Polyvinyl alcohol film as well as preparation method and application thereof

Abstract

The invention relates to the field of optical films, and discloses a polyvinyl alcohol film as well as a preparation method and application thereof. The method comprises the following steps: S1, mixing polyvinyl alcohol and an additive to obtain a membrane preparation stock solution; and S2, extruding and shunting the membrane-making stock solution obtained in the step S1 to obtain slurry I and slurry II, mixing the slurry I with the membrane-making stock solution obtained in the step S1, and molding the slurry II. The preparation method of the polyvinyl alcohol film is simple in process and efficient, and the obtained polyvinyl alcohol film can have good uniformity and optical performance at the same time.

Description

Technical Field

[0001] The present invention relates to the field of optical films, and in particular to polyvinyl alcohol and a preparation method and application thereof. Background Art

[0002] Polyvinyl alcohol (PVA) is a widely used water-soluble polymer. The polyvinyl alcohol optical film made of it has good optical and mechanical properties. The polarizer made of polyvinyl alcohol optical film after stretching and dyeing is a key component of liquid crystal display and determines the imaging quality of liquid crystal display.

[0003] Currently, polyvinyl alcohol (PVA) is made into PVA optical film through water washing, dissolution, extrusion, and cast coating. However, the dissolution process has high requirements on equipment, and the existing equipment is not stable enough, which leads to the production process easily generating impurities such as gel and bubbles, affecting the uniformity of the solution, and further leading to problems such as poor uniformity and instability of the optical film, which seriously limits the application of the optical film.

[0004] Therefore, there is an urgent need to provide a method for preparing a PVA optical film that can improve the uniformity and stability of the PVA optical film. Summary of the invention

[0005] The purpose of the present invention is to overcome the problems of poor uniformity and instability of PVA optical films in the prior art, and to provide a polyvinyl alcohol film and a preparation method and application thereof. The preparation method of the polyvinyl alcohol film is simple and efficient, and the obtained polyvinyl alcohol film can have good uniformity and optical performance stability at the same time.

[0006] In order to achieve the above object, the present invention provides a method for preparing a polyvinyl alcohol film in a first aspect, comprising the following steps:

[0007] S1, mixing polyvinyl alcohol and additives to obtain a film-making stock solution;

[0008] S2. Extrude and split the film-forming stock solution obtained in step S1 to obtain slurry I and slurry II, mix the slurry I with the film-forming stock solution in step S1, and shape the slurry II.

[0009] Preferably, in step S2, the extrusion and diversion of the film-making solution is carried out in a screw extrusion device, which includes a screw extruder and an intermittent screw connected to the screw extruder, and the intermittent screw is provided with a first liquid outlet and a second liquid outlet. The slurry I flows out through the first liquid outlet and mixes with the film-making solution in step S1, and the slurry II flows out through the second liquid outlet and is then formed.

[0010] Preferably, the intermittent screw comprises a first thread segment, a hollow segment and a second thread segment connected in sequence, the first liquid outlet is arranged at the first thread segment, and the liquid inlet and the second liquid outlet of the intermittent screw are arranged at the hollow segment.

[0011] Preferably, in step S2, the weight ratio of the slurry I to the slurry II is 1:1-20, more preferably 1:1-10, and even more preferably 1:1-4.

[0012] Preferably, in step S2, the conditions for extrusion diversion include at least: extrusion temperature of 90-150°C, pressure of 0.2-3MPa, and rotation speed of 20-100rpm.

[0013] Preferably, in step S1, the moisture content of the polyvinyl alcohol is 10-50wt%, the degree of polymerization is 2000-3000, and the degree of alcoholysis is 99-99.99 mol%.

[0014] Preferably, the additive contains a plasticizer and / or a surfactant, more preferably a plasticizer and a surfactant.

[0015] Preferably, the plasticizer is selected from at least one of glycerol, triacetin, polyglycerol, ethylene glycol, polyethylene glycol, propylene glycol, citric acid and dimethyl sulfate.

[0016] Preferably, the surfactant is selected from at least one of sodium dodecylbenzene sulfonate, sodium dodecyl sulfonate, sodium dodecyl sulfate, ammonium dodecyl sulfate, polyoxyethylene oleyl ether, oleic acid diethanolamide, sodium lauryl polyoxyethylene ether sulfate and stearylamide.

[0017] Preferably, the weight ratio of the polyvinyl alcohol, the plasticizer and the surfactant is 100:5-15:0.001-0.1.

[0018] Preferably, the mixing conditions at least include: a temperature of 90-150° C., a pressure of 0.2-3 MPa, and a rotation speed of 5-50 rpm.

