Polyvinyl alcohol film, method for producing the same, and polarizing film of polyvinyl alcohol

Abstract

This invention relates to the field of polyvinyl alcohol (PVA) film technology, and discloses a PVA film, its preparation method, and a PVA polarizing film. The PVA film exhibits a swelling degree of 110-140% after immersion in water at 28°C for 30 minutes; the PVA film also exhibits a dissolution rate of 100-600 mg / m³ after immersion in water at 40°C for 1 hour. 2 The difference in leaching amount at any location on the polyvinyl alcohol film, |ΔS|, is ≤25 mg / m³. 2 The swelling difference |ΔC| at any location on the polyvinyl alcohol film is ≤6%. The polarizing film prepared from the polyvinyl alcohol film of the present invention has more uniform color, shallower wrinkles, and fewer streaks.

Description

Technical Field

[0001] This invention relates to the field of polyvinyl alcohol film technology, specifically to a polyvinyl alcohol film, its preparation method, and a polyvinyl alcohol polarizing film. Background Technology

[0002] Polyvinyl alcohol (PVA) film optical films are optical films made primarily from polyvinyl alcohol (PVA). They can be dyed and stretched to create polarizers with excellent polarizing properties, making them a key material in the manufacture of polarizers for liquid crystal displays (LCDs) and organic light-emitting diodes (OLEDs). Besides LCDs, polarizers are widely used in sunglasses, anti-glare goggles, polarizing filters for cameras and camcorders, anti-glare devices for automotive headlights, and various polarizing microscopes and testing instruments.

[0003] As a key component of LCD display devices, polarizers are increasingly sought after for their superior display quality in recent years. Furthermore, with the trend towards larger or thinner screens in LCD TVs and other devices, polarizers and their corresponding PVA optical films must also meet the requirements for wider widths and thinner profiles.

[0004] Currently, when preparing wide and thin polarizers using PVA optical films, problems such as uneven dyeing, color spots, wrinkles, and internal contamination often occur, resulting in substandard polarizer quality. Summary of the Invention

[0005] The purpose of this invention is to overcome the problems of uneven dyeing, color spots, wrinkles, and internal contamination in existing polarizing films, and to provide a polyvinyl alcohol film, its preparation method, and a polyvinyl alcohol polarizing film. This polyvinyl alcohol film has good processability, is not easy to break or wrinkle, and the polarizing film prepared by the polyvinyl alcohol film of this invention has more uniform color, shallower wrinkles, and fewer stripes.

[0006] To achieve the above objectives, the first aspect of the present invention provides a polyvinyl alcohol film, wherein the polyvinyl alcohol film has a swelling degree of 110-140% after being immersed in water at 28°C for 30 minutes.

[0007] The leaching amount of the polyvinyl alcohol film after immersion in water at 40°C for 1 hour is 100-600 mg / m³. 2 ;

[0008] The difference in leaching amount at any location on the polyvinyl alcohol film, |ΔS|, is ≤25 mg / m³. 2 ;

[0009] The difference in swelling degree at any location on the polyvinyl alcohol film, |ΔC|, is ≤6%.

[0010] A second aspect of the present invention provides a method for preparing a polyvinyl alcohol film, wherein the method includes:

[0011] (1) Polyvinyl alcohol and water are prepared into a casting solution, and the casting solution is heated and dried by more than 6 drying rollers after being extended;

[0012] (2) The dried film is heat-treated to obtain a polyvinyl alcohol film;

[0013] In step (1), the temperature difference between two adjacent drying rollers is less than 15°C.

[0014] In step (2), the maximum temperature of the heat treatment is 115-140℃.

[0015] A third aspect of the present invention provides a polyvinyl alcohol film prepared by the above method.

[0016] A fourth aspect of the present invention provides a polyvinyl alcohol polarizing film, wherein the polyvinyl alcohol polarizing film is obtained by sequentially swelling, stretching, dyeing, stretching, cleaning, and drying the above-mentioned polyvinyl alcohol film.

[0017] Through the above technical solutions, the polyvinyl alcohol film, its preparation method, and the polyvinyl alcohol polarizing film provided by the present invention have the following beneficial effects.

