SE469033B - FIBER ARMED COMPOSITIONS MADE WITH POROESA POLYAMIDE HEART PARTICLES - Google Patents

Description

42: »cm xO 04 2 The composite industry has long been involved in finding ways to overcome these shortcomings. Considerable effort has been put in over the past two decades, aimed at the development of composites with improved fracture toughness. Since most of the commonly used matrix resins, as well as many of the reinforcing fibers, are generally brittle, much of this effort has been focused on searching for components with better toughness properties. Consequently, the search for tough matrix matrices has become the subject of numerous new patents and publications.

For decades, the plastics industry has used rubber modifiers to toughen rigid, often brittle thermoplastic and thermoset construction resins. Most often, the rubber is dispersed in the form of particles throughout the rigid resin. Various possibilities to change the interaction between the rubber particle and the rigid phase to improve the efficiency of the rubber component have also been investigated. For example, the rubber components have been modified by grafting to alter the compatibility with the rigid phase, and the addition of reactive functional groups to the rubber to promote bonding to the rigid phase has also been shown to be effective. Other approaches have involved the combination of various resins, for the production of mixtures and alloys with improved properties.

The methods used for toughening construction resins have been adapted for the toughening of the matrix resins commonly used in composite structures, as shown, for example, by Diamant and Moulton in "Development of Resin for Damage Tolerant Composites - A Systematic Approach", 29th National SAMPE Symposium, April 3-5, 1984. The preparation of alloys and mixtures by adding a more tough thermoplastic such as a polysulfone to an epoxy resin composition has also been shown to improve the toughness of the epoxy resin and give increased toughness, according to British Patent 1,306,231, published February 7, 1973. More recently it has been shown that combinations of an epoxy resin with end-functional thermoplastic show improved toughness. See U.S. Patent -F .- Ca 2+ CI) CN f.) J 3 4 498 948. Even more recently, curable combinations of epoxy resins and thermoplastics with reactive end functionality were said to improve the toughness of specially formulated matrix resins, provided that the unmixed resin after curing exhibits a specific phase-separated morphology with a crosslinked glassy phase dispersed within a glassy continuous phase.

See U.S. Patent 4,656,208. Further improvements are said to be achieved by the incorporation of a reactive rubber component which is said to be entrapped in the crosslinked dispersed glassy phase. See U.S. Patent 4,680,076. Even more recently, the use of an indigestible particle made from a rubber dispersed in the phase-separated crosslinked epoxy resin matrix has been proposed for toughening composites based on such matrix resins. See U.S. Patent 4,783,506. Although the addition of rubber, thermoplastics and the like generally improves the toughness and impact strength of unmixed resins, the effect on the resulting composites is not necessarily favorable. In many cases, the increase in the toughness of the composite can be only marginal, and a decrease in high temperature properties and in resistance to extreme environmental conditions such as exposure to water at high temperatures is often observed.

Composite structures that rely on complex manufacturing methods or on unique resin morphologies that are difficult to reproduce to achieve toughness improvements may require an impractical degree of control in manufacturing, which increases production costs and often results in uneven performance and poor reliability.

An alternative approach to the production of toughened composites has been the development of layered composite structures with layers of fibers embedded in a matrix resin alternated with layers of a thermoplastic resin, described in Japanese Patent Application 49-132669, published there. May 21, 1976. More recently, U.S. Patent 4,604,319 discloses layered fiber-resin composites having a plurality of fiber-reinforced matrix resin layers interleaved with thermoplastic layers of adhesive adherently bonded to the reinforced matrix resin layers.

Interleaf structures are usually made by impregnating continuous fiber to make a pre-impregnated mat, then laying the composite by alternating a pre-impregnated mat with sheets of thermoplastic film. The laminating package structure is then subjected to heat and pressure, to cure the matrix resin and bond the layers. The patent also describes interleaf layers which comprise a thermoplastic filled with a reinforcing material such as cut fibers, solid particles, hair crystals and the like. Although interleaved composite structures with improved toughness have been described, there has been some sacrifice of other physical properties including a decrease in glass temperatures along with an increase in creep at high temperatures. Additional difficulties with such composites may include a loss of rigidity for many such compositions, adhesion failure that may occur between layers made of different resins and deterioration in property during use due to poor solvent resistance. In addition, pre-impregnated mats based on thermoplastic resins generally suffer from a lack of tack, which complicates their production into composites and increases the degree of skill required to manufacture complex structures. This in turn can result in increased waste losses and a need for more complex quality control procedures, whereby manufacturing costs to achieve an acceptable level of operational reliability increase.

