Process for the preparation of a bopp white film

Abstract

The present application relates to a kind of preparation process of BOPP white film applied to the field of plastic film preparation, which introduces self-regulating dryer in the existing preparation process, first dry in the feeding stage, then use the waste heat to compensate dry in the discharging stage, effectively save energy consumption while also effectively improve drying effect, the humidity of drying gas is monitored to analyze the drying effect of raw material in real time, the temperature of compensating drying is adjusted according to the humidity monitored, effectively avoid the waste of energy, and increase the number of electric heating wire in series, effectively improve the heating effect of electric heating wire without increasing current, thereby effectively improve the drying effect, while also effectively save energy consumption, in addition, the increase of the number of electric heating wire can also effectively increase the heating area, thereby further effectively improve the drying effect.

Description

TECHNICAL FIELD

[0001] The application relates to a preparation process of a BOPP white film, in particular to a preparation process of a BOPP white film applied to the field of plastic film preparation. BACKGROUND

[0002] The BOPP white film is a biaxially oriented polypropylene film, which has high transparency, high gloss and good mechanical properties. In the preparation process of the BOPP white film, the first step is to dry the raw material. If the drying is not thorough, bubbles and water marks will be generated in the stretching process, affecting the quality of the film.

[0003] In order to solve the problem of drying the raw material, a certain plastic film preparation method in the market adopts a convection drying design, which has a certain market share.

[0004] The specification of Chinese patent CN111231290B discloses a plastic film blowing method. The method utilizes the high-temperature section of hot air for indirect heat exchange, and utilizes the lower-temperature section of hot air for reverse convection heat exchange drying mode, which can greatly reduce the space size of the master batch drying device while ensuring sufficient heat exchange efficiency, and improves the compactness of the device arrangement.

[0005] The specification of Chinese patent CN112918098A discloses an energy-saving and environment-friendly plastic film drying machine and method. The drying machine collects solar energy through multiple solar water heaters, circulates into the drying channel, increases the heat inside the drying channel through heat radiation, and cooperates with the electric heating wire for drying. The solar energy is reasonably used, the energy consumption is reduced, and the cost is reduced.

[0006] The prior art adopts the convection heat exchange mode, the combination of solar energy and electric heating wire for drying the plastic film. Although it can play a certain positive role, it is limited in actual operation. For example, the convection heat exchange drying mode, although the device is compact, the drying effect may not meet the requirements, and the solar water heater is easily affected by the weather. Therefore, the existing drying method is not the optimal way in the long run. SUMMARY

[0007] In view of the above prior art, the technical problem to be solved by the application is how to improve the drying effect of the raw material to prevent bubbles and water marks from appearing in the stretching process.

[0008] To solve the above problems, the application provides a preparation process of a BOPP white film, which comprises the following preparation steps:

[0009] S1, first put the polypropylene resin particles and white color masterbatch into the self-adjusting dryer to dry to remove moisture, prevent bubbles in the subsequent stretching process, the drying temperature is controlled at 90-100℃, the drying time is 2-3 hours;

[0010] S2, the dried polypropylene resin particles and white color masterbatch are put into the mixer for mixing and stirring, then the mixture is put into the extruder, the polypropylene resin particles are melted and extruded, a layer of melt film is obtained, then the melt film is cooled and solidified by the cooling roller, so that the BOPP white film blank is obtained;

[0011] S3, the preliminary BOPP white film blank obtained in the above step is sent into the longitudinal stretching machine and the transverse stretching machine in sequence for stretching, so as to improve the transparency and tensile strength of the BOPP white film, then the film is sent into the heat setting machine for heat setting treatment, and cooled to room temperature after setting, so that the BOPP white film is obtained, finally, the qualified product is cut, wound and packaged;

