Static mixer for homogenizing and temperature equalizing and method for preparing polyvinyl alcohol film by using static mixer

Abstract

The invention relates to the technical field of optical thin film manufacturing, in particular to a static mixer for homogenizing and temperature equalizing and a method for preparing a polyvinyl alcohol thin film by using the static mixer. The static mixer comprises an inner pipe, an outer sleeve and a high-precision temperature sensor. The static mixer disclosed by the invention adopts a dual heating mode of inner pipe electromagnetic heating and outer sleeve heating medium heating, and is matched with a plurality of high-precision temperature sensors to carry out high-precision point position temperature control, so that the problem of non-uniform temperature of existing equipment is solved, and the temperature range of a polyvinyl alcohol solution in a pipeline is controlled within 1 DEG C; the internal spiral structure optimizes the material mixing effect and improves the solution uniformity.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of optical film manufacturing, in particular to a static mixer for homogeneous temperature and a method for preparing a polyvinyl alcohol film by using the same. BACKGROUND

[0002] In the field of optical film manufacturing, polarizing film becomes one of the core components in the manufacturing process of display panels due to its unique linear polarization characteristics, and the performance of the polarizing film directly affects the display quality of the display panel. The polarizing film is prepared by a series of processes such as swelling, iodine dyeing and stretching, and the performance of the polyvinyl alcohol film as the base film for preparing the polarizing film is closely related to the performance of the polarizing film. The main factor restricting the further improvement of the performance of the polyvinyl alcohol film is the process uniformity. Poor uniformity not only affects the optical and physical properties of the film, but also reduces the overall production efficiency and the yield of the product. These technical problems restrict the further development of the high-performance polarizing film industry.

[0003] In the industrial manufacturing of polyvinyl alcohol film, the straight-through pipe with jacket heating is used for the pre-mold pipe, and the uneven heating inside and outside the polyvinyl alcohol solution flowing through the film is caused by the jacket heating. Further, the straight-through pipe with jacket heating is replaced by a general static mixer with jacket heating, and the continuous mixing and heat exchange of the flowing polyvinyl alcohol solution caused by the external heating and internal mixing can achieve the purpose of uniform mixing, but only relying on heat exchange, the temperature difference inside and outside the polyvinyl alcohol solution is still large, which is not preferred in industry.

[0004] In summary, the prior art lacks a pre-mold processing equipment and process that can simultaneously achieve precise temperature control and sufficient mixing, and it is difficult to solve the problem of poor uniformity of polyvinyl alcohol solution. Therefore, a new technical solution is needed to break through the above bottleneck. SUMMARY

[0005] In view of the problems of poor process uniformity and unstable film performance in the prior art of preparing polyvinyl alcohol film, the present application provides a static mixer for homogeneous temperature and a method for preparing polyvinyl alcohol film by using the same, which aims to optimize the structure of the pre-mold processing equipment and the process parameters, to realize the precise temperature control and sufficient mixing of the polyvinyl alcohol solution, to ultimately improve the optical performance and film thickness uniformity of the polyvinyl alcohol film, and to eliminate the horizontal and vertical stripe defects.

[0006] In order to achieve the above-mentioned purpose, in the first aspect, the present application provides a static mixer for homogeneous temperature, which comprises an inner tube, an outer sleeve and a high-precision temperature sensor; wherein, The outer sleeve is sleeved outside the inner tube, and a closed heat medium flow cavity is formed between the inner tube and the outer sleeve, two ends of the heat medium flow cavity are respectively provided with a heat medium inlet and a heat medium outlet, and the heat medium flow cavity is used for heating materials in the tube by circulating heat medium; The inner tube is composed of a spiral structure with electromagnetic heating function and a seamless steel tube, the spiral structure is fixedly arranged inside the seamless steel tube along the axial direction of the seamless steel tube, and the electromagnetic heating assembly of the spiral structure is electrically connected with an external power supply device through a wire to realize auxiliary heating of the materials in the inner tube. At least one high-precision temperature sensor is fixedly installed at the center of the inlet, the edge wall of the inlet, the center of the outlet, the edge wall of the outlet, the center of the pipe body of the static mixer, and the edge wall position corresponding to the center of the pipe body. The detection end of the high-precision temperature sensor extends into the material flow area in the tube, and directly contacts with the material to collect the material temperature data in real time.

[0007] Preferably, the working temperature of the static mixer is 85℃≤T≤95℃, preferably 89℃≤T≤92℃.

[0008] Preferably, the measurement accuracy of the high-precision temperature sensor is ±0.01~±1℃, and the response time is 0.1~2s.

