Preparation process for remoldable thermosetting resin materials

Abstract

1. A process for preparing a remoldable thermoset resin material comprising curing an epoxy resin, wherein the curing is carried out using (a) at least one imidazole compound and (b) at least one benzotriazole compound.

Description

[Technical field]

[0001] The present invention relates to a process for preparing a remoldable thermoset material. [Background technology]

[0002] Thermosetting resin materials are materials that will or have undergone a chemical reaction by the action of heat, catalysts, UV light, etc., resulting in a relatively infusible state, meaning that these materials have a high melting point and cannot be easily melted. Their use has developed in recent years due to the crosslinks formed during the curing process. Curing is the process in which a chemical reaction occurs to produce a hardening toughening of the resin. Curing can be induced by UV or under the action of heat, or by the use of additives, commonly referred to as curing agents or hardeners. The crosslinking process eliminates the risk of the product remelting when heat is applied, and these materials are becoming essential in the sectors of coatings, adhesives, electronic laminates (such as those used in the manufacture of printed circuit boards), electrical insulators, electronics, appliances and automotive parts (such as leaf springs, pumps and electrical components).

[0003] Thermoset materials generally exhibit better thermomechanical properties and chemical resistance than thermoplastic materials due to their chemically crosslinked nature. Commonly utilized thermoset materials include vulcanized rubber, fiber reinforced polymer composites, polyester resins, polyurethanes, melamine and epoxy resins.

[0004] In particular, epoxy offers certain advantages over other materials, such as low density, tack, drape, processability, and low cost. Thermosetting epoxy materials are derived from epoxy resins that are polymerized in the presence of co-reactive curing agents (also known as hardeners), catalytic curing agents (also known as accelerators or catalysts), or both. Thanks to their outstanding overall performance, epoxy resins have been widely used to manufacture various coatings, composites, and adhesives for almost all industrial fields, including aerospace, new energy, electronic information, insulators, etc. For example, epoxy resins account for more than 90% of the utilization of packaging resins in integrated circuits and semiconductors, and the demand for epoxy resins in the electronic information industry is expected to grow every year.

[0005] In general, agents for curing epoxy resins may include hardeners, such as polyamines, acid anhydrides, phenols, etc., and curing catalysts, such as boron trifluoride (BF3) complexes, dicyandiamide, dibasic acid hydrazides, tertiary amines, imidazole compounds, etc. However, the main drawbacks of these materials are that they have poor corrosion resistance and insufficient electrical and mechanical properties at high temperatures.

[0006] Due to the cross-linked structure of the molecular segments, once these materials are cross-linked, the thermosetting material cannot be repaired or dissolved when it is cured, and the high-cost fillers doped therein cannot be recycled. Furthermore, thermosetting materials are difficult to reshape. Up to now, it has been difficult to produce thermosetting materials with high mechanical strength that can be easily melted and reshaped many times.

[0007] From the viewpoint of resource recycling, it has been desired that after the use of thermosetting resin materials in automobiles, electrical appliances, electronics, etc., they should be recovered and remolded again for reuse. Since thermosetting resin materials undergo irreversible chemical changes, crosslinking, during processing, they are difficult to remold by conventional methods. This is why in recent years, players in this related field have been hoping to develop thermosetting resin materials with excellent remoldable properties that can be reused several times without loss of thermal and mechanical properties for sustainable development.

[0008] Several approaches for preparing thermosetting materials can be found in the literature. A method for preparing thermoplastic or thermosetting remoldable soft polyurethanes is described by Chen Hong M., Journal of Polymer Research, 2021, 28:201. In this document, a unified method for synthesizing different remoldable polyurethanes is proposed. Polyethylene glycol (PEG) diol is selected as the soft segment, polycaprolactone (PCL) diol as the hard segment, and hexamethylene diisocyanate (HDI) is selected as the chain extender to link PEG and PCL. Polyurethanes with an NCO / OH ratio of 1.2 are thermoplastic, while those with an NCO / OH ratio of 2.4 are thermosetting. All polyurethanes are soft and can be remolded at approximately room temperature. However, this process results in low tensile strength and low glass transition temperature (T ) of thermosetting polyurethanes with limited deformability and reworkability. g ) values. Furthermore, such thermoset polyurethanes are not suitable for high performance space applications.