[0019] Preferably, in step S2, the forming process includes: coating and drying the slurry II.

[0020] Preferably, the drying includes first drying and second drying, and the conditions of the first drying include at least a temperature of 50-130°C; the conditions of the second drying include at least a temperature of 50-110°C.

[0021] The second aspect of the present invention provides a polyvinyl alcohol film obtained by the preparation method described in the first aspect.

[0022] Preferably, the wet tensile elongation of the polyvinyl alcohol film is greater than 700%, the light transmittance is greater than 91%, and the haze is less than 0.1%; the number of bubbles with a diameter of 10-30 μm contained in the polyvinyl alcohol film is no more than 1 / 500 m 2 The number of bubbles with a diameter of 50 μm or more is 0; the number of gels with a diameter of 10-30 μm or more contained in the polyvinyl alcohol film is not more than 1 / 500m 2 , the number of gels with a diameter of more than 50 μm is 0.

[0023] Preferably, the thickness of the polyvinyl alcohol film is less than 70 μm.

[0024] The third aspect of the present invention provides use of the polyvinyl alcohol film described in the second aspect in preparing a polarizer.

[0025] Through the above technical scheme, the preparation method of the polyvinyl alcohol film provided by the present invention first mixes polyvinyl alcohol and additives to obtain a film-making stock solution, extrude and split the film-making stock solution to obtain slurry I and slurry II, and by mixing slurry I with the film-making stock solution again, the uniformity of the slurry and the melting effect of the raw materials can be improved, thereby improving the uniformity and optical properties of the prepared polyvinyl alcohol film; and, by mixing slurry I with the film-making stock solution, cross-links can be formed between molecular chains in the polyvinyl alcohol film, enhancing the interaction between molecular chains, thereby improving the mechanical properties and stability of the polyvinyl alcohol film during processing. The preparation method is simple and efficient, easy to operate, and has significant economic benefits.

[0026] Other features and advantages of the present invention will be described in detail in the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a production process flow chart of the polyvinyl alcohol film of the present invention;

[0028] Figure 2 It is a structural schematic diagram of a specific implementation mode of the melting kettle in the present invention;

[0029] Figure 3 It is a structural schematic diagram of a specific implementation mode of the screw extruder in the present invention;

[0030] Figure 4 These are polarizing microscope images of the polyvinyl alcohol films obtained in Examples 1 to 6 and Comparative Examples 1 to 2 of the present invention, wherein Figure (1) is Example 1, Figure (2) is Example 2, Figure (3) is Example 3, Figure (4) is Example 4, Figure (5) is Example 5, Figure (6) is Example 6, Figure (7) is Comparative Example 1, and Figure (8) is Comparative Example 2.

[0031] Reference numerals

[0032] 1-screw extruder; 2-intermittent screw; 2a-first liquid outlet; 2b-second liquid outlet; 21-first thread segment; 22-hollow segment; 23-second thread segment; 3-melting kettle; 3a-first feed port; 3b-second feed port; 3c-third feed port. DETAILED DESCRIPTION

[0033] The endpoints and any values ​​of the ranges disclosed in this article 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 each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0034] In a first aspect, the present invention provides a method for preparing a polyvinyl alcohol film, comprising the following steps:

[0035] S1, mixing polyvinyl alcohol and additives to obtain a film-making stock solution;

[0036] S2. Extrude and split the film-forming stock solution obtained in step S1 to obtain slurry I and slurry II, mix the slurry I with the film-forming stock solution in step S1, and shape the slurry II.

[0037] During the research process, the inventors of the present invention unexpectedly discovered that by first mixing polyvinyl alcohol and additives to obtain a film-forming stock solution, and then extruding and diverting the film-forming stock solution to obtain slurry I and slurry II, and by mixing slurry I with the film-forming stock solution again, the uniformity of the slurry and the melting effect of the raw materials can be improved, thereby improving the uniformity and optical properties of the prepared polyvinyl alcohol film; moreover, by mixing slurry I with the film-forming stock solution, cross-links can be formed between molecular chains in the polyvinyl alcohol film, thereby enhancing the interaction between the molecular chains, thereby improving the mechanical properties and stability of the polyvinyl alcohol film during the processing.

