Production method of low-winding polypropylene film

Abstract

The method for producing a low-rewind polypropylene film comprises the following steps: extruding a melt from a die head; blowing the melt onto a cold roller to form a cast sheet, winding the cast sheet cooled by the cold roller onto a stripping roller, and the stripping roller drives the cast sheet to be stripped off from the cold roller; stretching, stretching the stripped cast sheet, and performing shaping and cooling after stretching into a film. During shaping and cooling, a first nozzle blows a first airflow toward the front of the film, and a second nozzle blows a second airflow toward the back of the film, and the cooling amount of the second airflow is greater than that of the first airflow in the same time; and a polypropylene film is formed after the film is cooled. The present invention controls the temperature difference between the front and back of the cast sheet in the longitudinal direction by setting the temperature difference between the cold roller and the stripping roller, controls the temperature difference between the front and back of the film during shaping and cooling, and rolls the polypropylene film with the back facing the reel when rolling. Multiple processes are used to neutralize and inhibit the warping caused by the shrinkage of the cast sheet toward the cold roller during the rapid cooling of the cast sheet during the production of the polypropylene film.

Description

Technical Field

[0001] The invention relates to the field of polypropylene films, in particular to a production method of a low-rewinding polypropylene film. Background Art

[0002] The edge of the capacitor element made of metallized polypropylene film will curl after baking. After analysis, the different shrinkage rates of the front and back sides of the polypropylene film itself, the shrinkage deformation of the product due to moisture absorption, the poor thickness uniformity of the polypropylene film, the wrinkles / rebound during the curling process of the product, and the process of evaporating the metal film will all affect the edge curling of the metallized polypropylene film. The edge curling of the capacitor element will make the shape of the capacitor difficult to control, and the circuit will be distorted or the noise will increase. A polypropylene film that can improve the edge curling of the capacitor element is needed. Summary of the invention

[0003] The object of the present invention is to overcome the above-mentioned disadvantages and provide a method for producing a low-winding polypropylene film.

[0004] To achieve the above object, the technical solution of the present invention is: a method for producing a low-winding polypropylene film, comprising the following steps:

[0005] Rapidly cool the casting sheet, melt the polypropylene raw material and extrude the melt from the die head; use an air knife to blow the melt onto a cold roller to form a casting sheet, with the front side of the casting sheet attached to the cold roller; rotate the cold roller to transport the casting sheet, and the casting sheet is cooled on the cold roller; the casting sheet cooled on the cold roller is wound around the stripping roller with the back side attached to the stripping roller, and the temperature of the stripping roller is lower than that of the cold roller; the stripping roller drives the casting sheet to be stripped off from the cold roller;

[0006] Stretching, stretching the stripped cast sheet, stretching it into a film and then cooling it. During cooling, the first nozzle blows a first airflow toward the front of the film, and the second nozzle blows a second airflow toward the back of the film. The cooling amount of the second airflow is greater than that of the first airflow in the same time. After the film is cooled, a polypropylene film is formed;

[0007] Trimming, cutting the side edges of the polypropylene film formed after stretching to make the side edges flush;

[0008] Thickness measurement: measure the thickness of the polypropylene film after trimming;

[0009] Corona treatment: corona treatment is performed on one side of the trimmed polypropylene film;

[0010] Winding: Winding the corona treated polypropylene film.

[0011] When the front side of the cast sheet is attached to the cold roller for cooling, the shrinkage of the front side of the cast sheet is greater than that of the back side, and the cast sheet bends toward the front side. The temperature of the stripping roller of the present invention is lower than that of the cold roller, so that the cast sheet stripped from the cold roller shrinks toward the back side under the cooling of the stripping roller. By controlling the flow rate of the first airflow ejected from the first nozzle and the flow rate of the second airflow ejected from the second nozzle, the cooling rate of the front and back sides of the polypropylene film after stretching is controlled, so that the polypropylene film bends toward the back side, so as to offset the tendency of the cast sheet produced by attaching the melt to the cold roller to rapidly cool the cast sheet to bend toward the front side. After the offset, the produced polypropylene film has a low rewinding effect.

