.-60° C., the drying time is 25 s-180 s, and the drying humidity is 2% RH-40% RH.

5. The method for preparing a polarizer according to claim 1, characterized in that: The drying treatment method includes heating drying, far infrared drying, hot air drying or microwave drying.

6. The method for preparing a polarizer according to claim 1, characterized in that: The wet heat drying section is provided with a temperature and humidity sensor for feeding back the temperature and humidity in the wet heat drying section so that the temperature and humidity in the wet heat drying section are always within a preset range.

7. The method for preparing a polarizer according to claim 1, characterized in that: The wet heat drying section is provided with a tension adjustment mechanism, which is used to control the tension of the undried polarizing film at the entrance of the wet heat drying section to be smaller than the tension of the undried film at the entrance of the drying box, and the tension of the drying film at the exit of the wet heat drying section to be smaller than the tension of the undried film at the exit of the drying box; Wherein, the tension of the undried polarizing film at the inlet and outlet of the wet heat drying section is 5MPa-18MPa.

8. The method for preparing a polarizer according to claim 7, characterized in that: The tension adjustment mechanism comprises clamping rollers which are arranged at the inlet and outlet of the wet heat drying section and have adjustable rotation speed.

9. The method for preparing a polarizer according to claim 1, characterized in that: The protective film is attached to the surface of the dried polarizing film by a water-based adhesive or a light-curing adhesive.

10. The method for preparing a polarizer according to claim 1, characterized in that: The drying and curing temperature is 30° C.-92° C., and the drying time is 100s-1000s.

11. A polarizer, characterized in that: The polarizer is prepared by the method for preparing a polarizer according to any one of claims 1 to 10.

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