DESC:FIELD
The present disclosure relates to a high ethylene glycol containing carboxylated solid polyester resin and a process for its preparation. The present disclosure further relates to a powder coating composition.
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 they are used indicates otherwise.
Depolymerization refers to a process of converting a polymer into a monomer or a mixture of monomers.
Transesterification refers to a process in which an alcohol and an ester react in the presence of an acid or base to form a new ester.
Esterification refers to a chemical reaction in which an alcohol and an acid react to form an ester.
BACKGROUND
The background information hereinbelow relates to the present disclosure but is not necessarily prior art.
Powder coating compositions offer advantages such as high coating efficiency, excellent mechanical properties, zero-emission of volatile organic compounds, and the like. Carboxyl group-containing polyester resins are well known in the art and are in practice for use in the powder coatings. These polyesters are processed with epoxy compounds to form binding agents for powder coatings. However, the conventional polyester resin based powder coatings are associated with the limitations of surface defects such as cratering, fisheye, pinholes, and the like. The inability of the polyester resin based powder coatings to provide the desired surface smoothness is generally the result of the high viscosities of the polyester resins.
There is a growing interest in the use of cheaper raw materials in the preparation of the coating composition. Ethylene glycol is a cheap and readily available raw material used for the synthesis of polyester. However, the use of ethylene glycol beyond a certain percentage (5%) in a solid polyester resin causes some surface defects like cratering, fish eyes, and the like, which additionally requires higher loading of flow and levelling additives to eliminate/reduce the surface defects. Based on the characterization studies it has been identified that the ethylene glycol-based polyester provides low surface energy (<35 mN/m) as well as high water contact angle (>90°), which is responsible for poor flow and surface defects, whereas other polyester without ethylene glycol in the system provides low water contact angle (75-80°) and little higher surface free energy (43-45 mN/m).
Therefore, there is felt a need to provide a carboxylated solid polyester resin containing high ethylene glycol content which obviates the drawbacks mentioned hereinabove.
OBJECTS
Some of the objects of the present disclosure, which at least one embodiment herein satisfies, are as follows.
An object of the present disclosure is to ameliorate one or more problems of the prior art or to at least provide a useful alternative.
Yet another object of the present disclosure is to provide a carboxylated solid polyester resin containing high ethylene glycol content.
Still another object of the present disclosure is to provide a simple and environment-friendly process for the preparation of carboxylated solid polyester resin containing high ethylene glycol content.
Another object of the present disclosure is to provide a powder coating composition.
Still another object of the present disclosure is to provide a powder coating composition that comprises a carboxylated solid polyester resin containing high ethylene glycol content.
Yet another object of the present disclosure is to provide a powder coating composition that is devoid of surface defects.
Still another object of the present disclosure is to provide a simple and efficient process for the preparation of a powder coating composition.
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 relates to a carboxylated solid polyester resin containing high ethylene glycol content and a process for its preparation. The present disclosure further relates to a powder coating composition.
In an aspect, the carboxylated solid polyester resin has an ethylene glycol content in an amount in the range of 7 weight% to 20 weight% with respect to the total weight of the resin.
In another aspect, the process for the preparation of the carboxylated solid polyester resin comprises depolymerizing at least one polymer selected from virgin PET, recycled PET, and a copolymer of ethylene glycol and terephthalic acid by alcoholysis with at least one polyol to obtain a depolymerized mixture comprising polyol oligomer. The so obtained depolymerized mixture comprising polyol oligomer is esterified with at least one polyacid to obtain an esterified mixture comprising hydroxyl-terminated oligomers. The so obtained esterified mixture comprising hydroxyl-terminated oligomers is esterified with at least one polyacid to obtain the carboxylated solid polyester resin containing high ethylene glycol content. The polyacid is at least one independently selected from the group consisting of terephthalic acid, isophthalic acid, hexahydrophthalic anhydride, adipic acid, cyclohexane diacid, and trimellitic anhydride.
In still another aspect, a paint composition comprising a carboxylated solid polyester resin, wherein said polyester resin having ethylene glycol content in an amount in the range of 7 weight% to 20 weight% with respect to the total weight of the resin.
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.
Powder coating compositions offer advantages such as high coating efficiency, excellent mechanical properties, zero-emission of volatile organic compounds, and the like. Carboxyl group-containing polyester resins are well known in the art and are in practice for use in powder coatings. These polyesters are processed with epoxy compounds to form binding agents for the powder coatings. However, conventional polyester resin-based powder coatings are associated with the limitations of surface defects such as cratering, fisheye, pinholes, and the like. The inability of the polyester resin-based powder coatings to provide the desired surface smoothness is generally the result of the high viscosities of the polyester resins.
The present disclosure provides a carboxylated solid polyester resin containing high ethylene glycol content and a process for its preparation.
In an aspect of the present disclosure, the carboxylated solid polyester resin containing high ethylene glycol content has an ethylene glycol content in an amount in the range of 7 weight% to 20 weight% with respect to the total weight of the resin.
In an embodiment of the present disclosure, the carboxylated solid polyester resin containing high ethylene glycol content is characterized by acid value in the range of 10 KOH/g to 90 KOH/g. In an exemplary embodiment of the present disclosure, the acid value is 25 to 40 KOH/g.
In an embodiment of the present disclosure, the carboxylated solid polyester resin containing high ethylene glycol content is characterized by a melt viscosity in the range of 15 poise to 80 poise at 200 oC. In an exemplary embodiment of the present disclosure, the melt viscosity is 40 to 60 poise 200oC.
