Preparation process of BOPP white film

Abstract

The invention relates to a preparation technology of a BOPP white film applied to the field of plastic film preparation, and the technology is characterized in that a self-adjusting dryer is introduced in the existing preparation process, drying is carried out at a feeding stage, and then compensation drying is carried out at a discharging stage by utilizing waste heat, so that the energy consumption is effectively reduced, and meanwhile, the drying effect can be effectively improved; the raw material drying effect is analyzed in real time by monitoring the humidity of dried gas, the temperature during drying is adaptively adjusted and compensated according to the monitored humidity condition, energy waste is effectively avoided, the access number of the electric heating wires is increased in a series connection mode, the heating effect of the electric heating wires can be effectively improved under the condition that current is not increased, and the service life of the electric heating wires is prolonged. And meanwhile, energy consumption can be effectively reduced, in addition, the heating area can be effectively increased by increasing the number of the electric heating wires, and therefore the drying effect is further effectively improved.

Description

Technical Field

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

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

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

[0004] The specification of Chinese patent CN111231290B discloses a plastic film blowing method, which 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. This method can greatly reduce the spatial size of the masterbatch drying device while ensuring sufficient heat exchange efficiency, thereby improving the compactness of the device layout.

[0005] The specification of Chinese patent CN112918098A discloses an energy-saving and environmentally friendly plastic film drying machine and method. The dryer collects solar energy through multiple groups of solar water heaters, circulates it into a drying tunnel, increases the heat inside the drying tunnel by thermal radiation, and dries it in cooperation with electric heating wires. It rationally adopts clean and environmentally friendly solar energy, reduces energy consumption, and reduces costs.

[0006] The existing technology uses convection heat exchange, solar energy and electric heating wire combination to dry plastic film. Although it can play a certain positive role, it is subject to many limitations in actual operation. For example, the convection heat exchange drying method, 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 methods are not the best in the long run. Summary of the invention

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

[0008] In order to solve the above problems, the present invention provides a preparation process of a BOPP white film, comprising the following preparation steps: S1. First, put the polypropylene resin particles and the white masterbatch into a self-regulating dryer for drying to remove moisture and prevent bubbles from appearing during the subsequent stretching process. The drying temperature is controlled at 90-100°C and the drying time is 2-3 hours. S2, putting the dried polypropylene resin particles and the white coloring masterbatch into a mixer for thorough mixing and stirring, and then putting the mixture into an extruder, the extruder melts the polypropylene resin particles and extrude them to obtain a molten film, and then the molten film is cooled and solidified by a cooling roller, so as to obtain a BOPP white film blank; S3, the preliminary BOPP white film blank obtained in the above steps is successively sent to the longitudinal stretching machine and the transverse stretching machine for stretching, so as to improve the transparency and tensile strength of the BOPP white film, and then the film is sent to the heat setting machine for heat setting treatment after stretching, and cooled to room temperature after the setting is completed, so as to obtain the BOPP white film, and finally slitting, winding and packaging are carried out after passing the test; Among them, the self-regulating dryer includes a drying box, a conveyor belt is installed inside the drying box, and a feed hopper is installed on the upper side of one end of the drying box, an electric hair dryer 1 is installed at the middle position of the conveyor belt near the feed hopper, and the outlet of the electric hair dryer 1 faces above the conveyor belt, a gas recovery monitoring box is fixedly connected to the upper side wall of the drying box facing the electric hair dryer 1, and an exhaust fan and a humidity sensor are installed inside the gas recovery monitoring box, a waste heat discharge box is fixedly connected to the upper side wall of the drying box away from the electric hair dryer 1, and an exhaust fan is installed inside the waste heat discharge box, an electric hair dryer 2 that runs through the interior of the drying box is fixedly connected to the lower end of the waste heat discharge box, and the outlet of the electric hair dryer 2 faces the conveyor belt, the lower side wall of the drying box away from the feed hopper is connected to the discharge hopper, the drying box is also fixedly connected to a gas dehumidification box at a position between the gas recovery monitoring box and the waste heat discharge box, and ventilation pipes are connected between the two sides of the gas dehumidification box and the gas recovery monitoring box and the waste heat discharge box.

[0009] In the preparation process of the above-mentioned BOPP white film, a self-regulating dryer is introduced to dry the raw materials during the preparation process, which can not only effectively save energy consumption but also effectively improve the drying effect.

[0010] As a further improvement of the present application, the conveyor belt has a porous wavy structure and is made of a corrosion-resistant elastic composite material.

[0011] As a further improvement of the present application, a dehumidification net is clamped inside 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.

