JP2023145298A - 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 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 value of (W3-W4)/W3×100% is 0.50-3.00 wt.%. An optical film produced from the polyvinyl alcohol film has superior hue expression and a superior polarization degree.SELECTED DRAWING: Figure 2

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 polymer, which has properties such as transparency, mechanical strength, water solubility, and good processability, and is especially used in packaging materials or optical films for electronic products. Widely used in polarizing films.

A polarizing film obtained by processing a polyvinyl alcohol film through a subsequent polarizing process can control the brightness of the light beam passing through it, and is one of the essential components of display devices. The process of manufacturing a polarizing film from a polyvinyl alcohol film includes swelling, stretching, dyeing, etc. Specifically, a PVA film is placed in a solution and the above-mentioned process is performed, but by diffusing dye molecules between the polyvinyl alcohol molecules of the polyvinyl alcohol film and arranging them regularly, the polarizing film follows the direction of the arrangement. The light component parallel to the direction can be absorbed, and the light component in the perpendicular direction can be transmitted, so that the characteristic of polarized light is generated.

An ideal polarizing film should have properties such as uniform color, less color spots, no wrinkles, and good hue effect, and should be able to provide excellent optical properties. In order to improve the optical properties of polarizing films, conventional techniques use methods such as changing the structure of polyvinyl alcohol or adding functional groups (e.g. cationic groups) to change the viscosity and degree of saponification. It was common to improve optical properties.

However, in the prior art, when producing an optical film from a polyvinyl alcohol film, a problem often arises in that the hue of the finished product varies, such as an overall reddish or bluish hue. The inventor believes that the cause of the above-mentioned problem is probably that additives must be mixed when polyvinyl alcohol film is used for manufacturing optical films, but the additives are precipitated after the swelling process of polyvinyl alcohol film. , I noticed that this is because some of it remains on the film. For example, if the residual amount of the additive is too large, it occupies too much amorphous area on the film, and the cross-linking between the pentaiodine anion (I ₅ ^- ) and polyvinyl alcohol for absorbing long wavelength light is inhibited. This makes it difficult for this to occur, and the hue of the finished optical film tends to be reddish. On the other hand, if the residual amount of the additive is too small, the amount of crosslinking between I ₅ ^- and the amorphous region of polyvinyl alcohol becomes excessively large, and in this case, the amount of red light absorbed by the polarizing film increases. As a result, the hue of the finished optical film becomes blue-ish.

Furthermore, without being limited to any particular theory, the inventors believe that a number of factors are also involved in the above-described situation, such as contact during the manufacturing process of polyvinyl alcohol film, after formation of the preformed film. Factors such as the temperature of the heating roller used to dry the film, the temperature of the dryer that performs subsequent drying, and the temperature difference between the heating roller and the dryer all have at least a partial effect on the amount of additives that precipitate and remain after the film has swelled. I realized that it does have an impact.

Therefore, in order to solve the above problems, the present invention provides a polyvinyl alcohol film by controlling the residual amount of additives within a certain range, which can be used to produce an optical film with excellent hue expression. It will be done.

Specifically, the polyvinyl alcohol film provided in one embodiment of the present invention has an additive residual amount of 0.50 to 3.00 wt% after swelling and stretching. For the swelling and stretching described above, the polyvinyl alcohol film was stretched in water at a speed of 4.3 cm/min to double its length. The above-mentioned residual amount of additive was obtained from 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, when the polyvinyl alcohol film after swelling, stretching, and drying is analyzed by Fourier transform infrared spectroscopy (FTIR), the value of the intensity ratio at wavelength 3200 cm ^-1 and wavelength 1425 cm ^-1 is 0. 70 to 1.00.

In a preferred embodiment, when the polyvinyl alcohol film after swelling, stretching, and drying is analyzed by Fourier transform infrared spectroscopy, the value of the intensity ratio at wavelength 1140 cm ^-1 and wavelength 1425 cm ^-1 is 1.20 to 1. It is between .48 and .48. Preferably, the value of the intensity ratio is between 1.20 and 1.45.

In a preferred embodiment, the polyvinyl alcohol film has an initial additive content between 6 and 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 moisture content of the polyvinyl alcohol film is between 1.0 and 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.