In an embodiment of the present disclosure, the carboxylated solid polyester resin containing high ethylene glycol content is characterized by a number average molecular weight (Mn) in the range of 1000 Daltons to 5000 Daltons. In an exemplary embodiment of the present disclosure, the number average molecular weight is 3900 Daltons.
In an embodiment of the present disclosure, the carboxylated solid polyester resin containing high ethylene glycol content is characterized by weight average molecular weight (Mw) in the range of 4000 Daltons to 11000 Daltons. In an exemplary embodiment of the present disclosure, the weight average molecular weight is 9000 Daltons.
In an embodiment of the present disclosure, the carboxylated solid polyester resin containing high ethylene glycol content is characterized by z average molecular weight in the range of 12000 Daltons to 22000 Daltons. In an exemplary embodiment of the present disclosure, the z average molecular weight is 17000 Daltons.
In an embodiment of the present disclosure, the carboxylated solid polyester resin containing high ethylene glycol content is characterized by a polydispersity index (PDI) in the range of 2 to 4. In an exemplary embodiment of the present disclosure, the polydispersity index (PDI) is 2.3.
In an embodiment of the present disclosure, the carboxylated solid polyester resin containing high ethylene glycol content is characterized by glass transition temperature in the range of 48°C to 72°C by DSC thermogram. In an exemplary embodiment of the present disclosure, the glass transition temperature is 59°C.
In another aspect of the present disclosure, there is a process for preparing a carboxylated solid polyester resin containing high ethylene glycol content.
The reactants in the process include polyol, polyacid, antioxidant, polymer selected from virgin PET, recycled PET, and a copolymer of ethylene glycol, terephthalic acid, catalyst, and a curing catalyst. The term total weight of reactants represents the total weight of the reactants employed at various stages for the preparation of the carboxylated solid polyester resin containing high ethylene glycol content.
The process is described in detail.
In a first step, at least one polymer selected from virgin PET, recycled PET, and a copolymer of ethylene glycol and terephthalic acid is depolymerized by alcoholysis with at least one polyol to obtain a depolymerized mixture comprising polyol oligomer.
In an embodiment of the present disclosure, the step of depolymerizing is carried out by charging a predetermined amount of at least one polyol in a reactor in an inert atmosphere and heating the reactor at a first predetermined temperature followed by adding a predetermined amount of at least one first antioxidant in the presence of at least one catalyst to obtain a first reaction mixture. Separately obtaining a predetermined amount of at least one polymer selected from virgin PET, recycled PET, and a copolymer of ethylene glycol and terephthalic acid having a particle size in the range of 5mm to 50mm. Adding a first portion of the polymer to the first reaction mixture at a second predetermined temperature under stirring, followed by heating at a third predetermined temperature for a first predetermined time period to obtain a second reaction mixture. A second portion of the polymer is added to the second reaction mixture under stirring followed by raising the temperature to a fourth predetermined temperature and maintaining the temperature for a second predetermined time period to obtain a depolymerized mixture comprising polyol oligomer.
In an embodiment of the present disclosure, the depolymerization process involves the transesterification of the polymer.
In an embodiment of the present disclosure, at least one polyol is selected from the group consisting of methylpropanediol (MP Diol), neopentyl glycol, ethylene glycol, diethylene glycol, trimethylol propane, cyclohexane dimethylol, and butyl ethyl propanediol. In an exemplary embodiment of the present disclosure, the polyol is methylpropanediol (MP Diol). In another exemplary embodiment of the present disclosure, the polyol is neopentyl glycol.
In an embodiment of the present disclosure, the predetermined amount of polyol is in the range of 25 weight % to 35 weight% with respect to the total weight of reactants. In an exemplary embodiment of the present disclosure, the predetermined amount of polyol is 27.5 weight% with respect to the total weight of reactants.
In an embodiment of the present disclosure, the inert atmosphere is selected from the group consisting of nitrogen and argon. In an exemplary embodiment of the present disclosure, the inert atmosphere is nitrogen.
In an embodiment of the present disclosure, the first antioxidant is selected from triphenyl phosphite, pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate) (Irganox 1010). In an exemplary embodiment of the present disclosure, the first antioxidant is triphenyl phosphite.
In an embodiment of the present disclosure, the predetermined amount of the first antioxidant is in the range of 0.001 weight % to 0.25 weight% with respect to the total weight of reactants. In an exemplary embodiment of the present disclosure, the predetermined amount of the first antioxidant is 0.08 weight% with respect to the total weight of reactants.
In an embodiment of the present disclosure, the catalyst is at least one selected from the group consisting of zinc acetate, monobutyl tin oxide, dibutyl tin oxide, and stannous oxalate. In an exemplary embodiment of the present disclosure, the catalyst is zinc acetate.
In an embodiment of the present disclosure, the first predetermined temperature is in the range of 110°C to 130°C, preferably 120°C to 125°C. In an exemplary embodiment of the present disclosure, the first predetermined temperature is 125°C.
In an embodiment of the present disclosure, the second predetermined temperature is in the range of 110°C to 130°C, preferably 120°C to 125°C. In an exemplary embodiment of the present disclosure, the second predetermined temperature is 125°C.
In an embodiment of the present disclosure, the third predetermined temperature is in the range of 150°C to 160°C. In an exemplary embodiment of the present disclosure, the third predetermined temperature is 160°C.
In an embodiment of the present disclosure, the fourth predetermined temperature is in the range of 180°C to 200°C, preferably 190°C to 200°C. In an exemplary embodiment of the present disclosure, the fourth predetermined temperature is 200°C.
