JP2002531614A - Method for producing polyethylene terephthalate-polyethylene isophthalate copolymer - Google Patents

Abstract

  (57) [Summary] The present invention provides a method for preparing a polyethylene terephthalate-polyethylene isophthalate copolymer containing at least 8% isophthalic units. The process comprises (a) esterifying or transesterifying a mixture of terephthalic acid or methyl terephthalate and at least 8% by weight of isophthalic acid or methyl isophthalate with ethylene glycol, and (b) forming the esterification or transesterification. Polymerizing in the melt phase, (c) solidifying and granulating the resulting polymer, and (d) contacting the resulting particles with a liquid medium that is a non-solvent for the polymer, or heating the particles. And a second crystallizer including a means for forming a fluidized bed for fluidizing the particles by a flow of a heated gas. Crystallization is carried out by successive treatment in a crystallizer, and then (e) a step of post-polymerizing the crystallized particles in a solid phase. According to the crystallization step of the present invention, adhesion between polymer particles in post-condensation is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

TECHNICAL FIELD The present invention relates to a method for producing a polyethylene terephthalate-polyethylene isophthalate copolymer.

BACKGROUND OF THE INVENTION Polyethylene terephthalate is a thermoplastic material with many uses and its use is very extensive, for example in the field of textiles as well as in thermoforming materials. One use of polyethylene terephthalate is to produce hollow bodies such as bottles. Polyethylene terephthalate bottles can be used for non-carbonated, weakly carbonated, or strongly carbonated beverage containers. For a container of a strong carbonated beverage, it is important that the polymer can sufficiently suppress gas diffusion. This effect is called a barrier effect. In order to preserve the sparkling properties of the contents of the bottle for a long time, it is necessary to improve this property.

[0003] One of the recommended solutions for enhancing the barrier effect of polyethylene terephthalate is to utilize copolymer compositions based on terephthalic and isophthalic units. Japanese Unexamined Patent Publication (Kokai) No. 2-263619 discloses that a barrier effect is improved by allowing isophthalic units to be present in polyethylene terephthalate at a ratio of 8 to 13% by weight. Industrial production of such copolymers is difficult to implement. In fact, the polyesters utilized in the production of bottles must have a high molecular weight. Such high molecular weight polymers are obtained by pre-polymerization in the melt phase followed by post-polymerization in the solid phase. Such methods are known and widely used industrially for the production of polyethylene terephthalate. If more than 8% of isophthalic units are present in the polymer, it will be difficult to carry out solid-state post-polymerization with currently used techniques. Isophthalic units increase the amorphous nature of the polymer,
The molecular chains are more likely to move, and the solid particles are more likely to adhere at lower temperatures when they come into contact with each other than to polyethylene terephthalate. This adhesion phenomenon can be observed both in the post-polymerization reactor and in the crystallization vessel which is a preliminary stage of the post-polymerization. This phenomenon makes it impossible to transfer and recover the product from one step to another, and thus to make the copolymer.

SUMMARY OF THE INVENTION The present invention improves the process for producing polyesters containing at least 8% isophthalic units by avoiding adhesion between polymer particles during the crystallization and solid-state post-condensation stages. Suggest to do.

Means for Solving the Problems The present invention provides a method for producing a polyethylene terephthalate-polyethylene isophthalate copolymer containing at least 8% of isophthalic units, and includes at least the following steps. (A) Esterifying or transesterifying a mixture of terephthalic acid or methyl terephthalate and at least 8% by weight of isophthalic acid or methyl isophthalate with ethylene glycol. (B) The product from this esterification or transesterification is polymerized in the melt phase. (C) solidifying and granulating the resulting polymer. (D) a first crystallizer having a means for heating the particles and a means for uniformly retaining the particles by contacting the obtained particles with a liquid medium which is a non-solvent for the polymer, and a heated gas The crystallization is carried out by sequentially treating two crystallizers including a second crystallizer including a means for forming a fluidized bed for fluidizing particles by the flow of. Next, (e) the crystallized particles are subjected to solid phase post-polymerization.

