MXPA98006719A - Process to prepare copolysteres of tereftal acid, ethylenglycol, and 1,4-cyclohexandimethanol that exhibit neutral color, high clarity and brightness increment - Google Patents

Abstract

The present invention relates to a three-step process for preparing copolyesters that exhibit a neutral color, high clarity and increased brightness. The process involves reacting terephthalic acid, ethylene glycol, and 1,4-cyclohexanedimethanol in a molar ratio of total glycerol feed to dicarboxylic acid from 1.7: 1 to 6.0: 1 at a temperature of 240 ° C to 280 ° C, and a pressure of 15 psig (200 kPa) at 80 psig (650 kPa) to form an esterification product add a polycondensation catalyst and a toner, and polycondensen the product at a temperature of 260 ° C to 290 ° C and a reduced pressure to form a copolyester of high molecular weight

Description

PROCESS TO PREPARE IETTER COAT OF TEREFTAL ACID, ETHYLENE GLYCOL, AND 1.4-CYCLOHEXA DIMETHYL OUE EXHIBIT NEUTRAL COLOR, HIGH CLARITY AND INCREASED BRIGHTNESS DESCRIPTION OF THE INVENTION This invention relates to a three-step process for preparing copolyesters of terephthalic acid, ethylene glycol, and 1,4-cyclohexanedimethanol which It provides a product with neutral color, high clarity and increased brightness. Poly (1,4-cyclohexanedimethylene terephthalate) and more specifically, copolyesters thereof containing 30 to 90 mole percent of ethylene glycol are important commercial polyesters used in the production of plastic articles such as packaging materials, molded articles and films. . The manufacturing process historically used in the synthesis of these copolyesters involves an initial ester exchange reaction wherein the dimethyl terephthalate, ethylene glycol and 1,4-cyclohexanedimethanol are reacted in the presence of a suitable catalyst with the elimination of the methanol by-product . The product of this reaction is polycondensed under reduced pressure and high temperatures to produce the final product. One difficulty encountered in the manufacture of these copolymers is to obtain a product with a neutral color instead of a slightly yellowing dye. For the Applications where these polymers are formed into thick laminar articles, the yellowish dye is particularly objectionable. It is also economically desirable to produce these copolyesters using terephthalic acid in place of dimethyl terephthalate. Attempts to prepare such copolyesters with terephthalic acid following the teachings of the prior art with respect to the conditions for the esterification reaction, however, result in an esterification product with subsequent decreased activity in the polycondensation. The decreased activity is observed when comparing the polycondensation reaction initiating with an ester exchange product prepared using dimethyl terephthalate as a reagent in place of terephthalic acid. U.S. Patent No. 4,020,049 describes a process for preparing linear polyesters from a dicarboxylic acid and glycols. The proportions in moles of feed of the glycol to dicarboxylic acid from 1.05: 1 to 1.7: 1 are specified for the esterification reaction. U.S. Patent No. 4,020,049 is not relevant to the process of the present invention as it teaches the use of molar proportions of feed of the glyciol to dicarboxylic acid resulting in reduced polycondensation activity with copolyesters of poly (1-terephthalate, 4-cyclohexanedimethylene) containing 30 to 90 percent mol of ethylene glycol. U.S. Patent No. 5,198,530 describes a process for preparing polyesters by esterification of terephthalic acid with 1,4-cyclohexanedimethanol. The process uses proportions in moles of feed of glycol to dicarboxylic acid from 1.0: 1 to 1.5: 1 in the esterification reaction, and requires a glycol cleavage feed in the esterification reactor together with the catalyst. In addition, U.S. Patent No. 5,198,530 relates only to copolyesters having at least 80 mol% of 1,4-cyclohexanedimethylene terephthalate units. U.S. Patent No. 5,198,530 is not relevant to the process of the present invention where high molecular weight copolyesters are produced using 30 to 90% mol of ethylene glycol as coglycol together with higher molar feed ratios of glycol to dicarboxylic acid , and where no catalyst is required for esterification. This invention relates to a process for preparing copolyesters of terephthalic acid, ethylene glycol and 1,4-cyclohexanedimethanol which are characterized by a neutral color, high clarity and increased brightness. The process comprises the steps of: (1) reacting terephthalic acid, ethylene glycol, and 1,4-cyclohexanedimethanol in a molar ratio of feeding total glycols to dicarboxylic acid from 1.7: 1 to 6.0: 1 at a temperature of 240 ° C to 280 ° C and a pressure of 15 psig (200 kPa) at 80 psig (650 kPa) per 100 to 300 minutes for form an esterification product; (2) adding a polycondensation catalyst and 0.1 to 40 ppm of a toner to the esterification product of step (1), wherein the polycondensation catalyst is selected from the group consisting of titanium, germanium, antimony and combinations of the same; and (3) polycondensing the product of step (2) at a temperature of 260 ° C to 290 ° C and a reduced pressure of 400 mm Hg (50 kPa) to 0.1 mm Hg (0.01 kPa) for a sufficient time to form a copolyester having an inherent viscosity of at least 0.50 dl / g. The process comprising adding 10 to 100 ppm of a phosphorus stabilizer in step (2) or step (3). The process of the present invention is a three step process for preparing copolyesters of terephthalic acid, ethylene glycol and 1,4-cyclohexanedimethanol having 30 to 90 mole percent of ethylene glycol in the glycol component, based on 100 percent mole of dicarboxylic acid and 100 percent in mol of glycol. Specifically, the invention provides a improved process for carrying out the esterification reaction which results in an esterification product with improved activity in the subsequent polycondensation reaction. The improved activity in the esterification product provides a means for subsequent reduction of catalyst concentrations, increases in stabilizer concentrations, and reductions in polycondensation temperatures resulting in a high molecular weight copolyester product with a neutral color, high clarity, and improved brightness. In step (1), terephthalic acid, ethylene glycol and 1,4-cyclohexanedimethanol are reacted in a molar ratio of feed of total glycols to dicarboxylic acid from 1.7: 1 to 6.0: 1 to form an esterification product. Preferably, the molar ratio of feed is 1.0: 1 to 4.5: 1. The 1,4-cyclohexanedimethanol can be either cis or trans isomer, or mixtures of the two isomers. The 1,4-cyclohexanedimethanol is added in an amount approximately equal to the desired molar percentage in the final copolyester product, and the excess glycol in the reagent charge is ethylene glycol. The dicarboxylic acid component containing terephthalic acid can optionally be modified with up to 10 mole percent of another dicarboxylic acid. Optional dicarboxylic acids include aromatic dicarboxylic acids preferably having 8 to 14 carbon atoms, aliphatic dicarboxylic acids preferably having 4 to 12 carbon atoms and cycloaliphatic dicarboxylic acids preferably having 8 to 12 carbon atoms. Combinations of dicarboxylic acids can also be used. Specific examples of dicarboxylic acids other than terephthalic acids are isophthalic acid, naphthalenedicarboxylic acid, cyclohexanedicarboxylic acid, stybenedicarboxylic acid, succinic acid, glutaric acid, adipic acid, and azelaic acid. The * glycol component containing ethylene glycol and 1,4-cyclohexanedimethanol with up to 10 mole percent of an additional glycol can optionally be modified. Such additional crudes include cycloaliphatic glycols preferably having 3 to 20 carbon atoms and combinations thereof. Specific glycols other than ethylene glycol and 1,4-cyclohexanedimethanol are 1,2-propanediol, neopentyl glycol, 1,4-butanediol, 1,5-pentanediol, and 1,6-hexanediol. The copolyesters of this invention can also contain small amounts of trifunctional or tetrafunctional comonomers such as trimellitic anhydride, trimethylolpropane and pentaerythritol. The esterification reaction in step (1) is carried out at a temperature of 240 ° C to 280 ° C and a pressure of 15 psig (200 kPa) at 80 psig (650 kPa). Preferably, the esterification reaction is carried out at a temperature of 240 ° C at 260 ° C, more preferably 245 ° C to 255 ° C. Preferably, the esterification reaction is carried out at a pressure of 20 psig (240 kPa) at 50 psig (450 kPa). The reaction times for the esterification step (1) vary from 100 to 300 minutes, and are dependent on the selected temperatures, pressures and molar proportions of glycol feed to dicarboxylic acid. Catalysts are not required for the esterification reaction. The esterification reaction can be carried out in batch form, or in a series of continuous reactors. The reactants are preferably introduced into the esterification reactor as a suspension of terephthalic acid in the glycols, although