Composites with a thermoplastic toughened novolac-based epoxy resin matrix

Abstract

The present invention discloses a pre-impregnated composite material (prepreg) that can be cured / molded to form aerospace composite components. The prepreg comprises carbon reinforcing fibers and an uncured resin matrix. The resin matrix comprises an epoxy component that is a combination of a hydrocarbon novolac epoxy resin and a trifunctional epoxy resin and optionally a tetrafunctional epoxy resin. The resin matrix comprises a thermoplastic particulate component and polyethersulfone as a toughening agent.

Description

Technical Field

[0001] The present invention generally relates to pre-impregnated composite materials (prepregs) for preparing high-performance composite parts, particularly suitable for use as aerospace components. The present invention relates to novolac-based epoxy resins toughened with thermoplastic materials and used as the resin matrix in such prepregs. More particularly, the present invention relates to prepregs comprising a thermoplastic-toughened epoxy resin matrix composed of a novolac epoxy resin and a triglycidyl aminophenol epoxy resin. Background Art

[0002] Composite materials are typically composed of a resin matrix and reinforcement fibers as two main components. Composite materials are often required to operate in harsh environments, such as in the aerospace field, where the physical limits and characteristics of composite parts are critical.

[0003] Pre-impregnated composite materials (prepregs) are widely used in the manufacture of composite components. Prepregs are a combination of uncured resin and fiber reinforcement, typically in a form ready to be molded and cured into the final composite component. By pre-impregnating the fiber reinforcement with resin, manufacturers can carefully control the amount and location of resin impregnated into the fiber network and ensure that the resin is distributed within the network as desired. It is well known that the relative amounts of fiber and resin in a composite component, as well as the distribution of the resin within the fiber network, can affect the structural properties of the component.

[0004] Prepregs are the preferred materials for manufacturing load-bearing components or primary structural components, particularly aerospace primary structural components such as wings, fuselages, bulkheads, and control surfaces. It is important that these components have sufficient strength, damage tolerance, and other requirements conventionally determined for these components and structures.

[0005] The fiber reinforcements commonly used in aerospace prepregs are multidirectional woven fabrics or unidirectional tapes containing fibers extending parallel to each other. The fibers are usually in the form of bundles of a large number of individual fibers or monofilaments, which are called "tows." The fibers or tows can also be chopped and randomly oriented in the resin to form non-woven mats. These various fiber reinforcement configurations are combined with carefully controlled amounts of uncured resin. The resulting prepreg is usually placed between protective layers and rolled for storage or transportation to production equipment. The combination of carbon fiber and epoxy resin matrix has become a popular combination for aerospace prepregs.

[0006] Prepregs can also be in the form of short segments of randomly oriented chopped unidirectional tape to form a nonwoven mat of chopped unidirectional tape. This type of prepreg is called a "quasi-isotropic chopped" prepreg. Quasi-isotropic chopped prepreg is similar to the more traditional nonwoven fiber mat prepreg, except that the short lengths of chopped unidirectional tape (the pieces) are randomly oriented in the mat rather than in the chopped fibers. This material is typically used as a sheet molding compound to form parts and molds for making parts.

[0007] The compressive and tensile strengths of cured composite parts are primarily governed by the individual properties of the reinforcing fibers and the matrix resin, as well as the interaction between these two components. Furthermore, the fiber-to-resin volume ratio is an important factor. In many aerospace applications, it is desirable for composite parts to exhibit high compressive and tensile strengths. The open-hole compression (OHC) test is a standard measure of the compressive strength of composite materials. The open-hole tension (OHT) test is also a standard measure of the tensile strength of composite materials.

[0008] In many aerospace applications, it is desirable for composite parts to exhibit high compressive and / or tensile strength under both room temperature / dry conditions and hot / wet conditions. However, attempts to maintain high compressive and tensile strength often have a negative impact on other desired properties such as damage tolerance and interlaminar fracture toughness.

[0009] Selecting a higher modulus resin can be an effective way to increase the compressive strength of a composite material. However, this often results in a decrease in damage tolerance, which is typically measured by a reduction in compressive properties such as compression after impact (CAI) strength. Therefore, it is very difficult to achieve a simultaneous increase in both compressive strength and / or tensile strength without adversely affecting damage tolerance.

[0010] Multilayer prepregs are typically used to form composite components with a layered structure. Delamination of such composite components is an important failure mode. When two layers debond from each other, delamination occurs. Important design limiting factors include both the energy required to initiate delamination and the energy required to diffuse the delamination. The initiation and development of delamination are typically determined by testing mode I and mode II fracture toughness. Fracture toughness is typically measured using a composite material with unidirectional fiber orientation. The interlaminar fracture toughness of a composite material is quantitatively tested using G1c (Double Cantilever Beam) and / or G2c (End NotchFlex). In mode I, pre-cracked laminate failure is determined by peel force, and in mode II, cracking is diffused by shear force.

[0011] One way to improve the interlaminar fracture toughness of parts made from carbon fiber / epoxy prepregs has been to introduce thermoplastic sheets as intercalation layers between prepreg layers. However, this approach often results in a hard, non-sticky material that is difficult to use. Another approach has been to add thermoplastic particles to epoxy resins so that a resin interlayer containing thermoplastic particles is formed between the fiber layers of the final part. Polyamides have been used as such thermoplastic particles. It is also known to include thermoplastic toughening agents in epoxy resins. Toughening agents such as polyethersulfone (PES) or polyetherimide (PEI) are dissolved in the epoxy resin before being applied to the carbon fibers. Thermoplastic toughened epoxy resins comprising a combination of thermoplastic toughening particles and thermoplastic toughening agents have been used in combination with carbon fibers to prepare aerospace prepregs.

[0012] The epoxy resin matrix can include one or more types of epoxy resins. Various combinations of different types of epoxy resins are known to result in widely varying properties of the final composite component. The curing agent used to cure the epoxy resin matrix can also significantly affect the properties of the final composite component. When configuring epoxy resins for use as resin matrices in aerospace prepregs, it is difficult to predict whether new combinations of epoxy resin types and curing agents will also provide the desired property combinations required for aerospace components. This is particularly true when thermoplastic toughening agents and thermoplastic particles form part of the epoxy resin formulation. Therefore, when attempting to formulate new thermoplastic toughened epoxy resins in order to determine whether the resin is suitable for use as a resin matrix in aerospace prepregs, a large amount of testing is involved.

[0013] While existing aerospace prepregs are well suited for their intended use in providing strong and damage tolerant composite parts, there continues to be a need to provide aerospace prepregs that can be used to prepare composite parts that exhibit the desired combination of high tensile and compressive strength (OHC and OHT) while maintaining high levels of damage tolerance (CAI) and interlaminar fracture toughness (G1c and G2c). Summary of the Invention

[0014] According to the present invention, there is provided a pre-impregnated composite material (prepreg) that can be molded to form a composite part having high levels of strength as well as high levels of damage tolerance and interlaminar fracture toughness.

[0015] The pre-impregnated composite material of the present invention is composed of reinforcing fibers and an uncured resin matrix. The uncured resin matrix includes a resin component composed of a novolac epoxy resin and a triglycidylaminophenol epoxy resin or a combination of a triglycidylaminophenol epoxy resin and a tetrafunctional epoxy resin. The uncured resin matrix further includes a thermoplastic particle component, a thermoplastic toughening agent, and a curing agent.

[0016] The present invention also includes methods for making prepregs and methods for molding prepregs into a wide variety of composite parts. The present invention also includes composite parts made using the improved prepregs.

[0017] It has been discovered that resins having the above-described matrix resin formulations can be used to form prepregs that can be molded to form composite parts having unexpectedly high levels of interlaminar fracture toughness.

[0018] The above-described and many other features of the present invention and attendant benefits will be better understood by referring to the following detailed description taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is a perspective view of an aircraft illustrating an exemplary primary aircraft structure that may be prepared using the composite material according to the present invention.

[0020] Figure 2 is a partial view of a helicopter rotor blade illustrating an exemplary primary aircraft structure that may be prepared using the composite material according to the present invention. DETAILED DESCRIPTION

[0021] Uncured epoxy resin composition according to the present invention can be used for the numerous situations that wherein need thermoplastic toughening epoxy resin matrix.Although uncured epoxy resin composition can be used alone, composition is usually used as matrix resin, and this matrix resin is combined with fiber carrier to form the fibrous material that is made of fiber carrier and resin matrix.The form of composite material can be prepreg, partially cured prepreg or fully cured final parts.Term " uncured " is intended to comprise following material when being used in conjunction with the application with prepreg, the resin before being impregnated into fiber carrier, the resin matrix formed when impregnating fiber carrier with resin or composite material: it can stand certain curing, but it is not fully cured to form final composite part or structure.

[0022] Although uncured composite materials can be used for any intended purpose, they are preferably used to prepare parts for aerospace vehicles, such as commercial and military aircraft. For example, uncured composite materials can be used to prepare non-primary (secondary) aircraft structures. However, the preferred use of uncured composite materials is for structural applications, such as primary aircraft structures. Primary aircraft structures or components are those elements of fixed-wing or rotary-wing aircraft that experience significant stress during flight and are necessary for the aircraft to maintain controlled flight. Uncured composite materials can also be used in other structural applications, typically for the preparation of load-bearing components and structures.

