JP2023145299A - Polyvinyl alcohol film, optical film produced using the same, and manufacturing methods therefor - Google Patents

Abstract

To provide a polyvinyl alcohol film, an optical film produced using the same, and a manufacturing method therefor.SOLUTION: The present invention relates to a polyvinyl alcohol film, an optical film produced using the same, and a manufacturing method therefor. The polyvinyl alcohol film is evenly cut into multiple pieces along a width direction and then stretched in water at a rate of 4.3 cm/min to double the length and dried. Defining the weight of the stretched and dried polyvinyl alcohol film as W3 and the weight of the stretched and dried film stirred in pure water for five minutes and then made absolutely dry as W4, a standard deviation value of (W3-W4)/W3×100% is 0.05-0.60. An optical film produced from the polyvinyl alcohol film offers good dyeing uniformity.SELECTED DRAWING: Figure 1

Description

The present invention relates to polyvinyl alcohol (PVA) films that can be used in the production of optical films, particularly polarizing films.

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

A polarizing film obtained by processing a polyvinyl alcohol film in a polarizing process has a property of allowing only light rays in a specific direction to pass through, and thereby the brightness of the light rays passing through it can be controlled. Based on this property, polarizing films are used in various displays, glasses, and wearable devices. The process of manufacturing a polarizing film includes swelling, stretching, dyeing, etc. Specifically, a polyvinyl alcohol film is placed in a solution and the above-mentioned process is performed, but the dye molecules are diffused into and regularly arranged between the polyvinyl alcohol molecules of the polyvinyl alcohol film, and the polarizing film is Light components parallel to the direction can be absorbed, and light components in the perpendicular direction can be transmitted, resulting in polarized light characteristics.

In order to provide good optical properties, an ideal polarizing film should have properties such as uniform color, less color spots, no wrinkles, and good hue effect. Therefore, in the prior art, methods such as adjusting the structure of polyvinyl alcohol or adding functional groups (for example, cationic groups) are used to change the viscosity and degree of saponification, and to adjust the plasticizer content. It was common to improve optical properties by

In the prior art, when producing an optical film from a polyvinyl alcohol film, the problem of staining spots occurring on the finished product often occurred. The inventor believes that the cause of the above-mentioned problem is probably that additives must be mixed when polyvinyl alcohol film is used to manufacture optical films, but the additives are mixed after the polyvinyl alcohol film is swollen and stretched. It was noticed that this was because some of the particles were deposited and remained on the film. For example, if the distribution of the amount of additives deposited is non-uniform, iodide ions cannot be uniformly deposited on the film during subsequent dyeing, resulting in non-uniform dyeing.

Furthermore, without being limited to any particular theory, the inventors believe that a number of factors are also involved in the above-mentioned situation, for example, during the manufacturing process of polyvinyl alcohol film, the preformed film is exposed to heated rollers. Factors such as the temperature standard deviation of the dryer used for drying after drying and the temperature difference between the upper and lower surfaces of the preformed film in the dryer have at least an effect on the amount of additives precipitated and remaining after the film has swelled. I realized that it partially affects me.

Furthermore, the present inventor noticed that the slow axis angle after swelling and stretching when producing an optical film from a polyvinyl alcohol film is related to the degree of polarization of the finished polarizing film. Also, without being limited to any particular theory, the inventors believe that there are multiple factors during the preparation process of polyvinyl alcohol films that influence the above-mentioned situation. For example, these factors include 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 a surfactant.

Therefore, in order to solve the above-mentioned problems, the present invention provides a polyvinyl alcohol film by adjusting the standard deviation of the amount of additives remaining after swelling and stretching the polyvinyl alcohol film within a certain range. Used to produce optical films with uniform dyeing. Furthermore, the present invention obtains a polyvinyl alcohol film by adjusting the slow axis angle within a certain range after swelling and stretching of the polyvinyl alcohol film, and the polarizing film prepared thereby has a good degree of polarization. do.

Specifically, the polyvinyl alcohol film provided in one embodiment of the present invention has a standard deviation of the amount of residual additive after swelling and stretching of a plurality of polyvinyl alcohol films cut uniformly in the width direction of 0.05. ~0.60. Regarding the above-mentioned swelling and stretching, a plurality of polyvinyl alcohol films were stretched in water at a speed of 4.3 cm/min to double the length. The above-mentioned residual amount of additive was obtained by the calculation formula: (W3-W4)/W3×100%. In the formula, W3 is the weight after swelling and stretching the polyvinyl alcohol film and drying it, and W4 is the weight after swelling and stretching the polyvinyl alcohol film and drying it, then putting it in pure water and stirring for 5 minutes. This is the weight after drying again.

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

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

In a preferred embodiment, the average 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 of 6-15 wt%.

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

In a preferred embodiment, the polyvinyl alcohol film has a moisture content of 1.0 to 5.0 wt%.

An optical film provided in another embodiment of the present invention is made of the above-mentioned polyvinyl alcohol film.

