TWI853226B - Polyvinyl alcohol film, optical film produced by the same, and manufacturing method thereof - Google Patents

Abstract

The present invention relates to a polyvinyl alcohol film, an optical film produced by the same, and a manufacturing method thereof. After the polyvinyl alcohol film is averagely cut into plural pieces along the TD direction, it is stretched in water at a rate of 4.3 cm/min to double the length and dried, and the weight of the stretched and dried polyvinyl alcohol film is W3; the weight of the stretched and dried film stirred in pure water for 5 minutes and then made absolutely dry is W4, and the value of the standard deviation of (W3- W4)/ W3*100% is 0.05-0.60. The optical film made by the polyvinyl alcohol film has ideal dyeing uniformity.

Description

Polyvinyl alcohol film, optical film made therefrom and method for making the same

The present invention relates to a polyvinyl alcohol (PVA) film which can be used to make optical films, especially polarizing films.

Polyvinyl alcohol (PVA) film is a hydrophilic material obtained by coating and drying an aqueous solution containing polyvinyl alcohol polymer and plasticizer. It has high transparency, mechanical strength, water solubility, good processability and other properties. It has been widely used in packaging materials or optical films for electronic products, such as polarizing films.

The polarizing film obtained by polarizing polyvinyl alcohol film has the property of only allowing light in a specific direction to pass through, and can thereby control the brightness of the light passing through; based on this property, polarizing film is used in various displays, glasses and wearable devices. The so-called polarizing process generally includes steps such as swelling, stretching and dyeing; specifically, the polyvinyl alcohol film is placed in a solution to perform the above steps, so that the dye molecules diffuse into the polyvinyl alcohol molecules of the polyvinyl alcohol film and arrange regularly, so that the polarizing film can absorb the light component parallel to its arrangement direction, and allow the light component in the vertical direction to pass through and produce polarization characteristics.

In order to provide good optical properties, an ideal polarizing film should have uniform color, few color spots, no wrinkles, and good hue effects. Therefore, previous technologies usually adopt methods such as adjusting the structure of polyvinyl alcohol or adding functional groups (such as cationic groups) to change the viscosity or saponification degree; or adjust the plasticizer content to improve the optical properties.

In the prior art, when polyvinyl alcohol film is prepared into an optical film, the product often has the problem of uneven dyeing. The inventor of this case found that the cause of the above-mentioned problem may be that the polyvinyl alcohol film needs to be mixed with an additive when it is used to prepare an optical film, and the additive will precipitate after the polyvinyl alcohol film is expanded and stretched, and only a part of it will remain on the film; if the amount of the additive precipitated is unevenly distributed, it will cause the iodine ions to not be uniformly attached to the film during the subsequent dyeing, thus causing uneven dyeing.

The inventors of this case have further discovered that, without being limited by a specific theory, there are many factors related to the above situation, for example: in the process of preparing the polyvinyl alcohol film, the standard deviation of the oven temperature in which the initially formed film is dried after being passed through the hot rollers; and the temperature difference between the upper and lower surfaces of the initially formed film in the oven, etc., all of which at least partially affect the amount of additives precipitated and retained after the film is expanded.

Furthermore, the inventors of this case discovered that when the polyvinyl alcohol film is prepared into a polarizing film, the slow axis angle after expansion and stretching is related to the polarization degree of the finished polarizing film. Moreover, without being limited by a specific theory, the inventors of this case believe that there are multiple factors in the process of preparing the polyvinyl alcohol film that will affect the above situation, such as: the stirring temperature when heating and dissolving the polyvinyl alcohol resin, plasticizer and water, the frequency of changing the stirring direction; and the addition of surfactants.

Accordingly, in order to solve the above problems, the present invention provides a polyvinyl alcohol film by adjusting the standard deviation of the residual amount of additives after the polyvinyl alcohol film is expanded and stretched to a certain range, which is used to make an optical film with uniform dyeing. Furthermore, the present invention also obtains a polyvinyl alcohol film by adjusting the slow axis angle of the polyvinyl alcohol film after expansion and stretching to a certain range, and the polarizing film made from the polyvinyl alcohol film has good polarization degree.

Specifically, the present invention provides a polyvinyl alcohol film, which is cut into a plurality of polyvinyl alcohol films in a width direction and has a standard deviation of additive residues after swelling and stretching ranging from 0.05 to 0.60; the swelling and stretching is to stretch the plurality of polyvinyl alcohol films in water at a rate of 4.3 cm/min and then double the length; the additive residue is calculated by (W3- W4)/ W3*100%, wherein W3 is the weight of the polyvinyl alcohol film after swelling, stretching and drying, and W4 is the weight of the polyvinyl alcohol film after swelling, stretching and drying, and then placed in pure water for 5 minutes and stirred and then dried.

In a preferred embodiment, the average residual amount of additives in the plurality of polyvinyl alcohol films after swelling and stretching is 1.40 to 4.15 wt %.

In a preferred embodiment, the standard deviation of the slow axis angles of the plurality of polyvinyl alcohol films after swelling and stretching is 0.30 to 2.79.

In a preferred embodiment, the average value of the slow axis angle of the plurality of polyvinyl alcohol films after swelling and stretching is 89.00 to 91.00.