In a preferred embodiment, the optical film has a ratio of absorbance at a wavelength of 480 nm to absorbance at a wavelength of 700 nm under orthogonal conditions of 1.40 to 1.60.

A method for producing a polyvinyl alcohol film provided in yet another embodiment of the present invention includes the following steps.
(a) Polyvinyl alcohol resin, plasticizer, surfactant, and water are stirred and heated to a melting temperature of greater than 100° C. 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 n heated rollers whose temperature gradually decreases from high temperature to low temperature, and then enters a dryer with a plurality of sections to dry;
Among them, the temperature of the first heating roller is 84-92°C, the maximum temperature of the dryer is below 115°C, and the temperature difference between the nth heating roller and the first section dryer is below 30°C, and the nth heating roller is below 30°C. is between 10 and 20.

In a preferred embodiment, the dissolution temperature in step (a) is 120-140°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 plasticizer is used in an amount of 3 to 30 parts by weight based on 100 parts by weight of the polyvinyl alcohol resin.

The optical film manufactured using the polyvinyl alcohol film provided based on the above-mentioned characteristics of the present invention has excellent hue expression and polarization degree. Also, certain aspects of the present invention can be used to more accurately manufacture and control the above-mentioned polyvinyl alcohol films.

FIG. 2 is a conceptual diagram of FTIR peaks and corresponding chemical structures according to one embodiment of the present invention. 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 order to make the above and other objects, features, advantages and embodiments of the present invention more clear, the drawings are described below.

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 present invention provides a polyvinyl alcohol film, and after stretching the polyvinyl alcohol film in water at a speed of 4.3 cm/min, doubling its length and drying it, the weight of the polyvinyl alcohol film after stretching and drying is The value is W3, and the weight value after stirring the polyvinyl alcohol film after stretching and drying in pure water for 5 minutes and drying it again is W4, which is the value of (W3-W4)/W3 x 100%. is 0.50 to 3.00 wt%.

The present invention aims to adjust the amount of additives remaining in the polyvinyl alcohol film after swelling and stretching, that is, by simulating the conditions before dyeing the polarizing plate, the amount of additives remaining before it enters the dyeing tank. By controlling this, we can solve the problem of the polarizing film becoming red or blue. The inventor discovered that during the actual manufacturing process of polarizing plates, polyvinyl alcohol films undergo swelling and stretching processes, but during the swelling process, additives and other impurities in the polyvinyl alcohol are precipitated, and the final polarizing plate is Because the additives in each part of the polyvinyl alcohol film that is manufactured into the film change to some extent, measuring only the initial amount of additives in the polyvinyl alcohol film will not reflect the actual amount of additives in the polarizing plate manufacturing process. It was realized that it was not possible to express the residual state of additives, and that it was not possible to solve the problem of polarizing films becoming reddish or bluish. 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 swelling treatment (also referred to herein as swelling and stretching) in which the polyvinyl alcohol film is placed in water and stretched, and dyeing with a dichroic dye. This includes a dyeing process in which the film is uniaxially stretched, and a stretching process in which the film body is uniaxially stretched. 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. The residual amount of the additive is calculated using the formula: (W3-W4)/W3×100%, and may be the average value of a plurality of films (for example, 5 or more films) cut evenly in the width direction.

As used herein, "additive" includes, but is not limited to, plasticizers, surfactants, clouding agents, emulsifiers, or foaming agents. 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. Plasticizers and surfactants are low molecular weight compounds that increase the free volume of the material when blended with polymers. 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 film will not be able to enter the dyeing tank. When the iodide ions arrive, they cannot form complexes with polyvinyl alcohol in the free cavities (for example, the complex of I ₅ ^- with PVA), which reduces the ability of the polarizing film to absorb light in the long wavelength range and changes the hue. This leads to the problem of unevenness. Of these, the I ₅ ^-complex absorbs light with long wavelengths, and the I ₃ ^-complex absorbs light with short wavelengths, so if there is too little of the complex, there is a possibility that the polarizing film will become red or bluish. be.

