Production technology of PP thermoforming sheet by

2022-08-04
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The technology of "calendering method" to produce PP thermoformed sheets

pp (polypropylene) thermoformed sheets is currently the most widely used and the largest amount of sheets in positive pressure thermoforming in China. Even in the whole family of thermoforming sheets, they have already come from behind, almost equal to the amount of PVC and PS materials. At present, almost 100% of the "disposable" plastic jelly cups, sanitary cups for drinking water, soybean milk cups, tofu boxes, etc. that can be seen everywhere in the market are made of PP sheets by hot forming; In the domestic "disposable" plastic yogurt cup Market with an annual production of tens of billions or even tens of billions, PP material also accounts for more than half of the country; In daily life, "disposable" fast food boxes, instant noodle bowls, cold drink cups and other products are made of PP sheets by hot forming processing, which is more difficult to count. The application of plastic packaging products made of PP sheets by thermoforming in the fields of medicine, light industry, toys, food, tourism and so on is quite common. In addition to the heat resistance and good strength of PP material, the main reason is that PP material is one of the lightest plastic varieties, with a density of only 0.89-0.91g/cm and low material cost; Secondly, the price of raw materials is relatively cheap, the market supply is sufficient, and it is easy to buy; In addition, the production technology is easy to master, the ingredients are simple and easy to process; The most important thing is that the production equipment is cheap, which can easily lead to differences in experimental results

with the innovation of domestic sheet production lines, the introduction of foreign capital and imported equipment, and the application of new raw and auxiliary materials, the thermoforming industry is booming. Thermoforming sheet processing technology is also varied with different equipment, materials and uses. The increasingly mature sheet processing technology has gradually broken the old conventional theory. Now, even in the same sheet production line, qualified sheets with different uses, specifications and materials can be produced by different processes; Sheets of the same specification can also be processed with different equipment and processes. "No mode" brings great convenience to production

pp thermoformed sheets can be produced by calendering, calendering, salivation (with or without air knife) and other methods

in this article, we will talk about some technologies for producing various PP thermoformed sheets by "calendering". For your reference only, please criticize and correct any improper points

this paper is based on the simplest equipment configuration of "Extruder - T-head - vertical three roller calender - traction - coiling". (the high-grade sheet production line generally adopts "precision extrusion" technology, including PLC highly automated programmable computer control system, melt pump, static mixer, etc. the three rollers are mostly horizontal structure, and servo motors are used independently. I will tell you a few points of transmission below. It is equipped with an independent circulating water control system, and generally adopts "calendering method" Production. In general, in order to prevent the deformation of rollers and frames, which will affect the processing accuracy of sheets, it is not advocated to adopt "rolling method" in high-end sheet production lines in principle. Therefore, some high-grade sheet production lines have automatic protection function. When the sheet is produced by rolling method, if the three roll drive motor is overloaded, the whole production line will stop automatically.)

the biggest difference between "calendering method" and other methods is that there is obvious smooth and uniform residual glue rotating between the first and second rollers entered by the machine head, and the third roller generally does not need to press the middle roller

since there is some residual glue between the rollers, which plays a great role in stable production, the common electromechanical configuration can be met. That is, melt pump, static mixer and PLC highly automatic programmable computer control system are not required. It can reduce the investment cost and production cost. However, the strength of the roller and frame is higher than that of the "calendering method" and "salivating method", because the roller receives a large separation force. When the "rolling method" is used for production, the operation is convenient, the workers are easy to master the technical essentials, and the equipment maintenance is also very simple. At present, almost 100% of domestic equipment can meet the requirements. Therefore, when the "calendering" process is used to produce PP thermoformed sheets, it is more economical to use domestic equipment than imported equipment

selection of common PP raw materials for thermoforming: PP granular materials are usually extruded plate grade, sheet grade, drawing grade, narrow band grade or thermoforming grade

I. when the "calendering method" is used to process thick PP "positive pressure hot formed sheet" (0.50-2.50 mm), PP material has strong adaptability to equipment and loose process requirements

take the vertical three roll upper feeding as an example: when the "rolling method" is adopted for production, there is residual glue between the upper roll and the middle roll, which is as thin as a pencil. In the production of 0.50mm-2.5mm or even thicker positive pressure thermoforming PP sheets, the equipment has a wide range of adaptability and the process adjustment is relatively easy. In addition, it has the following advantages:

(1) when using the "calendering" process to produce PP positive pressure thermoformed sheets, PP materials have strong adaptability to screws and barrels:

whether it is the special, mutation, separation, l/d=22-25 single screw recommended in theory, or other new single screws such as gradual change, general use, exhaust, l/d=2o-35, barrier, shunt, etc, There are successful examples in actual production

this is because in actual production, each factory has different strengths, so it is impossible to have special equipment or configuration. In addition, due to the frequent replacement of materials, it is impossible to replace them with special barrels and screws every time. Therefore, in actual production, a sheet production line can be used to produce hips, CPS, ABS sheets, PP, PE sheets, PP degradable materials and PP, PE sheets containing filling masterbatch

for enterprises specializing in the production of sheet production line equipment, the sheet production lines launched are generally suitable for processing PP materials. Such as Tianjin Hengrui, Shanghai Jinwei, Jinhu, Shantou Dacheng, Weida, etc