separate addition of each reagent can also be used. The esterification reaction, when carried out according to the specified reaction parameters, results in an esterification product with polycondensation activity. The use of molar feed ratios smaller than those specified results in an esterification product with decreased activity in the subsequent polycondensation reaction. The improved polycondensation activity of the esterification product, when prepared with molar proportions of feed in the specified range, allows the use of lower levels of catalysts and milder temperatures in the reaction of subsequent polycondensation. In step (2), a polycondensation catalyst and a toner are added to the esterification product of step (1). The polycondensation catalyst of titanium, germanium and antimony is selected. Combinations of polycondensation catalysts can also be used. Titanium is usually added in the form of an alkoxide. Examples of titanium compounds which may be used are acetyltriisopropyl titanate, tetraisopropyl titanate, and tetraisobutyl titanate. Germanium and antimony can be in the form of oxides, organic salts and glycolates. The preferred polycondensation catalyst is titanium which is added in an amount of 10 to 60 ppm in the form of an alkoxide. The concentration of the polycondensation catalyst is related to the color of the desired product as well as the type and amount of stabilizers and toners used to retard or mask the yellow color. For optimum color, clarity and brightness, titanium is added in an amount of 12 to 25 ppm. A phosphorus stabilizer is added in step (2) or during the polycondensation reaction in step (3). The phosphorus stabilizer is added in an amount of 10 to 100 ppm, preferably 40 ppm to 70 ppm. Preferred phosphorus stabilizers are phosphoric acid or alkyl esters of the m-smos, diethyl acid phosphate, and trioctyl phosphate. Plus preferably, the phosphorus stabilizer is phosphoric acid. A toner in an amount of 0.1 to 40 ppm is added in step (2) to improve the neutral color characteristics of the copolyesters prepared by the present process. As used herein, the term "toner" includes organic pigments and inorganic pigments. In the present it has been determined that the use of more than 40 ppm of a toner, however, imparts a gray color to the copolyester and reduces the clarity of the copolyester. Using the esterification product prepared according to the process of this invention, together with low catalyst concentrations, lower polycondensation temperatures, and higher phosphorus levels allows the production of a polyester product with less inherent aridity. This allows the use of low levels of a toner to achieve the desired neutral color, and results in a copolyester which exhibits high clarity and gloss when formed into molded articles and thick sheets. A preferred inorganic toner is cobalt which can be added in the form of an organic acid salt such as cobalt acetate or cobalt propionate. Alternatively, they can be used as thermally stable organic colorful composite toners in the copolyester chain. Examples of suitable organic toner systems where thermally colored compounds are incorporated stable reactive sites in a polyester to improve the color of the polyester, such as certain blue and red substituted anthraquinones, are described in U.S. Patent No. 5,384, 377; No. 5,372,864; No, 5,340,910; and No. 4,745,174 which are incorporated herein by reference for their organic toner systems. In step (3), the product of step (2) undergoes a polycondensation reaction for a sufficient time to form a copolyester having an inherent viscosity of at least 0.50 dl / g. The polycondensation reaction is carried out at a temperature of 260 ° C to 290 ° C, preferably 270 ° C to 280 ° C. The polycondensation reaction is carried out under reduced pressure of 400 mm Hg (50 kPa) at 0.1 mm Hg (0.01 kPa) and the by-product glycol is eliminated as soon as it is produced. The molecular weight of the copolyester is indicated by a measurement of the inherent viscosity of the solution (VI), which is measured at 25 ° C by dissolving 250 mg of the copolyester in 50 ml of a solvent consisting of a 60/40 weight ratio of phenol and tetrachloroethane. The copolyesters of this invention have an inherent viscosity of 0.5 to 0.9 dL / g, preferably 0.7 to 0.8 dL / g. The following examples are proposed to illustrate but not limit the scope of this invention. All parts and percentages in the examples are on a weight basis unless stated otherwise.