[0023] Figure 1A fixed-wing aircraft is depicted at 10 and includes exemplary primary aircraft structures and components that can be prepared using uncured composite materials according to the present invention. The exemplary primary components or structures include wings 12, fuselage 14, and tail assembly 16. Wing 12 includes a plurality of exemplary primary aircraft components, such as ailerons 18, a leading edge 20, a wing strip 22, a spoiler 24, a trailing edge 26, and a trailing edge flap 28. Tail assembly 16 also includes a plurality of exemplary primary components, such as a rudder 30, a fin 32, a horizontal stabilizer 34, an elevator 36, and a tailplane 38. Figure 2 The outer end portion of a helicopter rotor blade 40 is depicted including a spar 42 as a primary aircraft structure and an outer surface 44. Other exemplary primary aircraft structures include a spar, and a plurality of flanges, clips, and connectors that connect the primary components together to form the primary structure.

[0024] The pre-impregnated composite materials (prepregs) of the present invention can be used as a replacement for existing prepregs to form composite parts in the aerospace industry and any other application where high structural strength and damage tolerance are required. The present invention includes replacing existing resins used to prepare prepregs with the resin formulations of the present invention. Therefore, the resin formulations of the present invention are suitable for use as matrix resins in conventional prepreg manufacturing and curing methods.

[0025] The prepreg composite material of the present invention is made up of reinforcing fiber and uncured resin matrix.Reinforcing fiber can be any conventional fiber structure for prepreg and composite sheet molding industry.Carbon fiber is preferably used as reinforcing fiber.

[0026] The resin used to form the resin matrix (matrix resin) includes a resin component consisting of a hydrocarbon novolac epoxy resin in combination with a trifunctional epoxy resin and optionally a tetrafunctional epoxy resin. The matrix resin further includes a thermoplastic particle component, a thermoplastic toughening agent, and a curing agent.

[0027] The hydrocarbon novolac epoxy resin preferably has a dicyclopentadiene backbone and is commercially available from Huntsman Corporation (The Woodlands, TX) as TACTIX 556. This type of hydrocarbon novolac resin is referred to herein as a dicyclopentadiene novolac epoxy resin. The chemical formula of TACTIX 556 is

[0028]

[0029] TACTIX 556 is an amber to dark semi-solid hydrocarbon novolac epoxy resin having an epoxy resin (ISO 3001) of 4.25 to 4.65 eq / kg and an epoxy equivalent weight (ISO 3001) of 215-235 g / eq. TACTIX 556 has a viscosity (ISO 9371B) of 2250 mPa s at 79°C. Dicyclopentadiene novolac epoxy resins other than TACTIX 556 may be used in place of TACTIX 556, provided they have the same chemical formula and properties. For example, another suitable dicyclopentadiene novolac epoxy resin is XD-1000-2L, which is commercially available from Nippon Kayaku Co., Ltd. (Chiyoda-ku, Tokyo). TACTIX 556 is the preferred hydrocarbon novolac epoxy resin for use in accordance with the present invention.

[0030] In the case of tetrafunctional epoxy resin, the amount of hydrocarbon novolac epoxy resin present in the uncured resin can be 8 to 20wt%, based on the gross weight of the uncured resin matrix. Preferably, the uncured resin will comprise 10 to 17wt% dicyclopentadiene novolac epoxy resin. Uncured resin formulations comprising 13 to 15wt% dicyclopentadiene novolac epoxy resin are particularly preferred because they provide an unexpectedly high G2c of about 13 when the ratio of polyimide particles to polyamide particles is 3.2: 1 to 2.8: 1. In this embodiment of the invention (it is referred to as DEN / TRIF / TETF matrix resin in this application), the uncured resin component is made up of dicyclopentadiene novolac epoxy resin, trifunctional epoxy resin and tetrafunctional epoxy resin.

[0031] In the DEN / TRIF / TETF matrix resin, a preferred exemplary trifunctional epoxy resin is triglycidyl para-aminophenol. Triglycidyl para-aminophenol is commercially available from Huntsman Advanced Materials (The Woodlands, TX) under the trade name Araldite MY0510. Another suitable trifunctional epoxy resin is triglycidyl meta-aminophenol. Triglycidyl meta-aminophenol is commercially available from Huntsman Advanced Materials (The Woodlands, TX) under the trade name Araldite MY0600 and from Sumitomo Chemical Co. (Osaka, Japan) under the trade name ELM-120. Other trifunctional epoxy resins may be provided provided that they have properties that are the same or similar to those of triglycidyl para-aminophenol or triglycidyl meta-aminophenol.

[0032] In the DEN / TRIF / TETF matrix resin embodiment, an exemplary tetrafunctional epoxy resin is N,N,N',N'-tetraglycidyl-4,4'-diaminodiphenylmethane (TGDDM), which is commercially available as Araldite MY720 and MY721 from Huntsman Advanced Materials (The Woodlands, TX), or ELM 434 from Sumitomo Chemical Industries, Ltd. (Chuo, Tokyo). Other tetrafunctional epoxy resins may be used provided they have properties that are the same or similar to those of N,N,N',N'-tetraglycidyl-4,4'-diaminodiphenylmethane.

[0033] The total amount of trifunctional epoxy resin and tetrafunctional epoxy resin in the DEN / TRIF / TETF matrix resin can be 35 to 45 wt %, based on the total weight of the uncured resin. Preferably, the weight ratio of trifunctional epoxy resin to tetrafunctional epoxy resin is 1.0:1.5 to 1.5:1.0. Particularly preferably, the weight ratio of trifunctional epoxy resin to tetrafunctional epoxy resin is 1.1:1.0 to 1.3:1.0.

[0034] In another embodiment of the present invention, the resin component only comprises dicyclopentadiene novolac epoxy resin and triglycidyl aminophenol epoxy resin. In the resin component of this embodiment (which is referred to as DEN / TRIF matrix resin in this application), the amount of dicyclopentadiene novolac epoxy resin present ranges from 4wt% to 30wt%, based on the gross weight of the uncured resin matrix. Preferably, the amount of dicyclopentadiene novolac epoxy resin present ranges from 17wt% to 27wt%, based on the gross weight of the uncured resin matrix. More preferably, the amount of dicyclopentadiene novolac epoxy resin present ranges from 20wt% to 24wt%, based on the gross weight of the uncured resin matrix.

[0035] In the DEN / TRIF matrix resin, the triglycidyl aminophenol epoxy resin is present in a range of 20 wt% to 55 wt% based on the total weight of the uncured resin matrix. Preferably, the triglycidyl aminophenol epoxy resin is present in a range of 26 wt% to 36 wt% based on the total weight of the uncured resin matrix. More preferably, the triglycidyl aminophenol epoxy resin is present in a range of 29 wt% to 33 wt% based on the total weight of the uncured resin matrix. Triglycidyl meta-aminophenol is a preferred type of triglycidyl aminophenol epoxy resin for use in the DEN / TRIF matrix resin.

[0036] In the DEN / TRIF matrix resin, the weight ratio of triglycidyl aminophenol epoxy resin to dicyclopentadiene novolac epoxy resin can be from 1:1 to 10.5:1. The preferred weight ratio of triglycidyl aminophenol epoxy resin to dicyclopentadiene novolac epoxy resin is from 1.2:1 to 1.6:1. Most preferably, the weight ratio of triglycidyl aminophenol epoxy resin to dicyclopentadiene novolac epoxy resin is about 1.4:1.

[0037] The uncured resin matrix according to the present invention also includes a thermoplastic particle component containing one or more types of thermoplastic particles. Exemplary thermoplastic particles are polyamide particles formed from the polymeric condensation product of a methyl derivative of bis(4-aminocyclohexyl)methane and an aliphatic dicarboxylic acid selected from decanedicarboxylic acid and dodecanedicarboxylic acid. The methyl derivative of bis(4-aminocyclohexyl)methane is referred to herein as the "amine component," which is also referred to as the methyl derivative of 4,4'-diaminocyclohexylmethane. This type of polyamide particle and its preparation method are described in detail in U.S. Patents 3,936,426 and 5,696,202, the contents of which are incorporated herein by reference.

[0038] The chemical formula of the amine component of the polymeric condensation product is

[0039]

[0040] wherein R2 is hydrogen and R1 is methyl or hydrogen.

[0041] The chemical formula of the monomer unit of the polymeric condensation product is shown below:

[0042]

[0043] The molecular weight of the polymeric condensation product will be from 14,000 to 20,000, with a molecular weight of about 17,000 being preferred.

[0044] The particle size of the polyamide particles should be less than 100 microns. Preferably, the size of the particles is 5 to 60 microns, more preferably 10 to 30 microns. Preferably, the average particle size is 15 to 25 microns. The shape of the polyamide particles can be regular or irregular. For example, the particles can be substantially spherical, or they can have a sawtooth shape.

