JPH045688B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is an advanced composite material with high strength, elastic modulus,
Furthermore, the present invention relates to prepregs used in structures that are required to have a high specific strength and specific modulus of elasticity, which are obtained by dividing these by specific gravity.

[Prior Art] Fiber-reinforced composite materials are heterogeneous materials that have reinforcing fibers and matrix resin as essential components.
Therefore, there is a large difference between the physical properties in the fiber axis direction and the physical properties in other directions. For example, it is known that resistance to falling weight impact is controlled by delamination strength, so improving the strength of reinforcing fibers does not lead to drastic improvements. Therefore, in addition to improving the toughness of the matrix resin, various improvements have been proposed for the purpose of improving physical properties in directions other than the fiber axis direction.

USP 3472730 (1969) describes a separate exterior film consisting of a thermosetting resin modified with an elastomeric substance on one or both sides of a fiber-reinforced sheet.
It has been disclosed that the delamination resistance can be improved by disposing a .

JP-A-51-58484 (JP-A-58-31296) discloses that moldability and bending strength can be improved by the presence of a polyether sulfone film on the surface of a fiber-reinforced epoxy resin prepreg. has been done.

In JP-A-54-3879, JP-A-56-115216, and JP-A-60-44334, short fiber chips, chopped strands, and milled fibers are arranged between the layers of a fiber reinforced sheet, It is disclosed that interlaminar strength is improved.

JP-A-60-63229 discloses that an epoxy resin film modified with an elastomer is disposed between the layers of fiber-reinforced prepreg to improve the interlayer strength.

USP 4539253 (1985) (corresponding to Japanese Patent Application Laid-open No. 60-231738) discloses that non-woven fabrics, woven fabrics, mats, and carriers made of epoxy modified with elastomers are made of lightweight fibers as a base material between layers of fiber-reinforced prepreg. It is disclosed that interlaminar strength can be improved by disposing a resin-impregnated film.

USP 4604319 (1986) (corresponding to Japanese Patent Application Laid-Open No. 60-231738) discloses that interlaminar strength can be improved by disposing a thermoplastic resin film between the layers of fiber-reinforced prepreg.

However, these methods are not only insufficiently effective, but also have their own drawbacks. When using an independent outer layer film containing an elastomer-modified thermosetting resin, the heat resistance decreases as the elastomer content increases, and the effect of improving interlaminar strength is very small when the elastomer content is low.

In addition, when a thermoplastic resin film is used, it is possible to achieve both heat resistance and interlaminar strength improvement effects by using a thermoplastic resin film with good heat resistance. adhesiveness) and drape properties are lost. Moreover, the general drawback of thermoplastic resins, such as poor solvent resistance, is reflected in the composite material.

Furthermore, the use of chopped short fibers or chopped strand milled fibers increases the thickness of the interlayers, resulting in a decrease in the strength of the composite as a whole.

On the other hand, prior to the present invention, the present inventors have improved the toughness of prepreg by localizing finely divided thermoplastic resin on the surface of prepreg.
We have invented a prepreg that provides a composite material with significantly improved impact resistance while retaining drapability.

However, these methods have the drawback that thermoplastic resins generally have poor solvent resistance. Furthermore, depending on the type of thermoplastic resin selected, the adhesion with the matrix resin may not be sufficient, and therefore some have drawbacks in impact resistance and fatigue resistance.

[Problems to be Solved by the Invention] Therefore, the present inventors conducted extensive research on prepregs that provide fiber-reinforced composite materials with excellent impact resistance, solvent resistance, and fatigue resistance without the above-mentioned drawbacks. This led to the invention of a prepreg that provides a composite material with excellent impact resistance, as well as good properties in terms of solvent resistance and fatigue resistance.