[0009] In a second aspect, the application provides a method for preparing a polyvinyl alcohol film by using the static mixer, and the method comprises the following steps: S1, dissolving polyvinyl alcohol, a plasticizer and a surfactant in water to form a uniform polyvinyl alcohol solution; S2, after the polyvinyl alcohol solution in step S1 is filtered by an extruder, a melt pump and a secondary filter, the solution is conveyed to the static mixer for mixing and temperature equalization; S3, after the polyvinyl alcohol solution mixed and temperature equalized in step S2 is cast to a casting roller through a mold, the film is dried by a drying roller and heat treated by an oven in sequence to obtain a polyvinyl alcohol film; In step S2, the static mixer is the static mixer of the application.

[0010] Preferably, in step S1, the plasticizer is selected from one or two or more of propylene glycol, glycerol, ethylene glycol, triethylene glycol, tetraethylene glycol, glyceryl triacetate, polyglycerol and trihydroxymethyl propane, and preferably is glycerol.

[0011] Preferably, the surfactant is selected from one or two or more of lauric acid diethanolamide, octadecanamide, sodium dodecyl sulfonate, sodium dodecyl benzene sulfonate, sodium dodecyl sulfate, ammonium dodecyl sulfate, polyoxyethylene dodecyl amine, oleic acid diethanolamide and potassium polyether phosphate ester.

[0012] Preferably, the amount of the plasticizer added is 6-40 parts by weight, and the amount of the surfactant added is 0.001-0.1 parts by weight, relative to 100 parts by weight of the polyvinyl alcohol.

[0013] Preferably, the polyvinyl alcohol has a polymerization degree of 1600≤M≤3200, preferably 2000≤M≤2800, and an alcoholysis degree of 97-99.99%, preferably 99.9-99.99%.

[0014] Preferably, in step S1, the dissolving conditions include a temperature of 100-150℃, preferably 100-140℃, and a time of 4-48h, preferably 8-24h.

[0015] Preferably, in step S2, the mixing and temperature uniformizing conditions include a residence time of the polyvinyl alcohol solution in the static mixer of 1-10min, preferably 2-3min.

[0016] Preferably, in step S3, the polyvinyl alcohol solution after mixing and temperature uniformizing satisfies the following conditions: the polymerization degree, temperature and viscosity of the polyvinyl alcohol solution satisfy the index 0.2≤α≤1, preferably 0.4≤α≤0.5. wherein, , is the average value of the viscosity of the polyvinyl alcohol solution, is the average value of the temperature of the polyvinyl alcohol solution, and M is the polymerization degree of the polyvinyl alcohol solution.

[0017] Preferably, in step S3, the drying conditions include a temperature of 40-120℃, preferably 50-100℃.

[0018] Preferably, the heat treatment conditions include a temperature of 50-120℃, preferably 70-100℃.

[0019] Preferably, the temperature of the static mixer, the mold and the casting roller is controlled at 85-95℃, and the temperatures of the three can be the same or different.

[0020] In a third aspect, the present application provides a polyvinyl alcohol film prepared according to the method of the present application, the polyvinyl alcohol film having a thickness of 15-70μm, an average transmittance of ≥92%, an average haze of ≤0.05%, and a thickness range of ≤2μm.

[0021] In the above technical solution, the static mixer of the application adopts a double heating mode of internal tube electromagnetic heating and outer sleeve heating medium heating, and a plurality of high-precision temperature sensors are matched to perform high-precision point temperature control, so as to solve the temperature unevenness problem of the existing equipment, so that the temperature range of the polyvinyl alcohol solution in the pipeline is controlled within 1 DEG C, the internal spiral structure optimizes the material mixing effect, and the solution uniformity is improved.

[0022] According to the Arrhenius formula η = η 0 · e (E η / RT), the viscosity has a certain proportional relationship with the temperature, the viscosity has a decisive effect on the processability and uniformity of the prepared polyvinyl alcohol film, and in the case that the temperature range is extremely small, the polyvinyl alcohol solution has excellent viscosity uniformity. Assuming that the viscosity average of the polyvinyl alcohol solution is , the temperature average is , and the polymerization degree is M, a characteristic index is obtained, under the condition that the temperature of the static mixer is controlled at 85-95 DEG C, the temperature range of the polyvinyl alcohol solution is ΔT≤1 DEG C, the characteristic index of the polyvinyl alcohol solution is 0.2≤α≤1, and the viscosity range is Δη≤1500 mPa·s.

[0023] The method for preparing the polyvinyl alcohol film of the application limits the alpha value, viscosity range and other key parameters of the polyvinyl alcohol solution, and combines with the temperature cooperative control of the whole process at 85-95 DEG C, so as to ensure the stability of the film preparation process. The prepared polyvinyl alcohol film has an average transmittance of ≥92.0%, an average haze of ≤0.05%, a thickness range of ≤2 microns, and no obvious horizontal and vertical stripes, can meet the use requirements of high-performance polarizing film base film, and can improve the production yield, so that the application has a wide application prospect.