Recently, the use of an indigestible particle made of a rubber dispersed in a phase-separated crosslinked epoxy resin matrix has been proposed for the toughening of composites based on such matrix resins. See U.S. Patent 4,783,506. Dispersion of rigid particulate modifiers in the matrix resin has also been described in the technique of toughening composite materials, and has been described, for example, in published European patent applications 0 274 899 and 0 351 025, as well as in US patent 4 863 787, the instructions of the latter three references are incorporated by reference>> O \ \ O (I) C11 (sl hereby as reference.

The compositions and methods currently available for the production of toughened composites thus require further improvement. Composites with improved impact strength, and in particular those with improved compressive strength after impact, would be a useful advancement in the art, and reliable methods of making such tough composites could find rapid acceptance, replacing the more complex and expensive manufacturing processes which are currently available for these purposes.

Summary of the Invention The present invention relates to layered composite structures comprising continuous fiber and a matrix resin composition, and more particularly to improved layered composite structures comprising continuous fiber embedded in a matrix resin composition toughened with a particulate modifier, the enhancement comprising the use of a particle modifier a substantially spheroidal, spongy structure, also described as porous polyamide particles, and to an agent for producing toughened layered composite. The resulting composite structures show a marked and unexpected improvement in toughness.

Detailed Description The improved composite structures of the present invention include discrete layers of continuous fiber embedded in a matrix resin, the layers being normally separated or separated by laminar regions or layers comprising matrix resins filled with finely divided polyamide resin in the form of particles having a substantially spheroidal, spongy 469 G55 6 structure, also described as porous polyamide particles.

The Matrix Resins The matrix resins useful in the production of toughened composites in accordance with the method of the present invention are the resin compositions commonly used in the art of fiber reinforced composites and may include both thermosetting and thermoplastic materials. However, thermosetting resins are preferred for most applications and the thermosetting resins stated to be useful in the method of the present invention include those most commonly used in the manufacture of fiber reinforced composites such as epoxy resins, cyanate resins, bismaleimide resins, BT resins comprising a combination of cyanates and bismaleimide resin components, mixtures of such resins and the like, as well as the commonly used crosslinkable polyester resins.

Many thermoset resins generally have low toughness and are consequently quite brittle, and composite structures based on such resins therefore benefit greatly from toughening in accordance with the teachings herein.

Thus, the preferred matrix resin composition is based on a thermoset resin, and particularly preferred are the well-known and commonly used epoxy compositions, generally comprising an epoxy resin and a suitable hardener, such as a diamine hardener or the like. The epoxy compositions may, if desired, include a suitable curing accelerator and such additional components as are commonly used in the heat cured composite art.

The epoxy resins that can be used are curable epoxy resins with a variety of epoxy groups per molecule. Such resins are widely used in the manufacture of composite materials, and many are readily available from commercial sources. Examples of such resins are polyglycidyl compounds, including the reaction products of multifunctional compounds such as alcohols, phenols, carboxylic acids, aromatic amines or aminophenols with epichlorohydrin, and epoxidized dienes or polyenes. Additional examples include diglycidyl ethers of diene-modified phenolic novolaks, cycloaliphatic epoxides such as the reaction products of multifunctional cycloaliphatic carboxylic acids with epichlorohydrin, cycloaliphatic epoxides, cycloaliphatic epoxy ethers and cycloaliphatic epoxies. Mixtures of epoxy resins can also be used. Preferred epoxides include bisphenol A epoxides, epoxy novolaokes, cycloaliphatic epoxy ethers and glycidylamines. A wide variety of these epoxy resins are available from commercial sources under trade names such as PGA-X from Sherwin Williams Company, DEN 431 and Tactix 56 from Dow Chemical Company, Glyamine 125 from F.I.C. Corp. and RD87-160, XU MY-722 and MY-720 from Ciba-Geigy Corp.

Diamine hardeners that can be used include the aromatic diamines conventionally used in the formulation of epoxy resins, such as, for example, 4,4'-diaminodiphenyl ether, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenyl sulfone, 3,3 ' -diaminodiphenyl sulfone, p-phenylenediamine, m-phenylenediamine, 4,4'-bis (aminodiphenyl) p-ropane, 4,4'-diaminodiphenyl sulfide, trimethylene glycol bis (p-aminobenzoate) and the like, as well as their various positional isomers. Also useful are the variety of multinuclear aromatic diamine hardeners such as those disclosed, for example, in U.S. Patents 4,579,885 and 4,517,321, and U.S. Patent 4,686,250, all incorporated herein by reference, as well as xylylenediamine, bis (aminomethyl) oclohexane. dioyandiamide and the like. The different diamond cores can be used alone or in combination.

