JPH0269566A - Fiber-reinforced composite material toughened with long thin rigid particle - Google Patents

Abstract

PURPOSE: To provide a toughened fiber-reinforced composite by forming independent layers formed of a continuous fiber buried in a matrix resin, and a thin layer area consisting of the matrix resin filled with elongated rigid particles between these layers.

CONSTITUTION: A hardening matrix resin product contains (A) a matrix resin product, preferably, 99-75 wt.% (hereinafter referred to as %) epoxy resin product consisting of 100 parts by weight (hereinafter referred to as part) epoxy resin having a plurality of epoxy groups, 6-150 parts diamine hardener and 0-30 parts thermoplastic polymer, and (B) 1-25% flake or fiber flock particle having an aspect ratio larger than 2:1 and a minimum dimension of 1-75 μm and formed of a rigid material selected from among polyamide, polyimide, polyacrylonitrile oxide and the like. This composite material has a thin layer consisting of the product formed between prepreg layers consisting of a continuous fiber and matrix resin.

COPYRIGHT: (C)1990,JPO

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to composite materials, and more particularly to tough impact-resistant fiber reinforced composite materials. More specifically, the present invention is directed to a method of toughening fiber reinforced composites +A and grains useful for toughening such composites.

Fiber reinforced composites are high strength, high modulus materials that are widely accepted for use in manufacturing consumer items such as sporting goods and equipment. Such materials are also increasingly finding acceptance for use as structural components in automotive applications, building structural components, and aircraft structural components. Typically, composites used in structural applications consist of structures in the form of continuous filaments or tiered fabrics embedded in a thermoplastic or thermoset matrix. Such composites can exhibit considerable strength and stiffness, and the potential for obtaining significant weight savings makes them very attractive for use in primary structural applications as metal replacements. I take it as a thing. However, its acceptance for many structural applications is limited by the fact that many of the composite materials currently available are brittle. The inability of such composites to withstand impact while possessing useful stiffness and compressive strength has been a significant problem for many years. Compensating for the low impact resistance of such materials has typically been accomplished by increasing the amount of material used. This method increases costs and
This reduces the weight savings that could be realized and makes them unacceptable for many applications.

[Conventional technology]

The composites industry has long been concerned with finding ways to overcome these drawbacks. Considerable effort has been directed over the past two decades toward developing composite materials with improved fracture toughness. Many of the commonly used matrix resins, as well as many of the reinforcing fibers, are brittle to boat fishing, so much of the effort has been focused on research into component replacements with better toughness properties. the result,
Research into tougher matrix resins has been the subject of a number of recent patents and publications.

For over ten years, the plastics industry has been using rubber modifiers to make stiffer and more brittle thermoplastics and FiJ! It has been used to strengthen hardenable engineering resins. The rubber was most often dispersed in the form of particles throughout the rigid resin. Various means have also been explored to modify the interaction between the rubber particles and the rigid phase to improve the effectiveness of the rubber component.

For example, rubber components have been modified to change their compatibility with the rigid phase by grafting, and the addition of reactive functional groups to the rubber to promote bonding to the rigid phase has also been effective. It has been shown that. Other methods include combining dissimilar resins to form blends and alloys with improved properties.

The methods used to strengthen engineering resins are described, for example, by Diamond and Moulton in ``Development of Resins for Fracture-Resistant Composites - A Systematic Approach'' (De
velopn+ent of Re5in for D
image Tolerant, (omposi
tes-A Systematic Appr.
oach, )” 1st Former 01 Country T Sanbe (5ANPE)
Symposium, April 3-5, 1984, has been adapted to strengthen matrix resins commonly used in composite structures. British patent 1: Forming alloys and blends by adding more ductile thermoplastic resins, such as polysulfone, to epoxy resin formulations also improves the ductility of the epoxy resin and provides enhanced stiffness. 306,231
．． Illustrated in accordance with publication February 7, 1973. More recently, silking of epoxy resins and terminally functional thermoplastic resins has been shown to exhibit enhanced stiffness. See U.S. Pat. No. 4,498,948; more recently, curable combinations of epoxy resins and thermoplastic resins with reactive terminal functional groups have been described to improve the toughness of specially formulated matrix resins. However, the pure resin after apotheosis exhibits a unique phase-separated morphology with a cross-linked glass-like phase dispersed within a glass-like continuous phase. US Patent 4°65fi
, 208. In history, it is stated that an improvement was made by including a reactive rubber component in the form of cross-linked particles to be contained in a cross-linked dispersed glass-like material. l-4,680°076
See.

[Problem to be solved by the invention]

Additions of rubber, thermoplastics, etc. generally improve the ductility and impact resistance of neat resins, but the effect on the resulting composite is not necessarily beneficial. In many cases, the increase in toughness of the composite can be negligible, and there is a deterioration in high temperature properties and a decrease in resistance to extreme environments, such as exposure to water at high temperatures. Better ζi
Can be seen. Composite structures that rely on complex manufacturing methods or unique resin morphologies that are difficult to reproducibly achieve improved toughness may require impracticable improvements during manufacturing. A high degree of control is required, increasing manufacturing costs and often resulting in poor performance and poor reliability.

