Biaxial stretching technology and application anal

2022-09-28
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Plastic film biaxial stretching technology and application analysis (II)

3 melt filter in order to remove impurities, gel particles, fish eyes and other foreign matters that may exist in the melt, a filter is often installed at the front and back of the metering pump on the melt pipeline. PET film production line usually adopts dish filter, which is made of stainless steel and stainless steel sintered felt. The size of stainless steel disc is Φ 12 inches, the filter aperture is generally μ。 The heating temperature of the filter is controlled at ℃

4 melt pipe

the function of melt pipe is to connect the extruder, metering pump, filter, etc. with the die head to let the melt pass through. The inner wall of the melt pipe is required to be highly clean and free of dead corners, and the length of the melt pipe connected in series should be as short as possible, so as to avoid the degradation of the melt due to stagnation and long residence time in it

after the melt from the extruder enters the melt pipe, it flows through the coarse filter, metering pump and fine filter and then enters the die head. In the case of a three-layer coextrusion line, a melt distributor is also configured above the die head. Filters, metering pumps and melt pipes can be heated by electricity or by heat transfer oil jackets. The heating temperature of melt tube is controlled at ℃

5 static mixer

when the melt flows through the melt pipe, there is a large temperature difference between the melt temperature along the pipe wall and the temperature in the melt center. In order to make the melt temperature entering the die uniform and ensure the uniform discharge of the die, it is necessary to install it inside the end of the melt pipe connecting the die. If the static mixer is dry, when the melt flows through the static mixer, The large load friction and wear testing machine (1000KN) will automatically produce the mixing function of opening closing opening closing, so as to achieve the purpose of homogenizing the melt temperature

sheet casting system

the sheet casting system mainly includes die head, quench roll, sheet casting attachment device, etc

1 die head: it is the key of cast sheet, which directly determines the uniformity of the shape and thickness of the cast sheet. Pet often adopts clothes hanger type. In 2010, the R & D expenditure of local enterprises accounted for only 1.77% of the enterprise's sales revenue on average. The opening of the die head was initially adjusted by several push/pull differential bolts with rings, and the opening of the die lip was fine adjusted by the automatic thickness measurement of the thickness gauge and the heating bolts fed back to the die head. The temperature of die head is controlled at about 275 ℃

2 quench roll (casting roll, commonly known as cold drum): PET melt flowing out of the die head in viscous flow state is quickly cooled on the quench roll rotating at a uniform speed to below its glass transition temperature to form a glass state cast sheet with uniform thickness. The purpose of quenching is to make the thick sheet into an amorphous structure and minimize its crystallization, so as to avoid adverse effects on the next drawing process. Therefore, the requirements for the casting roll are as follows: first, the surface temperature should be uniform and the cooling effect should be good; Second, the speed of quench roll is required to be uniform and stable. Cooling water of about 30 ℃ is supplied to the casting roll to ensure that the other pieces are cooled below 60 ℃

3 electrostatic adsorption device: its function is to make the cast sheet in close contact with the quench roll to prevent the quench roll from being entangled in air when rotating, so as to ensure the heat transfer cooling effect. The electrostatic adsorption device is composed of metal wire electrode, high voltage generator and electrode retraction torque motor. Its working principle is to use the thousands of volts of DC voltage generated by the high-voltage generator to turn the electrode wire and the casting roll into the negative pole and the positive pole respectively (the casting roll is grounded). The improvement of the effective resolution of the casting roll in this high-voltage static 1 flavor is to bring the static charge with opposite polarity to the casting roll due to electrostatic induction in the electric field at the expense of dynamic performance (bandwidth). Under the effect of opposite attraction, the surface of the casting roll and the quench roll are closely adsorbed together, Achieve the purpose of eliminating air and good heat transfer

for non-polar polymers such as PP, the effect of electrostatic adsorption is not as good as that of polar pet, so the air knife method is usually used for sheet casting in BOPP double drawing production line

longitudinal stretching (MDO)

longitudinal stretching refers to the longitudinal stretching of thick sheets from the casting machine for a certain number of times under the heating state. The longitudinal stretching machine is composed of preheating roll, stretching roll, cooling roll, tension roll and rubber pressing roll, infrared heating tube, heating unit and driving device

preheating rollers: generally, there are 8, the roller surface is chrome plated, arranged in a line, and the temperature is 60 ℃ -80 ℃

stretching roller: in case of single point stretching, there is a slow pulling roller and a fast pulling roller, and the surface is chrome plated. The temperature of slow drawing roller is 80 ℃ -85 ℃, and the temperature of fast drawing roller is 30 ℃

cooling rollers: there are generally 4, the roller surface is chrome plated, arranged in a line, and the temperature is 30 ℃ and 50 ℃

tension rollers: two, located above the first preheating roller and the fourth cooling roller respectively

longitudinal Rabbi: generally in 5 times, which is produced by the speed difference between the slow drawing roller and the fast drawing roller

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