DESC:FIELD OF INVENTION
The present invention relates to a formulation comprising fast cure solid epoxy phenolic curing agent/accelerator or epoxy silane grafted phenolic hardener that is a silicone grafted epoxy phenolic polymer having free phenolic groups and a process of synthesis of said fast cure solid epoxy phenolic curing agent suitable for epoxy powder coating formulations enabling exceptional flexibility, adhesion and cathodic disbondment resistance of said coatings and storage stability of epoxy powders prepared using such epoxy silane grafted phenolic hardener.
BACKGROUND ART
Conventionally Bisphenol-A (BPA) terminated epoxy curing agents are prepared by reacting Bisphenol A (BPA), with liquid epoxy resin followed by incorporation of 2-methyl imidazole or similar accelerator by melt blending into the molten curing agent at the end of the hardener preparation or addition of the same in the epoxy powder coating composition. For such epoxy powder coating applications, the need of the industry is for faster curing systems which tend to further increase the concentration of 2-methyl imidazole. Need for faster curing powder by industry led to higher levels of 2-methyl imidazole usage. However, it resulted into unintended consequence of low melting point mixtures leading to sintering during storage as a result of salt formation between 2-methyl imidazole and phenolic hydroxyl. Such curing agents lead to problems during application as powder coatings such as blockage of application equipment due to impact fusion and the formation of "cobwebs' during electrostatic application to hot objects.
On this reference is drawn to the following prior arts:
Improved properties of epoxy resins obtained by reacting an epoxy resin with a dihydric phenol in the presence of a sufficient quantity of a phosphonium catalyst such that the product resulting from reacting a mixture of the catalyst, epoxy resin and dihydric phenol has a percent epoxide difference from the theoretical percent epoxide of from about 0.5 to about 4.0 as disclosed in US4352918 (Ross C. Whiteside, et al.)
A process for reacting a phenol with an epoxy-containing compound, and a process for increasing the molecular weight of an epoxide by reacting the epoxide with a phenol in the presence of certain "hard cation/- non-nucleophilic anion' catalysts, preferably in the presence of a base, is described in US4358578 by Thomas F. Brownscombe. The preparation of higher molecular weight epoxy resins via the so-called fusion technique is provided wherein a lower molecular weight epoxy compound is reacted with a phenol in the presence of a suitable esterification catalyst is well known. While all these fusion compositions and processes are commercially useful, each has its own shortcomings, and hence there is a continuing need to find other alternative processes, especially alternative catalysts systems.
“Improving the corrosion performance of epoxy coatings by chemical modification with silane monomers” described under Surface and Coatings Technology Volume 201, Issue 8, 15 January 2007, Pages 4789-4795 (Wei-Gang, et al) discloses that commercial epoxy resins were chemically modified with various silane monomers under the catalysis of organotin compound, aiming to enhance the corrosion resistance of epoxy coatings on 2024-T3 aluminum substrates. Immersion studies conducted in 3.5 wt.% NaCl solution showed that the coating capacitance (Cc) decreases significantly after the silane modification, as measured by electrochemical impedance spectroscopy (EIS), indicating the higher resistance to water permeation. EIS measurements also indicated an enhancement in protectiveness of silane-modified epoxy coatings against substrate corrosion, which was characterized by higher charge transfer resistances (Rct) and lower double layer capacitance (Cdl) at substrate/electrolyte interface. The adhesion of epoxy coatings was also found to improve after the modification with silane components. The best performance was observed for coating system modified by 3-glycidoxypropyltrimethoxy silane (GPTMS).
“Preparation of Hybrid Composites Based on Epoxy, Novolac, and Epoxidized Novolac Resins and Silica Nanoparticles With High Char Residue by Sol-Gel method”, under Volume 39, Issue S4 Special Issue: Epoxy Composites of Polymer composites, 14 November 2017 (Abdollahi, Amin, et al), discloses that a facile method was developed for preparation of three hybrid composites by using tetraethyl orthosilicate oligomer-modified epoxy resin (MER), (3- glycidyloxypropyl) trimethoxysilane-modified novolac resin (MNR), epoxidized novolac resin (ENR), and silica nanoparticles (SiO2).
On the involvement of phenolic curing agents for epoxy resins, a phenolic curing agent for epoxy resin powder coatings is provided, prepared by combining (a) a linear phenolic hydroxyl-terminated resin having a weight per phenolic within the range of about 650 to about 8,000, preferably about 850 to about 950, (b) a dihydric phenol present in an amount such that the weight per hydroxyl of the mixture of (a) and (b) is within the range of about 240 to about 280, and (c) at least about 2 weight percent, based on the weight of the composition, of an imidazole cure accelerator, disclosed in US4767832 (Edward J. Marx). The described imidazole-accelerated curing agent is less susceptible to melting point depression and to sintering with storage than conventional imidazole-containing phenolic curing agents. The dihydric phenol-terminated epoxy resin is preferably prepared by reacting a dihydric phenol with a linear diepoxy resin in the presence of a phosphonium halide catalyst to produce a phenolic hydroxyl-terminated resin having a weight per hydroxyl within the range of about 650 to about 8,000.
A process for reacting a phenol, with an epoxy compound and resulting products disclosed in US3477990 (Mark F Dante & Harvey L Parry). A process for reacting a phenol with an epoxy-containing compound comprising reacting an epoxide having more than one 1, 2-epoxide group with a phenol in the presence of a phosphonium halide catalyst.
Thermosetting resin from a phenol and diglycidyl ether of a diphenol is described under US2506486 (Howard L Bender, et al.) relating to thermosetting compositions and to thermoset resins made therefrom. It is more particularly concerned with improved thermosetting compositions and thermoset resins made from a diphenol and a diglycidyl ether of a diphenol, as for instance, diphenylolmethane, CH2(C6H4OH)2 and the diglycidyl ether of diphenylolpropane. This prior invention also includes methods of making improved compositions and resins.
Process for reacting a phenol with an epoxy compound is disclosed in US3978027 (Clifford D. Marshall), comprising reacting a polyepoxide having more than one vicinal-epoxy group with a phenol in the presence of a potassium iodide catalyst. The products resulting from this process are also disclosed.
Process of reacting a phenol with a polyepoxide in the presence of an organic phosphine compound described under US3547881 (Albert C Mueller&Harvey L Parry) is provided whereby it was found that these particular compounds catalyze the reaction between the epoxy group and phenolic -OH group and is specific thereto without having effect on the reaction of alcoholic -OH group and epoxy group and/or the photopolymerization of the epoxy groups.
In view of the afore-discussed problems there is a need in the art to provide for highly reactive faster curing hardener/accelerator systems which would reduce the usage of the known accelerators including tertiary amines, 2-methyl imidazole in epoxy powder coating composition based applications that would not only facilitate fast curing at required baking temperature/ time but would also be prepared by facile process to lead to stable and such fast curing systems.