[Means for solving the problems] The present invention has the following configuration. In other words, the following components [A], [B], and [C] are essential, and 90% or more of component [C] is localized within a depth range of 30% of the thickness of the prepreg from the surface of the prepreg. Currently available prepreg [A]: Reinforced fiber made of long fibers [B]: Matrix resin [C]: Semi-IPN (polymer interpenetrating network structure) is created by a combination of thermoplastic resin and thermosetting resin.
(Explanation of reinforcing fibers made of long fibers) Component [A] of the present invention is a reinforcing fiber made of long fibers. The reinforcing fibers used in the present invention are generally used as high-performance reinforcing fibers and have good heat resistance and tensile strength. For example, the reinforcing fibers include carbon fiber, graphite fiber, aramid fiber,
Examples include silicon carbide fiber, alumina fiber, and boron fiber. Among these, carbon fibers and graphite fibers are most suitable for the present invention because they have good specific strength and specific modulus and are recognized to greatly contribute to weight reduction. All kinds of carbon fibers and graphite fibers can be used depending on the purpose, but the tensile strength is 450.
High strength and high elongation carbon fiber with Kgf/mm ² and tensile elongation of 1.6% or more is most suitable. Further, although long reinforcing fibers are used in the present invention, the length thereof is preferably 5 cm or more. If it is shorter than that, it becomes difficult to fully develop the strength of the reinforcing fibers as a composite material. Further, carbon fibers and graphite fibers may be used in combination with other reinforcing fibers. Furthermore, the reinforcing fibers are not limited in their shape or arrangement, and can be used in, for example, unidirectional, random directional, sheet-like, mat-like, woven-like, or braid-like forms. In particular, for applications that require high specific strength and specific modulus, an arrangement in which the reinforcing fibers are aligned in a single direction is most suitable, but a cross (woven) arrangement is easier to handle. are also suitable for the present invention.

(Description of matrix resin) Component [B] of the present invention is a matrix resin.

The matrix resin used in the present invention includes thermosetting resins and resins obtained by mixing thermosetting resins and thermoplastic resins.

The thermosetting resin used in the present invention is not particularly limited as long as it is a resin that can be cured by heat or external energy such as light or an electron beam to at least partially form a three-dimensional cured product. Preferred thermosetting resins include epoxy resins, which are generally used in combination with curing agents and curing catalysts. Particularly preferred epoxy resins suitable for the present invention are epoxy resins whose precursors are amines, phenols, and compounds having carbon-carbon double bonds.

Further, these epoxy resins may be used alone or in an appropriate combination.

Epoxy resins are preferably used in combination with epoxy curing agents. Any compound having an active group capable of reacting with an epoxy group can be used as the epoxy curing agent. Preferably, an amino group,
Compounds having an acid anhydride group or an azide group are suitable.

In the present invention, maleimide resins, resins with acetylene ends, resins with nadic acid ends, resins with cyanate ester ends, resins with vinyl ends, and resins with allyl ends are preferably used as the matrix resin in the present invention. These may be mixed with epoxy resin or other resins as appropriate. Further, a reactive diluent may be used, or a modifier such as a thermoplastic resin or an elastomer may be mixed and used.

A maleimide resin is a compound containing an average of two or more maleimide groups at its terminal ends. As the resin having a cyanate ester terminal, a cyanate ester compound of a polyhydric phenol typified by bisphenol A is suitable. Cyanate ester resin can be made into a resin suitable for prepregs, especially when combined with bismaleimide resin, and Mitsubishi Gas Chemical Co., Ltd.
BT resin is commercially available and suitable for the present invention. These generally have better heat resistance and water resistance than epoxy resins, but are inferior in toughness and impact resistance, so they are selected and used depending on the application. Even if these other thermosetting resins are used in place of the epoxy resin in the present invention, the effects of the present invention are the same. Furthermore, commercially available general-purpose resins are used as the vinyl-terminated resin and the allyl-terminated resin, but their heat resistance is inferior to the former group of resins, so they are mainly used as diluents.

In the present invention, it is also suitable to use a mixture of the above-mentioned thermosetting resin and a thermoplastic resin as the matrix resin. Thermoplastic resins suitable for the present invention are:
Carbon-carbon bonds, amide bonds, imide bonds in the main chain,
It is a thermoplastic resin having bonds selected from ester bonds, ether bonds, carbonate bonds, urethane bonds, urea bonds, thioether bonds, sulfone bonds, imidazole bonds, and carbonyl bonds.