[0045] An exemplary polyamide pellet is prepared from a polyamide wherein the amine component of the polymeric condensation product has the above formula, wherein both R1 and R2 are methyl and both R2 are hydrogen. Such polyamide pellets can be prepared from the polymeric condensation product of 3,3'-dimethyl-bis(4-aminocyclohexyl)methane and 1,10-decanedicarboxylic acid. The polyamide pellets are prepared as follows: 13,800 grams of 1,10-decanedicarboxylic acid and 12,870 grams of 3,3'-dimethyl-bis(4-aminocyclohexyl)methane are combined with 30 grams of 50% aqueous phosphoric acid, 150 grams of benzoic acid, and 101 grams of water in a heated receiving vessel. The mixture is stirred in an autoclave until homogeneous. Following compression, decompression, and venting stages, the polyamide condensation product is extruded as strands, passed under cold water, and pelletized to form polyamide pellets. Polyamide particles in which R1 are both methyl and R2 are both hydrogen can also be prepared from GRILAMID TR90, which is commercially available from EMS-Chime (Sumter, SC). GRILAMID TR90 is a polymeric condensation product of 3,3'-dimethyl-bis(4-aminocyclohexyl)-methane and 1,10-decanedicarboxylic acid.

[0046] Another exemplary polyamide particle is prepared from a polyamide wherein the amine component of the polymeric condensation product has the above formula, wherein both R1 and R2 are methyl. Such polyamide particles can be prepared in the same manner as described above, except that the polyamide is a polymeric condensation product of 3,3'-dimethyl-bis(4-aminocyclohexyl)-propane and 1,10-decanedicarboxylic acid. Polyamide particles wherein both R1 and R2 are methyl can also be prepared from CX7323, which is commercially available from Evonik (Mobile, AL). CX7323 is a polymeric condensation product of 3,3'-dimethyl-bis(4-aminocyclohexyl)-propane and 1,10-decanedicarboxylic acid. If desired, a mixture of these two exemplary polyamide particles can be used.

[0047] The thermoplastic particle component may include one or more types of polyamide particles commonly used in thermoplastic toughened epoxy resins, including, for example, polyamide (PA) 11, PA6, PA12, PA6 / PA12 copolymers, PA4, PA8, PA6.6, PA4.6, PA10.10, PA6.10 and PA10.12.

[0048] A preferred thermoplastic particle component comprises a first group of polyamide particles that do not comprise crosslinked polyamide, and a second group of polyamide particles that comprise crosslinked polyamide.

[0049] The first group of polyamide particles can be any of the following polyamide particles: which contain cross-linked polyamide and are commonly used in thermoplastic toughened epoxy resin based prepregs. Such particles are composed of the following: polyamide (PA) 11, PA6, PA12, PA6 / PA12 copolymers, PA4, PA8, PA6.6, PA4.6, PA10.10, PA6.10 and PA10.12. Non-cross-linked polyamide particles are commercially available from a number of sources. Suitable non-cross-linked polyamide 12 particles are available from Kobo Products under the trade name SP10L. SP10L can contain more than 98 wt% PA 12. The particle size distribution is from 7 microns to 13 microns, with an average particle size of 10 microns. The density of the particles is 1 g / cm 3 Preferably, the PA12 particles are at least 95 wt% PA12, excluding the moisture content.

[0050] Other suitable non-crosslinked particles are available from Arkema (Colombes, France) under the trade names Orgasol 1002 powder and Orgasol 3803 powder. Orgasol 1002 powder is composed of 100% PA6 particles with an average particle size of 20 microns. Orgasol 3803 is composed of particles with an average particle size of 17 to 24 microns, which are 80% PA12 and 20% copolymer. Orgasol 2002 is a powder composed of non-crosslinked PA12 particles that can also be used in the first group of particles.

[0051] The preferred non-crosslinked polyamide particles of the first group of thermoplastic particles are polyamide 11 particles, which are also commercially available from a number of sources. Preferred polyamide 11 particles are available from Arkema (Colombes, France) under the trade name Rislan PA11. These particles contain more than 98 wt% PA11 and have a particle size distribution of 15 to 25 microns. The average particle size is 20 microns. The density of the Rislan PA11 particles is 1 g / cm 3 It is preferred that the PA 11 particles are at least 95 wt% PA 11 excluding the moisture content.

[0052] The second group of thermoplastic polyamide particles are particles comprising crosslinked polyamide on the surface of the particles, crosslinked polyamide in the interior of the particles, or both. The crosslinked polyamide particles can be prepared from polyamide that has been crosslinked prior to particle formation, or non-crosslinked polyamide particles can be treated with a suitable crosslinking agent to prepare crosslinked polyamide particles.

[0053] Suitable crosslinked particles include crosslinked PA11, PA6, PA12, PA6 / PA12 copolymers, PA4, PA8, PA6.6, PA4.6, PA10.10, PA6.10 and PA10.12. Any crosslinking agent commonly used for crosslinking polyamides is suitable. Suitable crosslinking agents are epoxy-based crosslinkers, isocyanate-based crosslinkers, carbodiimide-based crosslinkers, acyl lactam-based crosslinkers and The preferred crosslinked particles are PA12 particles comprising PA12 crosslinked with an epoxy crosslinker. The processes for crosslinking thermoplastic polymers (including polyamides) are known. For example, see U.S. Patent No. 6,399,714, U.S. Patent No. 8,846,818, and U.S. Published Patent Application US2016 / 0152782A1. The contents of these three references are incorporated herein by reference.

[0054] Crosslinked PA12 particles are commercially available from Arkema (Colombes, France) under the trade name ORGASOL 2009 polyamide powder, also known as CG352. The PA12 particles present in ORGASOL 2009 polyamide powder are composed of at least 40% PA12 that has been crosslinked with an epoxy resin-based crosslinker. The average particle size of the ORGASOL 2009 crosslinked polyamide particles is 14.2 microns, with only 0.2% of the particles having a diameter greater than 30 microns. The melting point of the ORGASOL 2009 crosslinked particles is 180°C. The ORGASOL 2009 particles have a specific surface area of 1.9 and a moisture content of 0.34%.

[0055] The cross-linked polyamide particles should contain 40 to 70% cross-linked polyamide.Preferably, the cross-linked polyamide particles should each contain 40 to 60% cross-linked polyamide.

[0056] Preferably, the particle size of both the non-crosslinked polyamide particles and the crosslinked polyamide particles should be less than 100 microns. Preferably, the size of the particles is between 5 and 60 microns, more preferably between 5 and 30 microns. Preferably, the average particle size is between 5 and 20 microns. The shape of the particles can be regular or irregular. For example, the particles can be substantially spherical, or they can be particles with a sawtooth shape. Preferably, the average particle size of the non-crosslinked particles is larger than that of the crosslinked particles. Preferably, the average non-crosslinked particle size will be between 15 and 25 microns, and the average crosslinked particle size will be between 10 and 20 microns.

[0057] The thermoplastic particle component is present in the range of 5 wt % to 20 wt % based on the total weight of the uncured resin matrix. Preferably, the thermoplastic particle component will be present in the range of 7 to 17 wt %. When a combination of crosslinked and non-crosslinked particles is used, the relative amounts of non-crosslinked and crosslinked particles can vary. The weight ratio of non-crosslinked particles to crosslinked particles can be from 4:1 to 1.5:1. Preferably, the weight ratio of non-crosslinked particles to crosslinked particles will be from 3.5:1 to 2.5:1. A combination of non-crosslinked and crosslinked particles is a preferred thermoplastic particle component for DEN / TRIF matrix resin embodiments.

[0058] In DEN / TRIF matrix resin embodiments, the total amount of polyamide particles in the uncured resin may vary from 9 to 21 wt %, based on the total weight of the uncured resin. Preferably, the total amount of polyamide particles in the uncured resin will be from 11 to 19 wt %, based on the total weight of the uncured resin matrix. More preferably, the total amount of polyamide particles in the uncured resin will be from 12 to 17 wt %, based on the total weight of the uncured resin matrix.

[0059] The thermoplastic particle component may include a combination of polyimide particles and polyamide particles, wherein the polyamide particles are composed of a polymerized condensation product of a methyl derivative of bis(4-aminocyclohexyl)methane and an aliphatic dicarboxylic acid. This particle combination is a preferred thermoplastic particle component for DEN / TRIF / TETF matrix resin embodiments.

[0060] Preferred polyimide particles are commercially available from HP Polymer GmbH (Lenzig, Austria) as P84 polyimide molding powder. Suitable polyamide particles are also commercially available from Evonik Industries (Austria) under the trade name P84NT. The polyimide used to prepare the particles is disclosed in U.S. Patent 3,708,458, the contents of which are incorporated herein by reference. The polyimide is prepared by combining benzophenone-3,3',4,4'-tetracarboxylic dianhydride with a mixture of 4,4'-methylenebis(phenyl isocyanate) and toluene diisocyanate (either the 2,4-isomer or the 2,6-isomer). Amine analogs can be used in place of aromatic isocyanates and diisocyanates. The CAS registration number of the polyimide is 58698-66-1.