In an embodiment of the present disclosure, the first predetermined time period is in the range of 30 minutes to 50 minutes. In an exemplary embodiment of the present disclosure, the first predetermined time period is 40 minutes.
In an embodiment of the present disclosure, the second predetermined time period is in the range of 90 minutes to 180 minutes. In an exemplary embodiment of the present disclosure, the second predetermined time period is 120 minutes.
In an embodiment of the present disclosure, the first portion and the second portion of the polymer are independently in an amount in the range of 40 weight% to 60 weight% with respect to the total weight of the polymer. In an exemplary embodiment of the present disclosure, the first portion of the polymer is 50 weight % with respect to the total weight of the polymer. In another exemplary embodiment of the present disclosure, the second portion of the polymer is 50 weight % with respect to the total weight of the polymer.
In a second step, the depolymerized mixture comprising polyol oligomer is esterified with at least one polyacid to obtain an esterified mixture comprising hydroxyl-terminated oligomers.
In an embodiment of the present disclosure, at least one polyacid is selected from the group consisting of terephthalic acid, isophthalic acid, hexahydrophthalic anhydride, adipic acid, cyclohexane diacid, and trimellitic anhydride. In an exemplary embodiment of the present disclosure, the polyacid is terephthalic acid. In another exemplary embodiment of the present disclosure, the polyacid is isophthalic acid.
In an embodiment of the present disclosure, the esterification is carried out by maintaining the so obtained depolymerized mixture at a fifth predetermined temperature, followed by adding a predetermined amount of at least one first polyacid under stirring to obtain a third reaction mixture. The temperature of the so obtained third reaction mixture is raised at a rate of 3 °C to 5 °C per hour to attain a sixth predetermined temperature for a third predetermined time period to obtain a heated reaction mixture. Predetermined amounts of at least one second polyacid and at least one second antioxidant is added to the so obtained heated reaction mixture under stirring at a seventh predetermined temperature for a fourth predetermined time period to obtain a esterified mixture comprising hydroxyl-terminated oligomers.
In an embodiment of the present disclosure, the second antioxidant is at least one selected from triphenyl phosphite, and pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate) (Irganox 1010). In an exemplary embodiment of the present disclosure, the second antioxidant is triphenyl phosphite.
In an embodiment of the present disclosure, the predetermined amount of the second antioxidant is in the range of 0.01 weight% to 0.25 weight% with respect to the total weight of reactants. In an exemplary embodiment of the present disclosure, the predetermined amount of the second antioxidant is 0.02 weight% with respect to the total weight of reactants.
In an embodiment of the present disclosure, the first polyacid is at least one selected from the group consisting of terephthalic acid, isophthalic acid, hexahydrophthalic anhydride, adipic acid, cyclohexane diacid, and trimellitic anhydride. In an exemplary embodiment of the present disclosure, the first polyacid is terephthalic acid.
In an embodiment of the present disclosure, the predetermined amount of the first polyacid is in the range of 35 weight% to 45 weight% with respect to the total weight of reactants. In an exemplary embodiment of the present disclosure, the first polyacid is 38.38 weight% with respect to the total weight of reactants.
In an embodiment of the present disclosure, the second polyacid is at least one selected from the group consisting of terephthalic acid, isophthalic acid, hexahydrophthalic anhydride, adipic acid, cyclohexane diacid, and trimellitic anhydride. In an exemplary embodiment of the present disclosure, the second polyacid is a mixture of terephthalic acid and isophthalic acid.
In an embodiment of the present disclosure, the predetermined amount of the second polyacid is in the range of 5 weight% to 15 weight% with respect to the total weight of reactants. In an exemplary embodiment of the present disclosure, the second polyacid is 8 weight% with respect to the total weight of reactants.
In an embodiment of the present disclosure, the fifth predetermined temperature in the range of 180°C to 190°C. In an exemplary embodiment of the present disclosure, the fifth predetermined temperature is 190°C.
In an embodiment of the present disclosure, the sixth predetermined temperature in the range of 185°C to 215°C, preferably 190°C to 205°C. In an exemplary embodiment of the present disclosure, the sixth predetermined temperature is 190°C to 205°C.
In an embodiment of the present disclosure, the seventh predetermined temperature in the range of 225°C to 250°C, preferably 235°C to 245°C. In an exemplary embodiment of the present disclosure, the seventh predetermined temperature is 245°C.
In an embodiment of the present disclosure, the third predetermined time period is in the range of 1 hr to 4 hrs. In an exemplary embodiment of the present disclosure, the third predetermined time period is 3 hrs.
In an embodiment of the present disclosure, the fourth predetermined time period is in the range of 3 hrs to 6 hrs. In an exemplary embodiment of the present disclosure, the fourth predetermined time period is 5 hours.
In the last step, the so obtained esterified mixture comprising hydroxyl-terminated oligomers is esterified with at least one third polyacid to obtain the carboxylated solid polyester resin containing high ethylene glycol content.
In an embodiment of the present disclosure, the esterification is carried out by cooling the so obtained esterified reaction mixture comprising hydroxyl-terminated oligomers to an eighth predetermined temperature, followed by slowly adding at least one third polyacid under stirring to obtain a fourth reaction mixture. The so obtained fourth reaction mixture is cooled to a ninth predetermined temperature followed by adding a curing catalyst to obtain a fifth reaction mixture. The so obtained fifth reaction mixture is cooled at a temperature in the range of 25°C to 35°C to obtain the carboxylated solid polyester resin containing high ethylene glycol content.
