Method for reducing bubbles in preparation process of polyvinyl alcohol film, application of method, polyvinyl alcohol film and application of polyvinyl alcohol film

Abstract

The invention relates to the technical field of polyvinyl alcohol optical thin film production, and discloses a method for reducing bubbles in a polyvinyl alcohol thin film preparation process, an application of the method, a polyvinyl alcohol thin film and an application of the polyvinyl alcohol thin film. The method comprises the following steps: heating and melting a polyvinyl alcohol melt through an extruder, extruding through a die head, and drying and forming through a casting roller; and the vacuum degree of an area formed among the die head, the partition plate and the casting roller is controlled to be-0.08 MPa to-0.01 MPa. According to the method, micro-negative pressure is formed in the area by controlling the vacuum degree of the area, so that the prepared polyvinyl alcohol film is relatively small in bubble number and low in optical defect.

Description

Technical Field

[0001] The present invention relates to the technical field of the production of polyvinyl alcohol optical films, and particularly relates to a method for reducing bubbles in the preparation process of polyvinyl alcohol films and applications thereof, a polyvinyl alcohol film and applications thereof. Background Art

[0002] A polarizer is an optical film, and the imaging of a liquid crystal display must rely on a polarizer. At present, a polarizer is manufactured by swelling, dyeing, stretching, crosslinking, fixing, and heat-treating a polyvinyl alcohol optical film to produce a polarizing film, and then laminating a protective film such as a cellulose triacetate (TAC) film on the surface of the polarizing film to manufacture a polarizer. Among them, the polyvinyl alcohol optical film mainly plays a polarizing role. Therefore, in order to ensure that the polarizer has good light transmittance and polarization degree, its main raw material, the polyvinyl alcohol optical film, must have a uniform thickness, a flat film surface, and no defects such as bubbles and holes.

[0003] The polyvinyl alcohol optical film is usually manufactured by heating and melting polyvinyl alcohol by an extruder, extruding it into a die head, and drying and forming it by a casting roller. It mainly consists of an extrusion device, a casting device, a drying device, a winding device, etc. Due to its characteristics of high production speed and high output, it has currently become the main production equipment for polyvinyl alcohol optical films.

[0004] At present, there is a certain gap between the die head extrusion part and the casting roller during the film forming process, and the entry of air will easily form bubbles inside the film. Although in the prior art, it is adjusted by reducing the die head gap, the improvement effect is not obvious, and the generation of bubbles still seriously affects the quality of the film. Summary of the Invention

[0005] The purpose of the present invention is to overcome the problem that bubbles are easily generated during the preparation process of polyvinyl alcohol films in the prior art, resulting in poor film quality, and to provide a method for reducing bubbles in the preparation process of polyvinyl alcohol films and applications thereof, a polyvinyl alcohol film and applications thereof. The method controls the vacuum degree of the area formed between the die head, the partition plate and the casting roller, so that a micro negative pressure is formed in this area, and the influence of environmental disturbance factors is reduced, which can make the prepared polyvinyl alcohol film have fewer bubbles and low optical defects.

[0006] To achieve the above purpose, the first aspect of the present invention provides a method for reducing bubbles in the preparation process of polyvinyl alcohol films, the method comprising:

[0007] Heating and melting polyvinyl alcohol melt by an extruder, extruding it through a die head, and then drying and forming it by a casting roller;

[0008] Controlling the vacuum degree of the area formed between the die head, the partition plate and the casting roller to be -0.08 MPa to -0.01 MPa.

[0009] The second aspect of the present invention provides a polyvinyl alcohol film prepared by the method described in the first aspect of the present invention.

[0010] The third aspect of the present invention provides an application of the method described in the first aspect or the film described in the second aspect of the present invention in the optical field.