In a preferred embodiment, the optical film is a polarizing film. Preferably, the polarizing film has a degree of polarization of 99.8% or more.

A method for producing a polyvinyl alcohol film provided in yet another embodiment of the present invention includes the following steps.
(a) Stir the polyvinyl alcohol resin, surfactant, plasticizer, and water and heat to a melting temperature of over 100°C, maintain the temperature for 2 to 4 hours, and change the direction of stirring at least 3 times per hour. Invert to form a polyvinyl alcohol casting solution.
(b) A polyvinyl alcohol casting solution is poured into a casting drum and dried to prepare a preformed film.
(c) The preformed film is brought into contact with a plurality of heating rollers whose temperature gradually decreases from high temperature to low temperature, and then enters a dryer having a plurality of sections for heat treatment. Among them, the standard deviation (along the width direction) of the temperature of the dryer is 0.93 to 3.00, and the temperature difference between the upper and lower surfaces of the polyvinyl alcohol film in the dryer is 5° C. or less.

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

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

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

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

The polyvinyl alcohol film provided based on the above features of the present invention can be dyed uniformly and has a better degree of polarization. Also, the specific content of the present invention can be used to more precisely control and manufacture the above-mentioned polyvinyl alcohol films.

In order to make the above and other objects, features, advantages and embodiments of the present invention more clear, the drawings are described below.
1 is a conceptual diagram of a polyvinyl alcohol film manufacturing process based on one embodiment of the present invention. 1 is a conceptual diagram of a polyvinyl alcohol film manufacturing apparatus based on one embodiment of the present invention.

In this specification, the ratios of various features and constituent elements in the figures are not actual proportions, but are drawn using a drawing method based on a customary working method in order to best illustrate the specific features and constituent elements related to the present invention. It is drawn by In addition, in different figures, the same or similar component numbers refer to similar components or members.

In order to describe the present invention in more detail and completely, descriptions describing embodiments and specific examples of the present invention are provided below, but these are only examples of specific examples for carrying out or applying the present invention. It is not in the form of In this specification and the appended claims, the terms "one" and "the" may be interpreted as plural, unless the context clearly dictates otherwise. In addition, in this specification and the attached claims, unless otherwise stated, "installed on a certain object" refers to being directly or indirectly attached to the surface of a certain object, or in other forms. The definition of the surface shall be determined according to the implications of the preceding/paragraphs of the content of the specification and common knowledge in the field to which this specification pertains.

Although all numerical ranges and parameters specifying the present invention are approximate values, relevant numerical values in specific examples are shown as precisely as possible. However, it is essentially inevitable that any numerical value will include a standard deviation due to the particular test method. In this context, "about" generally refers to the actual value being within ±10%, 5%, 1%, or 0.5% of the specified value or range. Alternatively, the term "about" means that the actual value is within an acceptable standard error of the mean, as considered and determined by one of ordinary skill in the art to which this invention pertains. Accordingly, unless stated to the contrary, any numerical parameters disclosed in this specification and the appended claims may be considered approximations and may vary as necessary. At a minimum, the parameters of those numbers should be interpreted as numbers obtained by applying the number of significant digits indicated and the usual carry method.

The polyvinyl alcohol film provided by the present invention is uniformly cut in the width direction into a plurality of sheets, and after swelling and stretching, the standard deviation of the amount of additive remaining is 0.05 to 0.60. Regarding the above-mentioned swelling and stretching, a plurality of polyvinyl alcohol films cut evenly in the width direction were stretched in water at a speed of 4.3 cm/min to double the length. The above-mentioned residual amount of additive was obtained by the calculation formula: (W3-W4)/W3×100%. In the formula, W3 is the weight after swelling and stretching the polyvinyl alcohol film and drying it, and W4 is the weight after swelling and stretching the polyvinyl alcohol film and drying it, then putting it in pure water and stirring for 5 minutes. This is the weight after drying again. The standard deviation of the above-mentioned residual amount of additives is, for example, 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 any two numbers listed above, but are not limited to these. Additives are precipitated during the swelling process of a polyvinyl alcohol film, but in areas where the amount of precipitation is small, it is difficult for iodide ions to form complexes with polyvinyl alcohol, and conversely, where the amount of precipitation is large, more complexes are probably formed. Therefore, if the amount of precipitation is uneven, uneven staining will occur on the polarizing film.

According to a preferred embodiment of the present invention, the average value of the residual amount of the additive after swelling and stretching the plurality of polyvinyl alcohol films 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%.