In an embodiment of the present disclosure, the third polyacid is at least one selected from the group consisting of trimellitic anhydride, terephthalic acid, isophthalic acid, hexahydrophthalic anhydride, adipic acid, and cyclohexane diacid. In an exemplary embodiment of the present disclosure, the third polyacid is trimellitic anhydride.
In an embodiment of the present disclosure, the curing catalyst is at least one selected from the group consisting of Ethyl Triphenyl Phosphonium Bromide (ETPBr), methyl imidazole, isopropyl imidazole, 2-methyl imidazole, and tertiary butyl ammonium bromide. In an exemplary embodiment of the present disclosure, the curing catalyst is Ethyl Triphenyl Phosphonium Bromide (ETPBr).
In an embodiment of the present disclosure, the eighth predetermined temperature in the range of 210°C to 235°C. In an exemplary embodiment of the present disclosure, the eighth predetermined temperature is 220°C.
In an embodiment of the present disclosure, the ninth predetermined temperature in the range of 200°C to 220°C. In an exemplary embodiment of the present disclosure, the ninth predetermined temperature is 210°C.
Still, in another aspect of the present disclosure, there is provided a powder coating composition.
In an embodiment of the present disclosure, the paint composition comprises carboxylated solid polyester resin in an amount in the range of 20 weight% to 80 weight% with respect to the total weight of the composition, wherein said polyester resin having ethylene glycol content in an amount in the range of 7 weight% to 20 weight% with respect to the total weight of the resin; one of epoxy resin, triglycidyl isocyanurate (TGIC) in an amount in the range of 3 weight% to 20 weight% with respect to the total weight of the composition; at least one natural resin in an amount in the range of 0.1 weight% to 0.8 weight% with respect to the total weight of the composition; at least one levelling agent in an amount in the range of 0.2 weight% to 2 weight% with respect to the total weight of the composition; at least one pigment in an amount in the range of 10 weight% to 40 weight% with respect to the total weight of the composition; at least one filler in an amount in the range of 10 weight% to 50 weight% with respect to the total weight of the composition and optionally antistatic agent in an amount in the range of 0.02 weight% to 0.7 weight% with respect to the total weight of the composition.
In an embodiment of the present disclosure, the paint composition is a powder coating composition.
In an embodiment of the present disclosure, the ratio of the carboxylated solid polyester resin containing high ethylene glycol content to the epoxy resin is in the range of 1:1 to 1:3. In an exemplary embodiment of the present disclosure, the ratio of the carboxylated solid polyester resin containing high ethylene glycol content to the epoxy resin is 1:2.3.
In an embodiment of the present disclosure, the ratio of the carboxylated solid polyester resin containing high ethylene glycol content to the triglycidyl isocyanurate (TGIC) is in the range of 1:13 to 1:19. In an exemplary embodiment of the present disclosure, the ratio of the carboxylated solid polyester resin containing high ethylene glycol content to the triglycidyl isocyanurate (TGIC) is 1:13.1.
In an embodiment of the present disclosure, as ethylene glycol is a low-cost and readily available raw material, ethylene glycol is incorporated more and more in the polyester resin without affecting the surface property of the final paint film. Conventionally, in the course of incorporation of ethylene glycol in polyester formulation, it has been found that more than 5% of ethylene glycol causes surface defects, which requires higher loading of flow and leveling additive to get eliminated. However, in the present disclosure advantageously it was able to incorporate a higher dosage of ethylene glycol (up to 20%) without getting any surface defects.
Thus, the powder coating compositions of the present disclosure comprising the solid carboxylated polyester having high ethylene glycol content in the range of 7 weight% to 20 weight% with respect to the total weight of the resin and the paint composition when applied on the surface is free from craters, fish-eye, and pinholes.
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 experiments which are set forth for illustration purposes only and not to be construed for limiting the scope of the disclosure. The following experiments can be scaled up to industrial/commercial scale and the results obtained can be extrapolated to industrial scale.
EXPERIMENTAL DETAILS
Example 1: Preparation of the carboxylated solid polyester resin containing high ethylene glycol content in accordance with the present disclosure
11.9 kg of methylpropanediol and 15.62 kg of neopentyl glycol were charged into a reactor and nitrogen was purged slowly at a steady rate (to avoid glycol losses) throughout the reactor, raising the temperature to 125°C followed by adding 80 gm of triphenyl phosphite and 100 gm of zinc acetate under stirring and allow to mix for 10 minutes to obtain a first reaction mixture. Maintaining the temperature at 125°C, 11.84 kg of PET chips were added to the first reaction mixture under stirring, followed by raising the temperature to 160°C with continuous stirring for 40 minutes to ensure complete mixing to obtain a second reaction mixture. To the second reaction mixture, 11.84 kg of PET chips were added slowly followed by raising the temperature to 200°C, allowing mixing for 2 hours to obtain a depolymerized mixture comprising polyol oligomer, (Mixing for 2 hours ensures that no solid remains in the mixture if any solid particles are identified, heating was continued till all the PET flakes are dissolved, the clarity of the solution should be clear to a slight haze).
Maintaining the temperature of the reactor at 190°C, 38.38 kg of terephthalic acid was added to the depolymerized mixture comprising polyol oligomer under stirring to obtain a third reaction mixture. Slowly raising the temperature of the reactor from 190°C to 205°C at a rate of 3 to 5°C per hour, over a period of 3 hours while ensuring that the packed column condenser temperature did not exceed 100°C to avoid glycol loss (drain water of reaction from the decanter at regular intervals and collect in a barrel, the quantity of water drained was recorded). Further, the temperature from 205°C was increased to 220°C at a rate of 5°C to 6°C per hour while ensuring that the packed column condenser temperature does not exceed 100°C to avoid glycol loss, the temperature was slowly raised to attain a temperature of 235°C to 245°C while maintaining the overhead pack column condenser temperature of less than 100°C to obtain a heated reaction mixture.
