CN115782149A - Biaxially oriented polypropylene high-temperature-resistant coarsening film and preparation method thereof - Google Patents
Biaxially oriented polypropylene high-temperature-resistant coarsening film and preparation method thereof Download PDFInfo
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- CN115782149A CN115782149A CN202211448944.6A CN202211448944A CN115782149A CN 115782149 A CN115782149 A CN 115782149A CN 202211448944 A CN202211448944 A CN 202211448944A CN 115782149 A CN115782149 A CN 115782149A
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Abstract
The invention discloses a biaxially oriented polypropylene high-temperature-resistant coarsening film and a preparation method thereof, relating to the technical field of high polymer materials. According to the preparation method of the biaxially oriented polypropylene high-temperature-resistant coarsening film, the temperature parameters of each section in a production line are set, and the crystallization, stretching orientation and sizing of polypropylene molecules are controlled, so that the product performance suitable for the oil-impregnated high-pressure alternating current film foil capacitor is obtained, and the production of the biaxially oriented polypropylene high-temperature-resistant coarsening film with the high temperature resistance of 100 ℃ is realized. The film belongs to crystalline polypropylene resin, has strong temperature resistance, and is widely applied to the high-voltage alternating current film foil capacitor of the immersion oil for reactive power compensation of a power system.
Description
Technical Field
The invention relates to the technical field of high polymer materials, in particular to a biaxially oriented polypropylene high-temperature-resistant coarsening film and a preparation method thereof.
Background
The biaxially oriented polypropylene coarsened film is an ideal material for a solid insulating medium of a wet-type oil-immersed power capacitor, has high dielectric constant, high breakdown strength and low dielectric loss, has good impregnation performance, can thoroughly replace capacitor paper, can be used for manufacturing a full-film high-voltage oil-immersed power capacitor, and can greatly reduce the volume of the power capacitor. Therefore, biaxially oriented polypropylene roughened films have been used more and more widely in the power industry.
The coarsened film is a biaxially oriented polypropylene film with a coarsened surface. The production method has various methods, the production method which utilizes the transformation of beta crystals and adopts the flat film method to carry out bidirectional two-time stretching is the most common in the world at present, and the production is also carried out by the process in China. However, because the melting point of the polypropylene film is between 164 ℃ and 176 ℃, the high temperature resistance is always a weak item of the film, and when the test temperature is increased to 100 ℃, the pressure resistance can be obviously reduced.
Disclosure of Invention
The invention aims to provide a biaxially oriented polypropylene high-temperature-resistant coarsening film and a preparation method thereof, and solves the following technical problems:
the existing polypropylene resin material has poor high temperature resistance.
The purpose of the invention can be realized by the following technical scheme:
a preparation method of a biaxially oriented polypropylene high-temperature-resistant coarsening film comprises the following steps:
(1) Placing polypropylene resin in an extruder to prepare a polypropylene melt;
(2) Extruding a polypropylene melt, attaching one surface of the polypropylene melt to a chilling roller, cooling and solidifying the polypropylene melt, and cooling the other surface of the polypropylene melt by an air knife to prepare a polypropylene thick sheet;
(3) Longitudinally stretching the polypropylene thick sheet to prepare a longitudinally stretched film;
(4) And transversely stretching the film, then entering a traction roller station, and performing online thickness measurement, trimming and winding to obtain the polypropylene coarsening film.
As a further scheme of the invention: in the step (1), the polypropylene resin has a melt index of less than 3.5g/10min, a crystallinity of 40-50%, an ash content of less than 10ppm and an isotacticity of more than 98% at the temperature of 230 ℃/20 g.
As a further scheme of the invention: the polypropylene resin is dried by a resin drying system before being fed into the extruder.
As a further scheme of the invention: and (2) after the polypropylene resin sequentially passes through a metering pump, a filter and a melt pipeline in an extruder in the step (1), extruding the polypropylene resin through a T-shaped die head to obtain a polypropylene melt, wherein the extruder and the T-shaped die head adopt a double-extrusion and three-layer composite die head system.
As a further scheme of the invention: the extrusion temperature of the extruder is 210-235 ℃, and the T-shaped die head temperature of the extruder is 220-240 ℃.
As a further scheme of the invention: in the step (2), the chilling roller adopts a double-chilling-roller system, the temperature of the chilling roller is controlled to be 90-100 ℃, and the attaching time is 60-80s.
As a further scheme of the invention: the longitudinal stretching in the step (3) is specifically operated as follows: preheating the polypropylene thick sheet by a roller at 120-140 ℃, continuously passing through a roller at 140-150 ℃ and with speed difference, longitudinally stretching by taking the conveying direction of the polypropylene thick sheet as the longitudinal direction with the stretching ratio of 4-5 times, and then longitudinally heat-setting by the roller at 140-150 ℃.