[0038] In the present invention, there is no particular limitation on the device for extruding and diverting the film-making stock solution, as long as it can achieve the effect of extruding and diverting the film-making raw material. Preferably, in step S2, the extrusion and diversion of the film-making stock solution is carried out in a screw extruder, see Figure 1-Figure 3The screw extrusion device includes a screw extruder 1 and an intermittent screw 2 connected to the screw extruder 1. The intermittent screw 2 is provided with a first liquid outlet 2a and a second liquid outlet 2b. The slurry I flows out through the first liquid outlet 2a and mixes with the film-making stock solution in step S1. The slurry II flows out through the second liquid outlet 2b and is then formed. The film-making stock solution is extruded by the screw extruder 1 and enters the intermittent screw 2 to obtain slurry I and slurry II. The slurry I flows out from the first liquid outlet 2a of the intermittent screw 2 and mixes with the film-making stock solution in step S2 and then enters the screw extruder 1 again; the slurry II flows out from the second liquid outlet 2b of the intermittent screw 2 and is then formed. By remixing slurry I with the film-making stock solution and increasing the secondary degassing process of the slurry, the uniformity of the film-making stock solution can be improved, thereby improving the uniformity and optical properties of the polyvinyl alcohol film; moreover, slurry I can act as a cross-linking agent to promote the melting effect of the raw materials, form cross-links between molecular chains in the polyvinyl alcohol film, enhance the interaction between molecular chains, and improve the mechanical properties and stability of the polyvinyl alcohol film during the processing.

[0039] In the present invention, the screw extruder 1 can be a single screw extruder or a twin screw extruder. Preferably, the screw extruder 1 is a single screw extruder.

[0040] In the present invention, the screw extruder 1 may have 3 to 30 barrel sections.

[0041] According to the present invention, preferably, the intermittent screw 2 comprises a first thread segment 21, a hollow segment 22 and a second thread segment 23 connected in sequence, the first liquid outlet 2a is arranged at the first thread segment 21, and the liquid inlet and the second liquid outlet 2b of the intermittent screw 2 are arranged at the hollow segment 22. The material extruded by the screw extruder 1 enters the hollow segment 22 from the liquid inlet of the intermittent screw 2, and under the action of the first thread segment 21 and the second thread segment 22, part of the material (slurry I) is extruded through the first thread segment 21 and then flows out through the first liquid outlet 2a to mix with the film-making stock solution, and the other part of the material (slurry II) flows out through the second liquid outlet 2b, thereby achieving the slurry diversion effect.

[0042] In the present invention, preferably, the weight ratio of the slurry I to the slurry II is 1:1-20, specifically 1:1, 1:5, 1:10, 1:15, 1:20, or any value between the two aforementioned values. More preferably, it is 1:1-10, and more preferably, it is 1:1-4. The inventors have found that under this preferred embodiment, the slurry entering the intermittent screw 2 is subjected to the above-mentioned distribution, and a specific amount of slurry I is mixed again with the film-making stock solution in step S1, which further improves the uniformity of the slurry and the melting effect of the raw materials, thereby further improving the uniformity, mechanical properties and optical properties of the polyvinyl alcohol film.

[0043] According to the present invention, preferably, in step S2, the conditions for extrusion diversion include at least: the extrusion temperature is 90-150°C, specifically 90°C, 110°C, 130°C, 150°C, or any value between the foregoing two values; the pressure is 0.2-3MPa, specifically 0.2MPa, 1MPa, 2MPa, 3MPa, or any value between the foregoing two values; the rotation speed is 20-100rpm, specifically 20rpm, 40rpm, 60rpm, 80rpm, 100rpm, or any value between the foregoing two values.

[0044] According to the present invention, in order to further improve the uniformity, mechanical properties and optical properties of the polyvinyl alcohol film, preferably, the extrusion temperature is 110-140°C.

[0045] According to the present invention, preferably, in step S1, the moisture content of the polyvinyl alcohol is 10-50wt%, specifically 10wt%, 20wt%, 30wt%, 40wt%, 50wt%, or any value between the aforementioned two values; the degree of polymerization is 2000-3000, specifically 2000, 2500, 3000, or any value between the aforementioned two values; the degree of alcoholysis is 99-99.99 mol%, specifically 99 mol%, 99.5 mol%, 99.99 mol%, or any value between the aforementioned two values.

[0046] In the present invention, the method comprises: before the mixing in step S1, washing the polyvinyl alcohol with water. In this preferred embodiment, by washing the polyvinyl alcohol with water, small molecules therein can be eluted, further reducing the dissolution amount, thereby improving the uniformity of the polyvinyl alcohol film.

[0047] According to the present invention, preferably, the additive contains a plasticizer and / or a surfactant, and more preferably a plasticizer and a surfactant. The inventors have found that under this preferred embodiment, the synergistic effect of the plasticizer and the surfactant can improve the dissolution or melting of polyvinyl alcohol, improve the ductility and peelability of the polyvinyl alcohol film, and further improve the uniformity, mechanical properties and optical properties of the polyvinyl alcohol film.