Suitable epoxy resin compositions can be prepared according to methods and uses well known and commonly used in the resin art. In general, the matrix resin compositions comprise more than 2 parts by weight of diamine hardener per 100 parts by weight of epoxy resin. Although the particular level selected depends on the particular diamine used, preferably at least 3 parts by weight and more preferably from about 6 to about 150 parts by weight of diamine hardener per 4-69 'C335 8 100 parts by weight of epoxy resin are used. The amount of each component selected depends on the molecular weights of the individual components and the molar ratio of reactive amino (N-H) groups and epoxy groups desired in the final matrix resin system.

For most applications in pre-impregnated carpet and composite, sufficient diamine hardener was used to give a molar ratio of NH groups and epoxide groups in the range of from about 0.3 / l to 1.8 / 1, preferably from 0.4 / 1 to 1 , 3/1.

The compositions may further comprise a thermoplastic polymer to impart improved toughness to the resulting composite by increasing the toughness and impact strength of the cured resin composition.

When dissolved in the preparation before curing, thermoplastics can also increase the viscosity and film strength of the uncured resin, thereby improving the processability of the resin for use in impregnation work, and can provide pre-impregnated mat with better handling properties for use in composite manufacturing. A variety of thermoplastics are known in the art for use in combination with epoxy resins, including, for example, polyaryl ethers such as polyaryl sulfones and polyaryl ether sulfones, polyether ketones, polyphenylene ethers and the like, as well as polyarylates, polyamides, polyamide imides, polyether imides, polycarbonates, phenoxy carbonates similar. When the purpose of incorporating the thermoplastic is to improve the viscosity, processability and manageability properties, the selected thermoplastic is necessarily soluble in the uncured epoxy resin composition. The proportion of thermoplastic used depends in part on the selected thermoplastic and the particular end use in question. For most purposes, however, the composition comprises from 0 to 30 parts by weight of thermoplastic per 100 parts by weight of the combined diamine curing and epoxy resin components.

The epoxy compositions may also include an accelerator to increase the cure rate. The accelerators are selected from those known and used in the epoxy resin art and can be used CD (fl C) 1 469 9 in conventional amounts. Accelerators that may be found to be effective include Lewis acidamine complexes such as BF3: monoethylamine, BF3: triethanolamine, BF3: piperidine and BF3: 2-methylimidazole; amines such as imidazole, 1-methylimidazole, 2-methylimidazole, N, N-dimethylbenzylamine and the like; acid salts of tertiary amines such as p-toluenesulfonic acid: imidazole complexes and the like, salts of trifluoromethanesulfonic acid such as FC-520 (obtained from 3-M Company), organophosphonium halides, dicyandiamide, 4,4'-methylenebis (phenyldimethylurea) and 1 , 1'-dimethyl-3-phenylurea. Mixtures of such accelerators can also be used. For some end uses, it may also be desirable to include dyes, pigments, stabilizers, thixotropic agents and the like, and these and other additives may be incorporated as needed at levels generally used in the composite art. During curing, the matrix resin preparations, excluding any particulate additives, fillers and reinforcing agents that can be used, form a substantially uniform, continuous rigid phase.

The fibers Prior to curing, the matrix resin composition is combined with continuous fiber reinforcement or structural fibers as well as the particulate modifier used in the manufacture of toughened composites in accordance with the method of the present invention. Suitable fibers can be described in general terms as having a tensile strength greater than 6.89'108Pa and a tensile modulus greater than 14'109Pa. Fibers useful for these purposes include carbon or graphite fibers, glass fibers and fibers made from silicon carbide, alumina, titanium oxide, boron and the like, as well as fibers made from organic polymers such as polyolefins, poly (benzotialzole), poly ( benzimidazole), polyarylates, poly (benzoxazole), aromatic polyamides, polyaryl ethers and the like, and may include mixtures comprising two or more such fibers. Preferably, the fibers are selected from glass fibers, carbon fibers and aromatic polyamide fibers such as those fibers sold by DuPont 469 0323 10 Company under the trade name Kevlar. The fibers can be used in the form of continuous fiber cables of typically from 500 to 42,000 filaments, as continuous unidirectional bands or as webs.