Example 1 The esterification products are prepared using ethylene glycol (EG), terephthalic acid (ATF) and distilled cyclohexanedimethanol (CGDM), where the content of the copolyester CHDM is 31 mole percent of the total glycol content. The molar ratio of total glycols (EG + CHDM) to ATF is either 1.7: 1 or 1.4: 1 with the excess as EG. Esterification is performed at 40 psig (380 kPa) using a six-mole laboratory batch reactor equipped with a water column to remove the generated water vapor. The reactor is heated and the temperature is allowed to slowly increase to 240 ° C where the esterification reaction begins and the steam is distilled off. The completion of the reaction is indicated by a decrease in the temperature of the water column. Two esterification products are prepared with a molar feed ratio of 1.7: 1. One of the esterification products is prepared at a temperature of 240 ° C and the esterification requires 180 minutes to complete. At an average temperature higher than 255 ° C, the esterification reaction ends in 100 minutes. Two esterification products are prepared with a molar feed ratio of 1.4: 1. At a temperature lower than 240 ° C, the esterification requires 240 minutes to finish. At a higher average temperature of 255 ° C, the Esterification reaction ends in 120 minutes. After completion of the esterification reaction, the product is polymerized at 282 ° C using 38 ppm of titanium, 28 ppm of cobalt and 40 ppm of phosphorus. The polycondensation reactors are equipped with a stirrer, a side limb, a nitrogen inlet, and a heat source. After melting at 225 ° C, the temperature is increased to 282 ° C at 2 ° / min. The polycondensation reactions take place under reduced pressure of < 0.5 mm Hg (0.07 kPa) with stirring speed of 50 rpm. The results of the test are summarized in Table I. Batch esterification Laboratory polycondensation Molar proportion of Temperature Pressure Time IV feed ° C Ps_.i (kPa) (minutes) 1.7: 1 240 40 (380) 55 0.782 1.7: 1 255 40 (380) 55 0.741 1.4: 1 240 40 (380) 95 0.742 1.4: 1 255 40 (380) 95 0.765 These results in Table I clearly indicate the increased polycondensation activity in the esterification products prepared with the molar proportion of higher feed. The esterification products prepared with the molar proportion of 1.7: 1 feed achieve a V.I. from 0.72 dL / g to 0.78 dL / g within 50 to 55 minutes a 282 ° C. Esterification products made with a molar feed ratio of 1.4: 1 require 90 to 95 minutes at 282 ° C to achieve a V.I. from 0.72 to 0.78 dL / g. Example 2 The esterification products are prepared using ethylene glycol, terephthalic acid and cyclohexanedimethanol, where the content of the cyclohexanedimethanol of the copolyester is 31 mol% of the total glycol. The esterification reaction is carried out in two continuous reactors connected in series (R1 and R2). A third reactor is used as a rapid tank for collection of the esterification product. The molar ratio of feed of total glycols to terephthalic acid is varied from 2.0: 1 to 1.3: 1 with the excess as ethylene glycol. The reaction time is varied by adjusting the feed flow rate of the suspension to Rl. The fixed volume reactors have approximately a 2: 1 volume ratio with 2230 ml in Rl and 1100 ml in R2. The feed flow rate is varied from 10 to 19 ml / min. in such a way that the total esterification time varies from 180 to 360 minutes. The temperature of the first esterification reactor (Rl) is varied from 245 ° C to 260 ° C and the pressure is maintained at 37 psig (360 kPa). The temperature of the second esterification reactor (R2) is varied from 245 ° C to 267 ° C, and the pressure is varied from 10 to 27 psig (170 to 290 kPa). The esterification product is collected and polymerizes in reactors in laboratory batch in half mol portions. The reactors are equipped with an agitator, a lateral extremity, a nitrogen inlet and a heat source. The catalyst system has 48 ppm of titanium and 31 ppm of phosphorus. After ten minutes at 225 ° C, the temperature is increased to 282 ° C at 2 ° / min. The polycondensation reactions take place under reduced pressure of < 0.5 mm Hg (0.07 kPa) with stirring speed at 50 rpm. Each esterification product is polymerized for 60 minutes. The results of the test are summarized in Table II: ' TABLE II Continuous esterification Laboratory polycondensation Proportion Temperature ° C Pressure psig (kPa) Time Time VI molar in minutes minutes power Rl R2 Rl R2 2.0: 1 245 250 37 (360) 27/290) 180 60 0.756 2. 0: 1 260 270 37 (360) 27 (290) 180 60 0.738 2. 0: 1 245 250 37 (360) 27 (290) 320 60 0.731 1. 8: 1 245 250 37 (360) 27 (290) 180 60 0.738 1. 8: 1 245 250 37 (360) 10 (170) 180 60 0.700 1. 