According to at least one embodiment of the present invention, when a polyvinyl alcohol film after swelling, stretching, and drying is analyzed by Fourier transform infrared spectroscopy, the intensity ratio at a wavelength of 3200 cm ⁻¹ and a wavelength of 1425 cm ⁻¹ is The value is 0.70 to 1.00, for example, 0.71, 0.75, 0.77, 0.79, 0.81, 0.89, 0.90, 0.91, 0.93, Such as 0.95, 0.98 or 0.99. Further, the value of the intensity ratio at wavelength 1140 cm ^-1 and wavelength 1425 cm ^-1 is 1.48 or less, for example, 1.20, 1.26, 1.28, 1.31, 1.32, 1.33, 1.38, 1.42, 1.45 or 1.48, but may be in a range consisting of any two of the above values. According to a preferred embodiment of the invention, the value of the intensity ratio at wavelength 1140 cm ⁻¹ and wavelength 1425 cm ⁻¹ is between 1.20 and 1.48, preferably between 1.20 and 1.45. be.

Fourier transform infrared spectroscopy (FTIR) is a technique for obtaining infrared absorption and emission spectra of solids, liquids, or gases. Regarding the present application, as can be seen from ^the structural conceptual diagram of the polyvinyl alcohol film shown in FIG. Since it corresponds to the degree of alkalization, when measuring a polyvinyl alcohol film after swelling and stretching, the absorption peak at a wavelength of 3200 cm ^-1 can represent the plasticizer (eg, glycerin) in the film. The absorption peak at a wavelength of 1140 cm ⁻¹ can correspond to the main structure in the polyvinyl alcohol film skeleton, and exhibits polyvinyl alcohol crystallinity characteristic peaks (ν(CC) stretching vibrations). The absorption peak at a wavelength of 1425 cm ⁻¹ corresponds to CH in the polyvinyl alcohol film skeleton, and since its content is fixed, it can be a definite peak. As a result, the value of the intensity ratio of wavelength 3200 cm ^-1 and wavelength 1425 cm ^-1 exhibits a positive correlation with the residual amount of plasticizer in the polyvinyl alcohol film, and the value of OH (3200 cm ^-1 )/CH ₂ (1425 cm ^-1 ) The higher the FT-IR ratio, the greater the amount of plasticizer remaining in the polyvinyl alcohol film. The value of the intensity ratio of wavelength 1140 cm ^-1 and wavelength 1425 cm ^-1 exhibits a positive correlation with the crystallinity of the polyvinyl alcohol film, and in the measurement of polyvinyl alcohol film after swelling and stretching, CC (1140 cm ^-1 )/CH (1425 cm ⁻¹ ), the higher the FT-IR ratio, the higher the crystallinity of the polyvinyl alcohol film. The present invention utilizes the value of the above-mentioned FT-IR intensity ratio to adjust the residual amount of plasticizer and crystallinity of the polyvinyl alcohol film after swelling, stretching, and drying, thereby reducing the residual amount of plasticizer. Maintain within proper range and reduce crystallinity. As a result, a finished polyvinyl alcohol film can be obtained which is uniformly dyed and has a good hue.

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%.

The thickness of the polyvinyl alcohol film of the present invention may be between 20 and 100 μm, preferably between 60 and 75 μm, such as 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70 μm. , 71, 72, 73, 74 or 75 μm, but are not limited to these.

The present invention provides an optical film, which is made 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 a preferred embodiment provided by the present invention is 99.8% or more. Further, the optical film provided by the present invention has a ratio of absorbance at a wavelength of 480 nm to absorbance at a wavelength of 700 nm under orthogonal conditions of 1.40 to 1.60, for example, 1.40, 1.42, but not limited to 1.44, 1.46, 1.48, 1.50, 1.52, 1.54, 1.56, 1.58 or 1.60. Specifically, the measurement of the ratio of the absorbance at a wavelength of 480 nm to the absorbance at a wavelength of 700 nm can correspond to the hue expression of the optical film. Without being limited to any particular theory, the above data range of 1.4 to 1.6 can be considered to be a good and consistent hue representation.