[0012] Preferably, in the stretching step, the cast sheet is first stretched longitudinally and then stretched transversely;

[0013] Longitudinal stretching includes the following steps:

[0014] Longitudinal preheating, the cast sheet is wound around a preheating roller group for heating; the preheating roller group includes a first preheating roller and a second preheating roller, the temperature of the first preheating roller is higher than that of the second preheating roller, the front side of the cast sheet is attached to the first preheating roller and wound around the first preheating roller, and the back side of the cast sheet is attached to the second preheating roller and wound around the second preheating roller;

[0015] Longitudinal stretching, the preheated cast sheet is wound around a stretching roller group for stretching; the stretching roller group includes a first stretching roller and a second stretching roller, the temperature of the first stretching roller is higher than that of the second stretching roller, the front side of the cast sheet is close to the first stretching roller and is wound around the first stretching roller, and the back side of the cast sheet is close to the second stretching roller and is wound around the second stretching roller;

[0016] Longitudinal stretching and shaping, the stretched casting sheet is wound around a shaping roller group for shaping; the shaping roller group includes a first shaping roller and a second shaping roller, the temperature of the first shaping roller is higher than that of the second shaping roller, the front side of the casting sheet is attached to the first shaping roller and wound around the first shaping roller, and the back side of the casting sheet is attached to the second shaping roller and wound around the second shaping roller;

[0017] Transverse stretching: clamp the two sides of the longitudinally stretched cast sheet and stretch the cast sheet transversely to both sides to form a film.

[0018] In the longitudinal preheating step, by controlling the temperature of the first preheating roller and the second preheating roller, the temperature of the front side of the casting sheet is greater than the temperature of the back side, and the expansion amount of the front side of the casting sheet is greater than the expansion amount of the back side. In the longitudinal stretching step, by controlling the temperature of the first stretching roller and the second stretching roller, the temperature of the front side of the casting sheet is greater than the temperature of the back side during stretching, and the front side of the front side of the casting sheet is easier to stretch. In the longitudinal shaping step, by controlling the temperature of the first shaping roller and the second shaping roller, the temperature of the front side of the casting sheet is greater than the temperature of the back side, and the expansion amount of the front side of the casting sheet is greater than the expansion amount of the back side. The longitudinal stretching step neutralizes the tendency of the casting sheet to curl toward the front side in the quenching step, and the tendency of the casting sheet to curl toward the front side after stretching becomes smaller or does not curl.

[0019] Preferably, the transverse stretching comprises the following steps:

[0020] Horizontal stretching preheating: clamp the two sides of the longitudinally stretched casting with the clips on the conveyor line, and the conveyor line conveys the casting to the horizontal stretching preheating zone. The horizontal stretching preheating zone blows preheating hot air to the front of the casting and blows preheating hot air to the back of the casting to heat the casting. The heat of the upper preheating hot air is greater than the heat of the lower preheating hot air.

[0021] Transverse stretching: the conveyor line transports the casting to the transverse stretching area. The clips on both sides of the casting stretch the casting horizontally to form a film. The transverse stretching area blows upward stretching hot air to the front of the casting and blows downward stretching hot air to the back of the casting to heat the casting. The heat of the upward stretching hot air is greater than the heat of the downward stretching hot air.

[0022] Horizontal stretching and shaping: the conveyor line transports the film to the horizontal stretching and shaping area. The horizontal stretching and shaping area blows shaping hot air to the front of the film and blows shaping hot air to the back of the film. The heat of the upper shaping hot air is greater than that of the lower shaping hot air.

[0023] In the transverse preheating step, the heat of the upper preheating hot air is greater than the heat of the lower preheating hot air, and the temperature of the front side of the casting is greater than the temperature of the back side of the casting; in the transverse stretching step, the heat of the upper stretching hot air is greater than the heat of the lower stretching hot air, and the front side of the casting is more easily stretched during the transverse stretching process; in the transverse shaping step, the heat of the upper shaping hot air is greater than the heat of the lower shaping hot air, and the temperature of the front side of the film is greater than the temperature of the back side, and the tendency of the film to curl toward the front after shaping is neutralized.

[0024] Preferably, in the winding step, the back side of the polypropylene film is faced to the roll and is wound on the roll. The polypropylene film is wound with the back side facing the roll, which can resist the tendency of the polypropylene film to curl toward the front side.

[0025] Preferably, a lip is provided at the lower part of the die head, and the melt is extruded from the lip. A movable adjustment block and an electric control nut for driving the adjustment block to move are provided on the die head. One end of the adjustment block extends to the lip position, and the movable adjustment block can adjust the size of the lip.

[0026] In the thickness measurement step, the radiation head emits radiation to the film, the receiving head receives the radiation passing through the film and calculates the real-time thickness of the film according to the attenuation of the radiation, the control device compares the real-time thickness with the pre-stored standard thickness to obtain the compensation thickness, and the control device controls the electric control nut to drive the adjustment block to move according to the compensation thickness to adjust the size of the lip. The control device can adjust the thickness of the melt when it is extruded from the die head according to whether the thickness of the film meets the design requirements.