The present invention aims to adjust the standard deviation of the amount of additives remaining in the polyvinyl alcohol film after swelling and stretching, that is, to imitate the conditions before dyeing the polarizing film, and to add the additive before it enters the dyeing bath. Solve the problem of staining spots on polarizing films by controlling the standard deviation of the amount of residual agent. The present inventor discovered that during the actual manufacturing process of polarizing film, polyvinyl alcohol film undergoes swelling and stretching treatment, and during this process, additives and other impurities in polyvinyl alcohol are precipitated, resulting in polarizing film. Because the additive content in each part of the polyvinyl alcohol film that is manufactured into a film is different, it is not possible to measure the initial amount of additive in the polyvinyl alcohol film or the difference in the initial amount of additive in the actual manufacturing process of the polarizing plate. It was found that it was not possible to express the residual state of the additive when the test was carried out, and that it was not possible to solve the problem of dyeing spots on polarizing films. Specifically, the above parameters were specified based on the process of preparing a polyvinyl alcohol film into an optical film, particularly a polarizing film. The method for preparing a polarizing film from a polyvinyl alcohol film is not particularly limited, but suitable methods include a swelling/stretching treatment in which the polyvinyl alcohol film is immersed in water and stretched, a dyeing treatment in which the polyvinyl alcohol film is dyed with a dichroic dye, and a uniaxial treatment on the film body. It includes a stretching process that performs stretching. Among them, methods such as boric acid crosslinking treatment, fixing treatment, washing treatment, heat treatment, etc. may be further implemented as necessary. In that case, the order of each treatment is not particularly limited, but preferably the swelling treatment, the dyeing treatment, and the stretching treatment are performed in this order. Generally in the industry, when preparing a polarizing film, the approximate stretching ratio in a swelling tank is to stretch it to twice the length.

The residual amount of the additives mentioned above is determined by stirring the polyvinyl alcohol film after swelling, stretching, and drying in pure water for 5 minutes to precipitate the additives in the film. Specifically, the formula for calculating the amount of residual additive is (W3-W4)/W3 x 100%, and preferably, a number of films (for example, 5 or more) cut evenly in the width direction. It is an average value. In addition, in order to further improve the accuracy of this parameter used for evaluation, control, and selection of polyvinyl alcohol films, it is preferable to adopt a numerical range of the standard deviation of the residual amount of additives in this specification. "Standard Deviation" as used herein refers to the standard deviation of a sample, and is used to evaluate the degree of scattering of data in a sample group. Specifically, the formula for calculating the standard deviation s is as follows.
where x is the average value of the sample and n is the size of the sample.

As used herein, "additive" includes, but is not limited to, at least one of an initial additive, a surfactant, a clouding agent, an emulsifier, or a foaming agent. Among these, "plasticizers" can increase the flexibility of materials and liquefy them, and include, for example, phthalates, bis(2-ethylhexyl) phthalate (DEHP), glycerin, and dibutyl phthalate. (DBP), diisononyl phthalate (DINP), diisodecyl phthalate (DIDP), butylbenzyl phthalate (BBP), dioctyl phthalate (DOP), ethylene glycol, propylene glycol, diethylene glycol, diglycerin, triethylene glycol, tetraethylene Examples include, but are not limited to, glycol or trimethylolpropane. Preferably, the plasticizer is glycerin, ethylene glycol, propylene glycol, diethylene glycol, diglycerin, triethylene glycol, tetraethylene glycol or trimethylolpropane. "Surfactant" is not limited to cationic, anionic or nonionic surfactants, and includes, for example, carboxylate salts such as potassium laurate, sulfate ester salts such as sodium laureth sulfate, dodecylbenzenesulfonate, etc. sulfonate type, alkylphenyl ether type such as polyoxyethylene octylphenyl ether, alcoholic phenyl ether type such as polyethylene glycol monooctylphenyl ether, alkyl ester type such as polyoxyethylene laurate, polyoxyethylene lauryl amine Alkylamine type such as polyoxyethylene lauric acid amide, polypropylene glycol ether type such as polyoxyethylene polyoxypropylene ether, alkanolamide type such as lauric acid diethanolamide, oleyl diethanolamide, polyoxyethylene allyl Examples include, but are not limited to, allyl phenyl ether type such as phenyl ether, or sodium polyoxyethylene lauryl ether sulfate. According to a preferred embodiment of the invention, the polyvinyl alcohol film has an initial content of additives between 6 and 15 wt%, such as 7-14, 8-13, 9-12 or 10-11 wt%. etc.

According to a preferred embodiment of the present invention, the additives contained in 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 easily precipitated during the swelling process, leading to non-uniform additive residues in the dyeing process. Specifically, during the swelling process of polyvinyl alcohol film, some of the additive remains in the polyvinyl alcohol film, but if the residual amount is too large, the free cavity will be occupied by the additive, and the polyvinyl alcohol When the film reaches the dye bath, the iodide ions cannot form complexes with polyvinyl alcohol in the free cavities, and on the contrary, too little residual amount of additives will affect the molecular arrangement and cause excessive complexation. This results in the formation of staining spots on the entire polarizing film.

According to at least one embodiment of the present invention, the slow axis angle of the plurality of polyvinyl alcohol films cut uniformly in the width direction after swelling and stretching is 0.30 to 2.79, for example, 0.30 to 2.79. 30, 0.35, 0.43, 0.75, 0.91, 1.25 or 2.78. Preferably, the average value of the slow axis angles is 89.00 to 91.00, for example, 89.22, 89.90, 90.16, 90.17, 90.27, 90.29 or 90.64 etc.