8: 1 245 250 37 (360) 10 (170) 180 100 0.232 The results in Table II indicate the increased polycondensation activity in the esterification products prepared with the molar proportion of higher feed, and the increased polycondensation activity with lower temperatures and shorter esterification times. The esterification product with the highest polycondensation activity, indicated by V.I. Higher, it is produced using the molar proportion of feed of 2.0: 1, the low esterification temperatures and 180 minutes of total time of esterification. Increasing the esterification temperatures, while maintaining a 2.0: 1 molar feed ratio, decreases the polycondensation activity of the esterification product. Increasing the esterification reaction time from 180 to 320 minutes, while maintaining a 2.0: 1 molar feed ratio, also decreases the polycondensation activity. Decreasing the molar proportion of feed to 1.8: 1 distributes the polycondensation activity, and decreasing the pressure in the second esterification reactor decreases the polycondensation activity further. The esterification products produced with a molar proportion of olefin of 1.3: 1 are inactive in the polycondensation with a V. I. of less than 0.7 achieved after 100 minutes of condensation time.

Example 3 Esterification products are prepared with different compositions of 1,4-cyclohexanedimethanol (CHDM) using a suspension feed of ethylene glycol (EG), terephthalic acid (ATF), and 1,4-cyclohexanedimethanol (CHDM), where the CHDM content of the copolyester is either 12 mole percent or 62 mole percent of the total glycol content. The esterification reactions are carried out as described in Example 2. The molar ratio of feed of total glycols (EG + CHDM) to ATF is 2.0: 1 with the excess being EG. The temperature of the first esterification reactor (Rl) is 245 ° C, and the pressure is 37 psig (360 kPa). The temperature of the second esterification reactor (R2) is 250 ° C, and the pressure is 27 psig (290 (kPa).) The polycondensation is carried out at 282 ° C as described in Example 2 for an objective VI of 0.70. at 0.80, the test results are summarized in Table III.

TABLE III Continuous% molar esterification of Temperature Temperature ° C Pressure pe ig (kPa) Time Time VI CHDM molar minute minutes feed Rl R2 Rl R2 12% 2.0: 1 245 250 37 (360) 27 (290) 180 65 0.721 62% 2.0: 1 245 250 37 (360) 27 (290) 180 30 0.792 62% 1.8: 1 245 250 37 (360) 27 (290) 180 30 0.? 48 Table III indicates the polycondensation activity in esterification products prepared with different levels of 1,4-cyclohexanedimethanol. Table III clearly indicates increased polycondensation activity in the esterification products prepared with the molar proportion of the highest feed. The activity of increased polycondensation with a higher molar ratio of glycol to dicarboxylic acid is demonstrated with the esterification products of cyclohexanedimethanol in higher concentration, where an esterification product is prepared using the lower feed molar ratio compared to the molar feed ratio of 2.0: 1. The esterification product prepared with a molar proportion of feed of 1.8: 1, does not achieve V.I. objective within the 30 minutes of 1.3: 1 are inactive in the polycondensation with a V. I., while the esterification product prepared with a molar proportion of feed of 2.0: 1 achieves a V.I. of 0.79 dl / g in 30 minutes of condensation time, Example 4 molar ratio of feed of glycols to terephthalic acid from 4.3: 1 to 2.3: 1 with the excess being ethylene glycol. The residence time of total esterification is approximately 155 minutes. The temperature of the first esterification reactor (Rl) is varied from 250 ° C to 265 ° C, and the pressure is at 45 psig (410 kPa). The temperature of the second esterification reactor (R2) is varied from 250 ° C to 265 ° C, and the pressure is 27 psig (290 kPa). Titanium and phosphorus solutions, along with organic toner dyes, are added in the first of the two polycondensation reactors, also connected in series. The catalyst system used has 48 ppm of titanium and 31 ppm of phosphorus. The first polycondensation reactor (Pl) is maintained at 265 ° C at a pressure of 175 mm Hg (23 kPa). The approximate residence time in the continuous reactor PI is 65 minutes. The final polycondensation reactor (P2) has a horizontal design with motor-driven disc rings to improve the surface generation for the e-limination of ethylene glycol from the molten polymer as the polycondensation reaction progresses. The approximate time in the polycondensation reactor is 220 minutes, and the final polycondensation temperature is 272 ° C. The polycondensation reaction takes place under reduced pressure of about 1.0 mm Hg (0.13 kPa). After the polymerization, the molten polymer is extruded in a follow bath to cool and harden, cut into granules, and analyzed for inherent viscosity. The test results are summarized in Table IV.