[0009] An epoxy thermoset resin containing dynamic silyl ether bonds and having good shape memory and reworkability is described by Qinfeng Liu, Macromol. Chem. Phys., 2019, 220, 1900149. In this document, bisphenol A epoxy resin and polypropylene glycol diglycidyl ether are used together, and the epoxy resin is reacted with a coupling agent ((3-aminopropyl)triethoxysilane) to produce an epoxy thermoset material. The resulting thermoset epoxy resin has good rework, remold and shape memory ability. However, this method has several drawbacks. First, the process involves the use of solvents such as ethanol and potassium hydroxide to obtain the epoxy thermoset material, which leads to the growth of impurities and requires purification. Therefore, the resulting material has a very low glass transition (T g ) temperature and tensile strength. Also, these materials have very poor thermomechanical stability. Overall, such epoxy thermoset materials have low shape recovery, poor repeatability and small distortion, which makes them unsuitable for use.

[0010] Therefore, according to the prior art described above, it is possible to overcome the drawbacks of the prior art processes and in particular to produce a polyolefin having a high glass transition temperature (T g ), there is a need to produce thermosetting materials with fast cure kinetics that have high tensile strength, solvent resistance and thermomechanical stability. Summary of the Invention

[0011] The above mentioned disadvantages are now overcome by a first aspect of the present invention which relates to a process for preparing a remoldable thermoset resin material comprising curing an epoxy resin, wherein the curing is carried out using (a) at least one imidazole compound and (b) at least one benzotriazole compound.

[0012] A second aspect of the invention relates to a remoldable thermoset material obtainable by the process according to the invention.

[0013] These and other features, aspects, and advantages of the present subject matter will become better understood with reference to the following description and appended claims. [Brief description of the drawings]

[0014] [Figure 1] Shows reshapeability effect. [Diagram 2] The cure kinetics are shown. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Those skilled in the art will know that the present disclosure is subject to variations and modifications other than those specifically described. The present disclosure should be understood to encompass all such variations and modifications. The present disclosure also encompasses all such steps, features, compositions and compounds mentioned or shown herein, individually or collectively, and any and all combinations of any or more of such steps or features.

[0016] definition For convenience, before further description of the present disclosure, certain terms used in the specification and examples are summarized here. These definitions should be read in light of the remainder of the disclosure and understood as by those skilled in the art. Terms used in the present specification have meanings that are recognized and known to those skilled in the art, however, for convenience and completeness, certain terms and their meanings are presented below.

[0017] The articles "a", "an" and "the" are used to refer to one or to more than one (i.e. to at least one) of the grammatical object of the article.

[0018] The term "and / or" is inclusive of the meanings "and" and "or".

[0019] The terms "comprise," "include," "including," and "comprising" are used in an inclusive, open sense, meaning that additional elements may be included. Throughout this specification, unless the context requires otherwise, these terms and variations thereof, such as "comprise," will be understood to imply the inclusion of a stated element or step or group of elements or steps, but not the exclusion of any other element or step or group of elements or steps. The term "comprising" is used to mean "including, but not limited to." "Including" and "including, but not limited to" are used interchangeably.

[0020] Ratios, concentrations, amounts, and other numerical data may be presented in a range format herein. It should be understood that such range formats are used merely for convenience and brevity, and should be interpreted flexibly to include not only the numerical values ​​explicitly recited as the limits of the range, but also all individual numerical values ​​or subranges contained within the range, as if each numerical value and subrange were explicitly recited. For example, a temperature range of 60°C to 180°C should be interpreted to include not only the explicitly recited range of 60°C to 180°C, but also subranges such as 80°C to 110°C, 150°C to 160°C, etc., and individual amounts including subquantities within the stated range, such as 135°C and 175.5°C.

[0021] The present invention provides a process for preparing a remoldable thermoset resin material comprising curing an epoxy resin, wherein the curing is carried out using (a) at least one imidazole compound and (b) at least one benzotriazole compound.

[0022] The present invention also provides a remoldable thermoset material obtainable by the process of the present invention.

