WO2011011920A1

WO2011011920A1 - Amine-phenolic dual cure hardener blend for resin compositions

Info

Publication number: WO2011011920A1
Application number: PCT/CN2009/073018
Authority: WO
Inventors: Perrin Ren; Joseph Gan; Jack Jun Jie Wan; Yi Zhang
Original assignee: Dow Global Technologies LLC
Current assignee: Dow Global Technologies LLC
Priority date: 2009-07-31
Filing date: 2009-07-31
Publication date: 2011-02-03
Anticipated expiration: 2012-01-31
Also published as: TW201111408A

Abstract

Dual-cure hardener blends for a halogen-free epoxy resin composition are provided. Resin compositions made from the dual-cure hardener blends and composites made from the resin compositions are also provided. The dual-cure hardener blends are based on a blend of at least one amine-based curing agent and at least one phenolic curing agent. The dual-cure hardener blends can improve the B-stage pre-preg storage stability as well as the wettability and flow during processing for non-halogen epoxy resin systems containing phosphorus and/or nitrogen.

Description

AMINE-PHENOLIC DUAL CURE HARDENER BLEND FOR RESIN

COMPOSITIONS

FIELD OF THE INVENTION

[0001] The present invention relates to hardener blends that include an amine-based curing agent and a phenolic curing agent and to resin compositions that include the hardener blends.

BACKGROUND OF THE INVENTION

[0002] Strict thermal mechanical requirements and potential environmental concerns have led to the consideration of halogen-free flame retardants as replacements for older technologies based on some halogenated compounds, such as the different derivatives of tetrabromobispehnol-A. For example, epoxy resins having covalently attached flarne- retardants containing phosphorus and/or nitrogen have been employed to assure stability and compatibility and to achieve the flammability requirement of UL 94 VO and other important physical properties.

[0003] For use in composites, such as pre-pregs, epoxy resin systems require adequate resin stability during storage. An appropriate and consistent reactivity, and optimum and consistent resin flow properties are prerequisites for the compression molding of epoxy resin systems to produce laminates, such as multilayer circuit boards.

[0004] However, processability has proven more difficult to achieve in halogen-free epoxy resin systems compared with more conventional resin systems. To achieve UL 94 VO, high thermal stability, and anti-conductive anodic filament (CAF) requirements, halogen-free printed circuit boards (PCBs) utilizing phenolic cure and having high phosphorus content have been developed. The polyfunctional phenolic curing agents which are used often lead to high viscosity build-up during B-stage pre-preg preparation. Unfortunately, the high phosphorus content (e.g., up to 3.5% based on 100% solid components of the total formulation) often leads to higher moisture sensitivity for the pre-preg compared with more conventional FR-4 systems. After the pre-preg absorbs moisture, the pre-preg powder's minimum melting viscosity (MMV) tends to decrease and the flow during laminate pressing becomes higher with the ageing time. This poor storage stability of halogen-free resins is a critical issue for laminate manufacturing.

BRIEF SUMMARY OF THE INVENTION

[0005] One aspect of the invention provides a composition comprising an epoxy resin, optionally comprising at least one of phosphorus or nitrogen, and a hardener blend comprising an amine-based curing agent and a phenolic curing agent. The composition can be characterized in that a pre-preg powder made from the composition has an ΔMMV of no greater than 20% after 24 hours at 100% relative humidity and 25 ⁰C. This includes compositions characterized in that a pre-preg powder made from the composition has a ΔMMV of no greater than 15% after 24 hours at 100% relative humidity and 25 ⁰C, and further includes compositions characterized in that a pre-preg powder made from the composition has a ΔMMV < 0% after 24 hours at 100% relative humidity and 25 ⁰C. The compositions can optionally include one or more flame retardants or curing agents, including phosphorus-containing curing agents. In some embodiments, the compositions are halogen- free.

[0006] In some embodiments the composition has a weight ratio of hardener blend to epoxy resin of 0.5:1 to 1 :1, based on the total weight of solids content of the composition and weight ratio of phenolic curing agent to amine-based curing agent of 10:1 and 3:1 based on the total weight of the solids content of the amine and phenolic curing agents.

[0007] The phenolic curing agent can comprise phosphorus. For example, the phenolic curing agent can comprise a phosphorus containing bisphenol A resole resin, and can further comprise a phenolic novalac resin.

[0008] Examples of amine-based curing agents include DETDA and DICY.

[0009] The epoxy resin can be, for example an epoxy novolac resin.

[0010] In one specific embodiment of the composition, the amine-based curing agent comprises an aromatic amine comprising hydrophobic groups and the phenolic curing agent comprises a phosphorus-containing compound, the composition characterized in that a pre- preg powder made from the composition has a ΔMMV < 0% after 24 hours at 100% relative humidity and 25 ⁰C.

[0011] The compositions desirably satisfy the UL 94 VO flame retardant standard. [0012] Another aspect of the invention provides composites made from the compositions. One embodiment of such a composite comprises a porous reinforcement and a composition, as described above, impregnating the porous reinforcement. The porous reinforcement can be, for example, a plurality of fibers.

[0013] Another composite comprises a metal substrate and a composition, as described above, coated onto the metal substrate. The metal substrate can be, for example, a copper foil.