In a preferred embodiment, the polyvinyl alcohol film has an initial additive content ranging from 6 to 15 wt %.

In a preferred embodiment, the degree of polymerization of the polyvinyl alcohol film is between 1800 and 3000.

In a preferred embodiment, the water content of the polyvinyl alcohol film is between 1.0 and 5.0 wt %.

Another aspect of the present invention provides an optical film, which is made from the polyvinyl alcohol film as described above.

In a preferred embodiment, the optical film is a polarizing film; and preferably, the polarizing film has a polarization degree of not less than 99.8%.

In another aspect, the present invention provides a method for producing a polyvinyl alcohol film, comprising the following steps: (a) stirring and heating a polyvinyl alcohol resin, a surfactant, a plasticizer and water to a dissolution temperature greater than 100°C for 2 to 4 hours, and reversing the stirring direction at least three times per hour to form a polyvinyl alcohol solution; (b) casting the polyvinyl alcohol solution onto a casting drum, and drying to obtain a preformed film; and (c) contacting the preformed film with a plurality of hot rollers whose temperatures decrease from high to low, and then entering a plurality of ovens for heat treatment; wherein the standard deviation of the oven temperature (along the width direction) is 0.93 to 3.00, and the temperature difference between the upper and lower surfaces of the polyvinyl alcohol film in the oven does not exceed 5°C.

In a preferred embodiment, the dissolving temperature in step (a) is 130°C to 140°C.

In a preferred embodiment, the polyvinyl alcohol-based resin concentration in the polyvinyl alcohol casting solution of step (b) is 20.0 to 40.0%.

In a preferred embodiment, the final content of the surfactant is 0.10-0.20 wt %.

In a preferred embodiment, the oven in step (c) is a floating oven.

The polyvinyl alcohol film provided by the present invention based on the above definition can be uniformly dyed; and preferably, has good polarization. In addition, the definition content of the present invention can be used to more accurately regulate and manufacture the polyvinyl alcohol film as described above.

In order to make the description of the present invention more detailed and complete, the following provides an illustrative description of the implementation mode and specific embodiments of the present invention, but this is not the only form of implementing or using the specific embodiments of the present invention. In this specification and the attached patent scope, unless the context otherwise states, "a", "an" and "the" may also be interpreted as plural. In addition, in this specification and the attached patent scope, unless otherwise stated, "disposed on something" may be regarded as directly or indirectly contacting the surface of something by attachment or other forms, and the definition of the surface should be determined based on the context/paragraph meaning of the specification content and the common knowledge in the field to which this specification belongs.

Although the numerical ranges and parameters used to define the present invention are approximate values, the relevant numerical values in the specific embodiments have been presented as accurately as possible. However, any numerical value inherently inevitably contains standard deviations due to individual test methods. Here, "about" usually refers to the actual value within plus or minus 10%, 5%, 1% or 0.5% of a specific value or a range. Alternatively, the word "about" represents that the actual value falls within the acceptable standard error of the mean value, which is determined by a person of ordinary knowledge in the field to which the present invention belongs. Therefore, unless otherwise stated to the contrary, the numerical parameters disclosed in this specification and the attached patent application range are all approximate values and can be changed as needed. At least these numerical parameters should be understood as the indicated significant digits and the values obtained by applying the general rounding method.

The present invention provides a polyvinyl alcohol film, wherein the standard deviation of the residual amount of additives after the polyvinyl alcohol film is evenly cut into a plurality of pieces along the width direction and expanded and stretched is between 0.05 and 0.60; the expansion and stretching is performed by stretching the plurality of polyvinyl alcohol films evenly cut along the width direction in water at a rate of 4.3 cm/min, and then doubling the length; the residual amount of additives is calculated by (W3- W4)/ W3*100%, wherein W3 is the weight value of the polyvinyl alcohol film after expansion, expansion and drying, and W4 is the weight value of the polyvinyl alcohol film after expansion, expansion and drying, and then placed in pure water for 5 minutes and stirred and then dried. The standard deviation of the residual amount of the additive is, for example but not limited to: 0.05, 0.10, 0.15, 0.20, 0.25, 0.30, 0.35, 0.40, 0.45, 0.50, 0.55, 0.60 or between any two of the above values. The additive will precipitate during the swelling process of the polyvinyl alcohol film. The area with less precipitation will make it difficult for iodine ions to form complexes with polyvinyl alcohol. On the contrary, the area with more precipitation may form more complexes. Therefore, if the precipitation amount is uneven, it will lead to uneven dyeing of the polarizer.

According to a preferred embodiment of the present invention, the average residual amount of additives in the plurality of polyvinyl alcohol films after swelling and stretching is 1.40 to 4.15 wt %, for example: 1.44, 1.71, 1.92, 1.93, 2.91, 3.89 or 4.12 wt %, etc.