[0018] The polyvinyl alcohol film of the present invention exhibits a swelling degree of 110-140% after immersion in water at 28°C for 30 minutes, and a dissolution rate of 100-600 mg / m³ after immersion in water at 40°C for 1 hour. 2 The difference in leaching amount at any location on the polyvinyl alcohol film, |ΔS|, is ≤25 mg / m³. 2 Furthermore, when the swelling difference |ΔC| at any position on the polyvinyl alcohol film is ≤6%, the polyvinyl alcohol film has good processability, is not easy to break or wrinkle, and the resulting polarizing film has more uniform color, shallower wrinkles, and fewer stripes.

[0019] This invention controls the drying conditions of the casting solution after casting, ensuring the temperature difference between two adjacent drying rollers is less than 15°C, and also controls the maximum heat treatment temperature. Under the combined effect of these two factors, a specific degree of swelling, dissolution amount, and the difference in dissolution amount at any location on the film, |ΔS|, are obtained, ≤25 mg / m². 2 A polyvinyl alcohol film with a swelling difference |ΔC| ≤ 6% has good processability, is not easy to break or wrinkle, and the resulting polarizing film has more uniform color, shallower wrinkles, and fewer streaks. Detailed Implementation

[0020] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0021] The first aspect of the present invention provides a polyvinyl alcohol film, wherein the polyvinyl alcohol film has a swelling degree of 110-140% after being immersed in water at 28°C for 30 minutes.

[0022] The leaching amount of the polyvinyl alcohol film after immersion in water at 40°C for 1 hour is 100-600 mg / m³. 2 ;

[0023] The difference in leaching amount at any location on the polyvinyl alcohol film, |ΔS|, is ≤25 mg / m³. 2 ;

[0024] The difference in swelling degree at any location on the polyvinyl alcohol film, |ΔC|, is ≤6%.

[0025] In this invention, the swelling degree of the polyvinyl alcohol film after immersion in water at 28°C for 30 minutes is 110-140%, and the leaching amount of the polyvinyl alcohol film after immersion in water at 40°C for 1 hour is 100-600 mg / m³. 2 The difference in leaching amount at any location on the polyvinyl alcohol film, |ΔS|, is ≤25 mg / m³. 2 Furthermore, when the swelling difference |ΔC| at any position on the polyvinyl alcohol film is ≤6%, the polyvinyl alcohol film has good processability, is not easy to break or wrinkle, and the resulting polarizing film has more uniform color, shallower wrinkles, and fewer stripes.

[0026] Furthermore, the polyvinyl alcohol film has a swelling degree of 110-130% after being immersed in water at 28°C for 30 minutes.

[0027] Furthermore, the leaching amount of the polyvinyl alcohol film after immersion in water at 40°C for 1 hour is 100-400 mg / m³. 2 .

[0028] Furthermore, the difference in leaching amount at any location on the polyvinyl alcohol film, |ΔS|, is ≤20 mg / m³. 2 .

[0029] Furthermore, the difference in swelling degree at any position on the polyvinyl alcohol film, |ΔC|, is ≤5%.

[0030] According to the present invention, the thickness of the polyvinyl alcohol film is 20-75 μm.

[0031] Furthermore, the thickness of the polyvinyl alcohol film is 45-60 μm.

[0032] In this invention, the width of the polyvinyl alcohol film is 1-6m.

[0033] Furthermore, the width of the polyvinyl alcohol film is 2-5m.

[0034] A second aspect of the present invention provides a method for preparing a polyvinyl alcohol film, wherein the method includes:

[0035] (1) Polyvinyl alcohol and water are prepared into a casting solution, and the casting solution is heated and dried by more than 6 drying rollers after being extended;

[0036] (2) The dried film is heat-treated to obtain a polyvinyl alcohol film;

[0037] In step (1), the temperature difference between two adjacent drying rollers is less than 15°C.

[0038] In step (2), the maximum temperature of the heat treatment is 115-140℃.