OBJECTS OF THE INVENTION
It is thus the basic objective of the present invention to provide for highly reactive fast cure silicon grafted epoxy phenolic hardener/curing agent/ curing accelerator having free phenolic –OH groups.
It is another object of the present invention to provide for said highly reactive fast cure silicon grafted epoxy phenolic hardener/ curing accelerator that would reduce or eliminate the need of tertiary amine type accelerators, 2-methyl imidazole accelerators in epoxy powder coating composition-based applications.
It is yet another object of the present invention to provide for formulations comprising said highly reactive fast cure silicon grafted epoxy phenolic hardener/curing agent/ curing accelerator and a process for preparation of the same that would ensure smooth facile process to achieve desired softening point and melt viscosity of the grafted epoxy phenolic hardener while preventing polymerization/ gelation during the process considering the large excess of highly reactive phenolic hydroxyls from diphenols including bisphenol A and bisphenol F being present to be made available during such fast curing.
It is still another object of the present invention to provide for said highly reactive fast cure silicon grafted epoxy phenolic hardener/curing accelerator that would be effective for fusion bonded epoxy (FBE) functional powder coating applications suiting major areas of application of such powder coating systems including coatings on Rebar, coatings on electronic components, insulating components and coatings for protecting metal pipes/pipelines installed underground or coated steel reinforced concrete structures requiring high chemical/corrosion resistance.
SUMMARY OF THE INVENTION
Thus according to the basic aspect of the present invention there is provided an epoxy phenolic curing agent/ hardener adaptive to silicone grafting comprising a reaction product of diglycidyl ether of bisphenol A (DGEBA) or diglycidyl ether of bisphenol F (DGEBF) having Epoxide equivalent of 170-225, and, excess diphenols including bisphenol A/ bisphenol F in molar ratio of Epoxy: Diphenol of 1: 2.6-3.5.
Preferably the epoxy phenolic curing agent/hardener is provided as epoxy phenolic hardener wherein
said reaction product gives accelerated curing in presence of monophenols including para tertiary butyl phenol,
said reaction product is achieved by either reduced involvement or free of any involvement of conventional accelerators including tertiary amines, 2-methyl imidazole to the levels of 0-1.1 wt% to result in fast cure crack free coatings while formulating epoxy powder coating systems, and
said reaction product is fast cure solid epoxy phenolic curing agent having softening point of 75-100°C, Tg of 35-50°C and Weight Average Molecular Weight of 2000-3000 suitable for epoxy powder coating applications.
More preferably the epoxy phenolic curing agent/hardener as said epoxy phenolic hardener in being conventional accelerator free is triphenyl phosphine catalyzed epoxy phenolic hardener, which in having large excess of free phenolic groups as per said Epoxy: Diphenol ratio of 1:3.5 is adaptive to not only silicone grafting including epoxy silane grafting through reactive epoxy groups favouring epoxy silane grafted phenolic hardener, which in turn is further reactive with solid epoxy resins included in epoxy powder coating systems/compositions in having residual free phenolic groups to thereby enable fast cure coatings with exceptional flexibility, adhesion and cathodic disbondment resistance of said coatings and their storage stability.
According to another preferred aspect of the present invention the epoxy phenolic curing agent/hardener as said hardener when applied together with epoxy powder coating systems is fast cure displaying gel time of 8-12 secs @205?C, is free of cracks employable in highly corrosive environments giving higher flexibility at 180 degree, is able to bend free of cracks for different size of reinforcement bars (rebars/ Thermo-Mechanically treated bars) including 8 mm to 32 mm diameter bars, thereby enabling improved flexibility in 12 mm (about 0.47 in) rebar, Salt Spray ASTM B117 (800 hrs.) creepage of 1.2-1.8 mm, adhesion in respect of cathodic disbondment resistance ASTM G8 (mm), and Abrasion Resistance (ASTM D4060, CS 17 wheel , 1Kg) of 38-42 mg, Chemical resistance IS 13620 that is free from display of any under film corrosion.
Preferably the epoxy phenolic curing agent/hardener is provided wherein said reaction product having preferred molar ratio of Epoxy: Diphenol of 1:2.6-3.5 is based on reactants in levels of 30-40 wt.% Diglycidyl ether of Bisphenol A/ bisphenol F (EEW 170-225), 60-70 wt.% Bisphenol A/ bisphenol F, conventional accelerators selectively of tertiary amines including Benzyl trimethylammonium chloride, and/or 2-methyl imidazole in the levels of 0-1.1 wt.%, favouring said epoxy phenolic hardener for accelerated curing of epoxy powder coating systems.
More preferably the epoxy phenolic curing agent/hardener is provided wherein said epoxy phenolic hardener free of conventional accelerators including 2-methyl imidazole is triphenyl phosphine catalyzed reaction product of reactants in levels of 30-40 wt.% of Diglycidyl ether of Bisphenol A/bisphenol F (EEW 170-225), 60-70 wt.% Bisphenol A/ bisphenol F, 0.01-0.05 wt.% triphenyl phosphine also allowing said accelerated curing of epoxy powder coating systems.