[0061] The polyimide particles are composed of an aromatic polyimide having a repeating monomer having the formula:

[0062]

[0063] wherein 10 to 90% of the R groups in the total polymer are aromatic groups having the formula:

[0064]

[0065] The remaining R in the polymer is

[0066]

[0067] The polyimide particles in the powder typically have a size of 2 to 35 microns. A preferred polyimide powder will contain particles having a size of 2 to 30 microns, with an average particle size of 5 to 15 microns. Preferably, at least 90% by weight of the polyimide particles in the powder will have a size of 2 to 20 microns. The shape of the polyimide particles can be regular or irregular. For example, the particles can be substantially spherical, or they can have a jagged shape.

[0068] The polyimide particles comprise at least 95 wt% polyimide.Minorities (up to 5 wt%) of other materials may be included in the particles provided they do not adversely affect the overall characteristics of the particles.

[0069] The polyimide particles should have a glass transition temperature (Tg) of about 330° C., a density of 1.34 grams per cubic centimeter, and a linear thermal expansion coefficient of 50.

[0070] The total amount of thermoplastic particles in the uncured DEN / TRIF / TETF matrix resin embodiment is preferably 9 to 15 wt % based on the total weight of the uncured resin. To achieve high delamination resistance, the weight ratio of polyamide particles to polyimide particles may be 3.5:1.0 to 1.0:1.0. Preferably, the weight ratio of polyamide particles to polyimide particles is 3.2:1.0 to 2.8:1.0. In particularly preferred DEN / TRIF / TETF matrix resins, the amount of polyimide particles is 8 to 10 wt % based on the total weight of the uncured resin, and the amount of polyamide particles is 2 to 4 wt % based on the total weight of the uncured resin.

[0071] The uncured resin matrix includes at least one curing agent. Suitable curing agents are those that promote the curing of the epoxy-functional compounds of the present invention, particularly the ring-opening polymerization of such epoxy compounds. In a particularly preferred embodiment, such curing agents include those compounds that polymerize with one or more epoxy-functional compounds during their ring-opening polymerization. Two or more such curing agents may also be used in combination.

[0072] Suitable curing agents include anhydrides, particularly polycarboxylic anhydrides, such as nadic anhydride (NA), methylnadic anhydride (MNA - available from Aldrich), phthalic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride (HHPA - available from Anhydrides and Chemicals Inc., Newark, NJ), methyltetrahydrophthalic anhydride (MTHPA - available from Anhydrides and Chemicals Inc.), methylhexahydrophthalic anhydride (MHHPA - available from Anhydrides and Chemicals Inc.), endomethylenetetrahydrophthalic anhydride, hexachloroendomethylenetetrahydrophthalic anhydride (Chlorentic Anhydride - available from Velsicol Chemicals Inc.), and polycarboxylic anhydride. Corporation, Rosemont, Ill.), trimellitic anhydride, pyromellitic dianhydride, maleic anhydride (MA - available from Aldrich), succinic anhydride (SA), nonenylsuccinic anhydride, dodecenylsuccinic anhydride (DDSA - available from Anhydrides and Chemicals Inc.), polysebacic anhydride, and polyazelaic anhydride.

[0073] Other suitable curing agents are amines, including aromatic amines, for example, 1,3-diaminobenzene, 1,4-diaminobenzene, 4,4'-diamino-diphenylmethane, and polyaminosulfones, such as 4,4'-diaminodiphenylsulfone (4,4'-DDS - available from Huntsman), 4-aminophenylsulfone, and 3,3'-diaminodiphenylsulfone (3,3'-DDS). Likewise, suitable curing agents may include polyols such as ethylene glycol (EG—available from Aldrich), poly(propylene glycol), and poly(vinyl alcohol); and phenolic resins such as phenol-formaldehyde resins having an average molecular weight of about 550-650, p-tert-butylphenol-formaldehyde resins having an average molecular weight of about 600-700, and p-n-octylphenol-formaldehyde resins having an average molecular weight of about 1200-1400, available as HRJ 2210, HRJ-2255, and SP-1068, respectively, from Schenectady Chemicals, Inc., Schenectady, NY. Regarding the phenolic resin, a combination of CTU guanamine and a phenolic resin having a molecular weight of 398 may also be used, available as CG-125 from Ajinomoto USA Inc. (Teaneck, NJ).

[0074] Commercially available compositions from various sources may be present in the present invention as curing agents. One such composition is AH-154, a dicyandiamide-type formulation available from Ajinomoto USA Inc. Other suitable compositions include: Ancamide 400, a mixture of polyamide, diethylenetriamine, and triethylenetetramine; Ancamide 506, a mixture of amidoamine, imidazoline, and tetraethylenepentamine; and Ancamide 1284, a mixture of 4,4′-methylenedianiline and 1,3-phenylenediamine; these formulations are available from Pacific Anchor Chemical, Performance Chemical Division, Air Products and Chemicals, Inc., Allentown, Pa.

[0075] Additional suitable curing agents include imidazole (1,3-diaza-2,4-cyclopentadiene) available from Sigma Aldrich (St. Louis, Missouri), 2-ethyl-4-methylimidazole available from Sigma Aldrich, and boron trifluoride amine complexes such as Anchor 1170 available from Air Products & Chemicals, Inc.

[0076] Still other suitable curing agents include: 3,9-bis(3-aminopropyl-2,4,8,10-tetraoxaspiro[5.5]undecane, which is commercially available as ATU from Ajinomoto USA Inc.; and aliphatic dihydrazide, which is commercially available as Ajicure UDH, also from Ajinomoto USA Inc.; and thiol-terminated polysulfide, which is commercially available as LP540 from Morton International, Inc., Chicago, 111.

[0077] The curing agent is selected so that it cures the substrate at a suitable temperature. The amount of curing agent required to provide adequate curing of the substrate will vary depending on a variety of factors, including the type of resin to be cured, the desired curing temperature, and the curing time. Typical curing agents may also include cyanoguanidine, aromatic and aliphatic amines, anhydrides, Lewis acids, substituted ureas, imidazoles, and hydrazines. The specific amount of curing agent required for each specific situation can be determined through routine experimentation.

[0078] Exemplary preferred curing agents include 4,4'-diaminodiphenyl sulfone (4,4'-DDS) and 3,3'-diaminodiphenyl sulfone (3,3'-DDS), both commercially available from Huntsman.

[0079] The curing agent is present in an amount of 10 wt % to 30 wt % of the uncured resin matrix. In a DEN / TRIF matrix resin, the curing agent is present in an amount of 17 wt % to 27 wt %. More preferably, the curing agent is present in a range of 21 wt % to 25 wt % based on the uncured resin matrix. In a DEN / TRIF matrix resin, 4,4'-DDS is the preferred curing agent. It is preferably used as the sole curing agent in an amount of 20 wt % to 26 wt %. If desired, other curing agents such as 3,3'-DDS may be included in small amounts (less than 5 wt %).

[0080] In the DEN / TRIF / TETF matrix resin, the curing agent is present in an amount of 15 to 30 wt% based on the uncured resin. Preferably, the curing agent is present in an amount of 20 to 30 wt%. 3,3'-DDS is a preferred curing agent. It is preferably used as the sole curing agent in an amount of 24 to 28 wt% based on the total weight of the uncured resin. If desired, other curing agents such as 4,4'-DDS may be included in small amounts (less than 5 wt%).

[0081] Accelerators may also be included to enhance or promote curing. Suitable accelerators are any urone compounds commonly used to cure epoxy resins. Specific examples of accelerators that can be used alone or in combination include N,N-dimethyl, N'-3,4-dichlorophenyl urea (Diuron), N'-3-chlorophenyl urea (Monuron), and preferably N,N-(4-methyl-m-phenylenebis[N',N'-dimethylurea] (e.g., Dyhard UR500 available from Degussa).

[0082] Uncured resin matrix of the present invention also comprises thermoplastic toughening agent.Any suitable thermoplastic polymer can be used as toughening agent.Usually, thermoplastic polymer is added in resin mixture as particle, and described particle is dissolved in resin mixture by heating before adding solidifying agent.In case thermoplastic reagent is fully dissolved in hot matrix resin precursor (that is, the blend of epoxy resin), then precursor is cooled, and remaining composition (solidifying agent and insoluble thermoplastic particles) is added, and mixed with cooling resin blend.

[0083] Exemplary thermoplastic toughening agents / particles include any of the following thermoplastic materials, alone or in combination: polysulfone, polyethersulfone, polyetherimide, high performance hydrocarbon polymers, elastomers, and segmented elastomers.

[0084] Suitable toughening agents are, for example, granular polyethersulfone (PES), which is sold under the trade name Sumikaexcel 5003P and is commercially available from Sumitomo Chemicals (New York, NY). An alternative to 5003P is Solvay polyethersulfone 105RP, or non-hydroxyl terminated grades such as Solvay 1054P, which are commercially available from Solvay Chemicals (Houston, TX). Dense PES particles can be used as toughening agents. The form of the PES is not particularly important because PES dissolves during the formation of the resin. Dense PES particles can be prepared according to the teachings of U.S. Patent No. 4,945,154, the contents of which are incorporated herein by reference. Dense PES particles are also commercially available from Hexcel Corporation (Dublin, CA) as the trade name HRI-1. The average particle size of the toughening agent should be less than 100 microns to promote and ensure that the PES is completely dissolved in the matrix.

