KR20230139750A - Polyvinylalcohol film, an optical film manufactured thereby and manufacturing method of the same - Google Patents

Abstract

The purpose of the present invention is to provide a polyvinyl alcohol film, an optical film produced therefrom, and a method for producing the same.
The present invention relates to a polyvinyl alcohol film, an optical film produced therefrom, and a method for producing the same. After stretching the polyvinyl alcohol film in water at a speed of 4.3 cm/min, doubling the length and drying, the weight value of the polyvinyl alcohol film after stretching and drying is W3, and the polyvinyl alcohol film after stretching and drying is The weighed value after stirring in pure water for 5 minutes and further drying is W4, and the value of (W3 - W4) / W3 * 100% is 0.50 to 3.00 wt%. The optical film prepared from the polyvinyl alcohol film has excellent color expression and polarization degree.

Description

Polyvinyl alcohol film, an optical film manufactured thereby and manufacturing method thereof {Polyvinylalcohol film, an optical film manufactured thereby and manufacturing method of the same}

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

Polyvinyl alcohol (PVA) film is a type of hydrophilic polymer and has properties such as transparency, mechanical strength, water solubility, and good processability, and is widely used in packaging materials or optical films for electronic products, especially polarizing films. there is.

A polarizing film obtained by processing a polyvinyl alcohol film in a subsequent polarization process can control the brightness of passing light and is one of the essential components in a display device. The process of manufacturing a polarizing film from a polyvinyl alcohol film includes swelling, stretching, and dyeing. Specifically, the PVA film is placed in a solution and the above-described process is performed. By diffusing dye molecules into the polyvinyl alcohol molecules of the polyvinyl alcohol film and arranging them regularly, the polarizing film produces light parallel to the arrangement direction. It absorbs components and transmits light components in the vertical direction, creating polarization characteristics.

An ideal polarizing film should have characteristics such as uniform color, little color staining, no wrinkles, good color effects, etc., and should be able to provide excellent optical properties. In order to improve the optical properties of the polarizing film, in the prior art, the viscosity or saponification degree was changed using methods such as changing the structure of polyvinyl alcohol or adding a functional group (for example, a cationic group). It was common to improve optical properties.

However, in the prior art, when manufacturing an optical film from a polyvinyl alcohol film, a problem of color non-uniformity, such as the overall color of the finished product becoming reddish or pale, often occurred. The present inventor believes that the cause of the above-mentioned problem is that additives must be mixed when using a polyvinyl alcohol film for the production of an optical film, but the additive precipitates after the swelling process of the polyvinyl alcohol film, and some of it remains on the film. I found out that it was because I did it. For example, if the residual amount of the additive is too large, too much amorphous area on the film is occupied, making it difficult to form cross-linking between the pentaiodine anion (I ₅ ^- ) and polyvinyl alcohol to absorb long-wavelength light. The color of the finished optical film becomes 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 absorption of red light by the polarizing film becomes too large, causing the color of the finished optical film to change. It becomes pale.

In addition, the present inventor is not limited to a specific theory, but numerous factors are also involved in the above-mentioned situation, for example, the temperature of the heating roller contacted after the formation of the preformed film during the manufacturing process of the polyvinyl alcohol film, , it was found that factors such as the temperature of the dryer that subsequently performs drying and the temperature difference between the heating roller and the dryer all at least partially affect the amount of additives that precipitate and remain after the film undergoes swelling.

Accordingly, in order to solve the above-described problems, the present invention provides a polyvinyl alcohol film by controlling the residual amount of additives within a certain range, which is used in the production of an optical film with excellent color expression.

Specifically, the polyvinyl alcohol film provided in one aspect of the present invention has a residual amount of additives 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 the length. The residual amount of the above-described additive was obtained according to the calculation formula (W3 - W4) / W3 * 100%. Among them, 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, drying it, placing it in pure water, stirring it for 5 minutes, and then drying it further. .

In a preferred embodiment, when the polyvinyl alcohol film after swelling, stretching, and drying was analyzed by Fourier transform infrared spectroscopy (FTIR), the intensity ratio at a wavelength of 3200 cm ^-1 and a wavelength of 1425 cm ^-1 was 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 intensity ratio at a wavelength of 1140 cm ^-1 and a wavelength of 1425 cm ^-1 is between 1.20 and 1.48. am. 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 of 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%.

The optical film provided in another aspect of the present invention is manufactured from the polyvinyl alcohol film described above.

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

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

The method for producing a polyvinyl alcohol film provided in another aspect of the present invention includes the following steps. (a) The polyvinyl alcohol-based resin, plasticizer, surfactant, and water are stirred and heated to a dissolution temperature of more than 100°C to form a polyvinyl alcohol casting solution. (b) The polyvinyl alcohol casting solution is cast on a casting drum and dried to prepare a preformed film. (c) The preformed film is brought into contact with n heating rollers whose temperature gradually decreases from high temperature to low temperature, and then placed in a dryer equipped with a plurality of sections to be dried. Among them, the temperature of the first heating roller is 84 to 92 ℃, the maximum temperature of the dryer is 115 ℃ or less, and the temperature difference between the nth heating roller and the first section dryer is 30 ℃ or less, and n is between 10 and 20. am.

In a preferred embodiment, the dissolution temperature in step (a) is 120 to 140°C.