According to yet another preferred aspect of the present invention there is provided said epoxy phenolic curing agent/hardener wherein said epoxy phenolic hardener enables epoxy silane grafted phenolic hardener that is a triphenyl phosphine catalyzed reaction product of reactants in levels of 30-40 wt.% of Diglycidyl ether of Bisphenol A/ bisphenol F (EEW 170-225), 60-70 wt.% Bisphenol A/ bisphenol F, 0.01-0.05wt.% triphenyl phosphine, 0.50-1.00wt.% silane including 3-Glycidoxypropyltrimethoxy?Silane, and 0.50-1.2 wt.% monophenol including tertiary butyl phenol favouring said epoxy silane grafted phenolic hardener having remnant hydroxyl groups with corresponding desired attributes to allow accelerated curing of epoxy powder coating systems resulting in, crack free coats with excellent flexibility, and
wherein said epoxy silane grafted phenolic hardener is fast cure solid epoxy phenolic silane grafted curing agent having attributes including softening point of 75-100°C, Tg of 35-50°C and Weight Average Molecular Weight of 2000-3000.
Preferably the epoxy phenolic curing agent/ hardener based epoxy powder coating systems/ composition is provided comprising said 10-15wt.% hardener including epoxy phenolic hardener and/ or epoxy silane grafted phenolic hardener, 60-70 wt.% Diglycidyl ether of Bisphenol A/ bisphenol F (EEW 750-950), 1-3 wt.% Acrylic & Silica based flow control agent, 2-6 wt.% pigments, 15-20 wt.% extenders.
According to another aspect of the present invention there is provided a process for manufacturing epoxy phenolic curing agent/hardener comprising reacting diglycidyl ether of bisphenol A (DGEBA) or diglycidyl ether of bisphenol F (DGEBF) having Epoxide equivalent of 170-225, and, excess diphenols including bisphenol A/ bisphenol F in molar ratio of Epoxy: Diphenol of 1: 2.6-3.5 to obtain said epoxy phenolic hardener therefrom for silicon grafting enabling epoxy silane grafted phenolic hardener.
Preferably in said process for manufacturing epoxy phenolic curing agent/hardener as epoxy phenolic hardener or epoxy silane grafted phenolic hardener reactive with solid epoxy resins of said epoxy powder coating systems comprises steps of
(a) providing Diglycidyl ether of Bisphenol A/ bisphenol F (EEW 170-225) for reaction with Bisphenol A/ bisphenol F and heating to 125-150°C;
(b) charging conventional accelerators to the reaction mixture of step (a) including tertiary amines of Benzyl trimethylammonium chloride, 2-methyl imidazole in the levels of 0.05-1.1 wt%, OR, for conventional accelerator free reaction charging 0.01-0.05 wt.% triphenyl phosphine and observing for exotherm and subsiding of exotherm followed by maintaining the temperature in the range of 160-190°C and checking melt viscosity in the span of every 30-50 mins till 30-70 poise viscosity levels @ 120°C, 230 RPM, in spindle 09 on cone and plate Brookfield viscometer is reached that is followed by cooling and discharging the batch and obtaining said epoxy phenolic hardener therefrom.
Preferably in said process for manufacturing epoxy phenolic curing agent/hardener as epoxy silane grafted phenolic hardener reactive with solid epoxy resins of said epoxy powder coating system wherein after said step (b) post observing the exotherm based on said triphenyl phosphine addition in clear solution of step (a) and subsiding of exotherm, step (c) was performed by adding 0.50-1.00 wt.% silane including 3-Glycidoxypropyltrimethoxy?Silane after achieving melt viscosity of 15-20 poise @ 120° C, 230 RPM, in spindle 09 on cone and plate Brookfield viscometer followed by maintaining the temperature in the range of 160-175 °C and checking melt viscosity in the span of every 30-50 mins till melt viscosity of 30-70 poise @ 120° C, 230 RPM, in spindle 09 on cone and plate Brookfield viscometer is reached followed by cooling and discharging the batch to obtain said epoxy silane grafted phenolic hardener therefrom.
More preferably in the process for manufacturing epoxy phenolic curing agent/accelerator wherein after attaining the desired melt viscosity 0.50-1.5wt.% monophenol including para tertiary butyl phenol was added into the reaction mixture of said step (b) or (c) and allowed to mix for 5-10 minutes followed by discharging the batch of epoxy silane grafted phenolic hardener therefrom.
According to another preferred aspect of the process for manufacturing epoxy phenolic curing agent/ accelerator and epoxy powder coating system/ composition therefrom comprises the steps of
Providing said 10-15wt.% hardener including epoxy phenolic hardener and/ or epoxy silane grafted phenolic hardener hardener, 60-70 wt.% Diglycidyl ether of Bisphenol A/ bisphenol F/ bisphenol F (EEW 700-1050), 1-3 wt.% Acrylic & Silica based flow control agent, 2-6 wt.% pigments, 15-20 wt.% extenders and premixing the same in industrial mixer followed by feeding into twin-screw extruder, where they are heated and blended into a homogenous molten mass for extrusion and thereafter cooled and flaked before being ground into fine powdery particles that is sieved to achieve desired particle size distribution ensuring consistency in application during spraying on grit blasted panels and rods at elevated temperatures of 210–230°C to favour curing in 1-2 minutes to form the desired coat.