The particulate modifier The polyamide particles used in the practice of the present invention comprise a finely divided polyamide resin and have a substantially spheroidal, spongy structure. The polyamide particles generally have an average diameter between 1 and 75 μm, suitably from about 1 to 25 μm and preferably from about 2 to about 15 μm. The polyamide particles can be further characterized as porous, i.e. with a large internal pore volume, and powders made from such polyamide particles have a large effective surface area, generally greater than 5 m2 / g and preferably greater than about 9 m2 / g, to such a large as 30 m2 / g or more.

The effective surface area of such powders is determined according to the classical BET method. It is to be understood that the porous polyamide particles in other physical forms, such as flake-shaped, cylindrical polyamide particles or fibrid-like materials, may also be useful in the practice of the invention, however, such shapes are not preferred. Pore volume can also be considered as a measure of the porosity of the polyamide particle, and the polyamide particles useful in the practice of the present invention usually have large pore volumes, preferably greater than about 1.5 cm 3 / g to as large as 3.5 cm 3 / g or even greater. .

The porous polyamide particles useful in the practice of the present invention can be made of any rigid polyamide. The polyamide selected in its final particulate form has sufficient heat resistance, hardness and rigidity to resist melting, compaction or flattening under the pressures and temperatures encountered in the manufacture and curing of the laminate. In addition, the polyamide is selected to be substantially insoluble in the matrix resin composition prior to gelling so as to preserve the unique surface properties of the particle. n. 469 053 II The polyamide resins that can be used include any of the commonly available nylon resins, such as polycaprolactam (nylon 6), poly (hexamethylenediamine sebacamide) (nylon 6,6), polyundecanamide (nylon 11), polydodecanamide (nylon 12) and similar. The preparation of particles from such resins with the required porosity has been described in the art, for example in US 4,831,061, the teachings of which are incorporated herein by reference, as well as in US 2,359,877 and in Japanese Laid-Open Application 62-240325. A variety of porous polyamide particles and porous nylon-coated particulate forms such as titanium dioxide particles which may be suitable for use in the practice of the present invention are available, including porous nylon 6 particles, porous nylon 11 particles and porous nylon 12 particles.

The particulate modifiers used in the manufacture of composites may comprise only the porous polyamide particles of the present invention or may be mixtures of such particles with non-porous particles made, for example, from a crosslinked rubber or from a rigid resin, such as polystyrene, polyphenylene ethers. polysulfones or the like, comprising any of the wide variety of particulate modifiers known in the art for use in toughening composites.

The Composite Structures The toughened composite structures of the present invention comprise discrete layers formed of continuous fiber embedded in a matrix resin, which layers or layers are normally separated or separated, the layer surfaces defining laminar areas or spacer layers comprising matrix resins filled with the porous polyamide particles. The particles serve to separate the layers, and the thickness of the distance between the layers will therefore be directly related to the particle size. As used herein, the term "particle size" refers to the particle dimension that determines the distance between the layers, which for small, irregular or substantially spherical particles is generally the particle diameter. Since in most cases it is not possible to obtain particles which are all of the same size, the particulate modifiers will generally comprise mixtures of particles comprising a variety of particle sizes. The particle size can be determined by any of a variety of standard methods, such as by using a Coulter calculator or "Multisizer" apparatus, or by a Granulometer device. Particle modifiers which are useful and effective in toughening composites according to the embodiment According to the present invention, the majority of the particles have an average diameter ranging from 1 to about 75 microns. Mixtures of finely divided particulate materials suitable for the purposes of the present invention can be obtained by sorting particle mixtures using well known methods such as sight sorting and the like.

Use of particulate mixtures comprising a wide variety of particle sizes may have other adverse effects and are therefore less preferred. Dispersing particle mixtures evenly in the matrix resin preparation can become more difficult due to the presence of very large particles, and the coating properties of the filled resins become more variable. The presence of small amounts of very large (> 50 μm) particles dispersed throughout the film of uncured filled matrix resin adhered to one or both surfaces of a pre-impregnated mat tends to create significant peaks or raised points on the outside.

The presence of such raised points has the effect of a visible surface roughness, and reduces the surface tack of the pre-impregnated carpet by preventing complete and effective contact between layers in a laying operation. The reduced tack is particularly noticeable for particle mixtures which involve a wide distribution of particle sizes, and consequently narrowly dispersed particle mixtures are preferred. llx 469 C-Fsšš 13 The proportion of each component used in the manufacture of the toughened composites of the present invention depends in part on the intended end use, as well as on the particular resins, fibers and resin particles selected.