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

In a preferred embodiment, the amount of plasticizer is 3 to 30 parts by weight based on 100 parts by weight of the polyvinyl alcohol-based resin.

The optical film manufactured from the polyvinyl alcohol film provided based on the above-described definition of the present invention has excellent color expression and polarization degree. In addition, the contents of the present invention can be used to more accurately manufacture and control the polyvinyl alcohol film described above.

In order to make the above-mentioned and other objects, features, advantages and embodiments of the present invention clearer, the drawings are described as follows.
1 is a conceptual diagram of FTIR peaks and corresponding chemical structures based on an embodiment of the present invention.
Figure 2 is a conceptual diagram of a polyvinyl alcohol film manufacturing process based on an embodiment of the present invention.
Figure 3 is a conceptual diagram of a polyvinyl alcohol film manufacturing apparatus based on an embodiment of the present invention.
Meanwhile, the ratios of various features or components in the drawings are not actual proportions, but are drawn using a drawing method based on customary work methods in order to optimally represent specific features or components related to the present invention. It is showing. Additionally, in separate drawings, identical or similar component symbols indicate similar components or members.

In order to describe the present invention in more detail and without unnecessary details, descriptions of embodiments and specific examples of the present invention are provided below, but these are not the only specific embodiments for carrying out or applying the present invention. In this specification and the appended claims, unless otherwise indicated in the context, the terms “one” and “corresponding” may be construed as plural. In addition, in this specification and the appended claims, unless otherwise stated, “installed on something” can be considered to be directly or indirectly joined to the surface of something or in contact with it in some other way, and may be considered to be in contact with the surface of something in any other way. is to be judged based on the implications of the contents of the specification and the paragraphs before and after and common knowledge in the field to which this specification pertains.

The numerical ranges and parameters defining the present invention are all approximate values, but the relevant numerical values in specific embodiments are shown as accurately as possible. However, it is inherently inevitable that any numerical value will include standard deviations due to individual test methods. At this time, “about” generally refers to the actual value being within ±10%, 5%, 1%, or 0.5% of a specific value or range. Alternatively, the term "about" means that the actual value is within the allowable standard error of the average value, as considered and judged by a person skilled in the art to which the present invention pertains. Accordingly, unless otherwise stated, the numerical parameters disclosed in this specification and the appended claims are all approximate values and can be considered to be changed as necessary. At the very least, these numerical parameters should be interpreted as values obtained by applying the indicated valid digits and normal rounding methods.

The present invention provides a polyvinyl alcohol film, in which the polyvinyl alcohol film is stretched in water at a speed of 4.3 cm/min, the length is doubled and dried, and the weight value of the polyvinyl alcohol film after stretching and drying is W3. And, the weighed value after stretching and drying the polyvinyl alcohol film in pure water for 5 minutes and then drying it further is W4, and the value of (W3 - W4) / W3 * 100% is 0.50 to 3.00 wt%.

The present invention is to control the residual amount of additives in the polyvinyl alcohol film after swelling and stretching, that is, by imitating the conditions before dyeing the polarizing plate and controlling the residual amount of additives before it enters the dyeing tank, thereby preventing the polarizing film from becoming reddish or flaky. Solve the termination problem. When the inventor actually carries out the manufacturing process of the polarizing plate, the polyvinyl alcohol film undergoes swelling and stretching treatment. During the swelling process, additives and other impurities in the polyvinyl alcohol are precipitated, and the polyvinyl alcohol is finally manufactured into a polarizing film. Because the additives in each part of the film change somewhat, when only the initial amount of additives in the polyvinyl alcohol film is measured, the residual state of the additives when the polarizing plate manufacturing process is actually performed cannot be shown, and the polarizing film may appear reddish or reddish. I realized that I couldn't solve the problem of becoming pale. Specifically, the above-mentioned parameters are defined based on the process of preparing a polyvinyl alcohol film into an optical film, especially a polarizing film. The method of preparing a polyvinyl alcohol film into a polarizing film is not particularly limited, but is preferably a swelling treatment in which the polyvinyl alcohol film is placed in water and stretched (also referred to as swelling/stretching in this specification), and dyeing with a dichroic dye. processing, and a stretching treatment in which uniaxial stretching is performed on the film body. Among them, methods such as boric acid crosslinking treatment, fixing treatment, washing treatment, and heat treatment may be additionally performed as necessary. In this case, the order of each treatment is not particularly limited, but is preferably performed in the order of swelling treatment, dyeing treatment, and stretching treatment. In the art, generally, when preparing a polarizing film, stretching it to twice the length is the approximate stretching ratio in the swelling tank.

The residual amount of the additive mentioned above is obtained by stirring the polyvinyl alcohol film after swelling, stretching and drying in pure water for 5 minutes to precipitate the additive in the film. The formula for calculating the residual amount of additives is (W3 - W4) / W3 * 100%, and may be the average value of a plurality of films (for example, 5 or more sheets) cut equally in the width direction.