[0027] Preferably, when the cast sheet is rapidly cooled, a cooling device is provided on the outside of the cold roller, and the cooling device includes a box body, an air inlet pipe, and an air suction pipe. An arc surface is provided at one end of the box body, and the arc surface is arranged opposite to the cold roller. An air inlet cavity and an air suction cavity are provided in the box body, and the air inlet pipe is connected to the air inlet cavity, and the air suction pipe is connected to the air suction cavity. The arc surface is provided with a blowing hole connected to the air inlet cavity and an air suction hole connected to the air suction cavity. When the cold roller rotates counterclockwise, the density of the blowing holes on the arc surface gradually decreases along the clockwise direction, and the air suction holes are arranged on the clockwise side of the blowing holes. The cooling device is used to blow cooling gas to the back of the cast sheet on the cold roller to reduce the tendency of the cast sheet to curl from the front to the front due to the large temperature difference between the front and back of the cast sheet when the cast sheet is extremely cooled on the cold roller.

[0028] Preferably, in the cross-drawing preheating step,

[0029] The light source illuminates the casting sheet from a first angle, and the image acquisition module acquires an image of the position on the casting sheet illuminated by the light source and generates a product image;

[0030] The image processing module divides the image data into multiple sub-images according to the area size, and analyzes each sub-image to determine whether the film thickness corresponding to the sub-image exceeds the threshold value. When the film thickness corresponding to the sub-image exceeds the threshold value, the image processing module generates sub-image coordinate information;

[0031] The control device drives the heat source to heat the film position corresponding to the sub-image coordinate information according to the sub-image coordinate information. The heat source can be a hot air nozzle or an infrared light source, and the film wall thickness position is heated by hot pressing.

[0032] Preferably, the temperature of the cold roll is 85° C.-95° C., and the temperature of the air knife is less than 85° C. The temperature of the air knife is lower than the temperature of the cold roll, which can reduce the temperature difference between the front and back sides of the casting sheet.

[0033] By adopting the above technical scheme, the beneficial effects of the present invention are as follows: the present invention sets the temperature difference between the cold roller and the stripping roller, controls the temperature difference between the front and back sides of the casting sheet in the longitudinal direction, controls the temperature difference between the front and back sides of the film during shaping and cooling, and rolls the polypropylene film with the back side facing the reel when rolling it up. Multiple processes are used to neutralize and inhibit the warping caused by the casting sheet shrinking toward the cold roller during the rapid cooling of the casting sheet during the production of the polypropylene film. The polypropylene film produced by the present invention is flat and has no curling phenomenon. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a structural schematic diagram of the present invention;

[0035] Figure 2 This is a schematic diagram of the rapid cooling of the cast sheet in Example 1 of the present invention;

[0036] Figure 3 It is a schematic diagram of the structure of the present invention during longitudinal stretching;

[0037] Figure 4 It is a schematic diagram of the structure of the present invention during transverse stretching;

[0038] Figure 5 This is a schematic diagram of the rapid cooling of the cast sheet in Example 2 of the present invention;

[0039] Figure 6 It is a schematic structural diagram of the cooling device of the present invention;

[0040] Figure 7 It is a schematic diagram of the internal structure of the cooling device of the present invention;

[0041] Figure 8 This is a schematic diagram of the structure of Example 2 of the present invention during transverse drawing preheating.

[0042] Description of main reference numerals:

[0043] Die 11; lip 111; adjustment block 112; air knife 12; cold roller 13; stripping roller 14; cooling device 2; box 21; blowing hole 22; air inlet cavity 23; air suction cavity 24; air inlet pipe 25; air suction pipe 26; air suction hole 27; arc surface 28; air flow cavity 29; stretching device 3; preheating roller group 31; first preheating roller 311; second preheating roller 312; stretching roller group 32; first stretching roller 321; second stretching roller 322; shaping roller group 33; first shaping roller 331; second shaping roller 332; transverse preheating zone 34; transverse stretching zone 35; transverse shaping zone 36; casting sheet 4; film 41; control device 5; light source 63; image acquisition module 64; heat source 65; first nozzle 71; second nozzle 72. DETAILED DESCRIPTION

[0044] The present invention is further described below with reference to the accompanying drawings and specific embodiments.

[0045] Example 1

[0046] like Figure 1-Figure 4 As shown, the production method of the low-winding polypropylene film of the present invention comprises the following steps:

[0047] S1 quenches the cast sheet, melts the polypropylene raw material and extrude the melt from the die head 11; the melt extrusion temperature is 240℃-260℃. Figure 4 As shown, a lip 111 is provided at the lower part of the die head 11, and the melt is extruded from the lip. A movable adjusting block 112 and an electrically controlled nut for driving the adjusting block to move are provided on the die head 11. One end of the adjusting block extends to the lip position. The movable adjusting block 112 can adjust the size of the lip, thereby adjusting the thickness of the melt during extrusion.

