Polyvinyl alcohol film, optical film produced thereby, and method for producing the same

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

Technical Field

[0001] The present invention relates to a polyvinyl alcohol (PVA) film that can be used in the manufacture of optical films, particularly in the manufacture of polarizing films.

Background Art

[0002] 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 widely used in packaging materials or optical films of electronic products, particularly in polarizing films.

[0003] The polarizing film obtained by processing the polyvinyl alcohol film in the subsequent polarization process can control the brightness of the passing light rays and is one of the indispensable components in display devices. 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-mentioned processes are carried out. By diffusing and entering the dye molecules between the polyvinyl alcohol molecules of the polyvinyl alcohol film and arranging them regularly, the polarizing film can absorb the light components parallel to the arrangement direction, and the light components in the vertical direction are transmitted, so that the property of having polarization is produced.

[0004] An ideal polarizing film should have characteristics such as uniform color, few color spots, no wrinkles, and good hue effect, and be able to provide excellent optical properties. In order to improve the optical properties of the polarizing film, in the prior art, methods such as changing the structure of polyvinyl alcohol or adding functional groups (such as cationic groups) are generally used to change the viscosity and saponification degree to improve the optical properties.

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in the prior art, when manufacturing an optical film from a polyvinyl alcohol film, problems such as variations in hue often occur, for example, the hue of the finished product tends to be overall red-shifted or blue-shifted. The inventor of the present invention noticed that the reason for the above problems is probably that when using a polyvinyl alcohol film in the manufacture of an optical film, an additive must be mixed, but the additive is precipitated after the swelling process of the polyvinyl alcohol film, and part of it remains on the film. For example, if the residual amount of the additive is too large, it occupies too much of the amorphous region on the film and makes it difficult for the cross-linking bond between the pentaiodide anion (I5 - ) and polyvinyl alcohol to occur, resulting in the hue of the finished optical film being red-shifted. On the contrary, if the residual amount of the additive is too small, the amount of cross-linking bond between I5 - and the amorphous region of polyvinyl alcohol becomes excessively large. In this case, the absorption amount of the polarizing film for red light becomes too large, and the hue of the finished optical film becomes blue-shifted.

[0006] Furthermore, the inventor, although not limited to a specific theory, noticed that there are many factors related to the above situation. For example, during the manufacturing process of the polyvinyl alcohol film, factors such as the temperature of the heating roller that comes into contact after the formation of the preformed film, the temperature of the dryer that performs subsequent drying, and the temperature difference between the heating roller and the dryer all at least partially affect the amount of the additive that is precipitated and remains after the film body has swelled.

[0007] Therefore, in order to solve the above problems, the present invention provides a polyvinyl alcohol film by adjusting the residual amount of the additive within a certain range, which is used in the manufacture of an optical film having excellent hue performance.

Means for Solving the Problems

[0008] Specifically, the polyvinyl alcohol film provided in one embodiment of the present invention has an additive residue amount of 0.50 to 3.00 wt% after swelling and stretching. Regarding the above-mentioned swelling and stretching, the polyvinyl alcohol film was stretched in water at a speed of 4.3 cm / min to double its length. The above-mentioned additive residue amount was obtained from the calculation formula: (W3 - W4) / W3 × 100%. In the formula, W3 is the weight of the polyvinyl alcohol film after swelling, stretching, and drying, and W4 is the weight of the polyvinyl alcohol film after swelling, stretching, drying, putting it into pure water, stirring for 5 minutes, and then drying to absolute dryness again.

[0009] 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 a wavelength of 3200 cm -1 and a wavelength of 1425 cm -1 is 0.70 to 1.00.

[0010] 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 a wavelength of 1140 cm -1 and a wavelength of 1425 cm -1 is between 1.20 and 1.48. Preferably, the value of the intensity ratio is between 1.20 and 1.45.

[0011] In a preferred embodiment, the polyvinyl alcohol film has an initial additive content between 6 and 15 wt%.

[0012] In a preferred embodiment, the degree of polymerization of the polyvinyl alcohol film is between 1800 and 3000.

[0013] In a preferred embodiment, the water content of the polyvinyl alcohol film is between 1.0 and 5.0 wt%.

[0014] The optical film provided in another embodiment of the present invention is made of the above-mentioned polyvinyl alcohol film.

[0015] In a preferred embodiment, the optical film is a polarizing film. Preferably, the polarizing film has a polarization degree of 99.8% or more.

[0016] In a preferred embodiment, the optical film has a ratio value of absorbance at a wavelength of 480 nm to absorbance at a wavelength of 700 nm under perpendicular conditions of 1.40 to 1.60.

[0017] A method for manufacturing a polyvinyl alcohol film provided in still another embodiment of the present invention includes the following steps. (a) Stir a polyvinyl alcohol-based resin, a plasticizer, a surfactant, and water, and heat to a dissolution temperature exceeding 100 °C to form a polyvinyl alcohol casting solution. (b) Cast the polyvinyl alcohol casting solution onto a casting drum and dry it to prepare a preformed film. (c) After bringing the preformed film into contact with n heating rollers whose temperature gradually decreases from a high temperature to a low temperature, it enters a dryer having a plurality of sections and is dried, wherein the temperature of the first heating roller is 84 to 92 °C, the maximum temperature of the dryer is 115 °C or lower, and the temperature difference between the nth heating roller and the first section dryer is 30 °C or lower, and n is between 10 and 20.