[0024] Other features and advantages of the application will be described in detail in the following specific embodiment part. BRIEF DESCRIPTION OF DRAWINGS

[0025] The accompanying drawings are used to provide a further understanding of the application, and constitute a part of the specification, and are used to explain the application together with the following specific embodiments, but do not constitute a limitation on the application. In the drawings: Figure 1 It is a two-dimensional plane schematic diagram of the static mixer of the application.

[0026] Explanation of reference signs DETAILED DESCRIPTION

[0027] The specific embodiments of the application are described in detail below. It should be understood that the specific embodiments described herein are only used to illustrate and explain the application, and are not used to limit the application.

[0028] The endpoints of the ranges and any values disclosed herein are not limited to the precise values recited as the exact dimensions are not critical to the invention. Any numeric range recited is intended to include all values from the lower value to the upper value, inclusive of both values, and to also include any value approximately or about the exact value.

[0029] In the present invention, the viscosity is the "internal friction strength" of the fluid that resists the relative movement of adjacent flow layers. The viscosity range is the difference between the maximum and minimum values of the viscosity flowing through the static mixer, which indirectly reflects the uniformity of the polyvinyl alcohol solution.

[0030] In the present invention, the viscosity test method is not strictly limited, and can be determined according to the online viscosity test method commonly used in the art. For example, the following method can be used: an online viscometer is installed inside the static mixer pipe, the online viscometer is used to measure the viscosity of the polyvinyl alcohol solution flowing out of the mold, and the obtained data is statistically calculated to obtain the range.

[0031] As shown in Figure 1 In a first aspect, the present invention provides a static mixer for homogeneous and uniform temperature, comprising an inner tube, an outer sleeve, and a high-precision temperature sensor; wherein, The outer sleeve is sleeved outside the inner tube, and a closed heat medium flow cavity is formed between the inner tube and the outer sleeve, and the two ends of the heat medium flow cavity are respectively provided with a heat medium inlet and a heat medium outlet for heating the material in the pipe by circulating heat medium; The inner tube is composed of a spiral structure with electromagnetic heating function and a seamless steel pipe, the spiral structure is fixedly arranged inside the seamless steel pipe along the axis direction of the seamless steel pipe, and the electromagnetic heating component of the spiral structure is electrically connected with the external power supply device through wires to realize auxiliary heating of the material in the inner tube; At least one high-precision temperature sensor is fixedly installed at the center of the inlet, the edge wall of the inlet, the center of the outlet, the edge wall of the outlet, the center position of the pipe body of the static mixer, and the edge wall position corresponding to the center of the pipe body; The detection end of the high-precision temperature sensor extends into the material flow circulation area in the pipe, and the detection end is in direct contact with the material for real-time collection of material temperature data.

[0032] The static mixer of this invention adopts a dual heating method of inner tube electromagnetic heating and outer tube heat medium heating, and is equipped with multiple high-precision temperature sensors for high-precision point temperature control, which solves the problem of uneven temperature in existing equipment. The temperature difference can be controlled within 1°C. The internal spiral structure optimizes the material mixing effect and improves the uniformity of the solution. While controlling the temperature uniformity of the polyvinyl alcohol solution flowing through the pipe, it continuously mixes the polyvinyl alcohol solution and further homogenizes it.

[0033] In a preferred embodiment of the present invention, the operating temperature of the static mixer is 85℃≤T≤95℃, preferably 89℃≤T≤92℃.

[0034] In a preferred embodiment of the present invention, the high-precision temperature sensor has a measurement accuracy of ±0.01~±1℃ and a response time of 0.1~2s.

[0035] Secondly, the present invention provides a method for preparing polyvinyl alcohol films using the static mixer described herein, the method comprising the following steps: S1. Dissolve polyvinyl alcohol, plasticizer and surfactant in water to form a homogeneous polyvinyl alcohol solution; S2. The polyvinyl alcohol solution from step S1 is transported to a static mixer for mixing and homogenization after passing through an extruder, a melt pump, and a secondary filter. S3. The polyvinyl alcohol solution mixed and heated in step S2 is cast onto a casting roller through a mold to form a film. After film formation, it is dried by a drying roller and then heat-treated in an oven to obtain a polyvinyl alcohol film. In step S2, the static mixer is the static mixer described in this invention.

[0036] The method for preparing polyvinyl alcohol (PVA) films of this invention ensures stable film preparation by limiting key parameters such as the α value and viscosity range of the PVA solution, combined with coordinated temperature control throughout the process at 85-95℃. This results in PVA films with an average transmittance ≥92.0%, an average haze ≤0.05%, a thickness range ≤2μm, and no obvious horizontal or vertical streaks. This meets the requirements for high-performance polarizing film base films, while simultaneously improving production yield and demonstrating broad application prospects.