[0048] In the present invention, the plasticizer can be a plasticizer conventionally selected in the art. In order to further improve the dissolution or melting effect of polyvinyl alcohol and the uniformity, mechanical properties and optical properties of the polyvinyl alcohol film, preferably, the plasticizer is selected from at least one of glycerol, triacetin, polyglycerol, ethylene glycol, polyethylene glycol, propylene glycol, citric acid and dimethyl sulfate, and glycerol is more preferably used.

[0049] In the present invention, the surfactant may be a surfactant conventionally selected in the art. In order to further improve the peelability of the polyvinyl alcohol film and the uniformity, mechanical properties and optical properties of the polyvinyl alcohol film, preferably, the surfactant is selected from at least one of sodium dodecylbenzene sulfonate, sodium dodecyl sulfonate, sodium dodecyl sulfate, ammonium dodecyl sulfate, polyoxyethylene oil ether, oleic acid diethanolamide, sodium lauryl polyoxyethylene ether sulfate and octadecanoamide, and sodium dodecyl sulfate is further preferred.

[0050] The above substances can be purchased from commercial sources or prepared by oneself.

[0051] According to the present invention, preferably, the weight ratio of the polyvinyl alcohol, the plasticizer and the surfactant is 100:5-15:0.001-0.1. The inventors found that under this preferred embodiment, the synergistic effect between the polyvinyl alcohol, the plasticizer and the surfactant in the above specific dosage ratio can further improve the uniformity, mechanical properties and optical properties of the polyvinyl alcohol film.

[0052] According to the present invention, in order to further improve the mixing effect between polyvinyl alcohol, plasticizer and surfactant and the uniformity of polyvinyl alcohol film, preferably, in step S1, the mixing conditions at least include: temperature of 90-150°C, extrusion temperature of 90-150°C, specifically 90°C, 110°C, 130°C, 150°C, or any value between the above two values; pressure of 0.2-3MPa, specifically 0.2MPa, 1MPa, 2MPa, 3MPa, or any value between the above two values; speed of 5-50rpm, specifically 5rpm, 30rpm, 50rpm, or any value between the above two values. There is no special limitation on the mixing time, as long as the raw materials can be melted, and the test personnel can adjust it according to the specific situation.

[0053] In the present invention, the mixing of polyvinyl alcohol, plasticizer and surfactant can be carried out in a mixing device conventionally selected in the art. Preferably, see Figure 1 and Figure 2The mixing device is a melting kettle 3, which has a screw and a stirring rod inside. The melting kettle 3 is provided with a first feed port 3a, a second feed port 3b and a third feed port 3c. The third feed port 3c is connected to the first liquid outlet 2a on the intermittent screw 2, and the outlet of the melting kettle 3 is connected to the feed port of the screw extruder 1. The screw and the stirring rod in the melting kettle 3 make the raw materials mixed in the melting kettle 3, the additives (plasticizer and surfactant) are added to the melting kettle 3 from the first feed port 3a, the polyvinyl alcohol is added to the melting kettle 3 from the second feed port 3b, and the slurry I flowing out from the first liquid outlet 2a is added to the melting kettle from the third feed port 3c, thereby improving the uniformity of the mixing of the polyvinyl alcohol film raw materials and promoting the melting effect of the raw materials.

[0054] According to the present invention, a conventional shaping method in the art can be used. In order to further improve the shaping effect and product performance of the polyvinyl alcohol film, preferably, in step S2, the shaping process includes: coating and drying the slurry II.

[0055] In the present invention, the method further comprises: filtering the slurry II before coating and drying the slurry II. In this preferred embodiment, insoluble impurities in the slurry II can be removed, the impurity content in the polyvinyl alcohol film can be reduced, and the uniformity of the polyvinyl alcohol film can be further improved. There is no particular limitation on the filtering method in the present invention, and a filtering method well known to those skilled in the art can be used.

[0056] In the present invention, coating can be performed by a coating method conventionally selected in the art. For example, the coating process includes: coating the slurry II on a rotating drum or a steel belt.

[0057] According to the present invention, in order to further improve the forming effect of the polyvinyl alcohol film, preferably, the drying includes a first drying and a second drying, and the conditions of the first drying include at least: a temperature of 50-130°C, specifically 50°C, 100°C, 130°C, or any value between the foregoing two values; the conditions of the second drying include at least: a temperature of 50-110°C, specifically 50°C, 80°C, 110°C, or any value between the foregoing two values.