[0018] In a preferred embodiment, the dissolution temperature in step (a) is 120 to 140 °C.

[0019] In a preferred embodiment, the concentration of the polyvinyl alcohol-based resin in the polyvinyl alcohol casting solution in step (b) is 20.0 to 40.0%.

[0020] In a preferred embodiment, the plasticizer is 3 to 30 parts by weight with respect to 100 parts by weight of the polyvinyl alcohol-based resin.

Advantages of the Invention

[0021] The optical film manufactured using the polyvinyl alcohol film provided based on the above particulars of the present invention has excellent hue expression and polarization degree. Also, the specific content of the present invention can be used to manufacture and adjust the above polyvinyl alcohol film more precisely.

Brief Description of the Drawings

[0022]

Figure 1

Figure 2

Figure 3

Modes for Carrying Out the Invention

[0023] For a clearer understanding of the above and other objects, features, advantages and embodiments of the present invention, the drawings will be described as follows.

[0024] In this specification, regarding the ratios of various features and components in the drawings, they are not actual ratios. For showing the specific features and components related to the present invention in an optimal manner, they are drawn by a drafting method based on the conventional working method. Also, in different drawings, the same or similar component symbols refer to similar components and members.

[0025] To describe the present invention in more detail and comprehensively, the following descriptions of embodiments and specific examples of the present invention are presented. However, they are not the only forms of specific examples for implementing or applying the present invention. In this specification and the appended claims, unless otherwise stated in the context, the terms "one" and "said" can be interpreted as plural. Also, in this specification and the appended claims, unless otherwise stated, "being installed on an object" can be regarded as being directly or indirectly attached to or contacting the surface of the object in other forms, and the definition of the surface shall be determined by the implications of the context / paragraph of the content of this specification and the common knowledge in the field to which this specification belongs.

[0026] The numerical ranges and parameters specifying the present invention are all approximate numerical values. However, the relevant numerical values in specific examples are shown as precisely as possible. Nevertheless, any numerical value will inherently inevitably include the standard deviation resulting from individual test methods. Herein, "about" generally refers to the actual numerical value being within ±10%, 5%, 1% or 0.5% of a specific numerical value or range. Alternatively, the term "about" means that when considered and judged by those skilled in the art to which the present invention pertains, the actual numerical value is within the acceptable standard error of the average value. Therefore, unless otherwise explained, all the numerical parameters disclosed in this specification and the appended claims are approximate values and can be considered to vary as needed. At least, those numerical parameters should be interpreted as the values obtained by applying the indicated significant digits and the normal rounding method.

[0027] The present invention provides a polyvinyl alcohol film. After stretching the polyvinyl alcohol film in water at a speed of 4.3 cm / min and doubling its length and then drying, the weighed value of the stretched and dried polyvinyl alcohol film is W3. After stirring the stretched and dried polyvinyl alcohol film in pure water for 5 minutes and then drying it to absolute dryness again, the weighed value is W4. The value of (W3 - W4) / W3 × 100% is 0.50 - 3.00 wt%.

[0028] The present invention solves the problem that the polarizing film becomes red-shifted or blue-shifted by adjusting the additive residue amount of the polyvinyl alcohol film after swelling and stretching, that is, by simulating the conditions before dyeing the polarizing plate and controlling the additive residue amount before it enters the dyeing tank. The inventor found that when actually performing the manufacturing process of the polarizing plate, the polyvinyl alcohol film undergoes swelling and stretching treatment, but during the swelling process, additives and other impurities in the polyvinyl alcohol precipitate, and finally the additive amount in each part of the polyvinyl alcohol film used to manufacture the polarizing film changes somewhat. Therefore, when only measuring the initial amount of the additive in the polyvinyl alcohol film, it is impossible to represent the residual state of the additive when actually performing the manufacturing process of the polarizing plate, and it was found that the problem of the polarizing film becoming red-shifted or blue-shifted cannot be solved. Specifically, the above parameters are specified based on the process of preparing the polyvinyl alcohol film into an optical film, particularly a polarizing film. The method of preparing the polyvinyl alcohol film into a polarizing film is not particularly limited, but preferably includes a swelling treatment (also referred to as swelling and stretching in this specification) of immersing the polyvinyl alcohol film in water and stretching it, a dyeing treatment with a dichroic dye, and a stretching treatment of uniaxially stretching the film body. Among them, methods such as boric acid cross-linking treatment, fixing treatment, washing treatment, and heat treatment may be further performed as necessary. In that case, the order of each treatment is not particularly limited, but preferably, it is performed in the order of swelling treatment, dyeing treatment, and stretching treatment. In the industry, generally, when preparing a polarizing film, stretching it to twice its length is approximately the stretching ratio in the swelling tank.

[0029] The above-mentioned additive residue amount is obtained by stirring the swollen, stretched, and dried polyvinyl alcohol film in pure water for 5 minutes to precipitate the additives in the film. The additive residue amount is calculated by the formula: (W3 - W4) / W3 × 100%, and it may be the average value of a plurality of films (for example, 5 or more) cut evenly in the width direction.

