Description:
FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003

COMPLETE SPECIFICATION
(See section 10 and rule 13)
1. Title of the Invention
CROSSLINKING SYSTEM FOR FLUOROELASTOMERS
2. Applicant(s)
Name Nationality Address
GUJARAT FLUOROCHEMICALS LIMITED INDIAN INOX Towers, 17, Sector -16A, Noida – 201301, Uttar Pradesh, India

3. Preamble to the description

The following specification particularly describes the invention and the manner in which it is to be performed.

FIELD
The present disclosure relates to novel and safer crosslinking system for fluoroelastomers.

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 indicate otherwise.

FKM is a family of fluorocarbon-based fluoroelastomer materials defined by ASTM International standard. FKM is the American standard (ASTM) short form name for Fluoroelastomers or fluoro rubber material. F stands for Fluoro; the K is an abbreviation of the German word Kohlenstoff, meaning Carbon; and the M is the designation of saturated backbone rubber from ASTM

FFKM are perfluoroelastomeric compounds containing an even higher amount of fluorine than FKM fluoroelastomers.

Phr or phr (parts per hundred rubber) refers to a unit of measure used by rubber chemists to depict what amount of certain ingredients are needed.

BACKGROUND
The background information hereinbelow relates to the present disclosure but is not necessarily prior art.

Fluoroelastomers are an important class of high performance elastomers because of their versatility and unique combination of relevant properties. They have a wide range of applications in strategic materials, automobiles, aerospace, electronics, and energy sectors and the like. Fluoroelastomers have excellent thermal stability, oil resistance, excellent mechanical properties and abrasion resistance properties. These properties are mainly linked to the low polarizability and the strong electronegativity of the fluorine atom to its small van der Waals radius (1.32 Å) and to the strong C–F bond (485 kJ mol-1). Hence, fluoroelastomers exhibit high thermal, chemical, ageing and weather resistance, excellent inertness to solvents, hydrocarbons, acids and alkalis, low dielectric constants, low flammability, low refractive index, low surface energy and low moisture absorption.
Commercially available fluoroelastomers are mainly of two types: FKM elastomers and FFKM elastomers. FKM elastomers are highly fluorinated (perfluorinated), polymers in which vinylidene fluoride (VDF) is used as a partially fluorinated co-monomer. FFKM perfluoroelastomers are fully fluorinated hydrocarbons in which there are no C-H bonds, but they have ether linkage. FFKM can withstand exposure to almost any chemicals.

The curing reactions in FKM elastomers are associated with the strong polarity of C-F bonds that leads to polarization of molecules leading to the elimination of hydrogen fluoride (HF) under the influence of several factors such as incorporation of additives. Existing crosslinking systems are based on diamine derivatives, bisphenol derivatives, peroxides with co-agent and high energy radiation. Among them, bisphenol curing system is the most widely used system for crosslinking of fluoroelastomers. The bisphenol curing system has several issues, such as it causes endocrine disruption, reproductive disorders and other health hazards.

Fluoroelastomers and Perfluoroelastomers (elastomeric perfluoropolymers) exhibit outstanding high temperature tolerance and chemical resistance in both the cured and uncured states. These properties are attributable to the stability and inertness of the copolymerized fluoro and perfluorinated monomer units which form the major portion of the polymer backbone. Tetrafluoroethylene (TFE), perfluoro (methyl vinyl) ether, perfluoro (propyl vinyl) ether and others are disclosed in U.S. Pat. Nos. 3,467,638; 3,682,872; 4,035,565; 4,281,092; and 4,972,038.

Fluoro and perfluoro elastomers also, however, necessarily contain small quantities of less stable copolymerized cure site monomers and, in addition, many perfluoro elastomers contain reactive end-groups introduced by the use of chain transfer agents or molecular weight regulators during polymerization. Such moieties must have a high degree of reactivity in order to promote effective crosslinking and cure chemistry, but this reactivity inherently renders the polymers more susceptible to degradative chemical reactions, such as oxidation. Consequently, certain physical properties of the polymer, in particular compression set, and high temperature stress/strain properties, are adversely affected.

