Polyvinyl alcohol optical base film, base film production method, and polarizing plate

Abstract

The application discloses a kind of polyvinyl alcohol optical base film, base film preparation method and polarizing sheet, it is related to polarizing sheet technical field, when preparing base film, polyvinyl alcohol is put into dissolving kettle with plasticizer, surfactant, antioxidant etc., and deionized water is added;At the same time, acetyl acetyl modified polyvinyl alcohol is put into another dissolving kettle, and deionized water is added, and after swelling, temperature is respectively controlled to rise, then two kettle solutions are mixed evenly, and polyvinyl alcohol casting membrane stock solution is obtained;By adding acetyl acetyl modified polyvinyl alcohol to polyvinyl alcohol optical base film, and using crosslinking agent and acetyl acetyl to occur crosslinking reaction, stable crosslinking structure formed by chemical bond is generated in polyvinyl alcohol optical base film, so that polarizing sheet has certain intensity in the direction perpendicular to the stretching direction, guarantee polarizing film not to crack when being subjected to cold and hot impact, and the durability of polarizing sheet can be improved.

Description

Technical Field

[0001] This invention relates to the field of polarizer technology, specifically to a polyvinyl alcohol optical base film, a method for preparing the base film, and a polarizer. Background Technology

[0002] Polyvinyl alcohol (PVA) optical films are mainly used in the production of polarizers, with the end product being various types of liquid crystal displays (LCDs). The performance of PVA optical films affects the optical and physical properties of polarizers, such as polarization degree, transmittance, hue, weather resistance, and shrinkage resistance.

[0003] The current production method of polyvinyl alcohol optical film is to dissolve polyvinyl alcohol resin and auxiliary materials in ultrapure water to prepare a casting solution. The casting solution is then degassed by an extruder, cast into shape by a die, pre-dried by a drying guide roller, dried and shaped in a heat treatment oven, and finally wound up to obtain the finished polyvinyl alcohol optical base film. The polyvinyl alcohol optical base film is then swelled, dyed, cross-linked, stretched, washed, recolored, and dried to prepare a polarizing film. The polarizing film is then laminated with a TAC film to produce a polarizing sheet.

[0004] Since the polarizers mentioned above are made by stretching, the polyvinyl alcohol molecular chains become highly oriented due to stretching. In order to fix the highly oriented polyvinyl alcohol molecular chains, a large amount of boric acid is used to crosslink the polyvinyl alcohol. However, the crosslinking of polyvinyl alcohol molecular chains with boric acid mainly relies on complexation. The crosslinked structure is unstable and is prone to failure under harsh environments. Therefore, polarizers made by this method are prone to shrinkage under high temperature environments.

[0005] Furthermore, polyvinyl alcohol (PVA)-based films are hydrophilic polymers, making polarizers made from PVA optical films highly susceptible to deformation due to moisture absorption under high temperature and humidity conditions. Also, because the polarizing film is stretched 4-8 times, the PVA molecular chains are highly oriented in the stretching direction, resulting in high strength in that direction but low strength perpendicular to it. This leads to the problem that the film may crack along the absorption axis when subjected to thermal shock. Therefore, methods such as bonding one or both sides of the polarizer to a transparent protective film like cellulose triacetate have been used to supplement the polarizer's strength. Water-based adhesives are preferred for bonding the polarizer to the transparent protective film, as they improve weather resistance to some extent, but still do not fully meet the requirements for use in harsh environments.

[0006] Research on improving the weather resistance of polarizers mainly focuses on improving the performance of water-based adhesives for polarizers; the performance of protective films for polarizers; controlling the concentration of boric acid, iodine, and potassium iodide in polarizers; and applying waterproof materials to the outside of polarizer films or protective films to improve the durability of polarizers.

[0007] Other studies have suggested that to suppress the shrinkage of the polarizing film in polarizers, a polarizing film with a thickness of less than 10 μm should be used. Therefore, when producing thin polarizers, using acetyl-modified polyvinyl alcohol as a coating or adding it directly to polyvinyl alcohol in a certain proportion to dissolve together can improve the adhesion between the resin substrate and the polyvinyl alcohol-based resin layer, thereby suppressing defects such as the polyvinyl alcohol-based resin layer peeling off from the resin substrate. This allows for better dyeing and underwater stretching as described later.

[0008] While the above methods can improve the weather resistance of polarizers to some extent, there has been no report on the direct improvement of the weather resistance of polarizers by adding a certain proportion of acetyl-modified polyvinyl alcohol resin to the polyvinyl alcohol optical base film and adding a crosslinking agent that can crosslink with acetyl-acetyl groups during the production of the polarizer.