[0030] As used herein, the "additive" includes, but is not limited to, a plasticizer, a surfactant, a clouding agent, an emulsifier, or a foaming agent. Among them, the "plasticizer" can increase the flexibility of the material and liquefy the material. For example, it includes, but is not limited to, phthalate, bis(2-ethylhexyl) phthalate (DEHP), glycerin, dibutyl phthalate (DBP), diisononyl phthalate (DINP), diisodecyl phthalate (DIDP), butyl benzyl phthalate (BBP), dioctyl phthalate (DOP), ethylene glycol, propylene glycol, diethylene glycol, diglycerin, triethylene glycol, tetraethylene glycol, or trimethylolpropane. Preferably, the plasticizer is glycerin, ethylene glycol, propylene glycol, diethylene glycol, diglycerin, triethylene glycol, tetraethylene glycol, or trimethylolpropane. The "surfactant" is not limited to cationic, anionic, or non-ionic surfactants, and examples include carboxylate types such as potassium laurate, sulfate ester salt types such as sodium lauryl sulfate, sulfonate types such as dodecylbenzene sulfonate, alkyl phenyl ether types such as polyoxyethylene octyl phenyl ether, alcohol-based phenyl ether types such as polyethylene glycol mono octyl phenyl ether, alkyl ester types such as polyoxyethylene laurate, alkyl amine types such as polyoxyethylene lauryl amine, alkyl amide types such as polyoxyethylene lauric acid amide, polypropylene glycol ether types such as polyoxyethylene polyoxypropylene ether, alkanolamide types such as lauric acid diethanolamide and oleyl diethanolamide, allyl phenyl ether types such as polyoxyethylene allyl phenyl ether, or sodium polyoxyethylene lauryl ether 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 between 6 and 15 wt%, for example, 7 to 14, 8 to 13, 9 to 12, or 10 to 11 wt%, etc.

[0031] 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 blended with polymers, the free volume of the material increases. During the swelling process of the polyvinyl alcohol film, part of the additives remains in the polyvinyl alcohol film. However, if the remaining amount is too large, free cavities will be occupied by the additives. When the polyvinyl alcohol film reaches the dyeing bath, iodide ions cannot form a complex (e.g., a complex of I5 - and PVA) in the free cavities, resulting in a decrease in the ability of the polarizing film to absorb light in the long wavelength range and a problem of color variation. Among them, the I5 - complex absorbs light with long wavelengths, and the I3 - complex absorbs light with short wavelengths. Therefore, if there are too few complexes, the polarizing film may become red-shifted or blue-shifted.

[0032] 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 intensity ratio values at wavelengths 3200 cm -1 and 1425 cm -1 are 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, etc. Also, the intensity ratio values at wavelengths 1140 cm -1 and 1425 cm -1 are 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 it may also be in the range consisting of any two of the above numerical values. According to a preferred embodiment of the present invention, the intensity ratio values at wavelengths 1140 cm -1 and 1425 cm -1 are between 1.20 and 1.48, preferably between 1.20 and 1.45.

[0033] Fourier transform infrared spectroscopy (FTIR) is a technique for obtaining infrared absorption spectra and emission spectra of solids, liquids, or gases. Regarding this 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 corresponds to the degree of alkalinity in the polyvinyl alcohol film. Therefore, when measuring the polyvinyl alcohol film after swelling and stretching, the absorption peak at a wavelength of 3200 cm -1 can represent the plasticizer (e.g., 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 shows the polyvinyl alcohol crystallinity characteristic peak (ν(C-C) stretching vibrations). The absorption peak at a wavelength of 1425 cm -1 corresponds to C-H in the polyvinyl alcohol film skeleton, and since its content is fixed, it can be regarded as a definite peak. Thus, the value of the intensity ratio between 3200 cm -1 and 1425 cm -1 shows a positive correlation with the residual amount of plasticizer in the polyvinyl alcohol film. The higher the FT-IR ratio of OH(3200 cm -1 ) / CH2(1425 cm -1 ), the more the residual amount of plasticizer in the polyvinyl alcohol film. The value of the intensity ratio between 1140 cm -1 and 1425 cm -1 shows a positive correlation with the crystallinity of the polyvinyl alcohol film. In the measurement of the polyvinyl alcohol film after swelling and stretching, the higher the ratio of C-C(1140 cm -1 ) / C-H(1425 cm -1) The higher the FT-IR ratio, the higher the crystallinity of the polyvinyl alcohol film. According to the present invention, by adjusting the plasticizer residue amount and the crystallinity of the polyvinyl alcohol film after swelling, stretching, and drying using the value of the above-mentioned FT-IR intensity ratio, the plasticizer residue amount is maintained within an appropriate range, and the crystallinity is reduced. Thereby, a polyvinyl alcohol film finished product with uniform dyeing and a good hue can be obtained.

[0034] 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, etc., but not limited thereto. Also, 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 not limited thereto.

[0035] 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 not limited thereto.

[0036] The present invention provides an optical film, which is made from the above-mentioned polyvinyl alcohol film. The "optical film" described in this specification may refer to a polarizing film, a blue light cut 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 polarization degree of the polarizing film in the preferred embodiment provided by the present invention is 99.8% or more. Also, for the optical film provided by the present invention, the ratio of the absorbance at a wavelength of 480 nm to the absorbance at a wavelength of 700 nm under perpendicular conditions is 1.40 to 1.60, for example, 1.40, 1.42, 1.44, 1.46, 1.48, 1.50, 1.52, 1.54, 1.56, 1.58 or 1.60, but is not limited thereto. 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 a specific theory, the range between the above-mentioned data of 1.4 to 1.6 can be regarded as having a good and non-varying hue expression.