[0058] According to the present invention, in order to further improve the forming effect of the polyvinyl alcohol film, preferably, after the first drying and the second drying, the moisture content of the polyvinyl alcohol film is made to be 1-5wt%, specifically 1wt%, 2wt%, 3wt%, 4wt%, 5wt%, or any value between the above two values.

[0059] According to the present invention, in order to further improve the forming effect of the polyvinyl alcohol film, preferably, the first drying adopts multi-roll drying and the second drying adopts oven drying. The inventors found that under this preferred embodiment, the number of bubbles and gels in the polyvinyl alcohol film can be reduced, the occurrence of wrinkle defects can be reduced during the winding and output process, and the uniformity of the polyvinyl alcohol film can be further improved.

[0060] According to a particularly preferred embodiment of the present invention, a method for preparing a polyvinyl alcohol film is provided, the method comprising the following steps:

[0061] S1, polyvinyl alcohol, plasticizer and surfactant are mixed in a weight ratio of 100:5-15:0.001-0.1 at a temperature of 90-150° C., a pressure of 0.2-3 MPa and a rotation speed of 5-50 rpm to obtain a film-forming stock solution;

[0062] S2, extruding and splitting the film-making stock solution obtained in step S1 at a temperature of 110-140° C. and a pressure of 0.2-3 MPa to obtain slurry I and slurry II, mixing slurry I with the film-making stock solution in step S1, and coating and drying slurry II; the drying includes a first drying and a second drying, and the conditions of the first drying include at least: a temperature of 50-130° C.; the conditions of the second drying include at least: a temperature of 50-110° C.;

[0063] The weight ratio of slurry I to slurry II is 1:1-4; the moisture content of polyvinyl alcohol is 10-50wt%, the degree of polymerization is 2000-3000, and the degree of alcoholysis is 99-99.99 mol%; the plasticizer is selected from at least one of glycerol, triacetin, polyglycerol, ethylene glycol, polyethylene glycol, propylene glycol, citric acid and dimethyl sulfate; the surfactant is selected from at least one of sodium dodecylbenzene sulfonate, sodium dodecyl sulfonate, sodium dodecyl sulfate, ammonium dodecyl sulfate, polyoxyethylene oil ether, oleic acid diethanolamide, sodium lauryl polyoxyethylene ether sulfate and octadecylamide;

[0064] The extrusion and diversion of the film-making stock solution is carried out in a screw extrusion device, which includes a screw extruder 1 and an intermittent screw 2 connected to the screw extruder 1. The intermittent screw 2 is provided with a first liquid outlet 2a and a second liquid outlet 2b. Slurry I flows out through the first liquid outlet 2a and is mixed with the film-making stock solution in step S1. Slurry II flows out through the second liquid outlet 2b and is then formed; the intermittent screw 2 includes a first thread segment 21, a hollow segment 22 and a second thread segment 23 which are connected in sequence. The first liquid outlet 2a is provided at the first thread segment 21, and the liquid inlet and the second liquid outlet 2b of the intermittent screw 2 are provided at the hollow segment 22.

[0065] In the above preferred embodiment, the prepared polyvinyl alcohol film has good uniformity and optical stability, and also has good mechanical properties. The preparation method is simple and efficient, easy to operate, and has significant economic benefits.

[0066] In a second aspect, the present invention provides a polyvinyl alcohol film obtained by the preparation method described in the first aspect.

[0067] According to the present invention, preferably, the wet tensile elongation of the polyvinyl alcohol film is greater than 700%, the light transmittance is greater than 91%, and the haze is less than 0.1%; the number of bubbles with a diameter of 10-30 μm or more contained in the polyvinyl alcohol film is not greater than 1 / 500 m 2 The number of bubbles with a diameter of 50 μm or more is 0; the number of gels with a diameter of 10-30 μm or more contained in the polyvinyl alcohol film is not more than 1 / 500m 2 , the number of gels with a diameter of more than 50 μm is 0. The polyvinyl alcohol film having the above wet tensile rate, light transmittance, haze, and the above number of bubbles and gels has good uniformity, mechanical properties and optical properties, and has significant market prospects.

[0068] In the present invention, the wet tensile elongation at break of the polyvinyl alcohol film is measured by an elongation at break tester, and the measuring method refers to CN115855659A "PVA film tensile performance testing device and testing method", and the transmittance and haze are measured by a haze meter, and the measuring method refers to the national standard "GB / T 2410-2008 Determination of transmittance and haze of transparent plastics".

[0069] In the present invention, the polyvinyl alcohol film provided is mainly used for the preparation of polarizers. If the thickness of the polyvinyl alcohol film is too thin, the optical performance of the polarizer will be insufficient. If the film is too thick, it will be difficult to meet the requirements of lightness and thinness. Preferably, the thickness of the polyvinyl alcohol film is less than 70μm.

