WO2020033036A1

WO2020033036A1 - Epoxy resin composition

Info

Publication number: WO2020033036A1
Application number: PCT/US2019/036232
Authority: WO
Inventors: Timothy Morley; Rainer Koeniger; Martin Reimers; Luca LOTTI; Nebojsa JELIC; Zeljko SIKMAN
Original assignee: Dow Global Technologies Llc
Priority date: 2018-08-08
Filing date: 2019-06-10
Publication date: 2020-02-13

Abstract

A novel curable epoxy resin composition capable of fast curing and having an increased latency without negatively impacting the glass transition temperature or mechanical performance of the composition; the composition including (i) an epoxy resin compound; and (ii) a liquid-based hardener composition containing a combination of (a) at least one amine-based hardener, (b) at least one catalyst, (c) at least one sulfanilamide, and (d) at least one cycloaliphatic amine; and a composite article made from the above curable epoxy resin composition.

Description

EPOXY RESIN COMPOSITION

FIELD

The present invention relates to an epoxy resin composition and a composite made from such composition suitable for use in composite spring/suspension applications.

BACKGROUND

A fast curing performance window is critical for the mass production of carbon and glass fiber-based applications such as structural automotive body components and composite spring/suspension applications. For example, when considering glass fiber spring and suspension applications versus body structures there is typically a larger impact of the resin composition on the mechanical performance of the final composite, hence the resin composition should be carefully designed to obtain a good mechanical performance in the composite while maintaining a high cure speed.

A key processing design feature of any successful resin composition for the production of glass fiber spring or suspension components should be a composition’s open time that is as long as possible at the desired molding temperature while not limiting the demolding time. Typically, for the molding of spring and suspension components produced via the resin transfer molding process (RTM), the open time of the resin composition should be long enough at a mold temperature of 90 degrees Celsius (°C) to enable the injection of at least 1 kilogram (Kg) to over 10 Kg of the resin composition depending on the part size to be produced. This resin

composition injection volume can be expected to be even greater than 10 Kg when a multiple cavity mold is used. However, while epoxy resin compositions can be designed to inject the 1 Kg to 10 Kg composition injection volumes, the drawback is a significant increase in the time period from the mold filling time of the composition to the demolding time of the final composite. For example, such longer time periods can take as much as up to 15 minutes (min) to 20 min.

A fast curing resin system has been described for the aforementioned composite spring/suspension applications in U.S. Provisional Patent Application No. 62/503,975, entitled “SULFANILAMIDE CONTAINING EPOXY RESIN COMPOSITIONS”, filed May 10, 2017, by Morley et al. (Attorney Docket No. 79810). The above patent application discloses the use of a hardener composition containing: (1) sulfanilamide, (2) triethylenetetramine- European (TETA-E), (3) a suitable catalyst, and (4) a cycloaliphatic amine. The hardener composition disclosed in the above patent application is then subsequently reacted with an epoxy resin to give a fast (e.g., 300 seconds (s) or less) curing epoxy composition. The cycloaliphatic amine used in the hardener composition or formulation disclosed in the above patent application, is disclosed as being PACM, otherwise known as 4,4'-methylene-bis(cyclohexylamine).

It is well known to those skilled in the art that when fast curing formulations are mixed via hand and applied to a hot mold, the gel times are typically much longer than fast curing formulations that are mixed using an RTM machine. The reason is that RTM machines use high pressure mixing coupled with high resin temperatures which increases the reactivity, and hence shorten the gelation time, of the resin system. This is the case with the formulation disclosed in the above-mentioned patent application where a decrease in the gel time of 60 s is noted when the resin is mixed and applied with an RTM machine compared to a resin that is mixed and applied by hand.

While the hardener composition described in the above patent application provides an epoxy resin composition that exhibits good latency, it is still desired to provide a hardener composition that can provide a resin composition with increased latency (i.e., an increased open time) to allow for an extended infusion time of the resin composition while maintaining a sufficiently fast molding time of the resin composition; and still providing a fast demolding time of the final composite.

SUMMARY

In one embodiment, the present invention is directed to a hardener formulation or composition for a resin composition. The hardener composition includes, for example, a combination of (a) at least one hardener, (b) at least one catalyst, (c) at least one accelerator, and (d) at least one cycloaliphatic amine.

In another embodiment, the present invention relates to a two-component curable resin composition including (i) one or more polymer resins and (ii) the above hardener composition.

In still another embodiment, the present invention includes a composite comprising (A) at least one structural material such as heat resistant fibers and (B) the above two-component curable resin composition.

In yet other embodiments, the present invention includes processes of manufacturing:

(1) the above hardener composition, (2) the two-component curable resin and (3) the composite. In one preferred embodiment, the cycloaliphatic amine present in the above hardener composition can include, for example, isophorone diamine (IPDA). It has been found that a cycloaliphatic amine such as IPDA used in the above hardener composition can have a significant impact on the latency, and hence open time, of a curable resin system. For example, when using IPDA as the cycloaliphatic amine component of a hardener composition, the gel time of the resin system when processed via RTM can be significantly increased up to an additional 30 s while still maintaining the demold time of 300 s at the critical mold temperature of 90 °C.

As a result of the novel hardener composition using IPDA, a much longer infusion time can be obtained from a resin composition containing the novel hardener, particularly in producing large structures, while still allowing a fast demolding time. For example, with an injection rate of 100 grams per second (g/s) via a RTM, an additional 30 s of longer infusion time of a resin system can be realized using the hardener composition of the present invention. The longer infusion time can translate to, for example, a resin composition injection volume of up to a further 3,000 grams (g) of curable resin composition to be injected into a mold for forming composites.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a graphical illustration of a line graph showing gel time (i.e. latency) versus mold temperature for two resin compositions. A high latency is shown for the resin composition of Example 2 of the present invention when the composition is mixed using a RTM machine.

DETAILED DESCRIPTION

In one broad embodiment, a novel hardener composition is used with one or more polymer resins, such as an epoxy resin, to form a to a two-component curable resin composition; and in another embodiment, the curable resin composition can be cured with heat resistant fibers to form a composite article. The hardener composition includes, for example, a combination of (a) at least one hardener compound, (b) at least one catalyst compound, (c) at least one accelerator compound, and (d) at least one cycloaliphatic amine compound.

The hardener compound, component (a), used to form the hardener composition can include for example dicyandiamide (DICY), phenylene diamines (particularly the meta-isomer), bis(4-amino-3 ,5-dimethylphenyl)- 1 ,4-diisopropylbenzene, bis(4-amino-phenyl) 1 ,

4-diiospropylbenzene, diethyl toluene diamine, methylene dianiline, mixtures of methylene dianiline and polymethylene polyaniline compounds (sometimes referred to as PMDA, including commercially available products such as DL-50 from Air Products and Chemicals),

diaminodiphenylsulfone, phenolic hardeners including those represented by the following Structure (I):

where each Y independently represents a halogen atom, each z is independently a number from 0 to 4 and D is a divalent hydrocarbon group as described with regard to Structure (I) above.