The present invention solves the problem of uneven dyeing of polarizing film by adjusting the standard deviation of the residual amount of additives in the polyvinyl alcohol film after swelling and stretching, that is, by simulating the conditions before the polarizing film is dyed and controlling the standard deviation of the residual amount of additives before it enters the dyeing tank. The inventor found that the polyvinyl alcohol film will be subjected to swelling and stretching treatment during the actual polarizing film manufacturing process, and the additives and other impurities in the polyvinyl alcohol will precipitate during the process, which will cause the polyvinyl alcohol film that is finally made into a polarizing film to have different additive contents in different places. Therefore, if only the original amount of additives in the polyvinyl alcohol film or the difference in the original amount of additives is tested, it cannot represent the residual amount of additives during the actual polarizing film manufacturing process, and cannot solve the problem of uneven dyeing of the polarizing film. Specifically, the parameters are defined based on the process of making the polyvinyl alcohol film into an optical film; in particular, it refers to making it into a polarizing film. There is no particular limitation on the method of making the polyvinyl alcohol film into a polarizing film, and preferably it includes a swelling stretching treatment of stretching the polyvinyl alcohol film in water; a dyeing treatment of dyeing with a dichroic pigment; and a stretching treatment of uniaxially stretching the film. Wherein, boric acid crosslinking treatment, fixing treatment, cleaning treatment, heat treatment and the like can be further implemented as needed. At this time, there is no particular limitation on the order of the treatments, but it is preferably carried out in the order of swelling treatment, dyeing treatment and stretching treatment. Generally speaking, stretching to twice the length is the approximate stretching ratio of the swelling tank when the industry makes polarizers.

The residual amount of the additive is obtained by stirring the polyvinyl alcohol film after swelling, stretching and drying in pure water for 5 minutes to precipitate the additive in the film; specifically, the residual amount of the additive is calculated as (W3- W4)/ W3*100%, and it is preferably the average value of multiple pieces (such as 5 or more) of the film cut evenly along the width direction. In addition, in order to further improve the accuracy of this parameter for evaluating, controlling and screening the polyvinyl alcohol film, the present case preferably adopts the numerical range of the standard deviation of the residual amount of the additive. As used herein, "Standard Deviation" refers to the sample standard deviation, which is used to evaluate the degree of data dispersion in the sample group; specifically, the standard deviation s is calculated as follows: ; where x is the sample mean and n is the sample size.

As used herein, the term "additive" includes but is not limited to at least one of a primary additive, a surfactant, a clouding agent, an emulsifier or a foaming agent. The "plasticizer" can increase the softness of the material or liquefy the material, and includes, but is not limited to, phthalate (Phthalate), 2-ethylhexyl phthalate (DEHP), glycerol, dibutyl phthalate (DBP), diisononyl phthalate (DINP), diisodecyl phthalate (DIDP), butylbenzyl phthalate (BBP), dioctyl phthalate (DOP), ethylene glycol, propylene glycol, diethylene glycol, diglycerol, triethylene glycol, tetraethylene glycol or trihydroxymethylpropane, etc. Preferably, the plasticizer is glycerol, ethylene glycol, propylene glycol, diethylene glycol, diglycerol, triethylene glycol, tetraethylene glycol or trihydroxymethylpropane. The "surfactant" is not limited to cationic, anionic or non-ionic surfactants, and includes, but is not limited to, carboxylate type such as potassium laurate; sulfate type such as sodium lauryl polyether sulfate; sulfonate type such as dodecylbenzenesulfonate; alkylphenyl ether type such as polyoxyethylene octylphenyl ether; alcohol phenyl ether type such as polyethylene glycol monooctylphenyl ether; alkyl ester type such as polyoxyethylene laurate; alkylamine type such as polyoxyethylene laurylamine ether; alkylamide type such as polyoxyethylene laurylamide; polypropylene glycol ether type such as polyoxyethylene polyoxypropylene ether; alkanolamide type such as lauric acid diethanolamide, oleyl diethanolamide; allylphenyl ether type such as polyoxyalkylene allylphenyl ether or sodium lauryl polyoxyethylene ether sulfate. According to a preferred embodiment of the present invention, the polyvinyl alcohol film has an initial additive content of 6 to 15 wt %, such as 7 to 14, 8 to 13, 9 to 12 or 10 to 11 wt %, etc.

According to a preferred embodiment of the present invention, the additives of the polyvinyl alcohol film are mainly plasticizers and surfactants, or only plasticizers. Plasticizers and surfactants are low molecular weight compounds that increase the free volume of the material when blended with polymers. These additives are particularly prone to precipitation during the swelling process, and cause uneven residual amounts of additives during the dyeing process. Specifically, during the swelling process of the polyvinyl alcohol film, some of the additives will remain in the polyvinyl alcohol film. If the residual amount is too much, the free cavity will be occupied by the additives, so that when the polyvinyl alcohol film enters the dyeing tank, the iodine ions cannot enter the free cavity to form a complex with the polyvinyl alcohol. On the contrary, if the residual amount of the additive is too little, the molecular arrangement will be affected and the complex will be excessively formed, resulting in uneven dyeing of the entire polarizing film.

According to at least one embodiment of the present invention, the polyvinyl alcohol film is cut into a plurality of pieces along the width direction and the standard deviation of the slow axis angle after swelling and stretching is 0.30 to 2.79, for example, 0.30, 0.35, 0.43, 0.75, 0.91, 1.25 or 2.78, etc. Preferably, the average value of the slow axis angle is 89.00 to 91.00, for example, 89.22, 89.90, 90.16, 90.17, 90.27, 90.29 or 90.64, etc.