[0037] In another aspect, the present invention also provides a method for manufacturing a polyvinyl alcohol film. For the process and manufacturing apparatus thereof, reference can be made to the contents shown in FIGS. 2 and 3. The manufacturing method includes the following. In step S100, a polyvinyl alcohol-based resin, a surfactant, a plasticizer, and water are stirred and heated to form a polyvinyl alcohol casting solution. In step S102, the polyvinyl alcohol casting solution is cast onto a casting drum and dried to prepare a preformed film. In step S104, after the preformed film is brought into contact with n heating rollers whose temperature gradually decreases from high to low, it enters a dryer having a plurality of sections and is dried.

[0038] Specifically, in step S100, a polyvinyl alcohol-based resin, a plasticizer, a surfactant, and water are placed in the dissolution tank 110 and stirred, and heated to a dissolution temperature exceeding 100°C and dissolved for at least 180 minutes to form a polyvinyl alcohol solution. Among them, the dissolution temperature is preferably 120 to 140°C, for example, 120, 125, 130, 135, or 140°C, etc. Also, the addition amount of the plasticizer 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. If the content of the plasticizer is insufficient, crystals are likely to form in the formed polyvinyl alcohol film, affecting the dyeing effect in subsequent processing. On the contrary, if the content of the plasticizer is too high, the mechanical properties of the polyvinyl alcohol film will be impaired.

[0039] The concentration of the polyvinyl alcohol-based resin 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, etc. The calculation method of 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 will be too low, resulting in an excessive drying load and poor film-forming efficiency in the preparation of the polyvinyl alcohol film. On the contrary, if the content of the polyvinyl alcohol resin is too high, it will be difficult for the polyvinyl alcohol-based resin to dissolve uniformly as a whole, and clusters are likely to remain.

[0040] Specifically, in step S102, the polyvinyl alcohol casting solution is selectively filtered by a filter, introduced into the T-shaped slit die by a metering method, discharged, and cast onto the casting drum 120 to prepare the preformed film M. Also, 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, the productivity may decrease. On the contrary, if the speed of the casting drum 120 is too fast, the drying of the casting solution will be insufficient, and the peelability will decrease. Further, 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 between any two of the above numerical values. If the temperature of the casting drum 120 is too high, a foaming phenomenon is likely to occur in the casting solution.

[0041] Specifically, in step S104, after the preformed film M is peeled off from the casting drum 120, it is brought into contact with a plurality of heating rollers 130 to dry the upper and lower surfaces of the film body. Here, the first one of the plurality of heating rollers 130 is the hottest 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. 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 dryer with a plurality of sections may be a dryer with 2 to 10 sections, preferably 3 to 8 sections, for example, 3, 4, 5, 6, 7 or 8.

[0042] The aqueous polyvinyl alcohol solution and the additive are uniformly mixed before being discharged onto the casting drum. The amount of additive precipitated in the polyvinyl alcohol film can be controlled within a certain range by designing the drying conditions. When there is a large amount of additive residue in the polyvinyl alcohol film during the swelling, stretching, and dyeing processes of the polarizing film, the phenomenon that the polarizing film turns red occurs. When there is a small amount of additive residue in the polyvinyl alcohol film during the stretching and dyeing processes of the polarizing film, the phenomenon that the polarizing film turns blue occurs. The inventor of the present application noticed that the higher the maximum temperature of the dryer 140 and the temperature of the first heating roller 130, or the greater the temperature difference between the last heating roller 130 and the first section of the dryer 140, the higher the average value of the additive residue amount. Therefore, by further adjusting the above parameters, it is possible to control the amount of additive precipitated after swelling and stretching within a specific range, and a polyvinyl alcohol film with a better hue can be obtained.

[0043] The above-mentioned polyvinyl alcohol-based resin is obtained by forming a polyvinyl ester-based resin through the polymerization of a vinyl ester-based resin monomer and then performing a saponification reaction. Among them, the vinyl ester-based 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 preferably vinyl acetate. Also, a copolymer formed by copolymerizing an olefin compound or an acrylate derivative with the above-mentioned vinyl ester-based resin monomer can be used. The olefin compound includes ethylene, propylene, or butylene, etc., but the present invention is not limited thereto. The acrylate derivative includes acrylic acid, methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, or n-butyl acrylate, etc., but the present invention is not limited thereto.