Examples of suitable phenolic hardeners useful in the present invention may include dihydric phenols such as bisphenol A, bisphenol K, bisphenol F, bisphenol S and bisphenol AD, and mixtures thereof, and the mono-, di-, tri- and tetra-brominated counterparts of the

aforementioned phenols; and amino-functional polyamides; and mixtures thereof. Some of the above phenolic hardeners useful in the present invention are available commercially. For example, phenolic hardeners under the tradenames Versamide™ 100, Versamide™ 115, Versamide™ 125 and Versamide™ 140 are available from Henkel. And, for example, phenolic hardeners under the tradenames Ancamide™ 100, Ancamide™ 220, Ancamide™ 260A and Ancamide™ 350A are available from Air Products and Chemicals.

In other embodiments, the hardener compound useful in the present invention may include, for example, primary and/or secondary aliphatic amine compounds including for example linear or branched polyethyleneamines such as ethylenediamine, diethylenetriamine, triethylenetetraamine, tetraetylenepentamine, and the like, aminoethylpiperazine, amine terminated polyethers known under the tradename of Jeffamines, cycloaliphatic diamines such as bis-(p-aminocyclohexyl)methane (PACM), diaminocyclohexane (DACH),

bis-(dimethyldiaminocyclohexyl)methane (DMCH); and mixtures thereof.

The amount of the hardener compound present in the hardener composition can be generally in the range of from 5 weight percent (wt %) to 99 wt % in one embodiment; from 20 wt % to 90 wt % in another embodiment; and from 40 wt % to 80 wt % in still another embodiment, based on the weight of the hardener composition. The catalyst compound, component (b), used to form the hardener composition may include, for example, any one or more of suitable catalysts described in, for example, U.S. Patent

Nos. 3,306,872, 3,341,580, 3,379,684, 3,477,990, 3,547,881, 3,637,590, 3,843,605, 3,948,855, 3,956,237, 4,048,141, 4,093,650, 4,131,633, 4,132,706, 4,171,420, 4,177,216, 4,302,574,

4,320,222, 4,358,578, 4,366,295, and 4,389,520; and WO 2008/140906. Examples of suitable catalysts useful in the present invention may include imidazoles such as 2-methylimidazole; 2-ethyl-4-methylimidazole; 2-phenyl imidazole; tertiary amines such as triethylamine, tripropylamine, N,N-dimethyl-l-phenylmethaneamine and 2,4,6-tris((dimethylamino)- methyl)phenol and tributylamine; phosphonium salts such as ethyltriphenylphosphonium chloride, ethyltriphenylphosphonium bromide and ethyltriphenyl-phosphonium acetate;

ammonium salts such as benzyltrimethylammonium chloride and benzyltrimethylammonium hydroxide; various carboxylic acid compounds, and mixtures of any two or more thereof. In one preferred embodiment, the catalyst compound useful in the present invention may include for example 2,4,6-tris(dimethylaminomethyl)phenol.

The amount of the catalyst compound present in the hardener composition can be generally in the range of from 0.1 wt % to 40 wt % in one embodiment; from 1 wt % to 20 wt % in another embodiment; and from 1 wt % to 10 wt % in still another embodiment, based on the weight of the hardener composition.

The accelerator compound, component (c), used to form the hardener composition includes for example water; a compound having at least one hydroxyl group and an equivalent weight per hydroxyl group of up to 75; and mixtures thereof.

In some embodiments, the reaction mixture can contain water; a compound having at least one hydroxyl group and an equivalent weight per hydroxyl group of up to 75 in one embodiment, and up to 50 in another embodiment; and mixtures thereof. The water and/or the above compound having at least one hydroxyl group, if present, can be suitably present in small amounts, such as from 0.1 part by weight per part by weight of triethylene diamine (parts) to 10 parts in one embodiment; from 0.25 part to 5 parts in another embodiment; and from 1 part to 3 parts in still another embodiment.

Besides water, suitable compounds having at least one hydroxyl group may include, for example, alkanols such as methanol, ethanol, 1 -propanol, 2-propanol, 1 -butanol, 2-butanol, l-pentanol, neopentanol, l-hexanol, and the like, and mixtures thereof; alkylene glycols such as ethylene glycol, 1, 2-propane diol, 1, 3-propane diol, 1, 4-butane diol, neopentyl glycol, and the like, and mixtures thereof; poly(alkylene glycols) such as diethylene glycol, triethylene glycol, dipropylene glycol, tripropylene glycol, and the like, and mixtures thereof; glycol monoethers such as ethylene glycol monomethyl ether, diethylene glycol monomethyl ether, 1, 2-propane diol monomethyl ether, dipropylene glycol monomethyl ether, as well as the corresponding ethyl ethers; glycol monoesters such as ethylene glycol monoacetate, diethylene glycol monoacetate,

1, 2-propane diol monoacetate, dipropylene glycol monoacetate and the like, and mixtures thereof; higher functionality polyols such as glycerin, oligomers of glycerin, trimethylolpropane, trimethylolethane, pentaerythritol, erythritol, sorbitol, sucrose, and the like, and mixtures thereof; and mono- di- or trialkanolamines such as monoethanolamine, diethanolamine, triethanolamine, monoisopropanolamine, diisopropanolamine, triisopropanolamine, aminoethylethanolamine, and the like, and mixtures thereof. One of the preferred accelerator compounds useful in the present invention can be sulfanilamide.

Many of the widely used aromatic based amine hardener compositions of the prior art have some undesirable features such as insolubility in other compatible chemicals, and many of the prior art compositions are toxic. Sulfanilamide, containing a chemical structure as illustrated below by Structure (II), is generally considered to be non-toxic and has been found to be highly soluble in triethylenetetramine leading to formulations displaying improved mechanical performance when used to prepare a composite article, whilst at the same time displaying the ability to achieve a fast curing time.

The amount of the accelerator compound present in the hardener composition can be generally in the range of from 0.1 wt % to 30 wt % in one embodiment; from 1 wt % to 25 wt % in another embodiment; and from 5 wt % to 20 wt % in still another embodiment, based on the weight of the hardener component.

The cycloaliphatic amine compound, component (d), used to form the hardener composition can include, for example, one or more aminocyclohexanealkylamines.

Aminocyclohexanealkylamines are substituted cyclohexanes that have an amino substituent and an aminoalkylsubstitutent on the cyclohexane ring. Among the aminocyclohexanealkylamine compounds useful in the present invention can be those represented by the following Structure

(HI):

wherein R¹ is Ci-C₄ alkyl, each R is independently hydrogen or Ci-C₄ alkyl and m is a number from 1 to 8. Each R group in Structure (III) can be independently hydrogen or methyl, and R¹ can be methyl. In Structure (III), the -(CR₂)_m-NH₂ group may be positioned in ortho-, meta- or para- with respect to the amino group bonded directly to the cyclohexane ring. The -NH₂ and - (CR₂)_m-NH₂ groups in Structure (III) may be in the cis- or trans- positions with respect to each other. In Structure (III), the cyclohexane carbon atoms may contain substituent groups in addition to the -NH₂, -R¹ and -(CR₂)_m-NH₂ groups shown inert with respect to the epoxy-amine reaction. In one preferred embodiment, the cycloaliphatic amine compound corresponding to Structure (III) can be cyclohexanemethanamine, 4-amino-a,a,4-trimethyl-(9Cl), which is also known as p-menthane-l, 8-diamine or l,8-diamino-p-menthane.