Additives used in this specification include, but are not limited to, plasticizers, surfactants, whitening agents, emulsifiers, or foaming agents. Among them, “plasticizers” can increase the flexibility of materials or liquefy them, for example, phthalate, 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. Glycol or trimethylolpropane, etc., but is not limited thereto. 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, carboxylic acid salts such as potassium laurate, sulfuric acid ester salts such as sodium laureth sulfate, dodecylbenzenesulfonate, etc. sulfonate type, alkylphenyl ether type such as polyoxyethylene octylphenyl ether, alcohol-based phenyl ether type such as polyethylene glycol monooctylphenyl ether, alkyl ester type such as polyoxyethylene laurate, polyoxyethylene laurylamine, etc. Alkylamine type, alkylamide type such as polyoxyethylene lauric acid amide, polypropylene glycol ether type such as polyoxyethylene polyoxypropylene ether, alkanolamide type such as lauric acid diethanolamide and oleyldiethanolamide, Allyl phenyl ether types such as polyoxyethylene allyl phenyl ether, or polyoxyethylene lauryl ether sodium sulfate, etc., but are not limited thereto. According to a preferred embodiment of the present invention, the polyvinyl alcohol film has an initial additive content of between 6 and 15 wt%, for example, 7 to 14, 8 to 13, 9 to 12 or 10 to 11 wt%, etc. am.

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, and when combined with polymers, the free volume of the material increases. During the swelling process of the polyvinyl alcohol film, some additives remain in the polyvinyl alcohol film, but if the residual amount is too large, the free cavity is occupied by the additive, and when the polyvinyl alcohol film enters the dyeing tank, iodide ions In this free cavity, a complex with polyvinyl alcohol (for example, a complex between I ₅ ^- and PVA) cannot be formed, which reduces the ability of the polarizing film to absorb light in the long wavelength range, causing the problem of uneven color. I do it. Among them, the I ₅ ^- complex absorbs light of long wavelengths, and the I ₃ ^- complex absorbs light of short wavelengths, so if there is too little complex, there is a possibility that the polarizing film may become reddish or pale.

According to at least one embodiment of the present invention, when the polyvinyl alcohol film after swelling, stretching and drying is analyzed by Fourier transform infrared spectroscopy, the value of the intensity ratio at a wavelength of 3200 cm ^-1 and a wavelength of 1425 cm ^-1 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, 0.95, 0.98 or 0.99. In addition, the value of the intensity ratio at a wavelength of 1140 cm ^-1 and a wavelength of 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. It may be a range consisting of two arbitrary numbers. According to a preferred embodiment of the present invention, the intensity ratio at a wavelength of 1140 cm ^-1 and a wavelength of 1425 cm ^-1 is between 1.20 and 1.48, preferably between 1.20 and 1.45.

Fourier transform infrared spectroscopy (FTIR) is a technology for acquiring infrared absorption and emission spectra of solids, liquids, or gases. Regarding the present application, as can be seen by referring to the structural concept diagram of the polyvinyl alcohol film shown in FIG. 1, the absorption peak at a wavelength of 3200 cm ^-1 can correspond to OH in the polyvinyl alcohol film skeleton, and the polyvinyl alcohol film Since it corresponds to the degree of alkalization within the film, when measuring a polyvinyl alcohol film after swelling and stretching, the absorption peak at a wavelength of 3200 cm ^-1 can indicate the plasticizer (for example, glycerin) in the film body. The absorption peak at a wavelength of 1140 cm ^-1 can correspond to the main structure in the polyvinyl alcohol film skeleton, and polyvinyl alcohol crystallinity also shows a characteristic peak (υ(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 used as a definite peak. Accordingly, the value of the intensity ratio between wavelength 3200 cm ^-1 and wavelength 1425 cm ^-1 shows a positive correlation with the residual amount of plasticizer in the polyvinyl alcohol film, OH (3200 cm ^-1 ) / CH ₂ (1425 cm ^-1 ), the higher the FT-IR ratio, the greater the residual amount of plasticizer in the polyvinyl alcohol film. The value of the intensity ratio between the wavelength 1140 cm ^-1 and the wavelength 1425 cm ^-1 shows a positive correlation with the crystallinity of the polyvinyl alcohol film, and in the measurement of the 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 uses the above-mentioned FT-IR intensity ratio value to adjust the plasticizer residual amount and crystallinity of the polyvinyl alcohol film after swelling, stretching, and drying, thereby maintaining the plasticizer residual amount within an appropriate range and reducing the crystallinity. You can. Accordingly, a finished polyvinyl alcohol film with uniform dyeing and good color is obtained.

According to at least one embodiment of the present invention, the degree of polymerization of the polyvinyl alcohol film is between 1800 and 3000, for example, 1800, 1900, 2000, 2100, 2200, 2300, 2400, 2500, 2600, 2700, 2800, 2900 or 3000, but is not limited thereto. In addition, according to at least one embodiment of the present invention, the water content of the polyvinyl alcohol film is between 1.0 and 5.0 wt%, for example, 1, 1.1, 1.3, 1.5. , 1.7, 1.9, 2.0, 2.1, 2.3, 2.5, 2.7, 2.9, 3.0, 3.1, 3.3, 3.5, 3.7, 3.9, 4.0, 4.1, 4.3, 4.5, 4.7, 4.9 or 5.0 wt%, etc., but is not limited thereto. No.