In total, the composites comprise from about 20% to about 80% by weight of continuous fiber, the remainder comprising matrix resins and particles, with the particles in an amount of from 1 to about 25% by weight based on the combined weight of the particles and the matrix resin composition. Although the level of resin particles needed to seal the composite is within the specified range, the optimum level will necessarily vary depending on the type of matrix resin, the fiber content, the particle type and similar factors, and must therefore be determined for the particular fiber and resin system. which was used. In general, it is desirable to use the lowest level of particles that can provide the desired improvement in composite toughness. Although greater than optimal levels can be used, further improvements in toughness become marginal and other physical properties such as heat / moisture resistance can be adversely affected. Composites with a very high fraction of the particles located in the space between the layers are believed to be most effective in providing improvements in toughness at a minimal level of particles.

Comnosite Manufacturing The methods generally used for making layered composites can be readily adapted for making the composites of the present invention. Most often, such composites are made from impregnated tape comprising evenly arranged, parallel filaments of continuous fiber, or from resin-impregnated fabric woven of continuous fiber cable.

These impregnated fibrous structures, called pre-impregnated mats, can be prepared by impregnating tape or fabric with matrix resin compositions in an uncured state using any suitable method including melt coating, calendering, dip coating with a resin solution or 469 Ouš 14 a molten resin, melt pressing. or the fabric into a film of the matrix resin or the like.

The composite is then prepared by laying sheets or strips of the pre-impregnated mat to produce a layered stack or laminating package, and curing the laminating package, generally by heat and under pressure. The layers of pre-impregnated mat, each comprising continuous fiber and matrix resin in uncured form, have their adjacent surfaces adhered upon curing so that a uniform structure with discrete layers of continuous fiber embedded in a substantially continuous and substantially homogeneous matrix resin phase is formed.

In the preparation of the toughened composites of the present invention, it is necessary to distribute the porous polyamide particles evenly between each of the layers of pre-impregnated mat. A variety of methods can be used for this purpose, and the placement of particles at a surface of the pre-impregnated mat can be performed as a separate step before or during the laying operation, or integrated in the step of impregnating the tape or fabric. The former are referred to as two-step procedures, while the latter are referred to as one-step procedures.

Methods of performing the two-step process include physically distributing the particles by spraying, spraying, coating or similar operation on a surface of each strip or sheet of pre-impregnated mat during the laying operation; dispersing the particles evenly in the liquid matrix resin composition and coating the mixture on a surface of the pre-impregnated mat; produces a film of particle-filled matrix resin composition and interleaves the layers of pre-impregnated mat with the film during the laying operation and the like. Two-step methods based on a coating or interleaving step provide additional matrix resin, which ensures that sufficient matrix resin is available to fill the laminar areas between the layers formed by the particles.

In an alternative one-step method, the particles can be placed on a surface of the pre-impregnated mat during the impregnation step by dispersing the particles in the matrix resin and then performing the impregnation step. In this method, a fibrous structure having a surface layer of the filled resin can be produced, for example, by placing a film of filled resin on a surface of tape or fabric or by coating the filled resin directly on the surface. The continuous fiber is then embedded in the matrix resin by heating the fiber and resin structure in a melt pressing or ironing operation. The matrix resin is melted and a portion flows into the fiber structure, leaving behind, at the strip or fabric surface, matrix resin filled with the particles that are too large to enter the spaces of the fiber structure.

The one-step process can be seen as a filtration operation through which the fiber structure acts as a filter, which allows the matrix resin to pass while retaining at the surface those particles which are larger than the openings between the fibers.

As previously pointed out, other than the adaptations necessary to introduce the particles, the laying and curing steps used in the manufacture of the toughened composite structures are conventional. These process steps can be performed using the variety of conventional process devices and equipment and utilize such conventional process steps, adaptations and modifications that are commonly used in composite engineering.

The present invention will be better understood by reference to the following examples, which are given by way of illustration only. In the examples, all parts are by weight and all temperatures are given in degrees Celsius unless otherwise indicated. 469 033 EXAMPLE 16 The following materials and preparations were used in the examples.

Epoxy-1: Tactix 556: MY9612: MYO510: 3 3'-DDS: 4,4'-DDS: Omicure 94: 'Ü Fl H * U E11 U) ERR 4205: SED-m: BAPP: A mixture of tetraglycidyl derivatives of aromatic amines comprising about 40 mole percent N, N, N ', N'-tetraglycidyl-bis (4-amino-3-ethylphenyl) methane, about 47 mole percent (4-diglycidylamino-3-ethylphenyl) - ( 4-diglycidylaminophenyl) methane and about 12 mole percent N, N, N ', N'-tetraglycidyl-bis (4-aminophenyl) methane. An epoxy material obtained as RD87-160 from Ciba-Geigy.