[0023] The term "remoldable" as used within the framework of the present invention refers to the property of a thermosetting resin material that allows it to be reshaped again and again by heating without losing its thermal and mechanical properties. A thermosetting resin material is generally a liquid or malleable material at room temperature that irreversibly hardens upon heating or chemical addition. During heating or chemical addition, it forms certain bonds, called crosslinks, that hold the molecules in place and change the fundamental properties of the material, preventing it from melting. This process is called curing, and as a result, a thermosetting resin material cannot be melted and reshaped after it has hardened. The remoldable property is characterized by the glass transition temperature (T g It is possible to use the thermoset material without loss of its thermal and mechanical properties such as thermal expansion coefficient, tensile strength, fracture strain, storage modulus, thermal decomposition temperature, etc. With the property of being remoldable, such thermoset materials are strong, fully reworkable and recyclable and can be used in various sectors such as coatings, adhesives, electronic laminates (such as those used in the manufacture of printed circuit boards), electrical insulation, electronics, appliances and automotive parts (such as leaf springs, pumps and electrical components).

[0024] Within the context of the present invention, the expression "curable epoxy resin" is used according to its ordinary meaning, i.e. to denote a polymer containing multiple epoxide groups, which can produce a three-dimensional crosslinked thermoset structure by reaction of said epoxy groups with each other and / or with a suitable curing agent. As used herein, "epoxide groups" means vicinal epoxy groups, i.e. 1,2-epoxy groups. The epoxy resin used according to the present invention can be any conventional epoxy resin.

[0025] Examples of epoxy resins include glycidyl ether type epoxy resins prepared by the reaction of epichlorohydrin with polyhydric phenols such as bisphenol A, bisphenol F, bisphenol S, hexahydrobisphenol A, tetramethylbisphenol A, pyrocatechol, resorcinol, cresol, novolak, tetrabromobisphenol A, trihydroxybiphenyl, bisresorcinol, bisphenol hexafluoroacetone, tetramethylbisphenol F, and bixylenol; polyglycidyl ether type epoxy resins prepared by the reaction of epichlorohydrin with polyhydric (cyclo)aliphatic alcohols such as glycerol, neopentyl glycol, ethylene glycol, propylene glycol, butylene glycol, hexylene glycol, polyethylene glycol, and polypropylene glycol; glycidyl ether ester type epoxy resins prepared by the reaction of epichlorohydrin with hydroxycarboxylic acids such as p-oxybenzoic acid and β-oxynaphthoic acid; phthalic acid, methylphthalic acid, isophthalic acid, and the like. polyglycidyl ester type epoxy resins derived from polybasic carboxylic acids such as terephthalic acid, tetrahydrophthalic acid, hexahydrophthalic acid, endomethylenetetrahydrophthalic acid, endomethylenehexahydrophthalic acid, trimellitic acid, and high molecular weight aliphatic acids; glycidyl aminoglycidyl ether type epoxy resins derived from aminophenols and aminoalkylphenols; glycidyl aminoglycidyl ester type epoxy resins derived from aminobenzoic acid; glycidyl amine type epoxy resins derived from aniline, toluidine, tribromoaniline, xylylenediamine, diaminocyclohexane, bisaminomethylcyclohexane, 4,4'-diaminodiphenylmethane, and 4,4'-diaminodiphenylsulfone; epoxidized polyolefins, glycidyl hydantoin, glycidyl alkylhydantoin, and triglycidyl cyanurate; and monoepoxy compounds such as butyl glycidyl ether, phenyl glycidyl ether, alkylphenol glycidyl ether, glycidyl benzoate, and styrene oxide. They can be used independently or in admixture of two or more of them. The epoxy resins can be obtained according to methods known to those skilled in the art.

[0026] In the context of the present invention, the epoxy resin may comprise one or more epoxy resins. Typically, the epoxy resin of the present invention is a mixture of epoxy resins. In some embodiments, the epoxy resin may be advantageously selected from difunctional epoxy resins, trifunctional epoxy resins, tetrafunctional epoxy resins or mixtures thereof.

[0027] In some embodiments, the epoxy resin is a compound having two epoxy groups, such as a difunctional epoxy resin. A difunctional epoxy resin is generally an epoxy resin obtained from two functional epoxy groups (having two epoxy groups per molecule). Such an epoxy resin can be aromatic, alicyclic or aliphatic. Preferred examples of difunctional epoxy resins include bisphenol-type epoxy resins, epoxy resins having a biphenyl skeleton, epoxy resins having a naphthalene skeleton, epoxy resins having a binaphthalene skeleton and novolac-type epoxy resins. More preferably, the difunctional epoxy resin is a bisphenol-type epoxy resin, and most preferably, the difunctional epoxy resin is diglycidyl ether of bisphenol A (DGEBA).