[0014] Yet another aspect of the invention provides laminates incorporating the compositions or composites. In one embodiment, a laminate comprises a first layer comprising a porous reinforcement, a second layer comprising a metal and a continuous epoxy resin matrix binding the first layer and the second layer, the epoxy resin matrix comprising a cured composition comprising an epoxy resin, optionally comprising at least one of phosphorus or nitrogen, and a hardener blend comprising an amine-based curing agent and a phenolic curing agent. In this embodiment, the composition can be characterized in that a pre-preg powder made from the composition has an ΔMMV of no greater than 20% after 24 hours at 100% relative humidity and 25 ⁰C.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0015] Definitions:

[0016] Unless stated to the contrary, implicit from the context, or customary in the art, all parts and percents are based on weight and all test methods are current as of the filing date of this disclosure. For purposes of United States patent practice, the contents of any referenced patent, patent application or publication are incorporated by reference in their entirety (or its equivalent US version is so incorporated by reference) especially with respect to the disclosure of synthetic techniques, definitions (to the extent not inconsistent with any definitions specifically provided in this disclosure), and general knowledge in the art.

[0017] Numerical ranges include all values from and including the lower and the upper values, in increments of one unit, provided that there is a separation of at least two units between any lower value and any higher value. As an example, if a compositional, physical or other property or process parameter, such as, for example, melt viscosity, temperature, etc., is from 100 to 1,000, it is intended that all individual values, such as 100, 101, 102, etc., and sub ranges, such as 100 to 144, 155 to 170, 197 to 200, etc., are expressly enumerated. For ranges containing values which are less than one or containing fractional numbers greater than one (e.g., 1.1, 1.5, etc.), one unit is considered to be 0.0001, 0.001, 0.01 or 0.1, as appropriate. For ranges containing single digit numbers less than ten (e.g., 1 to 5), one unit is typically considered to be 0.1. These are only examples of what is specifically intended, and all possible combinations of numerical values between the lowest value and the highest value enumerated, are to be considered to be expressly stated in this disclosure.

[0018] The term "comprising" and its derivatives are not intended to exclude the presence of any additional component, step or procedure, whether or not the same is specifically disclosed. In order to avoid any doubt, any process or composition claimed through use of the term "comprising" may include any additional steps, equipment, additive, adjuvant, or compound whether polymeric or otherwise, unless stated to the contrary. In contrast, the term, "consisting essentially of excludes from the scope of any succeeding recitation any other component, step or procedure, excepting those that are not essential to operability. The term "consisting of excludes any component, step or procedure not specifically delineated or listed. The term "or", unless stated otherwise, refers to the listed members individually as well as in any combination.

[0019] "Polymer" means a polymeric compound prepared by polymerizing monomers, whether of the same or a different type. The generic term polymer thus embraces the term homopolymer, usually employed to refer to polymers prepared from only one type of monomer, and the term interpolymer as defined below.

[0020] "Interpolymer" means a polymer prepared by the polymerization of at least two different types of monomers. This generic term includes copolymers, usually employed to refer to polymers prepared from two different types of monomers, and polymers prepared from more than two different types of monomers, e.g., terpolymers, tetrapolymers, etc.

[0021] The term "pre-preg" means a composite of a porous reinforcement pre- impregnated with a curable resin composition. Pre -impregnation of the porous reinforcement can be carried out by a variety of methods, including, immersing the porous reinforcement in a curable resin composition, spraying the porous reinforcement with a curable resin composition, exposing the porous reinforcement to a stream of a curable resin composition and vacuum infiltrating the porous reinforcement with a curable resin composition. Following impregnation, any excess resin composition on the porous reinforcement is allowed to drain off, or is otherwise removed, to provide the "pre-preg". Examples of porous reinforcements from which pre-pregs can be fabricated include fiber-containing materials such as fibers, woven cloth, fiber mesh, fiber mats, and unwoven aramid reinforcements such as those sold under the trademark THERMOUNT, available from DuPont, Wilmington, Del. Preferably, such materials are made from glass, fiberglass, quartz, paper, which may be cellulosic or synthetic, a thermoplastic resin substrate such as aramid reinforcements, polyethylene, poly(p-phenyleneterephthalamide), polyester, polytetrafluoroethylene and poly(p-phenylenebenzobisthiazole), syndiotatic polystyrene, carbon, graphite, ceramic or metal. Preferred materials include glass or fiberglass, in woven cloth or mat form.

[0022] The term "B-stage pre-preg" refers to a pre-preg that has undergone processing at elevated temperatures, such that the pre-preg has undergone a partial cure.

[0023] The term "epoxy pre-preg" means a pre-preg made from a composite of a porous reinforcement pre-impregnated with an epoxy resin.

[0024] The term "laminate" refers to an article made by pressing together, under elevated temperatures and pressures, the multiple layers of a multi-layered structure that includes at least one layer of pre-preg, such that the layer(s) of pre-preg are completely or essentially completely cured.

[0025] "Minimum melt viscosity" (MMV) for a pre-preg powder refers to the minimum viscosity realized by the pre-preg powder as the temperature of the pre-preg powder is increased to a certain temperature. A pre-preg powder is a powder remaining after the reinforcements have been sifted out, or otherwise removed, from a pre-preg. Viscosity measurements are conducted on pre-preg powders so that the reinforcements do not affect the measured values. The minimum melt viscosity is the result of the competing effects of increasing temperature, which tends to decrease the pre-preg powder viscosity, and the progression of thermal curing, which tends to increase the viscosity. For the purposes of this disclosure, MMV is measured according to the procedures and conditions described in the Examples section, below.