[0037] In a preferred embodiment of the present invention, in step S1, the plasticizer is selected from one or more of propylene glycol, glycerol, ethylene glycol, triethylene glycol, tetraethylene glycol, triacetin, polyglycerol, and trimethylolpropane, preferably glycerol.

[0038] In a preferred embodiment of the present application, the surfactant is selected from one or two or more of lauric acid diethanolamide, octadecanamide, sodium dodecylsulfonate, sodium dodecylbenzenesulfonate, sodium dodecylsulfate, ammonium dodecylsulfate, polyoxyethylene dodecylamine, oleic acid diethanolamide, and potassium polyether phosphate ester.

[0039] In a preferred embodiment of the present application, the plasticizer is added in an amount of 6-40 parts by weight and the surfactant is added in an amount of 0.001-0.1 parts by weight, relative to 100 parts by weight of the polyvinyl alcohol.

[0040] In a preferred embodiment of the present application, the polyvinyl alcohol has a polymerization degree of 1600≤M≤3200, preferably 2000≤M≤2800, such as 1600, 1800, 2000, 2100, 2200, 2500, 2700, 2800, 3000, 3100 or 3200, and an alcoholysis degree of 97-99.99%, preferably 99.9-99.99%, such as 97%, 98%, 98.5%, 99%, 99.5%, 99.9%, 99.97% or 99.99%.

[0041] In a preferred embodiment of the present application, in step S1, the dissolving conditions include a temperature of 100-150°C, preferably 100-140°C, such as 100°C, 110°C, 115°C, 120°C, 130°C, 135°C, 140°C, 145°C or 150°C, and a time of 4-48h, preferably 8-24h, such as 4h, 6h, 8h, 10h, 12h, 14h, 16h, 20h, 22h, 24h, 28h, 30h, 35h, 40h or 48h.

[0042] In a preferred embodiment of the present application, in step S2, the mixing and temperature uniformizing conditions include a residence time of the polyvinyl alcohol solution in the static mixer of 1-10min, preferably 2-4min, such as 1min, 2min, 3min, 3.5min, 4min, 5min, 6min, 7min, 8min, 9min or 10min.

[0043] In a preferred embodiment of the present application, in step S3, the polyvinyl alcohol solution after mixing and temperature uniformizing satisfies the following condition: the polymerization degree, temperature and viscosity of the polyvinyl alcohol solution satisfy the index 0.2≤α≤1, preferably 0.4≤α≤0.5, where, , is the average viscosity of the polyvinyl alcohol solution, wherein T is the average temperature of the polyvinyl alcohol solution, M is the degree of polymerization of the polyvinyl alcohol solution, and a is an index, for example, a can be 0.2, 0.25, 0.3, 0.4, 0.45, 0.5, 0.6, 0.7, 0.8, 0.9, or 1.

[0044] In the present application, the static mixer of the present application is used to make the polyvinyl alcohol solution have an index a in the range of 0.2≤a≤1, a temperature range ΔT≤1℃, and a viscosity range Δη≤1500 mPa·s.

[0045] More preferably, the static mixer of the present application is used to make the polyvinyl alcohol solution have an index a in the range of 0.4≤a≤0.5, a temperature range ΔT≤0.5℃, and a viscosity range Δη≤1000 mPa·s.

[0046] In a preferred embodiment of the present application, in step S3, the drying conditions include a temperature of 40-120℃, preferably 50-100℃.

[0047] In a preferred embodiment of the present application, the heat treatment conditions include a temperature of 50-120℃, preferably 70-100℃.

[0048] In a preferred embodiment of the present application, the temperature of the static mixer, the die, and the casting roller is controlled in the range of 85-95℃, and the temperature of the three can be the same or different.

[0049] In a third aspect, the present application provides a polyvinyl alcohol film prepared by the method of the present application, wherein the polyvinyl alcohol film has a thickness of 15-70 μm, an average transmittance of ≥92%, an average haze of ≤0.05%, and a thickness range of ≤2 μm.

[0050] The present application will be described in detail below with examples. In the following examples, the drugs and reagents are all commercially available.

