KR20010093117A - Method for making poly(ethylene terephthalate)-poly(ethylene isophthalate) copolyesters - Google Patents

Abstract

The present invention relates to a process for producing poly (ethylene terephthalate) -poly (ethylene isophthalate) copolyester containing 8% or more of isophthal units. The process comprises the steps of: a) treating a mixture containing terephthalic acid or methyl terephthalate and at least 8% by weight of isophthalic acid or methyl isophthalate by esterification or transesterification using ethylene glycol, b) subjecting the esterified product to Polymerizing in the melt phase, c) solidifying and granulating, d) crystallizing the polymer by contact with a solvent-free liquid medium, or means for heating the granules and imparting a uniform residence time to the granules therein. A crystallization step by successively treating in two crystallizers of a second crystallizer comprising a first crystallizer and a means for producing a granulated bed fluidized by hot air flow, e) the solid state of the crystallized granules Postcondensation step into. The crystallization step according to one embodiment of the present invention makes it possible to prevent the granules from sticking together during the postcondensation step into a solid phase.

Description

Method for producing poly (ethylene terephthalate) -poly (ethylene isophthalate) copolyester {METHOD FOR MAKING POLY (ETHYLENE TEREPHTHALATE) -POLY (ETHYLENE ISOPHTHALATE) COPOLYESTERS}

Poly (ethylene terephthalate) is a thermoplastic material with many uses, which is widely used in the textile field, for example in the field of heat modified materials. One example of the use of such poly (ethylene terephthalate) is the production of hollow bodies such as bottles. Bottles made of such poly (ethylene terephthalate) can be used to accommodate non-carbonated beverages, soft carbonated beverages or strong carbonated beverages. In order to accommodate strong carbonated beverages, it is key that the polymer has good resistance to gas diffusion. This property is called a barrier effect. Thus, intensive research has been conducted to reinforce this property so that the beverage contained in the bottle can preserve the sparkle for a long time.

One of the proposed solutions for reinforcing the barrier properties of poly (ethylene terephthalate) is to use compositions of terephthal unit and isophthal unit system copolymers. Japanese Patent Application Publication No. J02263619 discloses that the presence of isophthalic units in the proportion of 8 to 13% by weight in poly (ethylene terephthalate) can enhance the barrier effect. Industrial production of such copolymers is difficult to perform. In fact, the polyester used to make the bottle must have a high molecular weight. This high molecular weight polymer is carried out by a postcondensation reaction to a solid state after the polymerization reaction in the molten phase. Such methods are known and have become the objective of well-known industrial development for the production of poly (ethylene terephthalate). The presence of at least 8% of isophthalic units in the polymer makes it difficult to industrially perform the postcondensation reaction to a solid state by the actual technique used. Isophthalic units emphasize the amorphous properties of the polymer, and the molecular chains become more fluid and the solid granules tend to stick to each other upon contact at lower temperatures than poly (ethylene phthalate). This sticking phenomenon is observed in the postcondensation enclosure, but can also be observed in the crystallization enclosure, which is a step prior to the postcondensation reaction. This phenomenon makes it impossible to transfer the product of that step to another step, thus making the copolymer impossible.

The present invention relates to a process for preparing poly (ethylene terephthalate) -poly (ethylene isophthalate) copolyester.

The present invention seeks to improve the process for the preparation of copolyesters comprising at least 8% isophthal units, while preventing the granules from sticking together during the crystallization step and the post-condensation step into a solid phase.

The present invention relates to a process for the preparation of poly (ethylene terephthalate) -poly (ethylene isophthalate) copolyesters containing at least 8% of isophthal units, the process comprising the following steps:

a) treating a mixture containing terephthalic acid or methyl terephthalate and at least 8% by weight of isophthalic acid or methyl isophthalate by esterification or transesterification with ethylene glycol,

b) polymerizing the esterified product in a molten phase,

c) solidification and granulation steps,

d) a crystallization step of contacting the polymer with a non-solvent liquid medium or a first crystallizer comprising heating means of the granules and means for imparting a uniform residence time to the granules therein, and a granulated layer fluidized by hot airflow A crystallization step by successively treating in two crystallizers of the second crystallizer comprising means for producing a

e) postcondensation of the crystallized granules in solid form to the desired degree of polymerization.

