MXPA97005443A - Improved procedure for production polyestrides - Google Patents

Abstract

A process is described for the production of aromatic polyester resins from resins with VI of 0.1 to 0.4 dl / g comprising the steps of mixing the resin with a tetracarboxylic acid dianhydride, extruding the resin in ribbon form, cooling the tape or the small pieces obtainable by cutting the tape, at a temperature between 150 ° C and 210 ° C and maintaining the same temperature for a sufficient time to obtain a crystalline product where the DSG curves thereof do not show presence of pre-melting peaks or only in a small amount

Description

IMPROVED PROCEDURE FOR THE PRODUCTION OF POLYESTER RESINS DESCRIPTIVE MEMORY The present invention relates to an improved process for the production of a polyester resin. Aromatic polyester reams that can be used in applications such as molding, extrusion, injection and similar operations require relatively high molecular weights corresponding to intrinsic viscosity (VI) values generally greater than 0.65-0.75 dl / g. The reams for film and fiber, on the other hand, have lower VI values, comprised between about 0.6 and 0.75 dl / g. The preparation of the resins is carried out by poly condensation of omega-1-aromatic acid, usually tereHalic acid or its alkyl diesters with an aliphatic glycol operating under temperature and pressure conditions so as to obtain a resin with values Do as high as possible. However, it is difficult to reach VI values above 0.65-0.75 dl / g due to the high molten barium viscosity that prevents efficient removal of the reaction by-products. The polycondensation reaction in molten barium state (hPC) is carried out under high vacuum to remove the reaction by-products. MPC poly condensation is an expensive operation that is desirable to avoid. The resin to be used for molding operations and the like, after the riPC stage, is subjected to solid state polycondensation treatment (SSP) in order to increase the VT to the desired values (Q. 75-L .2 dl / g). Prior to the treatment of SSP, the resin granules are subjected to a treatment treatment aimed at increasing as much as possible the potentiality of the polymer to avoid in the subsequent SSP the packing and the adhesion of the granules that were to be used. or other extreme conditions can lead to the plant being stopped. The SSP step requires a relatively long time (from some to 10 or more hours depending on the final VE value that will be obtained-). By working in the MPC step without high molten barium viscosity values and therefore with the relatively low polymer VI, it is possible to more easily remove the reaction by-products and thereby reduce their duration. The increase in VI for the desired values could therefore be obtained by SSP. However, there are limits to the reduction of the viscosity of the molten bath, mainly due to the presence of a large number of oligomers that are formed when operating under said conditions. The oligomers, in the next step of SSP, produce the formation of cyclic compounds whose presence has a negative influence on the flow capacity < the granules and therefore the regularity of the SSP operation. In order to overcome the above inconveniences, it was proposed in UO-A-93 00 226 to add the resins with a VI less than 0.57 dl / g an anhydride of an tetracarboxylic acid, for example. and anhydride ?? omelí 1 o (PMDA), and drive- the SSP reaction in the presence of said dianhi dpdo. The VI values of the resins with which the dianhydpide is applied in practice are not lower than 0.4 dl / g (in the examples, 0.408 dl / g). After the addition of the dianhydride, the resin is converted into pellets by conventional systems and then has to be subjected to cri ization in order to be able to carry out the SSP treatment. It has now unexpectedly been found that starting from the resins with VI values less than 0.4 dl / g and comprised between 0.1 and 0.4 dl / g, preferably 0.2-0.3 dl / g, added to the molten bath with a dianhydpide of tet acid The carboxylic acid, preferably an aromatic tetracarboxylic acid, yields resins having a molten bath strength sufficient to be extruded in the form of a cuttable ribbon, and which, if the tape or granules obtainable from the tape are subjected to crystallization in the exit of the extroyer, operating at a temperature of approximately 150 ° and 210 ° C for a long enough time, the crystalline organizations are obtained in such a way that in the DSC curves of the resin after the crystallization no pre-melted peaks are present, or present only in a limited quantity The crystallized resin thus obtained can be treated in the next step of SSP at higher temperatures than those normally used, with consequently significant reductions in the duration of the treatment. therefore, it has the advantage not only of being able to eliminate the crystallization treatments after the pellet formation of the resin, but also of exerting a positive influence on the passage of the SSP even when starting with resins with low VI. The addition of dianhydride with the molten bath resin also makes it possible to obtain crystallized reams with VI greater than that of the starting resin. obtained are characterized by a VI higher than 0.4 dl / g. After the treatment with SSP, the resins show VI values generally higher than 0.8 dl / g. In their DSC curves there is no presence of prefused peaks, or if they are present, their enthalpy of fusion is less than 5 3 / g. These resins are new products.

