DE1804552A1 - Process for increasing the degree of condensation of polyethylene terephthalate - Google Patents

Description

Process for increasing the degree of condensation of Poiya "thy 1 en terephthalate.

It is known that polyethylene terephthalate can be converted from low to high by thermal treatment in the melt and in vacuo Degrees of condensation can be brought. There is a limit to this process because of a certain degree of condensation in the degradation by thermal decomposition faster than the build-up is going on. It is also known that higher degrees of condensation than those achievable with melt condensation can be achieved if polyethylene terephthalate in solid Phase is heated to temperatures of over 200 C. This increase in Kondünsatioiiiägrudaü gives the material excellent mechanical propertieson. By processing in the injection molding process, any shaped body can be made with flat these mechanical properties have been produced. Just Injection molding processing places certain demands on the external shape of the thermoplastic to be processed. Of the Koliststoff must be readable enough that it evenly flows into the Injection molding machine is drawn in.

Is the thermal treatment of the feston, granulated polyethylene terephthalate carried out in a known manner, e.g. in agitator bowls, because of the softness and Tackiness of the polyethylene terephthalate at the required

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normal temperature to deformations, caking and abrasion phenomena, which make the reaction material unsuitable for processing in injection molding machines. In all procedures Similar phenomena can be observed where the reaction material is moved under mechanical stress.

To solid-phase condensed polyethylene terephthalate in To bring a shape suitable for injection molding processing, it is necessary to remove the material after the thermal treatment to melt again and re-granulate. This represents but is another costly process step, which also causes the polyester to partially degrade and thus partially reverses the result of the thermal treatment.

It therefore appears expedient to carry out the thermal treatment of the polyethylene terephthalate in the solid phase in such a way that the granulate form required for injection molding is used and that it is no longer changed during the thermal treatment in the solid phase. The thermal treatment must therefore be carried out on the stationary or only gently moving reaction material. A thawing apparatus could be used for this; however, it has the disadvantage that it is only suitable for continuous operation. Heating amorphous polyester granules in a fixed bed leads, according to experience packaging, which result in "that the Schüttühg loses its flowability. This has size Sch \ <rierigkeiten when delivering a result, in particular, ⁵ .if the ReaktiOrisgjut for reasons of saving time To be discharged, the reactor material would have to be exposed to a strong mechanical load , which in turn causes undesirable deformations and abrasion defects.

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I) Io indicated methods do not allow to use in toch ^ nisch satisfactory way the desired thermal treatment to be carried out in solid phase.

The present invention now relates to a process for increasing the degree of condensation of polyethylene terephthalate by thermal treatment dos crystallized in a known manner and dried polyester, which is characterized in that the polyester is at a temperature which 0 to 100, preferably 0 to 20 C below the intended Condensation temperature is, transferred into the reactor, as a reactor in which the condensation in the usual Way carried out in a stream of inert gas and / or under reduced pressure is used, an apparatus that is neither a cross-sectional ™ Has constriction in the direction of the product flow, still contains internals reaching into the product bed.

The inventive method of operation, which is suitable for both discontinuous and, with particular advantage, for continuous operation, is characterized by its simplicity. Due to the absence of moving and / or immobile internals such as agitator units, baffles etc. within the reactor in connection with the requirement to use the polyester to be condensed in a preheated and crystallized state, there are no disruptions either during the condensation or when the reaction mixture is discharged from the apparatus. Since the hot m

filled polyester itself - depending on the difference between Filling and condensation temperature - in reactor no more or expands only insignificantly, eliminates the risk of sticking of the polyeator granules by mutual pressing or Pressure against the reactor wall, which inevitably occurs when the reactor is heated up. It is therefore advisable to condensing polyester at a temperature which is as close as possible to the selected condensation temperature Introduce reactor. The polyester crystallized and dried in a known manner is therefore generally used when it is introduced

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in the reactor a temperature which is ό to at most 100, preferably 0 to 20 C below the intended condensation temperature from approx. 200 to 250 ° C.