[0026] "Delta MMV" (ΔMMV) for a pre-preg powder refers to the change in the MMV of a pre-preg powder when that pre-preg powder is stored for 24 hours at 100% relative humidity and 25 ⁰C. The initial MMV value for the pre-preg powder can be measured on a pre-preg sample immediately after the pre-preg has been fabricated. [0027] One aspect of the invention provides dual-cure hardener blends for halogen-free epoxy resin compositions. Other aspects of the invention provide resin compositions made from the dual-cure hardener blends and composites made from the resin compositions. The dual-cure hardener blends are based on a blend of at least one amine-based curing agent and at least one phenolic curing agent. The dual-cure hardener blends are useful for non-halogen epoxy resins containing phosphorus and/or nitrogen because they can improve the B-stage pre-preg storage stability as well as the wettability and flow during processing of the epoxy resin compositions. In particular, pre-preg powders made from the epoxy resin compositions and the dual-cure hardener blends are characterized by ΔMMVs of 20% or less. This includes embodiments in which the pre-preg powders are characterized by ΔMMVs of < 15% and further includes embodiments in which the pre-preg powders are characterized by ΔMMVs of < 0%. In addition the compositions and composites made therefrom can meet UL 94 VO flammability requirements.

[0028] "UL-94" is the Underwriters' Laboratory (UL) Bulletin 94 Tests for Flammability of Plastic Materials for Parts in Devices and Appliances. The material tested is UL 94 V-O classified if:

• None of the five test specimens burn for over 10 seconds at any time when the burner flame is removed.

• The total burning time of the 10 ignition test does not exceed 50 seconds.

• No test specimen burns either with a flame or afterglow to the clamp.

• No burning drops should fall which would cause the cotton underneath to ignite from any test specimen.

• The afterglow burning of no test specimen exceeds 30 seconds. The material tested is UL 94 V-I classified if: • None of the five test specimens burn for over 30 seconds at any time when the burner flame is removed.

• The total burning time of the 10 ignition test does not exceed 250 seconds.

• No test specimen burns either with a flame or afterglow to the clamp.

• No burning drops should fall which would cause the cotton underneath to ignite from any test specimen. • The afterglow burning of no test specimen exceeds 60 seconds. The material tested is UL 94 V-2 classified if:

• None of the five test specimens burn for over 30 seconds at any time when the burner flame is removed.

• The total burning time of the 10 ignition test does not exceed 250 seconds.

• No test specimen burns either with a flame or afterglow to the clamp.

• Only such burning pieces may fall from the test specimen, which burn only

momentarily, and of which some ignite the cotton underneath.

• The afterglow burning of no test specimen exceeds 60 seconds.

[0029] Once basic embodiment of a composition in accordance with the present invention includes an epoxy resin, optionally comprising at least one of phosphorus or nitrogen, and a hardener blend, the hardener blend comprising an amine-based curing agent and a phenolic curing agent. Each of these components is described in greater detail immediately below.

[0030] Epoxy Resins:

[0031] The compositions of the present invention include at least one epoxy resin. In some embodiments, the epoxy resin is a phosphorus- or nitrogen-containing epoxy resin. These are epoxy resins that have been covalently modified (desirably to meet UL 94 VO performance requirements) with a flame retardant compound, either as a side chain or as part of the polymer backbone itself. Examples of phosphorus- and nitrogen-containing epoxy resins are described in U.S. Patent Nos. 6,645,631, 6,617,029 and 5,756,638 and in European Patent No. EP 1,592,746. U.S. Patent No. 5,112,932 describes suitable oxazolidone modified epoxy resins.

[0032] The epoxy resin may be modified, for example, by reaction with a phosphorus element-containing or a nitrogen element-containing compound or monomer during or after the polymerization of the epoxy resin. Phosphorus and nitrogen element-containing compounds or monomers useful in the present invention generally contain reactive groups such as a phenolic group, an acid group, an amino group, an acid anhydride group, a phosphite group, or a phosphinate group which can react with the epoxy groups of the epoxy resin. Examples of phosphorus element-containing compounds include, for example, one or more of the following compounds: P-H functional compounds such as for example HCA, dimethylphosphite, diphenylphosphite, ethylphosphonic acid, diethylphosphinic acid, methyl ethylphosphinic acid, phenyl phosphonic acid, phenyl phosphinic acid, vinyl phosphoric acid, phenolic (HCA--HQ) and the like; tris(4-hydroxyphenyl)phosphine oxide, bis(2- hydroxyphenyl)phenylphosphine oxide, bis(2-hydroxyphenyl)phenylphosphinate, tris(2- hydroxy-5-methylphenyl)phosphine oxide; acid anhydride compounds such as M-acid-AH and the like; and amino functional compounds such for example bis(4- aminophenyl)phenylphosphate, and mixtures thereof.

[0033] The epoxy resins contain at least one vicinal epoxy group. The epoxy resin can be, for example, saturated or unsaturated, aliphatic, cycloaliphatic, aromatic or heterocyclic and may be substituted. The epoxy resin can also be monomeric or polymeric. The epoxy resin can be a polyepoxide. Polyepoxide as used herein refers to a compound or mixture of compounds containing more than one epoxy moiety.

[0034] The epoxy resins utilized in the composition of the present invention may be, for example, an epoxy resin or a combination of epoxy resins prepared from an epihalohydrin and a phenol or a phenol type compound, prepared from an epihalohydrin and an amine, prepared from an epihalohydrin and a carboxylic acid, or prepared from the oxidation of unsaturated compounds.

[0035] In one embodiment, the epoxy resins utilized in the compositions of the present invention include those resins produced from an epihalohydrin and a phenol or a phenol type compound. The phenol type compound includes compounds having an average of more than one aromatic hydroxyl group per molecule. Examples of phenol type compounds include dihydroxy phenols, biphenols, bisphenols, hydrogenated bisphenols, alkylated biphenols, alkylated bisphenols, trisphenols, phenol-aldehyde resins, novolac resins (that is the reaction product of phenols and simple aldehydes, preferably formaldehyde), phenol-aldehyde novolac resins, naphthal novolac resins, substituted phenol-aldehyde novolac resins, phenol- hydrocarbon resins, substituted phenol-hydrocarbon resins, phenol-hydroxybenzaldehyde resins, alkylated phenol-hydroxybenzaldehyde resins, hydrocarbon-phenol resins, hydrocarbon-alkylated phenol resins, or combinations thereof.