In another embodiment, the aminocyclohexanealkylamine compound useful in the present invention may include the compounds corresponding to the following chemical Structure (IV):

wherein in Structure (IV), R, Ri and m can be as defined before. In one preferred embodiment, each R group in Structure (IV) can be independently hydrogen or methyl and R¹ can be methyl. In Structure (IV), the -(CR₂)_m-NH₂ group may be positioned in ortho-, meta- or para- with respect to the amino group bonded directly to the cyclohexane ring. The -NH₂ and -(CR₂)_m-

NH₂ groups in Structure (IV) may be in the cis- or trans- positions with respect to each other. In

Structure (IV), the cyclohexane carbon atoms may contain inert substituent groups in addition to the -NH₂, -R¹ and -(CR₂)_m-NH₂ groups shown. In another preferred embodiment, the cycloaliphatic amine compound that corresponds to Structure (IV) can be 5-amino-l,3,3- trimethylcyclohexanemethyl-amine (isophorone diamine).

In another embodiment, the hardener composition of the present invention may contain a mixture of primary and/or secondary amine compounds such as one or more

aminocyclohexanealkylamines as described above. In another optional embodiment, the hardener composition of the present invention may contain a mixture of primary and/or secondary amine compounds described in the aforementioned U.S. Provisional Patent

Application No. 62/503,975. For example, the amine compounds may include

cyclohexanemethanamine, 4-amino-a,a,4-trimethyl-(9Cl), which is also known as p-menthane- 1, 8-diamine or l,8-diamino-p-menthane; 5-amino-l,3,3-trimethylcyclohexanemethylamine (isophorone diamine); and mixtures thereof.

The amount of the cycloaliphatic amine such as IPDA present in the hardener

composition can be generally in the range of from 5 wt % to 70 wt % in one embodiment; from 10 wt % to 60 wt % in another embodiment; and from 10 wt % to 50 wt % in still another embodiment, based on the weight of the hardener composition.

In one preferred embodiment, the cycloaliphatic amine compound useful in the present invention may include for example a cycloaliphatic amine such as IPDA. In Figure 1, there is shown data for a hardener composition of the present invention containing IPDA compared to a hardener composition that has no IPDA present in the composition, but instead, contains PACM. One of the benefits of using IPDA versus PACM is that IPDA provides more latency to the composition at lower temperatures (e.g., less than 100 °C) which are typical temperatures used for molding composites such as spring parts. Spring composite parts typically are approximately 3 centimeters (cm) compared to other standard composite parts which are approximately

2 millimeters (mm). Thus, spring composite parts are much thicker than standard composite parts; and generally, require more resin than most standard parts. Hence spring composite parts, using a greater amount of resin (e.g. more than 5 Kg), require a higher latency (e.g., higher than 100 s) for the resin composition. Another benefit of using the hardener composition of the present invention is that, while using IPDA to provide a long latency (e.g., longer than 100 s), by further changing the catalyst from known catalysts such as l,4-diazabicyclo[2.2.2]octane (DABCO) to the catalyst of the present invention such as 2,4,6-tris(dimethylaminomethyl)phenol (DMP-30) provides an even longer latency while at the same time not shortening the demold time (e.g., to less than 360 s) of the composite part.

The hardener composition may contain other optional components such as impact modifiers, internal mold release agents, pigments, antioxidants, preservatives, short (up to 6 inches (15.24 cm) in length in one embodiment, up to 2 inches (5.08 cm) in length in another embodiment, and up to ½ inch (1.27 cm) in length in still another embodiment) reinforcing fibers, non-fibrous particulate fillers including micron- and nanoparticles, electroconductive fillers, wetting agents, surfactants, toughening agents, flow modifiers, adhesion promoters, diluents, stabilizers, plasticizers, flame retardants, and mixtures thereof, as can be routinely selected by one of ordinary skilled in the art.

The amount of the optional compounds or additives present in the hardener composition, when used, can be generally in the range of from 0 wt % to 80 wt % in one embodiment; from 0.1 wt % to 70 wt % in another embodiment; and from 0.1 wt % to 60 wt % in still another embodiment, based on the weight of the hardener composition.

In one embodiment, and as one non-limiting illustration of the present invention, the hardener composition may comprise, based on the weight of the hardener composition, from 1 wt % to 100 wt % in one embodiment, from 10 wt % to 90 wt % in another embodiment, and from 20 wt % to 90 wt % in still another embodiment of (a) at least one hardener compound such as triethylenetetramine (TETA); from 0.1 wt % to 60 wt % in one embodiment, from 0.5 wt % to 50 wt % in another embodiment, and from 1 wt % to 40 wt % in still another embodiment of (b) at least one catalyst such as 2,4,6-tris(dimethylaminomethyl)phenol; from 0.1 wt % to 15 wt % in one embodiment, from 1 wt % to 15 wt % in another embodiment, and from 1 wt % to 10 wt % in still another embodiment of (c) at least one accelerator such as sulfanilamide; and from 5 wt % to 60 wt % in one embodiment, from 5 wt % to 50 wt % in another embodiment, and from 10 wt % to 40 wt % in still another embodiment of (d) a cycloaliphatic amine such as isophorone diamine (“IPDA”).

The hardener composition of the present invention has several beneficial properties and performances. For example, hardener composition can have a viscosity of from 1 millipascal seconds (mPa.s) to 10,000 mPa.s in one embodiment, from 1 mPa.s to 2,000 mPa.s in another embodiment; and from 1 mPa.s to 1,000 mPa.s in still another embodiment. The viscosity of the hardener composition can be measured by placing a sample of the composition in a rheometer (MCR301, Anton Paar) equipped with parallel plates (25 mm diameter, gap 1 mm) maintained under isothermal conditions at 25 °C and then measuring with a rotational speed [l/s] of 10 s ¹.

The hardener formulation of the present invention containing dissolved solid

sulfanilamide surprisingly remains a liquid without solid particles crashing out of solution even under process conditions including high pressure mixing and recycling on a Krauss Maffei RTM machine of up to 120 bar. The composition has been found to be stable under low temperature conditions after being stored in a refrigerator for over 6 months at a temperature of 5 °C.

In one broad embodiment, the process for making the hardener composition of the present invention includes admixing components (a)-(d) and optional component (e) described above. While the order of mixing is not critical, there is an unexpected benefit in using a preferred order of mixing the components (a)-(d) and optional component (e). For example, the components and one or more additional optional compounds can be mixed together in a vessel and mixed in conventional mixing equipment and under conventional mixing conditions as known in the art. In one preferred embodiment, the order of mixing the compounds can be as described in Table (I) and according to the following general mixing procedure:

Step (1): preheat a mixing vessel to a temperature of -25 °C;

Step (2): add I^st component, triethylenetetraamine-E, to the vessel;

Step (3): add 2^nd component, isophoronediamine, to the vessel;

Step (4): heat the mixture of step (3) to a temperature of 50 °C, and mix at 50 °C for

20 min;

Step (5): add 3^rd component, sulfanilamide, to the mixture of step (4);

Step (6): heat the mixture of step (5) to a temperature of 80 °C, and mix at 80 °C for

90 min;

Step (7): cool the mixture of step (6) to a temperature of 40 °C;

Step (8): add 4^th component, DMP-30 or Dabco, to the mixture of step (7);

Step (9): heat the mixture of step (8) to a temperature of 50 °C, and mix at 50 °C for 30 mins; and

Step (10): cool the mixture of step (9) to a temperature of -25 °C and end the procedure. Table (I)

The above general procedure and process conditions are advantageous for dissolving the sulfanilamide in the formulation and keeping the sulfanilamide in solution under high pressure 5 (e.g., greater than 100 bar) processing conditions and during storage of the formulation, even at low temperatures (e.g., less than 10 °C).