An apparatus made of stainless steel or enamel, which, as mentioned, does not protrude into the bed, is advantageously used as the reactor Internals contains «used. The cross section of the reactor is in the direction of the material flow from the top constant or increasing at the bottom. The arbitrary shape of the cross section is over the entire length of the reaction vessel the same, advantageously circular. The reactor can therefore be a simple, upright, cylindrical tube However, a tube with a slightly conical shape, e.g. with a downward opening angle of approx. 1, has proven particularly useful. The reaction mixture is heated on the one hand over the wall of the reaction vessel and on the other hand by introducing hot, inert gas, e.g. nitrogen, in the countercurrent direction. By the latter measure is · at the same time for the removal of volatile fission products taken care of.

In the discontinuous mode of operation, the preheated reaction material is heated in an immobile state. A deformation of the polyester granulate does not occur. Will thermal treatment of polyethylene terephthalate in the manner described carried out, then the polyester bed falls after one more Heating time of ten or more hours out of the reaction vessel by itself if the closure is at the lower end, will open. In the worst case, only a minor one is required Impact, by which the granulate is in no way damaged, in order to set the bed in motion. Agglomerates that could possibly have formed, have only low strength, so that they disintegrate when discharged.

In the case of continuous operation, the reaction mixture becomes _{uniform in the preheated state at the} upper end of the reaction vessel

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given, and discharged at the lower end. The filling slides slowly without mixing and without any deformation of the individual granulate particles through the reaction vessel. Caking that leads to undesirable shapes and discharge difficulties because of the slow downward movement are even less here than with the discontinuous Procedure in place.

The process according to the invention, which is not only suitable for the condensation of solid polyesters, but also in general for the thermal aftertreatment of plastic granules, such as * polyamide granules, is to be explained in more detail by the following examples

Example 1

In a vertical heated rack, made of V4A steel Ordering reaction tube of 250 mm length, 100 mat upper and 200 mm lower diameter knife are 35 kg solid, to 220 preheated polyalkylene terephthalate with a specific Viscosity of 800 once in the form of chips and in another case in the form of cylindrical rolls TO hours heated to 240 °. Pure nitrogen at a temperature of 24O ° is used passed through the bed from below. Then a flanged locking disc is attached to the lower end of the tube pulled out, the raw material then falling out is conveyed further to cool down. The product obtained has a specific viscosity of 1500, it is external not changed compared to the material used.

Example 2

A reaction tube as in Example 1, which is provided at the top with a device for the continuous introduction of granulate and a gas outlet ^a "i the lower end with a discharge mechanism, is made up of 35 kg of polyethylene preheated to 220 ° G"

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terephthalate granulate filled. Nitrogen with a temperature of 24 ° is blown in from below and at the same time the jacket is heated to 2 °. The apparatus is now regulated in such a way that 3.8 kg per hour of granules preheated to 235 ° C. are introduced into the tube and the same amount is discharged from the bottom. After about 9 hours the original filling of the tube has been discharged and a product is now obtained in continuous output which has a specific viscosity of 15Ο and is filled via a downstream cooling section.

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Claims (2)

Ge. klk claims t 1. A method for increasing the degree of condensation of polyethylene terephthalate by thenaic treatment of the polyester crystallized and dried in a known manner, characterized in that van the polyester with a temperature which is 0 to 100, preferably 0 to 20 ⁰ C below the intended condensation temperature, in transferred to the reactor, an apparatus serving as the reactor in which the condensation is carried out in the usual manner in a stream of inert gas and / or under reduced pressure which neither has a cross-sectional constriction in the direction of the product flow nor contains internals extending into the product bed. 2. The method according to claim 1, characterized in that as Reactor an upright tube with a downward facing one opening angle of approx. 1 ° is used. 00 982 ^r BATH ORIGINAL