[0051] Example 1 (1) 100 parts by weight of polyvinyl alcohol (PVA) resin (degree of polymerization 2100, alcoholysis degree 99.97 mol%), 15 parts by weight of glycerol, and 0.01 parts by weight of lauric acid diethanolamide were dissolved in water in a dissolving tank, and stirred and dissolved at a temperature of 110℃ for 26 hours to form a uniform polyvinyl alcohol solution; (2) The uniform polyvinyl alcohol solution in step (1) was conveyed to a static mixer with internal and external heating after passing through an extruder, a melt pump, and a secondary filter, at a feeding rate of 300 kg / h, the jacketed heating medium temperature and the internal spiral electromagnetic heating temperature of the static mixer were both set to 85℃, and the residence time of the solution in the static mixer was 3 minutes; The temperature of each point was detected by 6 high-precision temperature sensors, and the results were 85.2℃ at the center of the inlet, 85.5℃ at the edge wall of the inlet, 85.1℃ at the center of the outlet, 85.2℃ at the edge wall of the outlet, 85.1℃ at the center of the mixer tube, and 85.4℃ at the edge wall of the tube center, the temperature difference ΔT was 0.2℃, the solution viscosity difference Δη was 954mPa·s, and the index α was 0.46; Temperature difference ΔT=T max -T min =85.5-85.1=0.4℃; According to the test results of the rotary viscometer, the solution viscosity difference Δη=η max -η min =912mPa·s; Index =0.53, wherein, is the average temperature, is the average solution viscosity, and M is the polymerization degree; (3) The solution after homogenization and temperature equalization in step (2) is transported to a 90℃ mold and cast onto a 90℃ casting roller to form a preliminary film. The preliminary film is first dried by a 85℃ drying roller, and then enters a 80℃ oven for heat treatment, and finally a polyvinyl alcohol film is obtained, which is recorded as B1.

[0052] Example 2 (1) Take 100 parts by weight of PVA resin (polymerization degree 2100, alcoholysis degree 99.97mol%), 15 parts by weight of glycerol and 0.01 parts by weight of lauric acid diethanolamide in a dissolving tank and dissolve in water, and stir and dissolve at a temperature of 110℃ for 26h to form a uniform polyvinyl alcohol solution; (2) The uniform polyvinyl alcohol solution in step (1) is transported to an internally and externally heated static mixer after passing through an extruder, a melt pump and secondary filtration, with a feeding rate of 300kg / h. The jacketed heat medium temperature and the internal spiral electromagnetic heating temperature of the static mixer are both set to 90℃, and the residence time of the solution in the mixer is 3min; The temperature of each point was detected by 6 high-precision temperature sensors, and the results were 85.2℃ at the center of the inlet, 85.5℃ at the edge wall of the inlet, 85.1℃ at the center of the outlet, 85.2℃ at the edge wall of the outlet, 85.1℃ at the center of the mixer tube, and 85.4℃ at the edge wall of the tube center, the temperature difference ΔT was 0.2℃, the solution viscosity difference Δη was 954mPa·s, and the index α was 0.46; (3) The solution after homogenization and temperature equalization in step (2) is transported to a 90℃ mold and cast onto a 90℃ casting roller to form a preliminary film. The preliminary film is first dried by a 85℃ drying roller, and then enters a 80℃ oven for heat treatment, and finally a polyvinyl alcohol film is obtained, which is recorded as B2.

[0053] Example 3 (1) 100 parts by weight of PVA resin (polymerization degree 2100, alcoholysis degree 99.97 mol%), 15 parts by weight of glycerol and 0.01 part by weight of lauric acid diethanolamide were dissolved in water in a dissolving tank, stirred and dissolved at a temperature of 110°C for 26h to form a uniform polyvinyl alcohol solution; (2) The uniform polyvinyl alcohol solution in step (1) was transported to an inner and outer heated static mixer at a feeding rate of 300 kg / h after passing through an extruder, a melt pump and secondary filtration, the jacketed heat medium temperature and the internal spiral electromagnetic heating temperature of the static mixer were set to 95°C, and the solution stayed in the mixer for 3 min; The temperature at each point was detected by 6 high-precision temperature sensors, and the results were 95.2°C at the center of the inlet, 95.1°C at the edge wall of the inlet, 95.3°C at the center of the outlet, 95.3°C at the edge wall of the outlet, 95.1°C at the center of the mixer tube, and 95.1°C at the edge wall of the center of the tube, the temperature difference ΔT was 0.2°C, the solution viscosity difference Δη was 954 mPa·s, and the index α was 0.46; (3) The solution after homogenization and temperature equalization in step (2) was transported to a 90°C mold and cast onto a 90°C casting roller to form a preliminary film; the preliminary film was first dried by a 85°C drying roller, and then heat treated in an 80°C oven to obtain a polyvinyl alcohol film, which is recorded as B3.