Generally, the mixing of the components that make up the hardener composition can be carried out at a temperature of from 25 °C to 100 °C in one embodiment, from 25 °C to 90 °C in another embodiment, and from 40 °C to 85 °C in still another embodiment.

0 In one preferred embodiment, the hardener composition containing the molecule

sulfanilamide as an accelerator dissolves well in TETA producing a required liquid curing agent that can be used on common injection equipment such as a RTM machine. The solution of TETA and sulfanilamide can then be further mixed with the other components of the present invention, i.e., the catalyst and the cycloaliphatic amine compound, to form the hardener 5 composition. When the hardener composition is then subsequently reacted with a polymer resin such as epoxy resin, a significantly faster curing epoxy composition can be obtained while not impacting the thermal and mechanical properties or the performance of the composite formed from the curable resin composition.

The two-component curable resin composition of the present invention includes 0 (i) one or more polymer resins such as an epoxy resin; and (ii) the above-described hardener composition.

The polymer resin, component (i), useful for preparing the two-component curable resin composition of the present invention may include, for example, an epoxy resin and mixtures of two or more resins wherein at least one of the resins is an epoxy resin. For example, organic compounds having at least two epoxy groups that are reactive towards hardeners such as amine hardeners are useful in the present invention. In one embodiment, the epoxy resins can be selected from the group comprising, consisting essentially of, or consisting of epoxy resins based on bisphenol A diglycidyl ether, bisphenol F diglycidyl ether, cycloaliphatic types, and mixtures thereof. Examples of epoxy resins that can be used according to the present invention can include chain-extended bisphenol A resins with molecular weights of, for example, from 700 to 5,000; epoxidized novolaks; triglycidyl-p-aminophenol; tetraglycidylmethylenedianiline;

diglycidyl hexahydrophthalate; and mixtures thereof. In a preferred embodiment, bisphenol A- based epoxy resins and bisphenol F-based epoxy resins can be used according to the present invention. Cycloaliphatic types can include, by way of example, 3,4-epoxycyclohexyl- epoxyethane; 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate; or mixtures thereof.

Some examples of preferred embodiments of the resin compounds useful in the present invention may include one or more of the following epoxy resins: (1) from 1 wt % to 100 wt % in one embodiment, from 30 wt % to 100 wt % in another embodiment, and from 40 wt % to 100 wt % in still another embodiment of an epoxy resin referred to herein as“Epoxy Resin A” which is a diglycidyl ether of bisphenol-A having an epoxide equivalent weight (EEW) of about 180 grams/equivalent (g/eq) and containing about 0.5 wt % of monohydrolyzed species; (2) from 1 wt % to 100 wt % in one embodiment, from 10 wt % to 80 wt % in another embodiment, and from 20 wt % to 70 wt % in still another embodiment of an epoxy resin referred to herein as “Epoxy Resin B” which is a diglycidyl ether of bisphenol-A containing 15 wt % of core shell rubber particles, having an EEW of -180 g/eq, and commercially available from Olin Corp. as FORTEGRA™ 301; (3) from 1 wt % to 100 wt % in one embodiment, from 10 wt % to 80 wt % in another embodiment, and from 20 wt % to 70 wt % in still another embodiment of an epoxy resin referred to herein as“Epoxy Resin C” which is a diglycidyl ether of bisphenol A containing core shell rubber particles at a concentration of 25 wt % with respect to the diglycidyl ether of bisphenol-A, having an EEW of -180 g/eq, and commercially available from Kaneka Corp. as Kane Ace MX- 170; (4) from 1 wt % to 100 wt % in one embodiment, from 10 wt % to 90 wt % in another embodiment, and from 20 wt % to 80 wt % in still another embodiment of an epoxy resin referred to herein as“Epoxy Resin D” which is a diglycidyl ether of bisphenol-F and having an EEW of about 171 g/eq; and (5) from 1 wt % to 100 wt % in one embodiment, from 10 wt % to 90 wt % in another embodiment, and from 20 wt % to 80 wt % in still another embodiment of an epoxy resin referred to herein as“Epoxy Resin E” which is a mixture of diglycidyl ether of bisphenol-F resin and diglycidyl ether of bisphenol-A resin, and having an EEW of about 172 g/eq.

In one particular embodiment, the resin compound useful in the present invention can be an epoxy resin such as bisphenol-A diglycidyl ether epoxy resin, bisphenol-F diglycidyl ether epoxy resin, and mixtures thereof. Other different epoxy resin compositions may benefit from, and can be used in, the composition of the present invention, including for example, any of the epoxy resins available under the tradename VORAFORCE™. An example of a diglycidyl ether of bisphenol A epoxy resin that can be mixed with the hardener composition of the present invention can be VORAFORCE™ 5310 which has an EEW of 178 g/eq and is available from The Dow Chemical Company.

The amount of the polymer resin, component (i), used to prepare the curable resin composition can be generally in the range of from 40 wt % to 98 wt % in one embodiment; from 50 wt % to 95 wt % in another embodiment; and from 60 wt % to 90 wt % in still another embodiment, based on the weight of the fully formulated resin composition. Alternatively, the concentration of the hardener composition can be based on 100 parts by weight (pbw) of epoxy resin. For example, in one embodiment, the hardener in pbw can be 100: 17.9 with a range of 100:5 to 100:50.

The hardener composition, component (ii), useful for preparing the two-component curable resin composition of the present invention may include, for example, the hardener composition described above.

The amount of the hardener composition used to prepare the curable resin composition can be generally in the range of from 5 wt % to 50 wt % in one embodiment; from 10 wt % to 50 wt % in another embodiment; and from 10 wt % to 30 wt % in still another embodiment, based on the weight of the fully formulated resin composition. Alternatively, the polymer resin concentrations can include for example weights based on 100 parts by weight epoxy resin; and in such case the hardener pbw can be in the range of 100:5 to 100:50 in one general embodiment, and 100:17.9 in another embodiment. The epoxy resin composition may also contain an optional component or optional functional chemical for an intended application. Optional compounds or additives that may be added to the curable epoxy resin formulation of the present invention as component (iii), may include one or more of the optional compounds described above with reference to the optional additives, component (e), of the hardener composition.

The amount of the optional compounds or additives present in the curable resin composition, when used, can be generally in the range of from 0 wt % to 60 wt % in one embodiment; from 0.1 wt % to 50 wt % in another embodiment; and from 1 wt % to 40 wt % in still another embodiment, based on the weight of the resin composition.

The curable resin composition of the present invention has several beneficial properties and performances. For example, the curable resin composition of the present invention advantageously has been found to be capable of curing at high speeds even down to 60 s without loss of thermal and/or mechanical properties of the resulting composite made from the composition. For example, in one general embodiment, the fast curing speed of the composition can be from 20 s to 600 s, from 20 s to 300 s in another embodiment, and from 20 s to 240 s in still another embodiment.

In one broad embodiment, the process for making the curable resin composition of the present invention includes admixing components (i) and (ii); and optionally, component (iii) described above. The resin component (i) can be mixed together in a vessel with the hardener composition component (ii); and mixed in conventional mixing equipment and under conventional mixing conditions as known in the art. One or more additional optional compounds, as component (iii), may be added to the resin formulation as desired.