[0070] In the present invention, the thickness of the polyvinyl alcohol film is tested according to the method in "HG / T 4185-2011 Polyvinyl alcohol (PVA) film for polarizer".

[0071] In a third aspect, the present invention provides use of the polyvinyl alcohol film described in the second aspect in preparing a polarizer.

[0072] The present invention is described in detail below with reference to the embodiments, but the scope of the present invention is not limited thereby.

[0073] In the following examples, polyvinyl alcohol with a degree of polymerization of 2300 and a saponification degree of 99.99 mol% was purchased from Inner Mongolia Shuangxin Environmental Protection Materials Co., Ltd., model SG-01 。 Unless otherwise specified, other raw materials or reagents are conventional commercially available products.

[0074] In the following embodiments, the screw extrusion device includes a screw extruder 1 and an intermittent screw 2 connected to the screw extruder 1, the intermittent screw 2 is provided with a first liquid outlet 2a and a second liquid outlet 2b, the intermittent screw 2 includes a first thread segment 21, a hollow segment 22 and a second thread segment 23 connected in sequence, the first liquid outlet 2a is arranged at the first thread segment 21, the second liquid outlet 2b is arranged at the hollow segment 21, the melting kettle 3 is provided with a first feed port 3a, a second feed port 3b and a third feed port 3c, the third feed port 3c is connected to the first liquid outlet 2a on the intermittent screw 2, and the discharge port of the melting kettle 3 is connected to the feed port of the screw extruder 1.

[0075] Example 1

[0076] (1) 100 parts by mass of PVA (degree of polymerization: 2300, degree of saponification: 99.99 mol%) with a moisture content of 20 wt%, 10 parts by mass of glycerol as a plasticizer, and 0.1 parts by mass of sodium dodecyl sulfate as a surfactant were added to a melting kettle 3 (the maximum temperature of the jacket of the melting kettle was 140° C., the rotation speed was 30 rpm, and the pressure was 1.5 MPa) to obtain a film-forming stock solution;

[0077] (2) The film-making stock solution is transported to the intermittent screw 2 through the screw extruder 1 (the temperature of the screw extruder 1 and the intermittent screw 2 is 120°C, and the pressure is 1.8 MPa). A portion of the film-making stock solution (slurry I) entering the intermittent screw 2 is returned to the melting kettle 1 through the first liquid outlet 2a set at the upper end of the intermittent screw 2 for further mixing to achieve uniform mixing and eliminate bubbles; the other portion of the film-making stock solution (slurry II) entering the intermittent screw 2 is mixed and discharged through the second liquid outlet 2b set at the intermittent screw 2, and then passes through the melt pump; wherein the weight ratio of slurry I to slurry II is 1:4;

[0078] (3) The above-mentioned film-forming stock solution (slurry II) is filtered using a filter, and then the polyvinyl alcohol film-forming stock solution is cast onto a casting drum using a gear pump and a die coater, and formed into a polyvinyl alcohol film through high-temperature drying. The polyvinyl alcohol film is then peeled off from the casting drum and subjected to an oven heat treatment to obtain a polyvinyl alcohol film.

[0079] Example 2

[0080] (1) 100 parts by mass of PVA (degree of polymerization: 2300, degree of saponification: 99.99 mol%) with a moisture content of 25 wt%, 12 parts by mass of glycerol as a plasticizer, and 0.1 parts by mass of sodium dodecyl sulfate as a surfactant were added to a melting kettle 3 (the maximum temperature of the jacket of the melting kettle was 130° C., the rotation speed was 25 rpm, and the pressure was 1.4 MPa) to obtain a film-forming stock solution;

[0081] (2) The film-making stock solution is transported to the intermittent screw 2 through the screw extruder 1 (the temperature of the screw extruder 1 and the intermittent screw 2 is 110°C, 1.6MPa), and a part of the film-making stock solution (slurry I) entering the intermittent screw 2 is returned to the melting kettle 1 through the first liquid outlet 2a set at the upper end of the intermittent screw 2 for further mixing to achieve uniform mixing and eliminate bubbles; another part of the film-making stock solution (slurry II) entering the intermittent screw 2 and mixed evenly flows out through the second liquid outlet 2b set at the intermittent screw 2, and then passes through the melt pump; wherein, the weight ratio of slurry I to slurry II is 1:4;

[0082] (3) The above-mentioned film-forming stock solution (slurry II) is filtered using a filter, and then the polyvinyl alcohol film-forming stock solution is cast onto a casting drum using a gear pump and a die coater, and formed into a polyvinyl alcohol film through high-temperature drying. The polyvinyl alcohol film is then peeled off from the casting drum and subjected to an oven heat treatment to obtain a polyvinyl alcohol film.

