DESC:FIELD
The present disclosure relates to a process for the preparation of polyethylene terephthalate.
DEFINITIONS
As used in the present disclosure, the following terms are generally intended to have the meaning as set forth below, except to the extent that the context in which it is used indicate otherwise.
Yellowness Index: The term “yellowness index” refers to the measurement of the degree to which the color of a surface is shifted from preferred Blue (or colorless) towards yellow.
Pre-polymer: The term pre-polymer refers to a monomer or system of monomers that have been reacted to an intermediate molecular mass state. The pre-polymer is capable of further polymerization by reactive groups to a fully cured high molecular weight state.
BACKGROUND
The background information herein below relates to the present disclosure but is not necessarily prior art.
Polyesters, such as polyethylene terephthalate (PET) exhibit excellent mechanical strength, heat resistance, transparency and gas barrier properties. Due to these attributes, PET has been extensively used in food packaging applications, such as water, soft drink, juices, and thermoformed sheets. Polyester is also widely being used for producing fibers and yarns for wide variety of textile, and industrial applications.
PET is commercially produced using antimony based polycondensation catalysts. The major disadvantage with PET made with antimony based catalyst is the grey colour resulting from precipitation of antimony metal. Further, antimony shows some environmental concerns, due to leaching. Germanium catalysts are used as an alternative, which are capable of providing a brighter polymer, without grey cast, however germanium compounds are expensive and therefore increases the overall cost of production of PET.
Therefore, there is felt a process for preparing polyesters that mitigates the herein above mentioned drawbacks.
OBJECTS
Some of the objects of the present disclosure, which at least one embodiment herein satisfies, are as follows:
It is an object of the present disclosure to ameliorate one or more problems of the prior art or to at least provide a useful alternative.
An object of the present disclosure is to provide a process for the preparation of polyesters.
Another object of the present disclosure is to provide a process for preparation of polyethylene terephthalate having reduced yellowness index.
Other objects and advantages of the present disclosure will be more apparent from the following description, which is not intended to limit the scope of the present disclosure.
SUMMARY
The present disclosure related to a process for the preparation of polyethylene terephthalate. The process comprises mixing terephthalic acid, isophthalic acid and monoethylene glycol under stirring to obtain a mixture. An alkali hydroxide and a first catalyst are added to the mixture under stirring to obtain a slurry. The so obtained slurry is heated at a temperature in the range of 200 oC to 270 oC and at a pressure in the range of 1kg/cm2 to 4kg/cm2 to undergo esterification of the terephthalic acid to obtain esterified mixture. The esterified mixture is pre-polymerized by adding a second catalyst to obtain a pre-polymer. The pre-polymer is polymerized at a temperature in the range of 275 oC to 325 oC under a vacuum pressure less than 0.5 torr to obtain polyethylene terephthalate. In accordance with the process of the present disclosure, at least one thermal stabilizer, and/or at least one branching agent is added before, during or at the end of the esterification step (c). In an embodiment, the terephthalic acid is a purified terephthalic acid.
DETAILED DESCRIPTION
Embodiments are provided so as to thoroughly and fully convey the scope of the present disclosure to the person skilled in the art. Numerous details are set forth, relating to specific components, and methods, to provide a complete understanding of embodiments of the present disclosure. It will be apparent to the person skilled in the art that the details provided in the embodiments should not be construed to limit the scope of the present disclosure. In some embodiments, well-known processes, well-known apparatus structures, and well-known techniques are not described in detail.
The terminology used, in the present disclosure, is only for the purpose of explaining a particular embodiment and such terminology shall not be considered to limit the scope of the present disclosure. As used in the present disclosure, the forms "a,” "an," and "the" may be intended to include the plural forms as well, unless the context clearly suggests otherwise. The terms "comprises," "comprising," “including,” and “having,” are open ended transitional phrases and therefore specify the presence of stated features, integers, steps, operations, elements, modules, units and/or components, but do not forbid the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The particular order of steps disclosed in the method and process of the present disclosure is not to be construed as necessarily requiring their performance as described or illustrated. It is also to be understood that additional or alternative steps may be employed.