In another embodiment, the present invention also provides a method for manufacturing a polyvinyl alcohol film, and for the process and manufacturing apparatus, reference can be made to the contents shown in FIGS. 2 and 3. The manufacturing method includes the following. In step S100, polyvinyl alcohol resin, surfactant, plasticizer, and water are stirred and heated to form a polyvinyl alcohol casting solution. In step S102, a polyvinyl alcohol casting solution is cast into a casting drum and dried to prepare a preformed film. In 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 to be dried.

Specifically, in step S100, a polyvinyl alcohol resin, a plasticizer, a surfactant, and water are placed in a dissolution tank 110, stirred, and heated to a dissolution temperature of over 100 ° C. for at least 180 minutes, Form a polyvinyl alcohol solution. Among them, the melting temperature is preferably 120 to 140°C, for example, 120, 125, 130, 135 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 parts by weight, based on 100 parts by weight of the polyvinyl alcohol resin. , 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, 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 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. 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. For example, 0% by weight. 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 preparing the polyvinyl alcohol film 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. Further, the rotational speed of the casting drum 120 is approximately 3 to 12 m/min, preferably 5 to 10 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 85 to 95°C, and specifically, for example, 85, 87, 89, 91, 93, 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. Subsequently, drying is performed in a dryer 140 equipped with a plurality of sections. Further, the temperature of the first heating roller 130 is 84 to 92°C, for example, 84, 85, 86, 87, 88, 89, 90, 91 or 92°C. The maximum temperature of the dryer 140 is 115°C or less, for example, 80°C, 85°C, 90°C, 95°C, 100°C, 105°C, 110°C, or 115°C. The temperature difference between the nth heating roller 130 and the first section of the dryer 140 is 30°C or less, for example, 1°C, 5°C, 10°C, 15°C, 20°C, 25°C, or 30°C. n is between 10 and 20, for example 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 or 20. The multi-section dryer may be a dryer with 2 to 10 sections, preferably 3 to 8 sections, such as 3, 4, 5, 6, 7 or 8.

The aqueous polyvinyl alcohol solution and additives are uniformly mixed before being discharged onto the casting drum. The amount of additives precipitated in a polyvinyl alcohol film can be controlled within a certain range by designing the drying conditions. If there is a large amount of additives remaining in the polyvinyl alcohol film during the swelling, stretching, and dyeing processes of the polarizing film, the polarizing film will turn red. If the amount of additive remaining in the film is small, a phenomenon occurs in which the polarizing film becomes blue-ish. The inventor of the present application has determined that the higher the maximum temperature of the dryer 140 and the temperature of the first heating roller 130, or the larger the temperature difference between the last heating roller 130 and the first section of the dryer 140, the greater the amount of additive remaining. It was noticed that the average value of Therefore, by further adjusting the above-mentioned parameters, it is possible to control the amount of additive precipitation after swelling and stretching within a specific range, and it is possible to obtain a polyvinyl alcohol film with a better hue.

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.
Example

The non-limiting examples of aspects of the invention provided below are primarily intended to demonstrate each aspect of the invention and the effects achieved thereby.

1. Preparation of Polyvinyl Alcohol Film The following provides a non-limiting method of preparing a polyvinyl alcohol film. Eleven non-limiting example polyvinyl alcohol films (Examples 1 to 11) and four comparative example polyvinyl alcohol films (Comparative Examples 1 to 4) were prepared based on methods similar to those disclosed below. . However, the specific methods for preparing Examples 1-11 and Comparative Examples 1-4 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. Add 1800 kg of polyvinyl alcohol resin with an alkalization degree of >99.9% and a polymerization degree of about 2400, 4000 kg of water, and 207 kg of glycerin as a plasticizer, and the final surfactant content will be 0.15 wt%. Then, the temperature was raised to 140°C while stirring, and dissolved for 180 minutes while maintaining the temperature at 140°C. After uniformly dissolving, water was added to the polyvinyl alcohol resin solution until the resin concentration was 30.0%. A polyvinyl alcohol casting solution was obtained. Among them, the surfactant used in Examples 1 to 6 and Comparative Examples 1 and 2 was polyoxyethylene lauryl ether, and the surfactant used in Examples 7 to 11 and Comparative Examples 3 and 4 was polyoxyethylene lauryl ether. Sodium lauryl ether sulfate. 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 was peeled off from the casting drum, it was brought into contact with a plurality of heated rollers to dry both the top and bottom surfaces of the film, and then dried in a drier. The maximum temperature of the dryer was 115° C., and a finished polyvinyl alcohol film having a moisture content of 2.3 wt% was finally obtained.