Generally, the mixing of components (i) and (ii), and if desired optional component (iii), that make up the curable resin composition can be carried out at a temperature of from 20 °C to 150 °C in one embodiment, from 20 °C to 100 °C in another embodiment, and from 20 °C to 90 °C in still another embodiment. During mixing, or once the components (i) - (iii) are mixed forming the curable resin composition, the curable composition can be cured at a curing temperature of from 40 °C to 150 °C in one embodiment, from 40 °C to 130 °C in another embodiment, and from 60 °C to 100 °C in still another embodiment.

In one preferred embodiment, the cure can continue until the resulting cured polymer attains a glass transition temperature (Tg) in excess of the cure temperature. The Tg at the time of demolding can be at least 100 °C in one embodiment, at least 110 °C in another embodiment, at least 115 °C in still another embodiment and at least 120 °C in yet another embodiment. An advantage of the present invention is that such Tgs can be obtained with short curing times. This allows for short cycle times.

Once the components are mixed forming the curable resin composition, the curable composition can be further mixed with a structural material (e.g., fibers) and then the curable composition can be cured at the aforementioned curing temperatures to form a composite article. Accordingly, the composite of the present invention includes the reaction product of: (A) one or more structural materials; and (B) the two-component curable resin composition described above.

The structural additive or material, component (A), used in the curable resin composition can be for example substrates, particles, fibers, fillers, other structural additives; and mixtures thereof. In one embodiment, the structural material useful in the present invention may include for example impact modifiers in the form of particles. Suitable impact modifiers useful in the present invention may include natural or synthetic polymers having a Tg of lower than -40 °C. These polymers include natural rubber; styrene-butadiene rubbers; polybutadiene rubbers;

isoprene rubbers; poly ethers such as poly(propylene oxide), poly(tetrahydrofuran) and butylene oxide-ethylene oxide block copolymers; core-shell rubbers; mixtures of any two or more of the foregoing; and the like. The rubbers can be present in the form of small particles that become dispersed in the polymer phase of the composite. The rubber particles can be dispersed within the epoxy resin or hardener and preheated together with the epoxy resin or hardener prior to forming a hot reaction mixture.

In another embodiment, the structural material useful in the present invention may include for example fillers in the form of particulates. Suitable particulate fillers useful in the present invention can have an aspect ratio of less than 5 in one embodiment and less than 2 in another embodiment; and do not melt or thermally degrade under the conditions of the curing reaction. Suitable fillers useful in the present invention may include, for example, glass flakes; aramid particles; carbon black; carbon nanotubes; various clays such as montmorillonite; and other mineral fillers such as wollastonite, talc, mica, titanium dioxide, barium sulfate, calcium carbonate, calcium silicate, flint powder, carborundum, molybdenum silicate, sand, and the like; and mixtures thereof. Some fillers are somewhat electroconductive, and the presence of these fillers in the composite can increase the electroconductivity of the composite. In some applications, notably automotive applications, it is preferred that the composite is sufficiently electroconductive such that coatings can be applied to the composite using the so-called“e-coat” methods, in which an electrical charge is applied to the composite and the coating becomes electrostatically attracted to the composite. Conductive fillers of this type include, for example, metal particles (such as aluminum and copper), carbon black, carbon nanotubes, graphite and the like; and mixtures thereof. In one preferred embodiment, an electroconductive filler may be present in the curable resin composition.

In still another embodiment, the curable composite composition of present invention may include, for example, fibers as the structural material. Suitable fibers useful in the present invention may include, for example, heat resistant fibers, such as carbon fiber, glass fiber or mixtures thereof. For example, once the fibers are added to the curable composite composition, the mixture can be cured to form a shaped composite article comprising the cured resin containing the fibers.

The amount of the structural additive or material present in the curable resin composition can be generally in the range of from 0 wt % to 90 wt % in one embodiment; from 20 wt % to 90 wt % in another embodiment; and from 30 wt % to 80 wt % in still another embodiment, based on the weight of the curable resin composition.

The curable resin composition as described above can be used as component (B) of the curable composite composition to form a composite article. The amount of the curable resin composition used to prepare the composite can be generally in the range of from 5 wt % to 95 wt % in one embodiment; from 20 wt % to 80 wt % in another embodiment; and from 40 wt % to 70 wt % in still another embodiment, based on the weight of the curable resin composition.

Optional compounds, additives or materials may be added to the curable resin formulation of the present invention to prepare a composite article. The curable resin composition may contain an optional component or optional functional chemical for an intended application. Optional compounds or additives that may be added to the curable epoxy resin formulation of the present invention, as component (C), may include one or more of the optional compounds described above with reference to the optional additives, component (e), of the hardener composition such as one or more impact modifiers, internal mold release agents, reactive diluents, coalescents, pigments, dyes, particulate fillers, extenders, tackifiers, antioxidants and wetting agents.

For example, in one embodiment the epoxy resin and the hardener composition together with the structural material can be cured in the presence of an internal mold release agent such that the cured composite article can easily release from the mold tool without damage to the composite article and without the composite sticking to the mold tool. Such internal mold release agent may constitute up to 5 wt % in one embodiment and up to 1 wt % in another embodiment, based on the total weight of the reaction mixture. Suitable internal mold release agents useful in the present invention are well known and commercially available, including those marketed as Marbalease™ by Rexco-USA, Mold-Wiz™ by Axel Plastics Research Laboratories, Inc., Chemlease™ by Chem-Trend, PAT™ by Wiirtz GmbH, Waterworks

Aerospace Release by Zyvax, and Kantstik™ by Specialty Products Co. In addition to (or instead of) adding the internal mold release agent at the mixing head (or mixhead), it is also possible to combine such an internal mold release agent into the resin component and/or the hardener component before the resin component and the hardener component are brought together.

The amount of the optional compounds, additives or materials present in the curable resin composition, when used to form a composite, can be generally in the range of from 0 wt % to 50 wt % in one embodiment; from 0.1 wt % to 50 wt % in another embodiment; and from 1 wt % to 50 wt % in still another embodiment, based on the weight of the composition.

The composite article of the present invention has several beneficial thermal and/or mechanical performances and properties. For example, the composite can have an unexpectedly high Tg of more than 120 °C in one embodiment, from 100 °C to 150 °C in another embodiment, from 110 °C to 140 °C in still another embodiment; and from 110 °C to 135 °C in yet another embodiment. The Tg of the composite can be measured by the method described in ASTM E1356 (2014). Another surprising property of the composite article found in the present invention is the composite’s transparency when the final composite is observed visually.

In general, a composite article (or thermoset) can be formed from the curable composite composition of the present invention by mixing the epoxy resin component and the hardener component of the composition at proportions as described before and curing the resulting mixture. Either or both of the components can be preheated if desired before the two components are mixed with each other. It is generally necessary to heat the mixture to an elevated temperature to obtain a rapid cure. In a molding process such as the process for making molded composites described below, the curable reaction mixture is introduced into a mold, which may be, together with any reinforcing fibers and/or inserts as may be contained in the mold, preheated. The curing temperature may be, for example, from 40 °C to 200 °C. When a long gel time (at least 30 s in one embodiment and at least 40 s in another embodiment) is desirable, the curing temperature can be not greater than 130 °C. When both a long gel time and a short demold time is wanted, a suitable curing temperature can be from 60 °C to 120 °C in one embodiment, from 70 °C to 120 °C in another embodiment, and from 80 °C to 120 °C in still another embodiment.