These steps consist of the necessary operations in carrying out the manufacturing method. Such a manufacturing method may include others. Each of these steps may optionally be subdivided into basic operations within a number of devices.

Step a) of the ester reaction or transesterification reaction is fully described in the literature and aims for industrially important development for the preparation of poly (ethylene terephthalate). With poly (ethylene terephthalate), most contain terephthal units and at least 8% contain isophthal units. According to the ratio of the isophthal unit, the weight ratio of isophthalic acid in the mixture of isophthalic acid and terephthalic acid is mentioned. The copolymer according to the invention comprises at least 8% isophthalic units, which is the same method used to prepare poly (ethylene terephthalates), using a mixture of isophthalic acid and terephthalic acid or diesters of these compounds. It can be prepared by.

The polymerization step b) is the same as carried out in industry. This method consists of the condensation reaction in the molten state of the reaction product of step a). It is generally catalyzed by metal compounds such as antimony trioxide or titanium oxide. In the course of the reaction, the product becomes more and more viscous. Above a certain viscosity, practically the techniques used will not be able to sustain the reaction. The viscosity limit obtained in the molten phase is usually 85 ml / g. In order to obtain higher molecular weight compounds, solid condensation reactions must be carried out.

Viscosity is 25 ° C using a Ubbelohde viscometer for a solution of 0.005 g / mL of the polymer dissolved at 115 ° C in a mixture of 50% by weight of phenol and 50% by weight of 1,2-dichlorobenzene. Refers to the viscosity index (IV) measured in units of ml / g.

During step c), the molten polymer from step b) is granulated, for example by extrusion and cooling. Thus it becomes amorphous. The granules from this step can be used for certain applications after any crystallization step, or can be subjected to post-condensation treatment in solid form for applications requiring high molecular weight polymers. This is the case, for example, in the manufacture of hollow bodies such as bottles.

The postcondensation reaction to solid phase carried out during step e) consists in heating the granules at a temperature between the glass transition temperature of the polymer and its melting point. This condensation reaction involves the release of the reaction product, ethylene glycol and optionally water.

If the granules from step c) are not crystallized by the present invention, they will stick to each other, which makes it impossible to carry out the solid phase condensation step. Adhesion and agglomeration of the granules together is due to softening of the amorphous part substantially. Isophthalic units enhance the amorphous properties of these polymers, which makes crystallization difficult. The present invention proposes two embodiments of crystallization step d) of copolyesters comprising isophthalic units in concentrations higher than 8% by weight.

According to a first embodiment of the invention, the granules are crystallized by carrying out contact of the copolymer with a non-solvent liquid medium. Such liquid media are, for example, methylene chloride, dioxane, nitromethane, acetone, benzene, dimethylformamide, dimethylacetamide, methanol, ethanol, chloroform, trichloroethylene, tetrachloroethylene, carbon tetrachloride, toluene, benzyl alcohol, Methyl vinyl ketone and mixtures thereof. In particular, good results are obtained with acetone. Performing contact with the liquid medium can be carried out by any method, for example by dipping. This step can be performed continuously or discontinuously.

The liquid medium may be used at room temperature or below a temperature below the boiling point of the liquid. The temperature should be below the melting point of the treated polymer.

Performing contact with the liquid medium may advantageously be carried out in a polymer having a molecular weight of at least molecular weight corresponding to a viscosity index of about 30 ml / g. This method is applicable to polymers of high viscosity, in particular up to a viscosity index of about 90 ml / g. It is also applicable to polymers having a high viscosity index, in particular about 130 ml / g, in order to produce very high molecular weight compounds.

After the immersion step, a crystallization step by a conventional crystallization method by heating may be performed. This step is carried out in the same apparatus used for the crystallization of poly (ethylene terephthalate).

According to a second embodiment of the invention, there is provided a first crystallizer comprising heating means for granules and means for imparting a uniform residence time to the granules therein, and means for producing granulated layers fluidized by hot air flow. This is done by continuously passing the granules in the two kinds of apparatus of the second crystallizer.