2. Analysis and Measurement Methods To prepare a sample, first, a polyvinyl alcohol film was divided into five equal parts along the transverse direction (TD, also called the width direction), and the center part of the polyvinyl alcohol film after the equal parts was cut. did. The cut area of each piece was 5 cm in MD*10 cm in TD (MD refers to Machine Direction, that is, the machine direction or longitudinal 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 is stirred in pure water at 30°C/2000 ml using a stirrer (rotation speed 115 to 120 rpm) for 5 minutes to precipitate the initial additives, and after completion, the water on the surface of the polyvinyl alcohol film is dehydrated and dried. It was placed in a container and completely dried at 105° C. for 1 hour, and the weight was measured (W2). Then, the initial additive content becomes (W1-W2)/W1×100%. Adding the initial surfactant content to the initial plasticizer content gives the initial additive content.

2-2. Analysis of the amount of additive remaining after swelling 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 into five 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%. Adding the residual amount of plasticizer after swelling and stretching to the residual amount of surfactant after swelling and stretching gives the residual amount of additive after swelling and stretching.

2-3. Analysis of FTIR peak ratio (3200cm ^-1 /1425cm ^-1 )
To prepare the 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 the 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 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.

The analytical instrument used here was a Perkin Elmer Spectrum 100. The analysis conditions were as follows: After being left in a constant temperature and humidity chamber, FTIR analysis was performed in ATR transmission mode with four integrations in the 650 to 4000 cm ^-1 section. The FTIR peak intensity ratio was measured as [100-(3200 cm ^-1 transmission value)]/[100-(1425 cm ^-1 transmission value)], and the average value was determined for the FTIR peak ratio in the same TD direction.

2-4. Analysis of FTIR peak ratio (1140cm ^-1 /1425cm ^-1 )
To prepare the 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 the 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 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.

The analytical instrument used here was a Perkin Elmer Spectrum 100. The analysis conditions were as follows: After being left in a constant temperature and humidity chamber, FTIR analysis was performed in ATR transmission mode with four integrations in the 650 to 4000 cm ^-1 section. The measured FTIR peak intensity ratio was [100-(1140 cm ^-1 transmission value)]/[100-(1425 cm ^-1 transmission value)], and the average value was further determined for the FTIR peak ratio in the same TD direction.

2-5. Measurement of Hue 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 a Perkin Elmer Lambda 365 (equipped with an integrating sphere). As for measurement conditions, absorbance at a wavelength of 480 nm (A) and absorbance at a wavelength of 700 nm (B) were measured based on orthogonal conditions with an integrating sphere. Finally, the A/B ratio was used as hue ratio data.

2-6. Measurement of polarization degree expression The sample preparation method is a process of preparing a polyvinyl alcohol film into a polarizing film, and the process is generally as follows. First, a polyvinyl alcohol film prepared according to the above method was prepared into a test piece measuring 9 cm in the longitudinal direction and 10 cm in the width direction. Next, both ends of the test piece in the longitudinal direction are fixed to a stretching jig so that the size of the stretched part is 5 cm in the longitudinal direction x 10 cm in the width direction, and immersed in water at a temperature of 30 ° C. for less than 70 seconds. It was uniaxially stretched along the longitudinal direction at a stretching speed of 4.3 cm/min until it became twice the original length. The test piece was immersed in an iodine/potassium iodide aqueous solution containing 0.03 mass percent iodine and 3 mass percent potassium iodide at a temperature of 30° C., and stretched at 24 cm/min within 60 seconds. The film was uniaxially stretched in the longitudinal direction at a speed of 3.3 times the original length (second stage stretching). Subsequently, the test piece was immersed in an aqueous boric acid/potassium iodide solution containing 3% by weight boric acid and 3% by weight potassium iodide at a temperature of 30°C, and within about 20 seconds it was immersed in a 24cm/potassium iodide solution. The film was uniaxially stretched in the longitudinal direction (third stage stretching) until the length became 3.6 times the original length at a stretching speed of 10 minutes. Further, the test piece was immersed in an aqueous boric acid/potassium iodide solution containing 4% by mass of boric acid and about 5% by mass of potassium iodide at a temperature of 58°C, and stretched at a stretching speed of 24 cm/min. The film was uniaxially stretched in the longitudinal direction until it became 5.5 times the original length (fourth stage stretching). Finally, the test piece was fixed by immersing it in an aqueous potassium iodide solution containing 1.5% by mass of boric acid and 3% by mass of potassium iodide, and then placed in a dryer at 60°C for 4 minutes. It was dried to obtain a polarizing film.