DETAILED DESCRIPTION OF THE INVENTION
As described hereinbefore, the present invention provides for a formulation based on fast cure silicon grafted epoxy phenolic curing agent/accelerator and process thereof providing for said fast cure silicon grafted solid epoxy phenolic curing agent having softening point of 75-100°C, Tg of 35-50°C and Weight Average Molecular Weight of 2000-3000, suitable for epoxy powder coating applications.
According to an aspect of the present invention there is provided said formulation based on fast cure solid epoxy phenolic curing agent/accelerator is a silicone grafted epoxy phenolic polymer having free phenolic groups that act as curing agent as well as accelerator when combined with epoxy resins (epoxide equivalent of 700-1050) present in powder coating compositions and when subjected to curing at an elevated temperature of 210–230°C for 1-2 minutes.
According to another preferred aspect of the present invention there is provided said formulation based on fast cure solid epoxy phenolic curing agent comprising epoxy silane/silicone grafted epoxy phenolic polymer with free phenolic groups, which is a reaction product of diglycidyl ether of bisphenol A (DGEBA) or diglycidyl ether of bisphenol F (DGEBF) having Epoxide equivalent of 170-225, and, large excess of diphenols (including bisphenol A, bisphenol F) having preferred molar ratio of Epoxy : Diphenol of 1: > 2.5, enabling said free phenolic groups in large excess adapted for not only said epoxy silane grafted epoxy phenolic polymer but also adapted for further reactivity with solid epoxy resins included in epoxy powder coating applications. Preferably the epoxy phenolic polymer with free phenolic groups as said reaction product of diglycidyl ethers of bisphenols & diphenol (including bisphenol A, bisphenol F) thus obtained with large excess of free phenolic –OH groups could not only be grafted with selected levels of epoxy silane through reactive epoxy groups of epoxy silane with such phenolic -OH groups, but also due to such large excess of phenolic hydroxyls in said epoxy phenolic polymer leaves room for further reaction of the same with solid epoxy resins of powder coating formulations, thereby acting as a curing agent as well as accelerator favoring epoxy powder coating applications.
The present invention thus reduces the need of usage of 2-methyl imidazole or similar accelerator in curing agents as well as in powder coating compositions based on a simplified, unique and non-obvious approach of maintaining higher phenolic hydroxyls through controlled reaction of epoxy resins (including diglycidyl ethers of bisphenols & epoxy silanes), with diphenols, while not only ensures the presence of large excess of diphenols (including bisphenol A, bisphenol F) but also by processing at low temperature of 160-165°C max, with the involvement of suitable catalyst at select concentrations enables further grafting of epoxy silane in the polymer backbone. The present invention is thus about the formulation and process to synthesize fast cure solid epoxy phenolic curing agent having softening point of 75-100°C, Tg of 35-50°C and Weight Average Molecular Weight of 2000-3000 suitable for epoxy powder coating applications. This relates to a reaction product of diglycidyl ether of bisphenol A (DGEBA) or with diglycidyl ether of bisphenol F (DGEBF) having Epoxide equivalent of 170-225 with large excess of diphenols including bisphenol A, bisphenol F having preferred molar ratio of Epoxy: Diphenol of 1: > 2.5. The reaction product of epoxy and diphenol thus obtained is grafted with epoxy silane through reactive epoxy groups of epoxy silane with phenolic -OH groups and still leaving out large excess of phenolic hydroxyls for further reaction with solid epoxy resins. The free phenolic groups present in the silicone grafted epoxy phenolic polymer act as curing agent as well as accelerator when combined with epoxy resins (epoxide equivalent of 700-1050) in the powder coating compositions and subjected to curing at an elevated temperature of 210–230°C for 1–2 minutes. High reactivity of the epoxy phenolic hardener minimizes the need of tertiary amine type accelerator in the epoxy powder coating compositions to facilitate fast curing at required baking temperature/ time. The synthesis of such fast cure solid epoxy phenolic curing agent/accelerator or epoxy silane grafted phenolic hardener that is a silicone grafted epoxy phenolic polymer having free phenolic groups, involves a selectively special recipe and process. This relates to the efficient process controls and reaction sequence in presence of catalyst type/dosage for the reaction of firstly epoxy based bisphenols/ diglycidyl ethers of bisphenols with diphenols that is followed by further grafting with epoxy silane. The formulation and reaction parameter controls are selectively special to ensure smooth process to achieve desired softening point and melt viscosity of the grafted epoxy phenolic hardener preventing polymerization/ gelation during the process in view of large excess of highly reactive phenolic hydroxyls from diphenols including from bisphenol A/bisphenol F present that is made available for curing. Although there is technology available for the preparation of phenolic curing agent, but the present invention offers a uniquely designed epoxy silane grafted phenolic hardener for epoxy powder coating applications providing exceptional flexibility, adhesion and resistance to cathodic disbondment. Said fast cure solid epoxy phenolic curing agent/accelerator or epoxy silane grafted phenolic hardener/silicone grafted curing agent with large excess of phenolic hydroxyl group has been designed for functional fusion bonded epoxy (FBE) powder coating applications. Major areas of application of such powder coating systems are coatings on Rebar and would also find use to design fast curing epoxy powders for applications such as electronic components, insulating components, and high chemical resistance products.
The present invention is thus about a uniquely designed fast cure solid epoxy phenolic curing agent/accelerator or epoxy silane grafted phenolic hardener/silicone grafted phenolic curing agent for epoxy powder coatings. Advantageously, such fast cure solid epoxy phenolic curing agent/accelerator or epoxy silane grafted phenolic hardener/silicone grafted curing agent for epoxy powder coatings provides for a single layer coating, which can be used for highly corrosive environments and higher flexibility at 180 degree bending without any cracks on different size of reinforcement bars (rebars/ thermo-mechanically treated bars) like 8 mm to 32 mm diameter, thereby enabling improved flexibility, adhesion, cathodic disbondment resistance and storage stability of epoxy powders prepared using such epoxy silane grafted phenolic hardener.
Examples: Epoxy Phenolic Hardener/accelerator