[0048] The melt is blown onto the cold roller 13 by the air knife 12 to form a casting sheet 4, with the front side of the casting sheet 4 attached to the cold roller 13; the cold roller is rotated to transport the casting sheet, and the casting sheet 4 is cooled on the cold roller 13, and the temperature of the cold roller is 91.5°C. The casting sheet 4 cooled by the cold roller is wound around the stripping roller with the back side attached to the stripping roller, and the temperature of the stripping roller 14 is lower than that of the cold roller, and the temperature of the stripping roller 14 is 80°C-85°C; the stripping roller 14 drives the casting sheet 4 to be stripped off from the cold roller 13.

[0049] S2 stretching, stretching the stripped casting sheet, first stretching the casting sheet longitudinally, and then stretching it transversely. Figure 3 As shown, longitudinal stretching includes the following steps:

[0050] S2-1 longitudinal pulling preheating, the casting 4 is wrapped around the preheating roller group 31 for heating; the preheating roller group 31 includes a first preheating roller 311 and a second preheating roller 312. The front of the casting 4 is wrapped around the first preheating roller 311 against the first preheating roller 311, and the back of the casting 4 is wrapped around the second preheating roller 312 against the second preheating roller 312. The preheating roller group heats the casting 4. There are two preheating roller groups, namely the first preheating roller group and the second preheating roller group. The casting first passes around the first preheating roller group and then wraps around the second preheating roller group. The temperature of the first preheating roller of the first preheating roller group is 135°C, and the temperature of the second preheating roller of the first preheating roller group is 120°C. The temperature of the first preheating roller of the second preheating roller group is 140°C, and the temperature of the second preheating roller of the second preheating roller group is 130°C.

[0051] S2-2 longitudinal stretching, the preheated casting sheet 4 is wound around the stretching roller group 32 for stretching. The stretching roller group 32 includes a first stretching roller 321 and a second stretching roller 322, and the temperature of the first stretching roller 321 is higher than the temperature of the second stretching roller 322. The front side of the casting sheet 4 is wound around the first stretching roller 321, and the back side of the casting sheet is wound around the second stretching roller 322. A pressure roller is provided on the outer side of the first stretching roller and the second stretching roller, and the pressure roller presses the casting sheet, and the casting sheet is stretched by controlling the linear speed of the first stretching roller and the second stretching roller.

[0052] There are two stretching roller groups, namely the first stretching roller group and the second stretching roller group. The cast sheet is first stretched by the first stretching roller group and then enters the second stretching roller group for stretching. The temperature of the first stretching roller of the first stretching roller group is 145℃, the temperature of the second stretching roller of the first stretching roller group is 135℃, the temperature of the first stretching roller of the second stretching roller group is 150℃, and the temperature of the second stretching roller of the second stretching roller group is 140℃.

[0053] S2-3 longitudinal drawing and shaping, the stretched casting sheet 4 is wound on the shaping roller group 33 for shaping; the shaping roller group 33 includes a first shaping roller 331 and a second shaping roller 332, the temperature of the first shaping roller 331 is higher than the temperature of the second shaping roller 332, the temperature of the first shaping roller 331 is 145°C, and the temperature of the second shaping roller is 143°C. The front side of the casting sheet 4 is attached to the first shaping roller 331 and wound on the first shaping roller, and the back side of the casting sheet 4 is attached to the second shaping roller 332 and wound on the second shaping roller. The longitudinally stretched casting sheet is shaped on the shaping roller group.

[0054] There are two shaping roller groups, namely the first shaping roller group and the second shaping roller group. The casting piece is shaped by the first shaping roller group first and then enters the second shaping roller group for shaping. The temperature of the first shaping roller of the first shaping roller group is 150℃, the temperature of the second shaping roller of the first shaping roller group is 140℃, the temperature of the first shaping roller of the second shaping roller group is 150℃, and the temperature of the second shaping roller of the second shaping roller group is 140℃.

[0055] Transverse stretching: clamp the two sides of the longitudinally stretched casting and stretch the casting to both sides to form a film. Figure 4 As shown, transverse stretching includes the following steps:

[0056] S2-4 horizontal stretching preheating, use the clamps on the conveyor line to clamp the two sides of the longitudinally stretched casting, and the conveyor line transports the casting to the horizontal stretching preheating zone 34. The horizontal stretching preheating zone blows preheating hot air to the front of the casting and blows preheating hot air to the back of the casting to heat the casting. The heat of the upper preheating hot air is greater than the heat of the lower preheating hot air.