A mixture of oligomeric polyglycidyl ethers of polycyclic, hydroxy-substituted polyaromatic compounds with bridge bonds. An epoxy material obtained as Tactix 556 from Dow Chemical Company.

N, N, N ', N'-tetraglycidyl-4,4'-methylenedianiline.

An epoxy resin obtained as MY96l2 from Ciba Geigy. 0, N, N-triglycidyl-p-aminophenol. An epoxy resin obtained as MY0510 from Ciba Geigy. 3,3'-diaminodiphenyl sulfone. An aromatic diamine hardener, obtained as HT-9719 from Ciba Geigy. 4,4'-diaminodiphenyl sulfone. An aromatic diamine hardener, obtained as HT 9664 from Ciba Geigy N, N-dimethyl-N'-phenylurea, hardening accelerator obtained from Omicron Chemicals.

Polyetherimide thermoplastic resin obtained as Ultem 1000 from General Electric Company Polyetherulfone thermoplastic resin obtained as Victrex 200 from ICI, Ltd.

Bis (2,3-epoxycyclopentyl) ether from Union Carbide Corporation. 4,4'-bis (3-aminophenoxy) diphenylsulfone from Mallinkrodt Chemical Company 2,2-bis (4- (4'-aminophenoxy) phenyl) propane from Mallinkrodt Chemical Company Ü 469 Ü CN CN 17 §§3 ° TEA : Boron trifluoride-triethanolamine complex from Englehard Industries Particles Porous nylon: Particles of porous nylon, average particle size 10 μm, BET active surface 18.2 mz / g, pore volume 3.53 cm3 / g.

Non-porous nylon: Particles of non-porous nylon 12, average particle size 8 μm, BET effective surface 1.7 m2 / g, pore volume 1.10 cm 3 / g.

Fibers Carbon fiber: Thornel 1®fT 40 quality carbon fiber from Amoco Performance Products, Inc. This fiber typically has a filament number of 12,000 filaments per fiber cable, a yield of 0.44 g / m, a tensile strength of 5 , 58 ° 109 Pa, a tensile modulus of 290 Pa and a density of 1.81 g / ml.

In the examples, tapes made from the fiber were used to prepare pre-impregnated carpet with fiber basis weights of 140 to 150 g / m 2.

Test Procedures Particle sizes were determined by granulometer, and are given as mean particle size, while the BET effective surface area was determined by krypton BET technique and pore volume was determined by mercury porosimetry.

Compression After Impact Test (CAI).

This method, termed compression after the impact test, is generally considered to be a standard test method in the industry. The test pieces are plates measuring 15 x 10 cm, cut from fiber-reinforced composite sheets of 32 layers. The plates are first compressed by being subjected to a blow of 680.4 m-kg / m (1500 inlbs / in) in a Gardner impact tester, using a presser with a diameter of 15 .9 mm; a sheet thickness of 4.50 mm was adopted. The beaten plate is then placed in a jig and tested corner by side for residual compressive strength. The details are further described in "NASA Contractor Report 159293", NASA, August 1980.

The methods in the following examples are representative of those that can be used in the preparation of the resin compositions, the pre-impregnated mat and the composites useful in the practice of the present invention. The methods will be widely recognized by those skilled in the art as methods and methods commonly used in the manufacture of thermoset resin compositions and composites.

Example 1 An epoxy resin composition was prepared by heating 70.5 parts by weight of MY9612 epoxy material in a flask to 110 ° C with stirring, and then adding 29.5 parts by weight of 4,4'DDS diamine hardener and mixing at 110 ° C for 20 minutes. .

The mixture was cooled to 103 DEG C. and 15 g of nylon particles were added with vigorous stirring. After stirring for a total of 20 minutes, the resin was emptied from the reaction vessel and cooled.

A second preparation of the preparation was performed but the particles were omitted. Pre-impregnated mat was then prepared by a two-step method with the particulate modifier dispersed on one side thereof, substantially according to the procedure described herein. The pre-impregnated mat had a fiber basis weight of 194 g / m2 and a resin content of 38% by weight.

The 30 cm strip of pre-impregnated carpet was then laid in 38 cm x 38 cm laminate using a bearing configuration of [+ 45 / 9O / -45 / O] 4S and then cured in an autoclave under a pressure of 6.2 10 5 Pa at 355 ° C for 2 hours. After cooling, the resulting composite sheet was used to provide specimens for CAI evaluation. Data are summarized in Table 1.