TABLE IV Continuous esterification Laboratory polycondensation Proportion Temperature ° C Pressure psig (kPa) Time Time VI molar in minutes minutes feed Rl R2 Rl R2 4.3: 1 250 250 45 (410) 27 (290) 155 220 0.767 4.3: 1 255 265 45 (410 ) 27 (290) 155 220 0.748 2.3: 1 255 265 45 (410) 27 (290) 155 220 0.685 ( The results in Table IV clearly indicate the increased polycondensation activity in the esterification products prepared with the higher feed molar ratio, and the increased polycondensation activity at lower temperatures. The esterification product with the highest total polycondensation activity is produced using the highest feed molar ratio of 4.3: 1, and low esterification temperatures. Increasing the esterification temperatures, while maintaining a molar feed ratio of 4.3: 1, decreases the polycondensation activity of the esterification product, indicated by a lower V. I. Decreasing the molar ratio of feed to 2.3: 1 significantly decreases polycondensation activity, and V.I. can not be reached. objective. Example 5 The esterification products are prepared using ethylene glycol, terephthalic acid, and distilled 1,4-cyclohexanedimethanol, where the cyclohexanedimethanol content of the copolyester is 31 mole percent of the total glycol content. The esterification reaction is carried out in two continuous reactors connected in series as described in Example 2. The molar ratio of feed of total glycols to terephthalic acid of 2.0: 1 with the excess which is ethylene glycol and the total time of esterification it's 180 minutes The temperature of the first esterification reactor (Rl) is 245 ° C, and the pressure is 37 psig (360 kPa). The temperature of the second esterification reactor (R2) is 250 ° C, and the pressure is 27 psig (290 kPa). The polycondensation catalyst and the temperature are varied in this group of experiments to demonstrate the effect of the polycondensation catalyst level and the temperature on the proportion of yellow color formation in the final polymer. The color value b * is a yellow color measurement where a larger number is more yellow. Organic toner dyes are added to the esterification products, before fusion and polycondensation. The phosphorus level remains constant at 25 ppm and toner toner levels remain constant. The polycondensation reaction is carried out in reactors in laboratory batch as described in Example 2. After melting at 225 ° C, the temperature is increased to either 282 ° C or 272 ° C. Each esterification product is polymerized to a V.I. target of 0.72 to 0.78 dl / g. The copolyester products for inherent viscosity, catalyst levels and b * values are analyzed by Hunter Ultrascan. The test results are summarized in Table V.