[0012] The self-adjusting dryer comprises a drying box, a conveying belt is installed in the drying box, a feeding hopper is installed on the upper end of one side of the drying box, an electric hair dryer one is installed at the middle position of the conveying belt close to the feeding hopper, the outlet of the electric hair dryer one faces the upper side of the conveying belt, a gas recovery monitoring box is fixedly connected to the upper end side wall of the drying box opposite to the electric hair dryer one, an exhaust fan and a humidity sensor are installed in the gas recovery monitoring box, a waste heat discharge box is fixedly connected to the upper end side wall of the drying box away from the electric hair dryer one, an exhaust fan is installed in the waste heat discharge box, an electric hair dryer two is fixedly connected to the lower end of the waste heat discharge box and penetrates into the inside of the drying box, the outlet of the electric hair dryer two faces the conveying belt, a discharging hopper is communicated with the lower end side wall of the drying box away from the feeding hopper, a gas dehumidification box is further fixedly connected to the position of the drying box between the gas recovery monitoring box and the waste heat discharge box, and ventilation pipes are communicated between the two sides of the gas dehumidification box and the gas recovery monitoring box and the waste heat discharge box.

[0013] In the preparation process of the above BOPP white film, the raw materials are dried by introducing the self-adjusting dryer, which not only effectively saves energy consumption, but also effectively improves the drying effect.

[0014] As a further improvement of the present application, the conveying belt is of porous wave shape structure, and the conveying belt is made of corrosion-resistant elastic composite material.

[0015] As a further improvement of the present application, a dehumidification net is clamped in the inside of the gas dehumidification box, a net cover is fixedly connected to the upper end of the dehumidification net, and a sealing gasket is fixedly connected to the side wall of the net cover.

[0016] As a further improvement of the present application, the inner wall of the middle part of the electric hair dryer two is provided with a blowing port perpendicular to the conveying belt, and the inner walls on both sides of the blowing port of the electric hair dryer two are provided with mounting cavities, a plurality of parallel public electric heating wires and female electric heating wires are fixedly connected between the two mounting cavities, the plurality of public electric heating wires and female electric heating wires are arranged alternately, the lowermost part of the two mounting cavities is also fixedly connected with a terminal electric heating wire, one end of the public electric heating wire at the uppermost part is fixedly connected with an incoming power line, and the incoming power line is connected with the positive electrode of the power supply circuit, one end of the terminal electric heating wire opposite to the position of the incoming power line is fixedly connected with an outgoing power line, and the outgoing power line is connected with the negative electrode of the power supply circuit, the end of the public electric heating wire and the female electric heating wire away from each other is fixedly connected with a gate type conductive section, one end of the gate type conductive section is fixedly connected with a conductive head, the end of the public electric heating wire and the female electric heating wire away from the gate type conductive section is fixedly connected with a conductive seat matched with the conductive head, the inner wall of the mounting cavity is fixedly connected with a plurality of segmented conductive lines connected with the negative electrode of the power supply circuit, and the segmented conductive lines are attached to the gate type conductive section, the inner wall of the mounting cavity opposite to the gate type conductive section is also provided with an electric telescopic rod, and the output end of the electric telescopic rod is fixedly connected with an insulating pad abutting against the gate type conductive section, the drying box further comprises a humidity analysis module electrically connected with the humidity sensor, and the humidity analysis module is electrically connected with a control module, and the control module is electrically connected with a plurality of electric telescopic rods through a control processor.

[0017] As a further improvement of the present application, the gate type conductive section and the public electric heating wire and the female electric heating wire are also fixedly connected with an elastic conductive section, and the gate type conductive section and the elastic conductive section are made of elastic conductive material.

[0018] As a further improvement of the present application, the gate type conductive section and the public electric heating wire and the female electric heating wire are also fixedly connected with an elastic conductive section, and the gate type conductive section and the elastic conductive section are made of elastic conductive material.