As a further scheme of the invention: the number of longitudinally-drawn and stretched preheating rollers in the step (3) is 8.
As a further scheme of the invention: the transverse stretching in the step (4) is specifically operated as follows: the film is introduced into a transverse stretching machine, preheated at 165-175 ℃, passed through a transverse stretching area at 155-165 ℃, stretched transversely in a direction perpendicular to the film conveying direction at a transverse stretching ratio of 6-8 times, and then transversely heat-set through a heat-setting area at 160-170 ℃.
A biaxially oriented polypropylene high temperature resistant coarsened membrane is prepared by any one of the preparation methods.
The invention has the beneficial effects that:
(1) This application extruder and die head are through adopting two extrusion and compound die head systems, will extrude and divide into the main extrusion and assist and extrude, the main intermediate level of extruding the main control film, assist and extrude the ectonexine of main control film, through control main in the production process, assist the extrusion capacity ratio of extruding, extrude technological parameters such as the temperature setting of each section, realize the structure difference distribution of film inside and outside layer, when guaranteeing that the film top layer satisfies the alligatoring condition, improve the temperature resistance and the electrical property of film.
(2) The chilling roller is arranged, the polypropylene melt flowing out of the T-shaped die head is rapidly cooled and rapidly crystallized, and a cast sheet is formed. The cast sheet containing beta crystals is biaxially stretched at a temperature between the beta and alpha crystal melting points to induce surface roughening of the film. Control of surface roughness not only allows adjustment of the optical properties of the film, but is also important for thin film capacitor applications where a rough surface film can promote oil impregnation of the film foil capacitor. The invention adopts the double cold rollers, and the cast piece is molded by sequentially passing through the two cold rollers, so that both surfaces of the cast piece are cooled fully and uniformly, and the uniformity and the size control of the roughness of both surfaces are ensured.
(3) The longitudinal stretching of the application is divided into three stages, namely a preheating stage, a stretching stage and a shaping stage. According to the method, the number of the preheating rollers is increased from 6 to 8 on the basis of the existing process, and the function of rapid heating is realized. The first roller of the preheating section of the application selects lower temperature, starts from 120 ℃, and gradually increases, and when the last preheating roller is reached, the temperature is in the temperature interval of the beta crystal which just starts to melt. Mechanical breakdown of the beta crystals occurs when stretching is performed at a lower temperature, and the higher temperature in turn causes the beta crystals to nearly melt and recrystallize into alpha crystals, both of which cause the beta crystals to no longer exist before the film is unstretched. The stretching roll temperature is selected so that the beta crystals are molten but not yet recrystallized to form alpha crystals. If the stretching temperature is too low, the beta crystal on the surface can not be fully melted, which is not beneficial to the conversion of the beta crystal to the alpha crystal; if the temperature is too high, the film is too soft and sticky, and the film is easy to break. The preheating rate during longitudinal stretching also has a great influence on coarsening, rapid heating is favorable for coarsening, slow heating is unfavorable for beta-crystallization transformation during stretching, and the slab is preferably rapidly heated to a higher stretching temperature (150-155 ℃). This is because β crystal is unstable, and when the longitudinal drawing heating temperature reaches the melting point (145 ℃) or higher, β crystal is transformed to α crystal, and if heating is slow, the preheating time is long, and the slab is in contact with high temperature for a long time, so that β crystal is melted and recrystallized to α crystal in the preheating stage before drawing, and the crystalline transformation is completed. At the critical moment of stretching, however, no beta-crystal is melted and recrystallized, and no crystalline transformation and crystal breakage occur, thus being detrimental to the finish of the surface roughening of the film. If the heating is rapid, the slab is exposed to high temperatures for a short period of time, and the beta-crystals can only complete the melting process in the preheating stage before stretching, but not in time for recrystallization. This inhibits the beta-crystallization from re-crystallizing after melting in the preheating stage, so that the re-crystallization process occurs at a critical point in the drawing.
(4) In order to ensure continuous stretching, the longitudinal stretching ratio and the transverse stretching ratio are set according to the characteristics of the polypropylene resin, the stretching ratio is selected to be 35-40, the longitudinal stretching magnification is 4-5 times, and the transverse stretching magnification is 6-8.