Warner, John et al in WO 2018/005430 Al disclosed Bisphenol-A free crosslinking system based on a bis-electrophile and a polynucleophile and its application in can linings etc. It has disclosed the possible health hazards owing to bisphenols crosslinked in the polymer. The curing agents disclosed are a dianhydride, a bis-phenol (other than BPA), a polyepoxide, a bis-epoxide and a polyphenol, and a bis-styrene and an unsaturated polyester. However, these disclosures are not related to any fluoropolymer or fluoroelastomer.

Hintzer et al. in US patent 9,982,091B2 described cured fluoroelastomer composition comprising the reaction product of a curing reaction of the composition using a peroxide cure system, which is a commonly used cure system based on a peroxide cure reaction using appropriate curing compounds having or creating peroxides, which in turn are believed to generate free radicals. The fluoroelastomers suitable for use in peroxide curing systems (peroxide curable fluoroelastomers) contain reactive sites which include halogens, such as bromine and/or iodine. It is generally believed that the bromine or iodine atoms are abstracted in the free radical peroxide cure reaction, thereby causing the fluoropolymer molecules to cross-link and to form a three-dimensional network. The highly fluorinated elastomers of this invention may further contain other cure-sites which may be reactive to peroxide cure systems or which may be reactive to other cure systems, for example, but not limited to bisphenol curing systems or triazine curing systems. This invention discloses various peroxide initiators which include hydrogen peroxide, diacylperoxides, diacetylperoxide, dipropionylperoxide, dibutyrylperoxide, dibenzoylperoxide, benzoylacetylperoxide, diglutaric acid peroxide, dilaurylperoxide, and water soluble per-acids, salts such as ammonium, sodium or potassium salts. It also disclosed, suitable redox systems which include, a combination of peroxodisulphate and hydrogen sulphite or disulphite, a combination of thiosulphate and peroxodisulphate or a combination of peroxodisulphate and hydrazine.

Suzuki et al in US10,329,404 B2 disclose a process for preparing partially fluorinated elastomer using a cross linking system, wherein curing system used is either peroxides such as benzoyl peroxide, dichlorobenzoyl peroxide, dicumyl peroxide, 2,5-dimethyl-2,5-di (t butyl peroxy) hexane, di-t-butyl peroxide, t-butyl peroxybenzoate, And 2,5-dimethyl 2,5-di (t-butylperoxy) hexane-3, lauroyl peroxide or bisphenol or amine curable. It also disclosed use of different inorganic fillers like carbon black, graphite, clay, silica, talc, diatomaceous earth, barium sulfate, wollastonite, calcium carbonate, calcium fluoride, titanium oxide, and iron oxide.

Jochum et al. in US 10875948 disclosed peroxide curable fluoropolymers, fluoroelastomers having suitable having cure sites, which are reactive groups that can undergo cross-linking reactions in the presence of suitable cross-linking agents. The cure system is based on a peroxide cure reaction using appropriate curing compounds having or creating peroxides, which in turn are believed to generate free radicals.

However, it is well experienced to person skilled in the art having disadvantages of peroxide as curing (Crosslinking agent) viz, peroxide curing agents may have some disadvantages, including: low scorch safety, poor resistance to thermo-oxidative aging, weaker stability at high temperatures, poor tensile and tear strength, lower elastic and dynamic properties, tendency to decompose into smelly by-products such as volatile organic compounds (VOCs) etc.

Further use of crosslinking agent like Bisphenol A, AF or peroxide type have their inherent disadvantages of being not safe for exposure on health being possessing high potency posing risk on health being LD50, LC50 values are reportedly significantly low.
Also, fluoroelastomers derived from the disclosed crosslinking system and the process, often observed with drawbacks on most of the important curing parameters like variable or undesirable optimum cure time TC90, the scorch time TS1 or TS2, minimum torque (MH), maximum torque (ML) and the difference between the maximum and minimum torque ?M belong.

Hence, there exists a need to explore a unique and safe crosslinking system devoid of bisphenol system for fluoroelastomers that mitigates the drawbacks mentioned so far and provides at least an alternative solution.