[0036] In some embodiments, the epoxy resins utilized in the compositions of the invention preferably include those resins produced from an epihalohydrin and bisphenols, hydrogenated bisphenols, novolac resins, and polyalkylene glycols, or combinations thereof. Examples of bisphenol A-based epoxy resins useful in the present invention include commercially available resins such as D.E.R.™ 300 series and D.E.R.™ 600 series, commercially available from The Dow Chemical Company. Examples of epoxy Novolac resins useful in the present invention include commercially available resins such as D.E.N.™ 400 series, commercially available from The Dow Chemical Company.

[0037] In some embodiments, the epoxy resins utilized in the compositions of the invention include those resins produced from an epihalohydrin and resorcinol, catechol, hydroquinone, biphenol, bisphenol A, bisphenol AP (l,l-bis(4-hydroxyphenyl)-l -phenyl ethane), bisphenol F, bisphenol K, bisphenol C, phenol-formaldehyde novolac resins, alkyl substituted phenol-formaldehyde resins, phenol-hydroxybenzaldehyde resins, cresol- hydroxybenzaldehyde resins, naphthal novolac resins, dicyclopentadiene-phenol resins, dicyclopentadiene-substituted phenol resins, tetramethylbiphenol, or combinations thereof.

[0038] The preparation of such compounds is well known in the art. See Kirk-Othmer, Encyclopedia of Chemical Technology, 3rd Ed., Vol. 9, pp 267-289. Examples of epoxy resins and their precursors suitable for use in the compositions of the invention are also described, for example, in U.S. Pat. Nos. 5,137,990 and 6,451,898.

[0039] In some embodiments, the epoxy resins utilized in the compositions of the present invention include those resins produced from an epihalohydrin and an amine. Suitable amines include diaminodiphenylmethane, aminophenol, xylene diamine, anilines, or combinations thereof.

[0040] In some embodiments, the epoxy resins utilized in the compositions of the present invention include those resins produced from an epihalohydrin and a carboxylic acid. Suitable carboxylic acids include phthalic acid, isophthalic acid, terephthalic acid, tetrahydro- and/or hexahydrophthalic acid, endomethylenetetrahydrophthalic acid, isophthalic acid, methylhexahydrophthalic acid, or combinations thereof.

[0041] The epoxy resins can be advanced epoxy resins which are the reaction product of one or more epoxy resins components, as described above, with one or more phenol type compounds and/or one or more compounds having an average of more than one aliphatic hydroxyl group per molecule as described above. Alternatively, the epoxy resin may be reacted with a carboxyl substituted hydrocarbon, which is described herein as a compound having a hydrocarbon backbone, preferably a C1-C40 hydrocarbon backbone, and one or more carboxyl moieties.

[0042] In some embodiments, the epoxy resin is the reaction product of a polyepoxide and a compound containing more than one isocyanate moiety or a polyisocyanate. Preferably, the epoxy resin produced in such a reaction is an epoxy-terminated polyoxazolidone. Preferably, the epoxy resin component of the composition contains at least one oxazolidone- modified epoxy resin.

[0043] The resin content, by treated weight, of a pre-preg containing the epoxy-resin can be measured according to IPC TM-650 2.3.16.1C.

[0044] Amine-Based Curing Agents:

[0045] The term "amine-based curing agent" refers to compounds, either polymeric or monomeric, having at least one amino group or imino group capable of reacting with epoxy groups of the epoxy resin. The phrase "having at least one amino group or imino group" means that the amine-based curing agent can have at least one amino group and/or at least one imino group and may have one or more kinds of the group. The amine-based curing agent can be, for example, an aliphatic polyamine, an aromatic polyamine or an alicyclic polyamine.

[0046] Specific examples of the acyclic aliphatic polyamine-based curing agents include ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, propylenediamine, dipropylenetriamine, hexamethylenediamine, tri ethylenediamine, 2,5 -dimethylhexamethylenediamine, trimethylhexamethylenediamine, and bis(hexamethylene)triamine. Specific examples of cyclic aliphatic polyamine-based curing agents include 1 ,2-cyclohexanediamine, l,3-bis(aminomethyl cyclohexane), isophoronediamine, N-aminoethylpiperazine, bis(4-amino-3 -methylcyclohexyl)methane, bis(4-aminocyclohexyl)methane, and l,3,5-tris(aminomethyl)benzene. Specific examples of aromatic polyamine-based curing agents include diethyltolunediamine (DETDA), dimethyltolunediamine (DMTDA), dimethylthioltoluenediamine (DETTDA), m- phenylenediamine, metaxylenediamine, diaminodiphenylmethane, and diaminodiphenylsulfone. Dicyandiamide (DICY) is another specific example of an amine- based curing agent. In some embodiments, aromatic amines containing hydrophobic groups (e.g., DETDA) and DICY are preferred amine-based curing agents. [0047] Phenolic Curing Agents:

[0048] The term "phenolic curing agents" refers to compounds, either polymeric or monomeric, which have one or more phenolic hydroxyl (-OH) groups capable of reacting with epoxy groups of the epoxy resin at elevated temperatures, or which are capable of generating one or more phenolic hydroxyl groups capable of reacting with epoxy groups at elevated temperatures. The present compositions desirably include at least one phosphorus- containing phenolic curing agent.