As these thermoplastic resins, commercially available polymers may be used, or so-called oligomers having a lower molecular weight than commercially available polymers may be used. As the oligomer, an oligomer having a functional group capable of reacting with the thermosetting resin at the terminal or in the molecular chain is more preferable.

Mixtures of thermosets and thermoplastics give better results than when they are used alone.
This is because thermosetting resins generally have the disadvantage of being brittle but can be molded at low pressure in an autoclave, while thermoplastic resins have the advantage of being tough but are difficult to mold at low pressure in an autoclave. In order to exhibit contradictory characteristics,
This is because by mixing and using them, it is possible to balance physical properties and moldability.

It is also possible to mix a small amount of inorganic fine particles such as finely powdered silica or an elastomer with the epoxy resin.

(Description of fine particles) Component [C] is semi-IPN or semi-IPN made by a combination of thermoplastic resin and thermosetting resin.
These are fine resin particles that can be converted into IPN. Note that IPN is an abbreviation for Interpenetrating Polymer Network, and refers to an interpenetrating network structure of crosslinked polymers, while semi-IPN refers to an interpenetrating network structure of crosslinked polymers and linear polymers.

If we make microparticles by semi-IPNing a thermoplastic resin and a thermosetting resin, by selecting the composition, we can create microparticles that maintain the toughness of the particles themselves and have good solvent resistance and adhesion to the matrix resin. Obtainable. However, it is acceptable even if this semi-IPN is achieved during molding of the composite material. A composite material obtained by molding a prepreg containing this as component [C] has excellent impact resistance, solvent resistance, and fatigue resistance.

The thermoplastic resin used here has a main chain selected from carbon-carbon bonds, amide bonds, imide bonds, ester bonds, ether bonds, carbonate bonds, urethane bonds, urea bonds, thioether bonds, sulfone bonds, imidazole bonds, and carbol bonds. It is a thermoplastic resin with a bond that Specifically, vinyl resins such as polyacrylate, polyvinyl acetate, and polystyrene, polyamide, polyaramid, polyester, polyacetal, polycarbonate, polyphenylene oxide, polyphenylene sulfide, polyarylate, and polybenz Thermoplastic resins that belong to engineering plastics such as imidazole, polyimide, polyamideimide, polyetherimide, polysulfone, polyethersulfone, and polyetheretherketone, hydrocarbon resins such as polyethylene and polypropylene, cellulose acetate, and cellulose butyrate. Typical examples include cellulose derivatives. In particular, polyamide, polycarbonate, polyacetal, polyphenylene oxide, polyphenylene sulfide, polyarylate, polyester, polyamideimide, polyimide, polyetherimide, polysulfone, polyethersulfone, polyetheretherketone,
Polyaramid and polybenzimidazole have excellent impact resistance and are therefore suitable as materials for the fine particles used in the present invention. Among these, polyamide, polyetherimide, polyethersulfone, and polysulfone are preferable for the present invention because they have high toughness and good heat resistance, and semi-IPN fine particles with a thermosetting resin described later can be easily prepared. Polyamide has particularly excellent toughness, and by using a polyamide that belongs to the amorphous transparent nylon category, it can also have heat resistance.

Thermoplastic resin is a combination of thermoplastic resin and semi-
Anything that forms an IPN is fine. Specific examples include epoxy resins, bismaleimide resins, phenol resins, unsaturated polyester resins, and polyimide resins.

The ratio of the thermoplastic resin and thermosetting resin forming component [C] is such that the weight fraction of the thermoplastic resin is
About 30-99% is good. If it exceeds 99%, the solvent resistance of the fine particles will be poor, while if it is less than 30%, the impact resistance of the composite material will deteriorate due to insufficient toughness of the fine particles, which is not preferable. Particularly preferred is 50-98%.