Maintaining the temperature of the reactor at 245°C till the clarity of the resin was achieved (very slight haze will also work). The clarity was achieved when the reaction was 85% to 90% completed (water of Reaction collected was about 88% to 92% of the estimated value). On obtaining very slight hazy (hot and cold) resin, the melt viscosity and the acid value was tested.
The acid value of the heated reaction mixture was 5 mg to 10 mg KOH/gm and the melt viscosity was 3 to 8 Poise at 200°C in spindle 9.
To the heated reaction mixture, 3 kg of isophthalic acid, 5 kg of terephthalic acid, and 20 gm of triphenyl phosphite were slowly added under stirring at 235°C to 240°C followed by raising the temperature of the reactor to 245°C to 250°C and maintained for 5 hours to obtain a fourth reaction mixture comprising hydroxyl-terminated oligomers. The acid value of the fourth reaction mixture was in the range of 25 to30 mg KOH/g and the melt viscosity was in the range of 18 to 30 Poise at 200°C in spindle 9.
The fourth reaction mixture was cooled to 220°C, followed by adding 1.83 kg of trimetallic anhydride under stirring to obtain a fifth reaction mixture. The temperature of the fifth reaction mixture was maintained for 30 mins, the samples were drawn at regular intervals to check acid value and viscosity, vacuum was applied until the desired acid value and viscosity were achieved.
The fifth reaction mixture was cooled to 210°C followed by adding 40 gm of ethyl triphenyl phosphonium bromide to obtain a sixth reaction mixture. The sixth reaction mixture was cooled to 25°C to 35°C to obtain the carboxylated solid polyester resin containing high ethylene glycol content. The acid value of the resin was 25 to 40 KOH/g and the melt viscosity was 40 to 60 poise at 200°C in spindle 9. The so obtained resin was converted to flakes/granules of suitable sizes.
The number average molecular weight of the resin is 3900 Daltons, the weight average molecular weight is 9000 Daltons, z average molecular weight is 17000 Daltons, polydispersity index (PDI) is 2.3, and glass transition of 59°C by DSC thermogram.
COMPARATIVE EXAMPLES
Example 2: Preparation of the carboxylated polyester resin for hybrid powder coating
24.2 kg of neopentyl glycol, 10.07 kg of methylpropanediol, and 6 kg of diethylene glycol was charged into the reactor, and nitrogen was purged slowly at a steady rate (to avoid glycol losses) throughout the reactor, raised the temperature to 110 °C followed by adding 40 gm of triphenyl phosphite and 100 gm of dibutyl tin oxide under stirring and allowed to mix for 10 minutes to obtain a first reaction mixture. Maintaining the temperature of the reactor at 125°C, 52.87 kg of terephthalic acid was added to the first reaction mixture under stirring, raised the temperature to 190°C while ensuring the packed column condenser temperature was maintained at 100°C over a period of 2 hours to obtain a second reaction mixture.
Slowly raising the temperature from 190°C to 205°C at a rate of 2 to3°C per hour, over a period of 6 to7 hours while ensuring that packed column condenser temperature did not exceed 100°C to avoid glycol loss (drain water of reaction from the decanter at regular interval and collect in a barrel quantity of water drained was recorded). Further, the temperature from 205°C was increased to 220°C at a rate of 4°C to 5°C per hour over a period of 3-4 hours while ensuring that the packed column condenser temperature did not exceed 100°C to avoid glycol loss, the temperature was slowly raised to attain a temperature of 230°C to 232°C while maintaining overhead pack column condenser temperature of less than 100°C to obtain a third reaction mixture.
Maintained the temperature of the reactor from 230°C to 235°C till clarity of the resin was achieved. Generally, the clarity was achieved when the reaction was 85-90% completed (water of reaction collected was about 88% to 92% of the estimated value). The resin was required clear in hot as well as at ambient temperature. Test water of reaction collected for Refractive Index to estimate glycol losses.
The acid value of the third reaction mixture was 5 mg to 10 mg KOH/gm and melt viscosity was 3 to 8 Poise at 200°C in spindle 9.
To the third reaction mixture, 5 kg of terephthalic acid, 3 kg of isophthalic acid, and 20 gm of triphenyl phosphite were added under stirring at 235°C to 240°C and maintained at 240°C to 245°C for 4 to 5 hrs to obtain a fourth reaction mixture. The acid value of the fourth reaction mixture was 20 mg to 30 mg KOH/gm and melt viscosity was 12 to 20 Poise at 200 °C in spindle 9 (spindles are the essential component of the viscometer, used to measure the viscosity).
After attaining the desired parameters (provide cooling jerk to achieve a temperature of 210°C), maintaining the temperature at 210°C, added 1.7 kg of trimellitic anhydride followed by raising the temperature to 220°C to 225°C slowly to obtain a fifth reaction mixture. Further, maintaining the temperature, a sample was drawn every 30 mins and evaluated for acid value and viscosity, vacuum was applied until the desired acid value and viscosity was achieved.