[M 19 Control Example A. An epoxy resin composition was prepared essentially by the method of Example 1, but changing the modifier to non-porous nylon particles.

The thermosetting epoxy composition was used to prepare composites substantially as described in Example 1 for further evaluation. The composition of the composite and the property data are summarized in Table I.

Example 2. An epoxy resin composition was prepared by heating a solution of 25.4 parts by weight of MY0510 epoxy material and 37.3 parts by weight of MY9612 epoxy in 37.5 parts by weight of methylene chloride to 45 ° C. The mixture was stirred and methylene chloride was distilled with the addition of 15 parts by weight of PES polyether sulfone. The stirred mixture was further heated to remove the methylene chloride, finally to a reduced pressure of 9.5-104 Pa and a temperature of 110 ° C and kept at this temperature for 1 hour. 3,3'-DDS, 21.5 parts by weight, was then added over a period of 5 minutes and the mixture was then stirred at 100 DEG C. for 1 hour, under a vacuum of 9.5-104 Pa to remove residual solvent. The temperature was reduced to 90 ° C and 0, parts by weight of Omicure 94 were added, stirring was continued for 5 minutes and the resin was drained.

The resin was used as a base resin for making pre-impregnated mat and composite using porous nylon particles by the two-step method, essentially following the procedure described in Example 2. The resin and the particles were combined in the sigma sheet mixer at about 50 ° C and mixed for about 2 hours at 50-75 ° C to complete the dispersion of the particles. The final strip of pre-impregnated carpet had a fiber basis weight of 145 g / m2 and a resin content of 37.3% by weight. Composite specimens were prepared as in Example 1. The composition and property data of the composite are summarized in Table I. -lš O \ \ O C) 'ÄN Lu! Control Example B. The resin of Example 2 was combined with non-porous nylon particles and used to provide composite for comparative samples by following essentially the same procedure. The final strip of pre-impregnated mat had a fiber basis weight of 145 g / m 2 and a final resin content of 37% by weight.

Example 3. ERR-4205 epoxy resin; 42.0 parts by weight, placed in a resin cookware and heated with stirring to 130 ° C before adding 8.0 parts by weight of PEI. Heating was continued for 30 minutes until a homogeneous solution was obtained, then 34.8 parts by weight of SED-m were added and the mixture was cooled to 105 ° C and kept there. When the mixture was again homogeneous, 14.3 parts by weight of BAPP were added and heating was continued at 10 ° C for 10 minutes before cooling the mixture to 80 ° C, adding 0.9 parts by weight of BF 3 .TEA, mixing for another 10 minutes and then draining.

An interleaf composition was prepared from a portion of the resin by filling 2131 parts by weight of the frozen resin into a sigma mixer, mixing the resin until the temperature reached 35 ° C, about 15 minutes, and then adding 291 parts by weight of porous nylon particles. The mixture reached a temperature of 4500 while the mixing was continued for about 15 minutes to disperse the particles.

A pre-impregnated mat was prepared from the filled and unfilled resin by the two-step process, and then formed into a composite specimen substantially as described herein.

Control Example C. An epoxy resin composition having non-porous nylon particles was prepared essentially by the procedure of Example 3 and using the same base resin composition.

IP) A pre-impregnated mat was prepared from the filled and unfilled resins by the two-step process and then formed into a composite specimen substantially as described herein. 21 Further examples of composites according to the present invention were also prepared.

Example 4. A mixture of 800 g of Tactix 556 epoxy resin and 800 g of Epoxy-1 epoxy resin was placed in a 5 L resin flask and heated to 110 ° C. A solution of 165 g of PEI thermoplastic dissolved in 3000 g of methylene chloride was added with stirring over a period of 1.5 hours and then the solvent was removed.

The mixture was degassed by heating and stirring the mixture at 110 ° C and vacuum for 45 minutes to remove residual solvent before adding 590 g of 3,3'-DDS and stirring for 25 minutes to disperse the diamine. The resin was then drained and cooled.

A sample of the resin, 86 parts by weight, was filled into a sigma sheet mixer and allowed to warm to room temperature. Porous nylon particles, 14 parts by weight, were added and the mixture was sheared for about 60 minutes so that the particles were evenly dispersed, whereby a resin temperature of about 70 ° C was obtained. A film of the filled resin was prepared at a coating weight of 33 g / m 2 and combined using a pre-impregnated carpet machine with separately produced pre-impregnated carpet tape having a fiber content of 77% by weight and a fiber basis weight of 145 g. / m2, made from carbon fiber and the unfilled resin by substantially following the procedure of Example 1. The final strip of pre-impregnated mat had a fiber content of 37% by weight and a fiber basis weight of 145 g / m2 with particles of nylon 12 dispersed in the resin coating on a surface. Composites were prepared essentially by the methods of Example 1 to give sample plates with a plate thickness of 5.00 mm. Data regarding the properties of the composite are summarized in Table I.