The measuring 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°, then stacking two polarizing films with the same orientation direction. They were stacked in the same state and the light transmittance (H ₀ ) under the wavelength was measured, and two polarizing films were separately stacked with their alignment directions perpendicular and the light transmittance (H ₉₀ ) under the wavelength was measured. Finally, the degree of polarization data was obtained by calculating the degree of polarization=[(H ₀ −H ₉₀ )/(H ₀ +H ₉₀ )] ^1/2 .

3. Data contents of Examples and Comparative Examples First, the maximum temperature of the first heating roller and dryer during the polyvinyl alcohol film preparation process of Examples and Comparative Examples, and the temperature difference between the last heating roller and the first section dryer. Variables were set for the three items, and related analysis or measurement data were further obtained. Please refer to Table 1 for details.

As can be seen from the results, when the amount of additive remaining after swelling and stretching of the polyvinyl alcohol films of Examples 1 to 11 was adjusted within a certain range, the prepared polarizing films had good hue expression. In contrast, the residual amount of additive after swelling and stretching of the polyvinyl alcohol films of Comparative Examples 1 to 4 was greater than 3.00 wt% or less than 0.50 wt%, and the prepared polarizing films had good hue expression. There wasn't. In addition, the value of the FTIR intensity ratio of OH (3200 cm ^-1 )/CH ₂ (1425 cm ^-1 ) in Comparative Examples 1 to 3 is larger than 1.00, and the larger the amount of plasticizer remaining in the polyvinyl alcohol film, the more the hue is expressed. It means that it is getting worse. The value of the FTIR intensity ratio of OH (3200 cm ^-1 )/CH ₂ (1425 cm ^-1 ) in Comparative Example 4 was less than 0.70, and even if the residual amount of plasticizer in the polyvinyl alcohol film was too low, the hue expression was poor. I know it will happen.

Next, during the polyvinyl alcohol film preparation process of Examples and Comparative Examples, variables were controlled for two items such as polyvinyl alcohol dissolution time and polyvinyl alcohol resin concentration after dissolution, and related analysis or measurement data was further obtained. . Please refer to Table 2 for details.

As shown in Table 2, the present inventor found that the higher the degree of crystallinity of a polyvinyl alcohol film, the more likely it is that some undissolved polyvinyl alcohol crystal regions will exist during the preparation of a polarizing film, and the polyvinyl alcohol crystal regions will cause iodine to be absorbed into the film. It was noticed that the degree of polarization decreases as the light swells inside and becomes unable to enter. For example, Examples 8 and 9 and Comparative Examples 1 to 4 have high values of the FTIR intensity ratio of 1140 cm ^-1 /1425 cm ^-1 (greater than 1.45), indicating that the crystallinity of polyvinyl alcohol is high. Therefore, the degree of polarization does not reach 99.9%. On the other hand, in Examples 1 to 7, 10, and 11, the values of the FTIR intensity ratio of 1140 cm ^-1 /1425 cm ^-1 were all 1.45 or less, and the results showed that the polarization degree of the prepared polarizing film was In both cases, it has reached 99.9%.

According to Examples 1 to 11 in Table 2, the polyvinyl alcohol dissolution time of Example 9 and Comparative Examples 2 to 4 was 150 minutes, which was outside the range of 180 to 300 minutes of other Examples. The polyvinyl alcohol resin concentration after dissolution in Example 8 and Comparative Examples 1 and 3 was 35%, which was outside the range of 25 to 30%. The inventors have noticed that controlling the above variables causes the FTIR peak intensity ratio of 1140 cm ⁻¹ /1425 cm ⁻¹ to fall outside of the ideal range.