The purpose of the first crystallizer is to control the residence time of the granules in the crystallizer and to make the minimum crystallinity uniform. Any means by which each granule can obtain a uniform residence time in the hot medium and can be compared to move a portion of the granules relative to the rest of the granules can be used in the performance of the first crystallizer. For example, such means may consist of mechanical means of movement of the granules and means of moving a portion of the granules relative to the rest of the granules. This uniform first crystallization step of granulate allows to obtain a minimum degree of crystallinity to prevent the granules from sticking to each other during the second crystallization step. The second crystallization step is carried out in an apparatus in which the granules are acted upon by a stream of hot air for a generally longer time than the first crystallization step. Such a device can have a long residence time therein, thereby obtaining sufficient crystallinity to prevent the granules from sticking during the postcondensation reaction.

For example, the first crystallizer may comprise a container and a rotating means for adjusting the speed inside the container. Such containers are almost cylindrical in shape. The means for filling granules from step c) may be provided at one end, and the means for discharging granules may be provided at the other end. Such a device may have all known forms. Means for circulating the gas, for example oxygen or nitrogen, are provided. The rotating means moves the granules from one end of the container to the other end. To achieve this object, for example, it may consist of a shaft with attached propulsion means, such as a disk graded relative to the shaft or a screw without end. The shaft and the propulsion means may comprise a cavity therein in which the hot fluid is circulated. The hot fluid is circulated through the wall of the stirring means and the propulsion means together with the granules to facilitate heat exchange. In fact, it is advantageous for the shaft and the propulsion means to be internally provided with all other means capable of guiding fluid in the longitudinal direction of the outer surface and facilitating heat exchange. The form of the container and the propulsion device is advantageously adjusted and adjusted to prevent the formation of stagnant areas of granules inside the container. To prevent this phenomenon, a fixed bar may be provided in the container which disturbs the outflow of granules on the longitudinal axis of the device.

The hot fluid temperature circulating in the device is advantageously between 120 ° C. and 240 ° C. The residence time of the granules in the device is controlled by the rotational speed of the propulsion device or by adjustment of the shape. The residence time and temperature are controlled as above because it is advantageous that the crystallinity of the granules discharged in the apparatus is 20-42%.

The axis of rotation may be in the form of a truncated truncated cone located at the charging end of the granules. The stirring means and the pushing means thus form a contact surface with the granules increasing from one end of the container to the other end, the wider contact surface being located at the discharging end of the granules.

For example, the second crystallizer is configured to form a fluidized bed of granules by hot gas. For example, it may consist of an elongated enclosure divided into two parts by a horizontal plane or by an inclined plane. This separation is formed by a surface with a perforation of a diameter smaller than the size of the granules. This perforation allows the movement of hot gases (oxygen, nitrogen or air) between the two parts of the enclosure. The lower part is equipped with an inlet for hot gas at an adjustable flow rate with an advantageous temperature of 120 ° C to 240 ° C. The upper part is provided with a gas discharge means. It is also provided with charging and discharging means for the granules disposed at the ends of the enclosure. The flow rate of hot gas must be sufficient to flow the granular form. The granules traveling by the gas flux are moved from one end to the other end of the enclosure. The controlling parameter of the residence time in the crystallizer is the flow rate of the gas in the enclosure. The residence time in the enclosure and the temperature of the gas are adjusted to ensure that the crystallinity reaches 30-40% at the outlet of the crystallizer.

The device as described above does not include a pass face between the two parts of the enclosure. The manner of separation between the two parts of the enclosure can be further complicated, in particular by using a separation surface with multiple perforations.

The portion (top) of the enclosure containing the granules is partitioned by separation comprising means for passing the granules from one compartment to another. For example, the passing means is performed to form a separation smaller in size than the portion containing the granules.

After the crystallization step carried out by contact with the liquid, the crystallization step by heating or optionally by the continuous passage in the crystallizer as described above allows the crystallization temperature of the polymer to be the postcondensation temperature and to make the temperature uniform. Prior to postcondensation of the conditioning phase. This step consists in keeping the crystallized polymer close to the conditions of postcondensation at a temperature of 170 ° C. to 240 ° C. for a period of 20 minutes to 10 hours.