[0011] Through the above technical solutions, the method and application for reducing bubbles in the preparation process of polyvinyl alcohol film, the polyvinyl alcohol film and the application provided by the present invention obtain the following beneficial effects: By controlling the vacuum degree in the area formed between the die head, the partition plate and the casting roller, the generation of bubbles during the film forming process can be effectively avoided, and at the same time, the influence of environmental disturbance is reduced, further reducing the number of transverse stripes during the film forming process and avoiding serious optical defects. Detailed Embodiments

[0012] In the ranges disclosed herein, the endpoints and any values are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values and individual point values of each range, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0013] The first aspect of the present invention provides a method for reducing bubbles in the preparation process of polyvinyl alcohol film, characterized in that the method includes:

[0014] Melting polyvinyl alcohol melt by heating through an extruder, extruding through a die head, and then drying and forming through a casting roller;

[0015] Controlling the vacuum degree in the area formed between the die head, the partition plate and the casting roller to be from -0.08 MPa to -0.01 MPa.

[0016] In the present invention, the inventors have found through research that during the preparation process of polyvinyl alcohol film, when the melt flows from the die to the casting roller to form a wet film, it is very easy to wrap gas and thus form bubbles on the film. In addition, the wet film is affected by factors such as environmental disturbance, resulting in the appearance of transverse stripes on the prepared film and affecting the optical properties.

[0017] The inventors further found through research that by controlling the vacuum degree in the area formed between the die head, the partition plate and the casting roller, the influence of environmental disturbance can be effectively reduced. Further controlling the vacuum degree in this area to meet -0.08 MPa to -0.01 MPa can reduce the generation of bubbles during the film forming process, and while ensuring a certain light transmittance, further reduce the number of transverse stripes during the film forming process and not generate longitudinal stripes.

[0018] According to the present invention, the vacuum degree in the region formed between the die head, the partition plate and the casting roller is -0.06 MPa to -0.02 MPa.

[0019] In the present invention, when the vacuum degree in the region formed between the die head, the partition plate and the casting roller satisfies -0.06 MPa to -0.02 MPa, the number of bubbles can be further reduced, and the optical defects of the film can be further reduced.

[0020] According to the present invention, the drying temperature is 88 - 98 °C.

[0021] In the present invention, the casting roller has a heating function and can cast the extruded melt into a film and dry it.

[0022] According to the present invention, the temperature in the region between the die head and the casting roller is controlled to be 88 - 98 °C.

[0023] In the present invention, the inventors found through research that controlling the temperature in the region between the die head and the casting roller to satisfy the above range can effectively prevent the volatiles from condensing and dripping onto the casting roller and the film surface, resulting in the formation of spot defects in the film. Among them, the volatiles are generally plasticizers added in the art, and the types and dosages of the plasticizers will not be elaborated here.

[0024] Further, the temperature in the region between the die head and the casting roller is controlled to be 90 - 97 °C.

[0025] According to the present invention, the distance between the die head and the casting roller ≤ 30 mm.

[0026] In the present invention, when the distance between the die head and the casting roller satisfies the above range and is combined with the method of the present invention, the generation of bubbles can be further reduced.

[0027] Further, the distance between the die head and the casting roller is 15 - 20 mm.

[0028] According to the present invention, the degree of alcoholysis of the polyvinyl alcohol ≥ 95 mol%.

[0029] Further, the degree of alcoholysis of the polyvinyl alcohol ≥ 99 mol%, preferably ≥ 99.3 mol%.

[0030] According to the present invention, the degree of polymerization of the polyvinyl alcohol is 1000 - 8000, preferably 2000 - 6000.

[0031] According to the present invention, the heating and melting temperature is 95 - 110 °C, preferably 100 - 105 °C.

[0032] The second aspect of the present invention provides a polyvinyl alcohol film prepared by the method described in the first aspect of the present invention.

[0033] According to the present invention, the tensile strength of the film is ≥60 MPa, preferably ≥80 MPa.

[0034] According to the present invention, the number of bubbles in the film is ≤4 per m 2 .

[0035] According to the present invention, the thickness of the film is 40 - 60 μm.

[0036] According to the present invention, the light transmittance of the film is ≥90%, preferably ≥91%.

[0037] According to the present invention, the haze of the film is ≤1%.

[0038] According to the present invention, the transverse stripes on the surface of the film are ≤3 per m 2 , preferably ≤1 per m 2 .