Another method for producing a hardened composite was described in 1976.
Layered composite material having layers formed of fibers embedded in a matrix resin alternating with layers formed of a thermoplastic resin described in Japanese Patent Application No. 491326fi9 published on May 21, 2013 More recently, in U.S. X'F 4,604,319, multiple fiber-reinforced matrix resins were inserted with a thermoplastic bonded to a reinforcing 7 trix resin layer. Layered fiber-resin composites are disclosed having layers. The sandwiched structure is typically formed by impregnating continuous fibers to form a prepreg and then injecting the prepreg into a sheet of thermoplastic film. The stacked structure is then subjected to heat and pressure to harden the matrix resin and bond the layers together. This patent also covers Chiyo Sobutofiber, An intercalated layer of thermoplastic material filled with a reinforcing material such as solid particles and whiskers is disclosed.

A sandwiched composite structure with improved toughness was disclosed, but at some sacrifice in the physical properties of the pond, including a decrease in glass transition temperature with an increase in creep at high temperatures. Ta. Another difficulty in the history of such composites is the loss of stiffness, poor adhesion and solvent resistance that can occur between layers formed of dissimilar resins, which often makes such composites difficult to use. This includes deterioration of properties that occurs during use. Furthermore, prepregs based on thermoplastics generally lack plasticity, which makes fabrication into composites [E] and increases the technology required to create composite structures. This historically increases scrap losses and requires more complex quality control procedures,
Acceptance increases manufacturing costs to achieve acceptable levels of reliability.

The currently available compositions and methods for producing toughened composites are thus in need of further improvement.

Composites with impact resistance, and especially better compressive strength after impact, are a useful advance in this technology, and reliable methods of producing such toughened composites are rapidly gaining acceptance. It has the potential to replace complex and expensive manufacturing processes currently available for these purposes.

[Means to solve problems]

The present invention relates to layered composite structures comprising continuous fibers and matrix resin formulations toughened by the inclusion of elongated grains formed of a south-milled rigid material. More particularly, the present invention relates to elongated grain-filled matrices (M-lipid formulations) for use in producing toughened composite structures and to composite layered composite formulations prior to curing. A plurality of separate discrete Nvs containing continuous fibers embedded in the matrix resin by adding long grains to the matrix resin in the interspaces strengthens the formed laminated composite. These grains are shaped to bridge the openings between the individual filaments of the continuous fiber component of the composite structure and are inserted into the interbraid spaces during composite manufacture. The resulting composite structure shows a significant and unexpected improvement in toughness.

The toughened composite structure of the present invention includes distinct layers formed of continuous fibers embedded in a matrix, and these layers are comprised of 7i4 layered regions of matrix resin filled with elongated grains. or separated by layers or generally spaced apart.

7 TRIX RESIN Matrix resins useful in forming toughened composites in accordance with the practice of this invention are resin formulations commonly used in fiber reinforced composites that are heat-curable and heat-curable. Contains both plastic materials.

However, thermosetting resins are preferred for many applications, and thermosetting resins useful for this application include epoxy resins, cyanate resins, bismaleimide resins, BT resins consisting of a silk combination of cyanate and bismaleimide resin components, and These include mixtures of resins such as those commonly used to make fiber reinforced composites, as well as widely used crosslinkable polyester resins. Many thermoset resins generally have low ductility and are therefore very brittle.

Composite structures based on such resins therefore benefit greatly when toughened according to the teachings of the present invention.

Preferred matrix resin formulations are thus based on thermosetting resins, particularly the well-known and widely used epoxy formulations, which generally consist of an epoxy resin and a suitable curing agent, such as a diamine curing agent. It is based on things. The epoxy formulation may optionally additionally include a suitable curing agent, and such additional ingredients are commonly used in thermoset composite technology.

Epoxy resins that can be embedded 171 are curable cycloaliphatic epoxy resins having at least two epoxy groups per molecule. Such resins are commonly used to make composite materials and are often used in commercial
l? It can be easily done manually from i.

19μ of such resins are alcohol, phenol,
Polyglycidyl compounds including reaction products of polyfunctional cycloaliphatic compounds such as carboxylic acids or aromatic amines, shrimp chlorohydrin, and epoxidized dienes or polyenes. Further examples include reaction products of cycloaliphatic epoxides, such as polyfunctional cycloaliphatic carboxylic acids, with shrimp chlorhydrone, cycloaliphatic epoxides, cycloaliphatic epoxy ethers, and cycloaliphatic epoxy esters. Includes things. Mixtures of epoxy resins can also be used. Preferred epoxides include bisphenol A epoxide, epoxy novolacs, cycloaliphatic epoxy ethers, and glycidyl amines. A wide variety of these epoxy resins include, for example, PGA4 from Shelwin-Williams Company, DEN 431 from Dow Chemical Company, and Glyamin from FIC Corporation.
e) ] 25 and M from Ciba Kaigye Corporation
It is commercially available under trade names such as Y-720 and can be done manually.