[0054] Example 4 (1) 100 parts by weight of PVA resin (polymerization degree M, alcoholysis degree 99.97 mol%), 15 parts by weight of glycerol and 0.01 part by weight of lauric acid diethanolamide were dissolved in water in a dissolving tank, stirred and dissolved at a temperature of 110°C for 26h to form a uniform polyvinyl alcohol solution; (2) The uniform polyvinyl alcohol solution in step (1) was transported to an inner and outer heated static mixer at a feeding rate of 450 kg / h after passing through an extruder, a melt pump and secondary filtration, the jacketed heat medium temperature and the internal spiral electromagnetic heating temperature of the static mixer were set to 90°C, and the solution stayed in the mixer for 2 min; The temperature at each point was detected by 6 high-precision temperature sensors, and the results were 90.3°C at the center of the inlet, 89.9°C at the edge wall of the inlet, 90.2°C at the center of the outlet, 90.4°C at the edge wall of the outlet, 90.2°C at the center of the mixer tube, and 90.2°C at the edge wall of the center of the tube, the temperature difference ΔT was 0.5°C, the solution viscosity difference Δη was 1095 mPa·s, and the index α was 0.48; (3) The solution homogenized and uniformly heated in step (2) is transported to a 90℃ mold, and cast onto a 90℃ casting roller to preliminarily form a film; the preliminarily formed film is first dried by a 85℃ drying roller, and then enters an 80℃ oven for heat treatment, to finally obtain a polyvinyl alcohol film, which is recorded as B4.

[0055] Example 5 (1) 100 parts by weight of polyvinyl alcohol (PVA) resin (degree of polymerization M, alcoholysis degree 99.97 mol%), 15 parts by weight of glycerol and 0.01 part by weight of lauric acid diethanolamide are taken in a dissolving tank, and stirred and dissolved at a temperature of 110℃ for 26h to form a uniform polyvinyl alcohol solution; (2) The uniform polyvinyl alcohol solution in step (1) is transported to an inner and outer heated static mixer after passing through an extruder, a melt pump and secondary filtration, with a feeding amount of 180kg / h; the jacketed heat medium temperature and the internal spiral electromagnetic heating temperature of the static mixer are both set to 90℃, and the residence time of the solution in the mixer is 5min; The temperature of each point is detected by 6 high-precision temperature sensors, and the results are respectively 90.3℃ at the center of the inlet, 89.9℃ at the edge wall of the inlet, 90.2℃ at the center of the outlet, 90.4℃ at the edge wall of the outlet, 90.2℃ at the center of the pipe body, and 90.2℃ at the edge wall of the pipe body, with a temperature difference ΔT of 0.5℃, a solution viscosity difference Δη of 968mPa·s, and an index α of 0.48; (3) The solution homogenized and uniformly heated in step (2) is transported to a 90℃ mold, and cast onto a 90℃ casting roller to preliminarily form a film; the preliminarily formed film is first dried by a 85℃ drying roller, and then enters an 80℃ oven for heat treatment, to finally obtain a polyvinyl alcohol film, which is recorded as B4.

[0056] Comparative Example 1 Jacketed heating straight pipe (1) 100 parts by weight of polyvinyl alcohol (PVA) resin (degree of polymerization M, alcoholysis degree 99.97 mol%), 15 parts by weight of glycerol and 0.01 part by weight of lauric acid diethanolamide are taken in a dissolving tank, and stirred and dissolved at a temperature of 110℃ for 26h to form a uniform polyvinyl alcohol solution; (2) The uniform polyvinyl alcohol solution in step (1) is transported to a jacketed heating straight pipe after passing through an extruder, a melt pump and secondary filtration, with a feeding amount of 300kg / h; the pipe jacket temperature is set to 90℃, and the residence time of the solution in the pipe is 3min; The temperature of each point is detected by 6 high-precision temperature sensors, and the results are respectively 90.3℃ at the center of the inlet, 89.9℃ at the edge wall of the inlet, 90.2℃ at the center of the outlet, 90.4℃ at the edge wall of the outlet, 90.2℃ at the center of the pipe body, and 90.2℃ at the edge wall of the pipe body, with a temperature difference ΔT of 0.5℃, a solution viscosity difference Δη of 968mPa·s, and an index α of 0.48; (3) The solution in step (2) is transported to a 90℃ mold and cast onto a 90℃ casting roller to preliminarily form a film; the preliminarily formed film is first dried by a drying roller at 85℃ and then heat treated in an oven at 80℃ to finally obtain a polyvinyl alcohol film, which is recorded as D1.

[0057] Comparative Example 2 Jacketed heating ordinary static mixer (1) 100 parts by weight of polyvinyl alcohol (PVA) resin (polymerization degree 2100, alcoholysis degree 99.97 mol%), 15 parts by weight of glycerol and 0.01 part by weight of lauric acid diethanolamide are dissolved in water in a dissolving tank to form a uniform polyvinyl alcohol solution by stirring and dissolving at a temperature of 110℃ for 26h; (2) The uniform polyvinyl alcohol solution in step (1) is transported to a jacketed heating ordinary static mixer at a feeding rate of 300kg / h after passing through an extruder, a melt pump and secondary filtration, and the mixer jacket temperature is set to 90℃, and the solution stays in the mixer for 3min; The temperature of the pipe wall and the center point in the pipe is detected, and the results are 90.5℃ for the pipe wall and 88.8℃ for the center point in the pipe, the temperature difference ΔT is 1.7℃, the solution viscosity difference Δη is 2056mPa·s, and the index α is 0.48; (3) The solution in step (2) is transported to a 90℃ mold and cast onto a 90℃ casting roller to preliminarily form a film; the preliminarily formed film is first dried by a drying roller at 85℃ and then heat treated in an oven at 80℃ to finally obtain a polyvinyl alcohol film, which is recorded as D2.