[0009] Based on the above understanding, the purpose of this invention is to improve the durability of polarizers by improving the durability of the polarizing film itself. Summary of the Invention

[0010] The purpose of this invention is to provide a polyvinyl alcohol optical base film, a method for preparing the base film, and a polarizer; and to solve the following technical problems:

[0011] How to improve the durability of polarizers.

[0012] The objective of this invention can be achieved through the following technical solutions:

[0013] (I) Polyvinyl alcohol optical base film

[0014] This invention discloses a polyvinyl alcohol optical base film, which is composed of the following raw materials by weight: 100 parts of polyvinyl alcohol; 1-10 parts of acetoacetyl-modified polyvinyl alcohol; 1-25 parts of plasticizer; 0.01-1 part of surfactant; 0.01-0.5 parts of antioxidant; and 60-1000 parts of deionized water.

[0015] Furthermore, the degree of polymerization of the polyvinyl alcohol is not particularly limited, but it is preferably 1500-6500, more preferably 1700-5000, and even more preferably 2000-4000. By using polyvinyl alcohol with a degree of polymerization within this range, the resulting optical film has excellent durability and optical performance, and is easy to process, thereby reducing production costs. The degree of hydrolysis of the polyvinyl alcohol in this invention is not particularly limited, but considering water resistance and optical performance, the degree of hydrolysis of the polyvinyl alcohol is preferably 98.5% or more, more preferably 99.0% or more, and even more preferably 99.5% or more.

[0016] Furthermore, the degree of substitution of the acetoacetyl-modified polyvinyl alcohol is 0.1-40%. If the degree of substitution of the acetoacetyl group of the polyvinyl alcohol is less than 0.1%, the obtained polarizing film will have fewer cross-linked structures, which is insufficient to maintain the dimensional stability of the polarizing film under high temperature and high humidity. If the degree of substitution of the acetoacetyl group of the polyvinyl alcohol is greater than 40%, it will affect the solubility of the acetoacetyl-modified polyvinyl alcohol on the one hand, and will also cause the prepared solution to gel too quickly and have poor processing performance on the other hand.

[0017] The amount of acetyl-modified polyvinyl alcohol added must be 1-10 parts. If the amount of acetyl-modified polyvinyl alcohol added is less than 1 part, the resulting polarizing film will have fewer cross-linked structures, which is insufficient to maintain the dimensional stability of the polarizing film under high temperature and high humidity. If the amount added is more than 10 parts, too many cross-linked structures will be generated, resulting in a reduction in the number of hydroxyl groups on the polyvinyl alcohol molecular chain, which in turn leads to a decrease in the I3 content in the polarizing film. - I5 - The reduction in cross-linking structures formed with the hydroxyl groups on the highly oriented polyvinyl alcohol molecular chains affects the polarization degree of the polarizing film.

[0018] Furthermore, the type of plasticizer is not particularly limited; as a plasticizer, it needs to have a large number of hydroxyl groups in order to better plasticize polyvinyl alcohol. Therefore, polyols such as methanol, ethanol, ethylene glycol, glycerol, propylene glycol, sorbitol, and pentaerythritol can be selected; in this invention, the polyvinyl alcohol optical base film may contain one or more of these plasticizers.

[0019] The content of the plasticizer is more preferably 3-20 parts, and even more preferably 5-18 parts, based on 1-25 parts. If the plasticizer content is less than 1 part, the stretchability of the obtained polyvinyl alcohol optical base film will be greatly reduced. If the plasticizer content is more than 25 parts, the obtained polyvinyl alcohol optical base film will be too soft, resulting in reduced processing performance.

[0020] Furthermore, the type of surfactant is not particularly limited; the main function of the surfactant is to improve the film-forming properties of polyvinyl alcohol, suppress uneven thickness of the polyvinyl alcohol optical base film, and prevent it from being difficult to peel off from the polyvinyl alcohol casting roller; from the perspective of easy peeling, the surfactant is preferably anionic or nonionic, and particularly preferably nonionic; at the same time, one surfactant can be used alone, or two or more surfactants can be used in combination.

[0021] As an anionic surfactant, it can be one or a combination of two or more of carboxylic acid derivatives, sulfonates, sulfate esters, phosphate esters, N-acylaminocarboxylic acids, etc., for example, sodium dodecylbenzene sulfonate can be used; as a nonionic surfactant, it can be one or a combination of two or more of long-chain fatty alcohol polyoxyethylene ethers, alkylphenol polyoxyethylene ethers, fatty acid polyoxyethylene esters, polyoxyethylene alkylamines, polyoxyethylene alkylolamides, polyethers, etc.