[0006] These steps constitute the essential operations for performing the method. The method may include other steps. In addition, the element operation of each step can be shared by a plurality of devices.

[0007] The esterification or transesterification step of step (a) is described in the literature, an important industrial application of which is the production of polyethylene terephthalate.
By polyethylene terephthalate is meant here any composition whose predominantly terephthalic structure contains at least 8% of isophthalic units. The% of isophthalic units means the weight ratio of isophthalic acid in a mixture of isophthalic acid and terephthalic acid. The copolymer according to the invention contains at least 8% or more of isophthalic units and is produced in the same manner as for the production of polyethylene terephthalate, using a mixture of isophthalic acid and terephthalic acid.

The polymerization step (b) is likewise widely used industrially. This step is a process (
polymerizing the product from a) in the molten state. This step is generally catalyzed by a metal compound such as antimony trioxide, titanium oxide and the like. During the course of the reaction, the product continues to increase in viscosity. If the viscosity is higher than a specific viscosity, the reaction cannot be continued with a practically used technology. The limit of the viscosity index achieved in the molten phase is generally around 85 ml / g. To obtain a higher molecular weight substance, it is necessary to carry out solid phase condensation. The viscosity index (IV) is determined by comparing a solution of 0.005 g / ml in a mixture of 50% by weight of phenol and 50% by weight of 1,2-dichlorobenzene at 115 ° C.
It means the viscosity ml / g measured at 25 ° C. using a viscometer of the bbelohde type.

In step (c), the molten polymer from step (b) is granulated, for example, by extrusion and cooling. It is essentially amorphous. The particles obtained from this step can be used for specific applications as such or optionally after crystallization, or can be further subjected to solid-state post-polymerization for applications requiring higher molecular weight polymers. This is the case, for example, in the production of hollow bodies such as bottles.

[0010] The solid-state post-condensation carried out in step (e) consists of heating the particles to a temperature between the glass transition temperature of the polymer and its melting temperature. This condensation involves degassing of the reaction product, ethylene glycol and, optionally, water.

If the particles from step (c) do not crystallize according to the invention, adhesion will occur between them, making it impossible to carry out the step of solid phase condensation. The adhesion or aggregation of the particles is due to the softening of the amorphous part. Isophthalic units increase the amorphous nature of the polymer and make crystallization difficult. The present invention proposes two methods as step (d) for the crystallization of copolyesters containing isophthalic units in a concentration of more than 8%.

According to a first embodiment of the present invention, the particles are crystallized by contact with a liquid medium that is a non-solvent for the copolymer. This liquid medium includes methylene chloride, dioxane, nitromethane, acetone, benzene, dimethylformamide, dimethylacetamide, methanol, ethanol, chloroform, trichloroethylene, tetrachloroethylene, tetrachlorocarbon, toluene, benzyl alcohol,
It can be selected from methyl vinyl acetone and mixtures thereof. Acetone gives particularly good results. The contact with the liquid medium can be performed by any method such as immersion. This step can be performed continuously or discontinuously.

The liquid medium is used at ambient temperature or at a temperature below the boiling temperature of the liquid. The temperature must be lower than the melting temperature of the polymer to be treated.

Contact with a liquid medium is advantageously applicable to polymers having a molecular weight corresponding to a viscosity index of about 30 ml / g. A polymer having a higher viscosity index than this method,
It is especially applicable to polymers having a viscosity index of up to 90 ml / g. This method requires a very high viscosity index, for example 130 ml / g, to obtain a high molecular weight polymer.
It is also applicable to polymers having a viscosity index of up to.

After the dipping step, a crystallization step by ordinary crystallization such as heating can be performed. This step can be performed in the same equipment used for the crystallization of polyethylene terephthalate.