The process of the invention, when carried out continuously from the preparation step of the ream to the final SSP steps, comprises the following steps- a) polycondensation of a dicarboxylic or aromatic acid, or its alkyl diester, preferably acid terephthalic, with an aliphatic diol under conditions such that a ream is obtained with VI between nl and 0.40 dl / g; b) Mix the resin in the molten state with a dianhydride of a racarboxic acid, preferably a dianhydride, in a quantity between 0.01 and 2% on weight; c) extrusion of molten ream in ribbon form; d) Keep the tape at a temperature of 150 ° C and 210 ° C for a sufficient time for the crystallization of the ream, so in the DSC curves there is no prefund peaks or, if present, its enthalpy is less - of 5 / g; e) cut * the tape to form small pieces, preferably operating at temperatures close to those of crystallization (the cutting of the tape can also be carried out in cold conditions); f) Treatment with SSP of the small pieces operating at temperatures between approximately 160 ° and 250 ° C, preferably between 20 ° and 230 ° C, until obtaining the desired elevation in VE (0.8-1.2 dl / g). Steps a) to e) can be carried out separately from step f). The cutting of the tape can precede the crystallization phase, which is then ralized on the small pieces and not on the tape. Attachment with SSP is preferably carried out in a polymer fluid bed reactor in current or counter-current of a mrt gas (nitrogen). The weight ratio between the speed per hour of gas and the extracted polymer is preferably between 0.2 and 0.6. Preferably, the cooling of the ribbon at a temperature suitable for crystallization is carried out using nitrogen from the SSP step. Preferably, the crystallization temperature of the ribbon is between 10 ° and 190 ° C, with the time comprised between about 5 and 30 minutes. The tape can be collected on a metal conveyor belt maintained at crystallization temperature, operating in an inert gas atmosphere. Normally, after crystallization, the small pieces obtained can be subjected to setting with heat - in order to obtain improved crystallization of the polymer. The mixing of the molten resin bath with the tetracarboxylic acid dianhydride of stage (b) is carried out in mixers of conventional type, for example static mixers, formed from a tube provided with current circuit breakers. The residence time on the mixer is selected so as to avoid an excessive increase in ream VI, for example, greater than 0.6-0.7 dl / g. The time is usually less than 180 seconds. The polycondensation of the resin is carried out according to known techniques. It is preferable to operate ba or conditions through which resins with VI of 0.2-0.3 dl / g are obtained. The poly ester resins used in the process of the invention are obtained by polycononsation according to known methods of an aromatic dicarboxylic acid or its alkyl diester, preferably terephthalic acid or naphthalenedicarboxylic acids, with aliphatic diols, with 2-10 atoms of carbon, such as ethylene glycol, butiiengli col, i, 4-c-clohexane dirnet iol, 1-3-propylene glycol. Copolymers of polyalkyl ether and other terephthalate where up to 15% by weight of units derived from terephthalic acid are replaced by units derived from isophthalic acid and / or naphthalenedicarboxylic acids, and copolymers of polyethylene terephthalate and butyraterephthalate. they are the preferred resins. The reams before extrusion to form the belt can be mixed with additives such as stabilizers, colorants and nucleating agents normally used in the field of polyester reams. The addition of nucleating agents favors the next step of criticism. Tetracarboxylic acid dianhydpides preferably comprise, in addition to pyrantelitic dianhydride, the acid dianhydpides 3, 1, 3 ', 4'-difeni 11 and racarboxylic, 2,4,3', 4'-benzophenontet racarboyl, 1, 2, 3,4, -cyclobutant and r-a-carboxylic acid. In order to obtain resins with a particularly high melt-bath strength, particularly after mixing with dian-d-do, it is convenient to add the same as a concentrate with polycarbonate reams. The dianhydride is added in amounts of 0.01 to 2% by weight. The high-viscosity resins obtainable by the process of the invention can be used for molding, extrusion or blow molding, for example in the preparation of bottles for beverages and foamed material, or in the preparation of fibers and films. The following examples are given to illustrate but not to limit the invention. The intrinsic viscosity reported in the examples and indicated in the text is determined in the solution of 0.5 and of resin in 100 ml of a mixture of 60/40 by weight of phenol and tetrachloroethane at 25 ° C in accordance with ASTM D 4603-86 . The DSC curves were performed with a heating rate of 10 ° C / m? N.