TABLE V Continuous esterification Laboratory polycondensation Proportion Temperature ° C Pressure psig (kPa) Time Ti ppm Time VI b * molar in minutes minutes feed Rl R2 Rl R2 2.0: 1 245 250 37 (360) 27 (290) 180 48 40 0.731 9.3 2. 0: 1 245 250 37 (360) 27 (290) 180 30 55 0.730 8.0 2. 0: 1 245 250 37 (360) 27 (290) 180 48 70 0.729 8.1 2. 0: 1 245 250 37 (360) 27 (290) 180 30 85 0.741 6 2. 0: 1 245 250 37 (360) 27 (290) 180 16 85 0.760 4.9 The results in Table V indicate that the esterification products made with a high feed molar ratio have sufficient polycondensation activity to achieve a V. I. Goal with reduced levels of catalyst and reduced polycondensation temperatures. The results clearly indicate reduced yellow (b * minor) color formation with reduced catalyst level and reduced polycondensation temperatures. Since the esterification products are the same, and the phosphorus level and organic toner dye levels are constant, the factors which will affect the proportion of polycondensation and the amount of yellow color developed in the polymer are the catalyst level of polycondensation (Ti) and the polycondensation temperature. When the polycondensation reaction is carried out for V.I. target of 0.72 to 0.78 dl / g, the most yellow polymer is obtained using the highest temperature (282 ° C) and the level of titanium. highest (48 ppm Ti). Significantly lower yellow values are obtained at the lower polycondensation temperature (272 ° C) with the lowest b * value obtained with the lowest titanium level (16 ppm). Example 6 The esterification products are prepared using ethylene glycol, terephthalic acid, and distilled 1,4-cyclohexanedimethanol, wherein the cyclohexanedimethanol content of the copolyester is 31 mole percent of the total glycol content. The esterification reaction is carried out in two continuous reactors connected in series (R1 and R2). The molar ratio of feed of total glycols to terephthalic acid is 3.5: 1 with the excess being ethylene glycol. The total residence time of esterification is kept constant at about 185 minutes. The temperature of the first esterification reactor (Rl) is 255 ° C, and the pressure is 69 psig (580 kPa). The temperature of the second esterification reactor (R2) is 255 ° C, and the pressure is 2 > 7 psig (290 kPa). The polycondensation catalyst, the temperature and the phosphorus level are varied in this group of experiments to demonstrate the effect of the polycondensation catalyst level, the temperature and the phosphorus level on the proportion of yellow color formation in the final polymer. The color value b * is a yellow color measurement where a larger number is more yellow. Organic toner dyes are added to the esterification products, before fusion and polycondensing. The polycondensation reaction is carried out in reactors in laboratory batch as described in Example 2. After melting at 225 ° C, the temperature is increased to either 285 ° C or 275 ° C. Each esterification product is polymerized to a V.I. target of 0.72 to 0.78 dl / g. The copolyester products are analyzed for inherent viscosity, catalyst levels and b * values by Hunter Ultrascan. The test results are summarized in Table VI.

TABLE VI Polycondensation with 25 ppm P at 285 ° C Continuous esterification Laboratory polycondensation Proportion Temperature Pressure psig (kPa) Time Temperature Ti Time VI b * molar in ° C minutes ° C ppm minutes power Rl R2 Rl R2 3.5: 1 255 255 69 (580) 27 (290) 180 285 48 45 0.819 4.7 3. 5: 1 255 255 69 (580) 27 (290) 180 285 32 60 0.827 3.1 J Polycondensation with 45 ppm P at 275 ° C Continuous esterification Laboratory polycondensation Proportion Temperature Pressure psig (kPa) Time Temperature Ti Time VI b * molar in ° C minutes ° C ppm minutes power Rl R2 Rl R2 3.5: 1 255 255 69 (580) 27 (290) 180 275 32 130 0.755 -.06 3. 5: 1 255 255 69 (580) 27 (290) 180 275 16 130 0.751 -.23 The results in Table VI illustrate that esterification products made with a high feed molar ratio have sufficient polycondensation activity to achieve a V. I objective with reduced levels of catalyst and reduced polycondensation temperatures. The results clearly indicate significantly reduced yellow color formation (b * lower) with reduced catalyst level, reduced polycondensation temperatures and increased phosphorus level. Since the esterification products are the same, and the organic toner dye levels are constant, the factors which will affect the polycondensation activity and the amount of yellow color developed in the polymer are the level of polycondensation catalyst (Ti) , the polycondensation temperature and the phosphorus level.

The most yellow polymer is obtained using the high polycondensation temperature (285 ° C), and the highest titanium level (48 ppm Ti) with 25 ppm phosphorus stabilizer. The color is slightly improved by reducing the level by reducing the titanium level to 32 ppm. Significantly lower yellow values are obtained at the lower polycondensation temperature (275 ° C) with higher levels of phosphorus stabilizer (45 ppm P). Although much longer polycondensation time is required, the V.I. target from 0.72 to 0.78 dl / g and you get the value the value of b * lowest with the highest level titanium bass (16 ppm). Many variations will be suggested by themselves for those with experience in the art in light of the description detailed above. All of such obvious modifications are within the total proposed scope of the appended claims.