The terms first, second, third, etc., should not be construed to limit the scope of the present disclosure as the aforementioned terms may be only used to distinguish one element, component, region, layer or section from another component, region, layer or section. Terms such as first, second, third etc., when used herein do not imply a specific sequence or order unless clearly suggested by the present disclosure.
It is well known that the titanium (Ti) based catalysts used for the production of polyethylene terephthalate (PET) increases yellowness index. Further, known processes for preparation of PET use expensive metals in the catalyst system, such as Germanium.
The present disclosure provides a process for the preparation of polyethylene terephthalate (PET) having reduced yellowness index and at the same time also improves the polymerization rate both in melt phase and also in solid state polymerization, generally referred as SSP.
In an aspect of the present disclosure, there is provided a process for the preparation of polyethylene terephthalate. The process is described in detail as given below:
Firstly, a mixture is prepared by mixing terephthalic acid (TA), isophthalic acid (IPA) and monoethylene glycol (MEG) under stirring.
The terephthalic acid is purified terephthalic acid (PTA). The molar ratio of the terephthalic acid and the monoethylene glycol is in the range of 1:1 to 1:5. In an exemplary embodiment, the molar ratio of the terephthalic acid to the monoethylene glycol is 1:2.
The amount of the isophthalic acid is in the range of 0.2 to 0.5 wt% with respect to the terephthalic acid.
The addition of isophthalic acid reduces the crystallization in the process of preparation of polyethylene terephthalate and improves transparency. The addition of isophthalic acid also helps in retaining melt strength at higher temperature.
An alkali hydroxide and a first catalyst are added to the mixture under stirring to obtain a slurry.
The first catalyst is stannous oxalate.
The alkali metal hydroxide is selected from the group consisting of sodium hydroxide, potassium hydroxide, and calcium hydroxide. In an embodiment, the alkali metal hydroxide is sodium hydroxide. In accordance with the present disclosure, sodium hydroxide is added in the slurry as diethylene glycol (DEG) suppressant.
During the formation of the esterification product of terephthalic acid and ethylene glycol, diethylene glycol is readily formed, which is subsequently built into the polyester that is obtained during the polycondensation step. The incorporation of diethylene glycol moieties in the polyester reduces the melting point, reduces the glass transition temperature and crystallization level. Since the crystallization level is known to have an effect on the mechanical properties of the articles formed from such polyesters, it is believed that the incorporation of diethylene glycol moieties into the polyesters reduce the thermal stability and mechanical properties of such articles. Therefore, it is important to have the reduced content of diethylene glycol in PET.
The content of diethylene glycol residues in the polyester can be reduced by compounds that are capable of suppressing the formation of diethylene glycol from ethylene glycol. The esterification or transesterification takes place in the presence of a basic compound capable of suppressing the formation of diethylene glycol. The method produces polyester with a reduced amount of diethylene glycol moieties as in the polyester.
In accordance with the present disclosure, an alkali hydroxide is used as DEG suppressant. The alkali hydroxide is selected from the group consisting of sodium hydroxide, potassium hydroxide, and calcium hydroxide.
The so obtained slurry is esterified by heating at a temperature in the range of 200 oC to 270 oC and at a pressure in the range of 1kg/cm2 to 4kg/cm2 for a predetermined time period to obtain esterified mixture. At this temperature and pressure, the terephthalic acid undergoes esterification with monoethylene glycol.
The predetermined time period is in the range of 150 minutes to 250 minutes.
The esterified mixture is pre-polymerized by adding a second catalyst to obtain a pre-polymer.
In accordance with the process of the present disclosure, at least one thermal stabilizer, and/or at least one branching agent is added before, during or at the end of the esterification step.
In an embodiment, the second catalyst, at least one thermal stabilizer, and at least one branching agent are added after the step of esterification.
In another embodiment of the present disclosure, the at least one thermal stabilizer is added before the step of esterification.
In still another embodiment the second catalyst is added prior to the addition of thermal stabilizer. In another embodiment, the thermal stabilizer is added prior to the second catalyst.
The second catalyst is titanium catalyst. The titanium catalyst is selected from the group consisting of TiCl4, TiH4O4, TiO2, and Titanium tetrabutoxide. In an embodiment, the titanium catalyst is Ti (OH)4(TiH4O4). In an exemplary embodiment, the titanium catalyst is added in the form of slurry by using monoethylene glycol.