(5) The high-temperature resistant coarsened polypropylene film belongs to crystalline olefin resin, the working temperature can reach 100 ℃, the film has better heat resistance and dielectric property than the conventional polypropylene film, and the excellent voltage resistance can be exerted under the temperature condition of 100 ℃, and the sum of the longitudinal heat shrinkage rate and the transverse heat shrinkage rate at 120 ℃ is 1.5-2.5%; the direct current electric breakdown strength of the biaxially oriented polypropylene film with the thickness of 12 mu m at the temperature of 100 ℃ is not lower than 550V/mu m; dielectric loss factor at frequencies above 1MHz<3×10 -4 。
Detailed Description
The following will clearly and completely describe the technical solutions in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Example 1
A preparation method of a biaxially oriented polypropylene high-temperature-resistant coarsening film comprises the following steps:
(1) Using polypropylene resin with the melt index of less than 3.5g/10min, the crystallinity of 40-50%, the ash content of less than 10ppm and the isotacticity of more than 98%, preheating the polypropylene resin before melting the resin, extruding the melt into sheets through a die head by double extrusion, a double metering pump, a filter and a melt pipeline, wherein the opening of the die lip is 0.9mm, and the temperature of the T-shaped die head is 240 ℃ to obtain polypropylene melt;
(2) The polypropylene melt is closely attached to a main chilling roller at the temperature of 90-100 ℃, cooled and solidified, and the back of the polypropylene melt is cooled by an auxiliary chilling roller to prepare a polypropylene thick sheet;
(3) In a longitudinal stretching area, the longitudinal preheating temperature is set to be 120-140 ℃, the longitudinal stretching temperature is kept at 140-150 ℃, the stretching is carried out for 5 times along the length direction, and then the longitudinal heat setting is carried out through a roller at 140-150 ℃ to obtain a film;
(4) The film is introduced into a transverse stretcher, preheated at 165-175 ℃, stretched 7.0 times in the width direction at 155-165 ℃, subjected to heat setting treatment at 160-170 ℃, and finally enters a drawing roll station, and subjected to online thickness measurement and edge cutting until the film is evenly wound on a steel winding core to prepare the polypropylene coarsening film.
Comparative example 1
The preparation method of the polypropylene film comprises the following steps:
(1) Placing polypropylene resin with melt index less than 3.5g/10min, crystallinity of 40-50%, ash content less than 10ppm and isotacticity greater than 98% in an extruder to obtain polypropylene melt;
(2) The polypropylene melt is closely attached to a main chilling roller at the temperature of 90-100 ℃, cooled and solidified, and the back of the polypropylene melt is cooled by an auxiliary chilling roller to prepare a polypropylene thick sheet;
(3) In a longitudinal stretching area, the longitudinal preheating temperature is set to be 120-140 ℃, the longitudinal stretching temperature is kept at 140-150 ℃ and the film is stretched by 5 times along the length direction, and then the film is longitudinally heat-set through a roller at 140-150 ℃ to obtain the film;
(4) The film is led into a transverse stretcher, the film is stretched by 7.0 times in the width direction under the condition of 155-165 ℃, and finally the film enters a drawing roller station, and is subjected to online thickness measurement and edge cutting until the film is evenly wound on a steel winding core to prepare the polypropylene film.
Comparative example 2
The preparation was carried out as in example 1, except that the extrusion was changed to a single extrusion system, to obtain a biaxially oriented polypropylene film of the same thickness.
Comparative example 3
The preparation method was the same as example 1 except that cooling of the cast sheet was changed to cooling by a single chill roll to obtain a biaxially oriented polypropylene film of the same thickness.
Comparative example 4
The difference compared with example 1 is that only 6 preheating rolls were used for longitudinal stretching.
And (3) performance detection:
(1) Average thickness (μm): according to the 4.1.1 mechanical single layer method in GB/T13542.2. Measuring 27 points of the whole test sample strip with the width of about 100mm at equal distance by using a thickness tester, taking the median value of 27 measured values as the average thickness, and obtaining the detection data shown in table 1;
(2) Roughness average (μm): the 27 points measured by the above measurement method reported the maximum and minimum values, and then the individual value deviations were found, and the results are shown in Table 1.
(3) Heat shrinkage (MD/TD 120 ℃ C.): the shrinkage rate test method in GB/T13542.2 is adopted as the standard. A100 mm x 100mm sample is taken from the film, the longitudinal and transverse dimensions of the sample are measured respectively to be accurate to 0.5mm, then the sample is put into an oven at 120 ℃ for 10min, the sample is taken out of the oven, the temperature is cooled to room temperature, the longitudinal and transverse dimensions of the sample are measured again, the thermal shrinkage rate is calculated again, and the detection result is shown in table 1.
