CN100396719C - Method and device for heat treatment of polyester granules - Google Patents

Abstract

The invention relates to a method for the heat treatment of polyester granules to achieve partial crystallisation, wherein the polyester melt is fed to an underwater granulator and granulated, the granules obtained are fed to a water-solids separation device, the dried granules are fed to a movement device at a granule temperature above 100 ℃, and the granules leave the movement device at a temperature above 100 ℃. The invention also relates to a device for carrying out said method.

Description

Method and device for heat treatment of polyester granules

The present invention relates to a method and apparatus for heat treatment of polyester granules to achieve crystallization.

Polyethylene terephthalate, hereinafter referred to as PET, is a polyester with repeating ester groups.

PET can exist in different structures, namely non-crystalline (amorphous) form, crystalline form or partially crystalline form. Non-crystalline (amorphous) PET is mostly transparent, while crystalline PET is opaque or white. As Like all thermoplastics in amorphous or crystalline form, it is impossible for PET to achieve 100% crystallinity. Only a part of the PET structure can be oriented in the same direction, that is to say, crystallized. Crystalline regions and non-crystalline regions exist alternately. Therefore, Generally speaking, it refers to partial crystallization.

PET can achieve a crystallinity of about 50% to avoid particles or fine particles sticking to each other. That is to say, in this case, half of the molecular chains can be positioned in the same direction with each other, so that they are arranged in parallel, side by side, or around Therefore, in the partially crystalline region, the interaction force (van der Waals force) between the molecular chains will inevitably become larger. The molecular chains will also attract each other, so the gap between the molecules will also become smaller.

As a thermoplastic material, PET is moldable when the temperature reaches 250 ° C. The molecular chains will move, causing the plastic to melt and form a viscous substance, which can be made into almost any desired shape. When cooling These molecular chains are frozen again and the plastic solidifies in the desired shape – this is a simple principle that can be repeated many times. This method can also be used, for example, to manufacture PET bottles. The first step is to manufacture the so-called Preform. As the predecessor of the PET bottle, the preform already has a prepared thread. When the temperature reaches 100 ° C, the bottle becomes soft again and is stretched and blown into a bottle using compressed air (stretch blow molding method), so You can get the right bottle.

Current methods of manufacturing granular, crystalline PET include numerous and complex swirl bed or fluidized bed processes, which require large investments and high operating costs (DE 19848 245 A).

PET particles must be crystallized below the temperature at which the material becomes viscous, so as to avoid the particles flowing together and forming a solid, difficult to reprocess substance. Although the melting temperature of polyester after crystallization is between 240 ° C and 250 ° C , but it becomes viscous at temperatures above 70°C before crystallization.

As far as the entire process known today is used to produce dry PET pellets, they generally require very large production equipment because of the long crystallization times required.

For example, in US5 532 335 A, a method for heat treatment of polyester particles is proposed. In this method, the particles are introduced into a treatment container, and a liquid medium is also introduced into the container, and the particles and liquid medium mixed with each other. In this method, water under pressure or so-called superheated water is used as the liquid medium. By changing the pressure in the reaction vessel, its boiling temperature can be easily controlled. In one embodiment, Polyester pellets are treated at a temperature between 120°C and 182°C. Hot water is introduced into the treatment vessel at 160°C. As long as the pressure in the reaction zone is maintained at 7kg/ ^cm2 or higher, the hot water can Keep it in a liquid state and mix it with the particles. Obviously this method is very costly and uneconomical to implement.

Another known method of working with pneumatic handling also has its significant drawback, that is, the use of large quantities of inert gas. The energy costs and production costs are too high for practical mass production.

In GB 1 250 690 A, a method for producing polyethylene terephthalate particles suitable for die-casting (injection molding) in a solid phase after heat treatment is proposed. Here, in the usual melt polycondensation method The hot polyester melt produced at about 280°C is fed as starting material to an underwater pelletizer, where the hot plastic strands extruded from the nozzle are caught by the water jets from the ring nozzle and cooled The plastic belt is then conveyed through an underwater cooling zone to a cutting device. The pellets exit the cutting device and enter a screen, which separates the solids from the water, which is recycled through the cooler. The wet pellets are dried So that thermal subsequent solidification is possible. These particles are suitable for die casting, especially in the solid phase, if treated in thermal subsequent solidification at temperatures above 200°C.

The main feature of this method is that these products, which have been largely cooled by the pellet belt method (underwater cold-cut pelletizing system), must be reheated for further thermal processing, which requires Expends a lot of energy, which is lost in the previous cooling process.

In order to crystallize materials adequately in the state of the art, it is always necessary to supply sufficient external energy or heat during the crystallization process. This makes recycling of PET more difficult.

The object of the present invention is to propose a method for crystallizing PET granules which does not require external energy or heat to be supplied and which does not need to last for a long time.

To this end, the present invention provides a method for the heat treatment of polyester granules to achieve partial crystallization, wherein the polyester melt is pelletized; the granules are then heated at temperatures above 110° C. The temperature of the pellets is conveyed to a moving device, characterized in that the polyester melt is conveyed to an underwater hot-cut pelletizing system, and the obtained pellets are sent from the underwater hot-cut pelletizing system through a short transportation distance to an as Centrifuges for water-solid separation plants, moving and transporting the particles in a moving device, where a vibrating transport chute is used as said moving device, and finally, a thermal treatment leading to partial crystallization by means of the inherent heat present in the particles.