The thermal stabilizer is a phosphate compound, which is selected from the group consisting of lithium phosphate, lithium dihydrogen phosphate, dilithium hydrogenphosphate, sodium phosphate, sodium dihydrogen phosphate, disodium hydrogenphosphate, potassium phosphate, potassium dihydrogen phosphate, dipotassium hydrogenphosphate, strontium phosphate, strontium dihydrogen phosphate, distrontium hydrogenphosphate, zirconium phosphate, barium phosphate, aluminum phosphate, phosphoric acid and zinc phosphate. Sodium phosphate, sodium dihydrogen phosphate, disodium hydrogenphosphate, potassium phosphate, potassium dihydrogen phosphate and dipotassium hydrogenphosphate are preferred in accordance with the embodiments of the present disclosure.
In an embodiment, the phosphate compound is sodium dihydrogen phosphate.
The branching agent is selected from the group comprising pentaerythritol (C(CH2OH)4), trimesic acid (C6H3(COOH)3), pyromellitic acid (C6H2(COOH)4), pyromellitic dianhydride, trimellitic acid, trimellitic anhydride, and trimethylol propane (C2H5C(CH2OH)3). In an embodiment, the branching agent is pentaerythritol (C(CH2OH)4).
The pre-polymer is polymerized at a temperature in the range of 275 oC to 325 oC under a vacuum pressure less than 0.5 torr to obtain polyethylene terephthalate. In an exemplary embodiment, the polymerization is carried out at 290 oC under a vacuum pressure less than 0.5 torr.
The polymerization is selected from melt polymerization, solid state polymerization, and combination thereof. In an embodiment, the polymerization is carried out by melt polymerization. In another embodiment, the polymerization is carried out by solid state polymerization. In still another embodiment, the polymerization is carried out by melt polymerization followed by solid state polymerization.
A blue toner and a red toner are added to the pre-polymer prior to polymerization. The blue toner is used to mask the yellowness of the polymer (PET) and red toner is used to mask the greenish tinge of the polymer which comes due to higher loading of blue toner. In accordance with the present disclosure, the blue toner and red toner are added to the pre-polymer for obtaining a white polymer.
In accordance with the present disclosure, the intrinsic viscosity of polyethylene terephthalate obtained by the process of the present disclosure is in the range of 0.7 to 0.9 dl/g and the yellowness index of the so obtained polyethylene terephthalate is in the range of 1 to 3.
Titanium catalysts are being used for the production of polyesters using batch and continuous polymerization process. However, it is known that the titanium catalyst has a tendency to increase yellowness index in the resulting polyester. It has been surprisingly found in the present disclosure that the use of phosphate compounds such as, sodium dihydrogen phosphate reduces yellowness index to a large extent during the polymerization process. The time at which the phosphate compound is added to the polymerization is critical. It is found that incorporation of the phosphate compound during the esterification process improved melt phase polymerization rate there by increasing polyester production rate.
The use of branching agent, such as pentaerythritol (C5H12O4) results in enhanced reactivity and improves the solid state polymerization rate and thereby increases the overall productivity.
The use of the phosphate compound during the esterification stage of the polymerization process aids in the increase of the whiteness index and reduction of the yellowness index of the PET obtained. Further, the use of the phosphate compound aids in the increasing the melt polymerization rate.
The process exhibits enhanced productivity in melt phase polycondensation. The polyethylene terephthalate of the present disclosure can be used for making containers, yarns, films, sheets, straps, fibres using melt polymerization followed by solid phase polymerization (SSP), such that the enhanced activity shown in melt polycondensation is backed up by improved reactivity in SSP.
The foregoing description of the embodiments has been provided for purposes of illustration and not intended to limit the scope of the present disclosure. Individual components of a particular embodiment are generally not limited to that particular embodiment, but, are interchangeable. Such variations are not to be regarded as a departure from the present disclosure, and all such modifications are considered to be within the scope of the present disclosure.
The present disclosure is further described in light of the following laboratory scale experiments which are set forth for illustration purpose only and not to be construed for limiting the scope of the disclosure. These laboratory scale experiments can be scaled up to industrial/commercial scale and the results obtained can be extrapolated to industrial/commercial scale.