As used herein, "slow axis (or retarded axis)" refers to the axis with the largest in-plane refractive index, which can generally be used to present the direction of molecular arrangement in the sample; when the direction of molecular arrangement is offset, the sample will produce an increase in local orthogonal transmittance during polarization analysis, which will lead to a decrease in polarization. The slow axis of the polyvinyl alcohol film refers to the axis with a larger birefringence value, which is usually the direction of molecular arrangement. When the arrangement direction is offset, the local orthogonal transmittance will increase during polarization analysis, which will cause a decrease in polarization. Accordingly, this case uses a phase difference analyzer to measure the standard deviation of the slow axis angle of the multiple polyvinyl alcohol film samples after swelling and stretching, and by controlling it within a certain range, a polyvinyl alcohol film with better polarization is obtained.

According to at least one embodiment of the present invention, the degree of polymerization of the polyvinyl alcohol film is between 1800 and 3000, such as but not limited to: 1800, 1900, 2000, 2100, 2200, 2300, 2400, 2500, 2600, 2700, 2800, 2900 or 3000. On the other hand, according to at least one embodiment of the present invention, the water content of the polyvinyl alcohol film is between 1.0 and 5.0 wt%, such as but not limited to: 1, 1.1, 1.3, 1.5, 1.7, 1.9, 2.0, 2.1, 2.3, 2.5, 2.7, 2.9, 3.0, 3.1, 3.3, 3.5, 3.7, 3.9, 4.0, 4.1, 4.3, 4.5, 4.7, 4.9 or 5.0 wt%. In addition, according to at least one embodiment of the present invention, the thickness of the polyvinyl alcohol film is 20 to 100 μm, preferably 60 to 75 μm, for example: 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74 or 75 μm.

Furthermore, the present invention provides an optical film, which is made of the polyvinyl alcohol film as described above; the "optical film" described herein may refer to a polarizing film, an anti-blue light film, a filter, etc., and the present invention is not limited thereto. Preferably, the polyvinyl alcohol film of the present invention is used as a polarizing film. Furthermore, the polarizing degree of the polarizing film of a preferred embodiment provided by the present invention is not less than 99.8%, preferably 99.9%.

On the other hand, the present invention also provides a method for manufacturing the polyvinyl alcohol film, and the steps and manufacturing apparatus thereof can be referred to the contents shown in FIGS. 1 and 2 . The manufacturing method comprises: step S100: a polyvinyl alcohol resin, a surfactant, a plasticizer and water are stirred and heated to form a polyvinyl alcohol casting solution; step S102: the casting solution is cast into a casting drum and dried to obtain a preformed film; and step S104: the preformed film is contacted with n hot rollers whose temperature decreases from high to low, and then enters a multiple-stage oven for heat treatment.

Specifically, in step S100, a polyvinyl alcohol resin, a surfactant, a plasticizer and water are placed in a dissolving tank 110, stirred and heated to a dissolving temperature greater than 100°C, and the temperature is maintained for 2 to 4 hours and the stirring direction is reversed at least three times per hour to form a polyvinyl alcohol casting solution; wherein the dissolving temperature is preferably 130 to 140°C, for example: 130°C, 131, 132, 133, 134, 135, 136, 137, 138, 139 or 140°C. The amount of the plasticizer added is usually between 3 and 30 parts by weight, preferably between 7 and 20 parts by weight, such as 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29 or 30 parts by weight, relative to 100 parts by weight of the polyvinyl alcohol resin. If the content of the plasticizer is insufficient, the polyvinyl alcohol film formed is prone to crystallization and affects the dyeing performance of subsequent processing. On the contrary, if the content of the plasticizer is too high, the mechanical properties of the polyvinyl alcohol film will be destroyed. The final content of the surfactant is 0.10-0.20 wt%, for example but not limited to: 0.10 wt%, 0.15 wt%, 0.20 wt% or between any two of the above values; more preferably, the final content of the surfactant is 0.15 wt%. According to at least one embodiment, step S100 is performed in a dissolving tank. In addition, when the polyvinyl alcohol casting solution is prepared, the polyvinyl alcohol resin concentration is 10.0 to 60.0 wt%, preferably 15.0 to 40.0 wt%, and more preferably 20.0 to 40.0 wt%, for example: 10.0, 15.0, 20.0, 25.0, 30.0, 35.0, 40.0, 45.0, 50.0, 55.0 or 60.0 wt%, etc. The aforementioned polyvinyl alcohol resin concentration is calculated as polyvinyl alcohol resin/(polyvinyl alcohol resin+water+plasticizer+surfactant). If the polyvinyl alcohol resin content is insufficient, the viscosity of the polyvinyl alcohol casting solution will be too low, the drying load will be too large, and the film-forming efficiency of the prepared PVA film will be poor. On the contrary, if the polyvinyl alcohol resin content is too high, the polyvinyl alcohol resin will be difficult to dissolve uniformly as a whole, and clusters will easily remain.