[0019] As a further improvement of the present application, the gate type conductive section and the public electric heating wire and the female electric heating wire are also fixedly connected with an elastic conductive section, and the gate type conductive section and the elastic conductive section are made of elastic conductive material. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 The preparation flow chart of the first embodiment of the present application;

[0021] Figure 2A perspective view of the self-adjusting dryer according to the first embodiment of the present application;

[0022] Figure 3 A perspective view of the self-adjusting dryer according to the first embodiment of the present application;

[0023] Figure 4 A perspective view of the transmission belt according to the first embodiment of the present application;

[0024] Figure 5 A front view of the gas dehumidification tank according to the first embodiment of the present application;

[0025] Figure 6 A power supply schematic diagram of the second embodiment of the present application when one electric heating wire is connected;

[0026] Figure 7 A power supply schematic diagram of the second embodiment of the present application when two electric heating wires are connected;

[0027] Figure 8 A power supply schematic diagram of the second embodiment of the present application when three electric heating wires are connected;

[0028] Figure 9 A power supply schematic diagram of the second embodiment of the present application when four electric heating wires are connected;

[0029] Figure 10 A power supply schematic diagram of the second embodiment of the present application when five electric heating wires are connected.

[0030] Explanation of reference numerals in the drawings:

[0031] 1 drying tank, 2 transmission belt, 3 feeding hopper, 4 electric heating blower I, 5 gas recovery monitoring tank, 6 waste heat discharge tank, 7 electric heating blower II, 701 installation cavity, 8 gas dehumidification tank, 801 dehumidification net, 802 net cover, 803 sealing gasket, 9 ventilation pipe, 10 discharging hopper, 11 public electric heating wire, 12 female electric heating wire, 13 terminal electric heating wire, 14 incoming electric lead, 15 segmented lead, 16 outgoing electric lead, 17 gate type electrically conductive section, 1701 elastic electrically conductive section, 18 electrically conductive head, 19 electrically conductive seat, 20 electric telescopic rod. DETAILED DESCRIPTION

[0032] The two embodiments of the present application will be described in detail below with reference to the drawings.

[0033] First embodiment:

[0034] Figure 1 It is shown that it comprises the following preparation steps:

[0035] S1, first put the polypropylene resin particles and white color masterbatch into the self-adjusting dryer to dry to remove moisture, prevent bubbles in the subsequent stretching process, the drying temperature is controlled at 90-100℃, the drying time is 2-3 hours;

[0036] S2, the dried polypropylene resin particles and white color masterbatch are put into the mixer for mixing and stirring, then the mixture is put into the extruder, the polypropylene resin particles are melted and extruded to obtain a melt film, then the melt film is cooled and solidified by the cooling roller, so as to obtain the BOPP white film blank;

[0037] S3, the preliminary BOPP white film blank obtained in the above step is sent into the longitudinal stretching machine and the transverse stretching machine in sequence for stretching, so as to improve the transparency and tensile strength of the BOPP white film, then the film is sent into the heat setting machine for heat setting treatment, and cooled to room temperature after setting, so as to obtain the BOPP white film, finally, the qualified product is cut, wound and packaged;

[0038] Figure 2 、 4 It is shown that the self-adjusting dryer comprises a drying box 1, a transmission belt 2 is installed in the drying box 1, the transmission belt 2 is of a porous wave shape structure, and is made of a corrosion-resistant elastic composite material, the wave-shaped transmission belt can effectively increase the heating area, so that more polypropylene resin particles can be in contact with hot air, thereby effectively improving the drying effect, one end of the upper side of the drying box 1 is provided with a feeding hopper 3, an electric hair dryer one 4 is installed at the middle position of the transmission belt 2 close to the feeding hopper 3, and the outlet of the electric hair dryer one 4 faces the upper side of the transmission belt 2, a gas recovery monitoring box 5 is fixedly connected to the upper end side wall of the drying box 1 opposite to the electric hair dryer one 4, and an exhaust fan and a humidity sensor are installed in the gas recovery monitoring box 5, a waste heat discharge box 6 is fixedly connected to the upper end side wall of the drying box 1 away from the electric hair dryer one 4, and an exhaust fan is installed in the waste heat discharge box 6, specifically, in the process of drying the raw materials, the electric hair dryer one 4 first dries the raw materials, then the exhaust fan in the gas recovery monitoring box 5 blows the gas up, and then the exhaust fan in the waste heat discharge box 6 blows the recovered gas back to the raw materials, so as to realize the compensating drying of the raw materials, thereby effectively improving the drying effect and saving energy, the humidity sensor monitors the humidity of the recovered gas, and a large humidity indicates that there is still a large amount of moisture in the raw materials, and the drying is not complete, and a small humidity indicates that the moisture in the raw materials is small, and the drying effect meets the standard;