Surprisingly, even when the weight fraction of the thermosetting resin is as small as 2%, the effect of improving solvent resistance is large and the fatigue properties are also rapidly improved. On the other hand, it is thought that the toughness of the thermoplastic resin fine particles used decreases due to semi-IPN formation with the thermosetting resin, so the impact resistance of the composite material is lower than when the thermoplastic resin fine particles themselves are used. is normally expected. However, it has surprisingly been found that the impact resistance tends to improve in a range where the weight fraction of the thermosetting resin is small. This is thought to be due to the improved adhesion between the fine particles and the matrix resin due to semi-IPN.

When component [C] is a semi-IPN formed from polyamide and an epoxy resin, or fine particles capable of forming a semi-IPN, various properties of the final target composite material, such as impact resistance, solvent resistance, An optimal balance of fatigue resistance, heat resistance, etc. can be obtained. Furthermore, the creep property, which is a common drawback when thermoplastic resins are used as structural materials, can be improved by making them semi-IPN.

Moreover, the fact that the component [C] is a fine particle has the following advantages. In other words, fine particles exist in a dispersed state in the matrix resin, so
The tackiness and drape properties of the matrix resin are reflected in the prepreg properties, resulting in a prepreg with excellent handling properties.

Regarding the distribution of component [C], its presence in the surface layer of the prepreg, that is, between the prepreg sheets when molded into a composite material, makes it possible to obtain a composite material with excellent impact resistance. It is important to give.

When the usual component [C] is added, only the modification effect corresponding to the content of the component [C] in the matrix resin is expected, but if it is concentrated in the surface layer of the prepreg, the above-mentioned A completely unexpected and remarkable effect was discovered, far exceeding expectations based on the additivity of the material, and particularly in terms of improving impact resistance. The condition that satisfies this is that 90% or more of the component [C] is localized within a depth range of 30% of the thickness of the prepreg from the surface of the prepreg. If this condition is not met and component [C] enters deep inside the prepreg, the impact resistance of the composite material will be inferior to that which meets the condition.

It is more preferable if 90% or more of the constituent element [C] is localized within a depth range of 10% of the thickness of the prepreg from the surface of the prepreg because a more significant effect appears.

Note that the prepreg according to the present invention is optimal because the component [C] is unevenly distributed on both sides of the prepreg because it can be laminated freely regardless of the front and back sides of the prepreg.
However, the component [C] is only on one side of the prepreg.
Even if the prepregs have a similar distribution, the same effect can be obtained if the component [C] is always placed between the prepregs when stacking the prepregs. The present invention also includes a distribution in which the component [C] is biased.

The distribution state of the component [C] in the prepreg is evaluated as follows.

First, the prepreg is sandwiched between two smooth support plates and brought into close contact with each other, and the temperature is gradually raised over a long period of time to harden the prepreg. What is important at this time is to gel at the lowest possible temperature. If the temperature is raised before gelation occurs, the resin in the prepreg will flow and the component [C] will move, making it impossible to accurately evaluate the distribution state in the prepreg.

After gelation, the prepreg is cured by gradually increasing the temperature over an additional period of time. Using this cured prepreg, the cross section is enlarged 200 times or more and a photograph of 200 mm x 200 mm or more is taken.

Using this cross-sectional photograph, first determine the average thickness of the prepreg. The average thickness of the layer is measured at at least 5 arbitrarily selected points on the photograph, and the average thickness is taken. Next, draw a line parallel to the surface direction of the prepreg at a position 30% of the thickness of the prepreg from the surface that was in contact with both support plates. 30% of the surface that was in contact with the support plate
Quantify the area of the component [C] existing between the parallel lines on both sides of the prepreg, quantify this and the area of the component [C] that exists across the entire width of the prepreg, and calculate the ratio. The amount of component [C] present within 30% of the thickness of the prepreg from the surface of the prepreg is calculated. The area of the component [C] is determined by cutting out all the component [C] portions present in a predetermined area from the cross-sectional photograph and weighing them. In order to eliminate the influence of variations in the partial distribution of component [C],
This evaluation was performed over the entire width of the obtained photographs,
In addition, it is necessary to perform similar evaluations on five or more arbitrarily selected photographs and take the average.