Specifically, in step S102, the polyvinyl alcohol casting solution can be selectively filtered using a filter, and then the polyvinyl alcohol casting solution is quantitatively introduced into a T-slit film, and discharged and cast onto a casting drum 120 to form a primary film M. In detail, the rotation speed of the casting drum 120 is about 5 to 30 m/min, preferably 5 to 7 m/min. When the speed of the casting drum 120 is too slow, there is a risk of reduced productivity. On the contrary, when the speed of the casting drum 120 is too fast, the casting solution is not fully dried and the releasability is reduced. In addition, in a preferred embodiment, the temperature of the casting drum 120 is set at 90 to 95 °C, specifically, 90, 91, 92, 93, 94, 95 °C or between any two of the above values. If the temperature of the casting drum 120 is too high, the casting solution is prone to foaming.

Specifically, in step S104, the initially formed film M is peeled off from the casting drum 120 and then contacts a plurality of hot rollers 130 to dry the upper and lower surfaces of the film; wherein the first of the plurality of hot rollers 130 has the highest temperature among all the hot rollers 130, and the temperature of the subsequent hot rollers 130 is gradually reduced; and the number of the plurality of hot rollers 130 is between 10 and 20, for example: 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 or 20. Next, a heat treatment is performed using a plurality of sections of the oven 140; wherein the standard deviation of the temperature of the plurality of sections of the oven 140 (along the width direction) is 0.93 to 3.00, preferably 0.93 to 2.5, for example: 0.93, 1.0, 1.3, 2.3 or 2.5, etc. The so-called standard deviation of the temperature of the plurality of sections of the oven refers to the standard deviation of the temperature of each section. In the oven space, the standard deviation of the temperature (along the width direction) is 0.93 to 3.00, and the standard deviation is measured at 3 points along the width direction, and the average temperature of the oven is between 45 and 130°C; in addition, the multiple-section oven can be specifically 2 to 10 sections, preferably 3 to 8 sections, such as 3, 4, 5, 6, 7 or 8. Moreover, the temperature of the upper and lower cavities in the oven 140 can be adjusted by the hot air volume, so that the temperature difference between the upper and lower surfaces of the polyvinyl alcohol film being heat-treated in the oven 140 does not exceed 5°C, preferably 0.5 to 3.4°C, such as 0.51, 1.52, 1.87 or 3.4°C. According to at least one embodiment, the oven in step S104 is a floating oven. The temperature of the oven can be adjusted, for example, by adjusting the hot air volume of the upper and lower cavities to control the temperature. According to different embodiments, the heat treatment can also be performed using a hot roller.

The inventors of this case have discovered that by adjusting the standard deviation of the temperatures of the multiple-section oven 140 (along the width direction) and the temperature difference between the upper and lower surfaces of the polyvinyl alcohol film being heat-treated in the oven 140 within a specific range, the range of the residual amount of additives after the polyvinyl alcohol film is expanded and stretched can be effectively controlled, thereby achieving the effect of uniform dyeing. The inventors of the present case further discovered that by adjusting the stirring temperature and the frequency of changing the stirring direction when heating and dissolving the polyvinyl alcohol resin, plasticizer and water in the dissolving barrel 110, the dissolution can be made more uniform and the molecular arrangement direction of the film formed later can be made more regular; in addition, the addition or not of a surfactant affects the releasability of the initially formed film M, thereby preventing the molecular arrangement direction from being changed during its peeling; the above-mentioned specific factors affecting the molecular arrangement direction can substantially control the standard deviation range of the slow axis angle of the polyvinyl alcohol film after swelling and stretching, and accordingly improve the polarization degree of the polyvinyl alcohol film.

The above-mentioned polyvinyl alcohol resin is obtained by polymerizing vinyl ester resin monomers to form polyvinyl ester resins, and then performing saponification reaction; wherein the vinyl ester resin monomers include vinyl esters such as vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl valerate or vinyl octanoate, and the present invention is not limited thereto, preferably vinyl acetate. In addition, copolymers formed by copolymerization of olefin compounds or acrylate derivatives with the above-mentioned vinyl ester resin monomers can also be used; the olefin compounds include ethylene, propylene or butylene, and the present invention is not limited thereto. The acrylate derivatives include acrylic acid, methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate or n-butyl acrylate, and the present invention is not limited thereto.

The saponification degree/alkalization degree of the above-mentioned polyvinyl alcohol resin is preferably above 99.00% to obtain better optical properties, for example: 99.00% to 100.00%, 99.00% to 99.99%, 99.00% to 99.95%, 99.00% to 99.90%, 99.00% to 99.85%, 99.00% to 99.80%, 99.00% to 99.75%, 99.00% to 99.70%, 99.00% to 99.65%, 99.00% to 99.60%, 99.00% to 99.55%, 99.00% to 99.50%, 99.00% to 99.45%, 99.00% to 99.40 %, 99.00% to 99.35%, 99.00% to 99.30%, 99.00% to 99.25%, 99.00% to 99.20%, 99.00% to 99.15%, 99.00% to 99.10%, 99.00% to 99.05%, 99.20% to 100.00%, 99.20% to 99.99%, 99.20% to 99.95%, 99.20% to 99.90%, 99.20% to 99.85%, 99.20% to 99.80%, 99.20% to 99.75%, 99.20% to 99.70%, 99.20% to 99.65%, 99.20% to 99.60% , 99.20% to 99.55%, 99.20% to 99.50%, 99.20% to 99.45%, 99.20% to 99.40%, 99.20% to 99.35%, 99.20% to 99.30%, 99.20% to 99.25%, 99.40% to 100.00%, 99.40% to 99.99%, 99.40% to 99.95%, 99.40% to 99.90%, 99.40% to 99.85%, 99.40% to 99.80%, 99.40% to 99.75%, 99.40% to 99.70%, 99.40% to 99.65%, 99.40% to 99.60%, 99.40% to 99.55%, 99.40% to 99.50%, 99.40% to 99.45%, 99.60% to 100.00%, 99.60% to 99.99%, 99.60% to 99.95%, 99.60% to 99.90%, 99.60% to 99.85%, 99.60% to 99.80%, 99.60% to 99.75%, 99.60% to 99.70%, 99.60% to 99.65%, 99.80% to 100.00%, 99.80% to 99.99%, 99.80% to 99.95%, 99.80% to 99.90% or 99.80% to 99.85%, etc.