[0012] As a further improvement of the present application, a blowing port perpendicular to the conveyor belt is provided on the middle inner wall of the electric hair dryer, and installation cavities are provided on the inner walls on both sides of the blowing port of the electric hair dryer, and multiple male heating wires and female heating wires arranged in parallel are fixedly connected between the two installation cavities, and the multiple male heating wires and female heating wires are alternately arranged up and down, and the bottom of the two installation cavities are also fixedly connected to the terminal heating wire, one end of the top male heating wire is fixedly connected to the input power wire, and the input power wire is connected to the positive pole of the power supply circuit, and the end of the terminal heating wire opposite to the input power wire is fixedly connected to the output power wire, and the output power wire is connected to the negative pole of the power supply circuit, and the male heating wire and the female heating wire are far away from each other One end of each of the male and female heating wires is fixedly connected with a gate-type conductive segment, and one end of the gate-type conductive segment is fixedly connected with a conductive head, one end of the male heating wire and the female heating wire away from the gate-type conductive segment is fixedly connected with a conductive seat matching the conductive head, the inner wall of the installation cavity is fixedly connected with a plurality of segmented wires connected to the negative pole of the power supply circuit, and the segmented wires are fitted with the gate-type conductive segment, an electric telescopic rod is also installed on the inner wall of the installation cavity facing the gate-type conductive segment, and the output end of the electric telescopic rod is fixedly connected with an insulating pad that abuts against the gate-type conductive segment, the drying box also includes a humidity analysis module electrically connected to the humidity sensor, and the humidity analysis module is electrically connected to a control module, and the control module is electrically connected to the plurality of electric telescopic rods through a control processor.

[0013] As another improvement of the present application, an elastic conductive segment is fixedly connected between the gate-type conductive segment and the male heating wire and the female heating wire, and both the gate-type conductive segment and the elastic conductive segment are made of elastic conductive material.

[0014] As another improvement of the present application, the male heating wire, the female heating wire and the terminal heating wire are all sealed at the locations where they pass through the installation cavity, and the interior of the installation cavity is filled with insulating gas.

[0015] In summary, by introducing a self-regulating dryer into the existing preparation process, drying is first performed at the feeding stage, and then compensatory drying is performed at the discharging stage using the residual heat, which effectively saves energy consumption and can effectively improve the drying effect. The drying effect of the raw materials can be analyzed in real time by monitoring the humidity of the gas after drying, and the temperature during compensatory drying can be adaptively adjusted according to the monitored humidity conditions, effectively avoiding energy waste. In addition, the number of heating wires connected in series can be increased, and the heating effect of the heating wires can be effectively improved without increasing the current, thereby effectively improving the drying effect, and effectively saving energy consumption. In addition, the increase in the number of heating wires can also effectively increase the heating area, thereby further effectively improving the drying effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a preparation flow chart of the first embodiment of the present application; Figure 2A three-dimensional diagram of a self-regulating dryer according to a first embodiment of the present application; Figure 3 This is a cross-sectional perspective view of a self-regulating dryer according to a first embodiment of the present application; Figure 4 A three-dimensional diagram of a conveyor belt according to a first embodiment of the present application; Figure 5 This is a front cross-sectional view of a gas dehumidification box according to a first embodiment of the present application; Figure 6 This is a schematic diagram of the power-on of the second embodiment of the present application when an electric heating wire is connected; Figure 7 This is a schematic diagram of the power-on of the second embodiment of the present application when two heating wires are connected; Figure 8 This is a schematic diagram of the power-on of the second embodiment of the present application when three heating wires are connected; Fig. 9 This is a schematic diagram of the power-on of the second embodiment of the present application when four heating wires are connected; Fig.10 This is a schematic diagram of the power-on of the second embodiment of the present application when five heating wires are connected.

[0017] Description of the numbers in the figure: 1 drying box, 2 conveyor belt, 3 feed hopper, 4 electric hair dryer 1, 5 gas recovery monitoring box, 6 waste heat discharge box, 7 electric hair dryer 2, 701 installation cavity, 8 gas dehumidification box, 801 dehumidification net, 802 net cover, 803 sealing gasket, 9 ventilation pipe, 10 discharge hopper, 11 male heating wire, 12 female heating wire, 13 end heating wire, 14 power inlet wire, 15 segmented wire, 16 power outgoing wire, 17 gate conductive segment, 1701 elastic conductive segment, 18 conductive head, 19 conductive seat, 20 electric telescopic rod. DETAILED DESCRIPTION

[0018] Two implementation modes of the present application are described in detail below with reference to the accompanying drawings.

