JPH045689B2 - - 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 high specific strength and specific modulus of elasticity, which are obtained by dividing these by specific gravity. More specifically, the present invention relates to a prepreg that provides a structure with markedly improved strength in directions other than the reinforcing fiber direction, that is, non-fiber axial tensile strength and post-impact compressive strength, while ensuring the adhesiveness and flexibility of the prepreg.

[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 improving the strength of reinforcing fibers does not lead to drastic improvements because resistance to falling weight impact is controlled by delamination strength. 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.

[Problems to be Solved by the Invention] Therefore, the present inventors conducted intensive research on prepregs that do not have the above-mentioned drawbacks and provide excellent impact resistance. By using fine particles made of a resin with a large size _(1C ) and controlling the distribution of the fine particles, we were able to obtain a prepreg that has excellent impact resistance that far exceeds expectations, leading to the present invention.

[Means for Solving the Problems] The present invention requires the following components [A], [B], and [C] as described in the claims column, and the component [C] Prepreg in which 90% or more of the amount is localized within a depth range of 30% of the thickness of the prepreg from the surface of the prepreg [A]: Reinforced fiber consisting of long fibers [B]: Matrix resin [C] : Fine particles made of a resin having a G _1C of 1500 J/m ² or more (Description 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 tensile strength
High strength and high elongation carbon fiber with a tensile elongation of 450 Kgf/mm ² and 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. As epoxy resins suitable for the present invention, epoxy resins whose precursors are amines, phenols, and compounds having carbon-carbon double bonds are particularly preferred.

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 prepreg by combining it with bismaleimide resin, and is manufactured by 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 these, 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.

(Explanation of fine particles) Conventionally, it has been thought that in order to improve the impact resistance of fiber reinforced composite materials, it is necessary to increase the strain energy release rate (G _1C value) of the matrix resin. However, in order to achieve this, the matrix resin must have certain characteristics such as modulus of elasticity, elongation at break, heat resistance, water resistance, adhesion, tackiness, flexibility of the resin at room temperature, and melt flowability. There was a limit to satisfying both at the same time, as this would result in significant losses. However, according to the present invention, it has surprisingly been found that the impact resistance of a composite material can be significantly improved simply by localizing a resin having a G _1C above a certain level between layers in the form of fine particles. be. Since fine particles exist in a dispersed state in the matrix resin, the tackiness and drape properties of the matrix resin are reflected in the prepreg properties, resulting in a prepreg with excellent handling properties. That is, the prepreg according to the present invention simultaneously satisfies the impact resistance required for a composite material and the properties required of conventional matrix resins.

Moreover, since fine particles do not require the adhesion and drape properties that matrix resins should have,
There is a wide range of materials that can be selected as particulates.

For this reason, even resins that have conventionally been difficult to use as matrix resins despite their excellent performance can be used as components of matrix resins by being made into fine particles and used.
The performance of the matrix resin can be improved.

Material of the fine particles The fine particles may be of any material as long as they are made of a resin having a G _1C value of 1500 J/m ² or more. It is more preferable that the G _1C value is 3000 J/m ² or more. If the G _1C value is less than 1500 J/m ² , it is not preferable because the impact resistance when made into a composite material will not be sufficiently increased.

The G _1C value is evaluated using a resin plate molded from particulate material using the compact tension method or double torsion method specified in ASTM E399 (Type A4).

Distribution of fine particles Regarding the distribution of fine particles, the presence of uneven particles in the surface layer of the prepreg, that is, between the prepreg sheets when molded into a composite material, gives a composite material with excellent impact resistance. It is important for

With the addition of normal fine particles, only the modification effect corresponding to the content of fine particles in the matrix resin can be expected, but if they are concentrated in the surface layer of the prepreg, the prediction based on the additivity described above cannot be expected. Far beyond, especially when it comes to improving impact resistance,
A completely unexpected and remarkable effect was discovered. The condition that satisfies this is that 90% or more of the fine particles are from the surface of the prepreg to the thickness of the prepreg.
This means that it is localized within a 30% depth range. If this condition is exceeded and fine particles enter deep inside the prepreg, the impact resistance of the composite material will be inferior to that of a composite material that meets these conditions.

It is more preferable if 90% or more of the fine particles are localized within a depth range of 10% of the thickness of the prepreg from the surface of the prepreg, since a more significant effect appears.

Note that the prepreg according to the present invention has fine particles unevenly distributed on both sides of the prepreg.
It is optimal because it can be laminated freely regardless of the front and back sides of the prepreg. but,
Even if the prepreg has a similar distribution of fine particles on only one side of the prepreg, the same effect can be obtained if care is taken to ensure that the fine particles are between the prepregs when stacking the prepregs.
The present invention also includes a distribution in which fine particles are biased only on one side of the prepreg.