[0083] Example 3

[0084] (1) 100 parts by mass of 30 wt% PVA (degree of polymerization: 2300, degree of saponification: 99.99 mol%), 10 parts by mass of glycerol as a plasticizer, and 0.05 parts by mass of sodium dodecyl sulfate as a surfactant were added to a melting kettle 3 (the jacket temperature of the melting kettle was 130° C., the rotation speed was 20 rpm, and the pressure was 1.5 MPa) to obtain a film-forming stock solution;

[0085] (2) The film-making stock solution is transported to the intermittent screw 2 through the screw extruder 1 (the temperature of the screw extruder 1 and the intermittent screw 2 is 110° C., and the pressure is 1.6 MPa. A portion of the film-making stock solution (slurry I) entering the intermittent screw 2 is returned to the melting kettle 1 through the first liquid outlet 2a provided at the upper end of the intermittent screw 2 for further mixing to achieve uniform mixing and eliminate bubbles; another portion of the film-making stock solution (slurry II) entering the intermittent screw 2 and mixed evenly flows out through the second liquid outlet 2b provided at the intermittent screw 2, and then passes through the melt pump; wherein, the weight ratio of slurry I to slurry II is 1:2;

[0086] (3) The above-mentioned film-forming stock solution is filtered using a filter (slurry II), and then the polyvinyl alcohol film-forming stock solution is cast onto a casting drum using a gear pump and a die coater, and formed into a polyvinyl alcohol film through high-temperature drying. The polyvinyl alcohol film is then peeled off from the casting drum and subjected to an oven heat treatment to obtain a polyvinyl alcohol film.

[0087] Example 4

[0088] A polyvinyl alcohol optical film was prepared according to the method of Example 1, except that in step (1), the jacket temperature of the melting kettle was replaced to 110°C, and the temperatures of the screw extruder 1 and the intermittent screw 2 were replaced to 100°C.

[0089] Example 5

[0090] A polyvinyl alcohol film optical film was prepared according to the method of Example 1, except that in step (2), the weight ratio of slurry I to slurry II was replaced with 1:10.

[0091] Example 6

[0092] A polyvinyl alcohol optical film was prepared according to the method of Example 1, except that in step (1), polyvinyl alcohol was replaced by polyvinyl alcohol having a moisture content of 20%, a degree of polymerization of 2300, and a degree of alcoholysis of 98 mol%, purchased from Inner Mongolia Shuangxin Environmental Protection Materials Co., Ltd., model SG-01.

[0093] Comparative Example 1

[0094] Preparation of film-forming stock solution: 100 parts by mass of 25wt% PVA (degree of polymerization: 2300, degree of saponification: 99.99 mol%), 10 parts by mass of glycerol as a plasticizer, and 0.1 parts by mass of sodium dodecyl sulfate as a surfactant are fully dissolved in a dissolving kettle to obtain a film-forming stock solution; then the above-mentioned film-forming stock solution is coarsely filtered and extruded through an extruder (100°C, 0.5MPa); the above-mentioned film-forming stock solution is filtered using a filter, and then a gear pump and a die coater are used to cast the polyvinyl alcohol film-forming stock solution onto a casting drum, and a polyvinyl alcohol film is formed through high-temperature drying, and then the polyvinyl alcohol film is peeled off from the casting drum, and a polyvinyl alcohol film is obtained through heat treatment in an oven.

[0095] Comparative Example 2

[0096] The polyvinyl alcohol optical film was prepared according to the method of Example 1, except that the extrusion and diversion device of the film-making stock solution was eliminated, that is, the first liquid outlet 2a provided on the intermittent screw 2 was not subjected to the reflux process (it was in a closed state).

[0097] Test Case

[0098] The polyvinyl alcohol optical films prepared in Examples 1 to 6 and Comparative Examples 1 to 2 were heated to 500 m 2 The number of gels and bubbles in the film was tested, and the results are shown in Table 1; the polarizing microscope images of the polyvinyl alcohol films prepared in Examples 1 to 6 and Comparative Examples 1 to 2 are shown in Figure 4 ,in, Figure 4 (1) is Example 1, Figure 4 (2) is Example 2, Figure 4 (3) is Example 3, Figure 4 (4) is Example 4, Figure 4 (5) is Example 5, Figure 4 (6) is Example 6, Figure 4(7) is Comparative Example 1, Figure 4 (8) is Comparative Example 2; the wet tensile elongation, light transmittance, haze and specifications (length, width and thickness) of the polyvinyl alcohol optical films prepared in Examples 1 to 6 and Comparative Examples 1 to 2 were tested, and the results are shown in Table 1.