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

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, blue light cut film, filter lens, etc., but the present invention is not limited thereto. Preferably, the polyvinyl alcohol film of the present invention is a polarizing film. In addition, the polarization degree of the polarizing film of a preferred embodiment provided by the present invention is 99.8% or more. In addition, the optical film provided by the present invention has a ratio of the absorbance at a wavelength of 480 nm to the absorbance at a wavelength of 700 nm under direct conditions of 1.40 to 1.60, for example, 1.40, 1.42, 1.44, 1.46, 1.48, but is not limited to 1.50, 1.52, 1.54, 1.56, 1.58 or 1.60. Specifically, 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 color expression of the optical film. Although not limited to a specific theory, the above-mentioned data range between 1.4 and 1.6 can be considered to be good and non-deviating color expression.

In another aspect, the present invention also provides a method for producing a polyvinyl alcohol film, and the contents shown in FIGS. 2 and 3 can be referred to for the process and production equipment. The manufacturing method includes the following. Step S100: The polyvinyl alcohol-based resin, surfactant, plasticizer, and water are stirred and heated to form a polyvinyl alcohol casting solution. Step S102: The polyvinyl alcohol casting solution is cast in a casting drum and dried to prepare a preformed film. Process 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 equipped with a plurality of sections to dry.

Specifically, in step S100, the polyvinyl alcohol-based resin, plasticizer, surfactant, and water are placed in the dissolution tank 110, stirred, and heated to a dissolution temperature exceeding 100° C. for at least 180 minutes to dissolve, and a polyvinyl alcohol solution is prepared. form Among them, the dissolution temperature is preferably 120 to 140°C, for example, 120, 125, 130, 135 or 140°C. In addition, the amount of plasticizer added is usually between 3 and 30 parts by weight, preferably between 7 and 20 parts by weight, based on 100 parts by weight of the polyvinyl alcohol-based resin, for example, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29 or 30 parts by weight, etc. am. If the plasticizer content is insufficient, crystals are likely to form in the formed polyvinyl alcohol film, which will affect the dyeing effect in subsequent processing. Conversely, if the plasticizer content is too high, the mechanical properties of the polyvinyl alcohol film are damaged.

The polyvinyl alcohol-based 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, 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. The method for calculating the above-mentioned polyvinyl alcohol-based resin concentration is polyvinyl alcohol-based resin / (polyvinyl alcohol-based resin + water + plasticizer + surfactant). If the content of the polyvinyl alcohol-based resin is insufficient, the viscosity of the polyvinyl alcohol casting solution becomes too low, the drying load becomes excessively large, and the film-forming efficiency in preparing the polyvinyl alcohol film deteriorates. Conversely, 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 through a filter, the polyvinyl alcohol casting solution is introduced into a T-shaped slit die by a quantitative method, and is discharged and flexible on the casting drum 120 to prepare the polyvinyl alcohol casting solution. Prepare a molded film (M). Additionally, the rotation speed of the casting drum 120 is about 3 to 12 m/min, preferably 5 to 10 m/min. If the speed of the casting drum 120 is too slow, there is a risk that productivity may decrease. Conversely, if the speed of the casting drum 120 is too fast, drying of the casting solution becomes insufficient and peelability deteriorates. Additionally, in a preferred embodiment, the temperature of the casting drum 120 is set to 85 to 95°C, specifically, for example, 85, 87, 89, 91, 93, 95°C, or any two of the above. If the value is between the values and the temperature of the casting drum 120 is too high, bubbles are likely to occur in the casting solution.

Specifically, in step S104, the preformed film M is peeled from the casting drum 120 and then brought into contact with a plurality of heating rollers 130 to dry both the upper and lower sides of the film body. At this time, one of the plurality of heating rollers 130 has the highest temperature among all the heating rollers 130, and the temperature of the subsequent heating rollers 130 is adjusted to gradually decrease. Subsequently, drying is performed in a dryer 140 having a plurality of sections. Additionally, 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 lower, 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. A multi-section dryer can be a 2 to 10 section dryer, preferably 3 to 8 sections, for example 3, 4, 5, 6, 7 or 8.

The polyvinyl alcohol aqueous solution and additives are mixed uniformly before discharging into the casting drum. The amount of additive precipitation in the polyvinyl alcohol film can be controlled within a certain range depending on the design of drying conditions. If the amount of additives remaining in the polyvinyl alcohol film is large when performing the swelling, stretching, and dyeing processes of the polarizing film, the polarizing film may turn reddish, and when performing the stretching/dying processes of the polarizing film, the residual amount of additives in the polyvinyl alcohol film If this is small, a phenomenon in which the polarizing film becomes pale will occur. The inventor of the present application found that the higher the highest temperature of the dryer 140 and the temperature of the first heating roller 130, or the larger the temperature difference between the rearmost heating roller 130 and the first section of the dryer 140, the greater the residual amount of additive. We found that the average value was rising. 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 a polyvinyl alcohol film with better color can be obtained.

The above-described polyvinyl alcohol-based resin is obtained by forming a polyvinyl ester-based resin by polymerizing vinyl ester-based resin monomers and then performing a saponification reaction. Among them, the vinyl ester resin monomer includes vinyl esters such as vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl pentanoate, or vinyl octanoate, but the present invention is not limited thereto, and is preferably: It is vinyl acetate. Additionally, a copolymer formed by copolymerizing an olefin compound or acrylate derivative and the vinyl ester resin monomer described above can also be used. Olefin compounds include ethylene, propylene, or butylene, but the present invention is not limited thereto. Acrylate derivatives include acrylic acid, methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, or n-butyl acrylate, but the present invention is not limited thereto.