Example 1
Sn Raw material PBW
1 Diglycidyl ether of Bisphenol A (EEW 170-225) 35.00
2 Bisphenol A 64.94
3 Benzyl trimethylammonium chloride 0.06
Total 100.00

In a reaction flask equipped with a stirrer, a thermocouple, a condenser, a nitrogen inlet, and a heating mantle, Diglycidyl ether of Bisphenol A (EEW 170-225) was mixed with Bisphenol-A. The mixture was heated to 125-135°C , charged Benzyl trimethylammonium chloride and observed for exotherm. When exotherm subsided, provided heating to raise and maintain the temperature to 180-190°Cand checked for melt viscosity every 30-50 minutes till it reached 30-70 poise @ 120°C, 230 RPM, spindle 09 on cone and plate Brookfield viscometer. After achieving the desired viscosity,provide cooling jerk and discharge the batch.
Inference: The epoxy phenolic hardener obtained from above recipe showed longer gel time /slow reactivity with epoxy resin in powder coating.

Example 2
Sn Raw material PBW
1 Diglycidyl ether of Bisphenol A (EEW 170-225) 35.00
2 Bisphenol A 62.95
3 Tri phenyl phosphine 0.05
4 2-methyl imidazole 2.00
Total 100.00

In a reaction flask equipped with a stirrer, a thermocouple, a condenser, a nitrogen inlet, and a heating mantle, Diglycidyl ether of Bisphenol A (EEW 170-225) was mixed with Bisphenol-A. The mixture was heated up to 140-150°Cand charged Tri phenyl phosphine and observed for the exotherm. When exotherm subsided, maintain the temperature at 175-185°C and checked for melt viscosity every 30-50 minutes till it reached 30-70 poise @ 120°C, 230 RPM, spindle 09 on cone and plate Brookfield viscometer. After achieving the desired viscosity,provide cooling jerk and add 2- methylimidazole. Mix for 5-10 minutes and dischargethe batch.
Inference: Addition of 2-Methyl imidazole improved the reactivity in powder coating formulation but showed poor flexibility.

Example 3
Sn Raw material PBW
1 Diglycidyl ether of Bisphenol A (EEW 170-225) 35.00
2 Bisphenol A 63.94
3 Benzyl trimethylammonium chloride 0.06
4 2-methyl imidazole 1.00
Total 100.00

In a reaction flask equipped with a stirrer, a thermocouple, a condenser, a nitrogen inlet, and a heating mantle, Diglycidyl ether of Bisphenol A (EEW 170-225) was mixed with Bisphenol-A. The mixture was heated up to 140-150°C and charged Benzyl trimethylammonium chloride and observed for the exotherm. When exotherm subsided, maintain the temperature to 175-185°C and checked for melt viscosity every 30-50 minutes till it reached 30-70 poise @ 120°C, 230 RPM, spindle 09 on cone and plate Brookfield viscometer. After achieving the desired viscosity, provide cooling jerk and add 2-methyl imidazole. Mix for 5- 10 minutes and discharge the batch.
Inference: Reduced quantity of 2-methyl imidazole slowed reactivity means longer time in powder coating formulation and still inferior flexibility.
Example 4
Sn Raw material PBW
1 Diglycidyl ether of Bisphenol A (EEW 170-225) 35.00
2 Bisphenol A(I) 19.00
3 Benzyl trimethylammonium chloride(I) 0.04
4 Bisphenol A (II) 45.44
5 Benzyl trimethylammonium chloride (II) 0.02
6 3-Glycidoxypropyltrimethoxy?Silane 0.50
Total 100.00

In a reaction flask equipped with a stirrer, a thermocouple, a condenser, a nitrogen inlet, and a heating mantle, Diglycidyl ether of Bisphenol A (EEW 170-225) was mixed with Bisphenol-A (I). The mixture was heated up to 140-150°C and charged Benzyl trimethylammonium chloride (I) into the reaction vessel. After that batch temperature raised to 175-180°C and maintained for 1 hour and checked for epoxy equivalent weight. After achieving epoxy equivalent weight between “1600-2000”. Added Bisphenol-A (II) slowly followed by Benzyl trimethylammonium chloride (II) at 175-180°C and maintained the temperature. Checked for melt viscosity every 30 minutes till it reached 30-70 poise @ 120°C, 230 RPM, spindle 09 on cone and plate Brookfield viscometer. After achieving the desired viscosity, added 3-Glycidoxypropyltrimethoxy?Silane and allowed to mix for 5-10 minutes and discharged the batch.
Inference: The aforesaid example showed inferior flexibility in powder coating formulation.
Example 5
Sn Raw material PBW
1 Diglycidyl ether of Bisphenol A (EEW 170-225) 35.19
2 Bisphenol A 64.79
3 Tri phenyl phosphine 0.02
Total 100.00

In a reaction flask equipped with a stirrer, a thermocouple, a condenser, a nitrogen inlet, and a heating mantle, Diglycidyl ether of Bisphenol A (EEW 170-225) was mixed with Bisphenol-A. The mixture was heated up to 140-150°C, charged Tri phenyl phosphine and observed for the exotherm. When exotherm subsided, heated and maintained the temperature to 175-185°C. After attaining 180°C, checked for melt viscosity every 30-50 minutes till it reached 30-70 poise @ 120°C, 230 RPM, spindle 09 on cone and plate Brookfield viscometer. After achieving the desired viscosity discharged the batch.
Inference: Reduced catalyst quantity and single stage addition of bisphenol A provided better control in processing but inferior reactivity/ longer gel time.
Example 6
Sn Raw material PBW
1 Diglycidyl ether of Bisphenol A (EEW 170-225) 34.97
2 Bisphenol A 64.41
3 Tri phenyl phosphine 0.02
4 3-Glycidoxypropyltrimethoxy?Silane 0.60
Total 100.00

