PVA optical film for waterless ripple thin polaroid and preparation method of PVA optical film

Abstract

The invention discloses a preparation method of a PVA (polyvinyl alcohol) optical film for a waterless corrugated thin polarizer, which comprises the following steps: dissolving a PVA polymer and an additive in a solvent to prepare a film casting stock solution, extruding the film casting stock solution by an extruder, defoaming, filtering to form a liquid film, extruding the liquid film from a mouth mold, drying by a tape casting roller, and drying to obtain the PVA optical film for the waterless corrugated thin polarizer. And finally, the thin film enters a drying oven to be subjected to heat treatment, and the PVA optical film is obtained through rolling. According to the PVA optical film for the water-ripple-free thin polaroid and the preparation method of the PVA optical film, starting from the forming mechanism of water ripples, the forming rule of production parameters of extrusion casting on the water ripples is studied, and therefore the preparation technology of the water-ripple-free PVA optical film is formulated.

Description

Technical Field

[0001] The invention belongs to the technical field of optical elements, and in particular relates to a PVA optical film for a waterless corrugated thin polarizer and a preparation method thereof. Background Art

[0002] Polyvinyl alcohol optical film is mainly used in the production of polarizers, and the end products are various types of liquid crystal displays, such as display panels for televisions, computer monitors, mobile phones, car navigation and wearable electronic devices. PVA polarizers are made by swelling, dyeing, uniaxial stretching, boride cross-linking, and laminating triacetate cellulose TAC film with PVA optical film. As display panels develop towards thinner, more durable, and more transparent, polyvinyl alcohol polarizers are gradually developing towards thinner and more transparent directions.

[0003] PVA optical film is made of PVA resin through dissolution, extrusion, casting, drying and other processes. The stability of the casting and drying process affects the uniformity of the apparent quality of the PVA film, thereby determining the processing performance of the PVA film in the manufacturing process of the polarizer. After the PVA film is extruded by the casting machine, the liquid film flows down from the die opening through the die flow channel. Affected by extrusion, casting and its own gravity, the shaking during the stretching process can easily cause the film to be uneven during the drying process, and it is very easy to form periodic and penetrating water ripples on the surface of the film. PVA film with water ripples is easy to cause the polarizer to break during the processing of the polarizer. Secondly, the produced polarizer also has more serious water ripples and cannot be put into market application. In response to this problem, this patent plans to start from the formation mechanism of water ripples, study the formation law of water ripples caused by the production parameters of extrusion casting, and thus develop a preparation process for thin PVA optical film without water ripples. Summary of the invention

[0004] The purpose of the present invention is to overcome the above problems existing in the prior art, to provide a PVA optical film for a water-free thin polarizer and a preparation method thereof, and to study the effect of the production parameters of extrusion casting on the formation of water ripples based on the formation mechanism of water ripples, thereby formulating a preparation process for a water-free PVA optical film.

[0005] In order to achieve the above technical objectives and the above technical effects, the present invention is implemented through the following technical solutions:

[0006] In a first aspect, the present invention provides a method for preparing a PVA optical film for a waterless corrugated thin polarizer, the preparation method comprising the following steps:

[0007] First, the PVA polymer and additives are dissolved in a solvent to prepare a casting solution. The casting solution is extruded by an extruder for degassing and filtration to form a liquid film. The liquid film is then extruded from a die, dried by a casting roller, and pre-dried by a drying roller to prepare a film. Finally, the film is placed in an oven for heat treatment and then rolled up to obtain a PVA optical film.

[0008] Wherein, the additives include plasticizers, surfactants, antioxidants and ultraviolet absorbers;

[0009] The feeding rate of the extruder is 200-350kg / h;

[0010] The die head angle of the die is 15-30°; wherein the die head angle is the angle between the center line of the die and the vertical direction;

[0011] The die gap is 3-6 mm;

[0012] The die temperature is 92-98°C;

[0013] The temperature of the casting roll is 70-85°C.

[0014] Furthermore, the die gap is the shortest distance between the lower liquid portion of the die and the surface of the casting roller.

[0015] Further, the degree of polymerization of the PVA polymer is 1500-3000;

[0016] The alcoholysis degree of the PVA polymer is 98-99.9%, preferably 99 to 99.9%.

[0017] Furthermore, the PVA polymer includes at least one of a polyvinyl alcohol homopolymer and a polyvinyl alcohol copolymer modified product.