Diamine curing agents that can be used include aromatic diamines conventionally used in epoxy resin formulations, such as 4,4'-diaminodiphenyl ether, 4,4'-
Diaminodiphenylmethane, 4,4'-diaminodiphenylsulfone, 3,3'-diaminodiphenylsulfonenylene diamine, 4,4'-bis(aminodiphenyl)
Bua bread, 4,4°-diaminodiphenyl sulfide,
trimethylene glycol bis(p-7 minobenzoate) and the like, as well as their various fi2 a X forms. Also, various polynuclear aromatic diamine curing agents, such as U.S. Pat.
and 4,686,250 (incorporated herein by reference in their entirety), as well as xylene diamine, bis(aminomethyl)cyclohexane, and dicyandiamide. Various diamine curing agents are
Can be used alone or in combination.

Suitable epoxy resin formulations can be prepared according to methods and practices well known and commonly used in the resin art. Generally, matrix resin formulations contain more than 2 parts per 100 parts by weight of epoxy resin (pbw) of diamine curing agent. The particular levels selected will depend on the particular diamine used, but preferably at least 3 parts by weight of diamine plus 1 to 1 parts of diamine are used per 100 parts of epoxy resin, and more preferably from about 6 to about 150 parts by weight of diamine plus 1 to 1 weight parts of diamine. Ru. The choice of each component depends on the molecular weight of the individual component and the molar ratio of reactive amine (NH) groups to evoquine groups desired in the Ii1 final matrix resin system. For many prepreg and composite applications, N
- the molar ratio of μ groups to 1 texito group is approximately 0,3
/1-I, 8/I, preferably 0.4/1-1.3/
Sufficient diamine curing agent is utilized to provide a range of l.

The formulation may further include a thermoplastic polymer. Such materials enhance the ductility and impact resistance of the cured resin formulation, further contribute to the toughness of the resulting composite, are often effective in increasing the viscosity and film strength of the uncured resin, and are often effective during impregnation operations. Improve processability and handling in Boaryl ethers such as polyaryl sulfone, polyether ketone, oriphenylene ether, as well as polyarylates, polyamides, polyamide-imides,
Any of the various thermoplastics known in the art may be used in combination with epoxy resins, including polyetherimides, polycarbonates, phenoxy resins, etc., to improve their viscosity, processability, and handling properties. The thermoplastic selected is soluble in the uncured epoxy resin formulation, although it can be used as is effective to modify the composition. The proportion of thermoplastic used will depend in part on the thermoplastic selected and the particular end use intended. However, for many purposes, formulations with a
Contains ~30 pbw of thermoplastic.

The epoxy resin formulation may additionally contain accelerators to increase the rate of cure, including any +it accelerator known and used in the epoxy resin art in conventional amounts, such as Lewis acid:amine complexes, etc. BF3: Monoethylamine, BP
, nitriethanolamine, BF3:piperidine and B
F-,: 2-methylimidazole: amines, such as imidazole, l-methylimidazole, 2-methylimidazole, N,N-dimethylbenzylamine; acid salts of tertiary amines, such as p-toluenesulfonic acid: imidazole complex and salts of trifluoromethanesulfonic acid, such as FC-520 (obtained from 3-M Company), organic phosphonium halides, dicyandiamide, and 1,1-dimethyl-3-phenylurea.

Mixtures of such promoters can also be used. For some end uses it may be desirable to include dyes, pigments, stabilizers, thixotropic agents, etc., and these and other additives are included as needed at levels commonly practiced in the composites art. Upon curing, the matrix resin formulation forms a substantially single continuous rigid phase, excluding any such particulate additives that may be used.

[Fiber]

The matrix resin formulation is combined with continuous fiber reinforcement or structural fibers and particulate modifiers in forming a toughened composite according to the practice of the present invention. Suitable fibers are generally characterized by having a tensile strength greater than 100 kpi and a tensile modulus greater than 2 million psi. Fibers useful for such purposes include carbon or graphite fibers, glass fibers and fibers formed from silicon carbide, alumina, titania, boron, etc., and organic polymers such as polyolefins, poly(benzothiazole), etc. , poly(benzimidazole),
Included are fibers formed from polyarylates, poly(benzoxazole), aromatic polyamides, polyaryl ethers, and the like, and may also include mixtures containing two or more such fibers. Preferably these fibers are selected from glass fibers, carbon fibers and aromatic polyamide fibers, such as those sold by the DuPont Company under the trade name Kepler;
It can be used in the form of a continuous tow of 0 to 420.00 filaments, as a continuous unidirectional tape or as a woven fabric.

[Fine particulate modifier]

The grains used in the practice of this invention are finely divided, rigid materials, and can be described as elongated, meaning that at least one dimension of the grain is substantially larger than the smallest dimension of the grain. Whether the grain is cylindrical or columnar,
Cedar may be irregular or long in a single dimension, like a fiber, or long in two dimensions, like a plate, disc, or flake, including 0 grains. may be regular or irregular in cross section and preferably have an aspect ratio, i.e. the ratio of the longest dimension to the smallest dimension, of 2 =
Examples of suitable elongated grains, preferably larger than 1, include monofilament and fiber-like grains such as those found in floes, fiber bulbs, fibrils, etc., as well as films, chips, mechanically flattened grains, etc. Includes flakes and flake-like materials represented by grain fragments.