[0022] The surfactant content is more preferably 0.03-0.8 parts, and even more preferably 0.05-0.5 parts, based on 0.01-1 parts; by making the surfactant content above 0.01 parts, the film-forming and peeling properties can be improved; by making the surfactant content below 1 part, the surfactant exudation to the surface of the polyvinyl alcohol optical base film can be inhibited, thereby preventing the polyvinyl alcohol optical base film from deteriorating in quality.

[0023] Furthermore, the type of antioxidant is not particularly limited. The main function of the antioxidant is to help capture and neutralize free radicals and prevent oxygen and other oxygen agents from having an adverse effect on the polyvinyl alcohol molecular chain. Since the polyvinyl alcohol optical base film uses a large amount of water as a solvent, taking into account the water solubility of the antioxidant, one or two or more combinations of ascorbic acid, isoascorbic acid and its salts, phytic acid, amino acids, etc. can be selected. For example, sodium sulfite can be selected.

[0024] The antioxidant content is more preferably 0.02-0.4 parts, and even more preferably 0.04-0.3 parts, based on 0.01-0.5 parts. By making the antioxidant content above 0.01 parts, the polyvinyl alcohol molecular chains can be protected from oxidation. By making the antioxidant content below 0.5 parts, the seepage of antioxidant to the surface of the polyvinyl alcohol optical base film can be inhibited, thus preventing the quality of the polyvinyl alcohol base film from deteriorating.

[0025] (II) Preparation method of polyvinyl alcohol optical base film

[0026] A method for preparing a polyvinyl alcohol optical base film as described above includes the following steps:

[0027] S1: At an initial temperature of 20-35℃, polyvinyl alcohol, plasticizer, surfactant, and antioxidant are added to dissolving vessel one, followed by some deionized water; simultaneously, acetyl-modified polyvinyl alcohol is added to dissolving vessel two, along with the remaining deionized water; after both vessels have swelled for 0.5-2 hours, the temperature is raised separately using a programmed control system. For dissolving vessel one, the temperature is raised from the initial temperature to 90-180℃ in 1-5 hours, and then maintained at 90-180℃ with stirring for 1.5-7 hours; for dissolving vessel two, the temperature is raised from the initial temperature to 90-150℃ in 1-5 hours, ensuring that the temperature of dissolving vessel two after the temperature rises is higher than that of dissolving vessel one, and then maintained at 90-150℃ with stirring for 2-5 hours; finally, the solutions from both vessels are mixed evenly to obtain the polyvinyl alcohol casting film stock solution.

[0028] S2: The casting solution is degassed and filtered through an extruder and then cast through a die head; the formed film is pre-dried by a drying guide roller, then heat-treated in a humid heat oven, and then heat-treated in a heat treatment oven for shaping; finally, it is wound into a film to obtain a polyvinyl alcohol optical base film.

[0029] The dissolution method of the acetyl-modified polyvinyl alcohol (PVA) affects the final product performance. Industrially, to accelerate and ensure complete dissolution, PVA is typically dissolved under high temperature and pressure for an extended period. However, as shown in Formula 1, the acetyl group on the acetyl-modified PVA is linked to the PVA molecular chain via an ester group. This structure is prone to hydrolysis in high-temperature, high-pressure aqueous solutions. Therefore, acetyl-modified PVA is not suitable for prolonged dissolution under high temperature and pressure in aqueous solutions. Thus, this invention dissolves PVA and acetyl-modified PVA separately. After dissolution, the two solutions are mixed in a mixing tank to obtain the PVA casting stock solution. The structure of Formula 1 is shown below:

[0030]

[0031] In a further embodiment of the present invention, the plasticizer is selected as glycerin.

[0032] In a further embodiment of the present invention: the surfactant is sodium dodecylbenzenesulfonate.

[0033] In a further embodiment of the present invention: the surfactant is sodium dodecylbenzenesulfonate.

[0034] In a further embodiment of the present invention: in step S1, the initial temperature is 28°C.

[0035] In a further embodiment of the present invention: in step S1, the swelling time is 1 hour.

[0036] In a further embodiment of the present invention: when the temperature of the dissolving vessel is controlled by a program, it is raised from 28°C to 160°C within 3 hours, and then kept at 160°C with stirring for 1.5-7 hours, preferably 2-6 hours, and more preferably 3 hours.

[0037] In a further embodiment of the present invention: the temperature of the dissolving vessel is controlled by a second program to rise from 28°C to 110°C within 3 hours, and then kept at 110°C with stirring for 2-5 hours, preferably 2-4 hours, and more preferably 3 hours.