[0018] Furthermore, the modified groups in the polyvinyl alcohol copolymer modified product include at least one of olefins, acrylates, methacrylates, methacrylamide derivatives, vinyl esters, and vinyl halides; further, in the casting solution, the mass percentage of the modified groups in the polyvinyl alcohol copolymer modified product is not more than 10%.

[0019] Furthermore, the plasticizer includes any one or more of glycerol, diglycerol, polyglycerol, ethylene glycol, and propylene glycol mixed in any proportion;

[0020] The surfactant is a mixture of a nonionic surfactant and an anionic surfactant;

[0021] The solvent is deionized water.

[0022] Furthermore, in the film casting stock solution, the mass percentage of the plasticizer is 8-15%, and the mass percentage of the surfactant is 1.5-5.0‰.

[0023] Furthermore, the heat treatment is divided into several stages, and the temperature of the several stages is 80-90°C.

[0024] Further, the moisture content of the film is 8-15%;

[0025] The moisture content of the film after the heat treatment is 1-5%.

[0026] In a second aspect, the present invention provides a PVA optical film for a waterless corrugated thin polarizer, which is prepared by the preparation method of a PVA optical film for a waterless corrugated thin polarizer provided by an embodiment of the first aspect of the present invention.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] 1. The present invention provides a water-ripple-free thin PVA optical film for polarizer and a preparation method thereof. Starting from the formation mechanism of water ripples, the effect of the production parameters of extrusion casting on the formation of water ripples is studied, and the fundamental cause of the jitter of the PVA liquid film at the liquid outlet under the die is solved, thereby formulating a water-ripple-free thin PVA optical film preparation process.

[0029] 2. Since the evaporation rate of water vapor and the strength of the liquid film are the main reasons for the generation of water ripples, the liquid film strength can be increased by adjusting the casting parameters, and the factors causing water ripples can be eliminated by adjusting the raw material feed amount and the die parameters; specifically, in the present invention, by adjusting the raw material feed amount (i.e. the feed amount of the extruder), the die parameters (i.e. the die head angle, die gap, die temperature of the die) and the casting parameters (i.e. the temperature of the casting roller), the disturbance of external factors can be reduced, thereby effectively eliminating the water ripple problem occurring in the production and processing of thin PVA optical films, and finally producing a PVA optical film without water ripples, and providing guidance for the production of subsequent thin PVA products.

[0030] 3. In the present invention, the preferred feed rate of the extruder is 200-350kg / h. Too high a feed rate will lead to too fast extrusion rate and casting rate, which will lead to an increase in the amount of liquid film at the lower liquid of the die per unit time, a high amount of water vapor evaporation, causing the liquid film to shake, resulting in severe water ripples; secondly, too low a feed rate will affect the normal operating pressure of the extruder and cannot ensure stable production.

[0031] 4. In the present invention, the die head angle of the die is preferably 15-30°. Since the liquid film is dried by the casting roller after being extruded from the die, if the die head angle changes, the angle tangent to the casting roller will also change. When the liquid film is parallel and tangent to the casting direction of the casting roller, the water vapor evaporated from the liquid film will escape from both sides and will not affect the jitter of the liquid film, thereby reducing water ripples.

[0032] 5. In the present invention, the die gap is the shortest distance between the lower liquid part of the die and the surface of the casting roller. When the die gap is raised, the evaporation area of ​​the liquid film increases, the water vapor evaporates quickly, and the disturbance is reduced, so that there are fewer water ripples. If the die gap is too large, it will cause serious pre-stretching of the film, which may easily lead to film breakage in the downstream, while if the die gap is too small, the horizontal lines on the surface of the film will be aggravated, causing other apparent quality problems of the film. Therefore, the die gap is controlled at 3-6mm.

[0033] 6. In the present invention, the temperature of the casting roller is controlled at 70-85°C. The temperature of the casting roller determines the solidification rate of the liquid film in contact with the surface of the casting roller, and affects the fluctuation of the landing point of the liquid film on the surface of the casting roller. The fast solidification rate of the liquid film on the surface of the casting roller can effectively improve the strength of the liquid film after gravity stretching, thereby reducing the disturbance of water vapor evaporation and reducing water ripples. If the temperature of the casting roller is too high, the film solidification rate is fast and the water ripples disappear, but the film loses water seriously and the film curls seriously during the casting process; if the temperature of the casting roller is too low, the solidification rate is slow, the liquid film strength is low, and it is easily disturbed by the environment, resulting in serious water ripples.