[0044] The saponification degree / alkalization degree of the polyvinyl alcohol resin disclosed above is preferably 99.00% or more, whereby good optical properties can be obtained. Specifically, for example, it is 99.00% - 100.00%, 99.00% - 99.99%, 99.00% - 99.95%, 99.00% - 99.90%, 99.00% - 99.85%, 99.00% - 99.80%, 99.00% - 99.75%, 99.00% - 99.70%, 99.00% - 99.65%, 99.00% - 99.60%, 99.00% - 99.55%, 99.00% - 99.50%, 99.00% - 99.45%, 99.00% - 99.40%, 99.00% - 99.35%, 99.00% - 99.30%, 99.00% - 99.25%, 99.00% - 99.20%, 99.00% - 99.15%, 99.00% - 99.10%, 99.00% - 99.05%, 99.20% - 100.00%, 99.20% - 99.99%, 99.20% - 99.95%, 99.20% - 99.90%, 99.20% - 99.85%, 99.20% - 99.80%, 99.20% - 99.75%, 99.20% - 99.70%, 99.20% - 99.65%, 99.20% - 99.60%, 99.20% - 99.55%, 99.20% - 99.50%, 99.20% - 99.45%, 99.20% - 99.40%, 99.20% - 99.35%, 99.20% - 99.30%, 99.20% - 99.25%, 99.40% - 100.00%, 99.40% - 99.99%, 99.40% - 99.95%, 99.40% - 99.90%, 99.40% - 99.85%, 99.40% - 99.80%, 99.40% - 99.75%, 99.40% - 99.70%, 99.40% - 99.65%, 99.40% - 99.60%, 99.40% - 99.55%, 99.40% - 99.50%, 99.40% - 99.45%, 99.60% - 100.00%, 99.60% - 99.99%, 99.60% - 99.95%, 99.60% - 99.90%, 99.60% - 99.85%, 99.60% - 99.80%, 99.60% - 99.75%, 99.60% - 99.70%, 99.60% - 99.65%, 99.80% - 100.00%, 99.80% - 99.99%, 99.80% - 99.95%, 99.80% - 99.90% or 99.80% - 99.85%, etc.

Example

[0045] Hereinafter, the present invention will be described in more detail in conjunction with examples. However, it should be understood that these examples are for the purpose of helping to more easily understand the present invention and do not limit the scope of the present invention. Example

[0046] The non-limiting examples of each aspect of the present invention provided below are mainly for clarifying each aspect of the present invention and the effects achieved thereby.

[0047] 1. Preparation of polyvinyl alcohol film Hereinafter, a non-limiting method for preparing a polyvinyl alcohol film is provided. Based on a 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) were prepared. However, the specific methods for preparing Examples 1 to 11 and Comparative Examples 1 to 4 usually differ from the method disclosed below in one or more aspects.

[0048] Specifically, the method for preparing the polyvinyl alcohol film includes the following steps. 1800 kg of a polyvinyl alcohol-based resin with an alkalinity degree > 99.9% and a polymerization degree of about 2400, 4000 kg of water, and 207 kg of glycerin as a plasticizer are added. A surfactant is added so that the final content is 0.15 wt%. While stirring, the temperature is raised to 140 °C, and dissolution is carried out for 180 minutes while maintaining at 140 °C. After uniform dissolution, water is added to the polyvinyl alcohol-based resin solution until the resin concentration reaches 30.0% to obtain a polyvinyl alcohol casting solution. 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 sodium polyoxyethylene lauryl ether sulfate. After defoaming the polyvinyl alcohol casting solution, it is discharged from a T-shaped slit die and curtain-coated on a rotating high-temperature casting drum and dried to prepare a preformed film. After peeling the preformed film from the casting drum, it is brought into contact with a plurality of heating rollers to dry both the upper and lower surfaces of the film, and then dried in a dryer. The maximum temperature of the dryer is 115 °C, and finally, a polyvinyl alcohol film finished product with a moisture content of 2.3 wt% is obtained.

[0049] 2. Methods of Analysis and Measurement The method for preparing the sample is as follows. First, the polyvinyl alcohol film is divided into five equal parts along the transverse direction (also referred to as the Transverse Direction, TD, or width direction), and the central part of the polyvinyl alcohol film after equal division is cut. The cut area of each piece is set to MD 5 cm * TD 10 cm (MD refers to Machine Direction, that is, the machine direction or longitudinal direction, the long axis direction). Next, it is left in a thermo-hygrostat at 23 °C and a relative humidity (RH) of 50% for 24 hours.

[0050] The measurement conditions were as follows: First, the polyvinyl alcohol film was dried and dehydrated at 105 °C for 10 minutes and then weighed (W1). Next, the polyvinyl alcohol film was stirred in 2000 ml of pure water at 30 °C with a stirrer (rotation speed 115 - 120 rpm) for 5 minutes to precipitate the initial additives. After completion, the moisture on the surface of the polyvinyl alcohol film was dehydrated, placed in a dryer, and dried to a constant weight at 105 °C for 1 hour, and the weight was measured (W2). Then, the initial additive content is (W1 - W2) / W1 × 100%. Adding the initial surfactant content to the initial plasticizer content gives the initial additive content.

[0051] 2 - 2. Analysis of the residual amount of additives after swelling The method for preparing the sample was as follows: First, the polyvinyl alcohol film was divided into 5 equal parts along the transverse direction, and the central part of the polyvinyl alcohol film after equal division was cut. The cut area of each piece was set to MD 20 cm × TD 15 cm. Next, it was left in a thermostatic and humidistatic chamber at 23 °C and 50% RH for 24 hours. Next, the polyvinyl alcohol film (MD 5 cm × TD 15 cm) was fixed, and the polyvinyl alcohol film was stretched to twice its length at a rate of 4.3 cm / min in pure water at 30 °C. After completion, the moisture on the surface of the polyvinyl alcohol film was blotted dry, and it was left in a thermostatic and humidistatic chamber at 23 °C and 50% RH for 24 hours. Finally, a polyvinyl alcohol film of MD 5 cm × TD 10 cm was cut out from the stretched part.