[0058] Detection Example 1 The polyvinyl alcohol films obtained in Examples 1-5 and Comparative Examples 1-2 are detected for optical properties, film thickness and stripe conditions, and the specific data are shown in Table 1.

[0059] Table 1

[0060] From the above content and the data in Table 1, it can be seen that Comparative Example 1 uses a jacketed straight pipe without internal heating and mixing structure, and only relies on external jacket heating, and the maximum temperature difference is 2.6℃; Comparative Example 2 uses an ordinary static mixer, which has a basic mixing structure, but no electromagnetic auxiliary heating and multi-point temperature control, and the temperature difference is still high at 1.7℃; Examples 1-5 use the temperature control static mixer of the application, which is heated by double heating of the inner tube electromagnetic heating and the outer sleeve heating medium, and is controlled by 6 high-precision point sensors, and the temperature difference is ≤0.5℃, which is much lower than that of the comparative examples.

[0061] Meanwhile, the data in Table 1 shows that the smaller the temperature range is, the more stable and higher the transmittance is. The transmittance of the comparative example 1 is 91.84% because the temperature fluctuation is large, the polyvinyl alcohol molecules in the solution are not uniformly dissolved and distributed, resulting in a decrease in the light transmittance of the film; the transmittance of the examples 1-5 is stable at 92.09-92.12%, close to the optimal light transmittance of the optical film, because the temperature range is small and the polyvinyl alcohol molecules are uniformly distributed. The temperature range is positively correlated with the haze. The temperature range of the comparative example 1 is 2.6°C, the local viscosity difference of the solution is large, and micro-bubbles and structural defects are generated in the film after forming, so the haze is as high as 0.283%; the temperature range of the examples 1-5 is ≤0.5°C, the solution is uniform, the lowest haze is only 0.014%, the film is more transparent, and the strict requirement of the polarizing film base film for low haze is met. The temperature range is the key factor leading to horizontal and vertical stripes. The comparative examples 1-2 form obvious horizontal and vertical stripes because the temperature fluctuation causes the flow rate and solidification rate of the solution to be uneven during the casting and film forming; the flow rate and solidification rate of the solution of the examples 1-5 are stable because the temperature is precisely controlled, and the stripe condition is qualified, which completely solves the stripe defect problem of the prior art.

[0062] In addition, the viscosity range is directly related to the temperature range and is regulated by the alpha value. The temperature range of the comparative example 1 is large, the alpha value is 0.49, which is close to the examples, but the viscosity range is as high as 4231 mPa·s; the alpha value of the comparative example 2 is 0.48, which is the same as that of the examples 2-5, but the viscosity range is 2056 mPa·s, which is still much higher than that of the examples; the alpha value of the examples 1-5 is stable at 0.46-0.53 in the optimal interval of 0.2≤α≤1 by temperature control, and the viscosity range is ≤1114 mPa·s, and the viscosity range of most examples is ≤1000 mPa·s.

[0063] The static mixer of the application breaks through the traditional single external heating design, and creates a structure of double heating and multi-point precise temperature control, achieving precise control of the temperature range ≤0.5°C. The problems of poor light transmittance, high haze and stripe defects caused by uneven temperature are solved from the root, the visual performance of the optical film is greatly improved, and the demand of the display panel for high transparency and defect-free base film is met.

[0064] The application proposes a regulation concept of the characteristic index by controlling the alpha value in the interval of 0.2-1 and combining the homogenizing effect of the mixer, the viscosity range is ≤1500 mPa·s, or even ≤1000 mPa·s. The problems of uneven film thickness and unstable film forming caused by the viscosity fluctuation in the prior art are solved, the production yield is improved, the production cost of the enterprise is reduced, and the market competitiveness of the product is enhanced.

[0065] The preferred embodiments of the present application are described in detail above, but the present application is not limited to the specific details of the above-described embodiments, and various simple modifications can be made to the technical solutions of the present application within the technical concept of the present application, and these simple modifications all belong to the protection scope of the present application.

[0066] In addition, it should be noted that each specific technical feature described in the above specific embodiments can be combined in any appropriate manner without contradiction, and in order to avoid unnecessary repetition, the present application will not further describe various possible combinations.