EXPERIMENTAL DETAILS:
Comparative Example 1:
55 kg purified terephthalic acid (PTA) (46.3 kg) – monoethylene glycol (MEG) (35.5 kg) having mole ratio of 1:2 was mixed to obtain slurry. Isophthalic acid (IPA) – 1.8% (w/w) was also added in PTA-MEG slurry. NaOH (25 ppm as sodium) was added as a DEG suppressant. Stannous oxalate (70 ppm as compound) was added in the beginning of esterification reaction. Esterification reaction was carried out at 260 °C under 2 kg/cm2 of pressure. For polymer color adjustment, red toner (2 ppm) and blue toner (7 ppm) were also added after esterification reaction. Titanium hydroxide (10 ppm as Titanium) in a form of slurry in MEG was added as a catalyst at the end of esterification reaction. Melt polymerization was carried out under fine vacuum (< 0.5 torr) at 290°C. After achieving desired melt viscosity, material was taken out as a strand under water and converted in to chips using cutter.
Comparative Example – 2
55 kg. PTA (46.3 kg) and MEG (35.5 kg) having mole ratio of 1:2 was mixed to obtain slurry. Isophthalic acid (IPA) – 1.8% (w/w) was also added in PTA-MEG slurry. NaOH (25 ppm as sodium) was added as a DEG suppressant. Stannous oxalate (70 ppm as compound) was added in the beginning of esterification reaction. Esterification reaction was carried out at 260°C under 2kg/cm2 of pressure. For polymer color adjustment, red toner (2 ppm) and blue toner (7 ppm) were also added after esterification reaction. Titanium hydroxide (12 ppm as Titanium) in a form of slurry in MEG was added as a catalyst at the end of esterification reaction. Melt polymerization was carried out under fine vacuum (< 0.5 torr) at 290°C. After achieving desired melt viscosity, material was taken out as a strand under water and converted in to chips using cutter.
Preparation of Polyethylene terephthalate in accordance with the process of the present disclosure:
Example – 3
55 kg. PTA (47.1 kg) and MEG (35.5 kg) having mole ratio of 1:2 was mixed to obtain slurry. Isophthalic acid (IPA) – 0.4 % (w/w) was also added in PTA-MEG slurry. NaOH (25 ppm as sodium) was added as a DEG suppressant. Stannous oxalate (70 ppm as compound) was added in the beginning of esterification reaction. Esterification reaction was carried out at 260°C under 2kg/cm2 of pressure. Titanium hydroxide (10 ppm as Ti) in a form of slurry in MEG was added as a catalyst at the end of esterification reaction wherein the esterified mixture was pre-polymerized to obtain a pre-polymer. Phosphoric acid (10 ppm as Phosphorous) and for polymer color adjustment, red toner (2 ppm) and blue toner (7 ppm) were also added after esterification reaction. The pre-polymer was polymerized by melt polymerization which was carried out under fine vacuum (< 0.5 torr) at 290°C. After achieving desired melt viscosity, material was taken out as a strand under water and converted in to chips using cutter.
Example – 4
55 kg. PTA (47.1 kg) and MEG (35.5 kg) having mole ratio of 1:2 was mixed to obtain slurry. Isophthalic acid (IPA) – 0.4% (w/w) was also added in PTA-MEG slurry. NaOH (25 ppm as sodium) was added as a DEG suppressant. Stannous oxalate (70 ppm as compound) was added in the beginning of esterification reaction. Esterification reaction was carried out at 260°C under pressure of 2 kg/cm2. Titanium hydroxide (10 ppm as Ti) in a form of slurry in MEG was added as a catalyst at the end of esterification reaction wherein the esterified mixture was pre-polymerized to obtain a pre-polymer. Sodium dihydrogen phosphate (20 ppm as Phosphorous) and for polymer color adjustment, red toner (2 ppm) and blue toner (7 ppm) were also added after esterification reaction. The pre-polymer was polymerized by melt polymerization which was carried out under fine vacuum (< 0.5 torr) at 290°C. After achieving desired melt viscosity, material was taken out as a strand under water and converted in to chips using cutter.