When it is difficult to distinguish between component [C] and matrix resin, one is selectively dyed and observed. Although it is possible to observe using an optical microscope, depending on the stain, a scanning electron microscope may be more suitable for observation.

The shape of component [C] is not limited to a spherical shape. Of course, it may be spherical, but it may be in various shapes, such as a fine powder obtained by crushing a resin lump, or component [C] obtained by a spray drying method or a reprecipitation method. In addition, it may be in the form of milled fibers obtained by cutting the fibers into short lengths, or in the form of needles or whiskers.

The size of component [C] is expressed by particle size, and particle size in this case means the volume average particle size determined by centrifugal sedimentation velocity method or the like.

The size of component [C] need not be so large as to significantly disturb the alignment of the reinforcing fibers when it is made into a composite material. If the particle size exceeds 150 μm, the arrangement of reinforcing fibers may be disturbed or the interlayers of the composite material obtained by lamination may become thicker than necessary, resulting in a disadvantage of deteriorating the physical properties of the composite material.

The amount of component [C] is matrix resin.
A range of 1 part by weight to 100 parts by weight per 100 parts by weight is suitable. If it is less than 1 part by weight, the effect of component [C] will hardly be exhibited, and if it exceeds 100 parts by weight, it will be difficult to mix with the matrix resin, and
The tackiness and drapability of the prepreg will be significantly reduced.

In particular, when the rigidity of the matrix resin is utilized to develop the compressive strength of the composite material, the component [C] has a flexible property with high elongation at break and is used for the purpose of increasing the toughness between the layers of the composite material. Rather, a small range of 1 part by weight to 30 parts by weight is preferable.

Hereinafter, the present invention will be explained in more detail with reference to Examples.

Example 1 A unidirectional prepreg having the following configuration was manufactured. To manufacture prepreg, first prepare a prepreg with a weight fraction of 22% of the following resins A and B, and then paste a resin film on both sides of the prepreg with a thin layer of release paper coated with a blended resin of C and B. This was done by Note that the part by weight C below is the amount of fine particles contained in the prepreg resin finally obtained through the above two-step process.

A Reinforcing fiber - carbon fiber T800 (manufactured by Toray Industries, Inc.) B Matrix resin - a resin composition having the following composition 1 Tetraglycidyldiaminodiphenylmethane (manufactured by Sumitomo Chemical Co., Ltd., ELM434)
...80 parts by weight 2 Aminophenol-type epoxy resin (manufactured by Ciba Geigy Co., Ltd., 0510) ...20 parts by weight 3 4,4' Diaminodiphenylsulfone (manufactured by Sumitomo Chemical Co., Ltd., Sumikiure S)
...53.4 parts by weight) C Semi-IPN fine particles Amorphous transparent nylon (Mitsubishi Kasei Co., Ltd., Grilamid TR-55), bisphenol A type epoxy resin (Yuka Ciel Epoxy Co., Ltd., Epicoat)
828), and polyamide curing agent (Fuji Kasei Co., Ltd.)
The weight fraction of Tomide #296) is 96/3/
Semi-IPN fine particles with an average particle size of 16μ consisting of a ratio of
It was hot. The amount of resin per unit area is 69g/ ^m2 ,
The amount of carbon fiber per unit area was 149 g/m ² .

This prepreg was sandwiched between two smooth Teflon plates, and the temperature was gradually raised to 150°C for 7 days to cure it, and its cross section was observed. When the amount of fine particles present within a range of up to 30% of the thickness of the prepreg surface was evaluated, the value was 98%, indicating that the fine particles were localized between the layers. Cross-sectional observation was performed by selectively staining the microparticles with osmium tetroxide and using a scanning electron microscope.

Next, 32 sheets of this prepreg were laminated in a quasi-isotropic manner and molded using a normal autoclave at 180°C.
The test was carried out for 2 hours under a pressure of 6 kgf/cm ² . When the cross section was observed under an optical microscope after molding, it was confirmed that the semi-IPN particles were concentrated in the interlayer parts of the laminate.