[0038] In a further embodiment of the present invention: in step S1, the temperature of the two dissolving vessels is reduced to 90-110°C, preferably 100°C, and then the acetyl-acetyl modified polyvinyl alcohol solution is added to the polyvinyl alcohol dissolving vessel for mixing. The mixing time is 1-5 hours, preferably 2-4 hours, and more preferably 3 hours.

[0039] In summary, a preferred method for preparing a polyvinyl alcohol polarizing film can be obtained, and the steps are as follows:

[0040] S1: At an initial temperature of 28℃, polyvinyl alcohol, glycerol, sodium dodecylbenzenesulfonate, and sodium sulfite are added to dissolving vessel one, followed by some deionized water; simultaneously, acetyl-modified polyvinyl alcohol is added to dissolving vessel two, along with the remaining deionized water; after both vessels have swelled for 1 hour, the temperature is raised separately using a program control system. For dissolving vessel one, the temperature is raised from 28℃ to 160℃ within 3 hours and maintained at 160℃ with stirring for 3 hours; for dissolving vessel two, the temperature is raised from 28℃ to 110℃ within 3 hours and maintained at 110℃ with stirring for 3 hours; when the temperature of both vessels drops to 100℃, the solutions from both vessels are mixed for 3 hours until homogeneous, thus obtaining the polyvinyl alcohol casting film stock solution;

[0041] S2: The casting solution is degassed and filtered through an extruder and then cast through a die head; the formed film is pre-dried by a drying guide roller, then heat-treated in a humid heat oven, and then heat-treated in a heat treatment oven for shaping; finally, it is wound into a film to obtain a polyvinyl alcohol optical base film.

[0042] (III) Polarizing film using the above-mentioned polyvinyl alcohol optical base film as polarizing film and its preparation process

[0043] A polarizing film is obtained by using the aforementioned polyvinyl alcohol optical base film as the polarizing film, and subjecting the polarizing film to processes including swelling, dyeing, cross-linking, stretching, washing, color correction, drying, lamination, re-drying, and heat treatment; the specific steps are as follows:

[0044] S1: Peng Run

[0045] Before dyeing, the unstretched polyvinyl alcohol (PVA) optical base film is immersed in a swelling tank filled with a swelling aqueous solution to remove impurities such as dust or anti-blocking agents accumulated on the surface of the PVA optical base film, causing the PVA optical base film to swell. This is used to improve stretching efficiency, prevent uneven dyeing, and improve the physical properties of the PVA optical base film. As for the swelling aqueous solution, there are no particular restrictions on the use of swelling aqueous solutions known in the field. For example, pure water or deionized water can be used alone, or a small amount of small molecule alcohols such as glycerol or iodine salts such as potassium iodide can be added. Adding small molecule alcohols or iodine salts can improve processability while the polymer film swells. The temperature of the aqueous solution in the swelling tank can be 20-40°C, and the residence time can be 40-120 seconds.

[0046] S2: Staining

[0047] The swollen polyvinyl alcohol optical base film is immersed in the dyeing section, whereby the polyvinyl alcohol optical base film is immersed in a dyeing tank filled with a dyeing aqueous solution containing a dichroic substance, such as iodine, so that the polyvinyl alcohol optical base film adsorbs iodine; the dyeing tank contains KI / I2 / H3BO3, the KI concentration is preferably 0-4%, the I2 concentration is preferably 0-1%, the H3BO3 concentration is preferably 0-2%, the pH is preferably 3-6, the dyeing temperature is 25-38℃, and the residence time is 50-100 seconds.

[0048] S3: Crosslinking

[0049] The dyed polyvinyl alcohol optical base film is immersed in the crosslinking section, so that the dyeability brought by the physically adsorbed iodine molecules is not reduced by the external environment. The dyed polyvinyl alcohol film is immersed in the crosslinking aqueous solution, so that the adsorbed iodine molecules are fixed. The KI concentration in the crosslinking tank is preferably 1.8-5%, the H3BO3 concentration is preferably 3-5%, the pH is preferably 3-6, the temperature is preferably 25-38℃, and the residence time is 20-60 seconds.

[0050] S4: Extension

[0051] If the crosslinking reaction of iodine as a dichroic dye is insufficient, iodine molecules will detach due to a humid and hot environment, thus requiring a sufficient crosslinking reaction. In addition, in order to orient the iodine molecules between the molecules of polyvinyl alcohol and improve optical properties, stretching can be performed at the maximum stretch ratio in the crosslinking step. The stretching step can be performed simultaneously with the dyeing step S2 and the crosslinking step S3, or it can be performed separately. The stretching step can be performed at least once or multiple times. If it is performed multiple times, it can be performed separately in any step of the polarizer preparation process.