In a reaction flask equipped with a stirrer, a thermocouple, a condenser, a nitrogen inlet, and a heating mantle, Diglycidyl ether of Bisphenol A (EEW 170-225) was mixed with Bisphenol A. The mixture was heated up to 140-150°C and allowed to get clear homogeneous solution. Charged Tri phenyl phosphine into the reaction vessel and observed for the exotherm. When exotherm subsided, maintained the batch temperature to 160-170°C and checked for melt viscosity every 30-50 minutes and after achieving 15-20 poise @ 120°C, 230 RPM, added 3-Glycidoxypropyltrimethoxy?Silane. Continued to process at 160-170°C till melt viscosity reached 30-70 poise @ 120° C, 230 RPM, spindle 09 on cone and plate Brookfield viscometer. After achieving the desired viscosity discharged the batch.
Inference: Grafting of 3 Glycidoxypropyltrimethoxy?Silane in the reaction product of liquid epoxy and dihydric phenol showed good flexibility, adhesion and resistance to cathodic disbondment.
Example 7
Sn Raw material PBW
1 Diglycidyl ether of Bisphenol F (EEW 170-225) 30.29
2 Bisphenol A 69.09
3 Tri phenyl phosphine 0.02
4 3-Glycidoxypropyltrimethoxy?Silane 0.60
Total 100.00

In a reaction flask equipped with a stirrer, a thermocouple, a condenser, a nitrogen inlet, and a heating mantle, Diglycidyl ether of Bisphenol F (EEW 170-225) was mixed with Bisphenol A. The mixture was heated up to 140-150°C and after clarity appeared, Tri phenyl phosphine charged into reaction vessel and observed for the exotherm. When exotherm subsided, maintained the temperature to 160-175°C. Checked for melt viscosity every 30-50 minutes and after achieving 15-20 poise @ 120°C, 230 RPM add 3-Glycidoxypropyltrimethoxy?Silane into the reaction vessel. Keep further processing at 160-175°C till required melt viscosity of 30-70 poise @ 120°C, 230 RPM, spindle 09 on cone and plate Brookfield viscometer is attained. After achieving the desired viscosity discharge the batch.
Inference: Reaction product of Diglycidyl ether of Bisphenol F showed the similar results like with Diglycidyl ether of Bisphenol A in example 6.


Example 8
Sn Raw material PBW
1 Diglycidyl ether of Bisphenol A (EEW 170-225) 34.71
2 Bisphenol A 63.93
3 Tri phenyl phosphine 0.02
4 3-Glycidoxypropyltrimethoxy?Silane 0.59
5 Para tertiary butyl phenol 0.75
Total 100.00

In a reaction flask equipped with a stirrer, a thermocouple, a condenser, a nitrogen inlet, and a heating mantle, Diglycidyl ether of Bisphenol A (EEW 170-225) was mixed with Bisphenol-A. The mixture was heated up to 140-150°C and after clarity appeared, Tri phenyl phosphine charged into reaction vessel and observed for exotherm. When exotherm subsided, maintained the temperature to 160-175°C. Checked for melt viscosity after every 30-50 minutes and after achieving 15-20 poise @ 120°C, 230 RPM add 3-Glycidoxypropyltrimethoxy?Silane into the reaction vessel. Keep further processing at 160-175°C till required melt viscosity reaches 30-70 poise @ 120° C, 230 RPM, spindle 09 on cone and plate Brookfield viscometer. After achieving the desired melt viscosity, add para tertiary butyl phenol into the reaction vessel. Allow to mix for 5-10 minutes and discharge the batch.
Inference: Incorporation of monophenol in silicon grafted epoxy phenolic hardener just before discharging the batch provided accelerated curing with reduced gel time which is preferred aspect of application while formulating epoxy powder coatings.

Example 9
Sn Raw material PBW
1 Diglycidyl ether of Bisphenol A (EEW 170-225) 34.45
2 Bisphenol A 63.46
3 Tri phenyl phosphine 0.02
4 3-Glycidoxypropyltrimethoxy?Silane 0.59
5 Para tertiary butyl phenol 1.48
Total 100.00

In a reaction flask equipped with a stirrer, a thermocouple, a condenser, a nitrogen inlet, and a heating mantle, Diglycidyl ether of Bisphenol A (EEW 170-225) was mixed with Bisphenol A. The mixture was heated up to 140-150°C till clear homogeneous mass is obtained. Charged Tri phenyl phosphine into the reaction mass and observed for the exotherm. When exotherm subsided, heat to raise and maintain the temperature at 160-175°C. Check for melt viscosity every 30-50 minutes and after achieving 15-20 poise @120°C, 230 RPM, add 3-Glycidoxypropyltrimethoxy?Silane. Continue processing at 160-175°C till melt viscosity reached 30-70 poise @ 120° C, 230 RPM, spindle 09 on cone and plate Brookfield viscometer. After achieving the desired viscosity, add para tertiary butyl phenol into the reaction vessel, allow to mix for 5-10 minutes and discharge the batch.
Inference: Incorporation of higher amount of monophenol in silicon grafted epoxy phenolic hardener provided good reactivity with epoxy resin in powder coating in a similar manner as in example 8 but provided inferior flexibility.

Epoxy Powder Coating composition based on Epoxy Phenolic Hardeners & their evaluation:
Raw Materials PBW
Diglycidyl ether of Bisphenol A (EEW 750-950) 65
Epoxy Phenolic Hardener (Examples 1-9) 12
Acrylic & Silica based flow control agent 1.2
Titanium Dioxide 5
Phthalocyanine green 1
Calcite extender 15.8