The degree of saponification/alkalization of the polyvinyl alcohol resin disclosed above is preferably 99.00% or more, thereby obtaining good optical properties, but specifically, for example, 99.00% to 100.00%, 99.00% to 99.99. %, 99.00% to 99.95%, 99.00% to 99.90%, 99.00% to 99.85%, 99.00% to 99.80%, 99.00% to 99.75%, 99.00% to 99.70%, 99.00% to 99.65%, 99.00% to 99.60%, 99.00% to 99.55%, 99.00% to 99.50%, 99.00% to 99.45%, 99.00% to 99.40%, 99.00% to 99.35%, 99.00% to 99.30%, 99.00% to 99.25%, 99.00% to 9 9.20%, 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%.

[Example]

Hereinafter, the present invention will be described in more detail along with examples. However, it should be understood that these examples are intended to help the present invention be more easily understood and do not limit the scope of the present invention.

1. Preparation of polyvinyl alcohol film

Hereinafter, a non-limiting method for preparing a polyvinyl alcohol film is provided. Based on the method similar to the method disclosed below, 11 types of non-limiting example polyvinyl alcohol films (Examples 1 to 11) and 4 types of comparative example polyvinyl alcohol films (Comparative Examples 1 to 4) It was prepared. However, the specific methods for preparing Examples 1 to 11 and Comparative Examples 1 to 4 are usually different from the methods disclosed below in one or more aspects.

Specifically, the method for preparing a polyvinyl alcohol film includes the following steps. 1800 kg of polyvinyl alcohol-based 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 were added, and the surfactant was added so that the final content was 0.15 wt%, and stirred. The temperature was raised to 140°C, dissolution was performed for 180 minutes while maintaining the temperature at 140°C, and water was added to the uniformly dissolved polyvinyl alcohol-based resin solution to adjust the resin concentration until it reached 30.0%. A casting solution was obtained. Among them, the surfactant used in Examples 1 to 6 and Comparative Examples 1 and 2 is polyoxyethylene lauryl ether, and the surfactant used in Examples 7 to 11 and Comparative Examples 3 and 4 is polyoxyethylene lauryl ether. It is sodium sulfate. The polyvinyl alcohol casting solution was discharged from a T-shaped slit die after defoaming, and dried by curtain coating on a high-temperature rotating casting drum to prepare a preformed film. After the preformed film was peeled from the casting drum, the upper and lower sides of the film were dried by contacting a plurality of heating rollers and then dried in a dryer. The maximum temperature of the dryer was 115°C, and a finished polyvinyl alcohol film with a moisture content of 2.3 wt% was finally obtained.

2. Analysis and measurement methods

Below, analysis and measurement methods for Examples 1 to 11 and Comparative Examples 1 to 4 are provided to determine the properties of the polyvinyl alcohol film.

2-1. Analysis of initial content of additives

First, the sample preparation method was to divide the polyvinyl alcohol film into five parts along the transverse direction (transverse direction, TD, also known as the width direction), and cut the central part of the polyvinyl alcohol film after dividing into equal parts. The cut area of each part was MD 5 cm * TD 10 cm (MD refers to Machine Direction, i.e. machine direction or vertical direction, longitudinal direction). Next, it was left in a constant temperature and humidity chamber at 23°C and a relative humidity (RH) of 50% for 24 hours.

The measurement conditions were: first, the polyvinyl alcohol film was dried and dehydrated at 105°C/10 minutes, and then measured after drying (W1). Next, the polyvinyl alcohol film was stirred in pure water at 30°C/2000 ml for 5 minutes in a stirrer (rotation speed 115 to 120 rpm) to precipitate the initial additive, and after completion, the moisture on the surface of the polyvinyl alcohol film was dehydrated, It was placed in a dryer, dried at 105°C/1 hour, and its weight was measured (W2). In this case, the initial additive content is (W1 - W2) / W1 * 100%. Adding the initial content of the surfactant to the initial content of the plasticizer results in the initial content of the additive.

2-2. Analysis of residual amount of additives after swelling

First, the sample preparation method was to divide the polyvinyl alcohol film into 5 equal parts along the transverse direction, and cut the central portion of the polyvinyl alcohol film after dividing into equal parts. The cut area of each part was MD 20 cm * TD 15 cm. Next, it was left in a constant temperature and humidity chamber at 23°C and 50% RH for 24 hours. Next, a polyvinyl alcohol film (MD 5 cm * TD 15 cm) is fixed, the polyvinyl alcohol film is stretched to twice the length in pure water at 30°C at 4.3 cm/min, and after completion, the polyvinyl alcohol film is stretched. Moisture from the surface of the film was absorbed and left in a constant temperature and humidity chamber at 23°C and 50% RH for 24 hours. Finally, a polyvinyl alcohol film of MD 5 cm * TD 10 cm was cut from the stretched portion.

Measurement conditions: First, the stretched polyvinyl alcohol film was dried and dehydrated at 105°C/10 minutes, and measured after drying (W3). Next, the polyvinyl alcohol film was stirred in pure water at 30°C/2000 ml with a stirrer (rotation speed 115 to 120 rpm) for 5 minutes to precipitate glycerin and the surfactant, and after completion, the moisture on the surface of the polyvinyl alcohol film was removed. It was dehydrated, placed in a dryer, dried at 105°C/1 hour, and weighed (W4). At this time, the remaining amount of plasticizer after swelling is (W3 - W4) / W3 * 100%. Adding the residual amount of surfactant after swelling and stretching to the residual amount of plasticizer after swelling and stretching results in the residual amount of additives after swelling and stretching.