After cutting a quasi-isotropically hardened plate to 150 mm in length and 100 mm in width and applying a falling weight impact of 1500 inch-pounds/inch to the center, the damage area was measured using an ultrasonic flaw detector and was found to be 0.7 square inches. . Then,
The compressive strength after impact was measured according to ASTM D-695 and was 37.5 Kg/mm ² .

Furthermore, a unidirectional 16 ply laminate was formed using the same prepreg, cut into pieces of 1 cm in length and 10 cm in width, and boiled in methyl ethyl ketone for 24 hours, but no whitening phenomenon was observed on the surface. The bending strength of this specimen is
The strength was 178Kg/ ^mm2 , which was equivalent to the strength before immersion, which was 177Kg/ ^mm2 .

The fatigue resistance was evaluated by applying repeated loads (tensile) in the EDS (edge peel strength) test mode.
At a stress of Kg/mm ² , no peeling occurred even after 10 ⁶ repetitions.

Example 2 As fine particles, polyether sulfone 5003P (manufactured by Mitsui Toatsu Co., Ltd.), bisphenol A type epoxy resin (manufactured by Yuka Ciel Epoxy Co., Ltd., Epicoat 828), and 4,4'-diaminodiphenylmethane ( Hani Chemical
Co., Ltd.) with a weight fraction of 70/30/10.
Semi-IPN fine particles of 20μ were used. Otherwise, the same procedure as in Example 1 was repeated. After applying a falling weight impact of 1500 inch pounds per inch, the damage area was measured using an ultrasonic flaw detector and was found to be 2.0 square inches. Then, the compressive strength after impact was measured according to ASTM D-695 and found to be 30.1 Kg/mm ² . When this laminate was boiled in methyl ethyl ketone for 24 hours, no change in appearance was observed.

Comparative Example 1 As the fine particles, fine particles of amorphous transparent nylon (Grylamid TR-55) with an average particle size of 13 μm were used.
Otherwise, the same procedure as in Example 1 was repeated.
After applying a falling weight impact of 1500 inch pounds per inch, the damage area was measured using an ultrasonic flaw detector and was found to be 0.7 square inches. Next, ASTM
The compressive strength after impact was measured according to D-695 and was found to be 35.0 Kg/mm ² , which was good.

However, when the laminate was boiled in methyl ethyl ketone for 24 hours, the surface showed significant whitening, and its bending strength was 165 kg/ ^mm2 , which was 177 kg before immersion.
It decreased compared to Kg/mm ² .

In addition, in the fatigue test in EDS mode, 20Kg/mm ²
When a stress of 4×10 ⁵ times was applied repeatedly, plate edge peeling occurred.

Comparative Example 2 Polyethersulfone 5003P having an average particle size of 10 μm was used as the fine particles. Others are Example 1
The same procedure was repeated.

The area damaged by the falling weight impact was as large as 4 square inches, and the compressive strength after the impact was as low as 21.2 kg/mm ² .

Furthermore, when boiled in methyl ethyl ketone for 24 hours, a whitening phenomenon was observed on the surface.

[Effects of the Invention] The prepreg according to the present invention can obtain high impact resistance, solvent resistance, fatigue resistance, and creep resistance when made into a composite while ensuring tackiness and drapability as a prepreg. .

Claims (1)

[Claims] 1. The following components [A], [B], and [C] are essential, and 90% or more of component [C] is distributed from the surface of the prepreg to 30% of the thickness of the prepreg. Prepreg localized within a range of depth [A]: Reinforced fiber made of long fibers [B]: Matrix resin [C]: Semi-IPN (polymer interpenetration) formed by a combination of thermoplastic resin and thermosetting resin. mesh structure)
Resin fine particles 2 that can be converted into or semi-IPN Component [C] is an epoxy resin and semi-IPN
2. The prepreg according to claim 1, wherein the prepreg is fine particles made of polyamide that can be converted into polyamide or semi-IPN.