The "slow axis" used herein refers to the axial direction in which the refractive index is maximum within the plane, and is generally used to represent the direction of molecular arrangement in a sample. If there is a shift in the direction of molecular alignment, a state occurs in which the orthogonal transmittance partially increases in the polarization analysis of the sample, resulting in a decrease in the polarization degree. The slow axis of a polyvinyl alcohol film refers to an axis with a large birefringence value, and is usually in the direction of molecular alignment. If a deviation occurs in the alignment direction, a state occurs in which orthogonal transmittance partially increases when polarization degree analysis is performed, resulting in a decrease in the polarization degree. Therefore, in this application, we measure the standard deviation of the slow axis angle of multiple polyvinyl alcohol film samples after swelling and stretching using a phase difference analyzer, and control it within a certain range to obtain a good result. A polyvinyl alcohol film with a degree of polarization is obtained.

According to at least one embodiment of the invention, the degree of polymerization of the polyvinyl alcohol film is between 1800 and 3000, such as 1800, 1900, 2000, 2100, 2200, 2300, 2400, 2500, 2600, 2700, 2800. , 2900, or 3000, but is not limited to these. Also, according to at least one embodiment of the invention, the moisture content of the polyvinyl alcohol film is between 1.0 and 5.0 wt%, such as 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. Examples include, but are not limited to, 7, 3.9, 4.0, 4.1, 4.3, 4.5, 4.7, 4.9, or 5.0 wt%. Additionally, according to at least one embodiment of the invention, the thickness of the polyvinyl alcohol film is between 20 and 100 μm, preferably between 60 and 75 μm, such as 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74 or 75 μm.

Additionally, the present invention provides an optical film, which is prepared from the polyvinyl alcohol film described above. The "optical film" described herein may refer to a polarizing film, a blue light cutting film, a filter lens, etc., but the present invention is not limited thereto. Preferably, the polyvinyl alcohol film of the present invention is a polarizing film. Furthermore, the degree of polarization of the polarizing film of the preferred embodiment provided by the present invention is 99.8% or more, preferably 99.9%.

In another aspect, the present invention also provides a method for manufacturing a polyvinyl alcohol film, and for the process and manufacturing apparatus, the contents shown in FIGS. 1 and 2 can be referred to. The manufacturing method includes the following. Step S100: Stir and heat polyvinyl alcohol resin, surfactant, plasticizer, and water to form a polyvinyl alcohol casting solution. Step S102: A polyvinyl alcohol casting solution is poured into a casting drum and dried to prepare a preformed film. Step S104: The preformed film is brought into contact with n heating rollers whose temperature gradually decreases from high temperature to low temperature, and then entered into a dryer having a plurality of sections for heat treatment.

Specifically, in step S100, a polyvinyl alcohol resin, a surfactant, a plasticizer, and water are placed in a dissolution tank 110, stirred, heated to a dissolution temperature of over 100°C, and kept at a temperature for 2 to 4 hours. Maintain and reverse the stirring direction at least three times per hour to form a polyvinyl alcohol casting solution. The melting temperature is preferably 130 to 140°C, such as 130, 131, 132, 133, 134, 135, 136, 137, 138, 139 or 140°C. The amount of plasticizer added is usually between 3 and 30 parts by weight, preferably between 7 and 20 parts by weight, for example, 3, 4, 5, 6 parts by weight, based on 100 parts by weight of the polyvinyl alcohol resin. , 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 etc. If the content of the plasticizer is insufficient, crystals are likely to form in the polyvinyl alcohol film that is formed, which will affect the dyeing effect in subsequent processing. On the contrary, if the content of plasticizer is too high, the mechanical properties of the polyvinyl alcohol film will be impaired. The final content of surfactant is between 0.10 and 0.20 wt%, for example 0.10 wt%, 0.15 wt%, 0.20 wt% or between any two numbers mentioned above, but but not limited to. Preferably, the final content of surfactant is 0.15 wt%. According to at least one embodiment, step S100 is performed in a dissolution tank. Further, the polyvinyl alcohol resin concentration when preparing the polyvinyl alcohol casting solution is 10.0 to 60.0% by weight, preferably 15.0 to 40.0% by weight, more preferably 20.0 to 40.0% by weight. 40.0% by weight, 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% by weight, etc. The method for calculating the polyvinyl alcohol resin concentration described above is polyvinyl alcohol resin/(polyvinyl alcohol resin + water + plasticizer + surfactant). If the content of the polyvinyl alcohol resin is insufficient, the viscosity of the polyvinyl alcohol casting solution will become too low, the drying load will become excessively large, and the film forming efficiency in PVA film preparation will deteriorate. On the other hand, if the content of the polyvinyl alcohol resin is too high, it becomes difficult for the polyvinyl alcohol resin to dissolve uniformly as a whole, and clusters tend to remain.