The elongated rigid grains may be formed of any conventional rigid VR material, including rigid resins, vitrified or graphitized solids, crystalline materials, metals, ceramics, and the like. Many such materials are commercially available in suitable forms and are readily available.

Rigid resins that may be useful directly or as precursors in forming such grains include fully or partially cured rigid thermosets, rigid thermoplastics, and mixtures of such resins. is included.

These resins are characterized as rigid, meaning that the resin selected resists melting, compaction, or flattening in the final particle form under the pressures and temperatures encountered during laminate manufacturing and curing. It is meant to have sufficient heat resistance, hardness, and rigidity to Soft or rubbery resins having a glass transition temperature of less than or equal to about 15°C or a hardness value of less than or equal to about D-50 (Shore), and resins having a melting temperature substantially less than or equal to the expected processing temperature are , can melt or soften considerably during composite manufacture and are therefore not suitable for use as granules in the practice of the present invention.

If the particles are dispersed in a matrix resin formulation and then applied to a fiber reinforcement or prepreg, the particles are made of a material selected to be substantially free of microorganisms in the matrix resin formulation prior to gelation. is inevitably formed. Many fiber-forming rigid resins in the form of chopped fibers or flocks are readily available commercially or can be obtained in filament or fiber form and then processed by conventional means to give suitable flocks. You can.

Representative thermosetting, thermoplastic and natural materials that may be useful in the form of flocs or fiber bulbs as elongated rigid particles for toughening composites include rayon IL olefin fibers, aromatic and aliphatic polyamide fibers. , acrylic fibers, phenolic fibers, polyacrylonitrile IL pitch fibers, etc., as well as jute, cotton, wool and similar natural fibers. Many such fibers can be oxidized, carbonized, graphitized, or otherwise treated, making the fibers heat-hardened, toughened, and further converted into carbonized rayon fibers, heat-hardened or Formation of elongated grains suitable for the practice of the present invention, including oxidized polyacrylonitrile fibers and carbon or graphite fibers derived by carbonizing or graphitizing fibers formed from polyacrylonitrile, petroleum or coal tar pitch, etc. provides additional fibers that can be used to

Rigid thermosetting and thermoplastic resins can also be formed into films by well known methods and chopped to provide flakes suitable for use as molded particulate modifiers and The malleable resin can be molded into flakes or granules in commercially available equipment and then pressed under pressure, usually with a mill roll or the like while being heated, to form flakes. Can form similar grains.

Similar methods can be used to produce metal grains in the form of fibers, flocs and flakes, and various natural elJ
The materials can be produced in suitable crystalline or fiber-like forms and these materials can be useful as elongated grains. Glassy and graphitic solids in the form of fibrils and flakes are known in the art and include various fibers formed of silica, graphite, carbon, carbonized resins, carborundum, 7-random, boron and boron-containing compounds, etc. Included are flakes and fibrils, many of which are commercially available, and which are also useful for purposes of the present invention. Some of these materials are extremely hard, especially those that can cut or damage most continuous i&fiber reinforcements during manufacture, and the use of such materials is therefore of equal or greater hardness. km Not preferred except for use with 1m reinforcement.

Good adhesion between the elongated grains and the matrix resin can enhance hardening of the grains in toughened composites. Many of the grain precursor materials are known to exhibit good adhesion to thermoset matrix resins in a continuous wk-form; this may be an inherent property of the fibers or a surface treatment of the fibers. or may be the result of sizing, and grains formed from such precursors are particularly desirable for use in the practice of the present invention. It may be desirable to include functional groups that can react with the matrix resin and thereby become chemically bonded to modify the surface of the elongate grains or their film or fiber precursors. Alternatively, suitable grains can be formed from resins containing copolymerized carboxylic acid or carboxamide functional groups, or various phenols that can remain usefully reactive with the matrix resin after curing. and maleimide resins. The surface μ of the grains or their precursors can be increased by chemically bonding matrix resin to the grain surface or by improving the affinity of the grains for the matrix resin due to the presence of polar groups on the grain surface. Adhesion may be improved.

[Composite structure]

The toughened composite structure of the present invention includes separate layers formed of continuous fibers embedded in a matrix resin, and the layers or bries are separated or typically rf spaced apart. Separated, the surfaces of the layers define the /1 layer area, ie the spaced layers, which are composed of a matrix resin filled with elongated grains. The grains serve to separate the braai, and the thickness of the braai space is
Therefore, it is proportional to grain size. When the grains are in the form of film fragments or flakes, the grains can be dispersed as a single layer on the surface of the braai, or the grains can be stacked in brick-like cedar, depending on the processing method chosen. The spacing between the resulting blies is therefore a multiple of the flake thickness. Cylindrical grains, such as chopped fibers, flocks or fibrils, may be entangled or felted, providing spacing substantially greater than the cross-sectional dimensions of the grains, but preferred cylindrical grains are free from entanglement or felting. be of such nature and dimensions that it will not occur.