According to a second embodiment of the present invention, crystallization can be performed by passing the particles through two crystallizers. The first crystallizer has means for heating the particles and means for uniformly retaining the particles therein. The second crystallizer includes means for forming a fluidized bed for fluidizing the particles with the flow of the heated gas.

The purpose of the first crystallizer is to regulate the residence time of the particles in the crystallizer and to provide a uniform, minimal crystallization of the particles. Any means for providing each particle with a uniform residence time in the heating medium and for providing relative movement between the particles is the first.
Can be used to realize a crystallizer. This first stage of uniform crystallization of the particles
This is a step for obtaining a minimum degree of crystallinity for preventing adhesion or adhesion between particles in the second crystallization stage. The second crystallization stage is performed in an apparatus in which the particles are agitated by a stream of hot gas for a generally longer time than the first crystallization step. Such a device allows a long residence time therein and makes it possible to obtain a sufficient degree of crystallinity to avoid particle adhesion during post-condensation.

Illustratively, the first crystallizer has a vessel and variable speed rotating means therein. The container is substantially cylindrical. One end is provided with means for charging the particles from step (c) and the other end is provided with means for discharging the particles. Further, for example, a means for circulating oxygen or nitrogen gas can be provided. The rotating means serves to move the particles from one end of the container to the other. For this purpose, the rotating means can be constituted by a propeller, for example a shaft with a disk inclined with respect to the shaft, or an endless screw.
The shaft and the propeller may include a cavity therein for passing a heated fluid. The heated fluid is circulated through the walls of the agitating means and the propeller means in such a way as to allow maximum heat exchange with the particles. To this effect, the shaft and propeller means may advantageously have walls inside them to guide the fluid along the outer surface, or may be provided with other means for improving the heat exchange. The shapes of the container and propeller are adjusted and calculated to prevent the formation of stagnation zones of particles in the container. To avoid such phenomena, a stationary bar can be provided in the vessel that disrupts the normal flow of particles along the axis of the device.

The temperature of the hot fluid circulating inside the apparatus is advantageously between 120 ° C. and 240 ° C. The residence time of the particles in the apparatus can be controlled by adjusting the rotational speed of the propeller means and adjusting the shape thereof. The residence time and the temperature are adjusted so that the particles leave the apparatus, preferably with a crystallinity of 20 to 42%. The axis of rotation may be in the form of a truncated cone with a large diameter located at the loading end of the particles.
Then, the stirring means and the propeller means increase from one end of the container to the other end (
(A contact surface with the particles), the largest contact surface being located at the discharge end of the particles.

By way of example, the second crystallizer forms a fluidized bed of particles by hot gas. This device consists of an elongated container separated into two parts by a horizontal or inclined surface. This separation is provided by a surface with a plurality of holes of a diameter smaller than the size of the particles. These holes are for transferring hot gases (oxygen, nitrogen or air) between the two parts of the container. The lower part is preferably provided with a hot gas inlet with an adjustable flow rate between 120C and 240C. The upper portion has a gas outlet. The container further comprises means for charging and discharging the particles arranged at both ends. The flow of hot gas must be large enough to fluidize the bed of particles. Particles moved by gas reflux are also carried from one end of the container to the other. The residence time of the particles in the vessel and the temperature of the gas are advantageously adjusted so as to have a crystallinity of 30 to 48% on leaving the crystallizer.

The above means merely constitute a single passage surface between the two parts of the container. The manner in which the container is divided into two parts can be more complex, especially by utilizing a plurality of perforated surfaces.

[0022] The part of the container that receives the particles (upper part) can be demarcated by separation means having means for passing the particles from one to the other. For example, the passage means can be realized by providing a dividing means having a size smaller than a size of a portion for receiving particles.

Following the crystallization step, which takes place by contacting the particles with a liquid, optionally by further crystallization by heating, or by passing them sequentially through the crystallizer described above, Steps can be taken to bring the polymer at the post-condensation temperature to the temperature of the post-condensation or to homogenize the temperature. This step consists in maintaining the crystallized polymer under post-condensation conditions, that is to say at a temperature of 170 ° C. to 240 ° C. for 20 minutes to 10 hours. Other features and advantages of the present invention will become more apparent from the following examples.