[0049] The phenolic curing agents can be, for example, a novolac, bisphenol A novolac, cresol novolac, or naphthol novolac obtainable by condensation of phenols, bisphenol A, cresols, naphthols, xylenols and/or other alkyl phenols with a formaldehyde. Phenolic resoles, such as bisphenol A resoles, also can be used as phenolic curing agents. Phosphorus- containing bisphenol A resoles are well-suited for use as the phenolic curing agents of the present compositions.

[0050] Suitable phenolic curing agents include dihydroxy phenols, biphenols, bisphenols, alkylated biphenols, alkylated bisphenols, trisphenols, phenol-aldehyde resins, phenol- aldehyde novolac resins, substituted phenol-aldehyde novolac resins, phenol-hydrocarbon resins, substituted phenol-hydrocarbon resins, phenol-hydroxybenzaldehyde resins, alkylated phenol-hydroxybenzaldehyde resins, hydrocarbon-phenol resins, hydrocarbon-alkylated phenol resins, or combinations thereof. Preferably, the phenolic curing agent includes substituted or unsubstituted phenols, biphenols, bisphenols, novolacs, resoles or combinations thereof. The phenolic curing agent may also include the multi-functional phenolic cross-linkers described in U.S. Pat. No. 6,645,631, Column 4, lines 57-67 to Column 6, lines 1-57.

[0051] Examples of phenolic curing agents capable of generating phenolic hydroxyl functionalities are benzoxazines and polybenzoxazines. By "generating" herein it is meant that upon heating the curing agent compound, the curing agent compound transforms into another compound having phenolic hydroxyl groups, which acts as a curing agent.

[0052] Examples of commercially-available phenolic curing agents include DEH 85, DEH 87 and DEH 90, available from Dow Chemical Company.

[0053] In some embodiments, the weight ratio of phenolic curing agent to amine-based curing agent is between 80:1 and 1 :80, preferably between 50:1 and 1 :50, more preferably between 30:1 and 1 :30 and still more preferably between 10:1 and 1 :10. In some embodiments, the composition comprises 25 to 55 weight percent phenolic curing agent, based on the total weight of the solids content of the composition. This includes embodiments in which the composition comprises 30 to 50 weight percent phenolic curing agent, based on the total weight of the solids content of the composition and further includes embodiments in which the composition comprises 35 to 45 weight percent phenolic curing agent, based on the total weight of the solids content of the composition. In some embodiments, the composition comprises 1 to 15 weight percent amine-based curing agent, based on the total weight of the solids content of the composition. This includes embodiments in which the composition comprises 2 to 12 weight percent amine-based curing agent, based on the total weight of the solids content of the composition and further includes embodiments in which the composition comprises 3 to 10 weight percent amine-based curing agent, based on the total weight of the solids content of the composition.

[0054] Additional Curing Agents:

[0055] The compositions can further include additional curing agents that can also act as flame retardants. For example, the compositions can include phosphorus-containing curing agents, such as dioctyl phthalate (DOP) based curing agents (e.g., DOP-BN and DOP-HQ), melamine poly(phosphate), and poly(l,3 -phenyl ene methylphosphonate) (Fyrol PMP). European Patent No. EP 1,753,772 and U.S. Patent No. 6,403,220 describe suitable phosphorus containing curing agents, including DOP-BN).

[0056] Curing Catalysts:

[0057] The present compositions can further optionally include one or more curing catalysts (also referred to as a curing accelerator or cure activator). Such catalysts include nitrogen-containing compounds which catalyze the reaction of the epoxy resin with the curing agents. The nitrogen-containing catalyst compound can act with the curing agents to form an infusible reaction product between the curing agents and the epoxy resin in a final article of manufacture such as a structural composite or laminate. By an infusible reaction product, it is meant that the epoxy resin has essentially completely cured, which for example may be at a time when there is little or no change between two consecutive T_g measurements (ΔT_g). [0058] In one embodiment, the nitrogen-containing compound is a heterocyclic nitrogen compound, an amine or an ammonium compound. Preferably, the nitrogen-containing catalyst compound is an imidazole, a derivative of an imidazole, or mixtures thereof. Examples of suitable imidazoles include 2-methylimidazole (2-MI), 2-phenylimidazole (2- PI), 2-ethyl-4-methyl imidazole, and combinations thereof. Examples of suitable catalyst compounds also include those compounds listed in European Patent Specification EP 0 954 553 Bl.

[0059] The nitrogen-containing catalyst compounds of the present invention can be used alone, in combination with each other, or in combination with other accelerators or curing catalyst compounds known in the art. Other known general classes of catalyst compounds include, but are not limited to phosphine compounds, phosphonium salts, imidazolium salts, amines, ammonium salts, and diazabicyclo compounds as well as their tetraphenylborate salts, phenol salts and phenol novolac salts. Examples of suitable catalyst compounds to be used in combination with the nitrogen -containing catalyst compound of the present invention also include those compounds listed in U.S. Pat. No. 6,255,365.

[0060] The amount of catalyst utilized in the present compositions is an amount effective to catalyze the reaction of the epoxy resin with the curing agents. The amount of catalyst to be utilized depends upon the components utilized in the composition, the processing requirements, and the performance targets of the articles to be manufactured. In one embodiment, the amount of curing accelerators used is preferably from 0.001 percent to less than 10 percent by weight (based on total solids content of the composition), more preferably from 0.01 percent to 5 percent by weight, even more preferably from 0.02 percent to 2 percent by weight, and even most preferably from 0.04 percent to 1 percent by weight.