The filled resin spacing layers separating the brazes have an average thickness in the range of about 1 micron to about 75 microns. The composite toughening effect of such a filled matrix resin layer may be greatest for a layer that is substantially uniform in thickness;
This is best achieved by using grains that are substantially uniform in size. As used herein, the term "r-grain size" refers to the grain size that is determining braai separation;
For small irregular or substantially spherical grains, it is usually the thickness or smallest dimension of the grain. For fibrous grains, grain size is taken to refer to the diameter of the m fibers, while
For flaky grains, the term refers to the thickness of the flakes; in most cases, it is impractical to obtain grains that are uniform in size throughout, so fine-grained modifiers are usually mixed with a variety of grains. These mixtures are useful and effective in toughening composites, typically consisting of mixtures of grains ranging in size from 1 to about 75 microns, with the majority of grains ranging from 1 to about 75 microns.

The proportions of each component used to make the toughened composites of the present invention depend in part on the intended end use and on the particular resins, fibers, and particulate materials chosen. Generally, composites contain from about 20 to about 80% by weight continuous m&I
with the remainder consisting of the matrix resin and particulate modifier, with the particulate filler ranging from 1 to 50% based on the combined weight of the particulate modifier and matrix resin formulation.
It makes up about 25% by weight. The level of striated grains required to toughen the composite is within the stated range, but the optimum level depends on the type of matrix resin, fiber loading, class I of the grains, and similar factors. will necessarily vary and must therefore be determined for the particular fiber and resin type used. It is generally desirable to use the lowest level of grain that provides the desired improvement in the toughness of the composite.

More than the optimum level can be used, but the improvement in toughness is still marginal and other physical properties such as heat/wet strength may be adversely affected. The method of the present invention for toughening i-compounds provides composites with a very high proportion of grains located in the interbraid spaces, thus providing improved toughness at the lowest level of grains. It is well suited for.

[Composite material manufacturing]

The methods commonly used to produce layered composites are:
It can be easily adapted to produce composites of the present invention. Most commonly, such composites are formed from an impregnated tape of uniformly arranged parallel continuous wA fiber filaments or a resin-impregnated fabric woven from continuous TA fiber tow. These impregnated fibrous structures, termed prepregs, can be prepared by any method including melt coating, calendering, impregnation with resin solutions or molten resins, melt pressing tapes or fabrics onto a film of matrix resin. The tape or fabric can be made by impregnating the tape or fabric with the matrix resin formulation in the uncured state using conventional methods.

Composites are then made by stacking sheets or prepreg tapes to form a layered laminate or layup and curing the layup, usually under heat and pressure. The layers of prepreg, each containing continuous fibers and matrix resin in uncured form, have their adjacent surfaces adhered by curing to form separate layers embedded in a substantially continuous and substantially homogeneous matrix resin phase. Formed into a unitary structure having layers of continuous fibers.

In forming the toughened compositions of the present invention, it is necessary to uniformly distribute the elongated grains between each prepreg layer. Various methods can be used for this purpose; positioning the particulate modifier on the surface of the prepreg can be carried out as a separate step before or during the leiamab operation, or impregnating a tape or woven fabric. It can also be integrated at the stage of The former is called a two-stage process, and the latter is called a one-stage process.

Methods of carrying out the two-step process include sprinkling, spraying,
Physically distributing the grains by performing a push tip or similar operation on the surface of each rubreg tape or sheet during the layup operation, dispersing the particulate modifier uniformly into the liquid matrix resin formulation. and applying the mixture to the surface of the prepreg, forming a film of the matrix resin formulation loaded with particulate modifier, and inserting the brow of the prepreg between the films during a lay-up operation. It will be done. A two-step process based on an application or insertion step provides added matrix resin and ensures that a suitable matrix resin is available to fill the lamination areas between the briars formed by the particulate modifier.

In another one-step method, the particulate modifier is placed on the surface of the prepreg during the impregnation step by dispersing the particulate modifier into the matrix resin and then performing an impregnation step. I can do it.

Textile structures with a surface layer of filled resin are used for this purpose, for example by placing a film of filled resin on the surface of the fabric or by applying the filled resin directly onto the surface. carried out by. The continuous fibers are then embedded in a matrix resin by heating the fibers and resin structure during a melt press or ironing operation, the matrix resin is melted and some of it flows into the 1a groove structure, forming the tape or fabric. At the surface, it leaves a matrix resin filled with particles that are too large to fit into the interstices of the fibrous structure.

The one-step process can be viewed as a filtration action in which the m-phase structure acts as a filter, allowing the matrix resin to pass through while retaining particles on the surface that are larger than the openings between the fibers. The elongated grains of the present invention are particularly effective for use in step processes - as these grains can bridge the openings between continuous fibers and are thus retained on the surface of the prepreg. Cylindrical a! Contains It-like grains.

Other than the adaptation required to introduce grains as previously discussed, the stacking and curing steps used to produce toughened composite structures are conventional. These process steps can be performed using any of a variety of conventional process equipment and supplies, and may be adapted and modified as conventionally used in composite technology. use

The invention will be better understood in consideration of the following examples, which are given for illustrative purposes.

In the examples all parts are parts by weight and all degrees of IH are given in degrees Celsius unless otherwise stated.

〔Example〕

The following materials and formulations were used in the examples.