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

First, the sample preparation method was to divide the polyvinyl alcohol film into 5 equal parts along the transverse direction, and cut the central portion of the polyvinyl alcohol film after dividing into equal parts. The cut area of each part was MD 20 cm * TD 15 cm. Next, it was left in a constant temperature and humidity chamber at 23°C and 50% RH for 24 hours. Next, a polyvinyl alcohol film (MD 5 cm * TD 15 cm) is fixed, the polyvinyl alcohol film is stretched to twice the length in pure water at 30°C at 4.3 cm/min, and after completion, the polyvinyl alcohol film is stretched. Moisture from the surface of the film was absorbed and left in a constant temperature and humidity chamber at 23°C and 50% RH for 24 hours. Finally, a polyvinyl alcohol film of MD 5 cm * TD 10 cm was cut from the stretched portion.

The analytical meter used here is Perkin Elmer Spectrum 100. The analysis conditions were left in a constant temperature and humidity chamber, and then FTIR analysis was performed in ATR transmission mode with four integrated counts in the range 650 to 4000 cm ^-1 . 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 obtained for the FTIR peak ratio in the same TD direction.

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

First, the sample preparation method was to divide the polyvinyl alcohol film into 5 equal parts along the transverse direction, and cut the central portion of the polyvinyl alcohol film after dividing into equal parts. The cut area of each part was MD 20 cm * TD 15 cm. Next, it was left in a constant temperature and humidity chamber at 23°C and 50% RH for 24 hours. Next, a polyvinyl alcohol film (MD 5 cm * TD 15 cm) is fixed, the polyvinyl alcohol film is stretched to twice the length in pure water at 30°C at 4.3 cm/min, and after completion, the polyvinyl alcohol film is stretched. Moisture from the surface of the film was absorbed and left in a constant temperature and humidity chamber at 23°C and 50% RH for 24 hours. Finally, a polyvinyl alcohol film of MD 5 cm * TD 10 cm was cut from the stretched portion.

The analytical meter used here is Perkin Elmer Spectrum 100. The analysis conditions were left in a constant temperature and humidity chamber, and then FTIR analysis was performed in ATR transmission mode with four integrated counts in the range 650 to 4000 cm ^-1 . The FTIR peak intensity ratio was measured as [100 - (1140 cm ^-1 transmission value)] / [100 - (1425 cm ^-1 transmission value)], and the average value was additionally calculated for the FTIR peak ratio in the same TD direction.

2-5. Measurement of Color Representation

First, the sample preparation method is a process of preparing a polyvinyl alcohol film into a polarizing film. The method of preparing a polyvinyl alcohol film into a polarizing film is not particularly limited, but preferably includes a swelling treatment in which the polyvinyl alcohol film is placed in water and stretched, a dyeing treatment in which the polyvinyl alcohol film is dyed with a dichroic dye, and uniaxial stretching on the film body. It includes a stretching process that performs. Among them, methods such as boric acid crosslinking treatment, fixing treatment, washing treatment, and heat treatment may be additionally performed as necessary. In that case, the order of each treatment is not particularly limited, but is preferably performed in the order of swelling treatment, dyeing treatment, and stretching treatment.

Additionally, the measuring device used here is Perkin Elmer Lambda 365 (equipped with an integrating sphere). The measurement conditions were with an integrating sphere, and the absorbance (A) at a wavelength of 480 nm and the absorbance (B) at a wavelength of 700 nm were measured based on direct line conditions. Lastly, the ratio of A/B was used as color ratio data.

2-6. Measurement of polarization 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, the polyvinyl alcohol film prepared according to the method described above was prepared into a test piece measuring 9 cm in the longitudinal direction and 10 cm in the width direction. Next, both ends along the longitudinal direction of the test piece were fixed to a stretching jig so that the size of the stretched portion was 5 cm in the longitudinal direction × 10 cm in the width direction, and immersed in water at a temperature of 30°C for less than 70 seconds, at 4.3 cm/min. It was stretched uniaxially along the longitudinal direction until the original length was doubled at a stretching speed of . The test piece was immersed in an iodine/potassium iodide aqueous solution containing iodine at a concentration of 0.03 mass percent and potassium iodide at a concentration of 3 mass percent, and the temperature was 30°C, and the original length was 3.3 cm at a stretching speed of 24 cm/min within 60 seconds. It was uniaxially stretched along the longitudinal direction (second stage stretching) until it was doubled. Subsequently, the test piece was immersed in a boric acid/potassium iodide aqueous solution containing boric acid at a concentration of 3 mass percent and potassium iodide at a concentration of 3 mass percent, and having a temperature of 30°C, and returned to its original state within about 20 seconds at a stretching speed of 24 cm/min. It was uniaxially stretched along the longitudinal direction (third stage stretching) until it became 3.6 times the length. Additionally, the test piece was immersed in an aqueous boric acid/potassium iodide solution containing boric acid at a concentration of 4 mass percent and potassium iodide at a concentration of about 5 mass percent, and having a temperature of 58°C, and the original length was 5.5 cm at a stretching rate of 24 cm/min. It was uniaxially stretched along the longitudinal direction (fourth stage stretching) until it was doubled. Finally, the test piece was fixed by immersing it in an aqueous solution of potassium iodide containing boric acid at a concentration of 1.5 mass percent and potassium iodide at a concentration of 3 mass percent for 10 seconds to perform fixation, and dried in a dryer at 60°C for 4 minutes to obtain a polarizing film. .