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 background or to at least provide a useful alternative.

Another object of the present disclosure is to provide a safe and novel crosslinking system for fluoroelastomers.

Yet another object of the present disclosure is to provide a crosslinking system that is non-toxic.

Still another object of the present disclosure is to provide a crosslinking system that results in fluoroelastomers having improved cure characteristics, rheological characteristics, physico-mechanical properties, crosslink density and compression set resistance.

Yet another object of the present disclosure is to provide a process for the preparation of a crosslinking system for fluoroelastomers.

Still another object of the present disclosure is to provide a process for crosslinking the fluoroelastomers by using a crosslinking system.

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 OF INVENTION
In one aspect according to the present invention, it relates to a bisphenol free, safe crosslinking system for fluoroelastomers comprising the components:
a) a phase transfer catalyst selected from quaternary ammonium or phosphonium salt;
b) a non-bisphenol curing agent;
c) a dispersing agent;
d) a processing aid; and
e) at least one additive.

In another aspect according to the present invention, it relates to the process for preparing a crosslinking system for fluoroelastomers comprising stepwise mixing a curative agent, a phase transfer catalyst, a dispersing agent, a processing aid agent and an additive in the sequence to make pre-compound usable for crosslinking for fluoroelastomers / fluoropolymer. In the process of making fluoroelastomer using the novel crosslinking system, crosslinking system is added for pre-compounded fluoroelastomer at temperature ranging between 35-70°C for time duration ranging between 10-60 minutes followed by process subjected to maturation time ranging between 10- 50 hours.

In yet another aspect according to the present invention, it relates to the process for preparing a crosslinking system for fluoroelastomers comprising process for preparing a crosslinking system wherein the optimized quantities are comprising in the ranges -
a. a phase transfer catalyst in the range between 0.1 phr to 2.0 phr;
b. a non-bisphenol curative agent in the range between 0.1 phr to 4.0 phr;
c. a dispersing agent in the range between 0.2 phr to 3.0 phr;
d. a processing aid in the range between 0.5 phr to 5.0 phr; and
c. at least one additive in the range between 2.0 phr to 10 phr

Further aspects of the present invention are detailed in the description and examples sections below, wherein many changes can be made in the invention embodiments without departing from the scope of the disclosure.

DETAILED DESCRIPTION OF INVENTION
The present disclosure relates to a novel and safe crosslinking system free from bisphenols for fluoroelastomers.

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 the 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.

As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed elements.

The terms first, second, third, etc., should not be construed to limit the scope of the present disclosure as the aforementioned terms may be only used to distinguish one element, component, region, layer or section from another component, region, layer or section. Terms such as first, second, third etc., when used herein do not imply a specific sequence or order unless clearly suggested by the present disclosure.

In one embodiment according to the present invention, it provides a bisphenol-free, safe crosslinking system for fluoroelastomers comprising the components:
a) a phase transfer catalyst selected from quaternary ammonium or phosphonium salt;
b) a non-bisphenol curative agent;
c) a dispersing agent;
d) a processing aid; and
e) at least one additive.

In a further embodiment according to the present invention, the above-mentioned five components of the crosslinking system may be formulated as a single composition or as two or more components followed by other components of the compositions, while performing crosslinking process for the fluoroelastomers.

According to the present invention of bisphenol-free, safe crosslinking system for fluoroelastomers, wherein the step a) of the present embodiments, it provides phase transfer catalyst which are used for purpose of enhancing the reaction rates and improves crosslinking efficiency.

In a particular embodiment, inventors have used a phase transfer catalyst may be selected, but not limited to, quaternary ammonium salt or quaternary phosphonium salt.

In particular embodiment, inventors have used phase transfer catalyst as quaternary ammonium salt which are selected from cetyl trimethyl ammonium chloride, cetyl triethyl ammonium chloride, hexadecyl trimethyl ammonium chloride, lauryl trimethyl ammonium chloride, dodecyl trimethyl ammonium chloride, hexadecyl trimethyl ammonium iodide, cetyl trimethyl ammonium bromide, and cetyl trimethyl ammonium iodide or quaternary phosphonium salt which are selected from benzyl triphenyl phosphonium chloride, triphenylphosphonium chloride, trimethyl (4-vinyl benzyl) phosphonium chloride, and (methoxymethyl) triphenyl phosphonium chloride.