Epoxy resin formulation component parts by weight EP-1: and λ (2,34 N 1 K D Kame II) I
-F Tsum.

(Epoxy resin) 40.8 4.4'-His(3-minofenoxo)so phenylsurneno.

(Amine aphrodisiac) 48.1 Total amount of thylimide obtained as 48.1 EP-2 He-2 (2,3-μ; 4 knots 0 fill) 1.
-jl+.

(Epoxy resin) 41.8 4.4'-Hysterol (3-7 Minov I Hashi) No' Phenyl Sulfur Wood.

(Amine aphrodisiac) 49.4 8F 3 TEA See EP-1 0.9 PEI See EP-1 7.9 Total 100.0 EP-3 8F3: TEA; See EP-1 PEI; E
See P-1 0.9 7.4 Total 100.0 Particle Abbreviation Number Flock-1 Flock-2 Composition Precision cut 3 denier nylon fiber flock, length 500μ, Flock Industries Corbore Terrado IL! .

Precision cut oxidized polyacrylonitrile fiber flock, length 500μ, straight Radial 6B, flock industry Made of Zukorphorated, Ammo Ko performance 70 ducts Powered by Incorporated made from recycled fibers.

Flock-3 flakes-1 B5-1 Precision cut carbon fiber flock, length 500μ, diameter 6μ, R, K.

Powered by Textiles From fiber to flock industry Manufactured by Coholated Construction.

! Mil (7) '7 LuF M (Ulten) 10
Hexagonal flakes measuring approximately 0.008 inches (0,020 cm) cut from 0 OPEI film.

Spray-dried granules of carboxylated styrene-atadiene-acrylonitrile turbopolymer having a carboxyl functionality of approximately 0.038 equivalents per 100 g of resin, a Tg of 26°C and an average particle size of 13μ, B,F.

Accepted as manufactured by Butotsuri Sochi Company from Hycar 1578XI latex.

The floc and flake grains in the received form generally contained surface contaminants used in the cutting or chopping operation, such as process oils, cutting oils, and the like. Contaminants were generally removed by rinsing the grains with methylene chloride, followed by alcohol, and drying the grains before use to make composites. Alternatively, the granules are dispersed in a warm (60° C.) aqueous sodium carbonate solution for 1 hour, then collected by filtration, rinsed with solvent and dried.

Unless specified by fiber, the carbon fiber material used in the examples was a carbon fiber such as Thornel® Ta2O-42 from Amoco Performance Products, Inc. This fiber typically has a fiber count of 12,000 filaments per tow, a yield of 0.44 g/m, a tensile strength of 7
30 kpsi, tensile modulus 42 mpsi and density 1
．． It has 783/cc. In the examples, ribbons made from TA fibers were used to make prepregs with fiber areas μ 44-146 g/m 2 .

Test Procedure Compression After Impact Test This procedure, referred to as Compression After Impact Test or CAI, is generally considered a standard test method in the industry. The test sample was 6 x 4 inches (15,24 x lO,
16 cm) panels were cut from the fiber reinforced composite sheet. The panel was first placed in a Gardnern impact tester using a 578 inch (1,59 cm) diameter indenter!
The impact was applied by applying a 500 inch bond/inch impact to the center. The impacted panels were then placed in a jig and tested edgewise for residual compressive strength. For more details, see NASA Contract.

r Report 159293J, August 1980, NASA.

Glass Transition Temperature (T g ) T g values were obtained by standard differential thermal analysis (TGA) techniques, with a heating rate of 10° 1 min.

The methods in the following examples are representative of those that can be used to make resin formulations, prepregs, and composites useful in the practice of this invention. These methods are recognized by those skilled in the art as commonly used in the manufacture of thermoset resin formulations and composites.

Control Example A EP-1 resin formulation was mixed with 40.8 parts by weight (pb) of bis(2,3-epoxycyclopentyl) ether at 130 pb.
It was made by stirring while heating to 0.degree. C. and then adding 10.2 .mu.b of Ultem 1000 polyetherimide resin. While stirring and heating continued at 130°C, the resin melted in 1 hour, then 48.1 pbν of 4,
4'-bis(3-7minophenoxy)diphenylsulfone was added and the mixture was cooled to 90°C. The mixture was stirred and heated to 105°C for about 10 t, then cooled to 80°C,
Then 0.9 pbw of BF3-1' re-engineered ethanolamine complex was added with vigorous stirring. After stirring for another 10 minutes,
The resin was discharged from the reaction vessel and cooled.

The thermosetting epoxy formulation is manufactured by Meat Release Products Co., Ltd. W-89-5PT-6BE/PST
13.5 inches (34,29 cm) obtained as 3A
Width was coated onto silicone coated release paper. The coating was carried out with a coating weight of 41 gμ12 to give two rolls of coated paper.

A 12 inch (30,48c+a) wide ribbon of carbon fiber was made from 105 tow carbon fiber. To carve the preblebs by sandwiching the ribbon between films from two rolls and compressing it to give a chive of 67% by weight carbon fiber, * II area type μ 45 g/+2 and U approximately 5.5 mils thick. A prepure rag machine was used.