Method for evaluating the distribution of fine particles The distribution state of fine particles 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 fine particles 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 fine particles existing between parallel lines on both sides of the prepreg, quantify this and the area of fine particles existing over the entire width of the prepreg, and calculate the ratio from the surface of the prepreg to the thickness of the prepreg. The amount of fine particles present within 30% of the area is calculated. The area of the microparticles is determined by cutting out all the microparticles present in a predetermined area from a cross-sectional photograph and weighing them. In order to eliminate the influence of variations in the local distribution of fine particles, this evaluation was performed over the entire width of the obtained photograph, and the same evaluation was performed on five or more randomly selected photographs, and the average It is necessary to take

If it is difficult to distinguish between fine particles and matrix resin, selectively stain one of them and observe. Although it is possible to observe using an optical microscope, depending on the stain, a scanning electron microscope may be more suitable for observation.

Shape of Fine Particles Fine particles may have any shape. Of course, it may be spherical, but it may be in various shapes, such as fine powder obtained by crushing a resin lump, or fine particles obtained by spray drying or reprecipitation. 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.

Size of fine particles The size of fine particles 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 the fine particles need not be so large as to significantly disturb the alignment of reinforcing fibers when formed 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.

Amount of fine particles A suitable amount of fine particles is in the range of 1 part by weight to 100 parts by weight per 100 parts by weight of matrix resin. If the amount is less than 1 part by weight, the effect of the fine particles will hardly be apparent, 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, if the rigidity of the matrix resin is utilized to develop the compressive strength of the composite material while using fine particles that have a high flexibility at break elongation for the purpose of increasing the toughness between the layers of the composite material, it is preferable to A smaller range of 30 parts by weight is more suitable.

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

[Example] A unidirectional prepreg having the following configuration was manufactured. To manufacture prepreg, first prepare a prepreg with a weight fraction of 21% 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 Phenol novolac type epoxy resin (manufactured by Yuka Shell Epoxy Co., Ltd., Epicoat 154)
...60 parts by weight 2 Bisphenol A type epoxy resin (manufactured by Yuka Ciel Epoxy Co., Ltd., Epicoat 828)
...40 parts by weight 3 4,4'diaminodiphenylsulfone (manufactured by Sumitomo Chemical Co., Ltd., Sumikiure S)
...33.9 parts by weight) 4 Polyether sulfone 5200G (Mitsui Toatsu Co., Ltd.)
) ...10 parts by weight C Fine particles - Average particle size 15μ obtained by freeze-pulverizing polyamideimide (Torlon 4000T manufactured by Amoco)
Fine particles...15 parts by weight The weight fraction of resin in the obtained prepreg is 30%
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 .

After press-molding polyamide-imide into a resin plate, the G _1C value was measured using the compact tension method based on ASTM E399. 2350J/
It was ^m2 .

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 in the range from the prepreg surface to 30% of the thickness of the prepreg was evaluated, the value was 96%, indicating that the fine particles were sufficiently localized in the interlayer region.
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 fine particles were concentrated in the interlayer portions of the laminate.

After cutting a quasi-isotropically hardened board to 150 mm long and 100 mm wide, 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 2.2 square inches. . Then,
The compressive strength after impact was measured according to ASTM D-695 and was 30.2 Kg/mm ² .

[Comparative Example] As the fine particles, Bell Pearl R, which is a phenolic resin fine particle, was used instead of a crushed product of polyamideimide.
The same procedure as in Example was repeated except that -800 (average particle size 20 μm, manufactured by Kanebo Co., Ltd.) was used.

After press-molding Bell Pearl R-800 into a resin plate, the G _1C value was measured using the compact tension method based on ASTM E399, and it was 920 J/m ²
This was a low value.

When the amount of fine particles present in the range from the prepreg surface to 30% of the thickness of the prepreg was evaluated, the value was 95%, indicating that the fine particles were sufficiently localized in the interlayer region. 1500 inch pounds per molded part
After applying a falling weight impact of 1 inch, the damage area was measured using an ultrasonic flaw detector and was found to be 4.1 square inches. Then, the compressive strength after impact was measured according to ASTM D-695, and it was found to be 23.3 Kg/mm ² , which was significantly inferior to that of the examples.

[Effects of the Invention] The prepreg according to the present invention can obtain high impact resistance and non-fiber axis tensile strength when made into a composite while ensuring the 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 depth range [A]: Reinforcing fiber made of long fibers [B]: Matrix resin [C]: Fine particles made of resin with a G _1C of 1500 J/m ² or more.