[0052] The stretching tank contains KI / H3BO3. The concentration of H3BO3 in the stretching tank and the stretching temperature are key points. If the concentration of H3BO3 is too high, it is easy to cause film breakage and affect the stability of production. If the stretching temperature is too low, it will lead to a reduction in the upper limit of the stretching ratio, increase manufacturing costs and film thickness. Moreover, according to manufacturing experience, when the stretching temperature is higher, it is beneficial to the optical performance of the product. Therefore, the preferred concentration of KI in the stretching tank is 4-5%, the preferred concentration of H3BO3 is 3-4%, the total stretching ratio is 5-7 times, the preferred stretching temperature is 55-68℃, and the residence time is 60-120 seconds.

[0053] S5: Water washable

[0054] The polyvinyl alcohol optical base film is immersed in a washing tank filled with a water washing solution to remove unwanted residues such as boric acid that adhered to the polyvinyl alcohol optical base film in the previous steps. The water washing solution can be any water washing solution known in the art, such as water, and iodides may be added to it, but it is not limited to them. The temperature of the water washing tank can be 10-60°C, preferably 20-50°C.

[0055] S6: Complementary Colors

[0056] The iodine complex in the polyvinyl alcohol optical base film with physically adsorbed iodine complex is oriented close to the boric acid crosslinking to stabilize the iodine complex. It can also be used to correct the insufficient staining of the polyvinyl alcohol optical base film with iodine complex in the crosslinking step S3. The complementary color aqueous solution can use aqueous solutions known in the art without particular limitation. For example, it can contain water and boron compounds such as boric acid as solvents, and may also contain organic solvents and iodides that can dissolve together with water. The KI in the complementary color tank is preferably 3-5%, preferably 0-1% H3BO3, the pH is preferably 3-5.5, the temperature is preferably 20-30°C, and the residence time is 20-50 seconds.

[0057] S7: Drying

[0058] As a drying method, any drying method known in the field can be used without limitation, such as natural drying, air drying, heating drying, far-infrared drying, microwave drying, hot air drying, etc. For example, hot air drying can be performed at 20-100°C for 1-10 minutes; the drying temperature can be reduced to prevent the deterioration of the polarizer, but it is not limited to this, and the drying temperature is preferably below 100°C; the orientation of the iodine molecules being dyed can be further improved by the shrinkage caused by drying, and excellent optical properties can be obtained. The shrinkage refers to the narrowing of the film width;

[0059] Moreover, based on manufacturing experience, the temperature of the oven here not only affects its moisture content, but also further affects its weather resistance. As mentioned above, if too much moisture is locked inside the polarizing plate, it is easy to cause hydrolysis of boric acid at high temperature. Therefore, it is preferable to control the moisture content of the polyvinyl alcohol optical base film at 5-15% by controlling the temperature of the oven.

[0060] S8: Fit

[0061] After drying, the polyvinyl alcohol optical base film needs to be laminated with a protective film on one or both sides using a water-based adhesive or a light-curing adhesive. The protective film can be TAC or PET, etc. In the coating of the adhesive, casting method, Mayer rod coating method, gravure coating method, comma coating method, doctor blade coating method, mold coating method, dip coating method, spray coating method, etc. can be used.

[0062] S9: Re-drying

[0063] After the film lamination is completed, in order to remove the water contained in the adhesive layer formed by the water-based adhesive, a drying process to dry the film laminate is preferably performed, for example, by introducing the film laminate into a drying oven. The drying temperature is preferably 30-92°C; below 30°C, the protective film tends to peel off easily from the polarizing film, and above 92°C, the polarization performance of the polarizing film may deteriorate under the influence of heat; the drying time can be 100-1000 seconds, and from a productivity point of view, it is preferably 160-800 seconds, and more preferably 200-700 seconds.

[0064] S10: Heat treatment

[0065] After the drying process, a heat treatment process can be set up, which is carried out at room temperature or slightly above room temperature, such as 28-45°C, for about 10-500 hours; usually the heat treatment temperature is set to a temperature lower than the drying temperature.

[0066] It is particularly important to note that a crosslinking agent that reacts with acetoacetyl groups can be added in any stage or combination of any of the above steps S1-S6; the crosslinking agent described in this invention is not particularly limited, and its main function is to react chemically with acetoacetyl groups to form a crosslinked structure; therefore, it can be one or more combinations of diamines, dialdehydes, polyamines, polyaldehydes and their salts.

[0067] Preferably, the crosslinking agent in this invention is ethylenediamine.

[0068] Preferably, the amount of crosslinking agent added is 0.05%-1%; if the amount added is less than 0.05%, fewer crosslinking points will be generated, and the effect of inhibiting polarization film shrinkage will be poor; if the amount of crosslinking agent added is greater than 1%, the performance improvement will not be significant.