Additionally, the measuring device used here is Perkin Elmer Lambda 365. The measurement conditions are based on the standard method of JIS Z 8722. Visibility correction in the visible light range of 2° is performed using a C light source, and then two polarizing films are superimposed with the same orientation direction, and the light transmittance under the wavelength is measured. (H ₀ ) was measured, two polarizing films were separately stacked with the orientation directions perpendicular to each other, and the transmittance (H ₉₀ ) under the wavelength was measured. Finally, polarization data was obtained by calculating the equation: polarization = [(H ₀ - H ₉₀ ) / (H ₀ + H ₉₀ )] 1/2.

3. Data contents of examples and comparative examples

First, variables were set for the three items of the first heating roller, the highest temperature of the dryer, and the temperature difference between the rearmost heating roller and the first section dryer during the polyvinyl alcohol film preparation process of Examples and Comparative Examples, and related analysis was performed. Alternatively, additional measurement data was acquired. Details are as shown in Table 1.

According to Examples 1 to 11 in Table 1, the temperature of the first heating roller at the time of preparation is in the range of 84 to 92 ° C., the maximum temperature of the dryer is 115 ° C. or lower, and the rearmost heating roller and the first heating roller are in the range of 84 to 92 ° C. The temperature difference of the section dryer is less than 30℃. Among the analysis data of Examples 1 to 11 in Table 1, the average residual amount of additives ranges from 0.5 to 3 wt%. The result of dividing the average value of the additive residual amount by the initial additive content is 0.04 to 0.32. The FTIR peak ratio (3200 cm ^-1 / 1425 cm ^-1 ) is in the range of 0.70 to 1.00, and the FTIR peak ratio (1140 cm ^-1 / 1425 cm ^-1 ) is 1.48 or less. As can be seen from the expression results of Examples 1 to 11 in Table 1, the A/B value (corresponding to the color ratio) is in the range of 1.40 to 1.60, and is not limited to a specific theory, but the above-mentioned data range is 1.4. Between 1.6 and 1.6, color expression can be considered good and without deviation. In addition, the polarization degrees of Examples 1 to 11 in Table 1 are all 99.8% or more.

As can be seen from the results, when the residual amount of additives after swelling and stretching of the polyvinyl alcohol films of Examples 1 to 11 was adjusted to a certain range, the prepared polarizing film had good color expression. In comparison, the residual amount of additives 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 film had poor color expression. In addition, the value of the FTIR intensity ratio of OH (3200 cm ^-1 ) / CH ₂ (1425 cm ^-1 ) of Comparative Examples 1 to 3 is greater than 1.00, and the greater the amount of plasticizer remaining in the polyvinyl alcohol film, the worse the color expression. It indicates that The value of the FTIR intensity ratio of OH (3200 cm ^-1 ) / CH ₂ (1425 cm ^-1 ) in Comparative Example 4 is less than 0.70, and it can be seen that color expression deteriorates even if the residual amount of plasticizer in the polyvinyl alcohol film is too low. .

Next, during the polyvinyl alcohol film preparation process of Examples and Comparative Examples, variable control was performed on two items such as polyvinyl alcohol dissolution time and polyvinyl alcohol-based resin concentration after dissolution, and related analysis or measurement data were performed. was additionally acquired. Details are as shown in Table 2.

As shown in Table 2, the present inventors believe that the higher the crystallinity of the polyvinyl alcohol film, the easier it is for some undissolved polyvinyl alcohol crystal regions to exist during the preparation of the polarizing film, and the polyvinyl alcohol crystal regions make it possible for iodine to exist. It was found that the degree of polarization decreases as the film swells and becomes unable to enter. For example, Examples 8 and 9 and Comparative Examples 1 to 4 have a high FTIR intensity ratio of 1140 cm ^-1 / 1425 cm ^-1 (greater than 1.45), indicating that the crystallinity of polyvinyl alcohol is high, The degree of polarization does not reach 99.9%. In contrast, Examples 1 to 7, 10, and 11 all have FTIR intensity ratios of 1140 cm ^-1 / 1425 cm ^-1 of 1.45 or less, and the results show that the polarization degree of the prepared polarizing films all reaches 99.9%. there is.

According to Examples 1 to 11 in Table 2, the polyvinyl alcohol dissolution time in Example 9 and Comparative Examples 2 to 4 was 150 minutes, which is outside the range of 180 to 300 minutes in other examples. The polyvinyl alcohol-based resin concentration after dissolution in Example 8 and Comparative Examples 1 and 3 was 35%, outside the range of 25 to 30%. The present inventor found that the control of the above variables caused the FTIR peak intensity ratio of 1140 cm ^-1 / 1425 cm ^-1 to deviate from the ideal range.