Specifically, in step S102, the polyvinyl alcohol casting solution is selectively filtered with a filter, the polyvinyl alcohol casting solution is introduced into a T-shaped slit die in a quantitative manner, and is discharged and cast onto the casting drum 120. A preformed film M is prepared. Specifically, the rotational speed of the casting drum 120 is approximately 5 to 30 m/min, preferably 5 to 7 m/min. If the speed of casting drum 120 is too slow, productivity may decrease. On the other hand, if the speed of the casting drum 120 is too high, the casting solution will not be sufficiently dried and the releasability will deteriorate. Further, in a preferred embodiment, the temperature of the casting drum 120 is set at 90-95°C, and specifically, for example, at 90, 91, 92, 93, 94, 95°C, or between any two numbers mentioned above. However, if the temperature of the casting drum 120 is too high, foaming tends to occur in the casting solution.

Specifically, in step S104, the preformed film M is peeled off from the casting drum 120 and then brought into contact with a plurality of heating rollers 130 to dry both the upper and lower surfaces of the film body. Here, the first heating roller 130 among the plurality of heating rollers 130 has the highest temperature among all the heating rollers 130, and the temperature of the following heating rollers 130 is adjusted so as to gradually decrease. The number of the plurality of heating rollers 130 is between 10 and 20, for example, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20. Subsequently, heat treatment is performed in a dryer 140 equipped with a plurality of sections. Among them, the standard deviation (along the width direction) between the temperatures of the dryer 140 equipped with a plurality of sections is between 0.93 and 3.00, preferably between 0.93 and 2.5, for example: 0.93, 1.0, 1.3, 2.3 or 2.5, etc. The standard deviation of temperature of a dryer with multiple sections refers to the standard deviation of temperature in the dryer space of each section (along the width direction) of 0.93 to 3.00. The standard deviation was obtained by measuring three points equally in the width direction, and the average temperature of the dryer was between 45 and 130°C. Further, regarding the dryer with multiple sections, specifically, it may be a dryer with 2 to 10 sections, preferably 3 to 8 sections, for example, 3, 4, 5, 6, 7, or 8. . Furthermore, the temperature of the upper and lower cavities in the dryer 140 can be adjusted by the amount of hot air, thereby keeping the temperature difference between the upper and lower surfaces of the polyvinyl alcohol film during heat treatment in the dryer 140 to 5° C. or less. is 0.5 to 3.4°C, for example, 0.51, 1.52, 1.87 or 3.4°C. According to at least one embodiment, the dryer of step S104 is a floating dryer. The temperature of the dryer can be controlled, for example, by adjusting the amount of hot air in the upper and lower cavities. According to another embodiment, the heat treatment may be performed using heated rollers.

The present inventor has determined that the standard deviation (along the width direction) between the temperatures of the dryer 140 equipped with a plurality of sections and the temperature difference between the upper and lower surfaces of the polyvinyl alcohol film during heat treatment in the dryer 140 are within a specific range. It has been found that by adjusting the amount, the range of the amount of additive remaining after swelling and stretching of the polyvinyl alcohol film can be effectively controlled, thereby achieving the effect of making the dyeing uniform. Furthermore, the inventor of the present application has realized 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 tank 110, the dissolution becomes more uniform. The molecular alignment direction of the film body formed later can be made more regular, and the addition or non-addition of a surfactant affects the releasability of the preformed film M. I realized that it helps prevent change. The specific factors that affect the direction of molecular alignment mentioned above essentially control the standard deviation range of the slow axis angle after swelling and stretching of the polyvinyl alcohol film, and based on these, the degree of polarization of the polyvinyl alcohol film can be determined. can be improved.

The above-mentioned polyvinyl alcohol resin is obtained by forming a polyvinyl ester resin by polymerizing vinyl ester resin monomers and then performing a saponification reaction. Among them, vinyl ester resin monomers include vinyl esters such as vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl pentanoate, and vinyl octanoate, but the present invention is not limited to these, and suitable is vinyl acetate. Furthermore, a copolymer formed by copolymerization of an olefin compound or an acrylate derivative and the above-mentioned vinyl ester resin monomer can also be used. The olefin compounds include ethylene, propylene, butylene, etc., but the present invention is not limited thereto. Acrylate derivatives include, but are not limited to, acrylic acid, methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, or n-butyl acrylate.

The degree of saponification/degree of alkalization of the polyvinyl alcohol resin disclosed above is preferably 99.00% or more, thereby obtaining good optical properties, and specifically, for example, from 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%.

The present invention will be explained in more detail below along with Examples. However, it should be understood that these examples are provided to help the invention be more easily understood and are not intended to limit the scope of the invention.

1. Preparation of Polyvinyl Alcohol Film The following provides a non-limiting method of preparing a polyvinyl alcohol film. Seven non-limiting example polyvinyl alcohol films (Examples 1-7) and five comparative example polyvinyl alcohol films (Comparative Examples 1-5) were prepared based on methods similar to those disclosed below. . However, the specific methods for preparing Examples 1-7 and Comparative Examples 1-5 typically differ from the methods disclosed below in one or more aspects.