[0039] The third aspect of the present invention provides an application of the method described in the first aspect or the film described in the second aspect of the present invention in the optical field.

[0040] According to a specific embodiment of the present invention, the method for reducing bubbles in the preparation process of the polyvinyl alcohol film includes:

[0041] (1) Mix polyvinyl alcohol, plasticizer, surfactant and water in a ratio of 8 - 12:0.4 - 0.6:0.08 - 0.1:30 - 90 to prepare a film-forming stock solution. After degassing, it is extruded through an extruder after heating and melting to obtain a melt;

[0042] (2) The melt obtained in step (1) enters the die head for casting into a film. The temperature of the die head is controlled at 88 - 98 °C, and the vacuum degree in the area formed between the die head, the partition plate and the casting roller is adjusted to -0.08 MPa to -0.01 MPa, and the temperature is 88 - 98 °C. The preformed film is wound after subsequent drying and heat treatment to obtain a polyethylene film. Among them, the drying temperature is 60 - 80 °C, and the heat treatment conditions are 90 - 150 °C.

[0043] Among them, the plasticizer and the surfactant are both common plasticizers and surfactants in the art. For example, the plasticizer can be glycerol, and the surfactant can be at least one of sulfate anionic surfactants, sulfonate anionic surfactants, alkylamine nonionic surfactants, alkylamide nonionic surfactants and alkanolamide nonionic surfactants.

[0044] The present invention will be described in detail below through examples.

[0045] In the following examples, the tensile strength was measured by the method of GB / T 12683;

[0046] The number of bubbles, horizontal fine lines, and vertical fine lines in the film are measured by an on-line defect detector;

[0047] The light transmittance of the film is measured by the method of GB / T 2410;

[0048] The haze is measured by the method of GB / T 2410;

[0049] The thickness of the film is measured by a thickness gauge, where the measurement range is 0 mm - 0.2 mm and the resolution is 0.1 μm;

[0050] In the present invention, unless otherwise specified, the degree of alcoholysis of polyvinyl alcohol used in the examples and comparative examples is 99.8 mol% and the degree of polymerization is 2500.

[0051] Example 1

[0052] (1) 10 g of polyvinyl alcohol, 0.5 g of glycerol, 0.09 g of lauric acid diethanolamide, and 50 g of water are formulated into a film-forming stock solution. After degassing, it is extruded by an extruder after being heated and melted to obtain a melt;

[0053] (2) The melt obtained in step (1) enters the die head for casting film. The temperature of the die head is controlled at 92 °C, and the vacuum degree of the area formed between the die head, the baffle, and the casting roller is adjusted to -0.06 MPa, and the temperature is 90 °C. Among them, the distance between the die head and the casting roller is 20 mm. The preformed film is dried at 92 °C and heat-treated at 120 °C and then wound up to obtain a polyvinyl alcohol film A1 with a thickness of 50 μm and the thickness uniformity controlled within ±0.5 μm.

[0054] Example 2

[0055] According to the method of Example 1, the difference is that the vacuum degree of the area formed between the die head, the baffle, and the casting roller is adjusted to -0.04 MPa, and finally a film A2 with a thickness of 50 μm and the thickness uniformity controlled within ±0.5 μm is obtained.

[0056] Example 3

[0057] According to the method of Example 1, the difference is that the vacuum degree of the area formed between the die head, the baffle, and the casting roller is adjusted to -0.02 MPa, and finally a film A3 with a thickness of 50 μm and the thickness uniformity controlled within ±0.5 μm is obtained.

[0058] Example 4

[0059] According to the method of Example 1, the difference is that the temperature of the area formed between the die head, the baffle, and the casting roller is adjusted to 80 °C. Finally, a film A4 with a thickness of 50 μm and the thickness uniformity controlled within ±0.5 μm is obtained.

[0060] Example 5

[0061] According to the method of Example 1, the difference is that the distance between the die head and the casting roll is controlled to be 30 mm. Finally, film A5 with a thickness of 50 μm and a thickness uniformity controlled within ±0.5 μm is obtained.