[0039] Figure 3 、 5The lower end of the waste heat discharge box 6 is fixedly connected with the electric hair dryer two 7 penetrating into the inside of the drying box 1, and the outlet of the electric hair dryer two 7 faces the conveying belt 2. The lower end side wall of the drying box 1 away from the feeding hopper 3 is communicated with the discharging hopper 10. The drying box 1 is fixedly connected with the gas dehumidification box 8 at the position between the gas recovery monitoring box 5 and the waste heat discharge box 6. The inside of the gas dehumidification box 8 is clamped with the dehumidification net 801. The upper end of the dehumidification net 801 is fixedly connected with the net cover 802. The side wall of the net cover 802 is fixedly connected with the sealing gasket 803. The dehumidification net 801 dehumidifies the recovered gas, so as to prevent the gas containing water vapor from accumulating in the drying box 1 in a large amount and affecting the drying effect. The net cover 802 plays a role of installing and fixing the dehumidification net 801. The sealing gasket 803 can effectively eliminate the gap at the installation position and ensure a certain sealing performance, thereby effectively preventing gas leakage. The two sides of the gas dehumidification box 8 are communicated with the gas recovery monitoring box 5 and the waste heat discharge box 6 through the ventilation pipe 9.

[0040] The second embodiment is as follows:

[0041] Figure 6 The middle inner wall of the electric hair dryer two 7 is provided with a blowing port perpendicular to the conveying belt 2. The inner walls on both sides of the electric hair dryer two 7 are provided with installation cavities 701. The public electric heating wire 11, the female electric heating wire 12 and the terminal electric heating wire 13 penetrating through the installation cavities 701 are sealed. The inside of the installation cavities 701 is filled with insulating gas. When the gate type conductive section 17 is disconnected from the public electric heating wire 11 and the female electric heating wire 12, there may be electric arc. The electric arc may cause incomplete disconnection of the circuit. Therefore, the insulating performance is effectively improved by filling the insulating gas. A plurality of parallel public electric heating wires 11 and female electric heating wires 12 are fixedly connected between the two installation cavities 701. The plurality of public electric heating wires 11 and female electric heating wires 12 are alternately arranged upward and downward. The terminal electric heating wire 13 is fixedly connected to the lowermost of the two installation cavities 701. One end of the uppermost public electric heating wire 11 is fixedly connected with the power-in lead 14 connected with the positive electrode of the power supply circuit. The terminal electric heating wire 13 is fixedly connected with the power-out lead 16 opposite to the power-in lead 14. The power-out lead 16 is connected with the negative electrode of the power supply circuit.