Specifically, the method for preparing a polyvinyl alcohol film includes the following steps. 1,800 kg of polyvinyl alcohol resin with an alkalization degree of >99.9% and a polymerization degree of about 2,400, 4,000 kg of water, 207 kg of glycerin as a plasticizer, and a surfactant were added, and the temperature was raised to 140 ° C. with stirring. Melting was carried out for 180 minutes while maintaining the temperature at °C. Here, the stirring direction during dissolution can be changed at a certain frequency, thereby increasing the dissolution effect and preventing clusters from remaining. For example, the stirring direction is reversed three times per hour. Specifically, the surfactant used in Examples 1 to 4 and Comparative Example 1 was polyoxyethylene lauryl ether, and the surfactant used in Examples 5 to 6 and Comparative Example 3 was polyoxyethylene lauryl ether. sodium ether sulfates, and their final content is 0.15 wt%. Next, water was added to the uniformly dissolved polyvinyl alcohol resin solution to adjust the resin concentration to 30.0% to obtain a polyvinyl alcohol casting solution. After defoaming, the polyvinyl alcohol casting solution was discharged from a T-shaped slit die, curtain-coated onto a rotating high-temperature casting drum, and dried to prepare a preformed film. After the preformed film is peeled off from the casting drum, it is brought into contact with multiple heating rollers to dry both the upper and lower sides of the film, and then heat treated using a floating dryer, and the standard deviation of the dryer temperature (along the width direction) The temperature difference between the upper and lower surfaces of the film body during heat treatment in the dryer was controlled within a specific range.

2. Analysis and Measurement Methods Below, analysis and measurement methods for Examples 1 to 7 and Comparative Examples 1 to 5 are provided to determine the properties of polyvinyl alcohol films.

2-1. Analysis of Initial Content of Additives The sample preparation method was as follows: First, a polyvinyl alcohol film was divided into five equal parts along the width (Transverse Direction, TD) direction, and the center portion of the polyvinyl alcohol film after the equal parts was cut. The cut area of each piece was 5 cm MD x 10 cm TD (MD refers to Machine Direction, that is, the longitudinal direction or machine direction). Next, it was left for 24 hours at 23° C. and 50% relative humidity (RH) in a constant temperature and humidity chamber.

The measurement conditions were as follows: First, a polyvinyl alcohol film was dried and dehydrated at 105° C. for 10 minutes, and then weighed after drying (W1). Next, the polyvinyl alcohol film was stirred in 2000 ml of pure water at 30°C for 5 minutes with a stirrer (rotation speed 115 to 120 rpm) to precipitate glycerin, and after completion, the water on the surface of the polyvinyl alcohol film was dehydrated and placed in a dryer. It was then completely dried at 105° C. for 1 hour, and the weight was measured (W2). Then, the initial additive content becomes (W1-W2)/W1×100%.

2-2. Analysis of the amount of additive remaining after swelling and stretching The sample was prepared by first dividing a polyvinyl alcohol film into five equal parts along the transverse direction, and then cutting the polyvinyl alcohol film at the center after the equal parts. The cut area of each piece was 20 cm MD x 15 cm TD. Next, it was left in a constant temperature and humidity chamber at 23° C. and 50% RH for 24 hours. Next, the polyvinyl alcohol film (MD 5 cm x TD 15 cm) was fixed, and the polyvinyl alcohol film was stretched to double the length at 4.3 cm/min in pure water at 30°C. All moisture was absorbed, and the sample was left in a constant temperature and humidity chamber at 23° C. and 50% RH for 24 hours. Finally, a polyvinyl alcohol film measuring 5 cm in MD x 10 cm in TD was cut out from the stretched portion.

Measurement condition:
First, the stretched polyvinyl alcohol film was dried and dehydrated at 105° C. for 10 minutes, and weighed after drying (W3). Next, the polyvinyl alcohol film was stirred in pure water at 30°C/2000 ml using a stirrer (rotation speed 115 to 120 rpm) for 5 minutes to precipitate glycerin and surfactant, and after completion, the water on the surface of the polyvinyl alcohol film was dehydrated. It was then placed in a dryer and completely dried at 105° C. for 1 hour, and its weight was measured (W4). Then, the amount of plasticizer remaining after swelling is (W3-W4)/W3×100%.

2-3. Analysis of Slow Axis Angle after Swelling and Stretching To prepare a sample, first, a polyvinyl alcohol film was divided into five equal parts along the transverse direction, and the central part of the polyvinyl alcohol film after being divided into equal parts was cut. The cut area of each piece was 20 cm MD x 15 cm TD. Next, it was left in a constant temperature and humidity chamber at 23° C. and 50% RH for 24 hours. Next, the polyvinyl alcohol film (MD 5 cm x TD 15 cm) was fixed, and the polyvinyl alcohol film was stretched to double the length at a rate of 4.3 cm/min in pure water at 30°C, and after completion, Photonic Lattice PA series The average slow axis angle and its standard deviation within the stretching range (MD 5 cm x TD 5 cm) were measured using a phase difference analyzer. Here, the sample piece was placed so that the swelling/stretching direction (MD) was in the same direction as 90 degrees with respect to 0 degrees of the coordinate axis in the phase difference analyzer.