[0062] Comparative Example 1

[0063] According to the method of Example 1, the difference is that the vacuum degree in the area formed by the die head, the partition plate and the casting roll is not controlled, that is, the vacuum degree is 0. Finally, film D1 with a thickness of 50 μm and a thickness uniformity controlled within ±0.5 μm is obtained.

[0064] Comparative Example 2

[0065] According to the method of Example 1, the difference is that the vacuum degree in the area formed by the die head, the partition plate and the casting roll is controlled to be -0.1 MPa. Finally, film D2 with a thickness of 50 μm and a thickness uniformity controlled within ±0.5 μm is obtained.

[0066] Table 1

[0067] Film <![CDATA[Number of bubbles / m 2 > <![CDATA[Number of stripes (horizontal) / m 2 > <![CDATA[Number of stripes (vertical) / m 2 > Light transmittance / % Haze / % A1 1 0 0 91.83 0.29 A2 2 1 0 91.52 0.33 A3 2 1 0 91.48 0.4 A4 3 1 0 91.17 0.58 A5 3 1 0 91.33 0.37 D1 7 2 1 90.15 1.5 D2 5 1 0 90.45 1.2

[0068] It can be seen from the results in Table 1 that the polyvinyl alcohol film has the ability to reduce the number of bubbles and has fewer film defects

[0069] Examples 1-5 using the method of the present invention have good effects. Among them, all the films have no longitudinal stripe defects, and the number of transverse stripes does not exceed 1 strip / m 2 , and at the same time, the number of bubbles does not exceed 5 bubbles / m 2 , the light transmittance is not less than 91.4%, and the haze is not less than 0.6%.

[0070] For Examples 1-3 that meet the preferred scheme of the present invention, more excellent effects are significantly obtained. The number of bubbles does not exceed 2 bubbles / m 2 , the light transmittance is not less than 91%, and the haze is not less than 0.4%.

[0071] 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 technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and all fall within the protection scope of the present invention.

Claims

1. A method for reducing bubbles in the preparation of polyvinyl alcohol films, characterized in that, the method comprises: heating and melting polyvinyl alcohol melt through an extruder, extruding through a die head, and then drying and forming through a casting roller; controlling the vacuum degree in the area formed between the die head, the partition plate and the casting roller to be -0.08 MPa to -0.01 MPa.

2. The method according to claim 1, wherein, controlling the vacuum degree in the area formed between the die head, the partition plate and the casting roller to be -0.06 MPa to -0.02 MPa; preferably, the drying temperature is 88 - 98 °C.

3. The method according to claim 1 or 2, wherein, controlling the temperature in the area between the die head and the casting roller to be 88 - 98 °C, preferably 90 - 97 °C.

4. The method according to any one of claims 1 - 3, wherein, the distance between the die head and the casting roller ≤ 30 mm, preferably 15 - 20 mm.

5. The method according to any one of claims 1 - 4, wherein, the degree of alcoholysis of the polyvinyl alcohol ≥ 95 mol%, preferably ≥ 99 mol%, more preferably ≥ 99.3 mol%.

6. The method according to any one of claims 1 - 5, wherein, the degree of polymerization of the polyvinyl alcohol is 1000 - 8000, preferably 2000 - 6000.

7. The method according to any one of claims 1 - 6, wherein, the temperature of the heating and melting is 95 - 110 °C, preferably 100 - 105 °C.

8. A polyvinyl alcohol film prepared by the method according to any one of claims 1 - 7.

9. The film according to claim 8, wherein, the tensile strength of the film ≥ 60 MPa, preferably ≥ 80 MPa; Preferably, the number of air bubbles in the film ≤ 4 per m 2 ; preferably, the film thickness is 40 - 60 μm; preferably, the light transmittance of the film ≥ 90%, preferably ≥ 91%; preferably, the haze of the film ≤ 1%; Preferably, the transverse stripes on the surface of the film are ≤ 3 / m 2 , preferably ≤ 1 / m 2 .

10. The application of the method according to any one of claims 1 - 7 or the film according to claim 8 or 9 in the optical field.