Example – 5
Polymerization batch size was 55 kg. PTA (47.1 kg) – MEG (35.5 kg) mole ratio of 1:2 was maintained. Isophthalic acid (IPA) – 0.4% (w/w) was also added in PTA-MEG slurry. NaOH (25 ppm as sodium) was added as a DEG suppressant. Stannous oxalate (70 ppm as compound) was added in the beginning of esterification reaction. Sodium dihydrogen phosphate (10 ppm as Phosphorous) was added in the beginning of esterification process. Esterification reaction was carried out at 260°C under 2kg/cm2 of pressure. Titanium hydroxide (10 ppm as Ti) in a form of slurry in MEG was added as a catalyst at the end of esterification reaction wherein the esterified mixture was pre-polymerized to obtain a pre-polymer. Pentaerythritol (200 ppm as compound) was also added at the end of esterification reaction. The pre-polymer was polymerized by melt polymerization which was carried out under fine vacuum (< 0.5 torr) at 290°C. After achieving desired melt viscosity, material was taken out as a strand under water and converted in to chips using cutter.
Solid-state polymerization:
Solid-state polymerization was carried out under nitrogen atmosphere. Gas temperature kept at 217°C. Sampling was carried out intermittently to check IV. Targeted IV was 0.76 +/- 0.02 dl/g.
The details of Examples 1-5 are summarized in table 1 and the results of the so obtained PETs are summarized in Table 2 as given below.
Table 1:
Components Amount Comp Ex 1 Comp Ex
2 Example 3 Example 4 Example
5
PTA Kg 46.3 46.3 47.1 47.1 47.1
MEG Kg 35.5 35.5 35.5 35.5 35.5
PTA: MEG Mole ratio - 1 : 2 1 : 2 1 : 2 1 : 2 1 : 2
Isophthalic acid Wt% 1.8 1.8 0.4 0.4 0.4
NaOH ppm 25 25 25 25 25
H3PO4 as P ppm --- --- 10 --- ---
Sodium dihydrogen phosphate as P ppm --- --- --- 20 10
Pentaerythritol as branching agent ppm --- --- --- --- 200
Catalyst: Titanium hydroxide as Ti ppm 10 12 10 10 10
Blue Toner ppm 7 7 7 7 7
Red Toner ppm 2 2 2 2 2

Table 2-Results:
Property Unit of measurement Comp Ex 1 Comp Ex
2 Example 3 Example 4 Example
5
Intrinsic viscosity
(IV) dl/g 0.628 0.625 0.627 0.620 0.629
Lightness value (L*) Hunter 70.70 71.00 72.1 72.20 71.29
Yellowness index measured by CIA method (a*) - -2.30 -2.50 -2.60 -2.70 -2.87
Yellowness index measured by CIA method (b*) Hunter 3.10 3.50 2.9 2.60 1.85
Polymerization Time min 104 107 114 148 101
Intrinsic viscosity (IV) after solid state polymerization (SSP) process dl/g --- --- 0.768 (after 9 hrs) 0.749 (after 10 hours) 0.806 (after 8 hours)
The L*-axis is known as the lightness and the other two coordinates a* and b* represent redness-greenness and yellowness-blueness respectively.
Above results indicate that a catalyst combination of Titanium hydroxide, stannous oxalate and specific phosphorous additive is useful for producing heavy metal free polyethylene terephthalate. Color values, specifically b* color which is a measurement of yellowness index, indicate that sodium dihydrogen phosphate is an efficient thermal stabilizer that can be used with Titanium based catalyst. Addition sequence of phosphorous additive is also critical for obtaining improved melt polymerization process as indicated by melt polymerization time and yellowness measurement. It has also been observed that use of sodium dihydrogen phosphate along with pentaerythritol substantially improves solid state polymerization reaction and desired IV can be achieved in a lesser time with the above said combination.
TECHNICAL ADVANCEMENTS
The present disclosure described herein above has several technical advantages including, but not limited to, the realization of a process for preparing PET having reduced yellowness index. Further, the addition of the phosphate compound during esterification is capable of increasing the polymerization rate.
The embodiments as described herein above, and various features and advantageous details thereof are explained with reference to the non-limiting embodiments in the following description.
Throughout this specification the word “comprise”, or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.
The use of the expression “at least” or “at least one” suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the disclosure to achieve one or more of the desired objects or results.