[0039] In this invention, by controlling the drying conditions of the casting solution after casting, the temperature difference between two adjacent drying rollers is kept to less than 15°C, and the maximum temperature of the heat treatment is controlled. Under the combined effect of these two factors, the obtained specific swelling degree, dissolution amount, and the difference in dissolution amount at any position on the film |ΔS| ≤ 25 mg / m³ are achieved. 2 A polyvinyl alcohol film with a swelling difference |ΔC| ≤ 6% has good processability, is not easy to break or wrinkle, and the resulting polarizing film has more uniform color, shallower wrinkles, and fewer streaks.

[0040] Furthermore, the temperature difference between two adjacent drying rollers is less than 10°C.

[0041] According to the present invention, in step (1), the initial temperature T of the drying process is... a The drying temperature is 70-90℃, and the highest temperature T is... max The temperature is 80-125℃, and T a <T max .

[0042] In this invention, when the initial and maximum drying temperatures meet the aforementioned ranges, the obtained polyvinyl alcohol film exhibits good processability, is less prone to breakage and wrinkling, and the resulting polarizing film possesses uniform color, minimal internal contamination, and no streaks. In this invention, the temperature difference between the drying rollers can be the same or different during the same drying process. In this invention, the temperature of each drying roller can gradually increase during the drying process, reaching the maximum drying temperature. Once the drying roller reaches the maximum drying temperature, subsequent drying rollers can maintain that maximum drying temperature.

[0043] Further, in step (1), the initial drying temperature T a The highest drying temperature T is 70-80℃. max The temperature is 95-115℃.

[0044] In this invention, there is no special limitation on the number of drying rollers; for example, the number of drying rollers can be 6-30.

[0045] According to the present invention, in step (1), the degree of polymerization of the polyvinyl alcohol is 1700-5000.

[0046] In this invention, when the degree of polymerization of polyvinyl alcohol meets the above-mentioned range, the resulting polyvinyl alcohol film has good processing performance and mechanical properties.

[0047] Further, in step (1), the degree of polymerization of the polyvinyl alcohol is 2000-4000.

[0048] According to the present invention, the degree of alcoholysis of the polyvinyl alcohol is greater than or equal to 99 mol%.

[0049] In this invention, when the degree of hydrolysis of polyvinyl alcohol meets the above-mentioned range, the resulting polyvinyl alcohol film has excellent optical properties and good processing performance.

[0050] Furthermore, the degree of alcoholysis of the polyvinyl alcohol is 99.5-99.9 mol%.

[0051] According to the present invention, in step (1), the solid content of the casting solution is 5-30 wt%.

[0052] In this invention, when the solid content of the casting solution meets the above-mentioned range, the obtained polyvinyl alcohol film has good processability, and the polarizing film produced has a more uniform color.

[0053] Further, in step (1), the solid content of the casting solution is 5-15 wt%.

[0054] According to the present invention, the temperature of the casting solution is 80-110°C.

[0055] In this invention, when the temperature of the casting solution meets the above-mentioned range, the obtained polyvinyl alcohol film has good processability, and the polarizing film produced has the characteristic of having few defects.

[0056] Furthermore, the temperature of the casting solution is 85-105°C.

[0057] According to the present invention, in step (1), the casting solution further includes a plasticizer and a surfactant.

[0058] According to the present invention, based on 100 parts by weight of polyvinyl alcohol, the plasticizer is 8-17 parts by weight and the surfactant is 0.1-0.5 parts by weight.

[0059] Furthermore, based on 100 parts by weight of polyvinyl alcohol, the plasticizer is 10-15 parts by weight and the surfactant is 0.15-0.3 parts by weight.

[0060] According to the present invention, the plasticizer is selected from at least one of glycerol, succinic anhydride ester and polyethylene glycol.

[0061] According to the present invention, the surfactant is a nonionic surfactant and / or anionic surfactant.

[0062] In this invention, there is no special requirement for the minimum temperature of heat treatment, which can be adjusted according to the maximum temperature of drying. For example, the minimum temperature of heat treatment can be 75-85℃.

[0063] In this invention, the heat treatment time is 40-80 seconds.

[0064] In this invention, in step (1), after the casting solution is cast onto the casting roller through the T-die to become a blank film, it is heated and dried by more than 6 drying rollers.

[0065] In this invention, the temperature of the casting roller is 75-85℃.