[0085] In the DEN / TRIF matrix resin, the toughening agent is present in the range of 5 wt% to 15 wt%, based on the total weight of the uncured resin matrix. Preferably, the toughening agent is present in the range of 7 wt% to 12 wt%. More preferably, the toughening agent is present in the range of 8 wt% to 11 wt%.

[0086] In the DEN / TRIF / TETF matrix resin, the PES toughening agent is present in the range of 5 wt% to 26 wt%, based on the total weight of the uncured resin. Preferably, the toughening agent is present in the range of 7 wt% to 14 wt%. The preferred amount of PES for preparing resins with relatively low minimum viscosities (25-45 poise) is 7 to 9 wt%, based on the total weight of the uncured resin. The preferred amount of PES for preparing resins with relatively high minimum viscosities (55-75 poise) is 10 to 13 wt%, based on the total weight of the uncured resin.

[0087] The matrix resin may also include additional ingredients, such as property enhancers or modifiers, provided they do not adversely affect the tack and life of the prepreg or the strength and damage tolerance of the cured composite part. The property enhancers or modifiers, for example, may be selected from core-shell rubbers, flame retardants, wetting agents, pigments / dyes, UV absorbers, antimicrobial compounds, fillers, conductive particles, and viscosity modifiers.

[0088] Exemplary core-shell rubber (CSR) particles are composed of a crosslinked rubber core, typically a copolymer of butadiene, and a shell composed of styrene, methyl methacrylate, glycidyl methacrylate, and / or acrylonitrile. The core-shell particles are typically provided as particles dispersed in an epoxy resin. The particle size range of the particles is typically 50 to 150 nm. Suitable CSR particles are described in detail in U.S. Patent Publication No. US2007 / 0027233A1, the contents of which are incorporated herein by reference. Preferred core-shell particles are MX core-shell particles, which are available from Kane Ace (Pasadena, Texas). Preferred core-shell particles for inclusion in a DEN / TRIF matrix resin are Kane Ace MX-418. MX-418 is provided as a 25 wt% suspension of core-shell particles in a tetrafunctional epoxy resin. The core-shell particles in MX-418 are polybutadiene (PBd) core-shell particles having an average particle size of 100 nanometers.

[0089] Suitable fillers include, for example, any of the following, alone or in combination: silica, alumina, titania, glass, calcium carbonate, and calcium oxide.

[0090] Suitable conductive particles include, for example, any of the following, used alone or in combination: silver, gold, copper, aluminum, nickel, conductive grade carbon, buckminsterfullerene, carbon nanotubes, and carbon nanofibers. Metal-coated fillers may also be used, for example, nickel-coated carbon particles and silver-coated copper particles.

[0091] Potato-shaped graphite (PSG) particles are suitable conductive particles. The use of PSG particles in carbon fiber / epoxy composites is described in detail in U.S. Patent Publication No. US 2015 / 0179298A1, the contents of which are incorporated herein by reference. PSG particles are commercially available from NGS Naturgraphit (Germany) as SG25 / 99.95SC particles or from Nippon Power Graphite Company (Japan) as GHDR-15-4 particles. These commercially available PSG particles have an average particle size of 10-30 microns, with the GHDR-15-4 particles having a vapor-deposited coating of carbon on the outer surface of the PSG particles.

[0092] The uncured resin matrix may include a small amount (less than 5 wt%, preferably less than 1 wt%) of additional epoxy or non-epoxy thermosetting polymer resins. For DEN / TRIF / TETF matrix resins, the epoxy resin component comprises at least 95 wt% of DEN, TRIF and TETF, more preferably at least 99 wt% of the three epoxy resins. For DEN / TRIF matrix resins, the epoxy resin component comprises at least 95 wt% of DEN and TRIF, more preferably at least 99 wt% of the two epoxy resins. Suitable additional epoxy resins include difunctional epoxy resins, such as bisphenol A type epoxy resins and bisphenol F type epoxy resins. Suitable non-epoxy thermosetting resin materials for use in the present invention include, but are not limited to, phenolic resins, urea-formaldehyde resins, 1,3,5-triazine-2,4,6-triamine (Melamine), bismaleimide, vinyl ester resins, benzophenone If present, the additional thermosetting resin is preferably selected from epoxy resins, cyanate resins, benzophenone ... Oxazine resins and phenolic resins.

[0093] The uncured resin is prepared according to standard prepreg matrix resin processing. Typically, hydrocarbon novolac epoxy resin and other epoxy resins are mixed together at room temperature to form a resin mixture to which a thermoplastic toughening agent is added. The mixture is then heated to about 120°C and held for about 1 to 2 hours to dissolve the thermoplastic toughening agent. The mixture is then cooled to about 80°C and the remaining ingredients (if present, thermoplastic particle component, curing agent and other additives) are mixed into the resin to form the final uncured resin matrix for impregnating the fiber reinforcement.

[0094] Uncured resin is applied to the fiber reinforcement to form an uncured resin matrix according to any known prepreg manufacturing technology. The fiber reinforcement can be completely or partially impregnated with uncured resin. In an alternative embodiment, uncured resin can be applied to the fiber reinforcement as a separate layer, which is closest to and in contact with the fiber reinforcement, but will not fully impregnate the fiber reinforcement. The prepreg, also known as a semipreg, is usually covered on both sides with a protective film and rolled up for storage and transportation at the following temperatures, which usually remain sufficiently below room temperature to avoid premature curing. Actual resin matrix is not formed until the semipreg material is further processed and formed. If desired, any other prepreg manufacturing method and storage / transportation system can be used.

[0095] The fiber reinforcement of the prepreg can be selected from any glass fiber, carbon fiber, or aromatic polyamide (aramid) fiber. The fiber reinforcement is preferably carbon fiber. The preferred carbon fiber is in the form of a tow containing 3,000 to 50,000 carbon filaments (3K to 50K). Commercially available carbon fiber tows containing 6,000 or 24,000 carbon filaments (6K or 24K) are preferred.

[0096] The uncured matrix resin of the present invention is particularly effective in providing laminates having high strength properties and damage resistance when the carbon tow comprises 6,000 to 24,000 filaments, a tensile strength of 750 to 860 ksi, a tensile modulus of 35 to 45 Msi, a strain to failure of 1.5 to 2.5%, and a density of 1.6 to 2.0 g / cm 3 , with a unit length weight of 0.2 to 0.6 g / m. 6K and 12K IM7 carbon tows (available from Hexcel Corporation) are preferred. IM7 12K fiber has a tensile strength of 820 ksi, a tensile modulus of 40 Msi, a strain to failure of 1.9%, and a density of 1.78 g / cm 3 , the unit length weight is 0.45g / m. The tensile strength of IM7 6K fiber is 800ksi, the tensile modulus is 40Msi, the failure strain is 1.9%, and the density is 1.78g / cm 3 , with a unit length weight of 0.22 g / m. IM7 fiber and carbon fibers with similar properties are generally considered medium modulus carbon fibers. IM8 carbon fibers commercially available from Hexcel Corporation (Dublin, CA) are also a preferred type of medium modulus carbon fiber.

[0097] Fiber reinforcements can include fibers that are broken (i.e., pulled apart), selectively discontinuous, or continuous. The use of broken or selectively discontinuous fibers can aid in the layup of the composite material before full curing and improve its molding capabilities. Fiber reinforcements can be in the form of woven, non-crimped, non-woven, unidirectional, or multiaxial textile structures, such as quasi-isotropic chopped prepregs used to form sheet molding compounds. Woven forms can be selected from plain, satin, or twill weave styles. Non-crimped and multiaxial forms can have multiple plies and fiber orientations. These styles and forms are well known in the field of composite reinforcements and are commercially available from multiple companies, including Hexcel Reinforcements (Les Avenieres, France).

[0098] The prepreg may be in the form of a continuous tape, tow prepreg, web, or chopped lengths (chopping and slitting operations may be performed at any point after impregnation). The prepreg may be adhesive or laid film and may additionally have an implanted carrier in various forms (both woven and non-woven). The prepreg may be fully or only partially impregnated, for example to aid in the removal of air during the curing process.

[0099] The following exemplary DEN / TRIF / TETF resin formulations can be impregnated into a fibrous support to form a resin matrix according to the present invention (all weight percentages are based on total resin weight):

[0100] 1) 9 wt% to 11 wt% of dicyclopentadiene novolac epoxy resin ( 556); 21 wt % to 23 wt % of triglycidyl-p-aminophenol (MY0510); 17 wt % to 19 wt % of a tetrafunctional epoxy resin (MY721); 10 wt % to 13 wt % of polyethersulfone (5003P); 8 wt % to 10 wt % of polyimide particles (P84HCM); 2 wt % to 4 wt % of particles prepared from a condensation product of 3,3'-dimethyl-bis(4-aminocyclohexyl)-methane and 1,10-decanedicarboxylic acid (GRILAMID TR90); and 25 wt % to 28 wt % of 3,3'-DDS as a curing agent.