It is preferred to continue the cure until the resulting polymer attains a Tg in excess of the cure temperature. The Tg at the time of demolding may be at least 100 °C in one embodiment, at least 110 °C in another embodiment, at least 115 °C in still another embodiment, and at least 120 °C in yet another embodiment. An advantage of the present invention is that the Tg can be obtained with short curing times. This allows for short cycle times. The demold time at cure temperatures of from 80 °C to 130 °C in one embodiment and from 80 °C to 120 °C in another embodiment, can be 350 s or less in one embodiment, 300 s or less in another embodiment, and 240 s or less in still another embodiment.

The curable composite resin composition of the present invention is particularly useful for making fiber-reinforced composites by curing the composition in the presence of reinforcing fibers. These composites, in general, can be made by mixing the one or more polymer resins such as an epoxy resin, component (i), described above; and the above-described hardener composition, component (ii), described above to form a reaction mixture, wetting the fibers with the reaction mixture, and then curing the mixture at a curing temperature in the presence of the reinforcing fibers.

The reinforcing fibers can be thermally stable and have a high melting temperature, such that the reinforcing fibers do not degrade or melt during the curing process. Suitable fiber materials useful in the present invention can include, for example, glass, quartz, polyamide resins, boron, carbon, wheat straw, hemp, sisal, cotton, bamboo, gel-spun polyethylene fibers, and mixtures thereof. The reinforcing fibers can be provided in the form of short fibers (e.g., from 0.5 cm to 15 cm), long fibers (e.g., greater than 15 cm), or continuous rovings. The fibers can be provided in the form of a mat or other preform if desired; such mats or performs may in some

embodiments be formed by entangling, weaving and/or stitching the fibers, or by binding the fibers together using an adhesive binder. Preforms may approximate the size and shape of the finished composite article (or a portion thereof that requires reinforcement). Mats of continuous or shorter fibers can be stacked and pressed together, typically with the aid of a tackifier, to form preforms of various thicknesses, if required.

Suitable tackifiers useful in the present invention for preparing performs (from either continuous or shorter fibers) can include heat-softenable polymers such as described, for example, in U. S. Patent Nos. 4,992,228; 5,080,851; and 5,698,318. The tackifier should be compatible with and/or react with the polymer phase of the composite, so that there is good adhesion between the polymer and reinforcing fibers. A heat-softenable epoxy resin or mixture thereof with a hardener, as described in U. S. Patent No. 5,698,318, can also be useful in the present invention. The tackifier may contain other components, such as one or more catalysts, a thermoplastic polymer, a rubber, or other modifiers.

A sizing or other useful coating may be applied onto the surface of the fibers before the fibers are introduced into the mold. A sizing often promotes adhesion between the cured epoxy resin and the fiber surfaces.

The composite may be formed in a mold. In such a case, the reinforcing fibers may be introduced into the mold before the epoxy resin/hardener mixture. This is normally the case when a fiber preform is used. The fiber preform is placed into the mold and the epoxy resin/hardener mixture is then injected into the mold, where the mixture penetrates between the fibers in the preform, fills the cavity, and then cures to form a composite product.

Alternatively, the fibers (including a preform) can be deposited into an open mold, and the reaction mixture can be sprayed or injected onto the preform and into the mold. After the mold is filled in this manner, the mold is closed and the reaction mixture cured.

Short fibers can be injected into the mold with the hot reaction mixture. Such short fibers may be, for example, blended with the epoxy resin or hardener (or both) prior to forming the reaction mixture. Alternatively, the short fibers may be added into the reaction mixture at the same time as the epoxy and hardener are mixed, or afterward but prior to introducing the hot reaction mixture into the mold.

Alternatively, short fibers can be sprayed into a mold. In such cases, the reaction mixture can also be sprayed into the mold, at the same time or after the short fibers are sprayed in. When the fibers and reaction mixture are sprayed simultaneously, they can be mixed together prior to spraying. Alternatively, the fibers and reaction mixture can be sprayed into the mold separately but simultaneously. The sprayed materials may be spread and/or leveled using a doctor blade or similar device before closing the mold and performing the cure. In a process of particular interest, long fibers are chopped into short lengths and the chopped fibers are sprayed into the mold, at the same time as or immediately before the hot reaction mixture is sprayed in. Mesh materials often function as flow promoters.

Composites made in accordance with the present invention may have fiber contents of at least 10 volume percent (vol %) in one embodiment, at least 25 vol % in another embodiment, and at least 35 vol % in still another embodiment; and the fiber content can be up to 80 vol % in yet another embodiment, up to 70 vol % in even still another embodiment, and up to 60 vol % in even yet another embodiment.

The mold may contain, in addition to the reinforcing fibers, one or more inserts that do not become distorted or degraded at the temperatures encountered during the molding step. Such inserts may also function as reinforcements, may function as flow promoters, and in some cases may be present for weight reduction purposes. Examples of such inserts useful in the present invention may include, for example, wood; plywood; metals; various polymeric materials which may be foamed or unfoamed such as polyethylene, polypropylene, another polyolefin, a polyurethane, polystyrene, a polyamide, a polyimide, a polyester, polyvinylchloride and the like; various types of composite materials; and mixtures thereof.

The reinforcing fibers (and inserts, if any) may be enclosed in a bag or film such as is commonly used in vacuum assisted processes. The mold and the preform (and any other inserts, if any) may be heated to the curing temperature or some other useful elevated temperature prior to contacting the mold and the preform (and any other inserts, if any) with the reaction mixture. The mold surface may be treated with an external mold release agent, which may be solvent- or water-based. The particular equipment that can be used to mix the components of the reaction mixture of the present invention and to transfer the mixture to the mold is not considered to be critical to the present invention, provided the reaction mixture can be transferred to a mold before the reaction mixture attains a high viscosity or develops a significant amount of gels. The mixing apparatus can be of any type that can produce a homogeneous mixture of the epoxy resin and hardener (and any optional components that are also mixed in at this time); and various types of mechanical mixers and stirrers may be used to accomplish a homogeneous mixture. For example, two types of mixers useful in the present invention can be static mixers and

impingement mixers.

In addition, methods of manufacturing the fiber-reinforced composites can include a resin-transfer process or any variants of such resin-transfer process, for example, a reaction injection molding (RTM) process; a vacuum-assisted resin transfer molding (VARTM) process; and a Seeman Composites Resin Infusion Molding Process (SCRIMP). In some embodiments, the equipment used in the above processes can be modified to provide the requisite heating at the various stages of the process). Other fiber-reinforced composite manufacturing methods such as wet compression can also be used in the present invention. In the above processes, the reinforcing fibers can be formed into a preform first and which can then be placed into a mold.

A reaction mixture of an epoxy resin component and a hardener may then be injected into the mold, where the mixture flows around and between the fibers, fills the mold cavity, and cures to form the composite.

As aforementioned, one embodiment of the mixing and dispensing apparatus useful in the present invention can be, for example, an impingement mixer, which is a mixer commonly used in so-called reaction injection molding processes to form polyurethane and polyurea moldings. The epoxy resin and hardener composition (and other optional components) can be pumped under pressure into a mixing head, such as by impingement mixing, where the components are rapidly mixed together. The catalyst can be introduced with the epoxy resin, the hardener composition, or as a separate stream. The operating pressure of the incoming streams may range from a somewhat low value (for example, from 1 megapascal (MPa) to 6.9 MPa) to a high value (such as, for example, from 6.9 MPa to 200 MPa). In one preferred embodiment, the operating pressures in high pressure machines may range, for example, from 1,000 psi to 29,000 psi or higher (6.9 MPa to 200 MPa or higher), although some low- pressure machines that operate at significantly lower pressures may also be used.