(2) when using the "calendering method" process to produce PP positive pressure thermoformed sheet, PP material has strong adaptability to the head structure, speed regulation mode, transmission mode, temperature control mode, lip opening and feeding mode (upper feeding and lower feeding)

pp material has a wide processing range, so the temperature setting is also relatively wide. As the melting point of PP material is 164- - 170 ℃, in actual production, the processing temperature can be set from 170 ℃ to 270 ℃, which varies with the origin of materials, equipment and processing place

generally, there is no strict requirement for the opening of the lip, but the opening of the lip should be at least greater than the thickness of the sheet. In practice, there are many sheet specifications, so it is difficult to adjust the opening of the lip. Even the lip that produces the thickest sheet can be used all the time. Some use lip (thickness) opening ≈ sheet thickness x (1+10-30%); In some cases, when the thickness of the sheet is less than 0.8mm, the opening of the lip is 1.0mm; when the thickness of the sheet is greater than 0.8mm but less than 1.5mm, the opening of the lip is 2.0mm (because the thickness of the sheet for general thermoforming rarely exceeds 2.0mm)

the circulating water with common three roll temperature shall be controlled at 30 ℃ - 80 ℃. The three roller circulating water circuit has several modes such as series connection, parallel connection and independent control, which can meet the production requirements

for example:

a. sheet production line made in Taiwan: screw ф 150 mm X34, without exhaust single screw and barrel; Coat hanger head, 100mm wide, with damping strip; Roller ф 490mmx110mm, chain drive, hydraulic cylinder controls the lifting of upper and lower rollers; The independent circulating water tank automatically thermostatically controls the three roll temperature; Vertical lower feeding; DC variable frequency adjustable speed motor, power 300hp; The leftover materials are randomly crushed and then squeezed into the hopper for use; Vacuum feeding

when the "rolling method" is used to produce (thickness) 1.70 mm x (width) 710 mm CPP, the normal production process records are as follows:

(1) the ingredients are: 50kg of granular pt103 (Taiwan fuxine), 60kg of crushed material (50kg of thick crushed material, 10kg of thin crushed material), and 0.2kg of powdered transparent agent (made in Hong Kong)

(2) fuselage temperature control: 233-237-235-236-239-249-250-243 (unit: ℃)

(3) nose temperature control: 235-235-235-235 (unit: ℃)

(4) three roll water temperature control: (lower middle upper) 28.4-28.6-23.5 (unit: ℃)

(5) screw speed: 57.7 (r/min)

(6) three roll linear speed: 9.3 (m/min);the; Traction force: 30.8kn

(7) speed of main motor: 938 (r/min); Host current: 390a

(8) upper and lower roller status: both upper and lower rollers are pressed

(9) residual glue status: as thin as a ball point pen core, evenly distributed, in a straight line, on the top of the extruded blank. It only exists between the middle roll and the lower roll

(10) filtration: 80 mesh x2+100 mesh; Front pressure 230kg/cm

(11) lip opening: 2.3mm

(12) distance between the machine head and the center line of the three rollers: 100mm

(13) sheet quality: good surface and transparency (hot forming machine test to the positive pressing cup) good hot forming performance

note:

(a) during the test: both the upper and lower rollers are pressed; The remaining glue is as thin as the ball point pen core, evenly distributed in a straight line, and only exists between the middle roll and the lower roll on the upper side of the extruded blank; The temperature setting is quite random

(b) due to the large current of the main engine and the slow speed of the screw, the temperature of the machine body and head can be increased by 10-20 ℃

(c) through the test, when the upper and lower rolls are pressed, the residual glue exists not only between the upper roll and the middle roll, but also between the middle roll and the lower roll. The residual glue is as thin as a ballpoint pen core, evenly distributed and in a straight line, and the sheet can also be produced and used normally

(d) through the test, when the upper roll is not pressed, only the lower roll is pressed, and the remaining glue is as thin as a ballpoint pen core, evenly distributed and in a straight line, and exists only between the middle roll and the lower roll on the upper side of the extruded blank, the sheet can also be produced and used normally

(E) through the test, the forward temperature setting (235-260 ℃), reverse temperature setting (260-235 ℃) or setting of the fuselage are the same (245 ℃), and the sheets can be produced and used normally

Description:

(1) this production line is mainly used for "calendering" production of PP, hips, CPS and other sheets

(2) here, I just want to prove that it is feasible for this production line to produce PP thermoformed sheets by "rolling 12.0 method" from the perspective of process, and the forms are diverse

b. jp-750p sheet extrusion unit of Shantou Dazhou packaging machinery factory: screw ф 105 mm X35, exhaust single screw and barrel; Commutator speed regulating motor, power 100kW; Hanger type head with damping strip; Three roll specification ф 316 mmx800mm, chain drive; The manual worm reducer controls the lifting of the upper roller, and the lower roller cannot be lifted; Vertical upper feeding; The constant temperature circulating water tank controls the temperature of the three rollers

when the "calendering method" is used to produce (thick) 1.50mmx (wide) 580mmwpp biodegradable positive pressure thermoformed sheet, Normal production process records are as follows:

(1) ingredients: PP biological starch degradable granule (Xi'an Wanjie) 100kg + degradable crushed material 120kg

(2) body temperature: 180-185-190-190-195 (unit: ℃)

(3) head temperature: 195-190-195 (unit: ℃)

(4) filtration: 60 mesh x2+80 mesh x2

(5) residual glue state: coarse as index finger, evenly distributed, well rotated Smooth

(6) upper roll temperature: 40 ℃; Middle roll 45 ℃, lower roll: 30 ℃

(7) lip opening: 2.5mm

(8) when the size of residual glue remains appropriate, the speed of main machine and three rolls can be accelerated or slowed down at the same time

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