External shape (+ 45/90/-
-4510) 15X15 inches (3B, I) with 4s
X 38. Icm) stacked in laminate and autoclaved at 355”F (179,4℃) under 90psi pressure.
) for 2 hours. After cooling, the raw composite panels are
It was used to provide test specimens for compression after impact evaluation.

Control Example Day and C Using substantially the same procedure as used in Control Example A replacing the epoxy resin formulations of EP-3 (Example Date) and EP-2 (Example C), additional A control composite was constructed. Minor changes in handling were made to accommodate slight differences in the physical properties of the resin formulations, as would be readily understood by those skilled in the epoxy resin formulation art.

A one-step process was used to prepare the prepregs of Examples 1-3 in which particulate modifiers were mixed into the matrix resin and a film was formed by a coating step. The dried fiberware was then sandwiched between two such filled resin films in a 71 knob l/g machine to give a prepreg with fractionated grains in the resin on both surfaces.

In Example 2, a composite was produced using a two-step process in which low resin content prepreg chives were first made and then granulated by physically sprinkling the granules on one surface during a stacking operation. coated.

Example 1 49.4 pb of epoxy in a sigma plate mixer
Charge EPI solution (80/2 hat 1 ratio) and mix while heating to 100°C, then add 3.2ρbw floc-1
A filled EP-1 resin formulation was prepared by adding granules. Mixing was continued until the floc particles were uniformly dispersed, and 46.5 pb of 4,4'-bis(3-aminophenoxy) diphenylsulfone was added over 10 minutes, followed by continued heating and stirring for 20 minutes. . After cooling the mixture to 80° C., 0.9 phw of BF3:l-liethanolamine complex was added with stirring. Stirring was continued for an additional 10 minutes, after which the resin was drained.

A prepreg cheese having a fiber areal weight μ 145 g/II+2 and a resin content of 36.9 wt. gave. The majority of floc grains were localized on the prepreg surface. A composite panel was formed by the method of Comparative Example A.

Example 2 Carbon fiber and EP-3 were prepared substantially according to the procedure of Control Example A.
Made from epoxy resin formulation, fiber content 65@wt%
The pre-preg chives are shaped like [+45/90/-4
510] +5 x 15 inches (38,1
cm x 38. Icm) stacked into a laminate. One surface of the brachie during the stacking operation was coated with grains of Flake-1, giving a substantially uniform monolayer of flakes at a density of about 12 g/I12. The flakes are formed from Ultem film and are hexagonal in shape and approximately 0.
It had a diameter of 0.08 inches (0.02 cm) and a thickness of 1 mil.

The stack is then heated to 355''F at 90psi pressure.
Cured in an autoclave for 2 hours at (179,4°C),
Gave composite panels. Test samples were cut from the resulting panels and tested as before. Composite composition and property data are summarized in Table T.

Example 3 91 pb of EP-3 wood was loaded into a sigma blade mixer and sheared for 10 minutes at a resin temperature of 35°C, then one grain of 5°9 phw of floc and 3.1 pbw of ABS was added.
-1 resin granules were added. Mix for approximately 20 minutes to evenly distribute the particles and drain the resin. Example 1
Manufactured by the following procedure. Composite composition and property data are summarized in Table 1.

In Examples 4-6, a film of grain-filled resin formulation is combined with low resin content Arepreg tape and passed through a prepreg machine to provide a prepreg with grains dispersed throughout the surface of the resin. A two-step process was used to make the composite.

Example 4 A frozen sample of 91 pbw of EP-2 resin was charged to a sigma plate mixer and sheared until the resin reached a temperature of approximately 35° C. and homogeneous (10 minutes), then 2 grains of 9 pbw of floc were added. Afterwards, the flocs are evenly distributed and
The heating was continued until the resin temperature reached approximately 40°C. A filled resin film was prepared with a coating weight of 30 g/l and prepared with a prepreg cheese having a fiber content of 68% by weight made from carbon fiber and EP-2 resin using a prepreg machine according to the procedure of Example A. Together, they gave a prepreg cheese having a fiber content of 68% by weight and an area weight of 148 g/m2, with Flock-2 dispersed on one surface in a resin coating. The composite was made substantially according to the procedure of Example 1 and had a fiber volume fraction V
A test panel with f of 61.1 was obtained. The composition and property data of the composite are summarized in Table 1.

Example 5 Fiber stand μ173 manufactured from carbon fiber and EP-2 resin
The prepreg chives having a fiber content of 61% by weight were sandwiched between the two filled resin films of Example 4.
A final prepreg tape was obtained having a fiber area density of 14B3/m2. Practically the composite material Example 10 μ
Manufactured according to μ, m & I capacity Taraxin 3 Vf5
A test panel with 3.1 was given.

Composite composition and property data are summarized in Table I.

Example 6 A resin film filled with floc-3 grains was prepared substantially according to the procedure of Example 40 to produce 91 pbw of EP-2IIN.
, and 9 pbw of floc-3 grains.

combining the film with prepreg cheese having a fiber content of 73% by weight and made from carbon fiber and EP-2 resin;
Fiber content 63% by weight, and fiber area weight 147g/μ2
The final prepreg cheese was given.