Hereinafter, the present invention will be further described with detailed description and embodiments. However, it should be understood that these embodiments are only used to help the present invention to be more easily understood and are not used to limit the scope of the present invention.

1. Polyvinyl alcohol film preparation

The following provides a non-limiting method for preparing polyvinyl alcohol films. According to methods similar to those disclosed below, seven non-limiting examples of polyvinyl alcohol films (Examples 1-7) and five comparative examples of polyvinyl alcohol films (Comparative Examples 1-5) were prepared. However, the specific methods for preparing Examples 1-7 and Comparative Examples 1-5 are generally different from the methods disclosed below in one or more aspects.

Specifically, the method for manufacturing the polyvinyl alcohol film includes the following steps: adding 1800 kg of a polyvinyl alcohol resin having a degree of alkalization greater than 99.9% and a degree of polymerization of about 2400, 4000 kg of water, 207 kg of a plasticizer glycerol, and a surfactant, raising the temperature to 140°C while stirring, and maintaining the temperature at 140°C for 180 minutes for dissolution; wherein the stirring direction during dissolution can be switched at a certain frequency to increase the dissolution effect and thereby avoid residual clusters, for example: the stirring direction is reversed three times per hour. Specifically, the surfactant used in Examples 1-4 and Comparative Example 1 is lauryl alcohol polyoxyethylene ether, and the surfactant used in Examples 5-6 and Comparative Example 3 is lauryl alcohol polyoxyethylene ether sodium sulfate, and the final content thereof is 0.15 wt%. Then, water is added to the uniformly dissolved polyvinyl alcohol resin solution to adjust the resin concentration to 30.0%, so as to obtain a polyvinyl alcohol casting solution. After defoaming, the polyvinyl alcohol casting solution is discharged from the T-type narrow slit die lip, and cast onto a rotating high-temperature casting drum for drying to obtain a primary formed film. After the initial film is peeled off from the casting drum, it is contacted and dried on the upper and lower surfaces by multiple hot rollers, and then heat-treated in a floating oven. The standard deviation of the oven temperature (along the width direction) and the temperature difference between the upper and lower surfaces of the film during the heat treatment in the oven are controlled within a specific range.

2. Analysis and measurement methods

The following provides analysis and determination methods for Examples 1-7 and Comparative Examples 1-5 to determine the properties of the polyvinyl alcohol films.

2-1. Analysis of original additive content

First, the sample preparation method is to divide the polyvinyl alcohol film into 5 equal parts in the transverse direction (TD) direction, and then cut the middle of the polyvinyl alcohol film after the equal parts, and the cutting area of each piece is (MD 5cm*TD 10cm, MD refers to the machine direction, that is, the longitudinal direction or mechanical direction); then place it in a constant temperature and humidity chamber at 23℃ and relative humidity (RH) 50% for 24 hours.

The test conditions are to first dry the polyvinyl alcohol film at 105℃/10 minutes to remove water, and then weigh it after drying (W1). Then, the polyvinyl alcohol film is stirred at 30℃/2000 ml pure water with a stirrer (speed 115 to 120 rpm) for 5 minutes to precipitate glycerin. After completion, the water on the surface of the polyvinyl alcohol film is shaken off and placed in an oven at 105℃/1 hour to make it completely dry and measure the weight (W2). Based on this, the original additive content is (W1-W2)/W1*100%.

2-2. After swelling and stretching Additive Residue Analysis

First, the sample preparation method is to divide the polyvinyl alcohol film into 5 equal parts along the horizontal direction, and cut the middle of the polyvinyl alcohol film after the equal parts, and each cut area is (MD 20cm*TD 15cm); then place it in a constant temperature and humidity box at 23℃, 50%RH for 24 hours. Then fix the polyvinyl alcohol film (MD 5cm*TD 15cm), and stretch the polyvinyl alcohol film at 4.3 cm/min in 30℃ pure water to double the length. After completion, the water on the surface of the polyvinyl alcohol film is dried, and placed in a constant temperature and humidity box at 23℃, 50%RH for 24 hours; finally, cut out a polyvinyl alcohol film (MD 5cm*TD 10cm) in the stretched area.

Test conditions: First, dry the stretched polyvinyl alcohol film at 105℃/10 minutes to remove water, and weigh it after drying (W3); then stir the stretched polyvinyl alcohol film at 30℃/2000 ml pure water with a stirrer (speed 115 to 120 rpm) for 5 minutes to precipitate glycerin and surfactant, and then shake off the water on the surface of the polyvinyl alcohol film and put it in an oven at 105℃/1 hour to make it absolutely dry and measure the weight (W4). Based on this, the residual plasticizer after swelling is (W3-W4)/W3*100%.