Process
Premixed the above ingredients by using industrial mixer and then fed into a twin-screw extruder, where they are heated and blended into a homogenous molten mass. Once extruded, the material is cooled and flaked before being ground into fine particles. The powder is then sieved to achieve the desired particle size distribution ensuring consistency in application. Then powder can be sprayed on grit blasted panels and rods to test further properties. Coating and application parameters are mentioned below.
Application Parameters:
Application Method – Electrostatic spray gun
Voltage – 50 KV, Current – 35 µA, Powder Output – 40 %
Substrate – 6.4 mm steel panel with blasting profile Sa2.5
Application Temperature: Preheating at 230°C and post heated at 220°C for 5 mins
Film Thickness – 180 – 250 microns
Test results of epoxy phenolic hardener examples 1-9 in Epoxy powder coating formulation:
Test Results in Epoxy Powder coating formulation
Epoxy Powder Coating based on Gel time @205°C
In sec. Flexibility in 12 mm (about 0.47 in) rebar Salt Spray
ASTM B117
800 hrs
(Creepage, mm) Cathodic disbondment ASTM G8 (mm) Abrasion Resistance (loss in mg)
ASTM D4060 CS 17 wheel
1 KG weight Chemical resistance IS 13620
Example 1 11-13 Minor Cracks 2.8 4.3 65 No Undercutting
Example 2 9-10 Severe Cracks 3.2 6.2 72 No Undercutting
Example 3 10-12 Minor Cracks 3.0 5.4 56 No Undercutting
Example 4 9-10 Minor Cracks 2.6 3.9 52 No Undercutting
Example 5 10 - 11 No Cracks 1.8 2.8 40 No Undercutting
Example 6 9-10 No Cracks 1.2 1.4 38 No Undercutting
Example 7 8-9 No Cracks 1.3 1.6 42 No Undercutting
Example 8 8-9 No Cracks 1.5 1.8 40 No Undercutting
Example 9 8-9 Cracks 1.9 2.1 48 No Undercutting

Conclusion:
• Example 1 shows higher gel time means slower reactivity and poor flexibility and poor cathodic disbondment properties.
• Example 2 shows slightly lower gel time means slightly faster reactivity but seen brittleness as flexibility shows severe failure, as well as cathodic disbondment shows poor results.
• Example 3 shows higher gel time means slower reactivity as well as poor flexibility and poor cathodic disbondment results.
• Example 4 shows slightly lower gel time means slightly faster reactivity but seen poor flexibility and poor cathodic disbondment properties.
• Example 5 shows slow reactivity as gel time slightly higher side but shows improved results in flexibility and cathodic disbondment test.
• Example 6 shows good improvement in reactivity as gel time as slightly lower side and shows excellent results in flexibility and cathodic disbondment test.
• Example 7 shows excellent improvement in reactivity as gel time is at lower side and superior results seen in flexibility and cathodic disbondment test.
• Example 8 shows excellent improvement in reactivity as gel time is at lower side and excellent results seen in flexibility and cathodic disbondment test.
• Example 9 shows slightly lower gel time means slightly faster reactivity but seen brittleness as flexibility shows failure, as well as cathodic disbondment shows slightly lower results.
,CLAIMS:We Claim:

1. An epoxy phenolic curing agent/hardener adaptive to silicone grafting comprising a reaction product of diglycidyl ether of bisphenol A (DGEBA) or diglycidyl ether of bisphenol F (DGEBF) having Epoxide equivalent of 170-225, and, excess diphenols including bisphenol A/ bisphenol F in molar ratio of Epoxy: Diphenol of 1: 2.6-3.5.

2. The epoxy phenolic curing agent/hardener as claimed in claim 1 as epoxy phenolic hardener wherein
said reaction product gives accelerated curing in presence of monophenols including para tertiary butyl phenol,
said reaction product is achieved by either reduced involvement or free of any involvement of conventional accelerators including tertiary amines, 2-methyl imidazole to the levels of 0-1.1 wt% to result in fast cure crack free coatings while formulating epoxy powder coating systems, and
said reaction product is fast cure solid epoxy phenolic curing agent having softening point of 75-100°C, Tg of 35-50°C and Weight Average Molecular Weight of 2000-3000 suitable for epoxy powder coating applications.

3. The epoxy phenolic curing agent/hardener as claimed in claims 1 or 2 as said epoxy phenolic hardener in being conventional accelerator free is triphenyl phosphine catalyzed epoxy phenolic hardener, which in having large excess of free phenolic groups as per said Epoxy: Diphenol ratio of 1:3.5 is adaptive to not only silicone grafting including epoxy silane grafting through reactive epoxy groups favouring epoxy silane grafted phenolic hardener, which in turn is further reactive with solid epoxy resins included in epoxy powder coating systems/compositions in having residual free phenolic groups to thereby enable fast cure coatings with exceptional flexibility, adhesion and cathodic disbondment resistance of said coatings and their storage stability.
4. The epoxy phenolic curing agent/hardener as claimed in claims 1-3 as said hardener when applied together with epoxy powder coating systems is fast cure displaying gel time of 8-12 secs @205?C, is free of cracks employable in highly corrosive environments giving higher flexibility at 180 degree, is able to bend free of cracks for different size of reinforcement bars (rebars/ Thermo-Mechanically treated bars) including 8 mm to 32 mm diameter bars, thereby enabling improved flexibility in 12 mm (about 0.47 in) rebar, Salt Spray ASTM B117 (800 hrs.) creepage of 1.2-1.8 mm, adhesion in respect of cathodic disbondment resistance ASTM G8 (mm), and Abrasion Resistance (ASTM D4060, CS 17 wheel , 1Kg) of 38-42 mg, Chemical resistance IS 13620 that is free from display of any under film corrosion.

5. The epoxy phenolic curing agent/hardener as claimed in claims 1-4 wherein said reaction product having preferred molar ratio of Epoxy: Diphenol of 1:2.6-3.5 is based on reactants in levels of 30-40 wt.% Diglycidyl ether of Bisphenol A/ bisphenol F (EEW 170-225), 60-70 wt.% Bisphenol A/ bisphenol F, conventional accelerators selectively of tertiary amines including Benzyl trimethylammonium chloride, and/or 2-methyl imidazole in the levels of 0-1.1 wt.%, favouring said epoxy phenolic hardener for accelerated curing of epoxy powder coating systems.