[0019] The first implementation method: Figure 1 Shown, comprising the following preparation steps: S1. First, put the polypropylene resin particles and the white masterbatch into a self-regulating dryer for drying to remove moisture and prevent bubbles from appearing during the subsequent stretching process. The drying temperature is controlled at 90-100°C and the drying time is 2-3 hours. S2, putting the dried polypropylene resin particles and the white coloring masterbatch into a mixer for thorough mixing and stirring, and then putting the mixture into an extruder, the extruder melts the polypropylene resin particles and extrude them to obtain a molten film, and then the molten film is cooled and solidified by a cooling roller, so as to obtain a BOPP white film blank; S3, the preliminary BOPP white film blank obtained in the above steps is successively sent to the longitudinal stretching machine and the transverse stretching machine for stretching, so as to improve the transparency and tensile strength of the BOPP white film, and then the film is sent to the heat setting machine for heat setting treatment after stretching, and cooled to room temperature after the setting is completed, so as to obtain the BOPP white film, and finally slitting, winding and packaging are carried out after passing the test; Figure 2 , 4 As shown, the self-regulating dryer includes a drying box 1, a conveyor belt 2 is installed inside the drying box 1, the conveyor belt 2 is a porous wavy structure, and the conveyor belt 2 is made of corrosion-resistant elastic composite material, the wavy conveyor belt can effectively increase the heating area, so that more polypropylene resin particles are in contact with hot air, thereby effectively improving the drying effect, and a feed hopper 3 is installed on the upper side of one end of the drying box 1, an electric hair dryer 4 is installed at the middle position of the conveyor belt 2 near the feed hopper 3, and the outlet of the electric hair dryer 4 faces above the conveyor belt 2, and a gas recovery monitoring box 5 is fixedly connected to the upper side wall of the drying box 1 facing the electric hair dryer 4, and an exhaust fan is installed inside the gas recovery monitoring box 5. and humidity sensor, the side wall of the upper end of the drying box 1 away from the electric hair dryer 4 is fixedly connected with a waste heat discharge box 6, and an exhaust fan is installed inside the waste heat discharge box 6. Specifically, in the process of drying the raw materials, the electric hair dryer 4 first dries the raw materials, and then the exhaust fan in the gas recovery monitoring box 5 draws up the gas, and then the exhaust fan in the waste heat discharge box 6 blows the recovered gas back to the raw materials to achieve compensatory drying of the raw materials, thereby effectively improving the drying effect and effectively saving energy consumption. The humidity sensor monitors the humidity of the recovered gas. High humidity indicates that there is still a lot of moisture in the raw materials and the drying is not thorough. Low humidity indicates that there is little moisture in the raw materials and the drying effect meets the standard. Figure 3 , 5It is shown that the lower end of the waste heat discharge box 6 is fixedly connected with an electric hair dryer 7 that penetrates into the interior of the drying box 1, and the outlet of the electric hair dryer 7 faces the conveyor belt 2, and the lower end side wall of the drying box 1 away from the feed hopper 3 is connected with a discharge hopper 10, and the drying box 1 is located between the gas recovery monitoring box 5 and the waste heat discharge box 6 and is also fixedly connected with a gas dehumidification box 8, and the interior of the gas dehumidification box 8 is clamped with a dehumidification net 801, and the upper end of the dehumidification net 801 is fixedly connected with a mesh cover 802, and the side wall of the mesh cover 802 is fixedly connected with a sealing gasket 803, the dehumidification net 801 dehumidifies the recovered gas to prevent the gas containing water vapor from accumulating in large quantities in the drying box 1 and affecting the drying effect, the mesh cover 802 plays the role of installing and fixing the dehumidification net 801, and the sealing gasket 803 can effectively eliminate the gap at the installation location to ensure a certain degree of sealing, thereby effectively preventing air leakage, and ventilation pipes 9 are connected between the two sides of the gas dehumidification box 8 and the gas recovery monitoring box 5 and the waste heat discharge box 6.

