The prospects, uses and functions of polyester

Transesterification method: The ester exchange reaction uses a catalyst, which results in an increase in the ash content in the reactant. To ensure that the product has a sufficient degree of polymerization, the transesterification rate is required to be above 99%. The transesterification reaction can be operated under normal pressure, and the reaction is easy to control. Methanol is generated in the casein exchange reaction, so a methanol recovery device is required.

　2． Classification of polycondensation process

The polycondensation process is mainly divided into intermittent polycondensation, continuous polycondensation, semi-continuous polycondensation, etc.

Intermittent polycondensation: It is mainly composed of an esterification (or transesterification) reactor and a polycondensation reactor. Each reactor is fed in batches and discharged after reaction, and operates intermittently.

Continuous polycondensation: It consists of several reactors connected in series. The raw materials PTA/DMT, EG and additives, catalysts, matting agents, stabilizers, etc. are added in a certain proportion. The reaction products continuously enter the next reactor. , PET is produced in the final polycondensation kettle, and then continuously enters the cast belt to be pelletized and processed into PET slices or melted PET enters the direct spinning process for spinning.

Semi-continuous polycondensation: The characteristic of this process is that it can be adapted to produce small batches and multiple varieties of products. Semi-continuous polycondensation production is to add an intermediate storage tank after the first and second esterification reactors to store BHET, and then add it into the intermittent polycondensation reactor in batches to perform the polycondensation reaction, while the first and second esterification reactors It is similar to the continuous esterification process with the intermediate storage tank to complete semi-continuous polycondensation production.

Continuous knitting and polymerization production is large-scale. (www.ninbofp.com) At present, the annual output of a production line can reach more than 100,000 tons. Product quality is easy to control and production is easy to operate. Direct melt spinning eliminates the need for cutting, drying and melting processes, thereby savingWith the investment, production costs have dropped significantly. The intermittent polycondensation production process is simple and easy to change varieties and produce special varieties, but its production capacity is low, product quality is limited by each batch, uniformity and spinnability are poor, and consumption is high.

　3． Main equipment

Esterification reactor: Caseinization reactor is divided into two types: vertical and horizontal, and the reactor is divided into single chamber and multi-chamber. In batch polycondensation, one type of esterification reaction.

Transesterification reactor: The reactor types are divided into three types: multi-kettle type, multi-chamber type and tower type. Among the intermittent polycondensation processes, there is only a single-kettle type.

Precondensation polymerization reactor: divided into tank reactor with stirrer and capacity disk tower reactor without stirrer. There are two types of reactors: vertical and horizontal.

Condensation polymerization reactor: There are two types. One is a horizontal reactor, which has two types: single-axis and double-axis. Its components are composed of discs of different forms. The other is a squirrel cage disc reactor. (2) Production of polyester fiber Polyester fiber production methods include direct spinning and slice spinning.

　1． Production of polyester staple fiber

The production of polyester staple fiber is divided into slice spinning and direct spinning according to the different raw materials (PET) used (slices, melt). Post-processing includes bunching, stretching, heat setting, curling, cutting, packaging, etc.

Depending on the properties of the fiber required, different processes can be used. If you want to produce high-strength and high-modulus fibers, you can use two-stage stretching and tension heat setting processes; if you want to produce low-strength and high-modulus fibers, you can use Use one-stage stretching and tension heat setting process; if you want to produce low-strength and high-elongation fiber, you can use one-stage or two-stage stretching and relaxation heat-setting process; if you want to produce medium-strength and medium-elongation fiber, you can use two-stage stretching and semi-tension heat setting process.

Features of the chip spinning process: The chip spinning process (polyester factory and spinning factory) can be constructed in two separate places, so it is very flexible and can produce different products according to different chip quality requirements for each batch. Variety of fiber. However, due to the raw material PET, it needs to undergo drying, melting, screw extrusion and other processes before forming the melt, which increases the construction cost and production cost, and is not suitable for large-scale spinning needs.

Characteristics of the direct spinning process: The melt PET generated in the final polycondensation kettle can be directly spun without the need for belt casting, pelletizing, packaging, transportation to the spinning plant, unpacking, drying and reprocessing. Melting, etc., thus can not only save construction costs, but also significantly reduce production costs, thereby forming large-scale production, becoming competitive, and improving corporate economic benefits. Its disadvantage is that it is not suitable to change product varieties frequently, and if any failure occurs in any link upstream and downstream of spinning and polyester, the entire production line may be shut down. Therefore, the production management of direct spinning process is strict, and breakdown shutdown is avoided as much as possible. At present, my country’s polyester staple fiber production has reached a large scale, with the annual production capacity of a single line reaching 30,000 tons.

The main equipment for the production of polyester staple fiber is the spinning machine. The spinning machine is mainly composed of spinning box, cooling blower, spinning cylinder and winding into strips.

Spinning box: The spinning box is composed of melt distribution pipes (1, 2), metering pumps (3, 4) and spinning components (5). The arrangement of the melt distribution pipe must ensure that the flow time of the melt from the distribution head to the multiple spinning parts is the same, and the pressure drop must also be the same. The spinning box requires a constant temperature and good airtightness. The conduction steam generated by the electric heating of the conduction boiler is sent into the box to achieve the purpose of heat preservation.

The measuring pump is composed of a pair of gears, three plates and a transmission shaft. The metering pump has a simple structure and requires features such as easy assembly, disassembly and heating, material resistance to high temperatures of 450°C, high processing accuracy, and no leakage accidents. The spinning assembly consists of a melt introduction top plate (1~5), a distribution plate (6~7), a sand filter layer, a metal mesh (8~2), a spinneret (13) and a pressure-resistant plate (14, 15). The structure of the spinneret is related to the spinning state and the output of the spinning machine. The structural parameters of the spinneret include the number of holes, arrangement, hole diameter, hole geometry, etc. .

Cooling blowing: divided into two categories: vertical blowing and horizontal blowing. The purpose of cooling and blowing is to make the filament evenly cooled and have a uniform cross-sectional structure. Spin tube: The length of the spinning tube varies, while ensuring the cooling effect and smooth winding, it is generally about 3 meters.

Coiling into strips: It consists of tanker oiling, coiling, bunching, re-oiling, hauling, feeding and strip formation. Among them, the winding roller is the key component. Currently, a small roller is mostly used, which plays a steering role. 2. Production of polyester filament The production of polyester filament adopts melt spinning method, including slice spinning and continuous polycondensation. Melt direct spinning method. The spinning production process of polyester filament is divided into three process technologies: conventional spinning, medium-speed spinning and high-speed spinning according to the spinning speed.

Conventional spinning process: Conventional spinning is also called low-speed spinning. Generally, the spinning speed is 1000~1500 m/min, the drawing and twisting speed is 600~1100 m/min, the false twist deformation speed is 120~160 m/min, and the winding speed is 900~1200 m/min. It can be spun. 33~167 points special filament. The melt spinning temperature is controlled at 280~290℃, the screw extrusion pressure is controlled at 6.5~7.5 MPa, and the spinning component pressure is controlled at 9.8~24.5 MPa. Spinning generally uses side-blown cooling, the temperature is controlled at 20~30℃, and the wind speed is 0.3~0.5 m/min.