[0069] The beneficial effects of this invention are:

[0070] (1) When preparing polyvinyl alcohol optical base film, acetyl-modified polyvinyl alcohol is added to polyvinyl alcohol optical base film, and crosslinking agent is used to react with acetyl-modified polyvinyl alcohol when preparing polarizer, so that a stable crosslinking structure formed by chemical bonds is generated in polyvinyl alcohol optical base film. This crosslinking structure can maintain the stability of polyvinyl alcohol molecular chain in polyvinyl alcohol optical base film, thereby maintaining the dimensional stability of polarizer film, so that polarizer film shrinks less under high temperature and high humidity and polarizer film has a certain strength in the direction perpendicular to the stretching direction, ensuring that polarizer film will not crack when subjected to thermal shock;

[0071] (2) Since the acetyl group on the acetyl group-modified polyvinyl alcohol is connected to the molecular chain of polyvinyl alcohol by ester group, this structure is prone to hydrolysis reaction under high temperature and high pressure aqueous solution. Therefore, acetyl group-modified polyvinyl alcohol is not suitable for long-term dissolution in high temperature and high pressure aqueous solution. Therefore, in this invention, polyvinyl alcohol and acetyl group-modified polyvinyl alcohol are dissolved separately. After dissolution is completed, the two solutions are mixed in a mixing tank to obtain polyvinyl alcohol casting film stock solution, which is beneficial to improve the performance of polyvinyl alcohol.

[0072] (3) In the method for producing high weather-resistant polarizing film, acetyl-modified polyvinyl alcohol is added to the polyvinyl alcohol stock solution, and a crosslinking agent is added in the swelling, dyeing, crosslinking, stretching, washing, color matching, drying, lamination, and drying stages. The resulting crosslinked structure can fix the polyvinyl alcohol molecular chains, which can significantly improve the durability of the polarizing film. The polarizing film produced by the method of this invention has the characteristics of high polarization degree, low shrinkage rate, and good durability, which can meet the needs of downstream production. Detailed Implementation

[0073] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0074] Example 1

[0075] (1) At an initial temperature of 28°C, polyvinyl alcohol, glycerol, sodium dodecylbenzenesulfonate, and sodium sulfite were added to dissolving vessel one, and then some deionized water was added; at the same time, acetyl-modified polyvinyl alcohol was added to dissolving vessel two, and the remaining deionized water was added; after the two vessels swelled for 1 hour, the temperature was raised separately by program control. For dissolving vessel one, the temperature was raised from 28°C to 160°C within 3 hours, and then kept at 160°C and stirred for 3 hours; for dissolving vessel two, the temperature was raised from 28°C to 110°C within 3 hours, and then kept at 110°C and stirred for 3 hours; when the temperature of both vessels dropped to 100°C, the solutions in the two vessels were mixed for 3 hours until homogeneous, and the polyvinyl alcohol casting film stock solution was obtained.

[0076] (2) After the casting solution is degassed by the extruder, it is filtered and cast by the die head; the cast film is pre-dried by the drying guide roller, then heat-treated in the humid heat oven, and finally heat-treated in the heat treatment oven for shaping; after shaping, it is rolled into a film to obtain a polyvinyl alcohol optical base film containing acetyl group modified polyvinyl alcohol.

[0077] (3) Polyvinyl alcohol optical base film is processed into polarizer through swelling, dyeing, crosslinking, stretching, washing, color matching, drying, lamination and drying. In the polarizer manufacturing process, 0.4% ethylenediamine is added in the four steps of swelling, dyeing, stretching and washing.

[0078] Example 2

[0079] The only difference from Example 1 is that the amount of acetoacetyl-modified polyvinyl alcohol is 6 parts.

[0080] Example 3

[0081] The only difference from Example 1 is that the degree of substitution of the acetoacetyl-modified polyvinyl alcohol is 10%.

[0082] Example 4

[0083] The only difference from Example 1 is that the amount of ethylenediamine added is 0.8%.

[0084] Comparative Example 1

[0085] The only difference from Example 1 is that the amount of acetoacetyl-modified polyvinyl alcohol is 0.9 parts.

[0086] Comparative Example 2

[0087] The only difference from Example 1 is that the amount of acetoacetyl-modified polyvinyl alcohol is 11 parts.

[0088] Comparative Example 3

[0089] The only difference from Example 1 is that the degree of substitution of the acetoacetyl-modified polyvinyl alcohol is 41%.

[0090] Comparative Example 4

[0091] The only difference from Example 1 is that the degree of substitution of the acetoacetyl-modified polyvinyl alcohol is 10%.

[0092] Comparative Example 5

[0093] The only difference from Example 1 is that the amount of ethylenediamine added is 0.04%.