[0020] The second implementation method: Figure 6 As shown, a blowing port perpendicular to the conveyor belt 2 is provided on the middle inner wall of the electric hair dryer 2 7, and an installation cavity 701 is provided on the inner walls on both sides of the blowing port. The male heating wire 11, the female heating wire 12 and the terminal heating wire 13 are all sealed at the locations where they pass through the installation cavity 701, and the interior of the installation cavity 701 is filled with insulating gas. When the gate-type conductive segment 17 is disconnected from the male heating wire 11 and the female heating wire 12, an arc may exist, and the arc may cause the circuit to be incompletely disconnected. Therefore, the insulation performance is effectively improved by filling the insulating gas. A plurality of male heating wires 11 and female heating wires 12 arranged in parallel are fixedly connected between the two installation cavities 701, and the plurality of male heating wires 11 and female heating wires 12 are arranged alternately up and down, and a terminal heating wire 13 is also fixedly connected to the bottom of the two installation cavities 701, and one end of the top male heating wire 11 is fixedly connected to an inlet wire 14, and the inlet wire 14 is connected to the positive pole of the power supply circuit, and the end of the terminal heating wire 13 opposite to the inlet wire 14 is fixedly connected to an outlet wire 16, and the outlet wire 16 is connected to the negative pole of the power supply circuit; Figure 7 , 8 , 9 and Fig.10As shown, the ends of the male heating wire 11 and the female heating wire 12 that are away from each other are fixedly connected with a gate-type conductive segment 17, and an elastic conductive segment 1701 is also fixedly connected between the gate-type conductive segment 17 and the male heating wire 11 and the female heating wire 12, and the gate-type conductive segment 17 and the elastic conductive segment 1701 are both made of elastic conductive material, and the elastic conductive segment 1701 realizes the elastic connection between the gate-type conductive segment 17 and the male heating wire 11 and the female heating wire 12, so that the gate-type conductive segment 17 can be easily disconnected and connected with the male heating wire 11 and the female heating wire 12, and one end of the gate-type conductive segment 17 is fixedly connected with a conductive head 18, and the male heating wire 11 and the end of the female heating wire 12 away from the gate-type conductive segment 17 are fixedly connected to a conductive seat 19 matched with the conductive head 18, the inner wall of the installation cavity 701 is fixedly connected to a plurality of segmented wires 15 connected to the negative pole of the power supply circuit, and the segmented wires 15 are in contact with the gate-type conductive segment 17, and the inner wall of the installation cavity 701 facing the gate-type conductive segment 17 is also installed with an electric telescopic rod 20 (the specific model is selected according to actual needs and is not described in detail here), and the output end of the electric telescopic rod 20 is fixedly connected to an insulating pad that abuts against the gate-type conductive segment 17, and the drying box 1 also includes a humidity analysis module electrically connected to the humidity sensor The control module is electrically connected to the humidity analysis module, and the control module is electrically connected to the plurality of electric telescopic rods 20 through the control processor (the specific connection structure and control principle of this part are well-known technologies for technicians in the relevant field and 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. When the gas humidity is greater than the set monitoring threshold, it indicates that the drying effect of the raw material does not reach the 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 connected to the circuit by turning on the electric telescopic rod 20. Specifically, the number of electric heating wires connected to the circuit is increased in series. According to the characteristics of the series circuit, the more electrical appliances are added to the series circuit, the greater its total resistance will be. In this way, the heat generation of the entire device can be effectively increased, thereby effectively improving the drying effect, and no additional current is required. In addition, the heating wire is heated on the basis of recovering the gas, and the waste heat in the gas can save electricity consumption, thereby effectively saving energy consumption.

[0021] In summary, by introducing a self-regulating dryer into the existing preparation process, drying is first performed at the feeding stage, and then compensatory drying is performed at the discharging stage using the residual heat, which can effectively save energy consumption and effectively improve the drying effect. The drying effect of the raw materials can be analyzed in real time by monitoring the humidity of the gas after drying, and the temperature during compensatory drying can be adaptively adjusted according to the monitored humidity conditions, effectively avoiding energy waste. In addition, the number of heating wires connected in series can be increased, and the heating effect of the heating wires can be effectively improved without increasing the current, thereby effectively improving the drying effect, and effectively saving energy consumption. In addition, the increase in the number of heating wires can also effectively increase the heating area, thereby further effectively improving the drying effect.

[0022] In view of current practical needs, the above-mentioned implementation mode adopted in this application is not limited to the scope of protection. Various changes made within the knowledge scope of technical personnel in this field without departing from the concept of this application still fall within the scope of protection of the present invention.