Optionally, the resulting mixture (e.g., a mixture of epoxy resin, hardener composition and optional catalyst) can be passed through a static mixing device to provide further additional mixing before the mixture enters a mold apparatus. After the mixture passes through the static mixer, the mixture can be transferred into the mold cavity at a somewhat low operating pressure, such as up to 5 MPa in one embodiment or up to 1 MPa in another embodiment. Some or all of the pressure drop between the mixhead and the mold injection port often may take place through the static mixer. The static mixing device may be designed into the mold. This has the advantage of allowing the static mixing device to be opened easily for cleaning. In another preferred embodiment of the apparatus for conducting the process can be a reaction injection molding machine, such as is commonly used to processes large polyurethane and polyurea moldings. Such injection molding machines are available commercially from Krauss Maffei Corporation and Cannon or Hennecke.

In other embodiments, a hot reaction mixture can be mixed as before, and then the hot reaction mixture can be sprayed into the mold. The temperature in the spray zone of the mold can be maintained such that the temperature of the hot reaction mixture is maintained as described before.

The mold is typically a metal mold, but the mold may also be made of ceramic or of a polymer composite provided the mold is capable of withstanding the pressure and temperature conditions of the molding process. The mold may contain one or more inlets, in liquid communication with the mixer(s), through which the reaction mixture is introduced. The mold may contain vents to allow gases to escape as the reaction mixture is injected.

The mold is typically held in a press or other apparatus which can allow the mold to be opened and closed, and which can apply pressure on the mold to keep the mold closed during the filling and curing operations. The mold or press can be provided with a means by which heat and/or cooling can be provided.

In some embodiments of the foregoing process, the molded composite can be demolded in no more than 5 min in one embodiment, from 2 min to 5 min in another embodiment, and from 2 min to 4 min in still another embodiment, after the epoxy resin system has been introduced into the mold. In such processes, the reaction mixture introduced into the mold flows around and between the reinforcing fibers and fills the mold and then cures in the mold, such that a polymer having a Tg of at least 1 lO°C in one embodiment, at least 115 °C in another embodiment, and at least 120 °C in still another embodiment, can be formed within 5 min in one embodiment, and within 4 min in another embodiment, after the reaction mixture has been 5 introduced into the mold.

The composite product made using the curable composition of the present invention and the process of making the composition and composite may be used, for example, to make a wide variety of composite products, including applications that use fiber-reinforced organic matrix composites. For example, the present invention is useful for making various types of automotive 10 parts. In one exemplary embodiment, the composite product made from the curable composition of the present invention can be used for structural light-weight composites for the automotive industry, including for auto fiber-reinforced composite springs. Other examples of automotive parts made using the present invention include vertical and horizontal body panels, automobile and truck chassis components, and so-called“body-in-white” structural components. Body panel 15 applications include, for example, fenders, door skins, hoods, roof skins, decklids, tailgates and the like. Body panels often require a so-called“class A” automotive surface which has a high distinctness of image (DOI). For this reason, a filler in many body panel applications will include a material such as mica or wollastonite.

EXAMPLES

20 The following examples are presented to further illustrate the present invention in detail but are not to be construed as limiting the scope of the claims. Unless otherwise stated all parts and percentages are by weight.

Various raw materials (ingredients or components) used in the Inventive Examples (Inv. Ex.) and the Comparative Examples (Comp. Ex.) which follow are described herein below in 25 Table I.

Table - Raw Materials

Various designations and testing methods are used in the examples which follow and are described herein as follows:

“AHEW” stands for“amine hydrogen equivalent weight” and means the amount in grams 5 of an amine that yields one molar equivalent of hydrogen in reaction as measured by titration using ASTM D 2074-07 (2007).

“EEW” stands for“epoxy equivalent weight” and means the amount in grams of an epoxy resin that yields one molar equivalent of epoxy groups in reaction with amines.

“IPDA” stands for“isophorone diamine”.

10 “TETA” stands for“triethylenetetramine”.

“GT” stands for“gel time”.

“MT” stands for“molding temperature”.

EEW Measurements

EEW is determined using a Metrohm 801 Robotic USB sample processor XL and two 800 15 Dosino™ dosing devices for the reagents (Metrohm USA, Tampa, FL). The reagents used are perchloric acid in acetic acid 0.10 N and tetraethylammonium bromide. The electrode for the analysis is an 854 Iconnect™ electrode (Metrohm). For each sample, 1 g of dispersion is weighed out into a plastic sample cup. Then 30 mL of THF (tetrahydrofuran) is first added and mixed for 1 min to break the shell on the dispersion. Next, 32 mL of glacial acetic acid is added and mixed 20 for another 1 min to fully dissolve the sample. The sample is then placed on the auto sampler and all relevant data (e.g., sample ID, sample weight) is added to the software. From here the start button is clicked to start the titration. Thereafter, 15 mL of tetraethylammonium bromide is added, and then the perchloric acid is slowly added until a potentiometric endpoint is reached. Once the potentiometric endpoint is reached, the software calculates an EEW value based on the amount of sample and perchloric acid used.

Glass Transition Temperature (Tg)

“DSC Glass Transition Temperature Tg” means the glass transition temperature of a given material. DSC stands for dynamic differential scanning calorimetry; and DSC was used to determine the Tg value of the composite. To measure the Tg of a sample material, the sample is first heated in a heating ramp of +20 °C/min from 25 °C to 200 °C. The sample cell is kept isothermal at 200 °C for 3 min, and then cooled in a ramp of -20 °C/min down to 25 °C. The sample cell is then kept isothermal at 25 °C for 3 min, and thereafter, heated again with a heating ramp of +20 °C/min to 200 °C. The sample cell is kept isothermal at 200 °C for 3 min and then cooled in a ramp of -20 °C/min down to 25 °C. Tg onset and Tg midpoint are determined from the second heating segment.

Resin Transfer Molding

The manufacturing method of choice for making fiber-reinforced composites is a resin transfer molding (RTM) process. The resin transfer molding process includes forming reinforcing fibers into a preform which is then placed into a mold. A mixture of an epoxy resin component (at a temperature of, e.g., approximately 80 °C) and a hardener (at a temperature of, e.g., approximately 35 °C) is then injected into the mold, where the resin component flows around and between the fibers filling in the cavities. The epoxy resin composition is then allowed to cure to form the composite.