[0066] A third aspect of the present invention provides a polyvinyl alcohol film prepared by the above method.

[0067] A fourth aspect of the present invention provides a polyvinyl alcohol polarizing film, wherein the polyvinyl alcohol polarizing film is obtained by sequentially swelling, stretching, dyeing, stretching, cleaning, and drying the above-mentioned polyvinyl alcohol film.

[0068] This invention does not specifically limit the method for preparing polyvinyl alcohol (PVA) polarizing film. To obtain a PVA polarizing film with high color uniformity, according to a preferred embodiment of this invention, a PVA film is immersed in water at 25-35°C for swelling, followed by a first stretching, the stretching ratio being 1.3-1.7 times the initial length of the PVA film; the first-stretched PVA film is then immersed in a dyeing solution at 30-40°C for a second stretching, the stretching ratio being 2.8-3.2 times the initial length of the PVA film; the second-stretched PVA film is then subjected to a color-fixing treatment in a color-fixing solution at a color-fixing temperature of 45°C. The polyvinyl alcohol (PVA) film is subjected to a third stretch at -55℃, with the stretching ratio being 4.8-5.2 times the initial length of the PVA film. The PVA film after the third stretch is then cleaned at 25-35℃ for 10-20 seconds. The cleaned PVA film is then dried at 55-65℃ for 5-8 minutes to obtain a PVA polarizing film. The dyeing solution contains 1.5-2 wt% potassium iodide and 0.05-0.12 wt% iodine. The fixing solution contains 3-6 wt% boric acid and 3-6 wt% potassium iodide.

[0069] The present invention will be described in detail below through embodiments.

[0070] Dimensional swelling of polyvinyl alcohol (PVA) film: PVA film was cut into 30mm × 30mm test pieces. The actual length (L0) of each test piece was measured using vernier calipers. The test pieces were then immersed in 28℃ warm water for 30 minutes, and the length (L1) at the same location was measured. Samples were taken every 15cm along the width of the film and every 1m along the length to analyze film uniformity. Two samples were taken from each sampling point, and the average value was used as the dimensional swelling at that point. The total number of sampling points in both the length and width directions was no less than 20. The formula for calculating the dimensional swelling is as follows:

[0071]

[0072] In the formula:

[0073] χ — Size swelling degree, %;

[0074] L1—Length after soaking, mm;

[0075] L0—Length before soaking, mm.

[0076] Dissolution of polyvinyl alcohol film: Weigh 500g of water into a 1L beaker using a balance and place it in a water bath at a constant temperature of 40℃. Place the cut polyvinyl alcohol film samples (100mm×100mm square, 3 pieces) into the beaker and soak for 1 hour. Then, remove the polyvinyl alcohol film samples and stir the extract on a magnetic stirrer for 10 minutes.

[0077] Weigh 40g of boric acid and dissolve it in 1000mL of water and shake well; weigh 35g of potassium iodide and 12.70g of iodine and dissolve them in 1000mL of water and shake well; prepare a boric acid-iodine / potassium iodide colorimetric solution by mixing the boric acid solution and the iodine-potassium iodide solution at a volume ratio of 5:1 and shake well.

[0078] Accurately prepare polyvinyl alcohol standard solutions of different concentrations (0-500 μg / mL) and establish a standard working curve;

[0079] Take 25 mL of boric acid-iodine / potassium iodide colorimetric solution, dilute to 100 mL with polyvinyl alcohol film sample extraction solution, shake well, place at 20℃ for 15 min, and measure the absorbance of the solution.

[0080] Sampling was performed according to the sampling method for uniformity of dimensional swelling to test the uniformity of film dissolution.

[0081] The PVA dissolution amount is calculated according to formulas (2) and (3):

[0082] A = KC + b (2)

[0083] In the formula:

[0084] K—Slope of the standard working curve;

[0085] b—Intercept of the standard working curve;

[0086] A—Absorbance of the extract;

[0087] C—Concentration of extract, μg / mL;

[0088]

[0089] In the formula:

[0090] χ—Dissolution amount, mg / m³ 2 .