[0028] In some embodiments, the epoxy resin is a compound having three epoxy groups, such as a trifunctional epoxy resin. A trifunctional epoxy resin is generally an epoxy resin obtained from three functional epoxy groups (having three epoxy groups per molecule). Such an epoxy resin can be aromatic, cycloaliphatic or aliphatic. Preferred examples of trifunctional epoxy resins include isocyanurate type epoxy resins and p-aminophenol type epoxy resins. More preferably, the trifunctional epoxy resin is an aminophenol type epoxy resin, and most preferably, the trifunctional epoxy resin is triglycidyl p-aminophenol (TGAP).

[0029] In some embodiments, the epoxy resin is a compound having four epoxy groups, such as a tetrafunctional epoxy resin. A tetrafunctional epoxy resin is generally an epoxy resin obtained from four functional epoxy groups (having four epoxy groups per molecule). Such an epoxy resin can be aromatic, cycloaliphatic, or aliphatic. Preferred examples of tetrafunctional epoxy resins include m-xylenediamine type epoxy resins and diphenylmethane type epoxy resins.

[0030] In some preferred embodiments, the epoxy resin used in the present invention is a mixture of difunctional and trifunctional epoxy resins.

[0031] In one preferred embodiment, the epoxy resin is a mixture of a diglycidyl ether of bisphenol A (DGEBA) and a trifunctional epoxy resin. In another embodiment, the epoxy resin is a mixture of a difunctional epoxy resin and triglycidyl para-aminophenol (TGAP).

[0032] In the most preferred embodiment, the epoxy resin is a mixture of diglycidyl ether of bisphenol A (DGEBA) and triglycidyl para-aminophenol (TGAP).

[0033] In some embodiments, the epoxy resin optionally comprises other epoxy resins apart from the epoxy resin and / or mixture of epoxy resins of the present invention. Such epoxy resins may be any conventional epoxy resin as described above.

[0034] The amount of difunctional epoxy resin in the mixture of difunctional and trifunctional epoxy resins is generally at least 50% by weight, preferably at least 65% by weight, more preferably at least 80% by weight, based on the total amount of epoxy resins in the mixture, and more preferably at most 90% by weight, based on the total amount of epoxy resins in the mixture.

[0035] The amount of trifunctional epoxy resin in the mixture of difunctional and trifunctional epoxy resins is generally at least 10% by weight, preferably at least 25% by weight, more preferably at least 45% by weight, based on the total amount of epoxy resins in the mixture, and more preferably at most 65% by weight, more preferably at most 50% by weight, based on the total amount of epoxy resins in the mixture.

[0036] In some embodiments of the present invention, the amount of difunctional epoxy resin in the mixture is 50% to 90% by weight and the amount of trifunctional epoxy resin is 50% to 10% by weight. Preferably, the amount of difunctional epoxy resin in the mixture is 65% to 80% by weight and the amount of trifunctional epoxy resin is 35% to 20% by weight.

[0037] In some embodiments, the imidazoles used in the present invention generally have the formula (A): [ka] (wherein R1 and R2, which are equal or different, are hydrogen, halogen, carbonyl or hydrocarbon, preferably C1-C 12 independently selected from the group consisting of alkyl or alicyclic (wherein the alkyl group may be linear, branched or cyclic) and aryl groups, optionally containing one or more heteroatoms or heteroatom-containing groups; Without being exhaustive, suitable aryl groups may be selected from the list consisting of phenyl, tolyl, xylyl, and the like.

[0038] Preferably, R1 is C1 to C 12 R1 is an alkyl group and R2 is hydrogen, more preferably R1 is methyl and R2 is hydrogen, and most preferably the imidazole compound is 1-methylimidazole.

[0039] In another embodiment, the imidazole used in the present invention has the formula (B): [ka] (wherein R3 and R4, which are equal or different, are hydrogen, halogen, carbonyl or a hydrocarbon, preferably C1-C 12 independently selected from the group consisting of alkyl or alicyclic (wherein the alkyl group may be linear, branched or cyclic) and aryl groups, optionally containing one or more heteroatoms or heteroatom-containing groups; Without being exhaustive, suitable aryl groups may be selected from the list consisting of phenyl, tolyl, xylyl, and the like.