Herein, gel time and demold times are evaluated according to the following curing evaluation test: the epoxy resin (at approximately 80 °C) and hardener mixture (at

approximately 35 °C) are brought together in the required ratio using a high-pressure resin transfer molding machine. The resulting mixture is injected onto a mold preheated to the required temperature to form a disk of liquid on the surface of the mold. Time is measured from the point at which the mixture contacts the mold surface. The mold is maintained at the required temperature as the mixture cures. A line is scored through the liquid disk periodically, using a pallet knife or similar blade. The gelation time (GT) is the time after which the liquid material no longer flows into the scored line. The demold time is taken as the time when the disk has reached a sufficient level of cure and stiffness to be successfully demolded. Hand Mix/Hot Plate Experiments

To demonstrate the advantages of the present invention, a hot plate experiment was conducted. Gel time and demold time, for the resin composition samples prepared in the Examples herein, are evaluated according to a curing evaluation test using a hand mixing and hot 5 plate experiment as follows: An epoxy resin (at a temperature of approximately 40 °C) and a hardener mixture (at a temperature of approximately 25 °C) are brought together in a vessel at a required ratio; and then the two components are mixed together for 30 s. The resulting liquid mixture is poured onto the surface of a hot plate which is preheated to 90 °C. The liquid mixture poured onto the hot plate surface forms a disk of liquid on the surface of the hot plate. Time is 10 measured starting from the point at which the liquid mixture contacts the hot plate surface. The hot plate is maintained at 90 °C as the mixture cures. A line is scored, periodically, through the liquid disk that forms on the surface of the hot plate using a pallet knife or similar blade utensil. The gelation time (GT) is the time starting from the point the liquid mixture contacts the hot plate surface until the liquid mixture no longer flows into the scored line. Demold time (DMT) 15 is the time after pouring at which the disk can be removed from the hot plate surface as a solid, using the pallet knife or similar blade.

The test methods described above were performed on various resin systems described in Table II; and the test results are described in Table II and Figure 1.

Table - Compositions and Test Results

NcSfi for Table II: ⁽¹⁾The formulation of this Comp. Ex. uses an experimental hardener. ⁽²⁾The formulation of this Comp. Ex. is made according to the procedure described“Inventive Example 1” of U.S. Provisional Patent Application No. 62/503,975.

⁽³⁾Sulfanilamide

One of the objectives of the present invention is to provide a resin system exhibiting an optimum extended latency. An extension of latency (i.e., a long gel time or open time with a short curing time thereafter) can enable a much longer infusion time of a curable composition which can be highly beneficial particularly when producing large structures and when using multi-cavity tools with an objective of maintaining a fast demolding time.

Table II above describes the results of gel times for various formulations mixed via a hand protocol and a RTM machine protocol. Each of the formulations of the Examples (Comp. Ex. A-D and Inv. Ex. 1 and 2) described in Table II use VORAFORCE 5310 as the epoxy resin. The formulations of Comp. Ex. A and B are examples of formulations with a hardener that provides a slow curing (e.g., greater than 10 min) resin system with a demolding time (DMT) of 20 min compared to the fast curing (e.g., 5 min or less) formulations with a hardener

composition of the present invention Ex. 1 and 2 with a demolding time of 5 min.

The gel times of the resin systems of Comp. Ex. A and B are essentially the same when the resin systems are mixed via hand versus an RTM machine with high pressure mixing and high resin temperature as described in Table II. However, when a fast curing formulation is used, such as described in Comp. Ex. C and D with a demold time of 5 min, a shortening of gel time of 60 s between an RTM mixing and hand mixing protocol is observed. This shortening of gel time of the formulations of Comp. Ex. C and Comp. Ex. D, in turn, results in a shortening of the possible injection time of the resin system; and hence the lowering of the amount of resin that is possible to inject at the required mold temperature. This difference between hand mixing resin systems versus injection via a high-pressure RTM machine is a common phenomenon for fast curing resin systems.

The VORAFORCE 5310 epoxy resin formulations of Inv. Ex. 1 and 2 include the novel hardener composition of the present invention. Inv. Ex. 1 and 2 demonstrate that when the resin system of these two Examples is mixed with a hand mix protocol, the gel time of these resin systems is the same as Comp. Ex. C. However, surprisingly the RTM mix protocol used in Inv. Ex. 2 shows a much lower impact on the gel time (35 s longer GT with same DMT) versus Comp. Ex. D even when high pressure mixing and high resin temperature (80 °C resin) is employed. The increase in gel time (i.e., the higher latency) of the resin composition allows for a much longer infusion time of the resin, particularly in the process of manufacturing larger structures, while still allowing for a fast demolding time for the mold product produced with the resin composition. The present invention provides a much longer infusion time for a curable resin composition. For example, using an injection rate of 100 g/s, an additional 30 s longer infusion time can be realized while still allowing a fast demolding time (e.g., 30 s with an injection rate of 100 g/s) using the resin systems of the present invention; and therefore, the longer infusion time can advantageously enable a further 3,000 g of resin to be injected into a mold.

The results, shown in Figure 1, also compares the measurements of gel times for two resin compositions (the resin of Comp. D versus the resin of Inv. Ex. 2) at a variety of temperatures, for example from 90 °C to 130 °C, using an RTM machine. The data shows that when the gel times of the resin compositions are measured at a variety of mold temperatures (e.g., from 90 °C to 130 °C) using a RTM machine, at the high mold temperatures little difference in the gel times are observed for the two resin compositions. However, at the critical mold temperature of 90 °C, a much higher latency (i.e., a longer gel time) is observed for the resin formulations of the present invention (Inv. Ex. 2) containing IPDA versus the resin formulation of the prior art (Comp. Ex. D) containing PACM.

Claims

What Is Claimed is:

1. A liquid-based hardener composition comprising (a) at least one hardener compound, (b) at least one catalyst compound, (c) at least one accelerator compound, and (d) at least one cycloaliphatic amine compound.

2. The hardener composition of claim 1, wherein hardener composition, when present in a resin system, provides an increase in gel time to the resin system; wherein the gel time is increased up to at least an additional 10 seconds while still maintaining the demold time of at least 300 seconds at a mold temperature of at least 90 °C of the resin system.

3. The hardener composition of claim 1, wherein the at least one hardener compound includes an amine-based hardener.

4. The hardener composition of claim 1, wherein the at least one hardener compound includes triethylenetetramine.

5. The hardener composition of claim 1, wherein the at least one catalyst compound includes 2,4,6-tris(dimethylaminomethyl)phenol; l,4-diazabicyclo[2.2.2]octane; and mixtures thereof.

6. The hardener composition of claim 1, wherein the at least one accelerator compound includes a sulfanilamide compound containing a chemical structure of:

7. The hardener composition of claim 1, wherein the at least one cycloaliphatic amine is isophorone diamine.

8. The hardener composition of claim 1, comprising from 1 weight percent to 100 weight percent of the at least one hardener compound; from 0.1 weight percent to 15 weight percent of the at least one catalyst compound; from 0.1 weight percent to 60 weight percent of the at least one accelerator compound, and from 5 weight percent to 60 weight percent of the at least one cycloaliphatic amine, based on the total weight of the hardener composition.

9. A curable epoxy-based resin composition comprising (i) at least one or more epoxy resins; and (ii) the hardener composition of claim 1.

10. The curable epoxy-based resin composition of claim 9, further comprising (iii) a structural material.

11. The curable epoxy-based resin composition of claim 10, wherein the structural material includes heat resistant fibers.

12. A composite article comprising a hardener composition of claim 1.

13. A composite article comprising a cured product of: (i) at least one or more epoxy resins; (ii) the hardener composition of claim 1; and (iii) one or more structural materials.

14. The composite article of claim 13, wherein the structural material includes heat resistant fibers.

15. The composite article of claim 13, further comprising one or more of impact modifiers, internal mold release agents, reactive diluents, coalescents, pigments, dyes, particulate fillers, extenders, tackifiers, antioxidants and wetting agents.