[0101] 2) 13 wt% to 16 wt% of dicyclopentadiene novolac epoxy resin ( 556); 18 wt % to 20 wt % of triglycidyl-p-aminophenol (MY0510); 17 wt % to 19 wt % of a tetrafunctional epoxy resin (MY721); 10 wt % to 13 wt % of polyethersulfone (5003P); 8 wt % to 10 wt % of polyimide particles (P84HCM); 2 wt % to 4 wt % of particles prepared from a condensation product of 3,3'-dimethyl-bis(4-aminocyclohexyl)-methane and 1,10-decanedicarboxylic acid (GRILAMID TR90); and 25 wt % to 28 wt % of 3,3'-DDS as a curing agent.

[0102] 3) 16 wt% to 18 wt% of dicyclopentadiene novolac epoxy resin ( 556); 14 wt % to 16 wt % of triglycidyl-p-aminophenol (MY0510); 17 wt % to 19 wt % of a tetrafunctional epoxy resin (MY721); 10 wt % to 13 wt % of polyethersulfone (5003P); 5 wt % to 7 wt % of polyimide particles (P84HCM); 5 wt % to 7 wt % of particles prepared from a condensation product of 3,3'-dimethyl-bis(4-aminocyclohexyl)-methane and 1,10-decanedicarboxylic acid (GRILAMID TR90); and 25 wt % to 28 wt % of 3,3'-DDS as a curing agent.

[0103] 4) 13 wt% to 16 wt% of dicyclopentadiene novolac epoxy resin ( 556); 19 wt % to 21 wt % of triglycidyl-p-aminophenol (MY0510); 18 wt % to 20 wt % of a tetrafunctional epoxy resin (MY721); 7 wt % to 9 wt % of polyethersulfone (5003P); 2 wt % to 4 wt % of polyimide particles (P84HCM); 8 wt % to 10 wt % of particles prepared from a condensation product of 3,3'-dimethyl-bis(4-aminocyclohexyl)-methane and 1,10-decanedicarboxylic acid (GRILAMID TR90); and 25 wt % to 28 wt % of 3,3'-DDS as a curing agent.

[0104] 5) 9 to 11 wt% of dicyclopentadiene novolac epoxy resin ( 556); 21 wt % to 23 wt % of triglycidyl-p-aminophenol (MY0510); 19 wt % to 22 wt % of a tetrafunctional epoxy resin (MY721); 7 wt % to 9 wt % of polyethersulfone (5003P); 2 wt % to 4 wt % of polyimide particles (P84HCM); 8 wt % to 10 wt % of particles prepared from a condensation product of 3,3'-dimethyl-bis(4-aminocyclohexyl)-methane and 1,10-decanedicarboxylic acid (GRILAMIDTR90); and 26 wt % to 29 wt % of 3,3'-DDS as a curing agent.

[0105] With respect to the DEN / TRIF matrix resin embodiment of the present invention, a preferred exemplary DEN / TRIF matrix resin includes: 29 wt% to 33 wt% of triglycidyl-m-aminophenol (MY0600); 20 wt% to 24 wt% of a hydrocarbon novolac epoxy resin (TACTIX 556); 7 wt% to 11 wt% of polyethersulfone (5003P) as a toughening agent; 2 wt% to 7 wt% of cross-linked polyamide 12 particles (ORGASOL 2009); 9 wt% to 13 wt% of polyamide 11 particles (Rislan PA11), wherein the weight ratio of polyamide 11 particles to cross-linked polyamide 12 particles is 2.5:1.0 to 3.0:1, preferably 2.7:1 to 2.8:1; and 20 wt% to 26 wt% of 4,4'-DDS as a curing agent.

[0106] Another preferred DEN / TRIF matrix resin includes: 19 wt% to 23 wt% triglycidyl-m-aminophenol (MY0600); 14 wt% to 18 wt% hydrocarbon novolac epoxy resin (TACTIX556); 7 wt% to 11 wt% polyethersulfone (5003P) as a toughening agent; 9 wt% to 13 wt% polyamide 11 particles (Rislan PA11); 18-22 wt% core-shell particles (MX-418); and 21 wt% to 26 wt% 4,4'-DDS as a curing agent.

[0107] Prepregs can be molded using any standard technique for forming composite parts. Typically, one or more layers of prepreg are placed in a suitable mold and cured to form the final composite part. The prepregs of the present invention can be fully or partially cured using any suitable temperature, pressure, and time conditions known in the art. Typically, the prepreg will be cured in an autoclave at a temperature of 160°C to 190°C. The composite material can be cured using a method selected from the following: microwave radiation, electron beam, gamma radiation, or other suitable thermal or non-thermal radiation.

[0108] Composite parts made from the improved prepregs of the present invention can be used to make articles such as various primary and secondary aerospace structures (wings, fuselages, bulkheads, etc.), but can also be used in many other high performance composite applications, including automotive, rail and marine applications, where high compressive strength, interlaminar fracture toughness and impact damage resistance are required.

[0109] Examples 1-7 are examples of practice with respect to the DEN / TRIF / TETF matrix resin embodiment of the present invention, which are as follows:

[0110] Example

[0111] Example 1

[0112] Preferred exemplary resin matrices according to the present invention are listed in Table 1. The matrix resin was prepared by mixing the epoxy component with polyethersulfone at room temperature to form a resin blend. The resin blend was heated to 120°C for 60 minutes to completely dissolve the polyethersulfone. The mixture was cooled to 80°C, and the remaining ingredients were added and mixed thoroughly.

[0113] Table 1

[0114]

[0115] An exemplary prepreg was prepared by impregnating one or more layers of unidirectional carbon fiber with the resin formulation of Table 1. Unidirectional carbon fiber (12K IM8 from Hexcel Corporation) was used to prepare the following prepreg, wherein the matrix resin totaled 35 wt% of the total uncured prepreg weight and the fiber basis weight was 192 grams per square meter (gsm). A 26-ply laminate was prepared using a standard prepreg manufacturing process. The laminate was cured in an autoclave at 177°C for approximately 2 hours. The cured laminate was tested to determine interlaminar fracture toughness.

[0116] G2c is a standard test that provides a measure of the interlaminar fracture toughness of a cured laminate. G2c is determined as follows. A 26-ply unidirectional laminate is cured with a 3-inch fluoroethylene polymer (FEP) film inserted at the mid-plane of the ply along one edge perpendicular to the fiber direction to serve as a crack initiator. The laminate is cured in an autoclave at 177°C for 2 hours and a nominal thickness of 3.8 mm is obtained. Coalescing is confirmed by c-scan. G2c samples are machined from the cured laminate. G2c is tested at room temperature according to BSS7320. The G2c values listed below are the average of the first and second cracks observed during testing according to BSS7320.

[0117] The G2c of the cured 26-ply laminate was 10.22. Open hole tension (OHT) and open hole compression (OHC) were also measured according to standard procedures at room temperature and found to be above acceptable limits for structural components.

[0118] Example 2

[0119] Exemplary prepregs comprising a DEN / TRIF / TETR resin matrix having the formulation described in Table 2 were prepared in the same manner as in Example 1.

[0120] Table 2

[0121]

[0122] A 26-layer laminate was prepared in the same manner as in Example 1, cured, and G2c was measured at room temperature. G2c was 13.16. For structural components, OHT and OHC were also above acceptable limits.

[0123] Example 3

[0124] Exemplary prepregs were prepared in the same manner as in Example 1, except that the DEN / TRIF / TETF resin formulation listed in Table 3 was used as the prepreg resin matrix.

[0125] Table 3

[0126]

[0127] A 26-layer laminate was prepared in the same manner as in Example 1, cured, and G2c was measured at room temperature. G2c was 10.47. For structural components, OHT and OHC were also above acceptable limits.

[0128] Example 4

[0129] Exemplary prepregs were prepared in the same manner as in Example 1, except that the DEN / TRIF / TETF matrix resin formulation listed in Table 4 was used as the prepreg resin matrix.

[0130] Table 4

[0131]

[0132] A 26-layer laminate was prepared in the same manner as in Example 1, cured, and G2c was measured at room temperature. G2c was 9.15. For structural components, OHT and OHC were also above acceptable limits.

[0133] Example 5

[0134] Exemplary prepregs were prepared in the same manner as in Example 1, except that the resin formulation according to the present invention listed in Table 5 was used as the prepreg resin matrix.

[0135] Table 5

[0136]

[0137] A 26-layer laminate was prepared in the same manner as in Example 1, cured, and G2c was measured at room temperature. G2c was 9.50. For structural components, OHT and OHC were also above acceptable limits.

[0138] Example 6

[0139] Exemplary prepregs were prepared in the same manner as in Example 1, except that the resin formulation according to the present invention listed in Table 6 was used as the prepreg resin matrix.

[0140] Table 6

[0141]

[0142]

[0143] A 26-layer laminate was prepared in the same manner as in Example 1, cured, and G2c was measured at room temperature. G2c was 9.31. For structural components, OHT and OHC were also above acceptable limits.

[0144] Example 7

[0145] Exemplary prepregs were prepared in the same manner as in Example 1, except that the resin formulation according to the present invention listed in Table 7 was used as the prepreg resin matrix.