[0034] 7. In the present invention, in order to improve the strength of the liquid film, it is also necessary to increase the viscosity of the liquid film. Therefore, the die temperature is controlled at 92-98°C. If the die temperature is too high, the viscosity of the liquid film will decrease and the water ripples will become more serious. If the viscosity of the liquid film is too low, the die pressure will increase and the vertical lines of the film will be serious.

[0035] 8. In the present invention, the moisture content of the film prepared after pre-drying by a drying roller is 8-15%. This is because if the moisture content of the film is too low, it will cause serious curling of the film, and if the moisture content is too high, it will cause excessive crystallization of the internal structure of the film, resulting in too high a softening point and a large film modulus, which is easy to cause film breakage; the moisture content of the film after heat treatment is controlled to 1-5%. DETAILED DESCRIPTION

[0036] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0037] In a first aspect, the present invention provides a method for preparing a PVA optical film for a waterless corrugated thin polarizer, the preparation method comprising the following steps:

[0038] S1: PVA polymer and additives are dissolved in a solvent to prepare a film casting stock solution, and the film casting stock solution is extruded, degassed and filtered by an extruder to form a liquid film; wherein the feed rate of the extruder is 200-350kg / h;

[0039] Wherein, the PVA polymer is at least one of a polyvinyl alcohol homopolymer and a polyvinyl alcohol copolymer modified product;

[0040] The degree of polymerization of PVA polymer is 1500-3000;

[0041] The alcoholysis degree of PVA polymer is 98-99.9%;

[0042] If the PVA polymer contains a polyvinyl alcohol copolymer modified product, the modified group in the polyvinyl alcohol copolymer modified product includes at least one of olefins, acrylates, methacrylates, methacrylamide derivatives, vinyl esters, and halogenated vinyls;

[0043] If the PVA polymer contains a polyvinyl alcohol copolymer modification, the mass percentage of the modified group in the polyvinyl alcohol copolymer modification in the film casting stock solution is not greater than 10%;

[0044] The additives are plasticizers, surfactants, antioxidants and UV absorbers;

[0045] The plasticizer includes any one or more of glycerol, diglycerol, polyglycerol, ethylene glycol, and propylene glycol mixed in any proportion;

[0046] The surfactant is a mixture of a nonionic surfactant and an anionic surfactant;

[0047] In the film casting stock solution, the mass percentage of the plasticizer is 8-15%, and the mass percentage of the surfactant is 1.5-5.0‰;

[0048] The solvent was deionized water;

[0049] The UV absorber adopts the UV absorber commonly used in the production of PVA optical film;

[0050] S2: The liquid film is extruded from the die, dried by the casting roller, and then pre-dried by the drying roller to prepare a film. The moisture content of the prepared film is 8-15%;

[0051] The die head angle of the die is 15-30°; the die head angle is the angle between the center line of the die and the vertical direction;

[0052] The die gap is 3-6mm; the die gap is the shortest distance between the lower liquid part of the die and the surface of the casting roll;

[0053] The die temperature is 92-98°C;

[0054] The temperature of the casting roll is 70-85°C;

[0055] S3: After the film enters the oven for heat treatment, the moisture content of the heat-treated film is 1-5%, and the film is rolled up to obtain a PVA optical film;

[0056] The heat treatment is divided into several stages, and the temperatures of the several stages are independently selected from 80-90°C.

[0057] In a second aspect, the present invention provides a PVA optical film for a waterless corrugated thin polarizer, which is prepared by the preparation method of a PVA optical film for a waterless corrugated thin polarizer provided by an embodiment of the first aspect of the present invention;

[0058] Specifically, the thickness of the PVA optical film is 20 to 40 micrometers.

[0059] The following are specific examples. Unless otherwise specified, all raw materials in the following examples can be obtained from commercial sources.

[0060] Example 1

[0061] The present embodiment provides a method for preparing a PVA optical film for a waterless corrugated thin polarizer, and the preparation method is as follows: PVA polymer (polymerization degree 2200, alcoholysis degree 99%), sodium dodecylbenzene sulfonate, glycerol and antioxidant mixture with a total weight of 3500kg, and 6500L of deionized water are put into a reactor, stirred at 150°C, 0.4MPa for 6h to dissolve, and a PVA casting solution with a solute content of 35% is obtained; the formed casting solution is degassed and filtered by an extruder, extruded from a die, dried by a casting roller, and dried by a drying roller to prepare a film, and then the film enters an oven for heat treatment, and finally the PVA optical film is obtained by winding. The feed rate of the extruder is controlled to 200kg / h, the die angle is controlled to 15°, the die gap is controlled to 3.0mm, the casting roller temperature is set to 70°C, and the die temperature is controlled to 92°C.