[0040] Preferably, R3 is C1 to C 12 is an alkyl group and R4 is hydrogen, more preferably R3 is methyl and R4 is hydrogen, and most preferably the benzimidazole compound is 1-methylbenzimidazole.

[0041] The amount of the imidazole compound used in the present invention is generally 0.01 to 5 parts by weight per 100 parts by weight of the epoxy resin, more preferably 0.1 to 3.5 parts by weight per 100 parts by weight of the epoxy resin, and even more preferably 0.5 to 2 parts by weight per 100 parts by weight of the epoxy resin.

[0042] The amount of the benzotriazole compound used in the present invention is generally 1-65 parts by weight per 100 parts by weight of the epoxy resin, more preferably 5-50 parts by weight per 100 parts by weight of the epoxy resin, and even more preferably 15-35 parts by weight per 100 parts by weight of the epoxy resin.

[0043] In one embodiment of the present invention, the epoxy resin, the imidazole compound, and the benzotriazole compound are mixed together at the same time.

[0044] In another embodiment of the present invention, the imidazole compound and the benzotriazole compound are mixed first and the epoxy resin is then added to the mixture.

[0045] In some embodiments of the present invention, the epoxy resin and the imidazole compound are mixed first, and then the benzotriazole compound is added to the mixture.

[0046] In one preferred embodiment of the present invention, the epoxy resin and the benzotriazole compound are first mixed, and then the imidazole compound is added to the mixture.

[0047] The epoxy resin, imidazole compound and benzotriazole compound used in the present invention are advantageously dry mixed at room temperature and can be subsequently gently heated. The mixing is carried out by simply mixing without the use of any solvent. The imidazole compound and benzotriazole compound can be soluble in the epoxy resin without the inclusion of any solvent. Without being bound by theory, the use of a solvent can result in a decrease in the high heat properties of the corresponding cured thermoset material, and requires an additional purification step to remove impurities formed as a result of adding the solvent, increasing the working time of the entire process. In the method of the present invention, the reaction mixer does not contain a solvent.

[0048] The resulting mixture undergoes curing. Curing generally occurs first at room temperature, an initial curing stage. This stage controls the exotherm and aids in homogeneous crosslinking of the reaction mixture. The mixture forms a gel state. This is followed by a second cure at elevated temperatures that can vary over a wide range.

[0049] Preferably, the temperature of the second curing step is in the range of 50°C to 200°C, more preferably the temperature is in the range of 80°C to 160°C. The second curing step is performed to complete the curing process and harden the remaining parts of the mixture. The mixture is allowed to harden to a solid state and can be molded. Curing the mixture directly at high temperatures without forming a gel state makes the viscosity lower, allowing the mixture to flow or sag more easily.

[0050] Advantageously, various additives, such as diluents, pigments, fillers, fibrous materials, dyes, resins, polyolefins, plasticizers, and non-volatile extenders such as coal tar, coal tar pitch and asphalt bitumen, e.g. blown or cutback bitumen prepared from asphalt bitumen and aromatic lubricating oil extracts, pine oil, pine tar, lubricating oil and aromatic extracts thereof, may be added to the mixture before curing.

[0051] Advantageously, a solvent can be added after the step of mixing the epoxy resin, the imidazole compound and the benzotriazole compound.Suitable solvents are ketones such as acetone, methylcyclohexanone and diacetone alcohol; esters such as ethyl acetate and n-butyl acetate; glycol ethers such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether and their acetates.

[0052] Curing of the epoxy resin can be accomplished with or without the addition of other hardeners; nevertheless, it is preferred to use other hardeners in combination with the curable epoxy resin. As used herein, the term "other hardeners" refers to compounds other than the imidazoles and benzotriazoles of the curable epoxy resin that can be used as hardeners.

[0053] Common classes of curing agents for epoxy resins include amines (including polyamines), polyamidoamines, polyamides, acids, anhydrides, phenols, alcohols and thiols. Suitable curing agents can be selected from those for epoxy resins by anyone skilled in the art depending on the curable epoxy resin or mixture of resins selected for use herein.