2-4. Measurement of polarization degree expression The sample preparation method is first a step of preparing a polyvinyl alcohol film into a polarizing film. The method for preparing a polarizing film from a polyvinyl alcohol film is not particularly limited, but preferably includes a swelling treatment in which the polyvinyl alcohol film is immersed in water and stretched, a dyeing treatment in which the polyvinyl alcohol film is dyed with a dichroic dye, and a film body subjected to uniaxial stretching. This includes the stretching process performed. Among them, methods such as boric acid crosslinking treatment, fixing treatment, washing treatment, heat treatment, etc. may be further implemented as necessary. In that case, the order of each treatment is not particularly limited, but preferably the swelling treatment, the dyeing treatment, and the stretching treatment are performed in this order.

The measurement instrument used here was Perkin Elmer Lambda 365. The measurement conditions were based on the standard method of JIS Z 8722, using a C light source to perform visibility correction in the visible light region of 2 degrees, then stacking two polarizing films with the same orientation direction, and adjusting the The light transmittance (H ₀ ) was measured, and the light transmittance (H ₉₀ ) under the wavelength was measured by separately stacking two polarizing films with their alignment directions perpendicular. Finally, the degree of polarization data was obtained by calculating the degree of polarization=[(H ₀ −H ₉₀ )/(H ₀ +H ₉₀ )] ^1/2 .

2-5. Performance evaluation of dyeing uniformity A sample piece with a length of 30 cm x 30 cm was cut out from the obtained polarizing film, and a sample piece with a length of 30 cm x 30 cm was cut out between two sample pieces with orthogonal polarization states (single transmittance 43.5%, degree of polarization 99.9%). After sandwiching the sample piece at an angle of 45°, the color uniformity of the sample piece was observed in transmission mode using a lamp house with a light source illuminance of 14000 lx.

3. Data contents of Examples and Comparative Examples First, parameters were set for the following variables of Examples and Comparative Examples. Standard deviation of the temperature of the dryer during the polyvinyl alcohol film preparation process (along the width direction), temperature difference between the upper and lower surfaces of the polyvinyl alcohol film during heat treatment in the dryer, heating and dissolving polyvinyl alcohol resin, plasticizer, and water Dissolution method (stirring temperature and frequency of change of stirring direction), presence or absence of addition of surfactant (V: with addition/X: without addition). Please refer to Table 1 for details of the settings. In addition, if it is written as 1 in the melting method section of Table 1, it means "stirring type melting, stirring direction change frequency 3 (times/hour), and maximum melting temperature 130°C or higher". When the number 2 is written, it means "stirring dissolution, the frequency of stirring direction change is 1 (times/hour), and the maximum melting temperature is less than 130°C."

Next, under the conditions of Examples 1 to 7 and Comparative Examples 1 to 5 above, the amount of additive remaining after swelling and stretching (average and standard deviation values) and slow axis angle (average and standard deviation values) We further measured the characteristic parameters such as (values) and the effects associated with them. Please refer to Table 2 for details. In addition, in the state of staining uniformity in Table 2, "O" indicates that there are no staining spots, and "X" indicates that there are staining spots on 20% or more of the area. ing.

Referring to both Tables 1 and 2, during the preparation process of Examples 1 to 7, the standard deviation of the residual amount of additive after swelling and stretching in Examples 1 to 7 was 0.05, with the above-mentioned variable settings. 0.60, and it can be seen that this makes the dyeing of the polyvinyl alcohol films according to Examples 1 to 7 uniform. On the contrary, the standard deviation of the amount of additive remaining after swelling and stretching in Comparative Examples 1 to 5 was all undesirable, leading to uneven staining.

Further, with reference to Tables 1 and 2, with the above-mentioned variable settings, the standard deviations of the slow axis angles after swelling and stretching in Examples 1 to 7 are all between 0.30 and 2.79. It can be seen that all of the polyvinyl alcohol films prepared according to Examples 1 to 7 had a polarization degree of 99.8 or more. The standard deviations of the slow axis angles of Examples 1 to 6 are all less than 2, which means that all of the polyvinyl alcohol films prepared according to Examples 1 to 6 have an even better degree of polarization of 99.9 or more. It was equipped with On the contrary, the standard deviation of the slow axis angle after swelling and stretching in Comparative Examples 1 to 5 is all larger than 2.6, and the polyvinyl alcohol films prepared according to these comparative examples all have a standard deviation of 99.8. It had a degree of polarization.