In view of the above results, the present inventor has found that by controlling the amount of additives remaining after swelling and stretching the polyvinyl alcohol film within a certain range, the polarizing film prepared thereby will have good hue expression. I noticed that. In the polyvinyl alcohol film preparation process, three variables are the temperature of the first heating roller, the maximum temperature of the dryer, and the temperature difference between the last heating roller and the first section dryer. , can affect the residual amount of polyvinyl alcohol film additives and also affect the optical properties of optical films prepared therefrom. In addition, the results of dividing the average residual amount of additive in the polyvinyl alcohol film and the initial additive content, the FTIR peak ratio (3200 cm ^-1 /1425 cm ^-1 ), and the FTIR peak ratio (1140 cm ^-1 /1425 cm ^-1 ) By controlling it, it can also be used to prepare polyvinyl alcohol films with other ideal properties. Furthermore, the present inventors have also noticed that the polyvinyl alcohol dissolution time and the polyvinyl alcohol resin concentration after dissolution affect the crystallinity of the polyvinyl alcohol film and the degree of polarization of the optical film prepared thereby.

To summarize the above, the polyvinyl alcohol film provided by the present invention based on the above specification has a low crystallinity, and the optical film prepared thereby has excellent hue expression and polarization degree. Additionally, the definitions of the present invention can be used to more accurately manufacture, identify and sort the polyvinyl alcohol films described above.

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 (16)

A polyvinyl alcohol film having an additive residual amount of 0.50 to 3.00 wt% after swelling and stretching as defined below:
The swelling/stretching involves stretching the polyvinyl alcohol film 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 has an intensity ratio value of 0.70 to 1.00 at a wavelength of 3200 cm ⁻¹ and a wavelength of 1425 cm ⁻¹ when analyzed by Fourier transform infrared spectroscopy after swelling, stretching, and drying. , the polyvinyl alcohol film according to claim 1. The polyvinyl alcohol film has an intensity ratio value of 1.20 to 1.48 at a wavelength of 1140 cm ⁻¹ and a wavelength of 1425 cm ⁻¹ when analyzed by Fourier transform infrared spectroscopy after swelling, stretching, and drying. , the polyvinyl alcohol film according to claim 1. The polyvinyl alcohol film has an intensity ratio value of 1.20 to 1.45 at a wavelength of 1140 cm ⁻¹ and a wavelength of 1425 cm ⁻¹ when analyzed by Fourier transform infrared spectroscopy after swelling, stretching, and drying. , the polyvinyl alcohol film according to claim 1. The polyvinyl alcohol film according to claim 1, wherein the additives include a plasticizer and a surfactant. 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 8. The optical film according to claim 9, 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. The optical film according to claim 9, wherein the ratio of absorbance at a wavelength of 480 nm to absorbance at a wavelength of 700 nm under orthogonal conditions is 1.40 to 1.60. A method for producing a polyvinyl alcohol film according to any one of claims 1 to 8, comprising:
(a) stirring and heating the polyvinyl alcohol resin, plasticizer, surfactant, and water to a melting temperature of greater than 100°C 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) bringing the preformed film into contact with n heating rollers whose temperature gradually decreases from high temperature to low temperature, and then entering a dryer having a plurality of sections to dry it;
including;
The temperature of the first heating roller is 84 to 92°C, the maximum temperature of the dryer is 115°C or less, and the temperature difference between the nth heating roller and the first section dryer is 30°C or less, A method for producing a polyvinyl alcohol film, wherein n is between 10 and 20. The manufacturing method according to claim 13, wherein the melting temperature in step (a) is 120 to 140°C. The manufacturing method according to claim 13, wherein the polyvinyl alcohol resin concentration in the polyvinyl alcohol casting solution in step (b) is 20.0 to 40.0%. The manufacturing method according to claim 13, wherein the plasticizer is used in an amount of 3 to 30 parts by weight based on 100 parts by weight of the polyvinyl alcohol resin.