[0054] According to a preferred embodiment, the curing agent is selected among those that have only limited or no reactivity with the curable epoxy resin at room temperature but are capable of reacting with the epoxy groups of the curable epoxy resin at elevated temperatures, so that a formulation of the curable epoxy resin and the curing agent can be prepared and stored for a period of time before use.

[0055] Advantageously, curing is optionally carried out in the presence of an electrically or thermally conductive filler or a non-conductive filler.Suitable conductive fillers are carbon black, graphite, gold, silver, copper, platinum, palladium, nickel, aluminum, silicon carbide, boron nitride, diamond and alumina.Suitable non-conductive fillers are vermiculite, mica, wollastonite, calcium carbonate, titania, sand, glass, fused quartz, fumed silica, barium sulfate and particles of halogenated ethylene polymers such as trifluoroethylene, tetrafluoroethylene, vinylidene fluoride, vinylidene fluoride, vinylidene chloride and vinyl chloride or combinations thereof.

[0056] Curing is advantageously first carried out at room temperature for 1h to 55h, preferably 8h to 45h, more preferably 15h to 35h. After the first room temperature curing, it is further cured at a temperature of 20°C to 220°C, preferably at a temperature of 40°C to 190°C, more preferably at a temperature of 60°C to 180°C.

[0057] The remoldable thermosetting resin material is advantageously obtained by first heating an epoxy resin and a benzotriazole compound. The mixture is cooled to provide a resin mixture. The obtained resin mixture is then cooled at room temperature to further avoid crosslinking reactions. After the mixture is completely cooled, an imidazole compound is added to the resin mixture and mixed thoroughly. The obtained mixture is degassed under vacuum to obtain a final resin mixture, and the mixture is cured to obtain a remoldable thermosetting resin material.

[0058] In one preferred embodiment, the remoldable thermosetting resin material is obtained by first mixing a difunctional epoxy resin and a trifunctional epoxy resin in a standard beaker. Any air bubbles generated in the mixture during the mixing process are removed by degassing the resin by applying a vacuum in a vacuum oven at room temperature. Benzotriazole is then added into the resin mixture, which is uniformly dispersed in the resin mixture to form a paste-like viscous mixture. The mixture is heated with continuous stirring on a hot plate to melt the benzotriazole and mix it into the epoxy resin. The mixture becomes transparent when the benzotriazole is completely melted and mixed with the resin. The mixture is cooled to room temperature to avoid any excessive crosslinking reaction. Once the mixture is completely cooled to room temperature, imidazole is added to the mixture, which is then degassed at room temperature under vacuum in an oven. Any conventional mixing technique operated by a suitable mixing device can be used to achieve the mixing of the aforementioned components.

[0059] The remoldable thermoset material as obtained according to the present invention advantageously exhibits remoldability at temperatures between 90°C and 200°C, preferably between 120°C and 180°C, more preferably between 140°C and 150°C.

[0060] The remoldable thermoset materials as obtained according to the invention advantageously exhibit a glass transition temperature (Tg) between 70° C. and 150° C., preferably between 90° C. and 130° C., more preferably between 110° C. and 115° C. The glass transition temperature (Tg) is measured according to ASTM D3418 at midpoint by differential scanning calorimetry (DSC) at a scan rate of 20° C. / min.

[0061] The remoldable thermoset material as obtained according to the invention advantageously exhibits a tensile strength of at least 70 MPa, preferably at least 85 MPa, more preferably at least 99 MPa, as measured by a Universal Testing Machine (UTM) (Zwick / Z030).

[0062] A second aspect of the invention relates to a remoldable thermoset material obtainable according to the process of the invention.

[0063] Remoldable thermoset resin materials are generally obtained by curing an epoxy resin, where the curing is carried out according to the process of the present invention using (a) at least one imidazole compound and (b) at least one benzotriazole compound.

[0064] The remoldable thermosetting resin material as obtained by the process of the present invention can be advantageously used for the manufacture of cured articles by molding, coating or impregnating with a composition comprising at least one epoxy resin, at least one imidazole and at least one benzotriazole compound as previously described herein. The cured product adheres very well to a wide variety of substrates, such as steel, aluminum, glass, wood, concrete, etc., and the composition can be used as an adhesive for such materials, for encapsulating electrical devices and their parts, and for producing castings, laminates, moldings and coatings.