[0057] S2-5 horizontal stretching, the conveyor line conveys the casting to the horizontal stretching zone 35, the clips on both sides of the casting stretch the casting horizontally to form a film, the horizontal stretching zone blows upward stretching hot air to the front of the casting and blows downward stretching hot air to the back of the casting to heat the casting, and the heat of the upper stretching hot air is greater than the heat of the lower stretching hot air;

[0058] S2-6 horizontal stretching and shaping, the conveyor line conveys the film to the horizontal stretching and shaping area 36, ​​the horizontal stretching and shaping area blows shaping hot air to the front side of the film and blows shaping hot air to the back side of the film, and the heat of the upper shaping hot air is greater than the heat of the lower shaping hot air.

[0059] After being stretched into a film, it is shaped and cooled. During the shaping and cooling, the first nozzle 71 blows a first airflow toward the front of the film, and the second nozzle 72 blows a second airflow toward the back of the film. The cooling amount of the second airflow is greater than the cooling amount of the first airflow in the same time; after the film is cooled, a polypropylene film is formed.

[0060] S3 trimming is to trim the side edges of the polypropylene film formed after stretching to make the side edges flush.

[0061] S4 thickness measurement measures the thickness of the trimmed polypropylene film. The radiation head emits radiation to the film, the receiving head receives the radiation passing through the film and calculates the real-time thickness of the film according to the attenuation of the radiation. The control device compares the real-time thickness with the pre-stored standard thickness to obtain the compensation thickness. The control device controls the electric control nut to drive the adjustment block to move according to the compensation thickness to adjust the lip size.

[0062] S5 corona treatment: corona treatment is performed on one side of the trimmed polypropylene film.

[0063] S6 is a winding process for winding the corona-treated polypropylene film, and the back side of the polypropylene film is facing the roll and the film is wound on the roll.

[0064] In the process of the melt becoming a cast sheet and then stretching the cast sheet into a film, the front and back sides are cooled and heated multiple times. The formed polypropylene film has less stress and low rewinding properties.

[0065] Embodiment 2:

[0066] like Figure 1 , Figure 3-Figure 8 As shown, the production method of the low-winding polypropylene film of the present invention comprises the following steps:

[0067] S1 quenches the cast sheet, melts the polypropylene raw material and extrude the melt from the die head 11; the melt extrusion temperature is 240℃-260℃. Figure 4As shown, a lip 111 is provided at the lower part of the die head 11, and the melt is extruded from the lip. A movable adjusting block 112 and an electrically controlled nut for driving the adjusting block to move are provided on the die head 11. One end of the adjusting block extends to the lip position. The movable adjusting block 112 can adjust the size of the lip, thereby adjusting the thickness of the melt during extrusion.

[0068] The melt is blown onto the cold roller 13 by the air knife 12 to form a cast sheet 4. The temperature of the cold roller is 85℃-95℃, and the temperature of the air knife is less than 85℃. The front side of the cast sheet 4 is attached to the cold roller 13; the cold roller is rotated to transport the cast sheet, and the cast sheet 4 is cooled on the cold roller 13. The temperature of the cold roller is 91.5℃. The cold roller 13 rotates counterclockwise, and the cold roller 13 drives the cast sheet 4 to move while cooling. A cooling device 2 is provided on the outside of the cold roller.

[0069] like Figure 6 and Figure 7 As shown, the cooling device 2 includes a box body 21, an air inlet pipe 25, and an air suction pipe 26. An arc surface 28 is provided at one end of the box body 21, and the arc surface 28 is arranged opposite to the cold roller 13. The arc surface 28 extends in the clockwise direction and the distance from the cold roller 13 gradually increases. The box body is provided with a baffle on the outer side of the arc surface 28, and the baffle and the arc surface 28 form an air flow cavity 29. An air inlet cavity 23 and an air suction cavity 24 are provided in the box body 21, and the air inlet pipe 25 is connected to the air inlet cavity 23, and the air suction pipe 26 is connected to the air suction cavity 25. The arc surface 28 is provided with a blowing hole 22 connected to the air inlet cavity, and the arc surface 28 is provided with an air suction hole 27 connected to the air suction cavity 24. The density of the blowing holes 22 on the arc surface 28 gradually decreases in the clockwise direction, and the air suction hole 27 is provided on the clockwise side of the blowing hole 22. The air inlet pipe 25 delivers cold air into the air inlet cavity 23, and the cold air blows toward the cast sheet on the cold roller from the air blowing hole 27, cooling the back side of the cast sheet 4. The cold air moves along the air flow cavity 29, and after being heated by the cast sheet, it enters the air suction cavity 24 from the air suction hole and is sucked away by the air suction pipe 26. When the front side of the cast sheet is cooled on the cold roller, the back side of the cast sheet is also cooled by the cooling device.