[0146] Table 7

[0147]

[0148] A 26-layer laminate was prepared in the same manner as in Example 1, cured, and G2c was measured at room temperature. G2c was 7.30. For structural components, OHT and OHC were also above acceptable limits.

[0149] Comparative Examples 1-7

[0150] Comparative prepregs and laminates for the DEN / TRIF / TETF matrix resin embodiment were prepared, cured, and tested in the same manner as in Example 1, except that the resin formulations are listed in Table 8. The amounts listed in Table 8 are weight percentages of the total resin mixture. A 26-layer laminate was prepared, cured, and G2c measured at room temperature in the same manner as in Example 1. The G2c results are listed in the table.

[0151] Table 8

[0152]

[0153] The viscosity of the resin formulation should be such that the prepreg resin formulation can be properly impregnated or otherwise applied to the fiber reinforcement using an acceptable prepreg forming method. The viscosity curve of the resin can provide a guide to the suitability of the resin formulation for use as a prepreg resin. The viscosity curve is determined as follows: the temperature of the resin is increased from room temperature at a rate of 2°C / minute and the viscosity of the resin is monitored. When the resin is heated, the viscosity generally decreases to a minimum value and then increases as the polymerization reaction proceeds. The minimum viscosity of the resin and the temperature at which this minimum viscosity is reached provide an indication of the suitability of the resin for a given prepreg process. When the term "minimum viscosity" is used in this application, it means the minimum viscosity measured during the determination of the viscosity curve of the resin.

[0154] In many prepreg manufacturing processes, it is a minimum viscosity that allows sufficient resin flow during the formation of the prepreg to ensure complete impregnation of the fiber reinforcement. The required minimum viscosity of the prepreg resin in such processes depends on a number of factors, including the degree of impregnation desired, the impregnation temperature and pressure, the method used to achieve impregnation, and the type of fiber reinforcement.

[0155] For those prepreg processes requiring a relatively high viscosity prepreg resin, the preferred minimum viscosity of the prepreg resin is 55 to 75 poise (P). For prepreg processes requiring a relatively low viscosity prepreg resin, the preferred minimum viscosity of the prepreg resin is 25 to 45 Poise. It has been found that an amount of PES of 10-13 wt% provides a prepreg resin according to the present invention in the higher minimum viscosity range. An amount of PES of 7-9 wt% provides a prepreg resin according to the present invention in the lower minimum viscosity range.

[0156] The viscosity curves of Examples 1 to 7 and Comparative Examples 1 to 7 were determined. The minimum viscosity and the temperature at which the minimum viscosity was reached are listed in Table 9. The amounts of PES and TACTIX 556 resin in the formulations are also listed in the table along with the G2c values.

[0157] Table 9

[0158]

[0159] Examples 1-5 are exemplary DEN / TRIF / TETF resins having minimum viscosities that fall within the aforementioned high viscosity range. The DEN / TRIF / TETF resin formulation of Example 1 is preferred because it provides unexpectedly high G2c, i.e., exceeding 10, when using a combination of only 10.0 wt% TACTIX 556 resin with 9.0 wt% TR90 polyamide particles and 3.0 wt% P84 polyimide particles. Examples 3 and 4 (which use a combination of 17.0 wt% TACTIX 556 resin with 6.0 wt% TR90 polyamide particles and 6.0 wt% P84 polyimide particles) also unexpectedly achieve considerably higher G2c esters while maintaining the minimum viscosity within the desired high viscosity range.

[0160] The DEN / TRIF / TETF resin formulation of Example 2 is particularly preferred because it provides an increase in G2c when 14.10 wt% TACTIX 556 resin is used in combination with 9.0 wt% TR90 polyamide particles and 3.0 wt% P84 polyimide particles, increasing it to as much as 13.16. Such a high G2c value (13.16) is particularly unexpected.

[0161] The high G2c values achieved when TACTIX 556 resin is combined with the TR90 polyamide particles and P84 polyimide particles described above are unexpected, as Comparative Example 1 shows that using P84 polyamide particles alone (C1) provides a relatively low G2c of only 4.68. Comparative Example 2 shows that using TR90 polyamide particles alone (C2) provides a much higher G2c of 9.97. It is unexpected that the combination of P84 polyimide particles and TR90 polyamide particles can provide higher G2c values, decoupling the ability to achieve using either type of particle alone.

[0162] In contrast to Comparative Examples 1 and 2, Comparative Example 3 demonstrates an unexpected reduction in G2c (7.12) when 9.0 wt% P84 polyimide particles are combined with 3.0 wt% TR90 polyamide particles. In contrast to Comparative Examples 1-3, it was unexpected that adding any amount of P84 polyimide particles to a thermoplastic particle component comprised of TR90 polyamide particles would synergistically increase the G2c value to at least 10, as shown in Examples 1-3. It was particularly unexpected that a G2c of 13.6 could be achieved when the amount of TACTIX 556 resin was increased from 10.0 to 14.1 wt%, as shown in Examples 1 and 2.

[0163] The high G2c values obtained using the DEN / TRIF / TETF matrix resin formulations according to Examples 1-5 were achieved while maintaining a minimum viscosity of the resin between 25 and 75 poise. As shown in Comparative Example 2, the use of TR90 polyamide particles alone provided a relatively high G2c of 9.97. However, the minimum viscosity was 85.5 poise, which is above the desired high viscosity range of 55-75 poise.

[0164] Examples 6-7 are exemplary DEN / TRIF / TETF resins whose minimum viscosities fall within the aforementioned low viscosity range. The lower viscosity levels provided by using lower amounts (7-9 wt%) of PES (see Examples 6-7 and Comparative Examples 4-7) also result in reduced G2c levels in the cured laminates. Even so, the resin formulations of Examples 6-7 provide unexpectedly high G2c. A comparison of Example 6 with Comparative Example 6 (14.75 wt% TACTIX 556 resin) shows that when the thermoplastic particle component is changed from 12.0 wt% TR90 polyamide particles to a mixture of 9.0 wt% TR90 polyamide particles and 3.0 wt% P84 polyimide particles, G2c synergistically increases from 8.36 to 9.31. Moreover, a comparison of Example 7 with Comparative Example 4 (10.0 wt % TACTIX 556 resin) shows that when the thermoplastic particle component is changed from 12.0 wt % TR90 polyamide particles to a mixture of 9.0 wt % TR90 polyamide particles and 3.0 wt % P84 polyimide particles, G2c increases synergistically from 5.13 to 7.30.

[0165] The observed synergistic effect provided by the addition of polyimide particles to TR90 polyamide particles in a DEN / TRIF / TETF matrix resin is not expected to occur unless the thermoplastic particle component comprises at least 15 wt% polyimide particles, based on the total weight of the thermoplastic component, with the remainder of the thermoplastic particle component being TR90 polyamide particles. The synergistic effect is expected to end when the thermoplastic particle component comprises more than 70 wt% polyimide particles, based on the total weight of the thermoplastic component, with the remainder of the thermoplastic particle component being TR90 polyamide particles. The maximum synergistic effect is provided when the thermoplastic particle component comprises 20 to 30 wt% polyimide particles, based on the total weight of the thermoplastic component, with the remainder of the thermoplastic particle component being TR90 polyamide particles.

[0166] Inclusion of TACTIX 556 resin in the epoxy resin component of the DEN / TRIF / TETF matrix resin provides a significant increase in G2c fracture resistance. Examples 6 and 7 show that when the amount of TACTIX 556 resin is reduced from 14.75 to 10.0 wt%, G2c changes from 9.31 to 7.30. Comparative Example 5 shows that when the amount of TACTIX 556 resin is reduced to 5.0 wt%, G2c decreases to a low of 4.29. Comparative Examples 4 and 6-7 show that a similar decrease in G2c occurs when the amount of TACTIX 556 resin is reduced compared to a comparative resin containing only TR90 polyamide particles as the thermoplastic particle component. It is therefore preferred that the amount of hydrocarbon novolac epoxy resin present in the DEN / TRIF / TETF matrix resin formulation of the present invention is at least 8 wt%, based on the total weight of the resin.

[0167] Examples 8-23 are examples of the practice of the DEN / TRIF matrix resin embodiment of the present invention, which are as follows:

[0168] Example 8

[0169] Exemplary DEN / TRIF resin formulations according to the present invention are shown in Table 10. The uncured matrix resin was prepared by mixing the epoxy component with polyethersulfone at room temperature to form a resin blend, and heating the resin blend to 120°C for 60 minutes to completely dissolve the polyethersulfone. Following the same procedure as in Examples 1-7, the mixture was cooled to 80°C, and the remaining ingredients were added and mixed thoroughly.

[0170] Table 10

[0171]

[0172]

[0173] An exemplary prepreg was prepared by impregnating one unidirectional carbon fiber layer with the resin formulation of Table 10 to form a prepreg consisting of reinforcing fibers and an uncured resin matrix. The unidirectional carbon fibers were 12K IM7. The uncured resin matrix amounted to 35 wt% of the total uncured prepreg weight, and the uncured prepreg had a fiber basis weight of 145 grams per square meter (gsm).

[0174] The prepreg was used to form a laminate in the same manner as in Examples 1-7. The laminate was cured in an autoclave at 177° C. for approximately 2 hours to form a cured test laminate. The cured test laminate was divided into test specimens that were examined to determine open hole compressive strength (OHC) and open hole tensile strength (OHT).