To the fifth reaction mixture, 400 gm of ethyl triphenyl phosphonium bromide was added and mixed for 10 minutes to obtain a sixth reaction mixture. The acid value of the sixth reaction mixture was 30 mg to 36 mg KOH/gm and the melt viscosity was 40 to 55 Poise, at 200°C in spindle 9. The sixth reaction mixture was cooled to 25°C to 35°C to obtain the carboxylated polyester resin. The so obtained resin was converted to flakes/granules of suitable sizes.
Example 3: Preparation of ethylene glycol polyester resin for hybrid powder coating
11.45 kg of monoethylene glycol, 17.9 kg of methylpropanediol, and 300 gm of diethylene glycol were charged into the reactor, and nitrogen was purged slowly at a steady rate (to avoid glycol losses) throughout the reactor, and heated at 110 °C followed by adding 60 gm of triphenyl phosphite and 100 gm of dibutyl tin oxide under stirring and allow to mix for 10 minutes to obtain a first reaction mixture. Maintaining the temperature at 125°C, 57.89 kg of terephthalic acid was added to the first reaction mixture under stirring, raised the temperature to 190°C while ensuring the packed column condenser, the temperature was maintained at 100°C over a period of 2 hours to obtain a second reaction mixture.
Slowly raising the temperature from 190°C to 205°C at a rate of 2°C to 3°C per hour, over a period of 6-7 hours while ensuring that packed column condenser temperature did not exceed 100°C to avoid glycol loss, (drain water of reaction from the decanter at regular interval and collect in a barrel, the quantity of water drained was recorded). Further, the temperature from 205 °C was increased to 220°C at a rate of 4°C to 5°C per hour over a period of 3 to 4 hours while ensuring that packed column condenser temperature did not exceed 100 °C to avoid glycol loss, the temperature was slowly raised to attain a temperature of 230°C to 232°C while maintaining overhead pack column condenser temperature of less than 100 °C to obtain a third reaction mixture.
Maintained the batch temperature at 230°C to 235°C till clarity of the resin was achieved. Generally, clarity was achieved when the reaction was 85% to 90% complete (water of reaction collected was about 88% to 92% of the estimated value; acid value at this point was in the range of 5 to10 mg KOH/g). The resin was required to be clear in hot as well as at ambient temperature. Test water of reaction was collected for the refractive index to estimate glycol losses.
Once clarity was attained, the melt viscosity and the acid value were evaluated using the standard test method. The samples were drawn every 30 mins for testing melt viscosity and acid value till the endpoint to obtain a fourth reaction mixture. The acid value of the third reaction mixture was 5 mg to 10 mg KOH/gm and melt viscosity was 3 to 8 poise at 200°C in spindle 9. The appearance of the fourth reaction mixture was clear (hot and cold).
To the fourth reaction mixture, 10 kg of terephthalic acid 60 gm of triphenyl phosphite was added under stirring at 235°C to 240°C and maintained at 240°C to 245°C for 4 hrs to 5 hrs to obtain the fifth reaction mixture. Further, maintaining the temperature, the sample was drawn every 30 mins and evaluated for acid value and viscosity, vacuum was applied until the desired acid value and viscosity was achieved.
To the fifth reaction mixture, 40 gm of ethyl triphenyl phosphonium bromide was added and mixed for 10 minutes to obtain a fifth reaction mixture. The acid value of the fifth reaction mixture was 30 mg to 36 mg KOH/gm and melt viscosity was 40-55 Poise at 200°C in spindle 9. The fifth reaction mixture was cooled to 25°C to 35°C to obtain the polyester resin. The so obtained resin was converted to flakes/granules of suitable sizes.
The process of the present disclosure uses recycled PET thereby using less quantity of terephthalic acid during the preparation of carboxylated polyester resin containing high ethylene glycol content in view of the process of comparative examples 2 and 3 wherein a high amount of terephthalic acid is used, which is not desirable. Further, the process of the present application which is a four-step process completely incorporates the ethylene glycol into the polyester resin (example 1). The process of the comparative examples 2 and 3 is a three-step process and is not able to incorporate high ethylene glycol content into the polyester resin.
Example 4:
The powder coating composition was prepared by using the carboxylated polyester resin containing high ethylene glycol content obtained in Example 1 and Example 3 with epoxy and were coated on mild steel (MS) panels and evaluated for thickness, finish, levelling, gloss, reverse impact resistance, and direct impact by using ASTM D 2794 method. The details are provided below in Table – 1.
Table-1
Finished good properties for Polyester-Epoxy 70/30 hybrid
Substrate MS Panel (0.8 mm)
Batch ID No. International standard Powder coating composition (Carboxylated polyester resin of Example 1) Powder coating composition (Polyester resin of Example 3)
DFT (microns) 50 to 60 microns 50 to 60 microns 50 to 60 microns
Finish Good Good Throughout craters
Leveling No to slight orange peel No to slight orange peel Slight orange peel
Gloss @60° Spec- gloss (15-20) 15 19.6 17
Impact Direct (40 Kg.Cm) Pass Pass Pass
Reverse Impact (40 Kg.Cm) Pass Pass Pass
Bending (5 mm) Pass Pass Pass
Gel Time (Sec) 175 195 180

It is evident from the above results that the powder coating composition comprising polyester resin of example-3 shows the poor flow and finish. However, a powder coating composition comprising carboxylated polyester resin containing high ethylene glycol content of example 1 obtained from virgin PET or recycled PET, without using any other surface-active agent, the finish has been improved. The mechanical properties are also in line with the standard.
Example 5:
The powder coating composition was prepared using the carboxylated polyester resin containing high ethylene glycol content in Example 1 and TGIC and coated on mild steel (MS) panel and evaluated for thickness, finish, levelling, gloss, reverse impact resistance, and direct impact by using ASTM D 2794 method. The details are provided below in Table - 2.