In consideration of the above results, the present inventor found that if the residual amount of additives after swelling and stretching of the polyvinyl alcohol film is controlled to a certain range, the polarizing film prepared thereby will have good color expression. In the preparation process of the polyvinyl alcohol film, the three variables of the temperature of the first heating roller, the highest temperature of the dryer, and the temperature difference between the rearmost heating roller and the first section dryer are the polyvinyl alcohol film. It affects the residual amount of additives and may also affect the optical properties of the prepared optical film. In addition, as a result of dividing the average value of the additive residual amount of the polyvinyl alcohol film and the initial additive content, the FTIR peak ratio (3200 cm ^-1 / 1425 cm ^-1 ) and FTIR peak ratio (1140 cm ^-1 / 1425 cm ^-1 ) were controlled. By doing so, it can also be used to prepare a polyvinyl alcohol film having other ideal properties. In addition, the present inventor also found that the polyvinyl alcohol dissolution time and the polyvinyl alcohol-based resin concentration after dissolution affect the degree of 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-described definition has low crystallinity, and the optical film prepared thereby has excellent color expression and polarization degree. In addition, the definition of the present invention can be used to more accurately produce, identify, and select the polyvinyl alcohol film described above.

All ranges provided in this specification are meant to include a combination of each specific range within the allocated range and secondary ranges between allocated ranges. Additionally, unless otherwise specified, all ranges provided in this specification include the endpoints of the range. Therefore, ranges 1 to 5 specifically include 1, 2, 3, 4 and 5, and secondary ranges such as 2 to 5, 3 to 5, 2 to 3, 2 to 4, 1 to 4, etc.

All publications and patent applications referred to in this specification are hereby incorporated by reference, and each publication or patent application is specifically and individually indicated to be incorporated by reference for all purposes. . In case of any inconsistency between this specification and any publication or patent application incorporated herein by reference, this specification shall govern.

110: dissolution tank
120: Casting drum
130: Heating roller
140: dryer
M: Preformed film
S100 to S104: Process

Claims (16)

In the polyvinyl alcohol film, the residual amount of additive after swelling and stretching is 0.50 to 3.00 wt%, and the swelling and stretching is performed by stretching the polyvinyl alcohol film in water at a speed of 4.3 cm/min and doubling the length. , the residual amount of the additive is obtained by the calculation formula (W3 - W4) / W3 * 100%, where W3 is the weight after swelling and stretching the polyvinyl alcohol film and drying, and W4 is the weight of the polyvinyl alcohol film. A polyvinyl alcohol film, which is the weight after swelling, stretching, drying, placing in pure water, stirring for 5 minutes, and further drying. According to paragraph 1,
When the polyvinyl alcohol film is swollen, stretched, dried, and then analyzed by Fourier transform infrared spectroscopy, the polyvinyl alcohol film has an intensity ratio of 0.70 to 1.00 at a wavelength of 3200 cm ^-1 and a wavelength of 1425 cm ^-1 . film. According to paragraph 1,
When the polyvinyl alcohol film is swollen, stretched, dried, and then analyzed by Fourier transform infrared spectroscopy, the polyvinyl alcohol film has an intensity ratio of 1.20 to 1.48 at a wavelength of 1140 cm ^-1 and a wavelength of 1425 cm ^-1 . film. According to paragraph 1,
When the polyvinyl alcohol film is swollen, stretched, dried, and then analyzed by Fourier transform infrared spectroscopy, the polyvinyl alcohol film has an intensity ratio of 1.20 to 1.45 at a wavelength of 1140 cm ^-1 and a wavelength of 1425 cm ^-1 . film. According to paragraph 1,
The additive includes a plasticizer and a surfactant, a polyvinyl alcohol film. According to paragraph 1,
The polyvinyl alcohol film has an initial additive content of between 6 and 15 wt%. According to paragraph 1,
The polyvinyl alcohol film has a degree of polymerization between 1800 and 3000. According to paragraph 1,
The polyvinyl alcohol film has a water content of between 1.0 and 5.0 wt%. An optical film manufactured by the polyvinyl alcohol film according to any one of claims 1 to 8. According to clause 9,
Optical film, which is a polarizing film. According to clause 9,
The described optical film, wherein the polarization film has a degree of polarization of 99.8% or more. According to any one of claims 9 to 11,
An optical film, wherein the ratio of the absorbance at a wavelength of 480 nm to the absorbance at a wavelength of 700 nm under direct conditions is 1.40 to 1.60. (a) A process of stirring a polyvinyl alcohol-based resin, a plasticizer, a surfactant, and water and heating them to a dissolution temperature of more than 100° C. to form a polyvinyl alcohol casting solution;
(b) preparing a preformed film by casting the polyvinyl alcohol casting solution on a casting drum and drying it; and
(c) a step of contacting the preformed film with n heating rollers whose temperature gradually decreases from high temperature to low temperature, and then drying the preformed film by entering it into a dryer having a plurality of sections, wherein the first heating roller The temperature 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, and n is between 10 and 20. A method for producing a polyvinyl alcohol film according to any one of paragraphs 8. According to clause 13,
The manufacturing method has a dissolution temperature of 120 to 140° C. in step (a). According to claim 13 or 14,
The manufacturing method wherein the concentration of the polyvinyl alcohol-based resin in the polyvinyl alcohol casting solution in step (b) is 20.0 to 40.0%. According to claim 13 or 14,
The production method 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-based resin.