[0094] Comparative Example 6

[0095] The only difference from Example 1 is that the amount of ethylenediamine added is 1.1%.

[0096] Comparative Example 7

[0097] (1) At 28°C, 100 parts of polyvinyl alcohol, 12 parts of glycerol, 0.3 parts of sodium dodecylbenzenesulfonate, 0.2 parts of sodium sulfite, and 3 parts of acetoacetyl-modified polyvinyl alcohol with a degree of substitution of 5% were added to a dissolving vessel. 600 parts of deionized water were added, and after swelling for 1 hour, the temperature was raised from the initial temperature to 160°C within 3 hours and kept at 160°C for 3 hours with stirring to obtain polyvinyl alcohol casting film stock containing acetoacetyl-modified polyvinyl alcohol.

[0098] (2) The casting solution is then degassed by an extruder, filtered, and cast through a die. The cast film is pre-dried by a drying guide roller, then heat-treated in a humid oven, and finally heat-treated in a heat treatment oven for setting. After setting, it is wound into a film to obtain a polyvinyl alcohol optical base film containing acetyl group modified polyvinyl alcohol.

[0099] (3) Polyvinyl alcohol optical base film is processed into polarizer through swelling, dyeing, crosslinking, stretching, washing, color matching, drying, lamination and drying. In the polarizer manufacturing process, 0.4% ethylenediamine is added in the four steps of swelling, dyeing, stretching and washing.

[0100] Comparative Example 8

[0101] Compared with Example 1, the only difference is that ethylenediamine is not added in the four steps of swelling, dyeing, stretching and washing in the polarizer manufacturing process.

[0102] Comparative Example 9

[0103] (1) At 28°C, 100 parts of polyvinyl alcohol, 12 parts of glycerol, 0.3 parts of sodium dodecylbenzenesulfonate and 0.2 parts of sodium sulfite were added to a dissolving vessel, and 600 parts of deionized water were added. After swelling for 1 hour, the temperature was raised from the initial temperature to 160°C within 3 hours and kept at 160°C for 3 hours with stirring to obtain the polyvinyl alcohol casting film stock solution.

[0104] (2) The casting solution is then degassed by an extruder, filtered, and cast through a die. The cast film is pre-dried by a drying guide roller, then heat-treated in a humid oven, and finally heat-treated in a heat treatment oven for setting. After setting, it is wound into a film to obtain a polyvinyl alcohol optical base film containing acetyl group modified polyvinyl alcohol.

[0105] (3) Polyvinyl alcohol optical base film is processed into polarizer through swelling, dyeing, crosslinking, stretching, washing, color matching, drying, lamination and drying. In the polarizer manufacturing process, 0.4% ethylenediamine is added in the four steps of swelling, dyeing, stretching and washing.

[0106] Comparative Example 10

[0107] (1) At 28°C, 100 parts of polyvinyl alcohol, 12 parts of glycerol, 0.3 parts of sodium dodecylbenzenesulfonate and 0.2 parts of sodium sulfite were added to a dissolving vessel, and 600 parts of deionized water were added. After swelling for 1 hour, the temperature was raised from the initial temperature to 160°C within 3 hours and kept at 160°C for 3 hours with stirring to obtain the polyvinyl alcohol casting film stock solution.

[0108] (2) The casting solution is then degassed by an extruder, filtered, and cast through a die. The cast film is pre-dried by a drying guide roller, then heat-treated in a humid oven, and finally heat-treated in a heat treatment oven for setting. After setting, it is wound into a film to obtain a polyvinyl alcohol optical base film containing acetyl group modified polyvinyl alcohol.

[0109] (3) The polyvinyl alcohol optical base film is swollen, dyed, crosslinked, stretched, washed, colored, dried, laminated and dried to make a polarizing film.

[0110] To more intuitively understand the differences between Examples 1-4 and Comparative Examples 1-10, the main components, proportions, and process data of Examples 1-4 and Comparative Examples 1-10 are listed in Table 1, as follows:

[0111] Table 1

[0112]

[0113] The polarizers prepared in Examples 1-4 and Comparative Examples 1-10 were subjected to performance tests, and the test methods are as follows:

[0114] A. Optical performance test

[0115] The single-unit transmittance Ts and polarization degree P of the polarizer were tested using a spectrophotometer. The spectrophotometer selected was a JASCO V-7100 spectrophotometer manufactured in Japan.

[0116] B. Thermal shock test

[0117] The polarizing plate was cut and edge-ground to a size of 66*114mm, and then attached to the optical glass with adhesive. The plate was alternately kept at -40℃ for 30 minutes and at 80℃ for 30 minutes. After 100 cycles, the polarizing plate was removed and tested. OK means that no cracks larger than 300μm were produced; NG means that cracks larger than 300μm were produced.