(4) Breakdown strength of electric appliance at normal temperature (V/μm) and at 100 ℃ (V/μm): the method is based on a 50-point electrode method of 18.2.2 in GB/T13542.2. Under 150 ℃, adopting a single-layer sample test and adopting a continuous direct current boosting method, wherein the boosting speed is 200V/s, 50 points are uniformly measured at equal intervals, 5 points of the maximum value and the minimum value are respectively removed from the measured values of the 50 points, the arithmetic mean value of the other 40 points is calculated and used as the direct current electrical breakdown strength, and the detection result is shown in table 1;
(5) Dielectric loss tangent (1000 kHz): the method is subject to the method 1 of 17.1 in GB/T13542.2. The test frequency is 1000kHz, the test temperature is 23 +/-2 ℃, metal is evaporated in vacuum to be used as an electrode material, a measuring bridge is adopted for measurement, and the detection result is shown in Table 1.
Table 1: performance indices of the Polypropylene films prepared in examples 1-4
As can be seen from the numerical values in Table 1, the high-temperature-resistant roughened polypropylene film prepared by the preparation method has obvious advantage of high-temperature resistance at 100 ℃ compared with the conventional roughened polypropylene film, and the film can be used for capacitors for power transmission and transformation, locomotives and electric power in outdoor high-temperature environment.
While one embodiment of the present invention has been described in detail, the description is only a preferred embodiment of the present invention and should not be taken as limiting the scope of the invention. All equivalent changes and modifications made within the scope of the present invention shall fall within the scope of the present invention.
Claims (10)
1. A preparation method of a biaxially oriented polypropylene high-temperature-resistant coarsening film is characterized by comprising the following steps:
(1) Putting polypropylene resin into an extruder to prepare a polypropylene melt;
(2) Extruding a polypropylene melt, attaching one surface of the polypropylene melt to a chilling roller, cooling and solidifying the polypropylene melt, and cooling the other surface of the polypropylene melt by an air knife to prepare a polypropylene thick sheet;
(3) Longitudinally stretching the polypropylene thick sheet to obtain a longitudinally stretched film;
(4) And transversely stretching the film, then entering a traction roller station, and performing online thickness measurement, trimming and winding to obtain the polypropylene coarsening film.
2. The method for preparing the biaxially oriented polypropylene high temperature resistant roughened film according to claim 1, wherein in step (1), the polypropylene resin has a melt index of less than 3.5g/10min at 230 ℃/20g, a crystallinity of 40-50%, an ash content of less than 10ppm, and an isotacticity of > 98%.
3. The method for preparing the biaxially oriented polypropylene high temperature resistant roughened film according to claim 1, wherein the polypropylene resin is dried by a resin drying system before being fed into the extruder.
4. The method for preparing the biaxially oriented polypropylene high temperature resistant roughened film according to claim 1, wherein in step (1), the polypropylene resin is extruded through a T-shaped die after passing through a metering pump, a filter and a melt pipeline in sequence in an extruder to obtain a polypropylene melt, and the extruder and the T-shaped die adopt a double-extrusion and three-layer composite die system.
5. The method for preparing the biaxially oriented polypropylene high temperature resistant roughened film according to claim 4, wherein the extrusion temperature of the extruder is 210-235 ℃ and the T-die temperature of the extruder is 220-240 ℃.
6. The method for preparing the biaxially oriented polypropylene high-temperature-resistant coarsening film according to claim 1, wherein the chill roll in the step (2) adopts a double chill roll system, the temperature of the chill roll is controlled to be 90-100 ℃, and the attaching time is 60-80s.
7. The method for preparing the biaxially oriented polypropylene high temperature resistant roughened film according to claim 1, wherein the longitudinal stretching in step (3) is specifically performed by: preheating the polypropylene thick sheet by a roller at 120-140 ℃, continuously passing through a roller at 140-150 ℃ and with speed difference, longitudinally stretching by taking the conveying direction of the polypropylene thick sheet as the longitudinal direction with the stretching ratio of 4-5 times, and then longitudinally heat-setting by the roller at 140-150 ℃.
8. The method for preparing a biaxially oriented polypropylene high temperature resistant roughened film according to claim 7, wherein the number of longitudinally-stretched preheating rollers in step (3) is 8.
9. The method for preparing the biaxially oriented polypropylene high temperature resistant roughened film according to claim 1, wherein the transverse stretching in step (4) is specifically performed by: the film is introduced into a transverse stretching machine, preheated at 165-175 ℃, and passes through a transverse stretching area with the temperature of 155-165 ℃, the transverse stretching direction is vertical to the film conveying direction, the transverse stretching magnification is 6-8 times, and then transverse heat setting is carried out through a heat setting area with the temperature of 160-170 ℃.
10. A biaxially oriented polypropylene high temperature-resistant roughened film, characterized by being produced by the production method according to any one of claims 1 to 9.
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