Example 1 A polyethylene terephthalate-polyethylene isophthalate particle powder containing 10% of isophthalic units is prepared in a conventional manner. The viscosity index (IV) is 73
ml / g. Immerse the particles in acetone at 20 ° C. for 4 days. Dry for 12 hours at ambient temperature. Next, solid-phase post-condensation is performed at 214 ° C. for 31 hours under vacuum under evacuation.
The final viscosity index is 95 ml / g. The particles retain their dimensions and do not agglomerate.

Comparative Example 1 The same heat treatment was performed except that the above sample was immersed in acetone. The viscosity index at the outlet of the post-condensation is 92 ml / g and all particles agglomerate and no longer form a solid which can be used.

Example 2 A polyethylene terephthalate-polyethylene isophthalate particle powder containing 10% of isophthalic units is prepared in a conventional manner. The viscosity index (IV) is 73
ml / g. The particles are crystallized and then post-condensed in a continuous apparatus. The flow rate of the material is 3000 kg / h. The first crystallization is carried out using a crystallizer commercially available from Hosokawa-Bepex under the trade name TORUSDISC. The crystallizer mechanically sends particles from one end of the vessel to the other by a rotating screw heated by a fluid circulating in the crystallizer.
The rotation speed of the rotor is 9 revolutions / min and the residence time of the particles is on average 30 minutes.
The temperature of the circulating fluid in the screw is 187 ° C. The particles from this crystallization stage are then subjected to a second crystallization in a crystallizer with a fluid bed type OTWG 890, commercially available from BUHLER LTD. Gas flow rate is 62
6 m ³ / min and the residence time of the particles averages 70 min. The temperature of the circulating gas in the device is 175 ° C. The particles are then conditioned at 195 ° C. for 3 hours prior to solid post-polymerization. No agglomeration between particles was observed during the manufacturing process. The dimensions at the end of the post-condensation were identical to those at the beginning of the crystallization.

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Claims (8)

[Claims] 1. A method comprising: (a) esterifying or transesterifying a mixture of terephthalic acid or methyl terephthalate and at least 8% by weight of isophthalic acid or methyl isophthalate with ethylene glycol; Polymerizing in the melt phase, (c) solidifying and granulating the resulting polymer, and (d) contacting the resulting particles with a liquid medium that is a non-solvent for the polymer, or And a second crystallizer including a means for forming a fluidized bed for fluidizing the particles by the flow of a heated gas. Crystallization by sequentially treating with two crystallizers, and then (e) post-polymerizing the crystallized particles in a solid phase.
A process for producing a polyethylene terephthalate-polyethylene isophthalate copolymer containing at least 8% of isophthalic units. 2. A liquid medium comprising methylene chloride, dioxane, nitromethane, acetone, benzene, dimethylformamide, dimethylacetamide, methanol,
2. The method of claim 1, wherein the method is selected from ethanol, chloroform, trichloroethylene, tetrachloroethylene, tetrachlorocarbon, toluene, benzyl alcohol, methyl vinyl acetone, and mixtures thereof. 3. The method of claim 2, wherein the liquid medium is acetone. 4. The method according to claim 1, wherein the contact with the liquid medium is performed at a temperature lower than the melting point of the polymer. 5. The process according to claim 1, wherein the polymer from step (c) has a viscosity index of more than 30 ml / g. 6. The method according to claim 1, wherein a step of crystallization by heating is performed after the step of crystallization by contact with a liquid medium. 7. The means for providing a uniform residence time for the particles in the first crystallizer comprises:
2. The method of claim 1, wherein said means is a mechanical means for effecting the movement of particles within said crystallizer and between particles. 8. The method of claim 7, wherein the mechanical means is an endless screw.