[0052] Measurement conditions: First, the stretched polyvinyl alcohol film was dried and dehydrated at 105 °C for 10 minutes and then weighed (W3). Next, the polyvinyl alcohol film was stirred in 2000 ml of pure water at 30 °C with a stirrer (rotation speed 115 - 120 rpm) for 5 minutes to precipitate glycerin and the surfactant. After completion, the moisture on the surface of the polyvinyl alcohol film was dehydrated, placed in a dryer, and dried to a constant weight at 105 °C for 1 hour, and the weight was measured (W4). Then, the residual amount of the plasticizer after swelling is (W3 - W4) / W3 × 100%. Adding the residual amount of the surfactant after swelling and stretching to the residual amount of the plasticizer after swelling and stretching gives the residual amount of the additive after swelling and stretching.

[0053] 2-3. Analysis of FTIR peak ratio (3200 cm -1 / 1425 cm -1 ) The sample preparation method was as follows: First, the polyvinyl alcohol film was divided into five equal parts along the transverse direction, and the central part of the divided polyvinyl alcohol film was cut. The cut area of each piece was set to MD 20 cm × TD 15 cm. Next, it was left in a thermo-hygrostat at 23 °C and 50% RH for 24 hours. Next, the polyvinyl alcohol film (MD 5 cm × TD 15 cm) was fixed, and the polyvinyl alcohol film was stretched to twice its length at a rate of 4.3 cm / min in pure water at 30 °C. After completion, the moisture on the surface of the polyvinyl alcohol film was completely absorbed, and it was left in the thermo-hygrostat at 23 °C and 50% RH for 24 hours. Finally, a polyvinyl alcohol film of MD 5 cm × TD 10 cm was cut out from the stretched part.

[0054] The analytical instrument used here is a Perkin Elmer Spectrum 100. The analysis conditions were as follows: After leaving it in the thermo-hygrostat, FTIR analysis was performed in ATR transmission mode with 4 accumulations in the range of 650 - 4000 cm -1 . The FTIR peak intensity ratio was measured as [100 - (transmission value at 3200 cm -1 )] / [100 - (transmission value at 1425 cm -1 ). Further, the average value of the FTIR peak ratios in the same TD direction was obtained.

[0055] 2-4. Analysis of FTIR peak ratio (1140 cm -1 / 1425 cm -1 ) The method for preparing the sample was as follows: First, the polyvinyl alcohol film was divided into five equal parts along the transverse direction, and the central part of the polyvinyl alcohol film after equal division was cut. The cut area of each piece was set to MD 20 cm × TD 15 cm. Next, it was left standing for 24 hours under the conditions of 23 °C and 50% RH in a thermo-hygrostat. Next, the polyvinyl alcohol film (MD 5 cm × TD 15 cm) was fixed, and the polyvinyl alcohol film was stretched to twice its length at a rate of 4.3 cm / min in pure water at 30 °C. After completion, the moisture on the surface of the polyvinyl alcohol film was completely absorbed, and it was left standing for 24 hours in the thermo-hygrostat under the conditions of 23 °C and 50% RH. Finally, a polyvinyl alcohol film of MD 5 cm × TD 10 cm was cut out from the stretched part.

[0056] The analytical instrument used here was a Perkin Elmer Spectrum 100. The analytical conditions were as follows: After leaving it in the thermo-hygrostat, FTIR analysis was performed in the ATR transmission mode with 4 accumulations in the range of 650 - 4000 cm -1 The FTIR peak intensity ratio was measured as [100 - (transmission value at 1140 cm -1 )] / [100 - (transmission value at 1425 cm -1 ), and the average value was further obtained for the FTIR peak ratios in the same TD direction.

[0057] 2 - 5. Measurement of Hue Expression The method for preparing the sample is a process of preparing a polyvinyl alcohol film into a polarizing film. The method for preparing a polyvinyl alcohol film into a polarizing film is not particularly limited, but preferably includes a swelling treatment of stretching the polyvinyl alcohol film in water, a dyeing treatment of dyeing with a dichroic dye, and a stretching treatment of uniaxially stretching the film body. Among them, methods such as boric acid cross-linking treatment, fixing treatment, washing treatment, and heat treatment may be further carried out as necessary. In that case, the order of each treatment is not particularly limited, but preferably, it is carried out in the order of swelling treatment, dyeing treatment, and stretching treatment.

[0058] In addition, the measuring instrument used here is Perkin Elmer Lambda 365 (equipped with an integrating sphere). Under the measuring conditions, with the integrating sphere in place, the absorbance (A) at a wavelength of 480 nm and the absorbance (B) at a wavelength of 700 nm were measured based on the perpendicular condition. Finally, the ratio of A / B was used as the hue ratio data.