[0070] The casting sheet 4 cooled on the cold roller is wound around the stripping roller with its back side against the stripping roller. The temperature of the stripping roller 14 is lower than that of the cold roller, and the temperature of the stripping roller 14 is 80°C-85°C. The stripping roller 14 drives the casting sheet 4 to be stripped off from the cold roller 13.

[0071] S2 stretching, stretching the stripped casting sheet, first stretching the casting sheet longitudinally, and then stretching it transversely. Figure 3 As shown, longitudinal stretching includes the following steps:

[0072] S2-1 longitudinal drawing preheating, the cast sheet 4 is wound around the preheating roller group 31 for heating; the preheating roller group 31 includes a first preheating roller 311 and a second preheating roller 312. The front side of the cast sheet 4 is attached to the first preheating roller 311 and wound around the first preheating roller 311, and the back side of the cast sheet 4 is attached to the second preheating roller 312 and wound around the second preheating roller 312. The preheating roller group heats the cast sheet 4.

[0073] There are three preheating roller groups, namely the first preheating roller group, the second preheating roller group, and the third preheating roller group. The cast sheet is preheated by the first preheating roller group, the second preheating roller group, and the third preheating roller group in sequence. The temperature of the first preheating roller of the first preheating roller group is 130°C, and the temperature of the second preheating roller of the first preheating roller group is 120°C. The temperature of the first preheating roller of the second preheating roller group is 130°C, and the temperature of the second preheating roller of the second preheating roller group is 125°C. The temperature of the first preheating roller of the third preheating roller group is 140°C, and the temperature of the second preheating roller of the third preheating roller group is 130°C.

[0074] S2-2 longitudinal stretching, the preheated casting sheet 4 is wound around the stretching roller group 32 for stretching. The stretching roller group 32 includes a first stretching roller 321 and a second stretching roller 322, and the temperature of the first stretching roller 321 is higher than the temperature of the second stretching roller 322. The front side of the casting sheet 4 is wound around the first stretching roller 321, and the back side of the casting sheet is wound around the second stretching roller 322. A pressure roller is provided on the outer side of the first stretching roller and the second stretching roller, and the pressure roller presses the casting sheet, and the casting sheet is stretched by controlling the linear speed of the first stretching roller and the second stretching roller.

[0075] There are two stretching roller groups, namely the first stretching roller group and the second stretching roller group. The cast sheet is first stretched by the first stretching roller group and then enters the second stretching roller group for stretching. The temperature of the first stretching roller of the first stretching roller group is 145℃, the temperature of the second stretching roller of the first stretching roller group is 135℃, the temperature of the first stretching roller of the second stretching roller group is 150℃, and the temperature of the second stretching roller of the second stretching roller group is 140℃.

[0076] S2-3 longitudinal drawing and shaping, the stretched casting sheet 4 is wound on the shaping roller group 33 for shaping; the shaping roller group 33 includes a first shaping roller 331 and a second shaping roller 332, and the temperature of the first shaping roller 331 is higher than the temperature of the second shaping roller 332. The front side of the casting sheet 4 is attached to the first shaping roller 331 and wound on the first shaping roller, and the back side of the casting sheet 4 is attached to the second shaping roller 332 and wound on the second shaping roller. The longitudinally stretched casting sheet is shaped on the shaping roller group.

[0077] There are two shaping roller groups, namely the first shaping roller group and the second shaping roller group. The casting piece is shaped by the first shaping roller group first and then enters the second shaping roller group for shaping. The temperature of the first shaping roller of the first shaping roller group is 150℃, the temperature of the second shaping roller of the first shaping roller group is 140℃, the temperature of the first shaping roller of the second shaping roller group is 150℃, and the temperature of the second shaping roller of the second shaping roller group is 140℃.