In the step b) of the present embodiments, it provides a non-bisphenol curative agent, wherein a non-bisphenol curative agent replaces bisphenol compounds from the conventionally known curative agents to ensure effective crosslinking without compromising safety.

In the step b) of the present embodiments, it provides a non-bisphenol curative agent may be selected, but not limited to, phloroglucinol (1,3,5-trihydroxy benzene), resorcinol (1,3-di-hydroxy benzene), phloroglucinol glucuronide, flavylium salt of phloroglucinol, fenoterol, resorcinol monobenzoate, resorcinol monoacetate, ellagic acid or mixture thereof.

In a particular embodiment, inventors have used phloroglucinol (1,3,5-trihydroxy benzene) with the formula C6H3(OH)3, however, in another particular example, the curing was performed using resorcinol (1,3-di-hydroxy benzene) with the formula C6H4(OH)2.

Inventors have observed that phloroglucinol (1,3,5-trihydroxy benzene) exhibit IC50 value about 863.6 ±0.06 µM, which apparently more than 11 times safe and better compared to Bisphenol AF having reported IC50 value of about 73.04 ±0.07 µM making the crosslinking system safe and bisphenol free with equivalent or improved desirable elastomer characteristics.

The overall difference observed by the inventors of this present invention was to provide a safer alternative to bisphenol, which resulted in the non-toxic, economic and providing superior or similar physico-mechanical properties along with compression set resistance (C-set) for the present invention of crosslinking system for fluoroelastomers.

In the step c) of the present embodiments, it provides a dispersing agent which maintains uniform distribution of components during the processing within the fluoroelastomer matrix.

In a particular embodiment, inventors have used a dispersing agent may be selected, but not limited to, di-acetone alcohol, polyethylene glycol 400 (PEG 400), dimethyl sulphoxide (DMSO), dimethyl formamide, methyl sulphonyl methane, fluorosilicone and cyclohexanol.

In the step d) of the present embodiments, it provides a processing aid which facilitates processing, ensuring consistent material properties of elastomer.

In a particular embodiment, inventors have used a processing aid may be selected, from a group comprising a carnauba wax (Sourced from Nanjing Tianshi New Material Technologies Co., Ltd. No.29, Caofang Road, Luhe Development Zone, Nanjing, China), a beeswax, and candelilla wax (sourced from Longchang Chemical Co. Ltd., Shibu Development Zone, Changyi City, Weifang City, Shangdong Province, China).

In the step e) of the present embodiments, it provides at least one additive which provides additional performance benefits, such as improved thermal stability or chemical resistance.

In a particular embodiment, inventors have used additives selected from, but not limited to, magnesium oxide (MgO), calcium oxide (CaO), barium oxide (BaO), magnesium hydroxide Mg(OH)2, calcium hydroxide Ca(OH)2 and barium hydroxide Ba(OH)2.

In another embodiment according to the present invention, it provides a process for preparing a crosslinking system for fluoroelastomers comprising mixing a curative agent, a phase transfer catalyst, a dispersing agent, a processing aid agent and an additive in the sequence to make pre-compound usable for crosslinking for fluoroelastomers / fluoropolymer.

In another embodiment according to the present invention, it provides a process for preparing a crosslinking system for fluoroelastomers, wherein the quantities are comprising in the ranges -
a. a phase transfer catalyst in the range between 0.1 phr to 2.0 phr;
b. a non-bisphenol curative agent in the range between 0.1 phr to 4.0 phr;
c. a dispersing agent in the range between 0.2 phr to 3.0 phr;
d. a processing aid in the range between 0.5 phr to 5.0 phr; and
e. at least one additive in the range between 2.0 phr to 10.0 phr

In another embodiment according to the present invention, it provides a process of preparing cross-linked fluoroelastomers comprising –
a. mixing components of cross-linking system according to claim 1 to the fluoroelastomer to obtain a first mixture, wherein the first mixture comprising a phase transfer catalyst; a non-bisphenol curative agent; and a dispersing agent;
b. adding to the first mixture a processing aid agent and an additive to obtain a second mixture; and
c. allowing the second mixture for maturing to obtain the cross-linked fluoroelastomers

In yet another embodiments of the present invention, it provides the process wherein crosslinking system is added for pre-compounded fluoroelastomer at temperature ranging between 35- 70°C for time duration ranging between 10-60 minutes.