Table-2
Finished good properties of Polyester-TGIC 93/7 composition
Substrate MS panel (0.8 mm)
Batch ID No. Standard
Powder coating composition (Carboxylated polyester resin of Example 1)
DFT (microns) 60 to 70 microns 60 to70 microns
Finish Smooth, no defects Smooth
Leveling No to slight orange peel No to slight orange peel
Gloss @60° Spec- gloss (90-100) 93 to 95 93 to 94
Impact Direct (120 Kg .Cm) Pass Pass
Reverse Impact (100 Kg.Cm) Pass Pass
Bending(5mm) Pass Pass
Gel Time@190°C (Sec) 255 265

It is evident from the above table that by using the carboxylated polyester resin with high ethylene glycol content obtained from PET the finish of the final film has desired mechanical properties similar to formulations having non-ethylene glycol based polyester resin.
The process of the present disclosure uses recycled PET as a source of ethylene glycol thus reducing the cost of preparation of carboxylated polyester resin containing high ethylene glycol content. Further, if the ethylene glycol content in the polyester resin exceeds 5% of the resin, the powder coating composition when coated on a substrate exhibits surface defects such as cratering, fisheye, pinholes, and the like. Even though, the carboxylated polyester resin of the present application contains ethylene glycol content in an amount in the range of 7 weight% to 20 weight% with respect to the total weight of the resin but provides a coating composition that is free of surface defects and requires less amount of surface-active agent similar to a powder coating composition containing polyester resin without ethylene glycol, due to the process parameters and specific components used in the preparation of the carboxylated resin and powder composition prepared therefrom.
TECHNICAL ADVANCEMENTS
The present disclosure described hereinabove has several technical advantages including, but not limited to, the realization of the carboxylated solid polyester resin that,
• has high ethylene glycol content;
• uses recycled PET chips, hence environment friendly;
• reduces the use of terephthalic acid;
• high yield, less water of reaction removed.
a powder coating composition that;
• has excellent surface finish;
• has excellent mechanical performance;
• requires a low quantity of surface active agent:
• is free from defects such as craters, fisheye, and pinholes; and
• is economically significant (low cost).
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 invention to achieve one or more of the desired objects or results. While certain embodiments of the inventions have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Variations or modifications to the formulation of this invention, within the scope of the invention, may occur to those skilled in the art upon reviewing the disclosure herein. Such variations or modifications are well within the spirit of this invention.
The numerical values given for various physical parameters, dimensions and quantities are only approximate values and it is envisaged that the values higher than the numerical value assigned to the physical parameters, dimensions and quantities fall within the scope of the invention unless there is a statement in the specification to the contrary.
While considerable emphasis has been placed herein on the specific features of the preferred embodiment, it will be appreciated that many additional features can be added and that many changes can be made in the preferred embodiment without departing from the principles of the disclosure. These and other changes in the preferred embodiment of the disclosure 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 carboxylated solid polyester resin having an ethylene glycol content in an amount in the range of 7 weight% to 20 weight% with respect to the total weight of the resin.
2. The carboxylated solid polyester resin as claimed in claim 1, is characterized by having:
a) acid value in the range of 10 mg KOH/g to 90 mg KOH/g;
b) melt viscosity in the range of 15 poise to 80 poise at 200oC;
c) number average molecular weight (Mn) in the range of 1000 Daltons to 5000 Daltons;
d) weight average molecular weight (Mw) in the range of 4000 Daltons to 11000 Daltons;
e) z average molecular weight in the range of 12000 Daltons to 22000 Daltons;
f) polydispersity index (PDI) in the range of 2 to 4; and
g) glass transition temperature in the range of 48°C to 72°C by DSC thermogram.
3. A process for preparing a carboxylated solid polyester resin, said process comprising the following steps:
a) depolymerizing at least one polymer selected from virgin PET, recycled PET, and a copolymer of ethylene glycol and terephthalic acid by alcoholysis with at least one polyol to obtain a depolymerized mixture comprising polyol oligomer;
b) esterifying said depolymerized mixture comprising polyol oligomer with at least one polyacid to obtain a esterified mixture comprising hydroxyl-terminated oligomers; and
c) esterifying said esterified mixture comprising hydroxyl-terminated oligomers with at least one polyacid to obtain said carboxylated solid polyester resin;
wherein said polyacid in steps b) and c) is at least one independently selected from the group consisting of terephthalic acid, isophthalic acid, hexahydrophthalic anhydride, adipic acid, cyclohexane diacid, and trimellitic anhydride.
4. The process as claimed in claim 3, wherein said depolymerization is carried out by,
a) charging a predetermined amount of at least one polyol in a reactor in an inert atmosphere and heating the reactor at a first predetermined temperature followed by adding a predetermined amount of at least one first antioxidant in the presence of at least one catalyst to obtain a first reaction mixture;
b) separately obtaining a predetermined amount of at least one polymer selected from virgin PET, recycled PET, and a copolymer of ethylene glycol and terephthalic acid having a particle size in the range of 5 mm to 50 mm;
c) adding a first portion of said polymer to said first reaction mixture at a second predetermined temperature under stirring, followed by heating at a third predetermined temperature for a first predetermined time period to obtain a second reaction mixture; and
d) adding a second portion of said polymer to said second reaction mixture under stirring followed by raising the temperature to a fourth predetermined temperature and maintaining the temperature for a second predetermined time period to obtain said depolymerized mixture comprising polyol oligomer.