[0062] Example 2

[0063] This embodiment provides a method for preparing a PVA optical film for a waterless corrugated thin polarizer. This embodiment is prepared by the same method and conditions as in Example 1, except that:

[0064] The feed rate was increased to 350 kg / h, the casting roll temperature was increased to 85°C, and the die gap was 6 mm.

[0065] Example 3

[0066] This embodiment provides a method for preparing a PVA optical film for a waterless corrugated thin polarizer. This embodiment is prepared by the same method and conditions as in Example 1, except that:

[0067] The extruder feed rate was increased to 350 kg / h and the casting roll temperature was increased to 85°C.

[0068] Example 4

[0069] This embodiment provides a method for preparing a PVA optical film for a waterless corrugated thin polarizer. This embodiment is prepared by the same method and conditions as in Example 1, except that:

[0070] The die lip angle was increased to 30° and the die gap was 6 mm.

[0071] Example 5

[0072] This embodiment provides a method for preparing a PVA optical film for a waterless corrugated thin polarizer. This embodiment is prepared by the same method and conditions as in Example 1, except that:

[0073] The casting roll temperature was 75°C and the die temperature was 94°C.

[0074] Example 6

[0075] This embodiment provides a method for preparing a PVA optical film for a waterless corrugated thin polarizer. This embodiment is prepared by the same method and conditions as in Example 1, except that:

[0076] The extruder feed rate was 300 kg / h, the casting roll temperature was 80°C, and the die temperature was 98°C.

[0077] Example 7

[0078] This embodiment provides a method for preparing a PVA optical film for a waterless corrugated thin polarizer. This embodiment is prepared by the same method and conditions as in Example 1, except that:

[0079] The die lip angle is controlled at 20° and the die gap is 5mm.

[0080] Comparative Example 1

[0081] This comparative example provides a method for preparing a PVA optical film for a waterless corrugated thin polarizer. This example is prepared by the same method and conditions as Example 1, except that:

[0082] The extruder feed rate was increased to 400 kg / h.

[0083] Comparative Example 2

[0084] This comparative example provides a method for preparing a PVA optical film for a waterless corrugated thin polarizer. This example is prepared by the same method and conditions as Example 1, except that:

[0085] The casting roll temperature was reduced to 65°C and the die temperature was reduced to 92°C.

[0086] Comparative Example 3

[0087] This comparative example provides a method for preparing a PVA optical film for a waterless corrugated thin polarizer. This example is prepared by the same method and conditions as Example 1, except that:

[0088] The die gap is raised to 8mm.

[0089] Comparative Example 4

[0090] This comparative example provides a method for preparing a PVA optical film for a waterless corrugated thin polarizer. This example is prepared by the same method and conditions as Example 1, except that

[0091] The casting roll temperature was raised to 90°C.

[0092] Experimental example

[0093] The PVA optical films prepared in Examples 1-9 and Comparative Examples 1-4 were tested, and the relevant test contents and test standards are as follows.

[0094] Evaluation method for water ripples of PVA membranes: The intuitive manifestation of water ripples on the membrane is periodic water ripples in the wide direction. The surface of the membrane can be observed after the heat treatment. ○ represents good water ripples, and × represents severe water ripples.

[0095] PVA film curling evaluation method: The PVA optical films prepared in the above embodiments and comparative examples were subjected to curling tests. The PVA optical films were cut into 60*60mm rectangular sheets, and dovetail clamps were used to clamp the upper and lower ends along the casting direction to ensure that the dovetail clamps at both ends were aligned. The PVA sheet with dovetail clamps was immersed in deionized water at 30°C for 30s, and the curling degree of the film was observed. Among them, ○ represents a good degree of curling, and × represents severe curling. The results of all embodiments and comparative examples are shown in Table 1 below.

[0096] Evaluation method for other apparent quality problems of PVA film: The horizontal and vertical lines of PVA film are also apparent quality problems of PVA film. The horizontal lines can be observed through a polarizing filter, and the number of vertical lines on the film can be observed by the projection of a strong flashlight; among them, ○ indicates good horizontal lines, and × indicates severe horizontal lines. The evaluation results of other apparent quality problems of PVA optical films prepared in the above embodiments and comparative examples are shown in Table 1.