[0061] Ratio of Curing Agent to Epoxy Resin:

[0062] The ratio of curing agent to epoxy resin is desirably suitable to provide a completely, or essentially completely cured resin. The amount of curing agent which may be present can vary depending upon the particular curing agents used (due to the cure chemistry and curing agent equivalent weight). In one embodiment the weight ratio between the epoxy resin(s) and the phenolic and amine-based curing agents is between 0.1 :1 and 1 :0.1, preferably between 1 :0.5 and 0.5:1, and more preferably between 1 :0.8 and 0.8:1. In some embodiments, the composition comprises 30 to 55 weight percent curing agent based on the total solids content of the composition. This includes embodiments in which the composition comprises 35 to 55 weight percent curing agent based on the total solids content of the composition and further includes embodiments in which the composition comprises 40 to 50 weight percent curing agent based on the total solids content of the composition. In some embodiments, the composition comprises 40 to 70 weight percent epoxy resin based on the total solids content of the composition. This includes embodiments in which the composition comprises 45 to 65 weight percent epoxy resin based on the total solids content of the composition and further includes embodiments in which the composition comprises 40 to 60 weight percent epoxy resin based on the total solids content of the composition.

[0063] Other Additives and Solvents:

[0064] Optionally, the compositions of the present invention may further contain other components typically used in an epoxy resin composition particularly for making pre-pregs and laminates; and which do not detrimentally affect the properties or performance of the composition of the present invention, or the final cured product therefrom. For example, other optional components useful in the compositions include toughening agents; curing inhibitors; fillers; wetting agents; colorants; flame retardants; solvents; thermoplastics; processing aids; fluorescent compounds; such as tetraphenolethane (TPE) or derivatives thereof; UV blocking compounds; and other additives. The compositions of the present invention may also include other optional constituents such as inorganic fillers and additional flame retardants, for example antimony oxide, octabromodiphenyl oxide, decabromodiphenyl oxide, phosphoric acid and other such constituents including, but not limited to, dyes, pigments, surfactants, flow control agents, and plasticizers.

[0065] The compositions of the present invention can also optionally contain a solvent; or any of the components of the composition, such as the epoxy resin, curing agents, and/or catalyst compounds may optionally be used in combination with or separately be dissolved in a solvent. Preferably, the concentration of solids in the solvent is at least 50 percent and no more than 90 percent solids, preferably between 55 percent and 80 percent, and more preferably between 60 percent and 70 percent solids. Non-limiting examples of suitable solvents include ketones, alcohols, water, glycol ethers, aromatic hydrocarbons and mixtures thereof. Preferred solvents include acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, methylpyrrolidinone, propylene glycol monomethyl ether, propylene glycol monomethyl ether acetate, ethylene glycol monomethyl ether, methyl amyl ketone, methanol, isopropanol, toluene, xylene, dimethylformamide (DMF). A single solvent may be used, but also separate solvents may be used for one or more components.

[0066] The components of the compositions of the present invention can be mixed together in any order. For example, the composition can be produced by preparing a first composition comprising the epoxy resin, and a second composition comprising the phenolic and amine-based curing agents. Either the first or the second composition may also comprise a curing catalyst. All other components may be present in the same composition, or some may be present in the first, and some in the second. The first composition can then be mixed with the second composition to produce a curable flame retardant epoxy resin composition.

[0067] Composites:

[0068] The present compositions can be used to make composite materials by techniques such as by pultrusion, moulding, encapsulation or coating. In one embodiment, the present invention provides for a process for preparing a resin-coated article. The process steps include contacting an article or a substrate with a resin composition. The composition can be contacted with an article by any method known to those skilled in the art. Examples of such contacting methods include powder coating, spray coating, die coating, roll coating, resin infusion process, and contacting the article with a bath containing the composition. In another embodiment, the present invention provides for articles, especially pre-pregs and laminates, prepared by the process of the present invention.

[0069] Also provided are pre-pregs obtained by impregnating a porous reinforcement with an epoxy resin composition of the present invention. The present invention also provides metal-coated foils obtained by coating a metal foil with an epoxy resin composition of the present invention. The present invention further provides laminates with enhanced properties obtained by laminating the above pre-preg and/or the above metal-coated foil.

[0070] As mentioned above, the present compositions may be used to impregnate various reinforcements, including porous reinforcements. The reinforcing materials which can be coated with the compositions include any material which would be used in the formation of composites, pre-pregs, and/or laminates. Examples of appropriate substrates include fiber- containing materials such as woven cloth, mesh, mat, fibers, and unwoven aramid reinforcements such as those sold under the trademark THERMOUNT, available from DuPont, Wilmington, Del. Preferably, such materials are made from glass, fiberglass, quartz, paper, which may be cellulosic or synthetic, a thermoplastic resin substrate such as aramid reinforcements, polyethylene, poly(p-phenyleneterephthalamide), polyester, polytetrafluoroethylene and poly(p-phenylenebenzobisthiazole), syndiotatic polystyrene, carbon, graphite, ceramic or metal. Preferred materials include glass or fiberglass, in woven cloth or mat form.

[0071] In one embodiment, a reinforcing material is contacted with a resin composition (e.g., by contacting it with a bath of the composition), dissolved and intimately admixed in a solvent or a mixture of solvents. The coating occurs under conditions such that the reinforcing material is coated with the resin composition. Thereafter the coated reinforcing materials can be heated to a temperature sufficient to cause the solvents to evaporate, but below the temperature at which the resin composition undergoes significant cure during the heat exposure, although partial cure of the epoxy resin component (B-staging) can occur during heat-exposure.

[0072] One or more sheets of pre-preg can be processed into laminates, optionally with one or more sheets of electrically-conductive material such as copper. In such further processing, one or more segments or parts of the coated reinforcing material are brought in contact with one another and/or the conductive material. Thereafter, the contacted parts are exposed to elevated pressures and temperatures sufficient to cause the epoxy resin to cure wherein the resin on adjacent parts react to form a continuous epoxy resin matrix. Before being cured the parts can be cut and stacked or folded and stacked into a part of desired shape and thickness. In some embodiments it is desirable to subject the laminate or final product to a post cure outside of a press. This step is designed to complete the curing reaction. This post cure step may be performed in a vacuum to remove any components which may volatilize.