In view of the above results, the present inventor adjusted the numerical value of the standard deviation (along the width direction) of the temperature of the dryer and the numerical range of the temperature difference between the upper and lower surfaces of the polyvinyl alcohol film during heat treatment in the dryer. By doing this, it was possible to control the standard deviation range of the amount of additive remaining after swelling and stretching of the polyvinyl alcohol film, and it was realized that the effect of making the dyeing of the prepared polyvinyl alcohol film uniform was also achieved. Furthermore, the present inventor has found that the stirring temperature when heating and dissolving the polyvinyl alcohol resin, plasticizer, and water, the frequency of changing the stirring direction, and the presence or absence of the addition of a surfactant will all affect the swelling of the polyvinyl alcohol film. - It was noticed that it is substantially related to the standard deviation range of the slow axis angle after stretching, and that it affects the degree of polarization of the polyvinyl alcohol film.

The polyvinyl alcohol film provided based on the above characteristics of the present invention can be dyed uniformly and can have a better degree of polarization. Also, the specific features of the present invention can be used to more accurately control, manufacture and screen the above-mentioned polyvinyl alcohol films.

All ranges provided herein are meant to include each specific range within the assigned range and any combination of secondary ranges between the assigned ranges. Also, unless otherwise stated, all ranges provided herein are inclusive of the endpoints of the range. Thus, ranges 1-5 specifically include 1, 2, 3, 4, and 5, as well as secondary ranges such as 2-5, 3-5, 2-3, 2-4, 1-4, and so on.

All publications and patent applications referenced herein are herein incorporated by reference, and each publication or patent application is herein incorporated by reference for all purposes. clearly and individually. In the event of any discrepancies between this specification and any publications or patent applications incorporated by reference, the present specification will control.

110 Melting tank 120 Casting drum 130 Heating roller 140 Dryer M Preformed film S100 to S104 Process

Claims (15)

A polyvinyl alcohol film, which is uniformly cut in the width direction into a plurality of polyvinyl alcohol films, and has a standard deviation of the amount of residual additives of 0.05 to 0.60 after swelling and stretching. :
The swelling/stretching involves stretching the plurality of polyvinyl alcohol films in water at a speed of 4.3 cm/min to double the length;
The residual amount of the additive is calculated using the formula: (W3-W4)/W3×100% (wherein, W3 is the weight after swelling and stretching the polyvinyl alcohol film and drying it, and W4 is the weight after drying the polyvinyl alcohol film. This is the weight obtained after the alcohol film was swollen and stretched, dried, placed in pure water, stirred for 5 minutes, and then completely dried again. The polyvinyl alcohol film according to claim 1, wherein the average value of the amount of additive remaining after swelling and stretching of the plurality of polyvinyl alcohol films is 1.40 to 4.15 wt%. The polyvinyl alcohol film according to claim 1, wherein the standard deviation of slow axis angles of the plurality of polyvinyl alcohol films after swelling and stretching is 0.30 to 2.79. The polyvinyl alcohol film according to claim 1, wherein the average value of slow axis angles of the plurality of polyvinyl alcohol films after swelling and stretching is 89.00 to 91.00. The polyvinyl alcohol film according to claim 1, wherein the polyvinyl alcohol film has an initial additive content of 6 to 15 wt%. The polyvinyl alcohol film according to claim 1, wherein the polyvinyl alcohol film has a degree of polymerization of 1,800 to 3,000. The polyvinyl alcohol film according to claim 1, wherein the polyvinyl alcohol film has a moisture content of 1.0 to 5.0 wt%. An optical film produced from the polyvinyl alcohol film according to any one of claims 1 to 7. The optical film according to claim 8, which is a polarizing film. The optical film according to claim 9, wherein the film has a degree of polarization of 99.8% or more. A method for producing a polyvinyl alcohol film according to any one of claims 1 to 7, comprising:
(a) Stir the polyvinyl alcohol resin, plasticizer, surfactant, and water and heat to a melting temperature of over 100°C, maintain the temperature for 2 to 4 hours, and change the direction of stirring at least 3 times per hour. inverting to form a polyvinyl alcohol casting solution;
(b) casting the polyvinyl alcohol casting solution into a casting drum and drying to prepare a preformed film;
(c) contacting the preformed film with a plurality of heating rollers whose temperature gradually decreases from high temperature to low temperature, and then entering a dryer equipped with a plurality of sections to perform heat treatment;
A polyvinyl alcohol film, wherein the standard deviation (along the width direction) of the temperature of the dryer is 0.93 to 3.00, and the temperature difference between the upper and lower surfaces of the polyvinyl alcohol film in the dryer is 5° C. or less. manufacturing method. The manufacturing method according to claim 11, wherein the melting temperature in step (a) is 130 to 140°C. The manufacturing method according to claim 11, wherein the polyvinyl alcohol resin concentration in the polyvinyl alcohol casting solution in the step (a) is 20.0 to 40.0%. The manufacturing method according to claim 11, wherein the final content of the surfactant is 0.10 to 0.20 wt%. The manufacturing method according to claim 11, wherein the dryer in step (c) is a floating type dryer.