Other details and advantages of the invention will be apparent from the examples set forth below as examples.

Example 1

Copolymer granules of poly (ethylene terephthalate) -poly (ethylene isophthalate) containing 10% of isophthal units were prepared by conventional methods. The initial viscosity index (IV) is 73 ml / g. It was immersed in acetone for 4 hours at a temperature of 20 ° C. It was dried at room temperature for 12 hours. The postcondensation reaction was then carried out at 214 ° C. for 31 hours under vacuum in solid form. The final viscosity index is 95 ml / g. The granules preserved their size and did not aggregate.

Comparative Example 1

The control sample is heat treated similarly without being immersed in acetone. At the post-condensation outlet, the viscosity index was 92 ml / g and all granules aggregated and formed only unusable solid mass.

Example 2

Poly (ethylene terephthalate) -poly (ethylene isophthalate) polymer granules comprising 10% of isophthal units were prepared by conventional methods. The initial viscosity index (IV) is 73 ml / g. It was crystallized and postcondensed in a continuous apparatus. The flow rate of the material is 3,000 kg / h.

The first crystallization step was carried out in a crystallizer marketed by Societe Hosokawa-Bepex under the trademark TORUSDISC. Such crystallizers mechanically propel the granules from one end of the enclosure to the other end using a screw while heating and rotating by fluid circulating therein. The rotational speed of the rotor is 9 revolutions / minute, and the residence time of the granules is 30 minutes on average. The temperature of the fluid circulating in the screw is 187 ° C.

The granules from this crystallization step carry out a second crystallization step in the fluidized bed crystallizer of the model OTWG 890 available from Societe Buyler Limited. The flow rate of the gas is 626 m 3 / min (air), and the residence time of the granules is on average 70 minutes. The temperature of the gas circulating in the apparatus is 175 ° C.

The granules are thus conditioned before postcondensation to a solid state. Conditioning is carried out at 195 ° C. for 3 hours.

Solid condensation is carried out at 200 ° C. for 20 hours. The viscosity index of the polymer from this step is 110 ml / g.

During the preparation process, no agglomeration of granules was observed and the particle size at the postcondensation outlet was the same as the size at the onset of crystallization.

Claims (8)

A process for preparing a poly (ethylene terephthalate) -poly (ethylene isophthalate) copolyester containing at least 8% of isophthal units, comprising the following steps: a) treating a mixture containing terephthalic acid or methyl terephthalate and at least 8% by weight of isophthalic acid or methyl isophthalate by esterification or transesterification with ethylene glycol, b) polymerizing the esterified product in a molten phase, c) solidification and granulation steps, d) a crystallization step of contacting the polymer with a non-solvent liquid medium or a first crystallizer comprising heating means of the granules and means for imparting a uniform residence time to the granules therein, and fluidizing the granules by hot air flow A crystallization step by successively treating in two crystallizers of a second crystallizer comprising means for producing a granulated granular layer, e) postcondensation of the crystallized granules into a solid state. The method of claim 1, wherein the liquid medium is methylene chloride, dioxane, nitromethane, acetone, benzene, dimethylformamide, dimethylacetamide, methanol, ethanol, chloroform, trichloroethylene, tetrachloroethylene, carbon tetrachloride, toluene, benzyl alcohol , Methyl vinyl ketone and mixtures thereof. The method of claim 2 wherein the liquid medium is acetone. The process according to claim 1, wherein the contacting with the liquid medium is carried out at a temperature below the melting point of the polymer. 5. The process according to claim 1, wherein the polymer from step c) has a viscosity index higher than 30 ml / g. 6. The method according to any one of claims 1 to 5, characterized in that a crystallization step by heating is performed after the crystallization step by performing contact with a liquid medium. The method according to claim 1, wherein the means capable of adding a uniform residence time to the granules in the first crystallizer are mechanical means of moving the granules in the crystallizer and mechanical means for moving a part of the granules relative to the rest of the granules. How to. 8. The method of claim 7, wherein the mechanical means is a screw without end.