Remarks: 1. 2. 469 033 22 Table I Example Particle size CAIÉ number 10- Pa 1 Porous nylon 225 Control A Non-porous nylon 193 2 Porous nylon 336 Control B Non-porous nylon 300 3 Porous nylon 330 Control C Non-porous nylon 295 4 Porous nylon 328 For particle composition and porosity description, see text.

CAI = Compression After Impact, 680.4 m-kg / m (1500 in.-lb.- / in.) Stroke. For test procedure see the text.

Considering the CAI sample data presented in Table I, it can be seen that a variety of epoxy compositions are significantly improved in terms of damage tolerance when porous particles are used as modifiers. Compare the CAI results for Examples 1-3, prepared using porous nylon 12 particles with those of the control examples AC prepared with non-porous nylon 12 particles. The improvement is generally about 3-107 Pa, which will be appreciated by those skilled in the art. the area is considered a surprising and very significant increase in damage tolerance.

Also consider the excellent CAI properties of the composite from Example 4.

The invention will thus prove to be an improved fiber-reinforced composite or composition comprising discrete layers made of continuous structural fiber embedded in a matrix resin, the toughness of the composite being achieved by incorporating into the matrix resin component polyamide particles having a substantially spheroidal, spongy structure.

The polyamide particles generally have an average diameter between 1 d '23 and 75 μm, suitably from about 1 to 25 μm and preferably from about 2 to about 15 μm, and can be further characterized as having a large internal pore volume. Powders made from such particles have a large effective surface area, usually greater than 5 m 2 / g and more preferably greater than about 9 m 2 / g to as much as 30 m 2 / g or greater, as determined by the classical BET method. The invention will also be recognized to include an improved method of toughening fiber reinforced composites comprising continuous structural fiber embedded in a thermoset matrix resin with a particulate modifier dispersed therein, the improvement being the use of porous particles as defined.

Further modifications and variations will be apparent to those skilled in the art of resin formulation and composite manufacturing, and such variations and modifications will be included within the scope of the invention as defined by the appended claims.

Claims (10)

(TÅ »o oi m 29 PATENT REQUIREMENTS Fiber-reinforced composite comprising continuous structural fiber and rigid particles embedded in a thermoset matrix resin, characterized in that the rigid particles are porous and have a spheroidal spongy structure and are made of polyamide resin. A composite according to claim 1, characterized in that it comprises (a) an epoxy matrix resin composition and (b) continuous structural fiber embedded in said matrix resin, said structural fiber constituting a plurality of discrete layers defining layers comprising said matrix resin having porous rigid polyurea has a spheroidal, spongy structure and an average diameter in the range of from about 1 to about 75 microns dispersed therein. 3. n a d. Of said porous rigid polyamide particles comprising from A composite according to claim 1 or 2 characterized in - 1 to about 25% by weight of said matrix resin. 4. in that said epoxy matrix resin comprises at least one epoxy resin, A composite according to claim 1 or 2, characterized by an aromatic diamine hardener and, if desired, a thermoplastic. Said matrix resin comprises at least one epoxy resin, an aromatic diamine hardener and from about 5 to about 30 parts by weight, Composite according to claim 4, characterized in that based on the combined weight of the epoxy resin and diamine curing components, of a thermoplastic selected from the group consisting of polyaryl ethers and polyetherimides. 6. It comprises from about 20 to about composite according to any one of claims 1-5, characterized by - 80% by weight of said structural fiber. 7. that said structural fiber is carbon fiber. Composite according to Claim 6, characterized in that 469,033 ' Means for producing a fiber-reinforced composite comprising continuous structural fibers and rigid particles embedded in a thermoset matrix resin, characterized in that the rigid particles are porous with a spheroidal spongy structure and used to segregate a layered fibrous reinforced composite fiber structure. embedded in a bonded epoxy resin composite. Agent according to claim 8, characterized in that the polyamide particles have an average diameter in the range from 1 to 75 μm, suitably from 1 to 25 μm. 10. An agent according to claim 8 or 9, characterized in that the polyamide particles comprise from about 1 to about 25% by weight of the combined weight of epoxy resin composition and said particles.