2-3. Slow axis after expansion and stretching Angle Analysis

First, the sample preparation method is to divide the polyvinyl alcohol film into 5 equal parts along the horizontal direction, and cut the middle of the polyvinyl alcohol film after the equal parts, and each cut area is (MD 20cm*TD 15cm); then place it in a constant temperature and humidity box at 23℃, 50%RH for 24 hours. Then fix the polyvinyl alcohol film (MD 5cm*TD 15cm), and stretch the polyvinyl alcohol film at 4.3 cm/min in 30℃ pure water to double the length. After completion, the average slow axis angle and its standard deviation within the stretching range (MD 5cm*TD 5cm) are measured with a Photonic Lattice PA series phase difference analyzer; among them, the specimen is placed in the same direction as the expansion stretching stretching direction (MD) and the phase difference analyzer, which is 90 degrees away from the coordinate axis 0 degree.

2-4. Polarization performance measurement

First, the sample preparation method is to subject the polyvinyl alcohol film to a polarizing film process; the method for making the polyvinyl alcohol film into a polarizing film is not particularly limited, and preferably includes a swelling treatment of stretching the polyvinyl alcohol film in water; a dyeing treatment of dyeing with a dichroic pigment; and a stretching treatment of uniaxially stretching the film. If necessary, a boric acid crosslinking treatment, a fixing treatment, a cleaning treatment, a heat treatment, etc. can be further implemented. At this time, the order of each treatment is not particularly limited, but it is preferably carried out in the order of swelling treatment, dyeing treatment and stretching treatment.

On the other hand, the test instrument used here is Perkin Elmer Lambda 365; and the test conditions are based on the standard method of JIS Z 8722, using C light source to perform 2-degree visible light sensitivity correction, then overlapping two polarizing films with the same orientation direction, and measuring the transmittance (H ₀ ) at the wavelength, and overlapping two polarizing films with the orientation direction perpendicular to each other, and measuring the transmittance (H ₉₀ ) at the wavelength. Finally, the polarization data is calculated by the following formula.

2-5. Dyeing uniformity performance evaluation

A 30cm*30cm test piece was cut from the obtained polarizing film and sandwiched between two test pieces in the orthogonal polarization state (single transmittance is 43.5%, polarization degree is 99.9%) at an angle of 45°. The color uniformity of the test piece was observed in the transmission mode with a light box with a light source illumination of 14000 lx.

3. Implementation and comparative example data content

First, the following variables of the embodiment and comparative example are set with parameters: standard deviation of oven temperature (along the width direction) in the polyvinyl alcohol film manufacturing process; temperature difference between the upper and lower surfaces of the polyvinyl alcohol film during heat treatment in the oven; dissolution method (stirring temperature and frequency of change of stirring direction) when heating and dissolving the polyvinyl alcohol resin, plasticizer and water; whether the surfactant is added (V: indicates added/X: indicates not added). Please refer to Table 1 for detailed settings. It should be noted that the mark 1 in the dissolution method in Table 1 means "scraping dissolution, the frequency of changing the stirring direction is 3 times/hour, and the maximum dissolution temperature is above 130°C."; and the mark 2 means "scraping dissolution, the frequency of changing the stirring direction is 1 time/hour, and the maximum dissolution temperature is lower than 130°C." Table 1.

Next, the additive residue (average and standard deviation) and slow axis angle (average and standard deviation) after expansion and stretching were further measured under the conditions of the above-mentioned Examples 1 to 7 and Comparative Examples 1 to 5, and the related effects were further measured. Please refer to Table 2 for details. It should be noted that in the part of the uniform dyeing condition in Table 2, "O" represents the condition of no uneven dyeing; and "X" represents the condition of uneven dyeing of more than 20% of the area. Table 2.

Referring to Table 1 and Table 2 together, it can be seen that in the preparation process of Examples 1 to 7, under the setting of the above-mentioned variables, the standard deviation of the residual amount of additives of Examples 1 to 7 after swelling and stretching is between 0.05 and 0.60, thereby making the polyvinyl alcohol films according to Examples 1 to 7 uniformly dyed. On the contrary, the standard deviation values of the residual amount of additives of Comparative Examples 1 to 5 after swelling and stretching are not ideal, thereby causing uneven dyeing.

Furthermore, referring to Table 1 and Table 2 together, it can be seen that under the above-mentioned variable settings, the standard deviations of the slow axis angles after expansion and stretching of Examples 1 to 7 are all between 0.30 and 2.79, so that the polyvinyl alcohol films prepared according to Examples 1 to 7 all have a polarization degree of more than 99.8; preferably, the standard deviations of the slow axis angles of Examples 1 to 6 are all lower than 2, so that the polyvinyl alcohol films prepared according to Examples 1 to 6 all have a polarization degree of 99.9. On the contrary, the standard deviations of the slow axis angles after expansion and stretching of Comparative Examples 1 to 5 are all greater than 2.6, and the polyvinyl alcohol films prepared according to these comparative examples all have a polarization degree of 99.8.