5. The process as claimed in claim 3, wherein said esterification is carried out by,
a) maintaining said depolymerized mixture obtained as claimed in claim 4 at a fifth predetermined temperature, followed by adding a predetermined amount of at least one first polyacid under stirring to obtain a third reaction mixture;
b) raising a temperature of said third reaction mixture at a rate of 3°C to 5°C per hour to attain a sixth predetermined temperature for a third predetermined time period to obtain a heated reaction mixture; and
c) adding a predetermined amount of at least one second polyacid and at least one second antioxidant to said heated reaction mixture under stirring at a seventh predetermined temperature for a fourth predetermined time period to obtain said esterified mixture comprising hydroxyl-terminated oligomers.
6. The process as claimed in claim 3, wherein said esterification is carried out by,
a) cooling said esterified mixture comprising hydroxyl-terminated oligomers obtained as claimed in claim 5, to an eighth predetermined temperature, followed by slowly adding at least one third polyacid under stirring to obtain a fourth reaction mixture;
b) cooling said fourth reaction mixture to a ninth predetermined temperature followed by adding a curing catalyst to obtain a fifth reaction mixture; and
c) cooling said fifth reaction mixture at a temperature in the range of 25°C to 35°C to obtain said carboxylated solid polyester resin.
7. The process as claimed in claims 3 and 4, wherein said polyol is at least one selected from the group consisting of methylpropanediol (MP Diol), neopentyl glycol, ethylene glycol, diethylene glycol, trimethylol propane, cyclohexane dimethylol, and butyl ethyl propanediol.
8. The process as claimed in claim 4, wherein said inert atmosphere is selected from nitrogen and argon.
9. The process as claimed in claims 4 and 5, wherein said first antioxidant and said second antioxidant are independently selected from the group consisting of triphenyl phosphite, and pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate) (Irganox 1010).
10. The process as claimed in claim 4, wherein said catalyst is at least one selected from the group consisting of zinc acetate, monobutyl tin oxide, dibutyl tin oxide, and stannous oxalate.
11. The process as claimed in claim 4, wherein said first predetermined temperature is in the range of 110°C to 130°C; said second predetermined temperature is in the range of 110°C to 130°C; said third predetermined temperature is in the range of 150°C to 160°C; and said fourth predetermined temperature is in the range of 180°C to 200°C.
12. The process as claimed in claim 4, wherein said first predetermined time period is in the range of 30 minutes to 50 minutes and said second predetermined time period is in the range of 90 minutes to 180 minutes.
13. The process as claimed in claim 4, wherein said predetermined amount of polyol is in the range of 25 weight % to 35 weight% with respect to the total weight of reactants.
14. The process as claimed in claims 4 and 5, wherein said predetermined amount of said first antioxidant and said second antioxidant is independently in the range of 0.01 weight% to 0.25 weight% with respect to the total weight of reactants.
15. The process as claimed in claim 4, wherein said first portion and said second portion of said polymer is independently in an amount in the range of 40 weight% to 60 weight% with respect to the total weight of the polymer.
16. The process as claimed in claim 5, wherein said first polyacid is at least one selected from the group consisting of terephthalic acid, isophthalic acid, hexahydrophthalic anhydride, adipic acid, cyclohexane diacid, and trimellitic anhydride.
17. The process as claimed in claim 5, wherein said predetermined amount of said first polyacid is in the range of 35 weight% to 45 weight% with respect to the total weight of reactants.
18. The process as claimed in claim 5, wherein said second polyacid is at least one selected from the group consisting of terephthalic acid, isophthalic acid, hexahydrophthalic anhydride, adipic acid, cyclohexane diacid, and trimellitic anhydride.
19. The process as claimed in claim 5, wherein said predetermined amount of said second polyacid is in the range of 5 weight% to 15 weight% with respect to the total weight of reactants.
20. The process as claimed in claim 5, wherein said fifth predetermined temperature in the range of 180°C to 190°C; said sixth predetermined temperature in the range of 185°C to 215°C; and said seventh predetermined temperature in the range of 225°C to 250°C.
21. The process as claimed in claim 5, wherein said third predetermined time period is in range of 1 hr to 4 hrs; and said fourth predetermined time period in the range of 3 hrs to 6 hrs.
22. The process as claimed in claim 6, wherein said third polyacid is at least one selected from the group consisting of trimellitic anhydride, terephthalic acid, isophthalic acid, hexahydrophthalic anhydride, adipic acid, and cyclohexane diacid.
23. The process as claimed in claim 6, wherein said curing catalyst is at least one selected from the group consisting of Ethyl Triphenyl Phosphonium Bromide (ETPBr), methyl imidazole, isopropyl imidazole, 2-methyl imidazole, and tertiary butyl ammonium bromide.
24. The process as claimed in claim 6, wherein said eighth predetermined temperature is in the range of 210°C to 235°C; and said ninth predetermined temperature is in the range of 200°C to 220°C.
25. A paint composition comprising a carboxylated solid polyester resin as claimed in claim 1, wherein said polyester resin having ethylene glycol content in an amount in the range of 7 weight% to 20 weight% with respect to the total weight of the resin.
26. The paint composition as claimed in claim 25, wherein said paint composition is powder coating composition.

Dated this 17th day of March, 2022

_______________________________
MOHAN RAJKUMAR DEWAN, IN/PA – 25
of R.K.DEWAN & CO.
Authorized Agent of Applicant

TO,
THE CONTROLLER OF PATENTS
THE PATENT OFFICE, AT MUMBAI