[0042] Figure 7 、 8 、9 and Figure 10It is shown that the one end of the male electric heating wire 11 and the female electric heating wire 12 away from each other is fixedly connected with the gate type conductive section 17, and the gate type conductive section 17 and the male electric heating wire 11 and the female electric heating wire 12 are also fixedly connected with the elastic conductive section 1701, and the gate type conductive section 17 and the elastic conductive section 1701 are both made of elastic conductive material, the elastic conductive section 1701 realizes the elastic connection of the gate type conductive section 17 and the male electric heating wire 11 and the female electric heating wire 12, so that the gate type conductive section 17 and the male electric heating wire 11 and the female electric heating wire 12 can be conveniently disconnected and connected, and one end of the gate type conductive section 17 is fixedly connected with the conductive head 18, and the one end of the male electric heating wire 11 and the female electric heating wire 12 away from the gate type conductive section 17 is fixedly connected with the conductive seat 19 matched with the conductive head 18, the inner wall of the mounting cavity 701 is fixedly connected with a plurality of segmented conductive wires 15 connected with the negative electrode of the power supply circuit, and the segmented conductive wires 15 are attached to the gate type conductive section 17, and the inner wall of the mounting cavity 701 opposite to the gate type conductive section 17 is also provided with the electric telescopic rod 20 (the specific model is selected according to the actual demand, which will not be described in detail here), and the output end of the electric telescopic rod 20 is fixedly connected with the insulating pad abutting against the gate type conductive section 17, the drying box 1 further comprises a humidity analysis module electrically connected with the humidity sensor, and the humidity analysis module is electrically connected with a control module, and the control module is electrically connected with a plurality of electric telescopic rods 20 through a control processor (the specific connection structure and control principle of this part are the common technical knowledge of those skilled in the art, which will not be described in detail here), specifically, when the gas recovery monitoring box 5 recovers the gas, the humidity sensor transmits the monitored gas humidity data to the humidity analysis module in real time, when the gas humidity is less than the set monitoring threshold, it indicates that the drying effect of the raw material has reached the standard, and the moisture in the raw material has been dried, and when the gas humidity is greater than the set monitoring threshold, it indicates that the drying effect of the raw material is not up to standard, and there is still a lot of moisture in the raw material, then the humidity analysis module triggers the control module, and the control module controls the number of electric heating wires in the access circuit by turning on the electric telescopic rod 20, specifically, the number of electric heating wires in the access circuit is increased in series, according to the characteristics of the series circuit, the more the electric appliances in the series circuit, the greater the total resistance, so that the heat output of the whole device can be effectively improved, thereby effectively improving the drying effect, and without additional increase of current, in addition, the electric heating wire is heated on the basis of the recovered gas, and the waste heat in the gas can save the power consumption, thereby effectively saving the energy consumption.

[0043] In summary, by introducing the self-adjusting dryer in the existing preparation process, drying is first carried out in the feeding stage, and then compensation drying is carried out in the discharging stage by using waste heat, which effectively saves energy consumption and effectively improves the drying effect. The drying effect of the raw material is analyzed in real time by monitoring the humidity of the dried gas, and the temperature during compensation drying is adjusted according to the monitored humidity, effectively avoiding energy waste. In addition, the number of electric heating wires is increased in a series manner, which can effectively improve the heating effect of the electric heating wire without increasing the current, thereby effectively improving the drying effect and saving energy consumption. In addition, the increase in the number of electric heating wires can also effectively increase the heating area, thereby further effectively improving the drying effect.

[0044] In combination with the current actual demand, the above-mentioned embodiments adopted by the present application are not limited to this, various changes made within the knowledge range of those skilled in the art without departing from the concept of the present application still fall within the protection scope of the present application.