[0065] The method according to the invention overcomes the drawbacks of the prior art processes and has a number of advantages. It provides a remoldable thermoset material obtained without the use of any solvent, thereby not forming any impurities and eliminating the process of purification. The remoldable thermoset material as obtained by the process of the invention involves very little working time, is sustainable and can be remolded several times for reuse.

[0066] Reformability is achieved at temperatures above 150° C. The resulting thermoset materials have high glass transition temperatures (Tg) above 110° C., high tensile strengths above 85 MPa, good thermomechanical stability, excellent shape recovery, fast cure kinetics, high solvent resistance, high reproducibility and high distortion.

[0067] The examples provided herein further describe and demonstrate embodiments of the present invention. The examples are presented for illustrative purposes only and should not be construed as limitations of the present invention. EXAMPLES

[0068] Example (according to the present invention) The following examples illustrate the process for preparing a remoldable thermoset material.

[0069] raw materials: For the preparation of the thermosetting material the following starting materials were used: Difunctional epoxy (LAPOX® B11 (3101)), Atul Ltd; trifunctional epoxy (Araldite® MY 0510CH), Huntsman; benzotriazole (BTA), Sigma Aldrich; 1-methylimidazole (IM), Sigma Aldrich.

[0070] DSC technique is used to measure various properties of remoldable thermoset materials. The instrument used is a TA Instrument (Q2000). A Universal Testing Machine (UTM) is used to measure mechanical properties. The instrument used is a Zwick-Z030.

[0071] Stoichiometry: The epoxy resin, benzotriazole and imidazole stoichiometries are summarized in Table 1. Stoichiometry refers to the relationship between the amounts of raw materials taken during an experiment.

[0072] [Table 1]

[0073] Mixed Protocol: The di- and tri-functional epoxy materials were weighed out as per stoichiometry and mixed thoroughly in a beaker. The mixture of di- and tri-functional epoxy mixture was allowed to settle. In case of air bubble entrapment during the mixing process, the resin was degassed by applying vacuum in a vacuum oven at room temperature. Benzotriazole (BTA) was weighed out as per stoichiometry and added into the resin mixture. Benzotriazole was completely dispersed in the epoxy mixture to form a paste-type viscous mixture. Since benzotriazole is a solid, at this stage it was not soluble in the epoxy and remained only in dispersed form. The mixture was heated at 60°C with continuous stirring on an ultra hot plate for 1-2 minutes to melt the benzotriazole and mix it into the epoxy mixture. After complete melting of the benzotriazole, the mixture became transparent. The mixture was immediately cooled to room temperature to avoid further crosslinking reaction. After the mixture was cooled to room temperature, methylimidazole (MI) was added to the resin mixture as per stoichiometry and mixed thoroughly. The resulting resin and hardener mixture (benzotriazole and methylimidazole) were degassed in an oven under vacuum at room temperature for 15 minutes. The resin was poured into silicone molds to form specimens for testing.

[0074] Curing protocol: Hold: 24h at room temperature Hold: 80℃ for 1 hour Ramp: From 80℃ to 160℃ in about 1 hour (80℃→120℃→160℃) Hold: 160℃ for 2 hours

[0075] After the resin and hardener mixture was poured into a silicone mold, it was cured at room temperature for 24 h. After the initial room temperature cure, the material was further cured in an oven at 80° C. for 1 h. After 1 h at 80° C., the temperature was slowly increased to reach 80° C. to 160° C. in the oven within 1 h. At 160° C., the material was further cured for 2 h. After the curing process, the material was allowed to cool and equilibrate to room temperature overnight before proceeding for any characterization.

[0076] Samples were then taken to measure various properties of the formulations.

[0077] Remoldable properties: A rectangular aluminum thin sheet mold cavity was prepared to mold the samples into shape. The samples were first heated in the aluminum sheet cavity at 150°C to mold the article. Once the article was made, the samples were heated again at 140°C to remold the article. The original shape was restored in 60 seconds. The remoldability effect is shown in Figure 1.

[0078] The formulation appears to have good reshapeability / reversibility at elevated temperatures. Reshapeability is achieved at 140°C.

[0079] Thermal and Mechanical Properties Samples were taken for DSC analysis (TA Instrument-Q2000) and UTM (Zwick-Z030) to measure the thermal and mechanical properties, respectively, and the results are shown in Table 2.