6. The epoxy phenolic curing agent/hardener as claimed in claims 1-5 wherein said epoxy phenolic hardener free of conventional accelerators including 2-methyl imidazole is triphenyl phosphine catalyzed reaction product of reactants in levels of 30-40 wt.% of Diglycidyl ether of Bisphenol A/bisphenol F (EEW 170-225), 60-70 wt.% Bisphenol A/ bisphenol F, 0.01-0.05 wt.% triphenyl phosphine also allowing said accelerated curing of epoxy powder coating systems.

7. The epoxy phenolic curing agent/hardener as claimed in claims 1-6 wherein said epoxy phenolic hardener enables epoxy silane grafted phenolic hardener that is a triphenyl phosphine catalyzed reaction product of reactants in levels of 30-40 wt.% of Diglycidyl ether of Bisphenol A/ bisphenol F (EEW 170-225), 60-70 wt.% Bisphenol A/ bisphenol F, 0.01-0.05wt.% triphenyl phosphine, 0.50-1.00wt.% silane including 3-Glycidoxypropyltrimethoxy?Silane, and 0.50-1.2 wt.% monophenol including tertiary butyl phenol favouring said epoxy silane grafted phenolic hardener having remnant hydroxyl groups with corresponding desired attributes to allow accelerated curing of epoxy powder coating systems resulting in, crack free coats with excellent flexibility, and
wherein said epoxy silane grafted phenolic hardener is fast cure solid epoxy phenolic silane grafted curing agent having attributes including softening point of 75-100°C, Tg of 35-50°C and Weight Average Molecular Weight of 2000-3000.

8. The epoxy phenolic curing agent/hardener as claimed in claims 1-7 based epoxy powder coating systems/ composition comprising said 10-15wt.% hardener including epoxy phenolic hardener and/ or epoxy silane grafted phenolic hardener, 60-70 wt.% Diglycidyl ether of Bisphenol A/ bisphenol F (EEW 750-950), 1-3 wt.% Acrylic & Silica based flow control agent, 2-6 wt.% pigments, 15-20 wt.% extenders.

9. A process for manufacturing epoxy phenolic curing agent/hardener as claimed in claims 1-8 comprising reacting diglycidyl ether of bisphenol A (DGEBA) or diglycidyl ether of bisphenol F (DGEBF) having Epoxide equivalent of 170-225, and, excess diphenols including bisphenol A/ bisphenol F in molar ratio of Epoxy: Diphenol of 1: 2.6-3.5 to obtain said epoxy phenolic hardener therefrom for silicon grafting enabling epoxy silane grafted phenolic hardener.

10. A process for manufacturing epoxy phenolic curing agent/hardener as claimed in claims 1-9 as epoxy phenolic hardener or epoxy silane grafted phenolic hardener reactive with solid epoxy resins of said epoxy powder coating systems comprising steps of
(a) providing Diglycidyl ether of Bisphenol A/ bisphenol F (EEW 170-225) for reaction with Bisphenol A/ bisphenol F and heating to 125-150°C;
(b) charging conventional accelerators to the reaction mixture of step (a) including tertiary amines of Benzyl trimethylammonium chloride, 2-methyl imidazole in the levels of 0.05-1.1 wt%, OR, for conventional accelerator free reaction charging 0.01-0.05 wt.% triphenyl phosphine and observing for exotherm and subsiding of exotherm followed by maintaining the temperature in the range of 160-190°C and checking melt viscosity in the span of every 30-50 mins till 30-70 poise viscosity levels @ 120°C, 230 RPM, in spindle 09 on cone and plate Brookfield viscometer is reached that is followed by cooling and discharging the batch and obtaining said epoxy phenolic hardener therefrom.

11. The process for manufacturing epoxy phenolic curing agent/hardener as claimed in claims 3 or 7 as epoxy silane grafted phenolic hardener reactive with solid epoxy resins of said epoxy powder coating system wherein after said step (b) post observing the exotherm based on said triphenyl phosphine addition in clear solution of step (a) and subsiding of exotherm, step (c) was performed by adding 0.50-1.00 wt.% silane including 3-Glycidoxypropyltrimethoxy?Silane after achieving melt viscosity of 15-20 poise @ 120° C, 230 RPM, in spindle 09 on cone and plate Brookfield viscometer followed by maintaining the temperature in the range of 160-175 °C and checking melt viscosity in the span of every 30-50 mins till melt viscosity of 30-70 poise @ 120° C, 230 RPM, in spindle 09 on cone and plate Brookfield viscometer is reached followed by cooling and discharging the batch to obtain said epoxy silane grafted phenolic hardener therefrom.

12. The process for manufacturing epoxy phenolic curing agent/accelerator as claimed in claims 10 or 11 wherein after attaining the desired melt viscosity 0.50-1.5wt.% monophenol including para tertiary butyl phenol was added into the reaction mixture of said step (b) or (c) and allowed to mix for 5-10 minutes followed by discharging the batch of epoxy silane grafted phenolic hardener therefrom.

13. The process for manufacturing epoxy phenolic curing agent/accelerator as claimed in claims 10-12 and epoxy powder coating system/ composition therefrom comprising the steps of
Providing said 10-15wt.% hardener including epoxy phenolic hardener and/ or epoxy silane grafted phenolic hardener hardener, 60-70 wt.% Diglycidyl ether of Bisphenol A/ bisphenol F/ bisphenol F (EEW 700-1050), 1-3 wt.% Acrylic & Silica based flow control agent, 2-6 wt.% pigments, 15-20 wt.% extenders and premixing the same in industrial mixer followed by feeding into twin-screw extruder, where they are heated and blended into a homogenous molten mass for extrusion and thereafter cooled and flaked before being ground into fine powdery particles that is sieved to achieve desired particle size distribution ensuring consistency in application during spraying on grit blasted panels and rods at elevated temperatures of 210–230°C to favour curing in 1-2 minutes to form the desired coat.

Dated this the 13th day of November, 2024 Anjan Sen
Applicants Agent and Advocate
IN/PA-199