[0091] Thickness of polyvinyl alcohol film: Cut a sample 80 mm wide in either the width (TD) or length (MD) direction of the polyvinyl alcohol film. Lay the sample flat on the measuring platform of the mechanical contact thickness gauge, ensuring the sample is clean, smooth, and wrinkle-free. Multiple measurements are generally required, with a test interval of 20 mm, and more than 25 points are taken. Finally, calculate the average thickness.

[0092] Color uniformity of polyvinyl alcohol polarizing film: Polyvinyl alcohol polarizing film was cut into test pieces with a length of 30cm and a width of 30cm. After being overlapped in an orthogonal polarization state, the film was irradiated with a light box with an illuminance of 14000 lux (lx) and the color uniformity of the polarizing film was observed. The following criteria were used for evaluation.

[0093] 0…The entire surface is completely free of uneven dyeing.

[0094] 1… There is slight uneven staining in some areas.

[0095] 2…Slight uneven staining exists over a large area.

[0096] 3…There is obvious uneven staining.

[0097] Example 1

[0098] An aqueous solution was prepared by mixing 100 parts by weight of polyvinyl alcohol (average degree of polymerization 2200, degree of alcoholysis 99.9 mol%), 12 parts by weight of glycerol, 0.1 parts by weight of diethanolamide laurate, 0.1 parts by weight of sodium dodecylbenzenesulfonate, and water. The solid content of the casting solution was 15 wt%, and the solution temperature was 94 °C. The film was cast from a T-die onto a casting roller (the temperature of the casting roller was 80 °C) to form a preform. After being peeled off from the casting roller, the film was dried by subsequent drying rollers (temperature difference between two adjacent drying rollers was 5 °C, starting temperature was 70 °C, and maximum temperature was 110 °C). The film was then heat-treated at a minimum temperature of 80 °C and a maximum temperature of 120 °C for 50 s to obtain a polyvinyl alcohol optical film with a thickness of 60 μm and a width of 3000 mm.

[0099] The test results of polyvinyl alcohol film are shown in Table 1.

[0100] Example 2

[0101] Polyvinyl alcohol films were prepared according to the method of Example 1, except that the temperature difference between two adjacent drying rollers was 12°C, the drying start temperature was 85°C, and the maximum temperature was 100°C; the test results of the prepared polyvinyl alcohol films are shown in Table 1.

[0102] Example 3

[0103] Polyvinyl alcohol films were prepared according to the method of Example 1, except that the initial drying temperature was 90°C and the maximum drying temperature was 125°C; the test results of the prepared polyvinyl alcohol films are shown in Table 1.

[0104] Comparative Example 1

[0105] Polyvinyl alcohol (PVA) films were prepared according to the method in Example 1, except that the solid content of the casting solution was 15 wt%, and the minimum and maximum heat treatment temperatures were 80°C and 145°C, respectively. The test results of the prepared PVA films are shown in Table 1.

[0106] Comparative Example 2

[0107] Polyvinyl alcohol (PVA) films were prepared according to the method in Example 1, except that the minimum heat treatment temperature was 80°C, the maximum heat treatment temperature was 110°C, and the heat treatment time was 50 seconds. The test results of the prepared PVA films are shown in Table 1.

[0108] Comparative Example 3

[0109] Polyvinyl alcohol (PVA) films were prepared according to the method in Example 1, except that the films were dried by heating using drying rollers with a temperature difference of 30°C between adjacent drying rollers. The test results of the prepared PVA films are shown in Table 1.

[0110] Test case

[0111] Polyvinyl alcohol (PVA) films prepared in Examples 1-3 and Comparative Examples 1-3 were sequentially immersed in water at 30°C to swell and then subjected to a first stretching, the stretching ratio being 1.5 times the initial length of the PVA film. The swollen and stretched PVA film was then immersed in a dyeing solution at 35°C (the dyeing solution contained 1.8 wt% potassium iodide and 0.09 wt% iodine) for a second stretching, the stretching ratio being 3 times the initial length of the PVA film. The second stretched PVA film was then subjected to a color-fixing treatment in a color-fixing solution (the color-fixing solution contained 4 wt% boric acid and 5 wt% potassium iodide) at 50°C, followed by a third stretching, the stretching ratio being 5.0 times the initial length of the PVA film. The third stretched PVA film was then cleaned at 30°C for 10 seconds. Finally, the cleaned PVA film was dried at 60°C for 6 minutes to obtain a PVA polarizing film.