[0078] Transverse stretching: clamp the two sides of the longitudinally stretched casting and stretch the casting to both sides to form a film. Figure 4 As shown, transverse stretching includes the following steps:

[0079] S2-4 horizontal stretching preheating, using the clamps on the conveyor line to clamp the two sides of the longitudinally stretched casting sheet, and the conveyor line conveys the casting sheet to the horizontal stretching preheating zone 34. The light source 63 in the horizontal stretching preheating zone illuminates the casting sheet from a first angle, and the image acquisition module 64 acquires images of the positions on the casting sheet illuminated by the light source and generates product images;

[0080] The image processing module divides the image data into multiple sub-images according to the area size, and analyzes each sub-image to determine whether the film thickness corresponding to the sub-image exceeds the threshold value. When the film thickness corresponding to the sub-image exceeds the threshold value, the image processing module generates sub-image coordinate information;

[0081] The control device drives the heat source 65 to heat the film position corresponding to the sub-image coordinate information according to the sub-image coordinate information.

[0082] The horizontal preheating zone blows preheating hot air to the front of the casting and blows preheating hot air to the back of the casting to heat the casting. The heat of the upper preheating hot air is greater than the heat of the lower preheating hot air. The thicker part of the casting is preheated and the heating time is long.

[0083] S2-5 horizontal stretching, the conveyor line conveys the casting to the horizontal stretching zone 35, the clips on both sides of the casting stretch the casting horizontally to form a film, the horizontal stretching zone blows upward stretching hot air to the front of the casting and blows downward stretching hot air to the back of the casting to heat the casting, and the heat of the upper stretching hot air is greater than the heat of the lower stretching hot air;

[0084] S2-6 horizontal stretching and shaping, the conveyor line conveys the film to the horizontal stretching and shaping area 36, ​​the horizontal stretching and shaping area blows shaping hot air to the front side of the film and blows shaping hot air to the back side of the film, and the heat of the upper shaping hot air is greater than the heat of the lower shaping hot air.

[0085] After being stretched into a film, it is shaped and cooled. During the shaping and cooling, the first nozzle 71 blows a first airflow toward the front of the film, and the second nozzle 72 blows a second airflow toward the back of the film. The cooling amount of the second airflow is greater than the cooling amount of the first airflow in the same time; after the film is cooled, a polypropylene film is formed.

[0086] S3 trimming is to trim the side edges of the polypropylene film formed after stretching to make the side edges flush.

[0087] S4 thickness measurement measures the thickness of the trimmed polypropylene film. The radiation head emits radiation to the film, the receiving head receives the radiation passing through the film and calculates the real-time thickness of the film according to the attenuation of the radiation. The control device compares the real-time thickness with the pre-stored standard thickness to obtain the compensation thickness. The control device controls the electric control nut to drive the adjustment block to move according to the compensation thickness to adjust the lip size.

[0088] S5 corona treatment: corona treatment is performed on one side of the trimmed polypropylene film.

[0089] S6 is a winding process for winding the corona-treated polypropylene film, and the back side of the polypropylene film is facing the roll and the film is wound on the roll.

[0090] In the process of the melt becoming a cast sheet and then stretching the cast sheet into a film, the front and back sides are cooled and heated multiple times. The formed polypropylene film has less stress and low rewinding properties.

[0091] The above-mentioned are only preferred embodiments of the present invention and cannot limit the scope of implementation of the present invention. All equivalent changes and decorations made according to the scope of the patent application of the present invention should still fall within the scope of the present invention.