[0118] C High Temperature and High Humidity Durability Test

[0119] The polarizing plate was cut and edge-ground to a size of 66×114mm, and then attached to the optical glass with adhesive. It was then placed in a constant temperature and humidity chamber at 60℃ and 90%RH for 1000h. The polarizing plate was then removed and the width of the black edge caused by the shrinkage of the polarizing plate was measured with an optical image measuring instrument.

[0120] D Appearance Evaluation

[0121] The polarizer sample was attached to a smooth transparent acrylic sheet, assuming that the polarizer was attached to the visible side of the front panel. Its appearance was evaluated visually under fluorescent light according to the following criteria: evaluation was performed when viewed from the polarizer side and when viewed from the acrylic sheet side; OK means no precipitates were visible; NG means precipitates were visible.

[0122] The results of the tests conducted on Examples 1-4 and Comparative Examples 1-10 are listed in Table 2, as follows:

[0123] Table 2

[0124]

[0125] Analysis of the data in Table 2 shows that the polarizers prepared by the methods of Examples 1-4 have high transmittance and polarization degree, are not easy to crack under thermal shock, and have small shrinkage under high temperature and high humidity. Compared with the polarizers prepared by Comparative Examples 1-10, their durability is significantly improved.

[0126] The foregoing has provided a detailed description of one embodiment of the present invention, but this description is merely a preferred embodiment and should not be construed as limiting the scope of the invention. All equivalent variations and modifications made within the scope of the claims of this invention should still fall within the patent coverage of this invention.

Claims

1. A polyvinyl alcohol optical base film, characterized by, Consists of raw materials of the following weight components: Polyvinyl alcohol 100 parts; Acetyl acetyl modified polyvinyl alcohol 1-10 parts; Plasticizer 1-25 parts; Surfactant 0.01-1 parts; Antioxidant 0.01-0.5 parts; Deionized water 60-1000 parts; The degree of substitution of the acetyl acetyl modified polyvinyl alcohol is 0.1-40%; The plasticizer is one or more of methanol, ethanol, ethylene glycol, glycerol, propylene glycol, sorbitol, pentaerythritol; The surfactant is an anionic surfactant or a nonionic surfactant; The antioxidant is one or more of ascorbic acid, erythorbic acid and its salts, phytic acid, amino acids; The preparation method of the polyvinyl alcohol optical base film comprises the following steps: S1: At an initial temperature of 20-35℃, polyvinyl alcohol, plasticizer, surfactant, antioxidant are added to dissolving kettle one, and part of deionized water is added; at the same time, acetyl acetyl modified polyvinyl alcohol is added to dissolving kettle two, and the remaining deionized water is added; after swelling for 0.5-2 h, the temperature of the two kettles is controlled respectively, and the temperature of dissolving kettle one is raised from the initial temperature to 90-180℃ for 1-5 h, and is kept at 90-180℃ for 1.5-7 h; the temperature of dissolving kettle two is raised from the initial temperature to 90-150℃ for 1-5 h, and the temperature of dissolving kettle two is required to be higher than that of dissolving kettle one after being raised, and is kept at 90-150℃ for 2-5 h; finally, the solutions in the two kettles are mixed uniformly to obtain a polyvinyl alcohol casting solution; S2: The casting solution is defoamed by an extruder, filtered, and then flow-casted through a die; the formed film is pre-dried by a drying guide roller, then heat-treated in a wet heat oven, and then shaped in a heat treatment oven; finally, the film is wound to obtain a polyvinyl alcohol optical base film.

2. The polyvinyl alcohol optical base film according to claim 1, characterized by, In step S1, the method for finally mixing the solutions in the two kettles uniformly is: after the temperature of the two dissolving kettles is reduced to 90-110℃, the acetyl acetyl modified polyvinyl alcohol solution is added to the polyvinyl alcohol dissolving kettle for mixing, and the mixing time is 1-5 h.

3. A polarizing sheet characterized by comprising: The polyvinyl alcohol optical base film of claim 1 is selected as a polarizing film, and the polarizing film is subjected to the processes of wetting, dyeing, crosslinking, stretching, washing, color compensation, drying, lamination, re-drying, and heat treatment to obtain a polarizing sheet; wherein a crosslinking agent that can react with acetyl acetyl is added in one or more of the above wetting, dyeing, crosslinking, stretching, washing, and color compensation processes; The addition amount of the crosslinking agent that can react with acetyl acetyl is 0.01-1%; The crosslinking agent is one or more of diamines, dialdehydes, polyamines, polyaldehydes, and their salts.

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