[0112] The test results of the polyvinyl alcohol polarizing film are shown in Table 1 below.

[0113] Table 1

[0114]

[0115]

[0116] As can be seen from the results in Table 1, the polyvinyl alcohol film using the embodiments of the present invention has good processability, is not easy to break, is not easy to wrinkle, and the prepared polarizing film has more uniform color, shallower wrinkles, and fewer stripes.

[0117] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A polyvinyl alcohol film, characterized in that, The polyvinyl alcohol film has a swelling degree of 110-140% after being immersed in water at 28°C for 30 minutes. The leaching amount of the polyvinyl alcohol film after immersion in water at 40°C for 1 hour is 100-600 mg / m³. 2 ; The difference in leaching amount at any location on the polyvinyl alcohol film, |ΔS|, is ≤25 mg / m³. 2 ; The difference in swelling degree at any location on the polyvinyl alcohol film, |ΔC|, is ≤6%.

2. The polyethylene film according to claim 1, wherein, The polyvinyl alcohol film has a swelling degree of 110-130% after being immersed in water at 28°C for 30 minutes. Preferably, the leaching amount of the polyvinyl alcohol film after immersion in water at 40°C for 1 hour is 100-400 mg / m³. 2 ; Preferably, the difference in leaching amount at any position on the polyvinyl alcohol film, |ΔS|, is ≤20 mg / m³. 2 ; Preferably, the difference in swelling degree at any position on the polyvinyl alcohol film, |ΔC|, is ≤5%. Preferably, the thickness of the polyvinyl alcohol film is 20-75 μm, and more preferably 45-60 μm.

3. A method for preparing a polyvinyl alcohol film, characterized in that, The method includes: (1) Polyvinyl alcohol and water are prepared into a casting solution, and the casting solution is heated and dried by more than 6 drying rollers after being extended; (2) The dried film is heat-treated to obtain a polyvinyl alcohol film; In step (1), the temperature difference between two adjacent drying rollers is less than 15°C. In step (2), the maximum temperature of the heat treatment is 115-140℃.

4. The preparation method according to claim 3, wherein, In step (1), the temperature difference between two adjacent drying rollers is less than 10°C; Preferably, in step (1), the initial drying temperature T a The drying temperature is 70-90℃, and the highest temperature T is... max The temperature is 80-125℃, and T a <T max ; More preferably, in step (1), the initial drying temperature T a The highest drying temperature T is 70-80℃. max The temperature is 95-115℃.

5. The preparation method according to claim 3 or 4, wherein, In step (1), the degree of polymerization of the polyvinyl alcohol is 1700-5000, preferably 2000-4000; Preferably, the degree of alcoholysis of the polyvinyl alcohol is greater than or equal to 99 mol%, and more preferably 99.5-99.9 mol%.

6. The preparation method according to claim 3 or 4, wherein, In step (1), the solid content of the casting solution is 5-30 wt%, preferably 5-15 wt%. Preferably, the temperature of the casting solution is 80-110℃, and more preferably 85-105℃.

7. The preparation method according to claim 3 or 4, wherein, In step (1), the casting solution also includes plasticizers and surfactants; Preferably, based on 100 parts by weight of polyvinyl alcohol, the plasticizer is 8-17 parts by weight, more preferably 10-15 parts by weight; and the surfactant is 0.1-0.5 parts by weight, more preferably 0.15-0.3 parts by weight.

8. The preparation method according to claim 7, wherein, The plasticizer is selected from at least one of glycerol, succinic anhydride ester and polyethylene glycol; Preferably, the surfactant is a nonionic surfactant and / or anionic surfactant.

9. A polyvinyl alcohol film prepared by the method according to any one of claims 3-8.

10. A polyvinyl alcohol polarizing film, characterized in that, The polyvinyl alcohol polarizing film is obtained by sequentially swelling, stretching, dyeing, stretching, washing, and drying the polyvinyl alcohol film described in any one of claims 1-2 and 9.

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