The foregoing description of specific embodiments so fully reveal the general nature of the embodiments herein, that others can, by applying current knowledge, readily modify and/or adapt for various applications of such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein. Further, it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the disclosure and not as a limitation.
Having described and illustrated the principles of the present disclosure with reference to the described embodiments, it will be recognized that the described embodiments can be modified in arrangement and detail without departing from the scope of such principles.
While considerable emphasis has been placed herein on the particular features of this disclosure, it will be appreciated that various modifications can be made, and that many changes can be made in the preferred embodiment without departing from the principles of the disclosure. These and other modifications in the nature of the disclosure or the preferred embodiments will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the disclosure and not as a limitation.
,CLAIMS:WE CLAIM:
1. A process for preparing polyethylene terephthalate, said process comprising the following steps:
a. preparing a mixture by mixing terephthalic acid, isophthalic acid and monoethylene glycol under stirring;
b. adding an alkali hydroxide and a first catalyst to said mixture under stirring to obtain a slurry;
c. esterifying said slurry by heating at a temperature in the range of 200 oC to 270 oC at a pressure in the range of 1kg/cm2 to 4kg/cm2 to obtain esterified mixture;
d. pre-polymerizing said esterified mixture by adding a second catalyst to obtain a pre-polymer; and
e. polymerizing said pre-polymer at a temperature in the range of 275 oC to 325 oC under a vacuum pressure less than 0.5 torr to obtain polyethylene terephthalate,
wherein at least one thermal stabilizer and/or branching agent is added either before, during or at the end of esterification step (c).
2. The process as claimed in claim 1, wherein the terephthalic acid is a purified terephthalic acid.
3. The process as claimed in claim 1, wherein said alkali hydroxide is selected from the group consisting of sodium hydroxide, potassium hydroxide and calcium hydroxide.
4. The process as claimed in claim 1, wherein said first catalyst is stannous oxalate.
5. The process as claimed in claim 1, wherein said second catalyst is a titanium catalyst selected from the group consisting of titanium tetrachloride (TiCl4), titanium hydroxide (TiH4O4), titanium dioxide (TiO2), and Titanium tetrabutoxide (Ti(OBu)4).
6. The process as claimed in claim 1, wherein said thermal stabilizer is a phosphate compound selected from the group consisting of lithium phosphate, lithium dihydrogen phosphate, dilithium hydrogenphosphate, sodium phosphate, sodium dihydrogen phosphate, disodium hydrogenphosphate, potassium phosphate, potassium dihydrogen phosphate, dipotassium hydrogenphosphate, strontium phosphate, strontium dihydrogen phosphate, distrontium hydrogenphosphate, zirconium phosphate, barium phosphate, aluminum phosphate, phosphoric acid and zinc phosphate.
7. The process as claimed in claims 1 or 6, wherein said thermal stabilizer is selected from sodium dihydrogen phosphate, and phosphoric acid.
8. The process as claimed in claim 1, wherein said branching agent is selected from the group consisting of pentaerythritol (C(CH2OH)4), trimesic acid (C6H3(COOH)3), pyromellitic acid (C6H2(COOH)4), pyromellitic dianhydride, trimellitic acid, trimellitic anhydride, and trimethylol propane (C2H5C(CH2OH)3).
9. The process as claimed in claim 8, wherein said branching agent is pentaerythritol.
10. The process as claimed in claim 1, wherein the molar ratio of said terephthalic acid to said monoethylene glycol is in the range of 1:1 to 1:5.
11. The process as claimed in claim 1 or claim 10, wherein the molar ratio of said terephthalic acid to said monoethylene glycol is 1:2.
12. The process as claimed in claim 1, wherein the amount of said isophthalic acid is in the range of 0.2 to 0.5 wt% with respect to said terephthalic acid.
13. The process as claimed in claim 1, wherein a blue toner and a red toner is added to the pre-polymer prior to polymerization.
14. The process as claimed in claim 1, wherein said polymerization is carried out by melt polymerization, solid state polymerization and combination thereof.

15. The process as claimed in claim 1, wherein the intrinsic viscosity of the polyethylene terephthalate is in the range of 0.7 to 0.9 dl/g and the yellowness index in the range of 1 to 3.