[0080] [Table 2]

[0081] From Table 2, it appears that the sample has obtained excellent properties with a glass transition temperature of 115°C, a tensile strength of 99 MPa, a strain at break of 6%, a storage modulus of 2.4 GPa, low water absorption of 1.5% after 520 hours and remoldability above 150°C.

[0082] curing kinetics DSC analysis (TA Instrument-Q2000) was performed on the samples at different ramp rates to understand the cure kinetics of the samples. Ramp rates 1°C / min, 3°C / min, 5°C / min and 10.00°C / min up to 350.00°C. The cure kinetics are shown in Figure 2. In Figure 2, the light curve represents the formulation according to the invention; the dark curve represents the standard formulation (IM / dicyandiamide cured); the dotted line represents the point where cure begins for the formulation according to the invention; and the diagonal line represents the ramp rate temperature followed in the analysis.

[0083] The cure of the formulation according to the invention is complete in 25 minutes at maximum cure, whereas the cure of the standard formulation appears to be complete in 40 minutes at maximum cure. Hence, the formulation according to the invention has fast cure kinetics when compared to the commercially available fast curing formulation (IM / dicyandiamide cure).

[0084] Shelf Life Studies Samples were taken for DSC analysis (TA Instrument-Q2000) to measure shelf life at sub-ambient temperatures, and the results are shown in Table 3.

[0085] [Table 3]

[0086] Formulations stored at 0° C. and 5° C. for 24 h appear to exhibit a percentage of crosslinking and an increase in viscosity, which provides maximum flexibility and optimal physical properties for the cured resin.

[0087] According to the above results, the applicant can prepare a remoldable thermoset resin material by curing epoxy resin with a curable amount of benzotriazole compound and imidazole compound. The remoldable thermoset resin material obtained by the process of the present invention has excellent thermal and mechanical properties with a glass transition temperature (Tg) at 115°C, a tensile strength of 99 MPa, a breaking strain of 6%, a storage modulus of 2.4 GPa, a thermal decomposition temperature (Td) of 365 and a lap shear strength of 10.9. The remoldable thermoset resin material obtained by the above process of the invention has remoldability at 140°C, fast curing kinetics and excellent solvent resistance.

[0088] It provides thermosetting resin materials with remoldable properties and excellent glass transition temperature and tensile strength, which allows them to be restored and remolded several times, making it possible to reuse these thermosetting materials in automobiles, coatings, adhesives and automobile parts.

Claims

1. 1. A process for preparing a remoldable thermoset resin material comprising curing an epoxy resin, wherein the curing is carried out using (a) at least one imidazole compound and (b) at least one benzotriazole compound.

2. 2. The process of claim 1, wherein the epoxy resin comprises one or more epoxy resins.

3. 3. The process of claim 1 or 2, wherein the epoxy resin is a mixture of a difunctional epoxy resin and a trifunctional epoxy resin.

4. The process according to any one of claims 1 to 3, wherein the epoxy resin is a mixture of diglycidyl ether of bisphenol A (DGEBA) and triglycidyl para-aminophenol (TGAP).

5. 5. The process according to claim 3 or 4, wherein the difunctional epoxy resin is added in an amount of 65% to 100% by weight based on the total amount of epoxy resin.

6. The process according to any one of claims 3 to 5, wherein the trifunctional epoxy resin is added in an amount of 25% to 65% by weight based on the total amount of epoxy resin.

7. 7. The process according to any one of claims 3 to 6, wherein in the mixture of difunctional and trifunctional epoxy resins, the amount of difunctional epoxy resin is 50% to 90% by weight and the amount of trifunctional epoxy resin is 50% to 10% by weight.

8. 8. The process according to any one of claims 1 to 7, wherein the benzotriazole compound is added in an amount of 5 to 50 parts by weight per hundred parts by weight of the epoxy resin.

9. 9. The process according to any one of claims 1 to 8, wherein the imidazole compound is added in an amount of 0.1 to 3.5 parts by weight per hundred parts by weight of the epoxy resin.

10. The process according to any one of claims 1 to 9, wherein the imidazole compound is 1-methylimidazole.

11. The process according to any one of claims 1 to 10, wherein the epoxy resin and the benzotriazole compound are first mixed and the imidazole compound is added to the mixture.

12. A remoldable thermoset material obtainable by the process according to any one of claims 1 to 11.

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