[0175] OHC and OHT test specimens were examined under dry conditions (relative humidity 10% to 50%) at room temperature (21 to 24°C). OHC was tested according to D6-83079-71 Type II Level 1. OHT was tested according to D6-83079-62 Type I Level 1.

[0176] The cured test samples were also subjected to standard testing to determine damage resistance (CAI). Compression after impact (CAI) was determined using a 270 in-lb impact on a 32-ply quasi-isotropic laminate. The specimens were machined, impacted, and tested according to Boeing test method BSS7260 in accordance with BMS 8-276. The values were normalized to a standard cured laminate thickness of 0.18 inches.

[0177] The cured test specimens were also subjected to testing according to ASTM D5528 in the same manner as Examples 1-7 to determine G1c and G2c.

[0178] When the terms "OHT," "OHC," "CAI," "G1c," and "G2c," when used herein to define properties exhibited by a cured laminate, the terms refer to properties measured by the above-described test procedures.

[0179] Additional exemplary DEN / TRIF matrix resin formulations (Examples 9-23) are listed in Tables 11-13. The exemplary DEN / TRIF matrix resin formulations were used to prepare prepregs, which were cured and tested in the same manner as Examples 1-8, except that Examples 22 and 23 used 12K IM8 carbon fiber instead of 12K IM7 fiber. The results of the OHT, OHC, CAI, G1c, and G2c tests performed as described above for Examples 8-23 are listed in Tables 11-13.

[0180] Table 11

[0181]

[0182] Table 12

[0183]

[0184]

[0185] Table 13

[0186]

[0187] The matrix resin formulations of Examples 8-23 listed in Tables 11-13 are exemplary suitable DEN / TRIF matrix resins according to the present invention. Many other possible similar formulations are also feasible according to the present invention, provided that the cured laminates prepared using the DEN / TRIF resin formulations exhibit the following properties: 1) OHT of at least 140, preferably at least 150, and most preferably at least 160; 2) OHC of at least 70, preferably at least 75, and most preferably at least 80; 3) CAI of at least 45, preferably at least 50, and most preferably at least 55; 4) G1c of at least 3.0, preferably at least 3.2, and most preferably at least 3.5; and 3) G2c of at least 12.0, preferably at least 14.0, and most preferably at least 15.0.

[0188] The DEN / TRIF matrix resin formulations corresponding to Example 1 are preferred resin formulations because they provide very high fracture tolerance (G1c and G2c) while unexpectedly maintaining fairly high CAI, OHT, and OHC.

[0189] The DEN / TRIF matrix resin formulation corresponding to Example 20 is also a preferred resin formulation because it was found that including core-shell particles in a DEN / TRIF-type formulation provides high OHT and acceptable fracture resistance, as measured by G2c. Moreover, of all the DEN / TRIF examples tested, Example 20 unexpectedly outperformed the others in terms of R-curve fracture toughness, as measured by crack growth resistance (R-curve) analysis. R-curve analysis is a known type of test procedure that is commonly used to study the fracture mechanics of laminates and other materials. ASTM standard E561 is an example of a commonly used R-curve analysis procedure, with many variations of this procedure being commonly used. Laminates prepared using the DEN / TRIF exemplary formulation were tested using an R-curve testing procedure similar to ASTM E561. Example 20 was the only laminate to have an elevated R-curve. An elevated R-curve, as opposed to a negative or flat R-curve, is believed to indicate a high level of crack growth resistance and fracture toughness.

[0190] The DEN / TRIF matrix resin formulations are combined with medium modulus carbon fibers, such as IM7 or IM8, to form prepregs that can be used to form uncured prepregs that can be cured to form cured laminates having properties falling within the above-described ranges. To verify that each of the DEN / TRIF exemplary matrix resins meets the requirements of the present invention, each laminate must be tested to ensure that it meets or exceeds the OHT, OHC, CAI, G1c, and G2c limits, as described above.

[0191] Comparative Example 8 (see Table 13) involves the use of MY0510 instead of MY0610 in the resin component of the DEN / TRIF matrix resin. Comparative Example 8 was prepared and tested in the same manner as Examples 22-23. The OHT of Comparative Example 8 was 135. This is below the threshold OHT of 140, which is the value required for an acceptable matrix resin according to the present invention. A small amount of PSG particles was present in the matrix resin of Comparative Example 8. PSG particles were not present in Examples 22-23. The inclusion of a small amount of PSG particles is expected to have a relatively small effect on OHT. The relatively low OHT of Comparative Example 8 is believed to be at least partially due to the use of MY0510 instead of MY0610. Therefore, it is preferred that triglycidyl-m-aminophenol (MY0610) resin, rather than triglycidyl-p-aminophenol (MY0510) resin, be used in DEN / TRIF matrix resin embodiments.

[0192] The adverse effects of using MY0510 instead of MY0610 in DEN / TRIF matrix resin embodiments are in contrast to the beneficial effects observed when MY0510 is used instead of MY0610 in DEN / TRIF / TETF matrix resin embodiments. As shown by comparing Example 3 with Example 4, when MY0610 is used instead of MY0510 in DEN / TRIF / TETF matrix resin, G2c decreases from 10.47 to 9.15. Therefore, it is preferred that triglycidyl-p-aminophenol (MY0510) resin, rather than triglycidyl-m-aminophenol (MY0610) resin, be used in DEN / TRIF / TETF matrix resin embodiments.

[0193] Comparative Example 9 (see Table 13) involves using about 10 wt% of a difunctional epoxy resin (bisphenol A epoxy resin and bisphenol F epoxy resin) and The combination of 556 and MY721 in the epoxy resin component. The resulting OHC was 67.82, which is below the threshold of 70 for laminates prepared using the DEN / TRIF matrix resin formulation. Therefore, the inclusion of difunctional epoxy resins in any matrix resin embodiment should be kept below 5 wt%, preferably below 1 wt%, as discussed above.

[0194] Having thus described the exemplary embodiments of the present invention, those skilled in the art will appreciate that the disclosures herein are merely exemplary and that various other substitutions, adaptations, and modifications may be made within the scope of the present invention. Therefore, the present invention is not limited to the above-described embodiments, but is limited only by the appended claims.

Claims

1. A pre-impregnated composite material comprising: A) reinforcing fibers including carbon fibers; and B) an uncured resin matrix comprising, based on the total weight of the uncured resin matrix: a) an epoxy resin component consisting of 20 to 24 wt% of a hydrocarbon novolac epoxy resin and 29 to 33 wt% of a triglycidyl meta-aminophenol epoxy resin; b) 11 to 19 wt% of polyamide particles, which are: The polymeric condensation product of 1,10-decanedicarboxylic acid and an amine component having the formula Wherein both R2 are hydrogen, and both R1 are methyl or hydrogen; c) 10 wt% to 13 wt% of a polyethersulfone thermoplastic toughening agent; and d) 17 wt % to 27 wt % of a curing agent, wherein the curing agent comprises 4,4′-diaminodiphenyl sulfone and / or 3,3′-diaminodiphenyl sulfone.

2. A pre-impregnated composite material according to claim 1 wherein the uncured resin matrix comprises core-shell particles.

3. The prepreg composite material according to claim 1 , wherein the reinforcing fibers comprise a plurality of carbon fiber tows, each of the carbon fiber tows comprising 10,000 to 14,000 carbon filaments, wherein each of the carbon tows has a weight per unit length of 0.2 to 0.6 g / m, wherein each of the carbon tows has a tensile strength of 750 to 860 kpsi, and wherein each of the carbon tows has a tensile modulus of 35 to 45 MPa.

4. Composite part or structure which has been formed by curing the pre-impregnated composite material according to claim 1.

5. A composite component or structure according to claim 4, wherein the composite component or structure forms at least a part of the primary structure of an aircraft.

6. A method of preparing a pre-impregnated composite material curable to form a composite part, the method comprising the steps of: A) providing reinforcing fibers including carbon fibers; and B) impregnating the reinforcing fibers with an uncured resin matrix, wherein the uncured resin matrix comprises, based on the total weight of the uncured resin matrix: a) an epoxy resin component consisting of 20 to 24 wt% of a hydrocarbon novolac epoxy resin and 29 to 33 wt% of a triglycidyl meta-aminophenol epoxy resin; b) 11 to 19 wt% of polyamide particles, which are: The polymeric condensation product of 1,10-decanedicarboxylic acid and an amine component having the formula Wherein both R2 are hydrogen, and both R1 are methyl or hydrogen; c) 10 wt% to 13 wt% of a polyethersulfone thermoplastic toughening agent; and d) 17 wt % to 27 wt % of a curing agent, wherein the curing agent comprises 4,4′-diaminodiphenyl sulfone and / or 3,3′-diaminodiphenyl sulfone.

7. A method of making a pre-impregnated composite material according to claim 6, wherein the uncured resin matrix comprises core-shell particles.

8. A method of making a composite part or structure comprising the steps of: Providing a pre-impregnated composite material according to claim 1, and curing the pre-impregnated composite material.

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