EXAMPLE 1 A suspension of 18 mol of terephthalic acid and 24.12 mol of ethylene glycol are reacted in a reactor provided with a stirrer, at a temperature of 240 ° C and at a relative pressure of 1 bar for 270 minutes. The staging phase is followed by polycondensation operating at 270 ° C with a residual pressure of 20-25 mbapas for a duration of 260 minutes. After polycondensation, the VI of the polymer was 0.290 dl / g and the carboxyl number of 289 eq / T. The molten polymer bath was added with 0% by weight of PMDA and then extruded to form a ribbon which was run with hot nitrogen at a temperature of 175 ° C and maintained at this temperature for 10 hours. minutes The tape was then cut while it was hot and the small pieces were sent to a reactor for polycondensation in the solid state, operating in a stream of nitrogen and heating to 220 ° C. The duration of the polycondensation treatment was < ! < -• 10 hours; VI after treatment was 0.84 dl / g. Adhesion of the particles was not observed during the SSP phase. The DSC of the small pieces after crystallization showed a slight pre-melting peak at 160 ° C with H = 0.0257 _J / g. The melting peak occurred at 243 ° C, with H -40 J / g.

EXAMPLE 2 Example 1 was repeated with the difference that the tape was cooled to 180 ° C and kept at that temperature for 10 minutes. The DSC curve of the small pieces obtained showed a slight pressure peak at 169 ° C with H - 1751 J / g. The peak melting appeared at 243 ° C, with H = 42 J / g. The VI after the polycononsation in the solid state was 0.85 dl / g (figure 1).

EXAMPLE 3 Example 2 was repeated with the difference that the tape was cooled to 185 ° C and kept at that temperature for minutes. The DSC curve of the polymer obtained in this way does not show any pre-fusion. The melting peak is at 246 ° C with H = 39 J / g (Figure 2).

EXAMPLE OF COMPARISON 1 It was operated as in Example 1 with the only difference that the polymer did not contain PMDA. It was not possible to extrude the ream to form a ribbon.

Claims (12)

NOVELTY OF THE INVENTION CLAIMS

1. - A process for the preparation of polyester-aromatic resins starting from resin with intrinsic viscosity comprised between 0.1 and 0.4 dl / g added in the molten state with a dianhydride of tet racarboxic acid which comprises the steps of: a) Extrude the ream or the fo rm a tape; b) keep the belt at a temperature between 150 ° C and 210 ° C for a sufficient time to obtain a crystallized product in the DSC curves of which no pre-melting peaks are present or, if present, its enthalpy of fusion is less - of 5 J / g; c) cutting the tape to form small pieces, characterized in that step (c) could optionally precede step ib) which in this case is carried < ? out on small pieces and not on the tape.

2. A procedure according to claim 1, characterized in that the dianhydpide of a ticarboxylic acid is dianhydpide pyro! jt ico.

3. A method according to claims 1 and 2, further characterized in that the melted ribbon solidifies at a temperature between 170 ° C and 200 ° C in an inert gas stream.

4. A process according to claims 3, further characterized in that the resin is selected from the group consisting of copolymers of polyethylene terephthalate, polybutylene terephthalate, ethylene terephthalate in which 15 mol% of the units which derive terephthalic acid are subsumed by units derived from isophthalic acid and / or naphthalenedicarboxylic acids.

5. A method according to claims 1 to 4, further characterized in that the t rozo1; small particles are sent to a polycondensation reactor in the solid state (SSP).

6. A process according to claim 5, further characterized in that the small pieces are sent to the SSP shaft reactor while they are at a temperature comprised between 170 ° C and 200 ° C.

7. A process according to claims 5 and 6, further characterized in that the small pieces or the tape are maintained at the propagation temperature using the heat of the nitrogen recirculated from the SSP-reactor.

8. A process according to claims 5, 6 and 7, further characterized in that the treatment of poly condensation in the solid state is carried out at a compressed temperature between 160 ° and 250 ° C. 9.- Polyester reams obtained according to claims 5 to 8. 10.- Aromatic polyester resins with intrinsic viscosity greater than 0.4 dl / g which contains either n-dianhydride or an aromatic tetracarboxylic acid in an amount of 0.01 to 2. % by weight and in the DSC curves of which no pre-melting peaks are present, or if present, the melting enthalpy thereof is less than 5 J / g. 11. Resins according to claim 10, selected from the group consisting of polyethylene terephthalate copolymers, filled poly terephthalate and ethylene terephthalate in which up to 15 mole% qu < derived from terephthalic acid are replaced by units derived from isophthalic acid and / or naphthalendicarboxy acids lios. 12. Resins according to claims 10 and 11, further characterized in that the dianhydride is pyrimethic dihydride.