[0097] Table 1 Comparison of tensile properties of polarizers prepared from different embodiments and comparative examples

[0098]

[0099] It can be seen from Table 1 that after the casting solution in Examples 1, 2, 3 and 4 is subjected to tape casting and pre-drying, the feed rate is controlled between 200-350 kg / h, the temperature of the casting roller is controlled between 70 and 85°C, and the temperature of the die is controlled between 92 and 98°C. The obtained PVA optical film has good apparent quality and no obvious water ripples. In Comparative Examples 3 and 4, although a thin PVA optical film with good water ripples can be obtained by raising the die gap and increasing the temperature of the casting roller, other appearance problems also occur one after another, and the products produced cannot be used downstream.

[0100] Therefore, the present invention provides a method for preparing a water-ripple-free thin PVA optical film for polarizer. Starting from the formation mechanism of water ripples, the effect of the production parameters of extrusion casting on the formation law of water ripples is studied, and the fundamental cause of the liquid outlet jitter of the PVA liquid film under the die is solved, that is, by adjusting the raw material feeding amount (that is, the feeding amount of the extruder), the die parameters (that is, the die head angle, the die gap, the die temperature) and the casting parameters (that is, the temperature of the casting roller), the water ripple generation factors are eliminated and the liquid film strength is increased, thereby formulating a preparation process for a water-ripple-free thin PVA optical film (the thickness of the thinned PVA optical film product is 20 to 40 microns).

[0101] In the description of this specification, the description with reference to the terms "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0102] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments, and the above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, and these changes and improvements all fall within the scope of the present invention to be protected.

Claims

1. A method for preparing a PVA optical film for a waterless corrugated thin polarizer, characterized in that: The preparation method comprises the following steps: First, the PVA polymer and additives are dissolved in a solvent to prepare a casting solution. The casting solution is extruded by an extruder for degassing and filtration to form a liquid film. The liquid film is then extruded from a die, dried by a casting roller, and pre-dried by a drying roller to prepare a film. Finally, the film is placed in an oven for heat treatment and then rolled up to obtain a PVA optical film. Wherein, the additives include plasticizers, surfactants, antioxidants and ultraviolet absorbers; The feeding rate of the extruder is 200-350kg / h; The die head angle of the die is 15-30°; The die gap is 3-6 mm; The die temperature is 92-98°C; The temperature of the casting roll is 70-85°C.

2. The method for preparing a waterless corrugated thin polarizer PVA optical film according to claim 1, characterized in that: The die gap is the shortest distance between the lower liquid portion of the die and the surface of the casting roll.

3. The method for preparing a PVA optical film for a waterless corrugated thin polarizer according to claim 1, characterized in that: The degree of polymerization of the PVA polymer is 1500-3000; The alcoholysis degree of the PVA polymer is 98-99.9%.

4. The method for preparing a PVA optical film for a waterless corrugated thin polarizer according to claim 1, characterized in that: The PVA polymer includes at least one of a polyvinyl alcohol homopolymer and a polyvinyl alcohol copolymer modified product.

5. The method for preparing a PVA optical film for a waterless corrugated thin polarizer according to claim 4, characterized in that: The modified groups in the polyvinyl alcohol copolymer modified product include at least one of olefins, acrylates, methacrylates, methacrylamide derivatives, vinyl esters, and halogenated vinyls.

6. The method for preparing a PVA optical film for a waterless corrugated thin polarizer according to claim 1, characterized in that: The plasticizer includes any one or more of glycerol, diglycerol, polyglycerol, ethylene glycol, and propylene glycol mixed in any proportion; The surfactant is a mixture of a nonionic surfactant and an anionic surfactant; The solvent is deionized water.

7. The method for preparing a PVA optical film for a waterless corrugated thin polarizer according to claim 1, characterized in that: In the film casting stock solution, the mass percentage of the plasticizer is 8-15%, and the mass percentage of the surfactant is 1.5-5.0‰.

8. The method for preparing a PVA optical film for a waterless corrugated thin polarizer according to claim 1, characterized in that: The heat treatment is divided into several stages, and the temperature of the several stages is 80-90°C.

9. The method for preparing a PVA optical film for a waterless corrugated thin polarizer according to claim 1, characterized in that: The moisture content of the film is 8-15%; The moisture content of the film after the heat treatment is 1-5%.

10. A PVA optical film for a waterless corrugated thin polarizer, characterized in that: The optical film is prepared by the method for preparing the PVA optical film for the waterless corrugated thin polarizer according to any one of claims 1 to 9.

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