Correspondingly, the present invention also provides a device for carrying out the method of heat-treating polyester granules to achieve partial crystallization of the granules, having a melt pump, a filter screen changer and a granulator, characterized in that the granulator The granulator is an underwater hot-cut granulator, and a transport device for transporting the granules is arranged behind a water-solid separation device to keep the granules moving, wherein the granules are heated by the inherent heat of the granules during the transportation process. Crystallization, and, the transporter is designed as a vibrating transporter.

In other words, the following method is proposed: At the appropriate temperature, the PET starting material in the extruder is extruded. Immediately after that, the impurities are filtered out by means of a filter changer technology (Siebwechslertechnik). The polyester melt is are conveyed to an "Unterwasser-Heissabschlag-Granuliersystem" (Unterwasser-Heissabschlag-Granuliersystem), hereinafter referred to as "Underwater Granulier" and processed into granules which, by underwater granulation, assume the shape of spheres or lentils, and has a high core temperature.

These PET granules are transported at a very fast speed through a transport pipeline to a water-solid separation unit, wherein preferably hot water not exceeding 98° C. is used as the transport medium. According to this method of the present invention, it is important for its effectiveness The point is that the transportation distance between the granulation chamber and a water-solid separation device is relatively short.

PET pellets leave the water-solids separation unit with a core temperature of 130°C-180°C, since the aim is to maintain the extrusion temperature of PET for as long as possible.

The particles at this temperature then undergo a movement in which the crystallization process begins. According to the method according to the invention, the crystallization process is initiated by inherent heat and makes it possible for the product, the particles, to no longer agglomerate, nor Then stick to each other. Since the products to be crystallized are spherical or lentil-shaped, that is to say, the contact surface between them is as small as possible, which also improves this effect.

The residence time of spherical particles in this stage of movement is, for example, 3 to 8 minutes. After this stage, PET particles can reach a crystallinity of 40% or higher, and their temperature is kept above 100 ° C. Hot PET particles can be The pellets are transported to a silo or reprocessing station as the pellets will not stick together again.

It is also an object of the invention to provide a device with which the movement of the particles can be carried out in a more efficient manner.

Preferably, a so-called crystallization tank is provided as a movement device for the particles. This crystallization tank is constructed similarly to the particle transport chute, but is divided into successive cells as seen in the transport direction, which are separated from each other by partitions. Separated. The crystallization tank is also equipped with a vibration motor, so the particles on the crystallization tank can move continuously, and can transfer their own energy to other particles. PET particles are circulated in each small chamber, and the PET particles are not will stick together again.

With the method and device according to the invention, a gentle, economical and rapid crystallization of PET granules can be achieved.

Embodiments of the invention are described below with the aid of the accompanying drawings.

In the accompanying drawings, a melting pump and a filter screen changer are indicated by 1, and polyester is conveyed into it in the direction indicated by arrow F1. An underwater granulator 2 is provided at the outlet of the filter screen changer, Spherical or lentil-shaped granules are produced by this device. These granules are directed via a transport device to a water-solid separation unit 3, such as a centrifuge, where process water at a temperature above 80° C. is preferably used for transport of the granules The particles leave the water-solid separation device 3 with a temperature of more than 110°C and are transported to a transport chute 4, which is fed with air at position 5, which leaves the transport device 4 at position 6 and carries away the moisture. This transport device 4 is designed in the form of a transport chute with partitions 7 arranged transversely to the transport direction, the particles leave the transport device 4 with a particle temperature of more than 100° C. and can be conveyed via a so-called particle diversion 8 to a post-processing device 9 or silo 10. These granules achieve crystallinity of 40% or higher and have good handling properties.

Claims (9)

1. polyester granulate is heat-treated to reach the method for partial crystallization, wherein, the polyester melts is carried out granulation; Particle then is transported to a running gear with the particle temperature that is higher than 110 ℃ under the situation that does not have the input of outside energy or heat, it is characterized in that,

The polyester melts is flowed to a fervent granulating system under water,

With the particle that obtained under water earnestly granulating system be transported to a sedimentator as water-solid separating device through too short shipment distance,

Particle is moved in running gear and transport, wherein be to use vibration transportation chute as described running gear, last,

Cause the thermal treatment of partial crystallization to be achieved by means of the intrinsic heat that exists in the particle.

2. by the described method of claim 1, it is characterized in that, particle is sent to water-solid separating device from the granulation underwater system by means of the production process water of heat.

3. by the described method of claim 2, it is characterized in that the temperature of described production process water is 98 ℃.

4. by the described method of claim 1, it is characterized in that particle leaves described running gear with the particle temperature above 80 ℃.

5. be used to implement polyester granulate is heat-treated device with the method that reaches the particulate partial crystallization; have a Melting pump, a screen replacing device and a tablets press; it is characterized in that; tablets press is a fervent under water tablets press (2); and; be provided with one in a water-solid separating device (3) back and make the particle moving conveyer (4) of not stopping transport in order to transport particles; wherein; particle carries out crystallization by the intrinsic heat of particulate in transportation; and described conveyer (4) is designed to vibrate conveyer.

6. by the described device of claim 5, it is characterized in that conveyer (4) is configured to transport chute.

7. by the described device of claim 6, it is characterized in that distributing, it is a plurality of that separate each other and play the dividing plate (7) of a material iris action respectively to be provided with on the whole length of transportation chute.

8. by the described device of claim 5, it is characterized in that conveyer (4) is surrounded at least in part by a housing.

9. by the described device of claim 5, it is characterized in that, a sedimentator is set as water-solid separating device (3).

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