In view of the above results, the inventors have found that by adjusting the standard deviation of the oven temperature (along the width direction) and the range of the temperature difference between the upper and lower surfaces of the polyvinyl alcohol film during heat treatment in the oven, the standard deviation range of the residual amount of additives after the polyvinyl alcohol film is expanded and stretched can be controlled, and the effect of making the polyvinyl alcohol film uniformly dyed can be achieved. In addition, the inventors have found that the stirring temperature, the frequency of changing the stirring direction, and whether the surfactant is added when the polyvinyl alcohol resin, plasticizer and water are heated and dissolved are substantially related to the standard deviation range of the slow axis angle after the polyvinyl alcohol film is expanded and stretched, and further affect the polarization degree of the polyvinyl alcohol film.

The polyvinyl alcohol film provided by the present invention based on the above definition can be uniformly dyed; and preferably, can have good polarization. In addition, the definition content of the present invention can be used to more accurately regulate, manufacture and screen the polyvinyl alcohol film as described above.

Herein, all ranges provided are intended to include each specific range within the given range and the combination of sub-ranges between the given ranges. In addition, unless otherwise specified, all ranges provided herein include the endpoints of the ranges. Thus, the range 1-5 specifically includes 1, 2, 3, 4 and 5, as well as sub-ranges such as 2-5, 3-5, 2-3, 2-4, 1-4, etc.

All publications and patent applications cited in this specification are incorporated herein by reference, and each individual publication or patent application is specifically and individually indicated as incorporated herein by reference for any and all purposes. In the event of any inconsistency between this document and any publication or patent application incorporated by reference, this document controls.

110: Dissolving barrel 120: Casting drum 130: Hot roller 140: Oven M: Initial film forming S100~S104: Steps

In order to make the above and other purposes, features, advantages and embodiments of the present invention more clearly understood, the attached drawings are described as follows: Figure 1 is a schematic diagram of the polyvinyl alcohol film preparation process according to an embodiment of the present invention; Figure 2 is a schematic diagram of the polyvinyl alcohol film manufacturing device according to an embodiment of the present invention;

According to conventional working methods, various features and components in the figures are not drawn according to the actual scale, and the drawing method is to present the specific features and components related to the present invention in the best way. In addition, the same or similar component symbols are used to refer to similar components and parts between different figures.

without.

S100~S104: Steps

Claims (14)

A polyvinyl alcohol film, which is cut into multiple polyvinyl alcohol films in the width direction and has a standard deviation of additive residues after swelling and stretching ranging from 0.05 to 0.60; the swelling and stretching is to stretch the multiple polyvinyl alcohol films in water at a rate of 4.3 cm/min and then double the length; the additive residue is calculated by (W3-W4)/W3*100%, wherein W3 is the weight of the polyvinyl alcohol film after swelling, stretching and drying, and W4 is the weight of the polyvinyl alcohol film after swelling, stretching and drying, stirring in pure water for 5 minutes and then drying; wherein the standard deviation of the slow axis angle of the multiple polyvinyl alcohol films after swelling and stretching is 0.30 to 1.25. As in claim 1, the average residual amount of additives in the polyvinyl alcohol film after swelling and stretching is 1.40 to 4.15 wt%. For example, the polyvinyl alcohol film of claim 1, wherein the average value of the slow axis angle of the plurality of polyvinyl alcohol films after swelling and stretching is 89.00~91.00. As for the polyvinyl alcohol film of claim 1, the polyvinyl alcohol film has an initial additive content between 6 and 15 wt%. The polyvinyl alcohol film of claim 1, wherein the degree of polymerization of the polyvinyl alcohol film is between 1800 and 3000. As for the polyvinyl alcohol film of claim 1, the water content of the polyvinyl alcohol film is between 1.0 and 5.0 wt%. An optical film made from a polyvinyl alcohol film as claimed in any one of claims 1 to 6. The optical film in claim 7 is a polarizing film. As in claim 8, the optical film has a polarization degree of not less than 99.8%. A method for manufacturing a polyvinyl alcohol film as claimed in any one of claims 1 to 6, comprising: (a) stirring and heating a polyvinyl alcohol resin, a surfactant, a plasticizer and water to a dissolving temperature greater than 100°C, maintaining the temperature for 2 to 4 hours, and reversing the stirring direction at least three times per hour to form a polyvinyl alcohol casting solution; (b) casting the polyvinyl alcohol casting solution onto a casting drum, and drying to obtain a preformed film; and (c) contacting the preformed film with a plurality of hot rollers whose temperature decreases from high to low, and then entering a heat treatment in an oven with a plurality of sections; wherein the standard deviation of the oven temperature (along the width direction) is 0.93 to 3.00, and the temperature difference between the upper and lower surfaces of the polyvinyl alcohol film in the oven does not exceed 5°C. As in claim 10, the dissolution temperature of step (a) is 130°C to 140°C. As in the manufacturing method of claim 10, the polyvinyl alcohol resin concentration in the polyvinyl alcohol casting solution of step (a) is 20.0 to 40.0%. As in the manufacturing method of claim 10, the final content of the surfactant is 0.10-0.20wt%. As in the manufacturing method of claim 10, the oven in step (c) is a floating oven.

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