In still another embodiments of the present invention, it provides a process wherein cross linked fluoroelastomer product obtained after mixing is subjected to maturation time ranging between 10- 50 hours.

In another embodiments of the present invention, the cross-linked fluoroelastomers produced by using the crosslinking system of the present disclosure may be used in aerospace applications, automotive application, sealing, O-ring applications and the like.

In an embodiment, the crosslinking system doesn’t cause acute health hazards and is non-toxic.

In an embodiment, the cross-linked fluoroelastomers have significant curing characteristics as compared to the existing crosslinking system.

In an embodiment, the cross-linked fluoroelastomers have significant and superior physico-mechanical properties as compared to the existing crosslinking system.

In an embodiment, the cross-linked fluoroelastomers have a significant compression set resistance (C-set) as compared to the existing crosslinking system.

The present invention is more particularly described in the following example that is intended as illustration only, since numerous modifications and variations within the scope of the present invention will be apparent to those skilled in the art. Unless otherwise noted, all parts, percentages, and ratios reported in the following examples are on a weight basis, and all reagents used in the examples were obtained or are available from the chemical suppliers.

The following examples illustrate the nature of the invention and are provided for illustrative purposes only and should not be construed to limit the scope of the invention.
Reference Example: Using Bisphenol AF as Curing agent and phase transfer catalyst benzyl tri-phenyl phosphonium chloride (BTPPC)

In the Step -1, the curative agent as bisphenol AF (2.0 phr) is added in the experimental batch, along with the phase transfer catalyst benzyl tri-phenyl phosphonium chloride (BTPPC) (0.5 phr) are mixed for 5-10 min to prepare pre-compound.
Adding this pre-compound mixture of step-1 into FKM elastomer (100 phr)
Step-2 comprise the additive as magnesium oxide (3.0 phr), calcium hydroxide (6.0 phr), MT carbon black (30 phr) were added with the pre-compounded FKM elastomer at 50oC for 10-15 min.
Step-3 comprise the mixing process, which was performed assisted with Brabender Plasticorder PLE 330 (Viscosity test machine), operating at a rotor speed of 20-60 rpm, to produce a final compound.
Step-4 Allowing this for a maturation time of 12-24 h.
Step-5 The cure characteristics of the compound were assessed using a rubber process analyser (D-RPA 3000).

The assessed results as per the analysis performed is summarized below:
Property Value
MH 24.6 dN.m
Tc90 4.0 min
Tensile strength 14.8 MPa
Elongation at break 218.9 %
Compression set: 70 hours at 200 oC 14.1 %

EXAMPLE: 01
In the Step -1, the curative agent as phloroglucinol (0.5 phr) is added in the experimental batch along with the phase transfer catalyst benzyl tri-phenyl phosphonium chloride (BTPPC) (0.7 phr) and dispersing agent as fluorosilicone (0.5 phr) are mixed for 5-10 min to prepare pre-compound.

Adding this pre-compound mixture of step-1 into FKM elastomer (100 phr)
Step-2 comprise the additive as magnesium oxide (3.0 phr), calcium hydroxide (6.0 phr), MT carbon black and carnauba wax as processing aid were added with the pre-compounded FKM elastomer at 50oC for 10-15 min.
Step-3 comprise the mixing process, which was carried out in a Brabender Plasticorder PLE 330, operating at a rotor speed of 20-60 rpm, to produce a final compound.
Step-4 Allowing this for a maturation time of 12-24 h.
Step-5 The cure characteristics of the compound were assessed using a rubber process analyser (D-RPA 3000).