Claims

1. A method for producing a low-winding polypropylene film, characterized in that: The following steps are involved: Rapidly cool the casting sheet, melt the polypropylene raw material and extrude the melt from the die head; use an air knife to blow the melt onto a cold roller to form a casting sheet, with the front side of the casting sheet attached to the cold roller; rotate the cold roller to transport the casting sheet, and the casting sheet is cooled on the cold roller; the casting sheet cooled on the cold roller is wound around the stripping roller with the back side attached to the stripping roller, and the temperature of the stripping roller is lower than that of the cold roller; the stripping roller drives the casting sheet to be stripped off from the cold roller; Stretching, stretching the stripped casting sheet, first stretching the casting sheet longitudinally, and then stretching it transversely; Longitudinal stretching includes the following steps: Longitudinal preheating, the cast sheet is wound around a preheating roller group for heating; the preheating roller group includes a first preheating roller and a second preheating roller, the temperature of the first preheating roller is higher than that of the second preheating roller, the front side of the cast sheet is attached to the first preheating roller and wound around the first preheating roller, and the back side of the cast sheet is attached to the second preheating roller and wound around the second preheating roller; Longitudinal stretching, the preheated cast sheet is wound around a stretching roller group for stretching; the stretching roller group includes a first stretching roller and a second stretching roller, the temperature of the first stretching roller is higher than that of the second stretching roller, the front side of the cast sheet is close to the first stretching roller and is wound around the first stretching roller, and the back side of the cast sheet is close to the second stretching roller and is wound around the second stretching roller; Longitudinal stretching and shaping, the stretched casting sheet is wound around a shaping roller group for shaping; the shaping roller group includes a first shaping roller and a second shaping roller, the temperature of the first shaping roller is higher than that of the second shaping roller, the front side of the casting sheet is attached to the first shaping roller and wound around the first shaping roller, and the back side of the casting sheet is attached to the second shaping roller and wound around the second shaping roller; Transverse stretching, clamping the two sides of the longitudinally stretched casting sheet, and stretching the casting sheet transversely to both sides to form a film; Transverse stretching includes the following steps: Horizontal stretching preheating: clamp the two sides of the longitudinally stretched casting with the clips on the conveyor line, and the conveyor line conveys the casting to the horizontal stretching preheating zone. The horizontal stretching preheating zone blows preheating hot air to the front of the casting and blows preheating hot air to the back of the casting to heat the casting. The heat of the upper preheating hot air is greater than the heat of the lower preheating hot air. Transverse stretching: the conveyor line transports the casting to the transverse stretching area. The clips on both sides of the casting stretch the casting horizontally to form a film. The transverse stretching area blows upward stretching hot air to the front of the casting and blows downward stretching hot air to the back of the casting to heat the casting. The heat of the upward stretching hot air is greater than the heat of the downward stretching hot air. Horizontal stretching shaping: the conveyor line transports the film to the horizontal stretching shaping area, where the horizontal stretching shaping area blows shaping hot air to the front of the film and blows shaping hot air to the back of the film. The heat of the upper shaping hot air is greater than that of the lower shaping hot air. After being stretched into a film, it is shaped and cooled. During the shaping and cooling, the first nozzle blows a first airflow toward the front of the film, and the second nozzle blows a second airflow toward the back of the film. The cooling amount of the second airflow is greater than that of the first airflow in the same time. After the film is cooled, a polypropylene film is formed. Trimming, cutting the side edges of the polypropylene film formed after stretching to make the side edges flush; Thickness measurement: measure the thickness of the polypropylene film after trimming; Corona treatment: corona treatment is performed on one side of the trimmed polypropylene film; Winding up, and winding up the polypropylene film after corona treatment.

2. The method for producing a low-winding polypropylene film according to claim 1, characterized in that: In the winding step, the polypropylene film is wound on the roll with the back side facing the roll.

3. The method for producing a low-winding polypropylene film according to claim 1, characterized in that: The lower part of the die head is provided with a lip, and the melt is extruded from the lip. The die head is provided with a movable adjustment block and an electric control nut for driving the adjustment block to move. One end of the adjustment block extends to the lip position, and the movable adjustment block can adjust the size of the lip. In the thickness measurement step, the radiation head emits radiation to the film, the receiving head receives the radiation passing through the film and calculates the real-time thickness of the film based on the attenuation of the radiation, the control device compares the real-time thickness with the pre-stored standard thickness to obtain the compensated thickness, and the control device controls the electric control nut to drive the adjustment block to move according to the compensated thickness to adjust the size of the lip.

4. The method for producing a low-winding polypropylene film according to claim 1, characterized in that: When the cast sheet is rapidly cooled, a cooling device is provided on the outside of the cold roller, and the cooling device includes a box body, an air inlet pipe, and an air suction pipe. An arcuate surface is provided at one end of the box body, and the arcuate surface is arranged opposite to the cold roller. An air inlet cavity and an air suction cavity are provided in the box body, and the air inlet pipe is connected with the air inlet cavity, and the air suction pipe is connected with the air suction cavity. The arcuate surface is provided with blowing holes connected with the air inlet cavity and air suction holes connected with the air suction cavity. When the cold roller rotates counterclockwise, the density of the blowing holes on the arcuate surface gradually decreases along the clockwise direction, and the air suction holes are arranged on the clockwise side of the blowing holes.

5. The method for producing a low-winding polypropylene film according to claim 1, characterized in that: In the cross-drawing preheating step, The light source illuminates the casting sheet from a first angle, and the image acquisition module acquires an image of the position on the casting sheet illuminated by the light source and generates a product image; The image processing module divides the image data into multiple sub-images according to the area size, and analyzes each sub-image to determine whether the film thickness corresponding to the sub-image exceeds the threshold value. When the film thickness corresponding to the sub-image exceeds the threshold value, the image processing module generates sub-image coordinate information; The control device drives the heat source according to the sub-image coordinate information to heat the film position corresponding to the sub-image coordinate information.

6. The method for producing a low-winding polypropylene film according to claim 1, characterized in that: The temperature of the cold roller is 85℃-95℃, and the temperature of the air knife is less than 85℃.

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