[0059] 2-6. Measurement of Polarization Expression The method for preparing the sample 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 above method was made into a test piece with a length of 9 cm in the longitudinal direction and a width of 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 part was 5 cm in the longitudinal direction and 10 cm in the width direction, and it was immersed in water at a temperature of 30°C within 70 seconds and 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 aqueous solution of iodine with a concentration of 0.03 mass percent and potassium iodide with a concentration of 3 mass percent and at a temperature of 30°C, and uniaxially stretched along the longitudinal direction at a stretching speed of 24 cm / min within 60 seconds until it became 3.3 times the original length (second-stage stretching). Subsequently, the test piece was immersed in an aqueous solution of boric acid with a concentration of 3 mass percent and potassium iodide with a concentration of 3 mass percent and at a temperature of 30°C, and uniaxially stretched along the longitudinal direction at a stretching speed of 24 cm / min within about 20 seconds until it became 3.6 times the original length (third-stage stretching). Further, the test piece was immersed in an aqueous solution of boric acid with a concentration of 4 mass percent and potassium iodide with a concentration of about 5 mass percent and at a temperature of 58°C, and uniaxially stretched along the longitudinal direction at a stretching speed of 24 cm / min until it became 5.5 times the original length (fourth-stage stretching). Finally, the test piece was immersed in an aqueous solution of potassium iodide containing boric acid with a concentration of 1.5 mass percent and potassium iodide with a concentration of 3 mass percent for 10 seconds for fixation treatment, and dried in a dryer at 60°C for 4 minutes to obtain a polarizing film.

[0060] Also, the measuring instrument used here is Perkin Elmer Lambda 365. The measurement conditions are as follows: Based on the standard method of JIS Z 8722, visual sensitivity correction in the visible light region of 2° is performed using a C light source. Next, two polarizing films are overlapped with the same orientation direction, and the light transmittance (H0) at the wavelength is measured. Separately, two polarizing films are overlapped with perpendicular orientation directions, and the light transmittance (H 90 ) at the wavelength is measured. Finally, the polarization degree data is calculated by the formula: polarization degree = [(H0 - H 90 ) / (H0 + H 90 )] 1 / 2 and obtained by calculation with this formula.

[0061] 3. Data Contents of Examples and Comparative Examples First, variables were set for three items: the first heating roller, the maximum temperature of the dryer, and the temperature difference between the last heating roller and the first section dryer during the preparation process of the polyvinyl alcohol films in the examples and comparative examples, and related analysis or measurement data were further obtained. For details, please refer to Table 1.

[0062]

Table 1

[0063] As can be seen from the results, when the additive residue amounts after swelling and stretching of the polyvinyl alcohol films in Examples 1 to 11 were adjusted within a certain range, the prepared polarizing films had good hue performance. In contrast, the additive residue amounts after swelling and stretching of the polyvinyl alcohol films in Comparative Examples 1 to 4 were greater than 3.00 wt% or less than 0.50 wt%, and the prepared polarizing films had poor hue performance. Also, the FTIR intensity ratio values of OH(3200 cm -1 ) / CH2(1425 cm -1 ) in Comparative Examples 1 to 3 were greater than 1.00, indicating that the higher the plasticizer residue amount in the polyvinyl alcohol film, the worse the hue performance. The OH(3200 cm -1 ) / CH2(1425 cm -1The value of the FTIR intensity ratio of is less than 0.70, indicating that if the residual amount of plasticizer in the polyvinyl alcohol film is too low, the hue expression will deteriorate.

[0064] Next, during the preparation process of the polyvinyl alcohol films of the examples and comparative examples, two variables such as the dissolution time of polyvinyl alcohol and the concentration of the polyvinyl alcohol-based resin after dissolution were controlled, and related analysis or measurement data were further obtained. For details, please refer to Table 2.

[0065]

Table 2

[0066] As shown in Table 2, the inventor noticed that the higher the crystallinity of the polyvinyl alcohol film, the more likely it is that there are some undissolved polyvinyl alcohol crystal regions during the preparation of the polarizing film, and the iodine cannot swell and enter the film due to the polyvinyl alcohol crystal regions, resulting in a decrease in the degree of polarization. For example, Examples 8, 9 and Comparative Examples 1-4 have high values of the FTIR intensity ratio of 1140 cm -1 / 1425 cm -1 (greater than 1.45), indicating high crystallinity of polyvinyl alcohol, and the degree of polarization does not reach 99.9%. In contrast, Examples 1-7, 10 and 11 have values of the FTIR intensity ratio of 1140 cm -1 / 1425 cm -1 all of which are 1.45 or less, indicating that the degrees of polarization of the prepared polarizing films all reach 99.9%.

[0067] According to Examples 1-11 in Table 2, the polyvinyl alcohol dissolution times of Example 9 and Comparative Examples 2-4 are 150 minutes, outside the range of 180-300 minutes of the other examples. The concentrations of the polyvinyl alcohol-based resin after dissolution of Example 8 and Comparative Examples 1 and 3 are 35%, outside the range of 25-30%. The inventor found that the control of the above variables is related to 1140 cm -1 / 1425 cm -1It was noticed that the FTIR peak intensity ratio deviated from the ideal range.