EXAMPLES

[0073] Measurements:

[0074] Pre-preg stability, as characterized by the MMV, is measured by an Anton Pear physica MGR-301 rheometer with a cone plate of CP25-2 at a constant shearing rate. For the purpose of MMV measurements, samples are prepared as follows: pre-pregs are crumbled and filtered with 120 micro-screen nets. This provides a pre-preg powder with the glass reinforcement removed. Then 0.32g of the resulting powder is placed on a peltier plate that is pre-heated to 16O⁰C. The shear rate during first 100 seconds is set to 26 rpm/min, and then adjusted to 13 rpm/min for the last 250 seconds. Melting viscosity vs. time is monitored. The aged samples are prepared by storing the pre-preg powders in a humidity-controlled chamber for 24 hours at 100% relative humidity and 25 ⁰C, followed by measuring their MMVs to determine the ΔMMV values.

[0075] Materials:

[0076] In the examples below, XZ 92748.00 is an epoxy novolac resins at 85 wt% solids in 1 -methoxy-2-propanol (PM); XZ 92740.00 is a high Tg epoxy novolac resin available from the Dow Chemical Company; XZ 92749.00 is a phosphorus-containing phenolic curing agent available from the Dow Chemical Company (it is a blend of XZ 92535, a phenolic novolac resin at 50 wt% solids in methoxypropyl (PMA) and XZ 92741, a phosphorus containing bisphenol A resole at 57 wt% solids in PM.) DETDA is available from Albemarle Co. DICY is available from Darong Co. Ltd. Other materials are available from Aldrich Chemical Co. 2-phenylimidazole (10 wt% solids in Dowanol™, PM) and 2-methylimidazole are used as catalysts.

[0077] Example 1 : Control.

[0078] A control sample is made without a dual-cure hardener blend. The control sample is made from a mixture of the different components at the ratios listed in Table Ia. The mixture is placed on a shaker to mix.

[0079] Pre-pregs were prepared from the control sample by hand painting glass webs (E-7628 type) with the sample, and baking them in an oven at 17O⁰C for a few minutes to control the pre-preg's gel time for further stability testing. The MMV are measured by an Anton Pear MCR 301 rheometer according to the method described above. The results are shown in Table Ib.

[0080] The gel time for the control sample is 280 seconds (s), the bake time for the pre- preg is 270 s and the gel time for the pre-preg is 51 s. Table Ia

Table Ib

[0081] Example 2: Inventive Sample 1.

[0082] A working sample of a flame retardant epoxy resin composition in accordance with this invention is prepared by mixing the components listed in Table 2a according to the process described in Example 1. The MMVs are recorded as described above and the results are shown in Table 2b.

[0083] The gel time for this working sample is 297 seconds (s), the bake time for the pre-preg is 330 s and the gel time for the pre-preg is 45 s. The composition had a phosphorus content ("P%') of 3.12 %, based on the based on the solids content of the composition, an epoxy group stoichiometric mole weight ("Epo. MoL") of 0.31 and a curing group (including -OH and -NH) stoichiometric mole weight ("Hard. MoI.") of 0.30.

Table 2a

Table 2b

[0084] Example 3 : Comparative Sample 1. [0085] A comparative sample of a flame retardant epoxy resin composition is prepared by mixing the components listed in Table 3 a according to the process described in Example 1. The MMVs are recorded as described above and the results are shown in Table 3b.

[0086] The gel time for this comparative sample is 251 seconds (s), the bake time for the pre-preg is 235 s and the gel time for the pre-preg is 75 s.

Table 3a

Table 3b

[0087] Example 4: Inventive Sample 2.

[0088] A comparative sample of a flame retardant epoxy resin composition is prepared by mixing the components listed in Table 4a according to the process described in Example 1. The MMVs are recorded as described above and the results are shown in Table 4b.

[0089] The gel time for this comparative sample is 253 seconds (s), the bake time for the pre-preg is 330 s and the gel time for the pre-preg is 60 s. The composition had a phosphorus content ("P%') of 3.13 %, based on the based on the solids content of the composition, an epoxy group stoichiometric mole weight ("Epo. MoL") of 0.36 and a curing group (including -OH and -NH) stoichiometric mole weight ("Hard. MoI.") of 0.31.

Table 4a

Table 4b

MMV(PaS)

[0090] Example 5: Inventive Sample 3.

[0091] A working sample of a flame retardant epoxy resin composition in accordance with this invention is prepared by mixing the components listed in Table 5a according to the process described in Example 1. The film glass transition temperature is measured by DSC (differential scanning calorimetry) after the solvent is removed and cured on a 190 ⁰C hot plate for 90 min. The MMVs are recorded as described above and the results are shown in Table 5b.

[0092] The gel time for this working sample is 235 seconds (s), the bake time for the pre-preg is 200 s and the gel time for the pre-preg is 58 s. The composition had a phosphorus content ("P%') of 3.12 %, based on the based on the solids content of the composition, an epoxy group stoichiometric mole weight ("Epo. MoL") of 0.29 and a curing group (including -OH and -NH) stoichiometric mole weight ("Hard. MoI.") of 0.28.

Table 5a

Table 5b

[0093] Example 6: Inventive Example 4.

[0094] A working sample of a flame retardant epoxy resin composition in accordance with this invention is prepared by mixing the components listed in Table 6a according to the process described in Example 1. The film glass transition temperature is measured by DSC (differential scanning calorimetry) after the solvent is removed and cured on a 190 ⁰C hot plate for 90 min. The MMVs are recorded as described above and the results are shown in Table 6b.