The assessed results as per the analysis performed is summarized below:
Property Value
MH 15.2 dN.m
Tc90 3.9 min
Tensile strength 10.6 MPa
Elongation at break 195 %
Compression set: 70 h at 200 oC 32 %

EXAMPLE: 02
In the Step -1, the curative as resorcinol (0.65 phr) is added in the experimental batch, along with the phase transfer catalyst benzyl tri-phenyl phosphonium chloride (BTPPC) (0.7 phr), and dispersing agent as diacetone alcohol (0.5 phr) are mixed for 5-10 min to prepare pre-compound.

Adding this pre-compound mixture of step-1 into FKM elastomer (100 phr)
Step-2 comprise the additive as magnesium oxide (3.0 phr), calcium hydroxide (6.0 phr), MT carbon black and carnauba wax as processing aid were added with the pre-compounded FKM elastomer at 50oC for 10-15 min.
Step-3 comprise the mixing process, which was carried out in a Brabender Plasticorder PLE 330, operating at a rotor speed of 60 rpm, to produce a final compound.
Step-4 Allowing this for a maturation time of 12-24 h.
Step-5 The cure characteristics of the compound were assessed using a rubber process analyser (D-RPA 3000).

The assessed results as per the analysis performed is summarized below:
Property Value
MH 24 dN.m
Tc90 3.3 min
Tensile strength 11.2 MPa
Elongation at break 201 %
Compression set: 70 h at 200 oC 29 %

EXAMPLE: 03
In the Step -1, the Curative agent as phloroglucinol (0.5 phr) is added in the experimental batch, along with the Phase transfer catalyst cetyl trimethyl ammonium bromide (0.7 phr), and Dispersing agent as dimethyl sulfoxide (DMSO) (0.5 phr) are mixed for 5-10 min to prepare pre-compound.
Adding this pre-compound mixture of step-1 into FKM elastomer (100 phr)
Step-2 comprises the additive as magnesium oxide (3.0 phr), calcium hydroxide (6.0 phr), MT carbon black and carnauba wax as processing aid were added with the pre-compounded FKM elastomer at 50oC for 10-15 min.
Step-3 comprise the mixing process, which was carried out in a Brabender Plasticorder PLE 330, operating at a rotor speed of 60 rpm, to produce a final compound.
Step-4 Allowing this for a maturation time of 12-24 h.
Step-5 The cure characteristics of the compound were assessed using a rubber process analyser (D-RPA 3000).

The assessed results as per the analysis performed are summarized below:
Property Value
MH 17.2 dN.m
Tc90 4.2 min
Tensile strength 9.1 MPa
Elongation at break 189 %
Compression set: 70 h at 200 oC 32 %

EXAMPLE: 04
In the Step -1, the curative as -phloroglucinol (0.5 phr) is added in the experimental batch, along with the phase transfer catalyst benzyl tri-phenyl phosphonium chloride (BTPPC) (0.7 phr), and dispersing agent as dimethyl sulfoxide (DMSO) (0.5 phr) are mixed for 5-10 min to prepare pre-compound.
Adding this pre-compound mixture of step-1 into FKM elastomer (100 phr)
Step-2 comprise the additive as magnesium oxide (3.0 phr), calcium hydroxide (6.0 phr), MT carbon black and carnauba wax as processing aid were added with the pre-compounded FKM elastomer at 50oC for 10-15 min.
Step-3 comprise the mixing process, which was carried out in a Brabender Plasticorder PLE 330, operating at a rotor speed of 20-60 rpm, to produce a final compound.
Step-4 Allowing this for a maturation time of 12-24 h.
Step-5 The cure characteristics of the compound were assessed using a rubber process analyser (D-RPA 3000).