[0099] Table 1

[0100]

[0101] It can be seen from the results in Table 1 that, compared with Comparative Examples 1 and 2, the polyvinyl alcohol optical films prepared by the method provided by the present invention in Examples 1 to 6 can simultaneously have good uniformity, mechanical properties and optical properties. Moreover, the preparation method is simple and efficient, and easy to operate.

[0102] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A method for preparing a polyvinyl alcohol film, characterized in that: The following steps are involved: S1, mixing polyvinyl alcohol and additives to obtain a film-making stock solution; S2. Extrude and split the film-forming stock solution obtained in step S1 to obtain slurry I and slurry II, mix the slurry I with the film-forming stock solution in step S1, and shape the slurry II.

2. The preparation method according to claim 1, characterized in that: In step S2, the extrusion and diversion of the film-forming stock solution is carried out in a screw extrusion device, which includes a screw extruder (1) and an intermittent screw (2) connected to the screw extruder (1), and the intermittent screw (2) is provided with a first liquid outlet (2a) and a second liquid outlet (2b). The slurry I flows out through the first liquid outlet (2a) and is mixed with the film-forming stock solution in step S1, and the slurry II flows out through the second liquid outlet (2b) and is then formed.

3. The preparation method according to claim 2, characterized in that: The intermittent screw (2) comprises a first thread segment (21), a hollow segment (22) and a second thread segment (23) which are connected in sequence; the first liquid outlet (2a) is arranged at the first thread segment (21); and the liquid inlet and the second liquid outlet (2b) of the intermittent screw (2) are arranged at the hollow segment (21).

4. The preparation method according to claim 1, characterized in that: In step S2, the weight ratio of the slurry I to the slurry II is 1:1-20, more preferably 1:1-10, and even more preferably 1:1-4.

5. The preparation method according to any one of claims 1 to 4, characterized in that: In step S2, the conditions for extrusion diversion include at least: extrusion temperature of 90-150°C, pressure of 0.2-3MPa, and rotation speed of 20-100rpm.

6. The preparation method according to any one of claims 1 to 3, characterized in that: In step S1, the moisture content of the polyvinyl alcohol is 10-50wt%, the degree of polymerization is 2000-3000, and the alcoholysis degree is 99-99.99 mol%; Preferably, the additive contains a plasticizer and / or a surfactant, more preferably a plasticizer and a surfactant; Preferably, the plasticizer is selected from at least one of glycerol, triacetin, polyglycerol, ethylene glycol, polyethylene glycol, propylene glycol, citric acid and dimethyl sulfate; Preferably, the surfactant is selected from at least one of sodium dodecylbenzene sulfonate, sodium dodecyl sulfonate, sodium dodecyl sulfate, ammonium dodecyl sulfate, polyoxyethylene oleyl ether, oleic acid diethanolamide, sodium lauryl polyoxyethylene ether sulfate and octadecylamide; Preferably, the weight ratio of the polyvinyl alcohol, the plasticizer and the surfactant is 100:5-15:0.001-0.1; Preferably, the mixing conditions include at least: a temperature of 90-150° C., a pressure of 0.2-3 MPa, and a rotation speed of 5-50 rpm.

7. The preparation method according to any one of claims 1 to 3, characterized in that: In step S2, the molding process includes: coating and drying the slurry II; Preferably, the drying includes first drying and second drying, and the conditions of the first drying include at least a temperature of 50-130°C; the conditions of the second drying include at least a temperature of 50-110°C.

8. The polyvinyl alcohol film obtained by the preparation method according to any one of claims 1 to 7.

9. The polyvinyl alcohol film according to claim 8, characterized in that The wet tensile elongation of the polyvinyl alcohol film is greater than 700%, the light transmittance is greater than 91%, and the haze is less than 0.1%; the number of bubbles with a diameter of 10-30 μm contained in the polyvinyl alcohol film is not more than 1 / 500 m 2 The number of bubbles with a diameter of 50 μm or more is 0; the number of gels with a diameter of 10-30 μm or more contained in the polyvinyl alcohol film is not more than 1 / 500m 2 , the number of gels with a diameter of more than 50 μm is 0; Preferably, the thickness of the polyvinyl alcohol film is less than 70 μm.

10. Use of the polyvinyl alcohol film according to claim 8 in preparing polarizers.

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