Claims

1. A process for preparing a BOPP white film, characterized in that: The method comprises the following preparation steps: S1. First, put the polypropylene resin particles and the white masterbatch into a self-regulating dryer for drying to remove moisture and prevent bubbles from appearing during the subsequent stretching process. The drying temperature is controlled at 90-100°C and the drying time is 2-3 hours. S2, putting the dried polypropylene resin particles and the white coloring masterbatch into a mixer for thorough mixing and stirring, and then putting the mixture into an extruder, the extruder melts the polypropylene resin particles and extrude them to obtain a molten film, and then the molten film is cooled and solidified by a cooling roller, so as to obtain a BOPP white film blank; S3, the preliminary BOPP white film blank obtained in the above steps is successively sent to the longitudinal stretching machine and the transverse stretching machine for stretching, so as to improve the transparency and tensile strength of the BOPP white film, and then the film is sent to the heat setting machine for heat setting treatment after stretching, and cooled to room temperature after the setting is completed, so as to obtain the BOPP white film, and finally slitting, winding and packaging are carried out after passing the test; The self-regulating dryer comprises a drying box (1), a conveyor belt (2) is installed inside the drying box (1), and a feed hopper (3) is installed on the upper side of one end of the drying box (1), an electric hair dryer (4) is installed at a middle position of the conveyor belt (2) close to the feed hopper (3), and the outlet of the electric hair dryer (4) faces above the conveyor belt (2), a gas recovery monitoring box (5) is fixedly connected to the upper side wall of the drying box (1) facing the electric hair dryer (4), and an exhaust fan and a humidity sensor are installed inside the gas recovery monitoring box (5), and the upper side wall of the drying box (1) away from the electric hair dryer (4) is fixedly connected to the gas recovery monitoring box (5). A waste heat discharge box (6) is connected, and an exhaust fan is installed inside the waste heat discharge box (6). The lower end of the waste heat discharge box (6) is fixedly connected to an electric hair dryer (7) that penetrates into the interior of the drying box (1), and the outlet of the electric hair dryer (7) faces the conveyor belt (2). The lower end side wall of the drying box (1) away from the feed hopper (3) is connected to a discharge hopper (10). The drying box (1) is also fixedly connected to a gas dehumidification box (8) at a position between the gas recovery monitoring box (5) and the waste heat discharge box (6), and ventilation pipes (9) are connected between the two sides of the gas dehumidification box (8) and the gas recovery monitoring box (5) and the waste heat discharge box (6).

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

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

4. The process for preparing a BOPP white film according to claim 1, characterized in that: The middle inner wall of the second electric hair dryer (7) is provided with an air outlet perpendicular to the conveyor belt (2), and the inner walls of the second electric hair dryer (7) on both sides of the air outlet are provided with installation cavities (701), and a plurality of male heating wires (11) and female heating wires (12) arranged in parallel are fixedly connected between the two installation cavities (701), and the plurality of male heating wires (11) and female heating wires (12) are arranged alternately up and down, and the bottom of the two installation cavities (701) is also fixedly connected with a terminal heating wire (13), one end of the top male heating wire (11) is fixedly connected with an inlet wire (14), and the inlet wire (14) is connected to the positive pole of the power supply circuit, and the end of the terminal heating wire (13) opposite to the inlet wire (14) is fixedly connected with an outlet wire (16), and the outlet wire (16) is connected to the negative pole of the power supply circuit, and the ends of the male heating wire (11) and the female heating wire (12) away from each other are fixedly connected. Both are fixedly connected to a gate-type conductive segment (17), and one end of the gate-type conductive segment (17) is fixedly connected to a conductive head (18); one end of the male heating wire (11) and the female heating wire (12) away from the gate-type conductive segment (17) is fixedly connected to a conductive seat (19) matching the conductive head (18); the inner wall of the installation cavity (701) is fixedly connected to a plurality of segmented wires (15) connected to the negative pole of the power supply circuit, and the segmented wires (15) are in contact with the gate-type conductive segment (17); an electric telescopic rod (20) is also installed on the inner wall of the installation cavity (701) facing the gate-type conductive segment (17), and the output end of the electric telescopic rod (20) is fixedly connected to an insulating pad that abuts against the gate-type conductive segment (17); the drying box (1) also includes a humidity analysis module electrically connected to the humidity sensor, and the humidity analysis module is electrically connected to a control module, and the control module is electrically connected to the plurality of electric telescopic rods (20) through a control processor.

5. The process for preparing a BOPP white film according to claim 4, characterized in that: An elastic conductive segment (1701) is also fixedly connected between the gate-type conductive segment (17) and the male heating wire (11) and the female heating wire (12), and both the gate-type conductive segment (17) and the elastic conductive segment (1701) are made of elastic conductive material.

6. The process for preparing a BOPP white film according to claim 1, characterized in that: The male heating wire (11), the female heating wire (12) and the terminal heating wire (13) are all sealed at the locations where they pass through the installation cavity (701), and the interior of the installation cavity (701) is filled with insulating gas.

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