The composite was made substantially according to the procedure of Example 1, and the fiber fraction Vf56. A test panel with I was given. Composite composition and property data are summarized in Table I.

The composition and physical properties of the composites of Examples 1 to 6 were compared with Comparative Example A
-C are summarized in Table I below.

Table 1 EP-1 None 67.0 0.175 30.2 EP-3 EP-3 None 63.7 Flake-160,6 0,17831,[3 0,18641,6 12,8 EP-2 EP-2 EP-2 EP・2 None 62.3 Flock-268 Flock-261 Flock-363 0,187 0,170 0,198 0,185 32,6 41,7 50,2 45,3 Footnote: EP-1 etc. It is an epoxy formulation. Abbreviations for these and filled copper grains are summarized in the text. Filler content is weight percent based on (resin content plus filler). Fiber content is weight percent based on total composite.

CAI = Compression after impact, see main section for test procedures.

From consideration of the residual compressive strength of the examples and comparison with corresponding control examples, it has been found that separating the blies of layered composites by dispersing elongated grains in the matrix resin within the interply spacings For example, the addition of floc and flake grains is shown to provide a substantial improvement in toughness. As can be seen from comparison with Example C, the CAI properties are increased from 10 to 18 kps. Examples 4 and 5 where an increase in the percentage of filled epoxy resin reflected in an increase in the thickness of the composite and a decrease in the total fiber content of the composite results in an increase in CAI of only 9 kpsi. As can be seen, the degree of improvement depends in part on the particle level.

Mixtures of elongated grains and other resin grains can produce a similar degree of improvement, as can be seen by comparing Examples 3 and B. The level of improvement may also depend in part on the grain characteristics and the uniformity with which the grains are dispersed in the matrix resin in the glabellar region. In another composite manufacture using metallized polyester flakes carried out substantially according to the method of Example 2, the improvement in CAI corresponded to an increase of only about 2 kpsi. Micrograph X examination showed that the metallized flakes did not adhere well to the matrix resin and were not well dispersed. Similarly, composites based on nylon flock, floc-1 and epoxy resins derived from mixtures of tetraglycidyl and triglycidyl epoxy resins also
No increase in kpsi or CAI was given. Again, inspection of the micrographs showed that the matrix resin did not adhere well to the flocs, which further indicates that the flocs were not evenly distributed in the matrix resin.

Thus, the present invention is a matrix resin formulation filled with elongated grains for use in making toughened fiber-reinforced composite structures, and a method of toughening such composites. Recognize.

Toughened composites include separate layers formed from continuous fibers embedded in a matrix resin; This is achieved by including elongated grains. The elongated grains may be selected from fibers, flakes, and mixtures thereof, but must be formed of a rigid material having sufficient stiffness and difficulty to withstand the pressures and temperatures encountered in composite manufacturing. There is. The grains consist of elongated grains ranging in size from 1 to about 75 microns (l#, defined as the smallest dimension of the grain), and the majority grain size typically has a desired brining distance ranging from about 1 to 75 microns. chosen to give space. The method of toughening fiber reinforced composites of the present invention is applicable to composites formed using a variety of conventional matrix resins combined with fiber reinforcement. However, preferred composites are those based on thermoset matrix resins, more preferably those based on epoxy resin formulations.

For those skilled in the art of resin formulation and composite manufacturing,
It is obvious that improvements and changes may be made thereto, and such changes and modifications are within the scope of the invention as defined in the claims.

Claims (1)

Claims: 1.99 to about 75% by weight thermoset resin, an aspect ratio greater than 2:1, and a smallest dimension of about 1 to about 75% by weight.
1 to about 25 weight flakes or fiber flock particles formed of a rigid material in the micron (μ) range and selected from the group consisting of polyamide, polyimide, oxidized polyacrylonitrile, carbonized polyacrylonitrile, and mixtures thereof. A curable matrix resin formulation containing %. 2. Claim 1, wherein the thermosetting resin is an epoxy resin formulation containing 100 pbw of an epoxy resin having a plurality of epoxy groups, 6 to 150 pbw of an amine curing agent, and 0 to 30 pbw of a thermoplastic polymer. Curable matrix resin formulations as described in Section. 3. (a) 100 pbw cycloaliphatic epoxy ether, about 6 to about 150 pbw diamine curing agent, and about 0
99% to about 75% by weight of an epoxy resin formulation comprised of ~30 pbw of thermoplastic polymer, and (b) having an aspect ratio greater than 2:1 and a minimum dimension ranging from about 1 to about 75 microns (μ). and 1 to about 25% by weight of flake or flock particles formed of a rigid material selected from the group consisting of polyamide, polyimide, oxidized polyacrylonitrile, carbonized polyacrylonitrile, and mixtures thereof. Resin formulation. 4. According to claim 1 or 3, the particles are fiber flocks made of fibers selected from the group consisting of polyacrylonitrile fibers, polyamide fibers, oxidized polyacrylonitrile fibers, carbon fibers, and mixtures thereof. curable matrix resin formulation. 5. The curable matrix resin formulation according to claim 1 or 3, wherein the particles are polyimide flakes.