The assessed results as per the analysis performed is summarized below:
Property Value
MH 31.7 dN.m
Tc90 3.9 min
Tensile strength 13.8 MPa
Elongation at break 162 %
Compression set: 70 h at 200 oC 19 %

EXAMPLE: 05
In the Step -1, the curative agent as phloroglucinol (0.5 phr) is added in the experimental batch, along with the phase transfer catalyst benzyl tri-phenyl phosphonium chloride (BTPPC) (0.7 phr), and dispersing agent as dimethyl formamide (0.5 phr) are mixed for 5-10 min to prepare pre-compound.
Adding this pre-compound mixture of step-1 into FKM elastomer (100 phr)
Step-2 comprise the additive as magnesium oxide (3.0 phr), calcium hydroxide (6.0 phr), MT carbon black and carnauba wax as processing aid were added with the pre-compounded FKM elastomer at 50oC for 10-15 min.
Step-3 comprise the mixing process, which was carried out in a Brabender Plasticorder PLE 330, operating at a rotor speed of 60 rpm, to produce a final compound.
Step-4 Allowing this for a maturation time of 12-24 h.
Step-5 The cure characteristics of the compound were assessed using a rubber process analyser (D-RPA 3000).

The assessed results as per the analysis performed is summarized below:
Property Value
MH 15.1 dN.m
Tc90 3.2 min
Tensile strength 11 MPa
Elongation at break 211 %
Compression set: 70 h at 200 oC 28 %

EXAMPLE: 06
In the Step -1, the curative agent as phloroglucinol (0.5 phr) is added in the experimental batch, along with the phase transfer catalyst benzyl ammonium chloride (0.7 phr), and dispersing agent as dimethyl sulfoxide (DMSO) (0.5 phr) are mixed for 5-10 min to prepare pre-compound.
Adding this pre-compound mixture of step-1 into FKM elastomer (100 phr)
Step-2 comprise the additive as magnesium oxide (3.0 phr), calcium hydroxide (6.0 phr), MT carbon black and carnauba wax as processing aid were added with the pre-compounded FKM elastomer at 50oC for 10-15 min.
Step-3 comprise the mixing process, which was carried out in a Brabender Plasticorder PLE 330, operating at a rotor speed of 20-60 rpm, to produce a final compound.
Step-4 Allowing this for a maturation time of 12-24 h.
Step-5 The cure characteristics of the compound were assessed using a rubber process analyser (D-RPA 3000).

The assessed results as per the analysis performed is summarized below:
Property Value
MH 16.3 dN.m
Tc90 9.6 min
Tensile strength 11.3 MPa
Elongation at break 198 %
Compression set: 70 h at 200 oC 28

The unique bisphenol free, safe crosslinking system for fluoroelastomers developed according to the present invention comprising the components, a phase transfer catalyst selected from quaternary ammonium or phosphonium salt; a non-bisphenol curative agent; a dispersing agent; a processing aid; and an additive may be usable for commercial scale purposes for safe crosslinking fluoropolymer / fluoroelastomers development compared from reference example demonstrating use of bisphenol AF, which is often referred to as unsafe for polymers used in food grade polymers as their coatings.

TECHNICAL ADVANCEMENTS:
The present disclosure described hereinabove has several technical advantages including, but not limited to, the realization of a crosslinking system for fluoroelastomers, that:
• doesn’t cause acute health hazards;
• provides cross-linked fluoroelastomers having significant physic-mechanical properties;
• provides cross-linked fluoroelastomers having significant cure characteristics; and
• provides cross-linked fluoroelastomers improved or similar cure characteristics like rate of cure, state of cure and crosslinking density.

The embodiments herein and the various features and advantageous details thereof are explained with reference to the non-limiting embodiments in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.

The foregoing description of the specific embodiments so fully reveals the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.

The use of the expression “at least” or “at least one” suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the disclosure to achieve one or more of the desired objects or results.

Any discussion of documents, acts, materials, devices, articles or the like that has been included in this specification is solely for the purpose of providing a context for the disclosure. It is not to be taken as an admission that any or all of these matters form a part of the prior art base or were common general knowledge in the field relevant to the disclosure as it existed anywhere before the priority date of this application.

The numerical values mentioned for the various physical parameters, dimensions or quantities are only approximations, and it is envisaged that the values higher/lower than the numerical values assigned to the parameters, dimensions, or quantities fall within the scope of the disclosure unless there is a statement in the specification specific to the contrary.