[0068] In view of the above results, the inventor noticed that when the additive residue amount after swelling and stretching of the polyvinyl alcohol film is controlled within a certain range, the polarizing film prepared thereby has good hue expression. In the process of preparing the polyvinyl alcohol film, three variables, namely, the temperature of the first heating roller during the preparation process of the polyvinyl alcohol film, the maximum temperature of the dryer, and the temperature difference between the last heating roller and the first section dryer, affect the additive residue amount of the polyvinyl alcohol film, and can also affect the optical properties of the optical film prepared therefrom. Also, the division result of the average value of the additive residue amount of 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 ) can be used to prepare polyvinyl alcohol films with other ideal properties by control. Furthermore, the inventor also noticed that the dissolution time of polyvinyl alcohol and the concentration of the polyvinyl alcohol-based resin after dissolution affect the crystallinity of the polyvinyl alcohol film and the polarization degree of the optical film prepared thereby.

[0069] In summary, the polyvinyl alcohol film provided by the present invention based on the above particulars has low crystallinity, and the optical film prepared thereby has excellent hue expression and polarization degree. Also, the defined content of the present invention can be used to more accurately manufacture, identify, and select the above polyvinyl alcohol film.

[0070] All ranges provided in this specification are meant to include each specific range within the assigned range and combinations of secondary ranges between the assigned ranges. Also, unless otherwise specified, all ranges provided in this specification include the endpoints of the ranges. Thus, the range 1 - 5 includes specifically 1, 2, 3, 4, and 5, as well as secondary ranges such as 2 - 5, 3 - 5, 2 - 3, 2 - 4, 1 - 4, etc.

[0071] All publications and patent applications referenced in this specification are hereby incorporated by reference into this specification, and for all purposes, each publication or patent application is hereby clearly and individually indicated as being incorporated by reference into this specification. In the event of any inconsistency between this specification and any publication or patent application incorporated by reference into this specification, this specification shall govern.

Description of Reference Signs

[0072] 110 Dissolving tank 120 Casting drum 130 Heating roller 140 Dryer M Preformed film S100 - S104 Processes

Claims

1. A polyvinyl alcohol film having an additive residue amount after swelling and stretching defined below of 0.50 to 3.00 wt% and a water content of 1.0 to 5.0 wt%: The swelling and stretching is such that the polyvinyl alcohol film is left standing at 23°C and a relative humidity (RH) of 50% for 24 hours, then stretched 2-fold at a rate of 4.3 cm / min in pure water at 30°C, and then left standing at 23°C and a relative humidity (RH) of 50% for 24 hours, The additive residue amount is obtained from the calculation formula: (W3 - W4) / W3 × 100% (wherein W3 is the weight of the polyvinyl alcohol film after swelling and stretching and drying at 105°C for 10 minutes, and W4 is the weight of the polyvinyl alcohol film after swelling and stretching and then stirring in 30°C / 2000 ml of pure water with a stirrer at a rotation speed of 115 to 120 rpm for 5 minutes and drying at 105°C for 1 hour).

2. When the polyvinyl alcohol film is analyzed by Fourier transform infrared spectroscopy after swelling, stretching, and drying, 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. The polyvinyl alcohol film according to Claim 1.

3. When the polyvinyl alcohol film is analyzed by Fourier transform infrared spectroscopy after swelling, stretching, and drying, the value of the intensity ratio at a wavelength of 1140 cm －１ and a wavelength of 1425 cm －１ is 1.20 to 1.

48. The polyvinyl alcohol film according to Claim 1.

4. When the polyvinyl alcohol film is analyzed by Fourier transform infrared spectroscopy after swelling, stretching, and drying, the value of the intensity ratio at a wavelength of 1140 cm －１ and a wavelength of 1425 cm －１ is 1.20 to 1.

45. The polyvinyl alcohol film according to Claim 1.

5. The polyvinyl alcohol film according to claim 1, wherein the additive contains a plasticizer and a surfactant.

6. The polyvinyl alcohol film according to claim 1, having an initial additive content of 6 to 15 wt%.

7. The polyvinyl alcohol film according to claim 1, having a degree of polymerization of 1800 to 3000.

8. An optical film produced from the polyvinyl alcohol film according to any one of claims 1 to 7.

9. The optical film according to claim 8, which is a polarizing film.

10. The optical film according to claim 8, wherein the degree of polarization of the film is 99.8% or more.

11. The optical film according to claim 8, wherein the ratio of the absorbance at a wavelength of 480 nm to the absorbance at a wavelength of 700 nm under perpendicular conditions is 1.40 to 1.

60.

12. A method for producing the polyvinyl alcohol film according to any one of claims 1 to 7, comprising: (a) stirring a polyvinyl alcohol-based resin, a plasticizer, a surfactant, and water, and heating to a dissolution temperature exceeding 100 °C to form a polyvinyl alcohol casting solution; (b) casting the polyvinyl alcohol casting solution onto a casting drum and drying to prepare a preformed film; (c) contacting the preformed film with n heating rollers whose temperature gradually decreases from high to low, and then entering a dryer having a plurality of sections for drying. and 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, where n is between 10 and 20. A method for manufacturing a polyvinyl alcohol film.

13. The melting temperature of the step (a) is 120 to 140 °C. The manufacturing method according to claim 12.

14. The concentration of the polyvinyl alcohol-based resin in the polyvinyl alcohol casting solution in the step (b) is 20.0 to 40.0%. The manufacturing method according to claim 12.

15. The plasticizer is 3 to 30 parts by weight with respect to 100 parts by weight of the polyvinyl alcohol-based resin. The manufacturing method according to claim 12.

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