Claims

1. A process for preparing a BOPP white film, characterized in that: The preparation steps include the following: S1. First, put the polypropylene resin granules and white coloring masterbatch into a self-regulating dryer to remove moisture and prevent air bubbles from forming during the subsequent stretching process. The drying temperature is controlled at 90-100℃ and the drying time is 2-3 hours. S2. The dried polypropylene resin granules and white coloring masterbatch are put into a mixer for thorough mixing. Then the mixture is put into an extruder. The extruder melts the polypropylene resin granules and extrudes them to obtain a molten film. The molten film is then cooled and solidified by a cooling roller to obtain a BOPP white film preform. S3. The preliminary BOPP white film blank obtained in the above steps is fed into the longitudinal stretching machine and the transverse stretching machine for stretching to improve the transparency and tensile strength of the BOPP white film. After stretching, the film is sent to the heat setting machine for heat setting treatment. After setting, it is cooled to room temperature to obtain the BOPP white film. Finally, after passing the inspection, it is slit, rolled up and packaged. The self-regulating dryer includes a drying chamber (1), inside which a conveyor belt (2) is installed, and a feed hopper (3) is installed on the upper side of one end of the drying chamber (1). An electric heating blower (4) is installed at the middle position of the conveyor belt (2) near the feed hopper (3), and the outlet of the electric heating blower (4) faces the top of the conveyor belt (2). A gas recovery monitoring box (5) is fixedly connected to the upper side wall of the drying chamber (1) opposite to the electric heating blower (4), and an exhaust fan and a humidity sensor are installed inside the gas recovery monitoring box (5). The upper side wall of the drying chamber (1) away from the electric heating blower (4) is fixedly connected to... A waste heat discharge box (6) is connected, and an exhaust fan is installed inside the waste heat discharge box (6). An electric hot air blower (7) that penetrates into the drying box (1) is fixedly connected to the lower end of the waste heat discharge box (6). The outlet of the electric hot air blower (7) faces the conveyor belt (2). A discharge hopper (10) is connected to the lower side wall of the drying box (1) away from the feed hopper (3). A gas dehumidification box (8) is also fixedly connected to the drying box (1) in the middle position between the gas recovery monitoring box (5) and the waste heat discharge box (6). Ventilation pipes (9) are connected to both sides of the gas dehumidification box (8) between the gas recovery monitoring box (5) and the waste heat discharge box (6). The inner wall of the second electric heating blower (7) has a blower opening perpendicular to the conveyor belt (2), and the inner walls on both sides of the blower opening have mounting cavities (701). Multiple parallel male heating wires (11) and female heating wires (12) are fixedly connected between the two mounting cavities (701), with the male heating wires (11) and female heating wires (12) arranged alternately vertically. A terminal heating wire (13) is also fixedly connected to the bottom of each mounting cavity (701). One end of the male heating wire (11) is fixedly connected to an input conductor (14), and the input conductor (14) is connected to the positive terminal of the power supply circuit. The end of the end heating wire (13) opposite to the input conductor (14) is fixedly connected to an output conductor (16), and the output conductor (16) is connected to the negative terminal of the power supply circuit. Both the male heating wire (11) and the female heating wire (12) are fixedly connected to a gate-type conductive section (17) at their ends that are far apart from each other, and one end of the gate-type conductive section (17) is fixedly connected to a conductive head (18). The male heating wire (11) and the female heating wire (12) are fixedly connected to a conductive seat (19) that matches the conductive head (18) at the ends away from the gate-type conductive section (17). Multiple segmented wires (15) connected to the negative terminal of the power supply circuit are fixedly connected to the inner wall of the mounting cavity (701), and the segmented wires (15) are in contact with the gate-type conductive section (17). An electric telescopic rod (20) is also installed on the inner wall of the mounting cavity (701) facing the gate-type conductive section (17), and an insulating pad that abuts against the gate-type conductive section (17) is fixedly connected to the output end of the electric telescopic rod (20). The drying oven (1) also includes a humidity sensor electrically connected to it. The humidity analysis module is connected to the humidity analysis module, and the humidity analysis module is connected to the control module. The control module is electrically connected to multiple electric telescopic rods (20) through the control processor. The humidity sensor transmits the monitored gas humidity data to the humidity analysis module in real time. When the gas humidity is less than the set monitoring threshold, it indicates that the drying effect of the raw material has met the standard and the moisture in the raw material has been dried. When the gas humidity is greater than the set monitoring threshold, it indicates that the drying effect of the raw material has not met the standard and there is still a lot of moisture in the raw material. Then the humidity analysis module triggers the control module. The control module controls the number of heating wires in the circuit by opening the electric telescopic rods (20). An elastic conductive section (1701) is also fixedly connected between the gate-type conductive section (17), the male heating wire (11), and the female heating wire (12). Both the gate-type conductive section (17) and the elastic conductive section (1701) are made of elastic conductive material. The elastic conductive section (1701) realizes the elastic connection between the gate-type conductive section (17) and the male heating wire (11) and the female heating wire (12), which facilitates the disconnection and connection of the gate-type conductive section (17) and the male heating wire (11) and the female heating wire (12). The male heating wire (11), female heating wire (12) and end heating wire (13) are all sealed at the points where they pass through the mounting cavity (701), and the interior of the mounting cavity (701) is filled with insulating gas.

2. The preparation process of a BOPP white film according to claim 1, characterized in that: The conveyor belt (2) has a porous wavy structure and is made of corrosion-resistant elastic composite material.

3. The preparation process of a BOPP white film according to claim 1, characterized in that: The gas dehumidification box (8) is fitted with a dehumidification mesh (801) inside. The upper end of the dehumidification mesh (801) is fixedly connected to a mesh cover (802), and the side wall of the mesh cover (802) is fixedly connected to a sealing gasket (803).

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