While considerable emphasis has been placed herein on the components and component parts of the preferred embodiments, it will be appreciated that many embodiments can be made and that many changes can be made in the preferred embodiments without departing from the principles of the disclosure. These and other changes in the preferred embodiment, as well as other embodiments 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 bisphenol free, safe crosslinking system for fluoroelastomers comprising the components:
a) a phase transfer catalyst selected from quaternary ammonium or phosphonium salt;
b) a non-bisphenol curative agent;
c) a dispersing agent;
d) a processing aid; and
e) at least one additive.

2. A bisphenol free, safe crosslinking system as claimed in claim 1, wherein phase transfer catalyst as quaternary ammonium salt are selected from cetyl trimethyl ammonium chloride, cetyl triethyl ammonium chloride, hexadecyl trimethyl ammonium chloride, lauryl trimethyl ammonium chloride, dodecyl trimethyl ammonium chloride, hexadecyl trimethyl ammonium iodide, cetyl trimethyl ammonium bromide, and cetyl trimethyl ammonium iodide or quaternary phosphonium salt are selected from benzyl triphenyl phosphonium chloride, triphenylphosphonium chloride, trimethyl (4-vinyl benzyl) phosphonium chloride, and (methoxymethyl) triphenyl phosphonium chloride.

3. A bisphenol free, safe crosslinking system as claimed in claim 1, wherein non-bisphenol curative agent is selected from phloroglucinol (1,3,5-trihydroxy benzene), resorcinol (1,3-di-hydroxy benzene), phloroglucinol glucuronide, flavylium salt of phloroglucinol, fenoterol, resorcinol monobenzoate, resorcinol monoacetate, ellagic acid or mixture thereof.

4. A bisphenol free, safe crosslinking system as claimed in claim 1, wherein dispersing agent is selected from diacetone alcohol, polyethylene glycol 400 (PEG 400), dimethyl sulphoxide (DMSO), dimethyl formamide, methyl sulphonyl methane, fluorosilicone and cyclohexanol.

5. A bisphenol free, safe crosslinking system as claimed in claim 1, wherein processing aid agent is selected from carnauba wax or beeswax or Candelilla Wax or paraffin wax and additive is selected from magnesium oxide (MgO), calcium oxide (CaO), barium oxide (BaO), magnesium hydroxide Mg(OH)2, calcium hydroxide Ca(OH)2 and barium hydroxide Ba(OH)2.

6. The crosslinking system for fluoroelastomers as claimed in claim 1, wherein the quantities are comprising in the ranges and sequences-
a. a phase transfer catalyst in the range between 0.1 phr to 2.0 phr;
b. a non-bisphenol curative agent in the range between 0.1 phr to 4.0 phr;
c. a dispersing agent in the range between 0.2 phr to 3.0 phr;
d. a processing aid in the range between 0.5 phr to 5.0 phr; and
e. at least one additive in the range between 2.0 phr to 10.0 phr

7. A process of preparing cross-linked fluoroelastomers comprising –
a. mixing components of cross-linking system according to claim 1 to the fluoroelastomer to obtain a first mixture, wherein the first mixture comprising a phase transfer catalyst; a non-bisphenol curative agent; and a dispersing agent;
b. adding to the first mixture a processing aid agent and an additive to obtain a second mixture; and
c. allowing the second mixture for maturing to obtain the cross-linked fluoroelastomers.

8. A process of preparing cross-linked fluoroelastomers according to claim -7, wherein components of crosslinking system of step b. are added for pre-compounded fluoroelastomer at temperature ranging between 35- 70°C for time duration ranging between 10-60 minutes.

9. A process of preparing cross-linked fluoroelastomers according to claim -7, wherein step c. maturation time is ranging between 10- 50 hours.

10. A cross-linked fluorocarbon-based fluoroelastomer comprising
0.1 phr to 4.0 phr of a non-bisphenol curative agent selected from a group comprising of phloroglucinol, resorcinol, a phloroglucinol derivative, a resorcinol derivative, ellagic acid and mixture thereof.