[0067] In addition, various different embodiments of the present application can also be combined in any manner, as long as it does not deviate from the idea of the present application, and it should also be considered as disclosed by the present application.

Claims

1. A static mixer for homogenous temperature equalization, characterized by, The static mixer comprises an inner tube, an outer sleeve and a high-precision temperature sensor, wherein The outer sleeve is sleeved outside the inner tube, and a closed heat medium flow cavity is formed between the inner tube and the outer sleeve, two ends of the heat medium flow cavity are respectively provided with a heat medium inlet and a heat medium outlet for heating the material in the tube by circulating heat medium; The inner tube is composed of a spiral structure with electromagnetic heating function and a seamless steel tube, the spiral structure is fixedly arranged inside the seamless steel tube along the axial direction of the seamless steel tube, and the electromagnetic heating component of the spiral structure is electrically connected with an external power supply device through a wire to realize auxiliary heating of the material in the inner tube; At least one high-precision temperature sensor is fixedly installed at the center of the inlet, the edge wall of the inlet, the center of the outlet, the edge wall of the outlet, the center of the tube body of the static mixer and the edge wall position corresponding to the center of the tube body, respectively; The detection end of the high-precision temperature sensor extends into the material flow area in the tube, and directly contacts with the material for real-time collection of material temperature data.

2. The static mixer of claim 1, wherein, The working temperature of the static mixer is 85℃≤T≤95℃, preferably 89℃≤T≤92℃; The measurement accuracy of the high-precision temperature sensor is ±0.01~±1℃, and the response time is 0.1~2s.

3. A method for producing a polyvinyl alcohol film using the static mixer according to claim 1 or 2, characterized by, The method comprises the following steps: S1, dissolving polyvinyl alcohol, plasticizer and surfactant in water to form a uniform polyvinyl alcohol solution; S2, after the polyvinyl alcohol solution in step S1 is filtered by an extruder, a melt pump and a secondary filter, it is conveyed to a static mixer for mixing and temperature equalization; S3, the polyvinyl alcohol solution after mixing and temperature equalization in step S2 is cast into a film on a casting roll, and then dried on a drying roll and heat treated in an oven to obtain a polyvinyl alcohol film; In step S2, the static mixer is the static mixer of claim 1 or 2.

4. The method of claim 3, wherein, In step S1, the plasticizer is selected from one or more of propylene glycol, glycerol, ethylene glycol, triethylene glycol, tetraethylene glycol, glyceryl triacetate, polyglycerol and trihydroxymethyl propane, and preferably is glycerol; The surfactant is selected from one or more of lauric acid diethanolamide, octadecanamide, sodium dodecyl sulfonate, sodium dodecyl benzene sulfonate, sodium dodecyl sulfate, ammonium dodecyl sulfate, polyoxyethylene dodecyl amine, oleic acid diethanolamide and potassium polyether phosphate ester; The addition amount of the plasticizer is 6~40 parts by weight and the addition amount of the surfactant is 0.001~0.1 parts by weight, relative to 100 parts by weight of polyvinyl alcohol; The polyvinyl alcohol has a polymerization degree of 1600≤M≤3200, preferably 2000≤M≤2800, and an alcoholysis degree of 97~99.99%, preferably 99.9~99.99%.

5. The method according to claim 3 or 4, characterized in that, In step S1, the dissolving conditions include a temperature of 100~150℃, preferably 100~140℃, and a time of 4~48h, preferably 8~24h.

6. The method according to any one of claims 3-5, characterized in that, In step S2, the mixing and temperature equalization conditions include a residence time of the polyvinyl alcohol solution in the static mixer of 1~10min, preferably 2~4min.

7. The method according to any one of claims 3-6, characterized in that, In step S3, the mixed and temperature-adjusted polyvinyl alcohol solution satisfies the following conditions: the degree of polymerization, temperature and viscosity of the polyvinyl alcohol solution satisfy the index 0.2≤α≤1, preferably 0.4≤α≤0.5; wherein , is the average value of the viscosity of the polyvinyl alcohol solution, is the average value of the temperature of the polyvinyl alcohol solution, M is the degree of polymerization of the polyvinyl alcohol solution.

8. The method according to any one of claims 3-7, characterized in that, In step S3, the drying conditions include: the temperature is 40~120℃, preferably 50~100℃; The heat treatment conditions include: the temperature is 50~120℃, preferably 70~100℃.

9. The method according to any one of claims 3-8, characterized in that, The temperatures of the static mixer, the mold and the casting roller are all controlled at 85~95℃, and the temperatures of the three can be the same or different.

10. A polyvinyl alcohol film produced according to the method of any one of claims 3 to 9, characterized in that, The polyvinyl alcohol film has a thickness of 15~70μm, an average transmittance of ≥92%, an average haze of ≤0.05%, and a thickness range of ≤2μm.

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