[0095] The gel time for this working sample is 334 seconds (s) and the bake time for the pre-preg is 260 s. The composition had a phosphorus content ("P%') of 3.05 %, based on the based on the solids content of the composition, an epoxy group stoichiometric mole weight ("Epo. MoI.") of 0.326 and a curing group (including -OH and -NH) stoichiometric mole weight ("Hard. MoI.") of 0.331.

Table 6a

Table 6b

[0096] Example 7: Inventive Sample 5.

[0097] A working sample of a flame retardant epoxy resin composition in accordance with this invention is prepared by mixing the components listed in Table 7a according to the process described in Example 1. The MMVs are recorded as described above and the results are shown in Table 7b.

[0098] The gel time for this working sample is 294 seconds (s), the bake time for the pre-preg is 255 s and the gel time for the pre-preg is 41 s. The composition had a phosphorus content ("P%') of 2.93 %, based on the based on the solids content of the composition, an epoxy group stoichiometric mole weight ("Epo. MoI.") of 0.331 and a curing group (including -OH and -NH) stoichiometric mole weight ("Hard. MoI.") of 0.343.

Table 7a

Ingredient

Solid content (wt % ) | Solid weight (g) | Solution(g)

Table 7b

[0099] Example 8: Comparative Sample 2.

[00100] A comparative sample of a flame retardant epoxy resin composition is prepared by mixing the components listed in Table 8a according to the process described in Example 1.

The MMVs are recorded as described above and the results are shown in Table 8b.

[00101] The gel time for this comparative sample is 257 seconds (s), the bake time for the pre-preg is 315 s and the gel time for the pre-preg is 77 s. The composition had a phosphorus content ("P%') of 3.03 %, based on the based on the solids content of the composition, an epoxy group stoichiometric mole weight ("Epo. MoI.") of 0.275 and a curing group (including -OH and -NH) stoichiometric mole weight ("Hard. MoI.") of

0.277.

Table 8a

Table 8b

(DDS = diaminodiphenyl sulfone)

[00102] Example 9: Comparative Sample 3.

[00103] A comparative sample of a flame retardant epoxy resin composition is prepared by mixing the components listed in Table 9a according to the process described in Example 1. The MMVs are recorded as described above and the results are shown in Table 9b.

[00104] The gel time for this comparative sample is 252 seconds (s), the bake time for the pre-preg is 265 s and the gel time for the pre-preg is 45 s. The composition had a phosphorus content ("P%') of 3.03 %, based on the based on the solids content of the composition, an epoxy group stoichiometric mole weight ("Epo. MoI.") of 0.292 and a curing group (including -OH and -NH) stoichiometric mole weight ("Hard. MoI.") of 0.299.

Table 9a

(SAA = sulfanilamide) Table 9b

[00105] Example 10: Comparative Sample 4.

[00106] A comparative sample of a flame retardant epoxy resin composition is prepared by mixing the components listed in Table 10a according to the process described in Example 1. The MMVs are recorded as described above and the results are shown in Table 10b.

[00107] The gel time for this comparative sample is 272 seconds (s), the bake time for the pre-preg is 305 s and the gel time for the pre-preg is 84 s. The composition had a phosphorus content ("P%') of 3.03 %, based on the based on the solids content of the composition, an epoxy group stoichiometric mole weight ("Epo. MoI.") of 0.264 and a curing group (including -OH and -NH) stoichiometric mole weight ("Hard. MoI.") of 0.270.

Table 10a

(MDA = m-phenylene diamine)

Table 10b

[00108] It is specifically intended that the present invention not be limited to the embodiments and illustrations contained herein, but include modified forms of those embodiments including portions of the embodiments and combinations of elements of different embodiments as come within the scope of the following claims.

Claims

1. A composition comprising:

an epoxy resin; and

a hardener blend comprising:

an amine-based curing agent; and

a phenolic curing agent;

the composition characterized in that a pre-preg powder made from the composition has an ΔMMV of no greater than 20% after 24 hours at 100% relative humidity and 25 ⁰C.

2. The composition of Claim 1 characterized in that a pre-preg powder made from the composition has a ΔMMV of no greater than 15% after 24 hours at 100% relative humidity and 25 ⁰C.

3. The composition of Claim 1 characterized in that a pre-preg powder made from the composition has a ΔMMV < 0% after 24 hours at 100% relative humidity and 25 ⁰C.

4. The composition of Claim 1, in which the phenolic curing agent comprises phosphorus.

5. The composition of Claim 1, in which the amine curing agent comprises at least one of DETDA and DICY.

6. The composition of Claim 1, in which the epoxy resin is a phosphorus-containing epoxy resin or a nitrogen-containing epoxy-resin.

7. The composition of Claim 1 , further comprising at least one additional curing agent comprising phosphorus.

8. The composition of Claim 1, in which the amine-based curing agent comprises an aromatic amine comprising hydrophobic groups and the phenolic curing agent comprises a phosphorus-containing compound, the composition characterized in that a pre-preg powder made from the composition has a ΔMMV < 0% after 24 hours at 100% relative humidity and

25 ⁰C.

9. A composite comprising: a porous reinforcement; and

the composition of Claim 1 impregnating the porous reinforcement.

10. A laminate comprising:

a first layer comprising a porous reinforcement;

a second layer comprising a metal; and

a continuous epoxy resin matrix binding the first layer and the second layer, the epoxy resin matrix comprising a cured composition comprising:

an epoxy resin comprising at least one of phosphorus or nitrogen; and a hardener blend comprising:

an amine-based curing agent; and

a phenolic curing agent;