Claims (3)

1. CLAIMS 1. A Process for preparing coppolyesters of terephthalic acid, ethylene glycol and 1,4-cyclohexanedimethanol which have 30 to 90 percent mole of ethylene glycol in the glycol component, and are characterized by a neutral color, high clarity and increased brightness. The process comprises the steps of: (1) reacting terephthalic acid, ethylene glycol, and 1,4-cyclohexanedimethanol in a molar ratio of feed of total glycols to dicarboxylic acid from 1.7: 1 to 6.0: 1 at a * temperature of 240 ° C at 280 ° C and a pressure of 15 psig (200 kPa) at 80 psig (650 kPa) for 100 to 300 minutes to form an esterification product; (2) adding a polycondensation catalyst and 0.1 to 40 ppm of a toner to the esterification product of step (1), wherein the polycondensation catalyst is selected from the group consisting of titanium, germanium, antimony and combinations thereof; and (3) polycondensing the product of step (2) at a temperature of 260 ° C to 290 ° C and a reduced pressure of 400 mm Hg (50 kPa) to 0.1 mm Hg (0.01 kPa) for a sufficient time to form a copolyester having an inherent viscosity of at least 0.50 dl / g.
2. The process comprising adding 10 to 100 ppm of a phosphorus stabilizer in step (2) or step (3). 2. A process for preparing co-polyesters of terephthalic acid, ethylene glycol and 1,4-cyclohexanedimethanol having 30 to 90 mole percent of ethylene glycol in the glycol component, and characterized by a neutral color, high clarity and increased brightness. The process comprises the steps of: (1) reacting terephthalic acid, ethylene glycol, and 1,4-cyclohexanedimethanol in a molar ratio of feeding total glycols to dicarboxylic acid from 2.0: 1 to 4.5: 1 at a temperature of 240 ° C to 280 ° C and a pressure of 15 psig (200 kPa) at 80 psig (650 kPa) for 100 to 300 minutes to form an esterification product; (2) adding 10 to 60 ppm of titanium and 0.1 to 40 ppm of a toner to the esterification product of step (1); and (3) polycondensing the product of step (2) at a temperature of 260 ° C to 290 ° C and a reduced pressure of 400 mm Hg (50 kPa) to 0.1 mm Hg (0.01 kPa) for a sufficient time to form a copolyester having an inherent viscosity of at least 0.50 dl / g. The process comprising adding 10 to 100 ppm of a phosphorus stabilizer in step (2) or step (3).
3. 3. The process according to claim 2, characterized in that step (1) is carried out at a temperature of 245 ° C to 255 ° C, and a pressure of 20 psig (240 kPa) at 50 psig (450 kPa). . The process according to claim 2 characterized in that 12 ppm to 25 ppm of titanium is used as a polycondensation catalyst in step (2). 5. The process according to claim 1, characterized in that 40 ppm to 60 ppm of a phosphorus stabilizer are added. 6. The process according to claim 1, characterized in that the phosphorus stabilizer is osphoric acid. 7. The process according to claim 1, characterized in that the polycondensation temperature of step (3) is 270 ° C to 280 ° C. 8. The process according to claim 1 characterized in that up to 10 mol% of the terephthalic acid is replaced with a dicarboxylic acid selected from the group consisting of aromatic dicarboxylic acids having from 8 to 14 carbon atoms, aliphatic dicarboxylic acids which they have 4 to 12 carbon atoms, cycloaliphatic dicarboxylic acids having 8 to 12 carbon atoms and combinations thereof. 9. The process according to claim 1 characterized in that up to 10 mole percent of the glycols are replaced with a glycol selected from the group consisting of cycloaliphatic glycols having 6 to 20 carbon atoms, aliphatic glycols having 3 to 20 carbon atoms and combinations thereof. 10. The process according to claim 1, characterized in that it additionally contains 0.1 to 0.5 mole percent of a trifunctional or tetrafunctional comonomer. 11. The process according to claim 10, characterized in that the trifunctional or tetrafunctional comonomer is selected from the group consisting of trimellitic anhydride, trimethylolpropane and pentaerythritol.